Patent Publication Number: US-2012037287-A1

Title: Heavy duty pneumatic tire

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a pneumatic tire, more particularly to an arrangement of a longitudinal groove having a specific structure and axially inner oblique grooves connected thereto capable of improving the noise performance of a heavy duty tire. 
     All-season heavy-duty tires for use in trucks, buses and the like are usually provided in the tread portion with a block type tread pattern defined by tread grooves such as circumferentially extending longitudinal grooves and lateral grooves extending therefrom. 
     When compared with passenger car tires and the like, the tread grooves of a heavy duty tire are relatively wide and deep, therefore, such grooves are liable to generate noise sound during running. 
     In the case of the lateral grooves, the air in the lateral grooves is compressed when the lateral grooves come into the ground during rolling and the air is jetted out. Thus, so called pumping sound noise is generated. Further, the lateral groove edges hit the road surface, and so called pattern pitch noise is generated. 
     In the case of the longitudinal grooves, the longitudinal groove in the ground connecting patch forms a tube with both ends opened, and the air in the tube is excited by the pumping sound and pattern pitch noise and the tube is resonated, and so called resonance sound noise is generated. 
     In order to reduce such noise sound, in European patent application No. EF-1995081-A1, as shown in  FIG. 6(   a ) and  FIG. 6(   b ), a longitudinal groove (a) provided in the groove bottom (b) with a sound insulation wall (e) having a height (d) same as the depth (c) of the longitudinal groove (a) has been proposed by the assignee of the present invention. This sound insulation wall can reduce the pumping sound and resonance sound. 
     In recent years, however, demand for quiet tires is very high, and the above-mentioned sound insulation wall is not sufficient for such demand. 
     SUMMARY OF THE INVENTION 
     It is therefore, an object of the present invention to provide a heavy duty pneumatic tire, in which the pumping noise and resonance sound noise and further the pattern pitch noise are effectively suppressed, and the overall noise sound is further reduced to satisfy the recent demand for quiet tires. 
     According to the present invention, a heavy duty pneumatic tire comprises a tread portion provided with 
     a circumferentially continuously extending longitudinal groove disposed on each side of the tire equator, 
     a plurality of axially inner oblique grooves extending axially inwardly from the longitudinal groove, while inclining at an angle of from 20 to 40 degrees with respect to the tire axial direction, and 
     a sound insulation wall disposed within the longitudinal groove so as to rise from the groove bottom independently from the groove sidewalls, 
     the sound insulation wall extends continuously in the circumferential direction in a zigzag manner so as to have axially inner points and axially outer points at turning points of the zigzag, and 
     the distance between the sound insulation wall and the axially inner edge of the longitudinal groove is varied periodically in the tire circumferential direction so that the distance becomes minimal at each of the junctions of the longitudinal groove and the axially inner oblique grooves. 
     As described, the axially inner oblique grooves are inclined at an angle of from 20 to 40 degrees with respect to the tire axial direction, therefore, the deformation of the axially inner oblique grooves when contacting with the ground becomes gradual, and the flow velocity of the air jetted out of the lateral grooves (into the longitudinal groove for instance) is decreased, and thereby the pumping sound noise can be reduced. Further, the contact of the edges of the oblique grooves become gradual, therefore, the pattern pitch noise can be reduced. 
     Furthermore, by the sound insulation wall, the volume of the longitudinal groove is decreased, therefore, the occurrence of the resonance sound noise can be controlled. Still furthermore, since the distance between the sound insulation wall and the axially inner edge of the longitudinal groove becomes minimal at the junctions, the air flow from the axially inner oblique grooves into the longitudinal groove is controlled not to excite the air in the longitudinal groove, and thereby the resonance sound noise can be completely prevented. 
     Accordingly, it is possible to improve the noise performance to satisfy the recent demand. 
     In this application including specification and claims, various dimensions, positions and the like of the tire refer to those under a normally inflated unloaded condition of the tire unless otherwise noted. 
     The normally inflated unloaded condition is such that the tire is mounted on a standard wheel rim and inflate to a standard pressure but loaded with no tire load. 
     The undermentioned normally inflated loaded condition is such that the tire is mounted on the standard wheel rim and inflate to the standard pressure and loaded with the standard tire load. 
     The standard wheel rim is a wheel rim officially approved or recommended for the tire by standards organizations, i.e. JATMA (Japan and Asia), T&amp;RA (North America), ETRTO (Europe), TRAA (Australia), STRO (Scandinavia), ALAPA (Latin America), ITTAC (India) and the like which are effective in the area where the tire is manufactured, sold or used. 
     The standard pressure and the standard tire load are the maximum air pressure and the maximum tire load for the tire specified by the same organization in the Air-pressure/Maximum-load Table or similar list. For example, the standard wheel rim is the “standard rim” specified in JATMA, the “Measuring Rim” in ETRTO, the “Design Rim” in TRA or the like. The standard pressure is the “maximum air pressure” in JATMA, the “Inflation Pressure” in ETRTO, the maximum pressure given in the “Tire Load Limits at Various Cold Inflation Pressures” table in TRA or the like. The standard load is the “maximum load capacity” in JATMA, the “Load Capacity” in ETRTO, the maximum value given in the above-mentioned table in TRA or the like. 
     The tread width TW is the axial distance between the tread edges Te measured in the normally inflated unloaded condition. 
     The tread edges Te are the axial outermost edges of the ground contacting patch (camber angle=0) in the normally inflated loaded condition. 
     The term “groove width” means a width measured perpendicularly to the longitudinal direction of the groove concerned in the normally inflated unloaded condition. And the groove width refers to that measured at the open groove top unless otherwise noted. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a heavy duty pneumatic tire according to an embodiment of the present invention, under its normally inflated unloaded condition. 
         FIG. 2  is a developed view of the tread portion thereof. 
         FIG. 3  is a cross sectional view of the longitudinal groove. 
         FIG. 4  is a plan view of the longitudinal groove. 
         FIGS. 5(   a ) and  5 ( b ) are developed views of tread portions of comparative examples. 
         FIG. 6(   a ) is a developed view of a prior-art tread portion. 
         FIG. 6(   b ) is a cross sectional view taken along line x-x of  FIG. 6(   a ). 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings. 
     The heavy duty pneumatic tire  1  according to the present invention comprises a tread portion  2 , a pair of axially spaced bead portions  4  each with a bead core  5  therein, a pair of sidewall portions  3  extending between the tread edges and the bead portions, a carcass  6  extending between the bead portions  4 , and a belt  7  disposed radially outside the carcass  6  in the tread portion  2 . 
     The carcass  6  comprises at least one ply  6 A of cords arranged radially at an angle of 90 to 75 degrees with respect to the tire equator c, and extending between the bead portions  4  through the tread portion  2  and sidewall portions  3 , and turned up around the bead core  5  in each bead portion  4  from the inside to the outside of the tire so as to form a pair of turned up portions  6   b  and a main portion  6   a  therebetween. 
     In this embodiment, the carcass  6  is composed of a single carcass ply  6 A, and the carcass cords are steel cords. 
     The belt  7  comprises at least two cross breaker plies, each made of parallel cords laid at an angle of from 15 to 45 degrees with respect to the tire equator C. 
     In this embodiment, the belt  7  is composed of four breaker plies  7 A,  7 B,  7 C and  7 D, and steel cords are used as the breaker ply cords. 
     The tread portion  2  in this embodiment is provided with five circumferentially continuously extending longitudinal grooves: an axially inner longitudinal groove  9  disposed direction along the tire equator c, a pair of axially outermost longitudinal grooves  10  disposed one on each side of the longitudinal groove  9 , and a pair of middle longitudinal grooves  11  between the longitudinal grooves  9  and  10 . 
     The longitudinal grooves  9 ,  10  and  11  each have a groove top width W 1  and a groove depth D 1 . In view of the drainage, wear resistance and steering stability, the groove top width W 1  is preferably set in a range of not less than 2%, more preferably not less than 3%, but not more than 5%, more preferably not more than 4% of the tread width TW. And the groove depth D 1  is preferably set in a range of not less than 2%, more preferably not less than 4%, but not more than 12%, more preferably not more than 8% of the tread width TW. 
     In this embodiment, the axially outermost longitudinal groove  10  is wider than the axially inner longitudinal groove  9  which is wider than the middle longitudinal groove  11 . 
     As to the longitudinal grooves  9 ,  10  and  11 , straight grooves can be employed. 
     But, in this embodiment, zigzag grooves are employed because the groove edges are increased in the axial component and thereby the traction performance can be improved. 
     The axially outermost longitudinal groove  10  is made up of alternately inclining segments having substantially same lengths. The axially inner longitudinal groove  9  is made up of alternately inclining long segments and short segments. The middle longitudinal groove  11  is made up of alternately inclining long segments and short segments, wherein the ratio of the length of the short segment to the length of the long segment is larger than that of the axially inner longitudinal groove  9 . 
     Preferably, the inclination angles of the equi-length zigzag segments (angle θ 2  of longitudinal grooves  10 ) and the inclination angles of the long zigzag segments (angle θ 1  of longitudinal groove  9  and angle θ 3  of longitudinal groove  11 ) are set in a range of not more than 20 degrees with respect to the circumferential direction. If more than 20 degrees, the tread portion  2  is decreased in the rigidity in the tire circumferential direction, and there is a tendency that the straight running stability and steering stability are deteriorated. 
     As shown in  FIG. 2 , the tread portion  2  in this embodiment is provided with 
     crown oblique grooves  12  extending between the inner longitudinal groove  9  and middle longitudinal grooves  11 , 
     axially inner oblique grooves  13  extending between the middle longitudinal grooves  11  and axially outer longitudinal grooves  10 , and 
     axially outer shoulder lateral grooves  14  extending between the axially outer longitudinal grooves  10  and tread edges Te. 
     Therefore, the tread portion  2  is provided with a block pattern made up of center blocks cb between the axially inner longitudinal groove  9  and middle longitudinal grooves  11 , 
     middle blocks Mb between the middle longitudinal grooves  11  and axially outer longitudinal grooves  10 , and 
     shoulder blocks Sb between the axially outer longitudinal grooves  10  and tread edges Te. 
     The axially inner oblique grooves  13  are connected to the axial inwardly located zigzag turning points  10   x  of the axially outer longitudinal grooves  10  in order to secure the rigidity of the shoulder blocks Sb. 
     The axially outer shoulder lateral grooves  14  are connected to the axial outwardly located zigzag turning points  10   y  of the axially outer longitudinal grooves  10  in order to secure the rigidity of the middle blocks Mb. 
     The grooves  12 ,  13  and  14  each have a groove top width W 2  and a groove depth D 2 . In view of the drainage and steering stability, the groove top width W 2  is preferably set in a range of not less than 2%, more preferably not less than 3%, but not more than 6%, more preferably not more than 5% of the tread width TW. And the groove depth D 2  is preferably set in a range of not less than 1%, more preferably not less than 1.5%, but not more than 3%, more preferably not more than 2.5% of the tread width TW. 
     In this embodiment, all of the oblique grooves  12  and  13  have substantially same widths less than the width of the axially outer shoulder lateral grooves  14 . 
     The axially inner oblique grooves  13  are inclined at an angle α 1  with respect to the tire axial direction. The angle α 1  is preferably set in a range of not less than 20 degrees, more preferably not less than 25 degrees, but not more than 40 degrees, more preferably not more than 35 degrees. 
     Through various tests, the inventor found that, among the longitudinal grooves, the axially outer longitudinal grooves  10  have a great effect on the noise performance, therefore, it is important for the noise performance to improve the air flow in the axially outer longitudinal groove  10 . When the axially inner oblique groove  13  comes into contact with the ground, the air therein flows into the axially outer longitudinal groove  10 . By limiting the angle α 1  of the axially inner oblique grooves  13  within the above-mentioned range, the contact of the oblique groove with the ground becomes gradual, therefore, the velocity of the air flow from the lateral groove is decreased. As a result, the pumping sound generated by the axially inner oblique groove  13  is reduced, and further, the exciting of the air in the longitudinal groove is reduced and the occurrence of the resonance is prevented. 
     If the angle α 1  is less than 20 degrees, the velocity of the air flow increases and it becomes difficult to reduce the pumping sound noise. If the angle α 1  is more than 40 degrees, as the blocks divided by the oblique grooves  13  are decreased in the rigidity, vibration or deformation of the blocks is increased, therefore the air in the adjacent grooves is liable to be excited which result in the generation of noise sound. Further, due to the decreased rigidity and the increased deformation of the blocks, the resistance to wear and steering stability are liable to be deteriorated. 
     As to the number of the axially inner oblique grooves  13 , it is preferable that 35 to 65 grooves are circumferentially arranged on each side of the tire equator c. More preferably the number is not less than 40, still more preferably not less than 42, but not more than 60, still more preferably not more than 48. 
     If the number is more than 65, the middle blocks Mb are decreased in the rigidity and their deformation becomes increased, therefore, there is a tendency that the pumping sound noise increases. If less than 35, as the middle blocks Mb are increased in the rigidity, impact sound generated when the block edges hit the road surface has a tendency to increase the sound pressure level, and thereby the noise performance is deteriorated. 
     The crown oblique grooves  12  are preferably inclined at an angle α 3  of from 20 to 40 degrees with respect to the tire axial direction for the same reasons as the axially inner oblique grooves  13 . 
     In this embodiment, the axially inner oblique grooves  13  and crown oblique groove  12  extends straight, inclining in the same direction at the same angle in order to smoothen the drainage and improve the wet performance. 
     The oblique grooves  12  and  13  are connected to the longitudinal groove  11  as if the oblique grooves  12  and  13  respectively overlap the short zigzag segments of the longitudinal groove  11 . The oblique grooves  12  are connected to the zigzag turning points of the longitudinal groove  9 . 
     The axially outer shoulder lateral grooves  14  are not inclined, and extend at an angle α 2  of not more than 5 degrees with respect to the tire axial direction in order to increase the lateral stiffness (rigidity) of the shoulder blocks Sb and to thereby provide steering stability during cornering. 
     According to the present invention, the longitudinal grooves are provided with a sound insulation wall  17 . 
     In this embodiment, as shown in  FIGS. 1 ,  2  and  3 , only the axially outermost longitudinal grooves (namely, longitudinal grooves  10 ) are each provided in its groove bottom  10   u  with a sound insulation wall  17  rising radially outwardly from the groove bottom  10   u . This is because the axially outermost longitudinal grooves have the greatest influence on the noise performance, and the groove width is large enough to cause resonance as the zigzag is gentle. It is of course possible that the sound insulation wall  17  is formed in other longitudinal groove if needed, for example, only the middle longitudinal grooves  11 , or only the axially outer longitudinal grooves  10  and middle longitudinal grooves  11 . 
     The sound insulation wall  17  extends continuously in the tire circumferential direction within the longitudinal groove. 
     The cross-sectional shape of the sound insulation wall  17  is constant along the entire length of the sound insulation wall  17 . 
     The sound insulation wall  17  has a top surface  17   g , an axially inner wall surface  17   i  extending from the axially inner edge  17   c  of the top surface  17   g  to the groove bottom  10   u , and an axially outer wall surface  17   s  extending from the axially outer edge  17   t  of the top surface  17   g  to the groove bottom  10   u . In this example, as shown in  FIG. 3 , the cross sectional shape of the sound insulation wall  17  is a substantially rectangle. 
     The sound insulation wall  17  extends in the tire circumferential direction in a zigzag manner, preferably smoothly curved wavy manner so that alternating axially inner points  17   n  and outer points  17   p  are respectively formed on the axially inner wall surface  17   i  and outer wall surface  17   s  at the turning points of the zigzag. In this embodiment, the axially inner points  17   n  are the axially innermost points, and the axially outer points  17   p  are the axially outermost points. 
     The zigzag pitches of the sound insulation wall  17  are same as the zigzag pitches of the axially outer longitudinal groove  10 . Thus, the axially inner points  17   n  are respectively positioned within the circumferential extents  10 R of the junctions  10   c  (opening) of the axially inner oblique grooves  13  and the axially outer longitudinal groove  10 . 
     The axially outer points  17   p  are respectively positioned within the circumferential extents  10 L of the junctions  10   d  (opening) of the axially outer shoulder lateral grooves  14  and the axially outer longitudinal groove  10 . 
     The maximum angle θ 4  of the sound insulation wall  17  with respect to the tire circumferential direction is preferably not less than 3 degrees, more preferably not less than 5 degrees, but not more than 20 degrees, more preferably not more than 10 degrees. 
     If the maximum angle θ 4  is more than 20 degrees, as the deformation of the sound insulation wall  17  during running liable to concentrate at the turning points of zigzag, it becomes difficult to shut off the pumping sound noise from the axially inner oblique grooves  13 , and the noise performance is liable to deteriorate. 
     The axially outer longitudinal groove  10  has a pair of opposed groove sidewalls  10   w  and a groove bottom  10   u  extending therebetween. The groove sidewalls  10   w  are inclined so that the groove width continuously increases from the groove bottom  10   u  toward the radially outside. 
     By the sound insulation wall  17 , the axially outer longitudinal groove  10  is decreased in the groove volume, and the occurrence of the resonance sound noise is prevented. 
     By making the sound insulation wall  17  in a zigzag or wavy form, in comparison with a straight form, the surface area of the wall surfaces  17   i  and  17   s  is increased, and thereby the effect to attenuate the pumping sound noise is enhanced. 
     The distance Lm of the sound insulation wall  17  from the axially inner edge  10   i  of the axially outer longitudinal grooves  10  is varied periodically in the tire circumferential direction so that the distance Lm becomes minimal at the junctions  10   c . As the axially inner wall surface  17   i  of the sound insulation wall  17  comes near the junctions  10   c , namely, near the open ends of the axially inner oblique grooves  13 , the air flow from the axially inner oblique grooves  13  into the longitudinal groove is effectively controlled not to excite the air in the longitudinal groove. Accordingly, the occurrence of the resonance sound noise can be prevented. Further, even at high frequencies, the occurrence of the standing wave in the axially outer longitudinal groove  10  can be completely prevented. 
     If the distance Lm at the junctions  10   c  is too large, the effect of the sound insulation wall  17  to cut the noise sound coming into the longitudinal groove becomes insufficient. If too small, on the other hand, the wet performance is deteriorated, and further the resultant choke part liable to generate pumping sound. Therefore, the distance Lm at the junctions  10   d  is preferably set in a range of not less than 1 mm, more preferably not less than 1.5 mm, but not more than 5 mm, more preferably not more than 4 mm. 
     Further, it is preferable that, as shown in  FIG. 4 , the intersecting points K 1  (imaginary intersecting points) between the center lines G 12  of the axially inner oblique grooves  13  and the axially inner edge  10   i  (imaginary edge line  10   j ) of the axially outer longitudinal groove  10  are respectively shifted from the axially inner points  17   n  of the sound insulation wall  17  in the tire circumferential direction by distances Ln of 1 to 3 mm. 
     If the distance Ln is less than 1 mm, the water flow from the axially inner oblique grooves  13  to the axially outer longitudinal groove  10  is hindered and the wet performance is deteriorated. If the distance Ln is more than 3 mm, the flow passage from the axially inner oblique groove  13  to the longitudinal groove  10  becomes wide, and it becomes difficult to control the pumping sound noise. 
     Furthermore, it is preferable that, with respect to each of the axially outer longitudinal grooves  10 , the axially inner oblique grooves  13  which extend from the longitudinal groove  10  toward the axially inside are inclined to one circumferential direction, and 
     the above-mentioned intersecting points K 1  are shifted from the axially inner points  17   n  of the sound insulation wall  17  toward the above-mentioned one circumferential direction. More generically speaking, the axially inner points  17   n  are preferably positioned on or close to extensions of the widthwise center lines of the axially outer longitudinal grooves  10  in order to effectively control the air flow from the oblique grooves into the longitudinal groove, not to excite the air in the longitudinal groove. 
     Also, it is preferable that the distance Lm becomes maximal at a position within a range S between 45% and 55% (50+/−5%) of the circumferential pitch length between every two circumferentially-adjacent axially inner points  17   n . This range S is included in the above-mentioned circumferential extent  10 L of the junction  10   d . Namely, the distance Lm is increased at such positions that are farthest from the axially inner points  17   n , and as a result, the resistance to water flow of the axially outer longitudinal groove  10  is decreased and the wet performance can be improved. 
     It is preferable that the distance Lr of the sound insulation wall  17  from the axially outer edge  10   e  of the axially outer longitudinal groove  10  becomes minimal at the above-mentioned junctions  10   d.    
     It is preferable that the distance Lr at the junctions  10   d  is set in a range of not less than 1 mm, more preferably not less than 1.5 mm, but not more than 5 mm, more preferably not more than 4 mm, and that the intersecting points K 2  (imaginary intersecting point) between the center lines G 13  of the axially outer shoulder lateral grooves  14  and the axially outer edge  10   e  (imaginary edge line  10   k ) of the axially outer longitudinal groove  10  are shifted from the axially outer points  17   p  of the sound insulation wall  17  in the tire circumferential direction by a distance Lo of from 0 to 2 mm. Thereby, the transfer of noise sound from the longitudinal groove  10  to the axially outer shoulder lateral groove  14  is hindered, while maintaining drainage and wet performance.
 
Incidentally, the imaginary edge line  10   k  and above-mentioned imaginary edge line  10   j  of the axially outer longitudinal groove  10  can be defined by lines parallel with the opposed axially inner edge  10   i  and the opposed axially outer edge  10   e , respectively.
 
     The height H 1  of the sound insulation wall  17  is set in a range of not less than 90%, preferably not less than 95%, but not more than 105%, preferably not more than 100% of the groove depth D 1  of the axially outer longitudinal groove  10 . In this embodiment, the height H 1  is equal to the groove depth D 1 . If the height H 1  is less than 90%, it is difficult to shut off the noise sound. If the height H 1  is more than 105%, the sound insulation wall  17  is very liable to broken during running. 
     Preferably, the ratio t 1 /t 1   a  of the thickness t 1  of the sound insulation wall  17  at the top surface  17   g  to the thickness t 1   a  of the sound insulation wall  17  at the bottom  10   u  of the axially outer longitudinal groove  10  is not more than 1.0, preferably less than 1.0, more preferably not more than 0.85, but not less than 0.2, preferably not less than 0.5. In view of the demolding of the vulcanized tire, it is preferable that the sound insulation wall  17  is tapered toward the radially outside, namely, the ratio t 1 /t 1   a  of less than 1.0 is preferred. However, if the ratio t 1 /t 1   a  is less than 0.2, wear and cracks are liable to occur at the radially outer end portion. Further, as the rigidity becomes insufficient, it becomes difficult to shut off the noise sound. 
     As shown in  FIG. 3 , in the cross section of the sound insulation wall  17  taken perpendicular to the longitudinal direction thereof, the thickness t 1  of the sound insulation wall  17  at the top surface  17   g  is preferably set in a range of not less than 10%, more preferably not less than 20%, but not more than 50%, more preferably not more than 40% of the groove top width W 1  of the axially outer longitudinal groove  10 . 
     Therefore, the durability of the sound insulation wall  17  can be maintained for a long time. And a sufficient thickness is provided on the top surface side of the sound insulation wall  17 , therefore, leakage of the noise sound is efficiently prevented. As a result, the pumping sound noise coming from the oblique grooves and the resonance sound noise of the longitudinal groove are reduced, the noise performance can be effectively improved. 
     Comparison Tests 
     In order to confirm the effects of the present invention, truck/bus tires of size 275/80R22.5 (rim size: 7.50×22.5) having the internal tire structure shown in  FIG. 1  were prepared and tested for the noise performance and wet performance. 
     The test tires had the same specifications except for the specifications shown in Table 1. 
     Common specifications are as follows.
 
Tread width TW: 260 mm
 
Carcass: one ply of steel cords arranged radially at 90 degrees
 
Belt: four plies of steel cords
 
Longitudinal grooves ( 9 ,  10 ,  11 )
 
     top width W 1 : 7 to 12 mm 
     depth D 1 : 14 to 16 mm 
     oblique grooves ( 12 ,  13 ) 
     top width W 2 : 6 to 8 mm 
     depth D 2 : 14 to 16 mm 
     Sound insulation wall ( 17 ) 
     height H 1 : 90 to 105% of D 1   
     thickness t 1 : 10 to 50% of W 1   
     thickness ratio t 1 /t 1   a : 20 to 100%&lt; 
     &lt;Noise Performance Test&gt; 
     Using a 1.7 meter dia. test drum provided with an ISO road surface, the test tire inflated to 900 kPa (standard pressure) was run at 40 km/h under a tire load of 23.8 kN (70% of standard load) in an anechoic chamber, and the A-weighted sound pressure level was measured. The results are indicated in Table 1 by an index based on Embodiment 1 being 100, wherein the larger the index number, the lower the noise level. 
     &lt;Wet Performance Test&gt; 
     2D-type truck provided on all wheels with test tires inflated to 900 kPa was run on a wet asphalt road surface in a tire test course, and the test driver evaluated the running stability. The results are indicated in Table 1 by an index based on Embodiment 1 being 100, wherein the larger the index number, the better the wet performance. 
     From the test results, it was confirmed that the tires according to the present invention can be improved in the noise performance and wet performance in a well balanced manner. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Tire 
                 Ref. 1 
                 Ref. 2 
                 Ref. 3 
                 Ref. 4 
                 Ex. 1 
                 Ex. 2 
               
               
                   
               
               
                 Tread pattern 
                 FIG. 5(a) 
                 FIG. 5(b) 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
               
               
                 axially inner oblique groove 
               
               
                 number of grooves 
                 42 
                 42 
                 42 
                 42 
                 42 
                 42 
               
               
                 angle α1 (deg.) 
                 30 
                 30 
                 10 
                 50 
                 30 
                 20 
               
               
                 distance Lm at junctions (mm) 
                 — 
                 — 
                 2 
                 2 
                 2 
                 2 
               
               
                 distance Ln (sift) (mm) 
                 — 
                 — 
                 2 
                 2 
                 2 
                 2 
               
               
                 Test results 
               
               
                 noise performance 
                 90 
                 90 
                 92 
                 86 
                 100 
                 96 
               
               
                 wet performance 
                 70 
                 72 
                 85 
                 105 
                 100 
                 98 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Tire 
                 Ex. 3 
                 Ex. 4 
                 Ex. 5 
                 Ex. 6 
                 Ex. 7 
                 Ex. 8 
                 Ex. 9 
               
               
                   
               
               
                 Tread pattern 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
               
               
                 axially inner oblique groove 
               
               
                 number of grooves 
                 42 
                 42 
                 42 
                 42 
                 42 
                 42 
                 42 
               
               
                 angle α1 (deg.) 
                 40 
                 30 
                 30 
                 30 
                 30 
                 30 
                 30 
               
               
                 distance Lm at junctions (mm) 
                 2 
                 0.5 
                 1.2 
                 4.5 
                 6 
                 2 
                 2 
               
               
                 distance Ln (sift) (mm) 
                 2 
                 2 
                 2 
                 2 
                 2 
                 0 
                 1 
               
               
                 Test results 
               
               
                 noise performance 
                 94 
                 104 
                 102 
                 95 
                 93 
                 102 
                 102 
               
               
                 wet performance 
                 102 
                 92 
                 94 
                 103 
                 104 
                 93 
                 96 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Tire 
                 Ex. 10 
                 Ex. 11 
                 Ex. 12 
                 Ex. 13 
                 Ex. 14 
                 Ex. 15 
               
               
                   
               
               
                 Tread pattern 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
                 FIG. 2 
               
               
                 axially inner oblique groove 
               
               
                 number of grooves 
                 42 
                 42 
                 35 
                 39 
                 54 
                 65 
               
               
                 angle α1 (deg.) 
                 30 
                 30 
                 30 
                 30 
                 30 
                 30 
               
               
                 distance Lm at junctions (mm) 
                 2 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                 distance Ln (sift) (mm) 
                 3 
                 4 
                 2 
                 2 
                 2 
                 2 
               
               
                 Test results 
               
               
                 noise performance 
                 96 
                 93 
                 95 
                 99 
                 99 
                 94 
               
               
                 wet performance 
                 102 
                 103 
                 90 
                 95 
                 102 
                 103