Patent Publication Number: US-2011048601-A1

Title: Pneumatic tire having directional tread pattern

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Rule 53(b) divisional of U.S. application Ser. No. 11/597,742 filed on Nov. 27, 2006, which is a U.S. National Stage Application of PCT/JP2005/009792, which has an international filing date of May 27, 2005, and which claims priority from JP 2004-158059, filed May 27, 2004, JP 2004-158060, filed May 27, 2004, JP 2004-265904, filed Sep. 13, 2004, JP 2004-265905, filed Sep. 13, 2004, and JP 2004-265906, filed Sep. 13, 2004. The entire disclosures of the prior applications are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a pneumatic tire, particularly to the pneumatic tire which can obtain a high wet drainage property without sacrificing other capabilities. 
     BACKGROUND ART 
     In the pneumatic tire, a circumferential groove and a transverse groove are arranged in a tread to obtain wet performance (see Patent Documents 1 to 3). 
     Conventionally, in the pneumatic tire, various devices are made to improve tire performance (for example, see Patent Documents 4 to 7). In order to improve the drainage on a wet road surface, a groove volume is increased by increasing a groove width or a groove depth. 
     In a racing ultra-high performance vehicle tire, a technique of linearly arranging several circumferential grooves in a center region of the tread is taken to improve hydroplaning performance, and the technique increases a negative ratio. 
     Patent Document 1: Japanese Patent Laid-Open No. 57-194106 (FIG. 2) 
     Patent Document 2: Japanese Patent Laid-Open No. 3-10911 (FIGS. 1 and 2) 
     Patent Document 3: Japanese Patent Laid-Open No. 11-189011 (FIG. 1) 
     Patent Document 4: Japanese Patent Laid-Open No. 2001-225611 
     Patent Document 5: Japanese Patent Laid-Open No. 10-100615 
     Patent Document 6: Japanese Patent Laid-Open No. 2003-320814 
     Patent Document 7: Japanese Patent Laid-Open No. 63-061606 
     DISCLOSURE OF THE INVENTION 
     Subjects to be Addressed by the Invention 
     However, when the groove width or the groove depth is increased, a ground contact area is decreased on the dry road surface, and a shortage of rigidity may be cased in a land portion, which may result in lower roadholding ability on the dry road surface. An uneven wear-resistant property may be also decreased. 
     The following countermeasures are effective in improving the roadholding ability or the pattern noise property on the dry road surface. That is, the grove area is decreased to increase the ground contact area, and a step-shape bottom raising portion is provided in the transverse groove of an end portion of the land portion to enhance block rigidity. 
     However, in the above countermeasures, the groove volume is decreased and turbulence is generated in a water flow to affect the drainage property by the step, which results in drainage property and the roadholding ability to be decreased on the wet road surface. 
     In the racing ultra-high performance vehicle tire, a hydroplaning phenomenon is easily generated because of high running speed. In a racing ultra-high performance vehicle rear-tire, the hydroplaning phenomenon is easily generated from a low speed region because of wide ground contact width. Therefore, such techniques are taken as widening the groove width to increase the negative ratio or arranging the several linear major grooves in the center region so as to solve the hydroplaning phenomenon. However, the area of the land portion is decreased in the center region and a block width is also decreased, which results in a decrease in grip and a decrease in wear-resistant property. 
     In the racing ultra-high performance vehicle tire, a technique of continuously arranging rib-shape land portions in a central region in a tire axis direction is taken to improve handling performance. The land portions are continuously formed in the tire circumferential direction. However, the drainage property of the central region in the tire axis direction toward the tire width direction is decreased to cause the wet drainage property to be decreased in the central region in the tire axis direction. 
     In view of the foregoing, an object of the invention is to provide a pneumatic tire which can obtain a high wet drainage performance without sacrificing other capabilities (such as roadholding ability, pattern noise property, and wear-resistant property). 
     Means for Addressing the Subject 
     One aspect of the exemplary embodiments provides a pneumatic tire which has at least one circumferential wide major groove, plural transverse grooves, and a narrow circumferential minor groove. The circumferential wide major groove is provided in a center region in a tire width direction of a tread, the circumferential wide major groove is extended in a tire circumferential direction. The transverse groove is provided in the tread and extended from a tread end toward the circumferential wide major groove while inclined with respect to the tire circumferential direction. The narrow circumferential minor groove is arranged on an outside in a tire axis direction of the circumferential wide major groove and is extended in the tire circumferential direction. A groove width of the narrow circumferential minor groove is set narrower than that of the circumferential wide major groove. The tread has plural blocks which are zoned by the circumferential wide major groove, the transverse groove, and the narrow circumferential minor groove, the tread has a directional tread pattern in which each transverse groove being sequentially in contact with a road surface from a tire equatorial plane side toward the tread end during an on-load rotating operation. A width and a depth of the narrow circumferential minor groove in an area where the narrow circumferential minor groove zones the block are decreased from a kick-out side toward a stepping-on side of with respect to the block during the on-load rotating operation. 
     According to an aspect of the exemplary embodiments, the pneumatic tire has a directional pattern. Therefore, in the wet road surface driving, the water flows efficiently into the circumferential wide major groove, narrow circumferential minor groove, and transverse groove to obtain the high wet performance, 
     Because the high wet performance is obtained while the increase in negative ratio is suppressed, a wheel tread area of the block is secured to improve the wear-resistant property. 
     The handling performance is improved because the block rigidity is increased in the central region in the tire axis direction 
     Furthermore, during the on-load rotating operation, the width and depth of the narrow circumferential minor groove are decreased from the kickout side toward the stepping-on side of the block in the range where the block is zoned by the narrow circumferential minor groove. Therefore, the block rigidity is increased at the stepping-on side of the block that is positioned on both sides of the narrow circumferential minor groove. This improves the traction performance, brake performance, and cornering performance. 
     As used herein, the term “central region in tire width direction of tread” shall mean a central region when the tread is equally divided into three regions in the tire axis direction. 
     Another aspect of the exemplary embodiments of the pneumatic tire provides that the at least two narrow circumferential minor grooves are provided on the outside in the tire axis direction of the circumferential wide major groove, and the transverse groove includes a first transverse groove, a second transverse groove, and a third transverse groove. The first transverse groove is extended from the tread end and is coupled to the circumferential wide major groove while intersecting with the narrow circumferential minor grooves. The second transverse groove is arranged between the first transverse grooves, the second transverse groove is extended from the tread end and intersects with the narrow circumferential minor grooves, the second transverse groove is terminated while not coupled to the circumferential wide major groove. The third transverse groove is arranged between the first transverse groove and the second transverse groove, is extended from the tread end and terminated between the two narrow circumferential minor grooves. 
     According to an aspect of the exemplary embodiments, the first transverse groove, the second transverse groove, and the third transverse groove are arranged in the tread. The first transverse groove is extended from the tread end, and the first transverse groove is coupled to the circumferential wide major groove while intersecting with the narrow circumferential minor groove. The second transverse groove is arranged between the first transverse grooves, the second transverse groove is extended from the tread end while intersecting with the narrow circumferential minor groove, and the second transverse groove is terminated while not coupled to the circumferential wide major groove. The third transverse groove is arranged between the first transverse groove and the second transverse groove, and the third transverse groove is extended from the tread end and terminated between the two narrow circumferential minor grooves. Therefore, the length in the tire circumferential direction of the block zoned by the grooves can be sequentially formed to become a half from the tire equatorial plane side toward the tread end, and the wet drainage property can be increased on both sides of the tread while the block rigidity can be increased on the tread central region side to increase the traction performance, brake performance, and cornering performance. 
     Another aspect of the exemplary embodiments provides that tire equatorial plane-side terminal positions of the second transverse groove and third transverse groove are located in a central region of a block in the tire axis direction. [0023] 
     The tire equatorial plane-side terminal positions of the second transverse groove and third transverse groove are located in the central region in the tire axis direction of the block where each of the second transverse groove and third transverse groove is arranged. Therefore, the high wet drainage property, roadholding ability, and wear-resistant property can be obtained in a preferable manner. 
     When the tire equatorial plane-side terminal positions of the second transverse groove and third transverse groove are shifted to the outside in the tire axis direction from the central region in the tire axis direction of the block, the water existing on the block surface hardly flows into each transverse groove, and thereby the wet drainage property is undesirably decreased. 
     When the tire equatorial plane-side terminal positions of the second transverse groove and third transverse groove are shifted to the inside (tire equatorial plane side) in the tire axis direction from the central region in the tire axis direction of the block, undesirably the block rigidity is lowered to decrease the traction performance, brake performance, and cornering performance. 
     As used herein, the term “central region of block in tire axis direction” shall mean a central region when the block is equally divided into three regions in the tire axis direction. 
     Another aspect of the pneumatic tire provides that, assuming that W 2  is a groove width of the first transverse groove, W 3  is a groove width of the second transverse groove, and W 4  is a groove width of the third transverse groove, W 3  is set in a range of 60% to 110% of W 2  and W 4  is set in a range of 20% to 60% of W 2 . 
     Assuming that W 2  is a groove width of the first transverse groove, W 3  is a groove width of the second transverse groove, and W 4  is a groove width of the third transverse groove, W 3  is set in a range of 60% to 110% of W 2  and W 4  is set in a range of 20% to 60% of W 2 . Therefore, a balance can be achieved between the wet drainage property and the block rigidity in the region surrounded by the first transverse groove and the second transverse groove. 
     The groove width W 3  of the second transverse groove is set in a range of 60% to 110% of groove width W 2  of the first transverse groove, which allows the groove width W 3  of the second transverse groove to be approximately equalized to the groove width W 2  of the first transverse groove to secure the high wet drainage property. 
     When the groove width W 4  of the third transverse groove becomes lower than 20% of the groove width W 2  of the first transverse groove, undesirably the wet drainage property is decreased in the region surrounded by the first transverse groove and the second transverse groove. 
     On the other hand, when the groove width W 4  of the third transverse groove becomes more than 60% of the groove width W 2  of the first transverse groove, undesirably the block rigidity is decreased in the region surrounded by the first transverse groove and the second transverse groove. 
     Another aspect of the exemplary embodiments provides that the at least two narrow circumferential minor grooves are provided on the outside of the circumferential wide major groove in the tire axis direction, the transverse groove includes a first transverse groove and a second transverse groove, the first transverse groove being extended from the tread end, the first transverse groove being coupled to the circumferential wide major groove while intersecting with the narrow circumferential minor grooves, the second transverse groove being arranged between the first transverse grooves, the second transverse groove being extended from the tread end, the second transverse groove intersecting with the narrow circumferential minor groove on an outermost side in the tire axis direction while not intersecting with the narrow circumferential minor groove on an innermost side in the tire axis direction, the second transverse groove being terminated while not coupled to the circumferential wide major groove. The first transverse groove has a bottom raising portion on a side that locates at the circumferential wide major groove side and a groove depth is gradually decreased from a start point provided at the outside with respect to the circumferential wide major groove toward the circumferential wide major groove in the tire axis direction at the bottom raising portion. 
     According to an aspect of the exemplary embodiments, in the wet road surface driving, the water near the central region in the tire axis direction flows into the circumferential wide major groove, and other water flows into the first transverse groove. The water on the wheel tread of the block surrounded by the circumferential wide major groove and first transverse groove flows into the two grooves of the narrow circumferential minor groove and the second transverse groove. The tread has the directional patter. Therefore, in the wet road surface driving, the water flows efficiently into the circumferential wide major groove, narrow circumferential minor groove, first transverse groove, and second transverse groove to obtain the high wet performance. 
     Because the high wet performance is obtained while the increase in negative ratio is suppressed, the wheel tread area of the block is secured to improve the wear-resistant property. 
     According to an aspect of the exemplary embodiments, the first transverse groove has the bottom raising portion at the circumferential wide major groove side thereof, and the groove depth is gradually decreased from the start point on the outside in the tire axis direction toward the circumferential wide major groove. Therefore, in the wet road surface driving, the water near the central region in the tire axis direction is distributed by the bottom raising portion into the water flowing, that is one flowing is toward into the circumferential wide major groove and the other flowing is toward into the first transverse groove, thereby the wet drainage property is further improved. 
     The bottom raising portion can suppress the generation of water turbulence in the circumferential wide major groove to improve the wet drainage property. 
     The bottom raising portion reinforces the blocks on both sides of the bottom raising portion, so that the block rigidity is increased in the tread central region to improve the traction performance, brake performance, and cornering performance. 
     As used herein, the term “first transverse groove is coupled to circumferential wide major groove” shall mean that the first transverse groove is opened to the circumferential wide major groove while the groove depth of the first transverse groove is not more than 10% of itself (not including groove depth of 0 mm), or, when the groove depth of the first transverse groove is 0 mm in the opening portion on the circumferential wide major groove side, the width of the first transverse groove is not more than 3 mm in the tire axis direction at the opening region where the groove depth is 0 mm. 
     Another aspect of the exemplary embodiments provides that a length of the bottom raising portion in the tire axis direction is set in the range of 60 to 200% of a groove width of the circumferential wide major groove. 
     The size of the bottom raising portion in the tire axis direction is set in the range of 60 to 200% of the groove width of the circumferential wide major groove. Therefore, the wet drainage property can securely be improved by achieving an excellent balance between an amount of water flowing into the circumferential wide major groove and an amount of water flowing into the first transverse groove. 
     Another aspect of the exemplary embodiments provides that a depth of a top portion of the bottom raising portion is set to 10% or less of a groove depth of the first transverse groove when each depth is measured from a wheel tread surface of the tread. 
     When the depth of the top portion of the bottom raising portion is more than 10% of the groove depth of the first transverse groove in measuring the depth from the wheel tread surface (namely, when the groove depth in the bottom raising portion of the first transverse groove is more than 10% of the groove depth of the portions except for the bottom raising portion), the turbulence is generated in the water flowing in the circumferential wide major groove to decrease the wet drainage property, and the block rigidity is decreased in the tread central region (because the block reinforcement effect by the bottom raising portion is decreased). Therefore the traction performance, brake performance, and cornering performance cannot be improved. 
     Another aspect of the exemplary embodiments provides that the groove width of the second transverse groove is set in the range of 10 to 80% of the groove width of the first transverse groove. 
     The groove width of the second transverse groove is set in the range of 10 to 80% of the groove width of the first transverse groove, which allows a balance to be achieved between the wet drainage property and the block rigidity of the outside region in the tire axis direction of the tread. 
     When the groove width of the second transverse groove is lower than 10% of the groove width of the first transverse groove, a shortage of the groove volume is generated in the second transverse groove to decrease the wet drainage property. 
     On the other hand, when the groove width of the second transverse groove exceeds 80% of the groove width of the first transverse groove, because the wheel tread area is decreased in the outside region in the tire axis direction of the tread, the block rigidity is decreased to affect the cornering performance. 
     Another aspect of the exemplary embodiments provides that the narrow circumferential minor groove arranged on the outermost side in the tire axis direction is inclined toward a direction in which the narrow circumferential minor groove is sequentially in contact with the road surface from the tire equatorial plane side toward the tread end of the narrow circumferential minor groove during the on-load rotating operation. 
     In the plural narrow circumferential minor grooves, the narrow circumferential minor groove arranged on the outside in the tire axis direction is inclined toward the direction in which the narrow circumferential minor groove is sequentially in contact with the road surface from the tire equatorial plane side toward the tread end during the on-load rotating operation. Therefore, the wet drainage performance is improved near both the outsides in the tire axis direction in the tire ground contact portion. 
     Another aspect of the exemplary embodiments provides that, in the narrow circumferential minor groove, a groove wall on the tire equatorial plane side is linearly extended in the tire circumferential direction and has an angle with respect to a normal set to the wheel tread ranges from 40 degrees to 80 degrees. 
     The groove wall on the tire equatorial plane side of the narrow circumferential minor groove is linearly extended in the tire circumferential direction, and the angle with respect to the normal set to the wheel tread is set in the range of 40 degrees to 80 degrees (measured on the included angle side). Therefore, a balance can be achieved between the block rigidity of the block at the tire equatorial plane side of the narrow circumferential minor groove and the wet drainage property of the narrow circumferential minor groove. 
     When the angle with respect to the normal set to the wheel tread becomes lower than 40 degrees in the groove wall at the tire equatorial plane side of the narrow circumferential minor groove, undesirably the block rigidity is decreased on the tire equatorial plane side of the narrow circumferential minor groove. 
     On the other hand, when the angle with respect to the normal set to the wheel tread becomes exceeds 80 degrees in the groove wall at the tire equatorial plane side of the narrow circumferential minor groove, undesirably a shortage of the groove volume is generated in the narrow circumferential minor groove to decrease the wet drainage property. 
     Another aspect of the exemplary embodiments provides that, in the narrow circumferential minor groove, the groove wall at the tire equatorial plane side is coupled to the opposing groove wall at the outside in the tire axis direction at the stepping-on side with respect to the block. 
     In the narrow circumferential minor groove, on the kickout side of the block, the groove wall at the tire equatorial plane side is not coupled to the opposing groove wall at the outside in the tire axis direction. However, on the stepping-on side of the block, the groove was on the tire equatorial plane side is coupled to the opposing groove wall on the outside in the tire axis direction. 
     The groove wall on the tire equatorial plane side is coupled to the opposing groove wall on the outside in the tire axis direction. Therefore, the block rigidity can be enhanced on the outside of the narrow circumferential minor groove in the tire axis direction to improve the traction performance, brake performance, and cornering performance. 
     Another aspect of a pneumatic tire has plural grooves including a transverse groove in a tread, the transverse groove being extended while inclined with respect to a tire circumferential direction, and a bottom raising portion which raises the bottom of the transverse groove is formed on one side of the transverse groove in a tire width direction, and thereby the transverse groove is substantially opened to and terminated in another groove which is adjacent to the transverse groove on the one side in the tire width direction, the transverse groove is completely opened to other groove which is adjacent to the transverse groove on the other side in the tire width direction or the transverse groove is completely opened to a tread end, and the bottom raising portion forms an inclined surface at the grove bottom surface, a depth of the transverse groove to the inclined surface being gradually decreased from the other side to a top portion of the bottom raising portion in the tire width direction. 
     As used herein, the term “transverse groove is substantially opened to and terminated in another groove” shall mean that the terminal of the transverse groove is opened to another groove while the depth of the transverse groove is not more than 20% of the maximum depth thereof, or a portion whose groove depth is 0 mm is formed in the terminal and the length (width) in the tire width direction is not more than 3 mm in the portion where the groove depth is 0 mm. 
     The term “transverse groove is completely opened to other groove” shall mean that the transverse groove is opened while the opening depth of the transverse groove is larger than 20% of the maximum depth. 
     According to an aspect of the exemplary embodiments, the directional tread wheel pattern is formed in the wheel tread portion and the bottom raising portion is formed in the transverse groove. Therefore, in the wet road surface driving, the water near the bottom raising portion is distributed into the water flow, one flows into another groove on one side in the tire width direction (one side in tire axis direction) of the transverse groove and the other flows toward the other side in tire width direction through the transverse groove caused by the inclined surface. Therefore, the pneumatic tire having the excellent wet drainage property can be obtained. 
     The roadholding ability on the dry road surface, uneven wear-resistant property, and pattern noise property are improved because the rigidity is enhanced in the corner portion of the adjacent land portion by the bottom raising portion provision. This effect is remarkably exhibited in the corner portion which has an acute angle when viewed from the tire surface side, i.e., from the wheel tread side. 
     When one side in tire width direction of the transverse groove is opened to another groove at the position where the depth of the transverse groove is deeper than 20% of the maximum depth thereof, undesirably the block rigidity is decreased in the tread central region to decrease the traction performance, brake performance, and cornering performance while the turbulence is generated in the water flowing in another groove to decrease the wet drainage property. When the portion whose groove depth is 0 mm is formed in the one side in tire width direction of the transverse groove and, at the same time, the length (width) in the tire width direction is not more than 3 mm in the portion where the groove depth is 0 mm, undesirably a shortage of the groove volume is generated in the transverse groove to decrease the drainage property in the wet road surface. The unfavorable property is not generated because the one side in tire width direction of the transverse groove is substantially opened to and terminated in another groove. The plural grooves include at least the transverse groove, and the plural grooves may include the groove except for the transverse groove, e.g., the circumferential major groove. Another groove may be extended along the tire circumferential direction or another groove may be inclined with respect to the tire circumferential direction. 
     Another aspect of the exemplary embodiments provides that the transverse grooves may be formed at substantially equal intervals. 
     Another aspect of the exemplary embodiments provides that a length of a groove portion which has the inclined surface as a groove bottom surface is set in the range of 5 to 100% of a groove length of the transverse groove having the groove portion. 
     When the groove portion is shorter than 5% of the groove length of the transverse groove having the groove portion, the rigidity is decreased in the corner portion of the land portion adjacent to the bottom raising portion, and sometimes undesirably the roadholding ability on the dry road surface, uneven wear-resistant property, and pattern noise property are largely decreased. In the corner portions, this is remarkably exhibited in the corner portion which has an acute angle when viewed from the wheel tread side. When the groove portion is longer than 100% of the groove length of the transverse groove having the groove portion, the inclined surface is projected to another groove (such as the circumferential major groove) to obstruct the water flow in another groove, and undesirably the wet drainage property is decreased. 
     According to an aspect of the exemplary embodiments, the undesirable property is not generated because the groove length of the groove portion ranges from 5 to 100% of the groove length of the transverse groove. 
     Another aspect of the exemplary embodiments provides that the tread includes a circumferential major groove which is extended along the tire circumferential direction, a cross section of the bottom raising portion in a longitudinal direction of the groove is formed in a chevron shape, a one side inclined surface is formed as the grove bottom surface at the bottom raising portion, the groove depth is gradually increased from the top portion to the one side at the one-end-side inclined surface in tire width direction, a land portion adjacent to the transverse groove has an edge portion at the one side, the edge portion has an edge surface which is provided along the circumferential major groove and is chamfered in a tapered shape so that the edge surface forms the same surface as the one side inclined surface, and inclination angles of the one side inclined surface and the edge surface range from 30 to 60° with respect to a line parallel to a tire radial direction. 
     According to an aspect of the exemplary embodiments, the one side inclined surface has the same surface as the edge surface. Therefore, the rigidity is enhanced in the edge portion to improve the roadholding ability or uneven wear-resistant property in the dry road surface and wet road surface. In the wet road surface driving, the wet drainage property is further improved because the water on the land portion surface near the edge portion flows into circumferential major groove without generating the turbulence. 
     The one side inclined surface has the same surface as the edge surface, and the groove bottom terminal formed by the bottom raising portion coincides with the edge end of the edge surface at the circumferential major groove. Therefore, the water flows in the circumferential major groove while distributed without generating the turbulence. This also contributes to the improvement of the wet drainage property. 
     When the inclination angle is lower than 30°, in the wet road surface driving, undesirably the turbulence is generated when the water on the land portion surface near the edge portion flows into the circumferential major groove, and the wet drainage property is easily decreased. When the inclination angle is larger than 60°, because a shortage of the groove volume is easily generated in the circumferential major groove adjacent to the edge portion, undesirably the wet drainage property is easily decreased in the wet road surface driving. According to an aspect of the exemplary embodiments, the above trouble is never generated because the inclination angle is set in the range of 30 to 60°. 
     EFFECT OF THE INVENTION 
     Because the pneumatic tire of the invention has the above configurations, the pneumatic tire has the excellent effect that the high wet drainage performance can be obtained without sacrificing other capabilities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing a tread of a pneumatic tire according to a first embodiment of the invention; 
         FIG. 2A  is an enlarged plan view of the tread; 
         FIG. 2B  is a sectional view taken on line  2 B- 2 F of a first narrow circumferential minor groove; 
         FIG. 2C  is a sectional view taken on line  2 C- 2 C of the first narrow circumferential minor groove; 
         FIG. 2D  is a sectional view taken on line  2 D- 2 D of a second narrow circumferential minor groove; 
         FIG. 2E  is a sectional view taken on line  2 E- 2 E of the second narrow circumferential minor groove; 
         FIG. 3  is a plan view showing a tread of a pneumatic tire according to a second embodiment of the invention; 
         FIG. 4A  is an enlarged plan view of the tread; 
         FIG. 4B  is a sectional view taken on line  4 B- 4 B of a first narrow circumferential minor groove; 
         FIG. 4C  is a sectional view taken on line  4 C- 4 C of the first narrow circumferential minor groove; 
         FIG. 4D  is a sectional view taken on line  4 D- 4 D of a second narrow circumferential minor groove; 
         FIG. 4E  is a sectional view taken on line  4 E- 4 E of the second narrow circumferential minor groove; 
         FIG. 5A  is a sectional view taken on line  5 - 5  of a bottom raising portion shown in  FIG. 3 ; 
         FIG. 5B  is a sectional view showing a bottom raising portion according to another embodiment; 
         FIG. 5C  is a sectional view showing a bottom raising portion according to still another embodiment; 
         FIG. 6  is a plan view showing a tread of a pneumatic tire according to another embodiment; 
         FIG. 7  is a sectional view in a tire axis direction of a pneumatic tire according to a third embodiment; 
         FIG. 8A  is a plan view showing a tread of a pneumatic tire according to the third embodiment; 
         FIG. 8B  is a sectional view taken on line  8 B- 8 B of  FIG. 8A ; 
         FIG. 9A  is a plan view showing a tread of a pneumatic tire according to a fourth embodiment; 
         FIG. 9B  is a sectional view taken on line  9 B- 9 B of  FIG. 9A ; 
         FIG. 10A  is a plan view showing a tread of a pneumatic tire according to a fifth embodiment; 
         FIG. 10B  is a sectional view taken on line  10 B- 10 B of  FIG. 10A ; 
         FIG. 11A  is a plan view showing a tread of a pneumatic tire according to a sixth embodiment; 
         FIG. 11B  is a sectional view taken on line  11 B- 11 B of  FIG. 11A ; 
         FIG. 11C  is a sectional view taken on line  11 C- 11 C of  FIG. 11A ; 
         FIG. 12A  is a plan view showing a tread of a pneumatic tire according to a seventh embodiment; 
         FIG. 12B  is a sectional view taken on line  12 B- 12 B of  FIG. 12A ; 
         FIG. 12C  is a sectional view taken on line  12 C- 12 C of  FIG. 12A ; 
         FIG. 13A  is a plan view showing a tread of a pneumatic tire according to an eighth embodiment; 
         FIG. 13B  is a sectional view taken on line  13 B- 13 B of  FIG. 13A ; 
         FIG. 13C  is a sectional view taken on line  13 C- 13 C of  FIG. 13A ; 
         FIG. 14A  is a plan view showing a tread of a pneumatic tire according to a ninth embodiment; 
         FIG. 14B  is a sectional view taken on line  14 B- 14 B of  FIG. 14A ; 
         FIG. 15A  is a plan view showing a tread of a pneumatic tire according to a tenth embodiment; 
         FIG. 15B  is a sectional view taken on line  15 B- 15 B of  FIG. 15A ; 
         FIG. 16  is a plan view showing a tread of a conventional pneumatic tire; 
         FIG. 17  is a plan view showing a tread of another conventional pneumatic tire; 
         FIG. 18A  is a plan view showing a tread of still another conventional pneumatic tire; and 
         FIG. 18B  is a sectional view taken on line  18 B- 18 B of  FIG. 18A . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     First Embodiment 
     A first embodiment of a pneumatic tire of the invention will be described in detail with reference to the drawings. 
     As shown in  FIG. 1 , a circumferential wide major groove  14  is formed on a tire equatorial plane CL in a tread  12  of a pneumatic tire  10  of the first embodiment. The circumferential wide major groove  14  is linearly extended in a tire circumferential direction (directions of arrows A and B, the direction of arrow B is a tire rotating direction). First narrow circumferential minor grooves  16  extended in the tire circumferential direction are formed on the outside in a tire axis direction with respect to the circumferential wide major groove  14 . Second narrow circumferential minor grooves  18  extended in the tire circumferential direction are further formed on the outside in the tire axis direction with respect to the first narrow circumferential minor grooves  16 . 
     As shown in  FIG. 2A , a groove wall  16 A on the side of the tire equatorial plane CL of the first narrow circumferential minor groove  16  is linearly extended in the tire circumferential direction. In a groove wall  16 B on the outside in the tire axis direction of the first narrow circumferential minor groove  16 , an inclination angle of the groove wall  16 B with respect to the tire circumferential direction is increased from a stepping-on side toward a kickout side such that a distance (groove width) with the groove wall  16 A is widened. 
     As shown in  FIG. 2B , in the groove wall  16 A on the side of the tire equatorial plane CL of the first narrow circumferential minor groove  16 , it is preferable that a groove wall angle θ 16A  with respect to a normal HL to a wheel tread  12 A of the tread  12  range from 40 degrees to 80 degrees. In the first embodiment, the groove wall angle θ 16A  is set at 60 degrees. 
     In the first narrow circumferential minor groove  16 , a groove wall angle θ 16B  of the groove wall  16 B with respect to the normal HL is set at 5 degrees. 
     As shown in  FIGS. 2A and 2C , the groove wall  16 A is in contact with the groove wall  16 B in the area of a substantially central portion to the stepping-on side of the first narrow circumferential minor groove  16 . As shown in  FIG. 2C , a groove shape in cross section has a substantial V-shape in a portion where the groove wall  16 A is in contact with the groove wall  16 B. 
     In the first narrow circumferential minor groove  16  shown in  FIGS. 2A and 2B , the portion where groove wall  16 A is not in contact with the groove wall  16 B exhibits a reversal trapezoid while having a flat groove bottom  16 C. The flat groove bottom  16 C is parallel to the wheel tread  12 A of the tread  12  and is provided between a lower end of the groove wall  16 A and a lower end of the groove wall  16 B as shown in  FIG. 2B . 
     The groove depth is increased toward the kickout side (direction of arrow A) in the portion where the groove wall  16 A and groove wall  16 B of the first narrow circumferential minor groove  16  are in contact with each other. 
     As shown in  FIG. 1 , the second narrow circumferential minor grooves  18  is inclined with respect to the tire circumferential direction so as to sequentially come into contact with the road surface from the side of the tire equatorial plane CL toward the tread end  12 E during an on-load rotating operation. 
     As shown in  FIG. 2A , in the second narrow circumferential minor groove  18 , an angle (inclination angle α) of the groove wall  18 A on the side of the tire equatorial plane CL with respect to the tire circumferential direction is kept constant over the entire length. On the other hand, in the groove wall  18 B on the outside in the tire axis direction, an angle with respect to the tire circumferential direction is increased toward the kickout side. 
     In the groove wall  18 A of the second narrow circumferential minor groove  18 , it is preferable that the inclination angle α range from 3 degrees to 20 degrees. 
     As shown in  FIG. 2D , as with the first narrow circumferential minor groove  16 , in the second narrow circumferential minor groove  18 , it is preferable that the angle θ 18A  of the groove wall  18 A with respect to the normal HL to the wheel tread  12 A range from 40 degrees to 80 degrees. In the first embodiment, the groove wall angle θ 18A  is set at 60 degrees. 
     In the groove wall  18 B of the second narrow circumferential minor groove  18 , the groove wall angle θ 18B  with respect to the normal HL is set at 5 degrees. 
     As shown in  FIGS. 2A and 2E , as with the first narrow circumferential minor groove  16 , the groove wall  18 A is in contact with the opposing groove wall  18 B in the range of the substantial central portion to the stepping-on side of the second narrow circumferential minor groove  18 . As with the first narrow circumferential minor groove  16 , the groove shape in cross section has a substantial V-shape in a portion where the groove wall  18 A is in contact with the groove wall  18 B. 
     As shown in  FIGS. 2A and 2D , in the second narrow circumferential minor groove  18 , the portion where the groove wall  18 A is not in contact with the groove wall  18 B exhibits a flat groove bottom. The flat groove bottom is parallel to the wheel tread  12 A of the tread  12  and is provided between a lower end of the groove wall  18 A and a lower end of the groove wall  18 B. 
     As with the first narrow circumferential minor groove  16 , in the second narrow circumferential minor groove  18 , the groove depth is increased toward the kickout side in the area where the groove wall  18 A and groove wall  18 B are in contact with each other. 
     That is, in both the first narrow circumferential minor groove  16  and the second narrow circumferential minor groove  18 , the kick-out side is larger than the step-in side in the groove width and the groove depth. 
     As shown in  FIG. 1 , first transverse grooves  20 , second transverse grooves  22 , and third transverse grooves  24  are formed in the tread  12 . The first transverse groove  20  is extended from the tread end  12 E toward the tire equatorial plane CL, and the first transverse groove  20  is coupled to the circumferential wide major groove  14  while intersecting with the first narrow circumferential minor groove  16  and the second narrow circumferential minor groove  18 . The second transverse groove  22  is arranged between the first transverse grooves  20 , and the second transverse groove  22  is extended from the tread end  12 E toward the tire equatorial plane CL. The second transverse groove  22  intersects with the first narrow circumferential minor groove  16  and the second narrow circumferential minor groove  18 , and the second transverse groove  22  is terminated without coupling to the circumferential wide major groove  14 . The third transverse groove  24  is arranged between the first transverse groove  20  and the second transverse groove  22 , the third transverse groove  24  is extended from the tread end  12 E toward the tire equatorial plane CL, and the third transverse groove  24  is terminated between the first narrow circumferential minor groove  16  and the second narrow circumferential minor groove  18 . 
     The first transverse grooves  20 , the second transverse grooves  22 , and the third transverse grooves  24  are inclined with respect to the tire circumferential direction so as to sequentially come into contact with the road surface from the side of the tire equatorial plane CL toward the tread end  12 E during the on-load rotating operation. 
     The tread  12  is zoned into a first block  26 , a second block  28 , a stepping-on-side third block  30 , and a kickout-side third block  32 . The first blocks  26  are zoned on both sides of the circumferential wide major groove  14  in the tire axis direction by the circumferential wide major groove  14 , the first narrow circumferential minor groove  16 , the first transverse groove  20 , and the second transverse groove  22 . The second block  28  is zoned on the outside of the first block  26  in the tire axis direction by the first narrow circumferential minor groove  16 , the second narrow circumferential minor groove  18 , the first transverse groove  20 , the second transverse groove  22 , and the third transverse groove  24 . The stepping-on-side third block  30  and the kickout-side third block  32  are located on the outside of the second block  28  in the tire axis direction. The stepping-on-side third block  30  is zoned by the second narrow circumferential minor groove  18 , the first transverse groove  20 , and the third transverse groove  24 . The kickout-side third block  32  is zoned by the second narrow circumferential minor groove  18 , the second transverse groove  22 , and the third transverse groove  24 . 
     A tire equatorial plane-side end portion of the second transverse groove  22  is terminated at a central portion of the first block  26  in the tire axis direction, and a tire equatorial plane-side end portion of the third transverse groove  24  is terminated at a central portion of the second block  28  in the tire axis direction. 
     At this point, assuming that W 2  is the groove width of the first transverse groove  20 , W 3  is the groove width of the second transverse groove  22 , and W 4  is the groove width of the third transverse groove  24 , preferably W 3  is set in the range of 60% to 110% of W 2  while W 4  is set in the range of 20% to 60% of W 2 . 
     In the first embodiment, the groove width W 3  of the second transverse groove  22  is set in the range of 64 to 100% of the groove width W 2  of the first transverse groove  20 , and the groove width W 4  of the third transverse groove  24  is set in the range of 28 to 42% of the groove width W 2  of the first transverse groove  20 . 
     A first transverse siping  34  is formed in a circumferential central portion of the first block  26 , and the first transverse siping  34  couples the second transverse groove  22  and the circumferential wide major groove  14 . In the first block  26 , a second transverse siping  36  is also formed between the first transverse siping  34  and the first transverse groove  20 , and the second transverse siping  36  couples the first narrow circumferential minor groove  16  and the circumferential wide major groove  14 . 
     Longitudinal sipings  38  are formed in the stepping-on-side third block  30  and the kickout-side third block  32  respectively. The longitudinal siping  38  is extended from a kickout edge toward the stepping-on side, and the longitudinal siping  38  is terminated at a block central portion. 
     (Action) 
     The tread pattern of the pneumatic tire  10  of the first embodiment is formed in a directional pattern. Therefore, in the wet road surface driving, the water between the pneumatic tire  10  and the road surface flows efficiently into the circumferential wide major groove  14 , the first narrow circumferential minor groove  16 , the second narrow circumferential minor groove  18 , the first transverse groove  20 , the second transverse groove  22 , and the third transverse groove  24 , and the high wet performance is obtained while the increase in negative ratio is suppressed. Because the high wet performance is obtained while the increase in negative ratio is suppressed, the wheel tread area can be secured in each block to increase the wear-resistant property. 
     A circumferential length of the second block  28  becomes a substantial half of the first block  26 , and each of the circumferential lengths of the stepping-on-side third block  30  and kickout side third block  32  becomes a substantial half of the second block  28 . Therefore, the wet drainage property can be improved on both the sides of the tread while the block rigidity can be increased on the tread central region to improve the traction performance, brake performance, and cornering performance. Furthermore, when the pneumatic tire  10  of the first embodiment is used in a front wheel, the handling performance is improved by increasing the block rigidity of the central region in the tire axis direction. 
     In the range where the block is zoned by the first narrow circumferential minor groove  16  and the second narrow circumferential minor groove  18 , the widths and the depths of the first and second narrow circumferential minor grooves  16  and  18  are decreased from the kickout side toward the stepping-on side of the block during the on-load rotating operation. Therefore, the block rigidity of the stepping-on side is increased to improve the traction performance, brake performance, and cornering performance in the block adjacent to the first narrow circumferential minor groove  16  and the second narrow circumferential minor groove  18 . 
     The tire equatorial plane-side terminal position of the second transverse groove  22  is located at the central region of the first block  26  in the tire axis direction, and the tire equatorial plane-side terminal position of the third transverse groove  24  is located at the central region of the second block  28  in the tire axis direction. Therefore, the water existing on the wheel tread of each block can efficiently be drained, and the block wheel tread area (related to wear-resistant property) and the block rigidity (related to roadholding ability) can be secured while the high wet drainage performance is obtained. Accordingly, the high wet drainage performance, roadholding ability, and wear-resistant property can be obtained in a preferable manner. 
     The groove wall  16 A on the side of the tire equatorial plane CL of the first narrow circumferential minor groove  16  is linearly extended in the tire circumferential direction, and the angle θ 16A  with respect to the normal to the wheel tread  12 A is set in the range of 50 degrees to 80 degrees. Therefore, a balance can be achieved between the rigidity of the first block  26  that is provided at the tire equatorial plane CL side with respect to the first narrow circumferential minor groove  16  and the wet drainage property of the first narrow circumferential minor groove  16 . 
     At the block stepping-on side of the first narrow circumferential minor groove  16 , the groove wall  16 A at the side of the tire equatorial plane CL is coupled to the opposing groove wall  16 B at the outside in the tire axis direction. Therefore, the rigidity can be enhanced to improve the traction performance, brake performance, and cornering performance in the second block  28  that is provided at the outside of the first narrow circumferential minor groove  16  in the tire axis direction. 
     Similarly, at the block stepping-on side of the second narrow circumferential minor groove  18 , the groove wall  18 A on the side of the tire equatorial plane CL is coupled to the opposing groove wall  18 B on the outside in the tire axis direction. Therefore, the rigidity can be enhanced in the third block  30  that is provided at the outside of the second narrow circumferential minor groove  18  in the tire axis direction. 
     The groove width W 3  of the second transverse groove  22  is set in the range of 60% to 110% of the groove width W 2  of the first transverse groove  20 , and the groove width W 4  of the third transverse groove  24  is set in the range of 20% to 60% of the groove width W 2  of the first transverse groove  20 . Therefore, a balance can be achieved between the wet drainage property and the block rigidity in the region surrounded by the first transverse groove  20  and the second transverse groove  22 . 
     The groove width W 3  of the second transverse groove  22  is set substantially equal to the groove width W 2  of the first transverse groove  20 , namely, the groove width W 3  of the second transverse groove  22  is set in the range of 60% to 110% of the groove width W 2  of the first transverse groove  20 , which secures the high wet drainage property. 
     The second narrow circumferential minor groove  18  arranged in the outermost side in the tire axis direction is inclined so as sequentially come into contact with the road surface from the side of the tire equatorial plane CL toward the tread end  12 E during the on-load rotating operation. Therefore, the wet drainage performance is improved near both the outsides in the tire axis direction of the tire ground contact surface portion. 
     Accordingly the pneumatic tire  10  of the first embodiment is suitable for the use of the racing ultra-high performance vehicle front-tire. 
     The wet drainage performance cannot be improved when the inclination angle α is lower than three degrees in the groove wall  18 A of the second narrow circumferential minor groove  18 . 
     On the other hand, when the inclination angle α is more than 20 degrees, the block end at the kick-out side of the second block  28  that is adjacent to the second transverse groove  22  becomes an acute angle, which results in the undesirable shortage of the block rigidity. 
     (Test Example) 
     A tire of Conventional example and a tire of the present Example are attached to the front wheel of the actual vehicle, and a test is performed to confirm the effect of the invention. In the test, the tire of Example is compared to the tire of Conventional example for the hydroplaning, wet circuit lap time, and wet grip. 
     Hydroplaning: the vehicle runs on the wet road surface whose water depth is 2 mm, and hydroplaning generation speed is measured. The evaluation is displayed as an index in which the hydroplaning generation speed is set at 100 in the conventional tire. As the index is increased, the hydroplaning generation speed is enhanced. Therefore, the higher index indicates that the tire has the excellent wet drainage property. 
     Wet circuit lap time: a lap time is measured when the vehicle runs round on the wet road surface (test course) whose water depth is 2 mm. The evaluation is displayed as an index in which the lap time is set at 100 in the conventional tire. As the index is decreased, the lap time is shortened. Therefore, the lower index indicates that the tire has the excellent wet circuit running property. 
     Wet grip: a feeling evaluation is performed by a test driver when the vehicle runs round on the wet road surface (test course) whose water depth is 2 mm. The evaluation is displayed as an index in which the feeling is set at 100 in the conventional tire. As the index is increased, the tire has the excellent wet grip. 
     The tire of Example: the pneumatic tire of the above-described first embodiment is used. 
     The tire of Conventional example: a pneumatic tire having a tread pattern shown in  FIG. 16  is used. 
     As shown in  FIG. 16 , in a tread  502  of a pneumatic tire  500  of Conventional example, a circumferential wide major groove  504  is formed on the tire equatorial plane CL. 
     In the tread  502 , plural first transverse grooves  506  are formed on both sides of the circumferential wide major groove  504 . The first transverse groove  506  is extended from a tread end  502 E toward the circumferential wide major groove  504 , and the first transverse groove  506  is coupled to the circumferential wide major groove  504 . A second transverse groove  508  is formed between the first transverse grooves  506 . The second transverse groove  508  is extended from the tread end  502 E toward the circumferential wide major groove  504 , and the second transverse groove  508  is terminated at a middle portion between the tire equatorial plane CL and the tread end  502 E. 
     A minor groove  510  is coupled to the middle portion of the first transverse groove  506 . The minor groove  510  is extended toward the stepping-on side and the minor groove  510  is terminated in the block. 
     Sizes are RAR  265 / 55 R 13  (tread width is 200 mm) in the tires of Conventional example and Example. Table 1 shows specifications of each tire. 
     Test vehicle wheel alignment: 
     front-wheel toe angle (toe-out side) of 1 mm and negative camber angle of 4°, 
     rear-wheel toe angle (toe-in side) of 1 mm and negative camber angle of 3° 
     Table 2 shows the test results. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Conventional 
                   
               
               
                   
                 example 
                 Example 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Circumferential wide major groove: 
                 2.8 
                 2.8 
               
               
                 groove depth D0 (mm) 
               
               
                 Circumferential wide major groove: 
                 13   
                 13   
               
               
                 groove width W0 (mm) 
               
               
                 First and second narrow circumferential 
                 — 
                 1.3 to 2.8 
               
               
                 minor grooves: groove depth D1 (mm) 
               
               
                 First and second narrow circumferential 
                 — 
                 4.0 
               
               
                 minor grooves: groove width W1 (mm) of 
               
               
                 middle portion 
               
               
                 Circumferential inclination angle α 
                 — 
                 8   
               
               
                 (degree) to tire equatorial plane-side 
               
               
                 groove wall 
               
               
                 of second narrow circumferential minor 
               
               
                 groove 
               
               
                 First transverse groove: groove depth D2 
                 2.8 
                 2.8 
               
               
                 First transverse groove: groove width W2 
                 12 to 20 
                 14 to 19 
               
               
                 Second transverse groove: groove depth 
                 — 
                 2.8 
               
               
                 D3 
               
               
                 Second transverse groove: groove width 
                   
                  9 to 19 
               
               
                 W3 
               
               
                 Third transverse groove: groove depth D4 
                 2.8 
                 2.8 
               
               
                 Third transverse groove: groove width 
                 6 to 9 
                 4 to 8 
               
               
                 W4 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Conventional 
                   
               
               
                   
                 Name 
                 example 
                 Example 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Hydroplaning 
                 100 
                 110 
               
               
                   
                 Wet circuit lap time 
                 100 
                 96 
               
               
                   
                 Wet grip 
                 100 
                 120 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen from the test results, in the pneumatic tire of Example to which the invention is applied, all the hydroplaning, wet circuit lap time, and wet grip are improved compared with the pneumatic tire of Conventional example. 
     Second Embodiment 
     A second embodiment of a pneumatic tire of the invention will be described in detail with reference to the drawings. 
     As shown in  FIG. 3 , a circumferential wide major groove  114  is formed on the tire equatorial plane CL in a tread  112  of a pneumatic tire  110  of the second embodiment. The circumferential wide major groove  114  is linearly extended in the tire circumferential direction. First narrow circumferential minor grooves  116  extended in the tire circumferential direction are formed on the outside of the circumferential wide major groove  114  in a tire axis direction. Second narrow circumferential minor grooves  118  extended in the tire circumferential direction are further formed on the outside of the first narrow circumferential minor grooves  116  in the tire axis direction. 
     As shown in  FIG. 4A , a groove wall  116 A of the first narrow circumferential minor groove  116  that is provided at the tire equatorial plane CL side is linearly extended in the tire circumferential direction. In a groove wall  116 B of the first narrow circumferential minor groove  116  provided at the outside in the tire axis direction, the inclination angle of the groove wall  116 B with respect to the tire circumferential direction is increased from the stepping-on side toward the kickout side such that a distance (groove width) formed between the groove wall  116 A and the groove wall  116 B is widened. 
     As shown in  FIG. 4B , in the groove wall  116 A, it is preferable that the groove wall angle θ 16A  with respect to the normal HL to a wheel tread  112 A of the tread  112  range from 50 degrees to 80 degrees. In the second embodiment, the groove wall angle θ 16A  is set at 60 degrees. 
     In the first narrow circumferential minor groove  116 , the groove wall angle θ 16B  of the groove wall  116 B is set at 5 degrees. 
     As shown in  FIGS. 4A and 4C , the groove wall  116 A is in contact with the groove wall  116 B in the area of the substantially central portion to the stepping-on side of the first narrow circumferential minor groove  116 . As shown in  FIG. 4C , the groove shape in cross section has the substantial V-shape in a portion where the groove wall  116 A is in contact with the groove wall  116 B. 
     In the first narrow circumferential minor groove  116  shown in  FIGS. 4A and 4B , the portion where groove wall  116 A is not in contact with the groove wall  116 B exhibits a reversal trapezoid while having a flat groove bottom  116 C. The flat groove bottom  116 C is parallel to the wheel tread  112 A of the tread  112  and is provided between a lower end of the groove wall  116 A and a lower end of the groove wall  116 B as shown in  FIG. 4B . 
     The groove depth is increased toward the kickout side in the portion where the groove wall  116 A and groove wall  116 B are in contact with each other in the first narrow circumferential minor groove  116 . 
     As shown in  FIG. 4A , as with the groove wall  116 A of the first narrow circumferential minor groove  116 , a groove wall  118 A at the tire equatorial plane CL side of a second narrow circumferential minor groove  118  is linearly extended in the tire circumferential direction. In the groove wall  118 B provided at the outside of the second narrow circumferential minor groove  118  in the tire axis direction, the inclination angle with respect to the tire circumferential direction is increased from the stepping-on side toward the kickout side such that the distance (groove width) formed between the groove wall  118 A and the groove wall  118 B is widened. 
     As shown in  FIG. 4D , as with the first narrow circumferential minor groove  116 , in the second narrow circumferential minor groove  118 , it is preferable that in the groove wall  118 A, the angle θ 18A  with respect to the normal HL to the wheel tread  112 A range from 50 degrees to 80 degrees. In the second embodiment, the groove wall angle θ 18A  is set at 60 degrees. 
     In the groove wall  118 B of the second narrow circumferential minor groove  118 , the groove wall angle θ 18E  is set at 5 degrees. 
     As shown in  FIGS. 4A and 4D , as with the first narrow circumferential minor groove  116 , the groove wall  118 A is in contact with the opposing groove wall  118 B in the area of the substantial central portion to the stepping-on side in the second narrow circumferential minor groove  118 . As with the first narrow circumferential minor groove  116 , the groove shape in cross section has the substantial V-shape in the portion where the groove wall  118 A is in contact with the groove wall  118 B. 
     As shown in  FIGS. 4A and 4E , as with the first narrow circumferential minor groove  116 , in the second narrow circumferential minor groove  118 , the portion where groove wall  118 A is not in contact with the groove wall  118 B has the flat groove bottom that is parallel to the wheel tread  112 A of the tread  112 . The flat groove bottom is formed between the lower end of the groove wall  118 A and the lower end of the groove wall  118 B. 
     As with the first narrow circumferential minor groove  116 , the groove depth is increased toward the kickout side in the portion where the groove wall  118 A and groove wall  118 B are in contact with each other in the second narrow circumferential minor groove  118 . 
     That is, in both the first narrow circumferential minor groove  116  and the second narrow circumferential minor groove  118 , the stepping-on side is larger than the kickout side in the groove width and the groove depth. Therefore, the block rigidity is secured while the drainage property is improved. 
     As shown in  FIG. 3 , first transverse grooves  120  and second transverse grooves  122  are formed in the tread  112 . The first transverse groove  120  is extended from the tread end  112 E toward the tire equatorial plane CL, and the first transverse groove  120  is coupled to the circumferential wide major groove  114  while intersecting with the first narrow circumferential minor groove  116  and the second narrow circumferential minor groove  118 . The second transverse groove  122  is arranged between the first transverse grooves  120 , and the second transverse groove  122  is extended from the tread end  112 E toward the tire equatorial plane CL. The second transverse groove  122  intersects with the second narrow circumferential minor groove  118 , and the second transverse groove  122  is terminated in the middle portion between the first narrow circumferential minor groove  116  and the second narrow circumferential minor groove  118 . 
     The tread  112  is zoned into a first block  126 , a second block  128 , a stepping-on-side third block  130 , and a kickout-side third block  132 . On both sides of the circumferential wide major groove  114  in the tire axis direction, the first blocks  126  are zoned by the circumferential wide major groove  114 , the first narrow circumferential minor groove  116 , and the first transverse groove  120 . The second block  128  is zoned at the outside of the first block  126  in the tire axis direction by the first narrow circumferential minor groove  116 , the second narrow circumferential minor groove  118 , the first transverse groove  120 , and the second transverse groove  122 . The stepping-on-side third block  130  and the kickout-side third block  132  are located at the outside of the second block  128  in the tire axis direction while zoned by the second narrow circumferential minor groove  118 , the first transverse groove  120 , and the second transverse groove  122 . 
     The first transverse groove  120  has a bottom raising portion  140  at the side of the circumferential wide major groove  114 . 
     As shown in  FIGS. 3 and 5 , the bottom raising portion  140  of the second embodiment is formed from an end portion of the first transverse groove  120  that is provided at the side of the circumferential wide major groove  114  to the outside in the tire axis direction. Accordingly, the groove wall of the circumferential wide major groove  114  is linearly extended along the tire circumferential direction, and there is no irregularity in the groove wall. 
     In the bottom raising portion  140 , the end portion at the side of the circumferential wide major groove  14  is highest and the height is gradually decreased toward the outside in the tire axis direction. As shown in  FIG. 5 , the sectional shape in a longitudinal direction (the tire width direction) exhibits a substantial triangle. 
     As shown in  FIG. 3 , in the second embodiment, a top portion  140 A of the bottom raising portion  140  is linearly arranged at an extended line of a wheel tread opening edge portion of the circumferential wide major groove  114 . 
     As shown in  FIG. 3 , in the second embodiment, a base  140 B of the bottom raising portion  140  is linearly formed in the tire circumferential direction (parallel to top portion  140 A). 
     As shown in  FIG. 3 , in the bottom raising portion  140 , it is preferable that a size in tire axis direction L 0  be in the range of 60 to 200% of a groove width size W 0  of the circumferential wide major groove  114 . In the second embodiment, the size in tire axis direction L 0  is set at 123% of the groove width size W 0 . 
     As shown in  FIG. 5A , in the bottom raising portion  140  of the second embodiment, the top portion  140 A becomes a vertex of the triangle, and the top portion  140 A has no width when viewed from a cross section in the longitudinal direction (the tire width direction). Alternatively, as shown in  FIGS. 5B and 6 , the top portion  140 A may have a width L 1 . 
     However, the width L 1  of the top portion  140 A is set to 3 mm or less when the position of the top portion  140 A is flush with the wheel tread  112 A of the tread  112 . 
     As shown in  FIG. 5C , a depth d at the top portion  140 A is set to 10% or more of a groove depth D (portion except for bottom raising portion  140 , i.e., the deepest portion). 
     As shown in  FIG. 3 , a tire equatorial plane-side end portion of the second transverse groove  122  is terminated in the central portion of the second block  128  in the tire axis direction. 
     Preferably the groove width W 3  of the second transverse groove  122  is set in the range of 10 to 80% of the groove width W 2  of the first transverse groove  120 . The groove width W 3  of the second transverse groove  122  of the second embodiment is set in the range of 14 to 50% of the groove width W 2  of the first transverse groove  120 . 
     A transverse siping  134  is formed in the central portion of the first block  126  in the circumferential direction. The transverse siping  134  is extended from the first narrow circumferential minor groove  116  toward the block central, and the transverse siping  134  is terminated in the block central portion. 
     Longitudinal sipings  138  are formed in the central portion of the stepping-on-side third block  130  in the tire axis direction and the central portion of the kickout-side third block  132  in the tire axis direction respectively. The longitudinal siping  138  is extended from kickout edge toward the stepping-on side, and the longitudinal sipings  138  is terminated in the block central portion. 
     (Function) 
     In the pneumatic tire  110  of the second embodiment, when the vehicle runs on the wet road surface, the water near the central portion in the tire axis direction flows into the circumferential wide major groove  114 , and other water flows into the first transverse groove  120 . 
     The water on the wheel tread of the block surrounded by the circumferential wide major groove  114  and the first transverse groove  120  flows into the circumferential wide major groove  114 , the first narrow circumferential minor groove  116 , and the second transverse groove  122 . 
     The tread pattern of the pneumatic tire  110  is formed in a directional pattern. Therefore, when the vehicle runs on the wet road surface, the water between the pneumatic tire  110  and the road surface flows efficiently into the circumferential wide major groove  114 , the first narrow circumferential minor groove  116 , the second narrow circumferential minor groove  118 , the first transverse groove  120 , and the second transverse groove  122 , and the high wet performance is obtained while the increase in negative ratio is suppressed. 
     Because the high wet performance is obtained while the increase in negative ratio is suppressed, the wheel tread area can be secured in each block to improve the wear-resistant property. 
     In the area where the block is zoned by the first narrow circumferential minor groove  116  and the second narrow circumferential minor groove  118 , the widths and the depths of the first and second narrow circumferential minor grooves  116  and  118  are decreased from the kickout side toward the stepping-on side of the block that are defined during the on-load rotating operation. Therefore, the block rigidity on the stepping-on side is increased to improve the traction performance, brake performance, and cornering performance in the block adjacent to the first narrow circumferential minor groove  116  and the second narrow circumferential minor groove  118 . 
     The groove wall  116 A that is provided at the side of the tire equatorial plane CL in the first narrow circumferential minor groove  116  is linearly extended in the tire circumferential direction, and the angle θ 16A  with respect to the normal to the wheel tread  112 A is set in the range of 50 degrees to 80 degrees. Therefore, a balance can be achieved between the rigidity of the first block  126  at the side of the tire equatorial plane CL with respect to the first narrow circumferential minor groove  116  and the wet drainage property of the first narrow circumferential minor groove  116 . 
     At the block stepping-on side of the first narrow circumferential minor groove  116 , the groove wall  116 A is coupled to the opposing groove wall  116 B that is provided at the outside in the tire axis direction. Therefore, the rigidity can be enhanced to improve the traction performance, brake performance, and cornering performance in the second block  128  that is provided at the outside of the first narrow circumferential minor groove  116  in the tire axis direction. 
     Similarly, at the block stepping-on side of the second narrow circumferential minor groove  118 , the groove wall  118 A provided at the side of the tire equatorial plane CL is coupled to the opposing groove wall  118 B provided at the outside in the tire axis direction. Therefore, the rigidity can be enhanced in the third block  130  that is provided at the outside of the second narrow circumferential minor groove  118  in the tire axis direction. 
     The groove width of the second transverse groove  122  is set in the range of 10% to 80% of the groove width of the first transverse groove  120 . Therefore, a balance can achieved between the wet drainage property and the block rigidity in the region at the outside in the tire axis direction of the tread  112 . 
     Accordingly the pneumatic tire  110  of the second embodiment is suitable for the use of the racing ultra-high performance vehicle rear-tire. 
     (Test Example) 
     The tire of Conventional example and the tires of the present Examples to which the invention is applied are attached to the rear wheel of the actual vehicle, and the test is performed to confirm the effect of the invention. In the test, the tires of Examples are compared to the tire of Conventional example for the hydroplaning, wet circuit lap time, and wet grip. 
     Hydroplaning: the vehicle runs on the wet road surface whose water depth is 2 mm, and hydroplaning generation speed is measured. The evaluation is displayed as an index in which the hydroplaning generation speed is set at 100 in the conventional tire. As the index is increased, the hydroplaning generation speed is enhanced. Therefore, the higher index indicates that the tire has the excellent wet drainage property. 
     Wet circuit lap time: a lap time is measured when the vehicle runs round on the wet road surface (test course) whose water depth is 2 mm. The evaluation is displayed as an index in which the lap time is set at 100 in the conventional tire. As the index is decreased, the lap time is shortened. Therefore, the lower index indicates that the tire has the excellent wet circuit running property. 
     Wet grip: the feeling evaluation is performed by the test driver when the vehicle runs round on the wet road surface (test course) whose water depth is 2 mm. The evaluation is displayed as an index in which the feeling is set at 100 in the conventional tire. As the index is increased, the tire has the excellent wet grip. 
     The tire of Example 1: the pneumatic tire shown in  FIG. 3  of the second embodiment is used. 
     The tire of Example 2: the pneumatic tire shown in  FIG. 6  of the second embodiment is used. The top portion of the bottom raising portion has the width of 2 mm. 
     The tire of Conventional example: a pneumatic tire having a tread pattern shown in  FIG. 17  is used. 
     As shown in  FIG. 17 , in a tread  602  of a pneumatic tire  600  of Conventional example, a circumferential wide major groove  604  is formed on the tire equatorial plane CL. 
     In the tread  602 , plural first transverse grooves  606  are formed on both sides of the circumferential wide major groove  604 . The first transverse groove  606  is extended from a tread end  602 E toward the circumferential wide major groove  604 , and the first transverse groove  606  is coupled to the circumferential wide major groove  604 . A second transverse groove  608  is formed between the first transverse grooves  606 . The second transverse groove  608  is extended from the tread end  602 E toward the circumferential wide major groove  604 , and the second transverse groove  608  is terminated at the middle portion between the tire equatorial plane CL and the tread end  602 E. 
     A minor groove  610  is coupled to the middle portion of the first transverse groove  606 . The minor groove  610  is extended toward the stepping-on side and the minor groove  610  is terminated in the block central portion. 
     The numeral  612  designates siping formed in the land portion. 
     Sizes are RAR325/55R13 (tread width is 250 mm) in the tires of Conventional example and Examples. Table 3 shows specifications of each tire. 
     Test vehicle wheel alignment: 
     front-wheel toe angle (toe-out side) of 1 mm and negative camber angle of 4°, 
     rear-wheel toe angle (toe-in side) of 1 mm and negative camber angle of 3° 
     Table 4 shows the test results. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Conventional 
                   
                   
               
               
                   
                 example 
                 Example 1 
                 Example 2 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Circumferential wide 
                 2.8 
                 2.8 
                 2.8 
               
               
                 major groove 
               
               
                 Groove depth D0 
               
               
                 (mm) 
               
               
                 Circumferential wide 
                 17   
                 17   
                 17   
               
               
                 major groove 
               
               
                 Groove width W0 
               
               
                 (mm) 
               
               
                 First and second 
                 — 
                 1.3 to 2.8 
                 1.3 to 2.8 
               
               
                 narrow circumferential 
               
               
                 minor grooves 
               
               
                 Groove depth D1 
               
               
                 First and second 
                 — 
                 4.0 
                 4.0 
               
               
                 narrow circumferential 
               
               
                 minor grooves 
               
               
                 Groove width W1 
               
               
                 (mm) of middle 
               
               
                 portion 
               
               
                 First transverse groove 
                 2.8 
                 2.8 
                 2.8 
               
               
                 Groove depth D2 
               
               
                 (mm) 
               
               
                 First transverse groove 
                 13 to 15 
                 14 to 20 
                 14 to 20 
               
               
                 Groove width W2 
               
               
                 (mm) 
               
               
                 Second transverse 
                 2.8 
                 2.8 
                 2.8 
               
               
                 groove 
               
               
                 Groove depth D3 
               
               
                 (mm) 
               
               
                 Second transverse 
                 6 to 9 
                  2 to 10 
                  2 to 10 
               
               
                 groove 
               
               
                 Groove width W3 
               
               
                 (mm) 
               
               
                 Bottom raising portion 
                 — 
                 16   
                 16   
               
               
                 With L0 (mm) 
               
               
                 Bottom raising portion 
                 — 
                 0   
                 2   
               
               
                 Top portion width L1 
               
               
                 (mm) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                   
                 Conventional 
                   
                   
               
               
                   
                 Name 
                 example 
                 Example 1 
                 Example 2 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Hydroplaning 
                 100 
                 115 
                 113 
               
               
                   
                 Wet circuit lap time 
                 100 
                 92 
                 90 
               
               
                   
                 Wet grip 
                 100 
                 115 
                 117 
               
               
                   
                   
               
            
           
         
       
     
     As can be seen from the test results, in the pneumatic tires of Examples 1 and 2 to which the invention is applied, all the hydroplaning, wet circuit lap time, and wet grip are improved compared with the pneumatic tire of Conventional example. 
     Third Embodiment 
     A third embodiment of a pneumatic tire of the invention will be described in detail with reference to the drawings. 
     As shown in  FIG. 7 , a pneumatic tire  210  according to the third embodiment includes a carcass  212 . The carcass  212  includes cords which are substantially extended in the radial direction, and both end portions are folded by bead cores  211  respectively. The carcass  212  is formed by a single layer or multilayer. 
     A belt layer  214  in which plural belt plies are laminated is embedded on the outside in a tire radial direction of a crown portion  12 C of the carcass  212 . A tread portion  218  in which the grooves are arranged is formed on the outside in the tire radial direction of the belt layer  214 . 
     As shown in  FIG. 8A , in a wheel tread portion  219  of the tread portion  218 , a first outer major groove  222 A extended in the tire circumferential direction is formed on one surface side with respect to the tire equatorial plane CL, and a second outer major groove  222 B extended in the tire circumferential direction is formed on the other surface side with respect to the tire equatorial plane CL. Each of the first outer major groove  222 A and the second outer major groove  222 B is formed at the position which is close to a quarter point Q of a width W of the wheel tread portion  219 . The first outer major groove  222 A and the second outer major groove  222 B zone the wheel tread portion  219  into a central region  220  and side regions  221 . 
     In both the side regions  221 , lug grooves  226  are formed at substantially equal intervals in the tire circumferential direction, and the tire equatorial plane-side end portion of the lug groove  226  is substantially opened to and terminated in the first outer major groove  222 A or the second outer major groove  222 B. 
     Both the end portions in the tire width direction of each lug groove  226  are extended across the tread end such that the water can be drained to the outside in the tire width direction. As used herein, the term “tread end” shall mean an outermost ground contact portion in the tire width direction, in the case where the pneumatic tire is attached to a standard rim defined by JATMA YEAR BOOK (2004, specification of THE Japan Automobile tire Manufacturers Association), the pneumatic tire is filled with an inner pressure of 100% of a pneumatic pressure (maximum pneumatic pressure) corresponding to a maximum load capacity (bold load in an inner pressure-load capacity corresponding table) in an application size and ply rating in JATMA YEAR BOOK, and the maximum load capacity is applied to the pneumatic tire. When TRA specification or ETRTO specification is applied to a place where the pneumatic tire is used or a place where the pneumatic is manufactured, the test is subject to each specification. 
     In the central region  220 , a first inner major groove  224 A extended in the tire circumferential direction is formed on one side surface with respect to the tire equatorial plane CL, and a second inner major groove  224 B extended in the tire circumferential direction is formed on the other surface with respect to the tire equatorial plane CL. Each of the first outer major groove  222 A, second outer major groove  222 B, first inner major groove  224 A, and second inner major groove  224 B is the major groove having the groove depth D 0 . The first inner major groove  224 A and the second inner major groove  224 B are arranged at the positions such that a distance between the first inner major groove  224 A and the second inner major groove  224 B, a distance between the first outer major groove  222 A and the first inner major groove  224 A, and a distance between the second outer major groove  222 B and the second inner major groove are substantially equalized to one another. 
     A central land portion row  228 , a first adjacent land portion row  230 , and a second adjacent land portion row  232  are formed in the central region  220 . The central land portion row  228  is zoned by the first inner major groove  224 A and the second inner major groove  224 B. The first adjacent land portion row  230  is zoned by the first outer major groove  222 A and the first inner major groove  224 A. The second adjacent land portion row  232  is zoned by the second outer major groove  222 B and the second inner major groove  224 B. 
     Plural central inclined grooves (lug grooves)  234  are formed in the central region  220 . The central inclined grooves  234  are formed at substantially equal intervals so as to cross the central land portion row  228 , and the central inclined grooves  234  are extended while inclined with respect to the tire circumferential direction. As a result, a land portion  229  is formed in the central land portion row  228  by the first inner major groove  224 A, second inner major groove  224 B, central inclined grooves  234  adjacent to each other in the tire circumferential direction. The land portions  229  are arrayed in the tire circumferential direction so as to stride over both the sides of the tire equatorial plane CL. 
     Plural first inclined grooves  236  are arranged in the central region  220 . The first inclined grooves  236  are formed at substantially equal intervals so as to cross the first adjacent land portion row  230 , and the first inclined grooves  236  are extended while inclined with respect to the tire circumferential direction. As a result, a land portion  231  is formed in the first adjacent land portion row  230  by the first inner major groove  224 A, first outer major groove  222 A, first inclined grooves  236  adjacent to each other in the tire circumferential direction. The land portions  231  are arrayed in the tire circumferential direction. The inclination direction of the first inclined groove  236  is opposite to the inclination direction of the central inclined groove  234 . 
     Similarly, plural second inclined grooves  238  are arranged in the central region  220 . The second inclined grooves  238  are formed at substantially equal intervals so as to cross the second adjacent land portion row  232 , and the second inclined grooves  238  are extended while inclined with respect to the tire circumferential direction. As a result, a land portion  233  is formed in the second adjacent land portion row  232  by the second inner major groove  224 B, second outer major groove  222 B, second inclined grooves  238  adjacent to each other in the tire circumferential direction. The land portions  233  are arrayed in the tire circumferential direction. The inclination direction of the second inclined groove  238  is similar to the inclination direction of the first inclined groove  236 . 
     The groove length is set at L 0  for each of the central inclined groove  234 , first inclined groove  236 , and second inclined groove  238 . The groove depth is set at D 1  (see  FIG. 8B ) in the groove portion except for the later-mentioned bottom raising portion for each of the central inclined groove  234 , first inclined groove  236 , and second inclined groove  238 . 
     (First Inclined Groove) 
     A first bottom raising portion  242  which raises the groove bottom is formed near a first inner major groove-side end  236 J in the first inclined groove  236 , so that the first inclined groove  236  is substantially opened to and terminated in the first inner major groove  224 A (also see  FIG. 8B ). 
     A cross section of the first bottom raising portion  242  in the tire width direction (longitudinal direction of the groove) is formed in a chevron shape, the first inner major groove-side end  236 J has the highest peak where a first edge line  244  is formed, and a first inclined surface  246  is formed as the groove bottom surface. In the first bottom raising portion  242 , the groove depth is gradually increased from the first inner major groove-side end  236 J toward a first outer major groove-side end  242 K at the bottom raising portion  242  (namely, the groove depth is gradually decreased from the first outer major groove-side end  242 K of the first bottom raising portion  242  toward the first inner major groove-side end  236 J). 
     The first inclined groove  236  is completely opened to the first outer major groove  222 A at the first outer major groove-side end  236 K of the first inclined groove  236 . 
     A groove length L 1  of a groove portion  236 P in which the first inclined surface  246  is formed as the groove bottom surface is set in the range of 5 to 100% of the groove length L 0  of the first inclined groove  236  having the groove portion  236 P. 
     The position of the first edge line  244  in the tire width direction is located at the same position as the groove edge of the first inner major groove  224 A. 
     (Central Inclined Groove) 
     A central bottom raising portion  252  which raises the groove bottom is formed near a first inner major groove-side end  234 J of the central inclined groove  234 , so that the central inclined groove  234  is substantially opened to and terminated in the first inner major groove  224 A. 
     As with the first bottom raising portion  242 , a cross section in the tire width direction (longitudinal direction of the groove) of the central bottom raising portion  252  is formed in a chevron shape, the first inner major groove-side end  234 J has the highest peak where a central edge line  254  is formed, and a central inclined surface  256  is formed as the groove bottom surface. In the central bottom raising portion  252 , the groove depth is gradually increased from the first inner major groove-side end  234 J toward a second inner major groove-side end  252 K at the central bottom raising portion  252  (namely, the groove depth is gradually decreased from the second inner major groove-side end  252 K of the central bottom raising portion  252  toward the first inner major groove-side end  234 J). 
     The central inclined groove  234  is completely opened to the second inner major groove  224 B at the second inner major groove-side end  234 K of the central inclined groove  234 . 
     The groove length of a groove portion  234 P in which the central inclined surface  256  is formed as the groove bottom surface is set in the range of 5 to 100% of the groove length of the central inclined groove  234  having the groove portion  234 P. 
     The position of the central edge line  254  in the tire width direction is located at the same position as the groove edge of the first inner major groove  224 A. 
     (Second Inclined Groove) 
     A second bottom raising portion  262  which raises the groove bottom is formed near a second inner major groove-side end  238 J of the second inclined groove  238 , so that the second inclined groove  238  is substantially opened to and terminated in the second inner major groove  224 B. 
     As with the central bottom raising portion  252 , a cross section in the tire width direction (longitudinal direction of the groove) of the second bottom raising portion  262  is formed in a chevron shape, the second inner major groove-side end  238 J has the highest peak where a second edge line  264  is formed, and a second inclined surface  266  is formed as the groove bottom surface. In the second bottom raising portion  262 , the groove depth is gradually increased from the second inner major groove-side end  238 J toward a second outer major groove-side end  262 K at the second bottom raising portion  262  (namely, the groove depth is gradually decreased from the second outer major groove-side end  262 K toward the second inner major groove-side end  238 J at the second bottom raising portion  262 ). 
     The second inclined groove  238  is completely opened to the second outer major groove  222 B at the second outer major groove-side end  238 K thereof. 
     The groove length of a groove portion  238 P in which the second inclined surface  266  is formed as the groove bottom surface is set in the range of 5 to 100% of the groove length of the second inclined groove  238  having the groove portion  238 P. 
     The position of the second edge line  264  in the tire width direction is located at the same position as the groove edge of the second inner major groove  224 B. 
     (Lug Groove) 
     The lug grooves  226  have the same basic configuration, action, and effect on both the sides of the tire equatorial plane CL. Therefore, the lug groove  226  indicated on the left of  FIG. 8A  (one surface side of the tire equatorial plane CL) will be described, and the description will be omitted for the lug groove  226  on the right. 
     A lug groove bottom raising portion  272  which raises the groove bottom is formed near a first outer major groove-side end  226 J of the lug groove  226 , so that the lug groove  226  is substantially opened to and terminated in the first outer major groove  222 A (also see  FIG. 8B ). 
     A cross section of the lug groove bottom raising portion  272  in the tire width direction (longitudinal direction of the groove) is formed in a chevron shape, the first outer major groove-side end  226 J has the highest peak where a lug groove edge line  274  is formed, and a lug groove inclined surface  276  is formed as the groove bottom surface. In the lug groove bottom raising portion  272 , the groove depth is gradually increased from the first outer major groove-side end  226 J toward a tread end-side end  272 K at the lug groove bottom raising portion  272  (namely, the groove depth is gradually decreased from the tread end-side end  272 K toward the first outer major groove-side end  226 J at the lug groove bottom raising portion  272 ). 
     The lug groove  226  is completely opened at a tread end T. 
     The groove length of a groove portion  226 P in which the lug groove inclined surface  276  is formed as the groove bottom surface is set in the range of 5 to 100% of the groove length of the lug groove  226  having the groove portion  226 P. 
     The position of the lug groove edge line  274  in the tire width direction is located at the same position as the groove edge of the first outer major groove  222 A. 
     The respective length of the groove portion where the groove bottom is formed is set at L 1  (see  FIG. 8B ) for each of the central inclined surface  256 , first inclined surface  246 , second inclined surface  266 , and the lug groove inclined surface  276 . 
     (Function) 
     As described above, in the third embodiment, the directional tread pattern is formed in the wheel tread portion  219 , and the central bottom raising portion  252 , first bottom raising portion  242 , second bottom raising portion  262 , and lug groove bottom raising portion  272  are formed in the central inclined groove  234 , first inclined groove  236 , second inclined groove  238 , and lug groove  226  respectively. 
     Therefore, in wet road surface driving, the water near the central bottom raising portion  252  is distributed into the water which flows into the first inner major groove  224 A while not guided by the central inclined surface  256  and the water which flows into the second inner major groove  224 B while guided by the central inclined surface  256 . The water near the first bottom raising portion  242  is distributed into the water which flows into the first inner major groove  224 A while not guided by the first inclined surface  246  and the water which flows into the first outer major groove  222 A while guided by the first inclined surface  246 . The water near the second bottom raising portion  262  is distributed into the water which flows into the second inner major groove  224 B while not guided by the second inclined surface  266  and the water which flows into the second outer major groove  222 B while guided by the second inclined surface  266 . The water near the lug groove bottom raising portion  272  is distributed into the water which flows into the first outer major groove  222 A while not guided by the lug groove inclined surface  276  and the water which flows into the tread end T while guided by the lug groove inclined surface  276 . Accordingly, the pneumatic tire having the excellent wet drainage property is obtained. 
     The roadholding ability on the dry road surface, uneven wear-resistant property, and pattern noise property are improved, because the rigidity is enhanced in the corner portion (particularly, the corner portion  231 C which has an acute angle when viewed from the side of the wheel tread portion  219 ) of the adjacent land portion  231  with the provision of the first bottom raising portion  242 . The same effect can be obtained in corner portions of land portions adjacent to the central bottom raising portion  252 , the second bottom raising portion  262  and lug groove bottom raising portion  272 . 
     Fourth Embodiment 
     Then, a fourth embodiment will be described with reference to  FIG. 9A . In a pneumatic tire according to the fourth embodiment, when compared with the third embodiment, a first outer major groove  322 A is formed in place of the first outer major groove  222 A, a second outer major groove  322 B is formed in place of the second outer major groove  222 B, a first inner major groove  324 A is formed in place of the first inner major groove  224 A, and a second inner major groove  324 B is formed in place of the second inner major groove  224 B. Instead of the lug grooves  226 , a lug groove  326  is formed on one surface side of the tire equatorial plane CL, and a lug groove  327  is formed on the other surface side of the tire equatorial plane CL. The basic configuration, function, and effect of a second inclined groove  338  are similar to those of a first inclined groove  336 , so that the description of the second inclined groove  338  will be omitted. The basic configuration, action, and effect of the lug groove  327  are similar to those of the lug groove  326 , so that the description of the lug groove  327  will be omitted. 
     The fourth embodiment is similar to the third embodiment in the positions and lengths of a central inclined groove  334 , a first inclined groove  336 , and the lug groove  326 . However, the fourth embodiment differs from the third embodiment in the shape and position of the bottom raising portion formed in each inclined groove. 
     (First Inclined Groove) 
     A first bottom raising portion  342  which raises the groove bottom is formed near a first inner major groove-side end  336 J of the first inclined groove  336 , so that the first inclined groove  336  is substantially opened to and terminated in a first inner major groove  324 A. 
     A cross section of the first bottom raising portion  342  in the tire width direction (longitudinal direction of the groove) is formed in a chevron shape, and a first edge line  344  is formed in parallel with the tire circumferential direction at a top portion  342 U. A first inner major groove-side first inclined surface  345  and a first outer major groove-side first inclined surface  346  are formed as the groove bottom surface in the first bottom raising portion  342  (see  FIG. 9B ). In the first inner major groove-side first inclined surface  345 , the groove depth is gradually increased from the first edge line  344  toward the first inner major groove  324 A. In the first outer major groove-side first inclined surface  346 , the groove depth is gradually increased from the first edge line  344  toward a first outer major groove-side end  342 K at the first bottom raising portion  342 . In the fourth embodiment, the surface height of the first edge line  344  is equalized to the surface height (namely, height of wheel tread F) of a land portion  331  adjacent to the first inclined groove  336 . Accordingly, the depth from the wheel tread F to the first edge line  344  becomes 0 mm. 
     An edge portion  331 E of the land portion  331  on the first inner major groove side has an edge surface  331 ES that is provided along the first inner major groove  324 A and is chamfered in the tapered shape. The first inner major groove-side first inclined surface  345  is inclined at an inclination angle θ 1  with respect to the tire radial direction such that the first inner major groove-side first inclined surface  345  has the same plane as the edge surface  331 ES. Accordingly, the position of the first edge line  344  in the tire width direction is set at the same position as an upper edge of the edge surface  331 ES. The inclination angle θ 1  is set in the range of 30 to 60°. 
     (Central Inclined Groove) 
     A central bottom raising portion  352  which raises the groove bottom is formed near a first inner major groove-side end  334 J of the central inclined groove  334 , so that the central inclined groove  334  is substantially opened to and terminated in the first inner major groove  324 A. 
     As with the first bottom raising portion  342 , a cross section of the central bottom raising portion  352  in the tire width direction (longitudinal direction of the groove) is formed in a chevron shape, and a central edge line  354  is formed in parallel with the tire circumferential direction at a top portion of the central bottom raising portion  352 . A first inner major groove-side central inclined surface  355  and a second inner major groove-side central inclined surface  356  are formed in the central bottom raising portion  352 . In the first inner major groove-side central inclined surface  355 , the groove depth is gradually increased from the central edge line  354  toward the first inner major groove  324 A. In the second inner major groove-side central inclined surface  356 , the groove depth is gradually increased from the central edge line  354  toward a second inner major groove-side end  352 K of the central bottom raising portion  352 . In the fourth embodiment, the surface height of the central edge line  354  is equalized to the surface height (namely, height of wheel tread F) of a land portion  329  adjacent to the central inclined groove  334 . Accordingly, the depth from the wheel tread F to the central edge line  354  becomes 0 mm. 
     An edge portion  329 E of the land portion  329  on the first inner major groove side has an edge surface  329 ES which is provided along the first inner major groove  324 A and is chamfered in the tapered shape. In the first inner major groove-side central inclined surface  355 , the inclination angle θ 1  is set with respect to the tire radial direction such that the first inner major groove-side central inclined surface  355  has the same plane as the edge surface  329 ES. Accordingly, the position of the central edge line  354  in the tire width direction is set at the same position as an upper edge of the edge surface  329 ES. The inclination angle θ 1  is set in the range of 30 to 60°. 
     (Lug Groove) 
     A lug groove bottom raising portion  372  which raises the groove bottom is formed near a first outer major groove-side end  326 J of the lug groove  326 , so that the lug groove  326  is substantially opened to and terminated in a first outer major groove  322 A. 
     A cross section of the lug groove bottom raising portion  372  in the tire width direction (longitudinal direction of the groove) is formed in a chevron shape, and a lug groove edge line  374  is formed in parallel with the tire circumferential direction at a top portion of the lug groove bottom raising portion  372 . A first outer major groove-side lug groove inclined surface  375  and a tread end-side lug groove inclined surface  376  are formed in the lug groove bottom raising portion  372 . In the first outer major groove-side lug groove inclined surface  375 , the groove depth is gradually increased from the lug groove edge line  374  toward the first outer major groove  322 A. In the tread end-side lug groove inclined surface  376 , the groove depth is gradually increased from the lug groove edge line  374  toward a tread end-side end  372 K. In the fourth embodiment, the surface height of the lug groove edge line  374  is equalized to the surface height (namely, height of wheel tread F) of a land portion  331  adjacent to the lug groove  326 . Accordingly, the depth from the wheel tread F to the lug groove edge line  374  becomes 0 mm. 
     An edge portion  325 E of the land portion  325  on the first outer major groove side has an edge surface  325 ES which is provided along the first outer major groove  322 A and is chamfered in the tapered shape. In a first outer major groove-side lug groove inclined surface  375 , the inclination angle θ 1  is set with respect to the tire radial direction such that the first outer major groove-side lug groove inclined surface  375  has the same plane as the edge surface  325 ES. Accordingly, the position of the lug groove edge line  374  in the tire width direction is set at the same position as an upper edge of the edge surface  325 ES. The inclination angle θ 1  is set in the range of 30 to 60°. 
     As described above, in the fourth embodiment, the first inner major groove-side central inclined surface  355  and the edge surface  329 ES form the same plane, the first inner major groove-side first inclined surface  345  and the edge surface  331 ES also form the same plane, and the first outer major groove-side lug groove inclined surface  375  and the edge surface  325 ES also form the same plane. Accordingly, the rigidity is enhanced in each of the edge portions where the edge surfaces are formed, and the roadholding ability is improved on the dry road surface. In the wet road surface driving, the water flows along the respective two surfaces forming the same plane without generating the turbulence, so that the wet drainage property is further improved. 
     Fifth Embodiment 
     Then, a fifth embodiment will be described with reference to  FIG. 10A . In a pneumatic tire according to the fifth embodiment, when compared with the fourth embodiment, a first outer major groove  422 A is formed in place of the first outer major groove  322 A, a second outer major groove  422 B is formed in place of the second outer major groove  322 B, a first inner major groove  424 A is formed in place of the first inner major groove  324 A, and a second inner major groove  424 B is formed in place of the second inner major groove  324 B. A central inclined groove  434  is formed in place of the central inclined groove  334 , a first inclined groove  436  is formed in place of the first inclined groove  336 , and a second inclined groove  438  is formed in place of the second inclined groove  338 . A lug groove  426  is formed in place of the lug groove  326  on one surface side of the tire equatorial plane CL, and a lug groove  427  is formed in place of the lug groove  327  on the other surface side of the tire equatorial plane CL. The basic configuration, function, and effect of the second inclined groove  438  are similar to those of the first inclined groove  436 , so that the description of the second inclined groove  438  will be omitted. The basic configuration, function, and effect of the lug groove  427  are similar to those of the lug groove  426 , so that the description of the lug groove  427  will be omitted. 
     The fifth embodiment is similar to the fourth embodiment in the positions and lengths of the central inclined groove  434 , first inclined groove  436 , and lug groove  426 . However, the fifth embodiment differs from the fourth embodiment in the shape and position of the bottom raising portion formed in each inclined groove. 
     (First Inclined Groove) 
     A first bottom raising portion  442  which raises the groove bottom is formed near a first inner major groove-side end  436 J of the first inclined groove  436 , so that the first inclined groove  436  is substantially opened to and terminated in a first inner major groove  424 A. 
     A cross section of the first bottom raising portion  442  is formed in a chevron shape in the tire width direction (longitudinal direction of the groove), and a first edge line  444  is formed in parallel with the tire circumferential direction at a top portion of the first bottom raising portion  442 . A first inner major groove-side first inclined surface  445  and a first outer major groove-side first inclined surface  446  are formed in the first bottom raising portion  442  (see  FIG. 10B ). In the first inner major groove-side first inclined surface  445 , the groove depth is gradually increased from the first edge line  444  toward the first inner major groove  422 A. In the first outer major groove-side first inclined surface  446 , the groove depth is gradually increased from the first edge line  444  toward a first outer major groove-side end  442 K of the first bottom raising portion  442 . In the fifth embodiment, the position of the first edge line  444  is located closer to the center side of the first inner major groove  424 A in the tire width direction than the position of an upper edge of an edge surface  431 ES of a land portion  431 . The depth D 2  from the wheel tread F to the first edge line  444  is set such that the first inner major groove-side first inclined surface  445  and the edge surface  429 ES form the same plane. 
     (Central Inclined Groove) 
     A central bottom raising portion  452  which raises the groove bottom is formed near a first inner major groove-side end  434 J of the central inclined groove  434 , so that the central inclined groove  434  is substantially opened to and terminated in a first inner major groove  422 A. 
     As with the first bottom raising portion  442 , a cross section of the central bottom raising portion  452  is formed in a chevron shape in the tire width direction (longitudinal direction of the groove), and a central edge line  454  is formed in parallel with the tire circumferential direction at a top portion of the first bottom raising portion  442 . A first inner major groove-side central inclined surface  455  and a second inner major groove-side central inclined surface  456  are formed in the central bottom raising portion  452 . In the first inner major groove-side central inclined surface  455 , the groove depth is gradually increased from the central edge line  454  toward the first inner major groove  422 A. In the second inner major groove-side central inclined surface  456 , the groove depth is gradually increased from the central edge line  454  toward a second inner major groove-side end  452 K of the central bottom raising portion  452 . In the fifth embodiment, the position of the central edge line  454  in the tire width direction is located closer to the center side of the first inner major groove  424 A than the position of an upper edge of an edge surface  429 ES of a adjacent land portion  429 . The depth D 2  from the wheel tread F to the central edge line  454  is set such that the first inner major groove-side central inclined surface  455  and the edge surface  429 ES form the same plane. 
     (Lug Groove) 
     A lug groove bottom raising portion  472  which raises the groove bottom is formed near a first outer major groove-side end  426 J of the lug groove  426 , so that the lug groove  426  is substantially opened to and terminated in the first inner major groove  422 A. 
     A cross section of the lug groove bottom raising portion  472  is formed in a chevron shape in the tire width direction (longitudinal direction of the groove), and a lug groove edge line  474  is formed in parallel with the tire circumferential direction at a top portion of the lug groove bottom raising portion  472 . A first outer major groove-side lug groove inclined surface  475  and a tread end-side lug groove inclined surface  476  are formed in the lug groove bottom raising portion  472 . In the first outer major groove-side lug groove inclined surface  475 , the groove depth is gradually increased from the lug groove edge line  474  toward the first outer major groove  422 A. In the tread end-side lug groove inclined surface  476 , the groove depth is gradually increased from the lug groove edge line  474  toward a tread end-side end  472 K. In the fifth embodiment, the position in the tire width direction of the lug groove edge line  474  is located closer to the center side of the first outer major groove  422 A than the position of an upper edge of an edge surface  425 ES of a land portion  425 . The depth D 2  from the wheel tread F to the lug groove edge line  474  is set such that the first outer major groove-side lug groove inclined surface  475  and the edge surface  425 ES form the same plane. 
     According to the fifth embodiment, the volume of the lug groove is increased to improve the wet drainage property in the wet road surface driving. 
     Sixth Embodiment 
     A pneumatic tire  810  of a sixth embodiment will be described below. 
     As shown in  FIG. 11A , in a wheel tread portion  819  of a tread portion  818 , a center major groove  817  having the groove depth D 0  and the groove width W 0  is formed on the tire equatorial plane CL. On both sides of the tire equatorial plane CL, outside major grooves  822  are formed along the tire circumferential direction at the position close to a quarter point Q of a width of a wheel tread portion  819 . The outside major grooves  822  zone the wheel tread portion  819  into a central region  820  and side regions  821 . 
     Lug grooves  824  are formed at substantially equal intervals in the tire circumferential direction, and the tire equatorial plane-side end portion of the lug groove  824  is substantially opened to and terminated in the outside major groove  822 . 
     The end portion in the tire width direction of each lug groove  824  is extended across the tread end such that the water can be drained to the outside in the tire width direction. 
     In the central region  820 , plural inclined grooves  832  are arranged on both sides of the tire equatorial plane CL so as to sandwich the tire equatorial plane CL. The inclined groove  832  is opened to the outside major groove  822 , and the inclined groove  832  is extended to the center major groove  817  while inclined with respect to the tire circumferential direction. The inclined groove  832  has the groove depth D 1 , and each inclined groove  832  is substantially opened to and terminated in the center major groove  817 . 
     As a result, a land portion row  842  is formed in the central region  820  by the center major groove  817 , the outside major groove  822 , and the inclined grooves  832  adjacent to each other in the tire circumferential direction. The land portion rows  842  includes a pair of land portions  840  that are provided in parallel each other with respect to the tire equatorial plane CL. 
     During the on-load tire rotating operation, when the pneumatic tire  810  is rotated to move the ground contact surface toward a U direction, the inclined grooves  832  separated by the tire equatorial plane are inclined toward the opposite directions with respect to tire circumferential direction such that the groove edge of the inclined groove  832  is sequentially in contact with the road surface from the center major groove  817  side of the inclined groove  832  toward the outside major groove  822  side. Thus, the inclined grooves  832  are formed such that the directional pattern is formed, and thereby the drainage property can be secured with the inclined grooves  832  corresponding to a stream line. 
     A bottom raising portion  839  which raises the groove bottom is formed near the terminal of the inclined groove  832 . The bottom raising portion  839  whose cross section is formed in the chevron shape includes an outside inclined surface  836  and an inside inclined surface  838  (see  FIG. 11B ). The outside inclined surface  836  forms the outside groove bottom of the inclined groove  832  in the tire width direction. The inside inclined surface  838  forms the inside groove bottom in the tire width direction of the inclined groove  832 . 
     An edge portion  843  of the land portion  840  on the side of the center major groove  817  is formed along the center major groove  817  and is chamfered in the tapered shape so as to have an inclined surface  844  which forms the same surface as the inside inclined surface  838  (see  FIG. 11C ). 
     A groove length L 1  of a groove portion  832 PE in which the outside inclined surface  836  is formed as the groove bottom (in other words, the groove length L 1  of the groove portion  832 PE in which the groove depth is gradually increased from the later-mentioned edge line  846 ) ranges from 5 to 40% of a tire ground contact width W. A groove length L 2  of a groove portion  832 PC in which the inside inclined surface  838  is formed as the groove bottom ranges from 8 to 45% of a width W 0  of the center major groove  817 . 
     The edge portion  843  is substantially parallel to the tire circumferential direction. An edge line  846  formed by the outside inclined surface  836  and the inside inclined surface  838  is substantially parallel to the tire circumferential direction. The edge line  846  forms a top portion of the bottom raising portion  839 . 
     The edge line  846  is formed in parallel with the wheel tread portion  819 . The surface height of the edge line  846  is set to the same surface height of the land portion  840  (namely, the height of the wheel tread), so that the depth of the edge line  846  from the wheel tread becomes 0 mm. 
     As described above, in the sixth embodiment, the tread wheel pattern is formed in the wheel tread portion  819 , and the bottom raising portion  839  having the chevron shape in cross section is formed in the inclined groove  832 . Therefore, in the wet road surface driving, the water near the central portion in the tire width direction of the wheel tread portion  819  is distributed into the water flowing into the center major groove  817  by the inside inclined surface  838  and the water flowing in the inclined groove  832  toward the outside in the tire width direction by the outside inclined surface  836 . Therefore, the pneumatic tire of the sixth embodiment has the excellent wet drainage property. 
     The roadholding ability on the dry road surface and the uneven wear-resistant property are improved, because the rigidity is enhanced in the corner portion (particularly, the corner portion  841  of the adjacent land portion  840  which has an acute angle when viewed from the side of the wheel tread F) by the bottom raising portion  839 . 
     The edge portion  843  of the land portion  840  on the side of the center major groove  817  is provided along the center major groove  817  and is chamfered in the tapered shape so as to have the same surface as the inside inclined surface  838 . Accordingly, the rigidity of the edge portion  843  is enhanced to improve the roadholding ability on the dry road surface. In the wet road surface driving, the water flows along the surfaces of the edge portion  843  and inside inclined surface  838  without generating the turbulence, so that the wet drainage property is further improved. 
     The edge portion  843  is substantially parallel to the tire circumferential direction, and the edge line  846  formed by the outside inclined surface  836  and the inside inclined surface  838  is substantially parallel to the tire circumferential direction. Therefore, the water near the central portion in the tire width direction of the wheel tread portion  819  is further easily distributed into the water flowing into the center major groove  817  by the inside inclined surface  838  and the water flowing in the inclined groove  832  toward the outside in the tire width direction by the outside inclined surface  836 . Accordingly, the pneumatic tire of the sixth embodiment has the excellent wet drainage property. 
     Seventh Embodiment 
     A seventh embodiment will be described below. As shown in  FIG. 12A , the pneumatic tire of the seventh embodiment differs from that of the sixth embodiment in the shape and position of a bottom raising portion  849  formed in an inclined groove  852  of a wheel tread portion  850 . 
     The bottom raising portion  849  which raises the groove bottom is formed near the terminal of the inclined groove  852 . The bottom raising portion  849  whose cross section in the tire width direction is formed in the chevron shape includes an outside inclined surface  856  and an inside inclined surface  858  (see  FIG. 12B ). The outside inclined surface  856  forms the outside groove bottom of the inclined groove  852  in the tire width direction. An inside inclined surface  858  forms the inside groove bottom of the inclined groove  852  in the tire width direction. 
     The position of an edge line  857  formed by the outside inclined surface  856  and the inside inclined surface  858  in the tire width direction is located closer to the position near the tire equatorial plane CL when compared with the sixth embodiment. The edge line  857  is formed in parallel to the wheel tread portion  850 , and the surface height of the edge line  857  is set deeper than the surface height of the land portion  840  (namely, height of wheel tread F) by D 2 . The inside inclined surface  858  and the inclined surface  844  at the edge portion  843  of the land portion  840  form the same surface. 
     According to the seventh embodiment, in addition to the effect of the sixth embodiment, the groove volume is increased in the region of the bottom raising portion  849  where the inclined groove has the chevron shape in cross section. Therefore, the wet drainage property is excellent in the wet road surface driving. 
     Eighth Embodiment 
     An eighth embodiment will be described below. As shown in  FIG. 13A , a pneumatic tire of the eighth embodiment differs from that of the sixth embodiment in the shape and position of a bottom raising portion  859  formed in an inclined groove  862  of a wheel tread portion  860 . 
     The bottom raising portion  859  which raises the groove bottom is formed near the terminal of the inclined groove  862 . The bottom raising portion  859  whose cross section in the tire width direction is formed in the chevron shape includes an outside inclined surface  866 , a top-portion plane  865 , and the inside inclined surface  838  (see  FIG. 13B ). The outside inclined surface  866  forms the outside groove bottom of the inclined groove  862  in the tire width direction. The top-portion plane  865  is continued to the tire equatorial plane side of the outside inclined surface  866 , and the height of the top-portion plane  865  is similar to that of the land portion  840 . The inside inclined surface  838  described in the sixth embodiment is continued to tire equatorial plane side of the top-portion plane  865 . 
     A width L 3  of the top-portion plane  865  in the tire width direction is not more than 3 mm. 
     According to the eighth embodiment, in addition to the effect of the sixth embodiment, the rigidity is enhanced in the corner portion of the land portion  840  adjacent to the bottom raising portion  859 . Therefore, the roadholding ability on the dry road surface and the uneven wear-resistant property are improved. 
     Ninth Embodiment 
     A pneumatic tire  910  of a ninth embodiment will be described below. 
     As shown in  FIG. 14A , in a wheel tread portion  919  of a tread portion  918 , circumferential major grooves  922 A and  922 B are formed along the tire circumferential direction both sides of the tire equatorial plane CL, and the circumferential major grooves  922 A and  922 B are formed at the position close to a quarter point Q of a width of a wheel tread portion  919 . The circumferential major grooves  922 A and  922 B zone the wheel tread portion  919  into a central region  920  and side regions  921 . 
     Lug grooves  924  are formed at substantially equal intervals in the tire circumferential direction, and the tire equatorial plane-side end portion of the lug groove  924  is substantially opened to the circumferential major grooves  922 A or  922 B. 
     The end portion in the tire width direction of each lug groove  924  are extended across the tread end such that the water can be drained to the outside in the tire width direction. 
     In the central region  920 , on the right of the tire equatorial plane CL on  FIG. 14A , plural first inclined grooves  926  are formed at substantially equal intervals in the tire circumferential direction. The first inclined groove  926  is completely opened to the circumferential major groove  922 A, and the first inclined groove  926  is extended toward the tire center while inclined with respect to the tire circumferential direction. On the left of the tire equatorial plane CL on  FIG. 14 , plural second inclined grooves  928  are formed at substantially equal intervals in the tire circumferential direction. The second inclined groove  928  is completely opened to the circumferential major groove  922 B, and the second inclined groove  928  is extended toward the tire center while inclined with respect to the tire circumferential direction. The first inclined groove  926  is substantially opened to and terminated at the groove wall of the second inclined groove  928 . The second inclined groove  928  is terminated while not opened to other inclined grooves. 
     As a result, a land portion row  929  including land portions  931  is formed in the central region  920 . The land portions  931  are formed at substantially equal intervals in the tire circumferential direction, and the land portion  931  is zoned by the circumferential major groove  922 , the first inclined groove  926 , and the second inclined groove  928 . 
     Thus, in the ninth embodiment, the pairs of inclined grooves including the first inclined groove  926  and the second inclined groove  928  are arrayed at substantially equal intervals in the tire circumferential direction. During the on-load tire rotating operation, when the pneumatic tire  910  is rotated to move the ground contact surface toward the U direction, the first inclined groove  926  and the second inclined groove  928  are inclined toward the opposite directions with respect to tire circumferential direction such that the groove edges of the first inclined groove  926  and second inclined groove  928  are sequentially in contact with the road surface from the tire center toward the side of the circumferential major groove  922 . Thus, the first inclined groove  926  and the second inclined groove  928  are formed so as to form the directional pattern, and thereby the drainage property can be secured with the inclined grooves corresponding to the flowing direction. 
     A bottom raising portion  930  which raises the groove bottom of the first inclined groove  926  is formed in the terminal portion of the first inclined groove  926 . As a result, the first inclined groove  926  is substantially opened to and terminated at the groove wall of the second inclined groove  928  (also see  FIG. 14B ). 
     A cross section of the bottom raising portion  930  in the tire width direction (longitudinal direction of the groove) is formed in a chevron shape, a first terminal  926 J has the highest peak where an edge line  934  is formed, and a first inclined surface  936  is formed as the groove bottom surface. In the bottom raising portion  930 , the groove depth is gradually increased from the first terminal  926 J toward a circumferential major groove-side end  930 K at the bottom raising portion  930  (namely, the groove depth is gradually decreased from the circumferential major groove-side end  930 K toward the first terminal  926 J at the bottom raising portion  930 ). 
     The edge line  934  is formed in a top portion  930 U of the bottom raising portion  930  (see  FIG. 14B ), and the edge line  934  is located on an opened-side groove edge line  928 E of the second inclined groove  928 . 
     A groove length L 1  of a groove portion  926 P in which the first inclined surface  936  is formed as the groove bottom surface is set in the range of 5 to 100% of the groove length of the first inclined groove  926  having the groove portion  926 P. 
     D 2  is a groove depth of the first inclined groove  926 , and L 0  is a length in which the first inclined groove  926  is opened to the second inclined groove  928 , i.e., the length of the edge line  934 . The second inclined groove  928  has the groove depth of D 1 . θ 1  is an inclination angle at the terminal portion of the first inclined groove  926  with respect to the tire circumferential direction, and O 2  is an inclination angle at the terminal portion of the second inclined groove  928  with respect to the tire circumferential direction. 
     In the ninth embodiment, the surface height of the edge line  934  is equalized to the surface height (namely, height of wheel tread F) of the land portion  931 . Accordingly, the depth D 3  from the wheel tread F to the edge line  934  becomes 0 mm in the ninth embodiment. 
     As described above, in the ninth embodiment, the tread wheel pattern is formed in the wheel tread portion  919 , the bottom raising portion  930  is formed while having the chevron shape in cross section, and the edge line  934  is located on the opened-side groove edge line  928 E. Therefore, in the wet road surface driving, the water near the bottom raising portion  930  of the wheel tread portion  919  is distributed into the water which flows into the circumferential major groove  922 A through the first inclined groove  926  while guided by the first inclined surface  936  and the water which flows into the circumferential major groove  22 B through the second inclined groove  928 . Accordingly, the pneumatic tire having the excellent wet drainage property is obtained in the ninth embodiment. 
     The rigidity in the tire width direction is increased by the bottom raising portion  930  at a corner portion  931 B of the land portion having the large angle formed between the first inclined groove  926  and the second inclined groove  928 . And the rigidity in the tire circumferential direction is increased by the bottom raising portion  930  at a corner portion  931 S of the land portion having the small angle. Accordingly, the roadholding ability on the dry road surface and the uneven wear-resistant property are improved. 
     Tenth Embodiment 
     A tenth embodiment will be described below. As shown in  FIG. 15 , a pneumatic tire of the tenth embodiment differs from that of the ninth embodiment in a tread pattern formed in a central region of a wheel tread portion  939 . 
     On the right of  FIG. 15  of the tire equatorial plane CL of the central region, first inclined grooves  946  are formed like the first inclined grooves  926  described in the ninth embodiment. In the first inclined groove  946 , a first bottom raising portion  940  is formed like the bottom raising portion  930  described in the ninth embodiment. 
     On the left of the tire equatorial plane CL at the central region on  FIG. 15 , second inclined grooves  948  are formed in place of the second inclined groove  928  described in the ninth embodiment. The tenth embodiment differs largely from the ninth embodiment in that a second bottom raising portion  942  whose cross sectional view in the tire width direction is similar to that of the first bottom raising portion  940  is formed in the terminal portion of the second inclined groove  948 . The second inclined groove  948  is substantially opened to and terminated at the groove wall of the first inclined groove  946 . 
     As a result, a first edge line  944  formed in a top portion  940 U of the first bottom raising portion  940  and the second edge line  945  formed in the top portion of the second bottom raising portion  942  are arranged in a zigzag manner along the tire circumferential direction. In the first bottom raising portion  940 , a first inclined surface  941  is formed like the first inclined surface  936  in the ninth embodiment. In the second bottom raising portion  942 , a second inclined surface  943  is formed like the first inclined surface  941 . In the second inclined surface  943 , the groove depth is gradually increased from the second edge line  945  to the side of the circumferential major groove  922 B. 
     A zigzag appearance circumferential minor groove  950  which is substantially continued in the tire circumferential direction is formed in the tenth embodiment. Accordingly, in the wet road surface driving, the water in the region where the zigzag appearance circumferential minor groove  950  is arranged in the wheel tread portion is distributed into both sides of the first edge line  944  and the second edge line  945 . Therefore, the wet drainage property is further improved. 
     Experimental Examples 
     The inventor performs experiments to compare the pneumatic tire according to the invention and the conventional pneumatic tire in the performance. In the experimental example, the sizes of all the pneumatic tires are PSR 225/45R17 and the tread width (in loading JATMA measurement standard internal pressure) is 180 mm. 
     The tires are attached to the actually running vehicle, the tire internal pressure is set at 220 kPa, and performance is evaluated by performing the experiments on the loading condition that two persons get on board in front seats. The performance evaluation includes (1) the roadholding ability on the dry road surface, (2) the hydroplaning property, (3) the roadholding ability on the wet road surface, (4) the uneven wear-resistant property, and (5) the pattern noise property. 
     First, the inventor performs the experiments with the pneumatic tire of Conventional example. 
     For the pneumatic tire of Conventional example, as shown in FIG.  18 A., in a wheel tread portion  719  of a tread portion  718 , outer major grooves  722  are formed along the circumferential direction on both sides of a tire equatorial plane, and the outer major grooves  722  are formed at the position of a quarter point Q of the width of the wheel tread portion  719 . The outer major grooves  722  zone the wheel tread portion  719  into a central region  720  and side regions  721 . 
     As with the pneumatic tire  210  of the third embodiment, in the sides regions  721 , lug grooves  726  are formed at substantially equal intervals in the tire circumferential direction, and the tire equatorial plane-side end portion of the lug groove  726  is opened to the outer major groove  722 . 
     In the central region  720 , inner major grooves  724  extended in the tire circumferential direction are formed on both sides of the tire equatorial plane CL respectively. The inner major groove  724  is arranged at the position where the distance between the inner major grooves  724  is substantially equalized to the distance between the outer major groove  722  and the inner major groove  724 . The inner major groove  724  and the outer major groove  722  have the groove depth D 0 . 
     In the central region  720 , inclined grooves  736  are formed at substantially equal intervals in tire circumferential direction on both sides of the tire equatorial plane CL. The inclined groove  736  is opened to the outer major groove  722  and the inner major groove  724 , and the inclined groove  736  is extended while inclined with respect to the tire circumferential direction. The inclination direction of the inclined groove  736  is similar to that of the pneumatic tire  210  of the third embodiment. As a result, land portion rows  730  including the land portions  731  are formed. A pair is formed by the two land portions  731  with respect to the tire equatorial plane CL, and the land portion  731  is formed by the outer major groove  722 , the inner major groove  724 , and the inclined grooves  736  adjacent to each other in the tire circumferential direction. 
     Central inclined grooves  734  are formed at substantially equal intervals in tire circumferential direction. The central inclined groove  734  is opened to the inner major grooves  724  located on both sides of the tire equatorial plane CL, and the central inclined groove  734  is extended while inclined with respect to the tire circumferential direction. The inclination direction of the central inclined groove  734  is similar to that of the pneumatic tire  210  of the third embodiment. As a result, a central land portion row  728  including the land portion  729  is formed. The land portion  729  crossing the tire equatorial plane CL is formed by the inner major grooves  724 , and the central inclined grooves  734  adjacent to each other in the tire circumferential direction. 
     The inclined groove  736  and the central inclined groove  734  have the groove length L 0  and the groove depth D 1 . 
     Table 5 shows the tread pattern conditions of the pneumatic tire of Conventional example. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Pneumatic tire 
                 Pneumatic 
                 Pneumatic 
                 Pneumatic 
               
               
                   
                 of Conventional 
                 tire of 
                 tire of 
                 tire of 
               
               
                   
                 example 
                 Example 1 
                 Example 2 
                 Example 3 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Groove width of 
                 8.3 
                 8.3 
                 8.3 
                 8.3 
               
               
                 major groove 
               
               
                 D0 (mm) 
               
               
                 Groove width of 
                 6.7 
                 6.7 
                 6.7 
                 6.7 
               
               
                 inclined groove 
               
               
                 D1 (mm) 
               
               
                 Groove length 
                 32 
                 32 
                 32 
                 32 
               
               
                 of inclined 
               
               
                 groove 
               
               
                 L0 (mm) 
               
               
                 Groove length 
                   
                 16 
                 7E 
                 16 
               
               
                 of groove 
               
               
                 portion 
               
               
                 L1 (mm) 
               
               
                 Inclination 
                   
                   
                 45 
                 45 
               
               
                 angle 
               
               
                 θ1 (°) 
               
               
                 Depth of top 
                   
                 0 
                 0 
                 1 
               
               
                 portion 
               
               
                 D2 (mm) 
               
               
                   
               
            
           
         
       
     
     In the experiment in which the conventional pneumatic tire is used, each index of the performance evaluation is defined as follows. (1) For the roadholding ability on the dry road surface, the roadholding ability is defined by feeling during which the vehicle runs in various driving modes on the dry circuit course, and the index is set at 100 for a reference value. (2) For the hydroplaning property, the vehicle runs on the wet road surface whose water depth is 10 mm, and the hydroplaning generation speed is measured. The index is set at 100 for the reference value. (3) For the roadholding ability on the wet road surface, the roadholding ability is defined by feeling during which the vehicle runs in various driving modes on the wet circuit course, and the index is set at 100 for the reference value. (4) For the uneven wear-resistant property, a wear step between the blocks adjacent to each other in the tire circumferential direction and a difference in wear amount between the central region  720  and the side regions (shoulder region)  721  are measured after 5000 km driving on a general road, and the index is set at 100 for the reference value. (5) For the pattern noise property, a noise amount is measured in the vehicle during when the vehicle runs on the smooth road surface at a speed of 60 km/h, and the index is set at 100 for the reference value. 
     Table 6 shows the indexes. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 Pneumatic 
                   
                   
                   
               
               
                   
                 tire of 
                 Pneumatic 
                 Pneumatic 
                 Pneumatic 
               
               
                   
                 Conventional 
                 tire of 
                 tire of 
                 tire of 
               
               
                   
                 example 
                 Example 1 
                 Example 2 
                 Example 3 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Roadholding 
                 100 
                 105 
                 110 
                 108 
               
               
                 ability on dry road 
               
               
                 surface 
               
               
                 Hydroplaning 
                 100 
                 105 
                 105 
                 106 
               
               
                 property 
               
               
                 Roadholding 
                 100 
                 105 
                 108 
                 110 
               
               
                 ability on wet road 
               
               
                 surface 
               
               
                 Uneven wear- 
                 100 
                 105 
                 110 
                 109 
               
               
                 resistant property 
               
               
                 Pattern noise 
                 100 
                 105 
                 110 
                 108 
               
               
                 property 
               
               
                   
               
            
           
         
       
     
     The inventor uses the pneumatic tire  210  according to the third embodiment as the pneumatic tire of Example 1. In the pneumatic tire of Example 1, the tread pattern is formed under the conditions shown in Table 5. 
     The experiment is performed under the same conditions as the pneumatic tire of Conventional example. (1) For the roadholding ability on the dry road surface, the index which becomes relative evaluation for the pneumatic tire of Conventional example is computed by the feeling of the driver. (2) For the hydroplaning property, the hydroplaning generation limit speed is measured to compute the index which becomes relative evaluation for the pneumatic tire of Conventional example. (3) For the roadholding ability on the wet road surface, the index which becomes relative evaluation for the pneumatic tire of Conventional example is computed by the feeling of the driver. (4) For the uneven wear-resistant property, similarly the wear step and the difference are measured to compute the index which becomes relative evaluation for the pneumatic tire of Conventional example. (5) 
     For the pattern noise property, the noise amount is measured in the vehicle during when the vehicle runs on the smooth road surface at the speed of 60 km/h, and the index which becomes relative evaluation for the pneumatic tire of Conventional example is computed. Table 6 shows the computed indexes. 
     In Table 6, it is indicated that, as the index is increased, the performance becomes better. That is, when the index is increased, the roadholding ability on the dry road surface or wet road surface becomes better, the hydroplaning generation speed is increased, the wear step or wear amount is decreased, and the pattern noise is decreased. 
     The inventor also uses the pneumatic tire according to the fourth embodiment as the pneumatic tire of Example 2. In the pneumatic tire of Example 2, the tread pattern is formed under the conditions shown in Table 5. 
     In the experiment in which the pneumatic tire of Example 2 is used, as with the pneumatic tire of Example 1, the indexes which become the relative evaluation are computed for (1) the roadholding ability on the dry road surface, (2) the hydroplaning property, (3) the roadholding ability on the wet road surface, (4) the uneven wear-resistant property, and (5) the pattern noise property. Table 6 shows the computed indexes. 
     The inventor uses the pneumatic tire according to the fifth embodiment as the pneumatic tire of Example 3. In the pneumatic tire of Example 3, the tread pattern is formed under the conditions shown in Table 5. 
     In the experiment in which the pneumatic tire of Example 3 is used, as with the pneumatic tires of Examples 1 and 2, the indexes which become the relative evaluation are computed for (1) the roadholding ability on the dry road surface, (2) the hydroplaning property, (3) the roadholding ability on the wet road surface, (4) the uneven wear-resistant property, and (5) the pattern noise property. Table 6 shows the computed indexes. 
     As is clear from Table 6, the pneumatic tires of Examples 1 to 3 have the good capabilities for all the performance evaluations (1) to (5) compared with the pneumatic tire of Conventional example. 
     Thus, the embodiments of the invention are explained only by way of example. However, various changes and modifications could be made without departing from the scope of the invention. Obviously the right range of the invention is not limited to the above embodiments. 
     In the invention, the circumferential major groove is not limited to one which is linearly extended in the tire circumferential direction. For example, a circumferential major groove which is extended in the tire circumferential direction in a zigzag manner may be used as the circumferential major groove of the invention. However, in the case where the circumferential major groove is formed in the zigzag manner, in order to secure the drainage property, it is preferable to secure a portion through which the water passes linearly in the tire circumferential direction, that is the so-called see-through portion groove (a spatial portion which is continued in the circumferential direction while not obstructed by a projection (projected in the tire width direction) of a side wall in a bent portion of the circumferential major groove formed as the zigzag manner). 
     INDUSTRIAL APPLICABILITY 
     As described above, the pneumatic tire according to the invention is suitable to for the attachment to the vehicle in which the high wet performance is required. 
     EXPLANATION OF THE REFERENCE NUMERALS 
     
         
           10  pneumatic tire 
           12  tread 
           12 A wheel tread 
           14  circumferential wide major groove 
           16  first narrow circumferential minor groove 
           18  second narrow circumferential minor groove 
           20  first transverse grooves 
           22  second transverse groove 
           24  third transverse groove 
           26  first block 
           28  second block 
           30  stepping-on-side third block 
           32  kickout-side third block 
         CL tire equatorial plane 
           110  pneumatic tire 
           112  tread 
           112 A wheel tread 
           114  circumferential wide major groove 
           116  first narrow circumferential minor grooves 
           118  second narrow circumferential minor grooves 
           120  first transverse grooves 
           122  second transverse grooves 
           126  first block 
           128  second block 
           130  stepping-on-side third block 
           132  kickout-side third block 
           210  pneumatic tire 
           219  wheel tread portion 
           222 A first outer major groove (circumferential major groove) 
           222 B second outer major groove (circumferential major groove) 
           224 A first inner major groove (circumferential major groove) 
           224 B second inner major groove (circumferential major groove) 
           226  lug grooves (transverse groove) 
           226 J first outer major groove-side end (one end in tire width direction) 
           226 P groove portion 
           228  central land portion row (land portion row) 
           229  land portion 
           230  first adjacent land portion row (land portion row) 
           231  land portion 
           232  second adjacent land portion row (land portion row) 
           233  land portion 
           234  central inclined grooves (transverse groove) 
           234 J first inner major groove-side end (one end in tire width direction) 
           234 K second inner major groove-side end (other end in the tire width direction) 
           234 P groove portion 
           236  first inclined groove (transverse groove) 
           236 J first inner major groove-side end (one end in tire width direction) 
           236 K first outer major groove-side end (other end in the tire width direction) 
           236 P groove portion 
           238  second inclined groove (transverse groove) 
           238 J second inner major groove-side end (one end in tire width direction) 
           238 K second outer major groove-side end (other end in the tire width direction) 
           238 P groove portion 
           242  first bottom raising portion (bottom raising portion) 
           246  first inclined surface (inclined surface) 
           252  central bottom raising portion (bottom raising portion) 
           256  central inclined surface (inclined surface) 
           262  second bottom raising portion (bottom raising portion) 
           266  second inclined surface (inclined surface) 
           272  lug groove bottom raising portion 
           322 A first outer major groove (circumferential major groove) 
           322 B second outer major groove (circumferential major groove) 
           324 A first inner major groove (circumferential major groove) 
           324 B second inner major groove (circumferential major groove) 
           325  land portion 
           325 E edge portion 
           325 ES edge surface 
           326  lug grooves (transverse groove) 
           326 J first outer major groove-side end (one end in tire width direction) 
           327  lug groove 
           329  land portion 
           329 E edge portion 
           329 ES edge surface 
           331  land portion 
           331 E edge portion 
           331 ES edge surface 
           334  central inclined grooves (transverse groove) 
           334 J first inner major groove-side end (one end in tire width direction) 
           336  first inclined groove (transverse groove) 
           336 J first inner major groove-side end (one end in tire width direction) 
           342  first bottom raising portion (bottom raising portion) 
           342 U top portion 
           345  first inner major groove-side first inclined surface (one-end-side inclined surface) 
           346  first outer major groove-side first inclined surface (inclined surface) 
           352  central bottom raising portion (bottom raising portion) 
           355  first inner major groove-side central inclined surface (one-end-side inclined surface) 
           356  second inner major groove-side central inclined surface (inclined surface) 
           372  lug groove bottom raising portion 
           375  first outer major groove-side lug groove inclined surface 
           376  tread end-side lug groove inclined surface (inclined surface) 
           422 A first outer major groove (circumferential major groove) 
           422 B second outer major groove (circumferential major groove) 
           424 A first inner major groove (circumferential major groove) 
           424 B second inner major groove (circumferential major groove) 
           434  central inclined grooves (transverse groove) 
           436  first inclined groove (transverse groove) 
           438  second inclined groove (transverse groove) 
           426  lug grooves (transverse groove) 
           427  lug groove 
           436 J first inner major groove-side end (one end in tire width direction) 
           442  first bottom raising portion (bottom raising portion) 
           445  first inner major groove-side first inclined surface (one end in tire width direction) 
           446  first outer major groove-side first inclined surface (inclined surface) 
           434 J first inner major groove-side end (one end in tire width direction) 
           452  central bottom raising portion (bottom raising portion) 
           455  first inner major groove-side central inclined surface (one end in tire width direction) 
           456  second inner major groove-side central inclined surface (inclined surface) 
           426 J first outer major groove-side end (one end in tire width direction) 
           472  lug groove bottom raising portion 
           475  first outer major groove-side lug groove inclined surface (one end in tire width direction) 
           476  tread end-side lug groove inclined surface (inclined surface) 
         T tread end 
         θ 1  inclination angle 
           810  pneumatic tire 
           817  center major groove (groove) 
           819  wheel tread portion 
           832  inclined grooves 
           832 PE groove portion 
           832 PC groove portion 
           836  outside inclined surface 
           838  inside inclined surface 
           839  bottom raising portion 
           840  land portion 
           843  edge portion 
           846  edge line 
           849  bottom raising portion 
           850  wheel tread portion 
           852  inclined groove 
           856  outside inclined surface 
           857  edge line 
           858  inside inclined surface 
           859  bottom raising portion 
           860  wheel tread portion 
           862  inclined groove 
           865  top-portion plane 
           866  outside inclined surface 
           869  wheel tread portion 
           877  center major groove (groove) 
           882  inclined groove 
           890  land portion 
         F wheel tread 
           910  pneumatic tire 
           919  wheel tread portion 
           922 A, B circumferential major grooves 
           926  first inclined grooves (inclined groove) 
           926 P groove portion 
           928  second inclined groove (inclined groove) 
           928 E opened-side groove edge line 
           930  bottom raising portion 
           934  edge line 
           936  first inclined surface (inclined surface) 
           939  wheel tread portion 
           940  first bottom raising portion (bottom raising portion) 
           941  first inclined surface (inclined surface) 
           942  second bottom raising portion (bottom raising portion) 
           943  second inclined surface (inclined surface) 
           944  first edge line (edge line) 
           945  second edge line (edge line) 
           946  first inclined groove 
           948  second inclined grooves 
           950  zigzag appearance circumferential minor groove 
           956  first inclined groove (inclined groove) 
           958  second inclined groove (inclined groove) 
           969  wheel tread portion 
           972 A, B circumferential major groove 
           976  first inclined groove (inclined groove) 
           978  second inclined groove (inclined groove)