Patent Publication Number: US-2023137725-A1

Title: Pneumatic tire

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2021-177088 filed on Oct. 29, 2021, which is incorporated herein by reference in its entirety including the specification, claims, drawings, and abstract. 
     TECHNICAL FIELD 
     The present disclosure relates to a pneumatic tire, and in particular to a pneumatic tire having a tread including a circumferential groove and a lug groove. 
     BACKGROUND 
     In the related art, pneumatic tires are known which have a tread including a plurality of circumferential grooves and a plurality of lug grooves connected to the circumferential grooves and extending along a tire width direction (for example, JP6319385 B). In the tire disclosed in JP 6319385 B, in order to reduce rolling resistance while snow traction performance is maintained, raising portions are formed in portions of the circumferential groove other than an intersection with an extension of the lug groove, and in the lug groove. 
     However, in the tire disclosed in JP 6319385 B, air tends to be easily accumulated in the intersection of the circumferential groove with the extension of the lug groove. Because of this, during travel of a vehicle to which the tire is fitted, an air pumping sound, which is tire noise, tends to be generated due to the air accumulated in the above-described intersection. 
     An advantage of the present disclosure lies in the provision of a pneumatic tire in which the snow traction performance can be improved, the rolling resistance can be reduced, and the air pumping sound can be reduced. 
     SUMMARY 
     According to one aspect of the present disclosure, there is provided a pneumatic tire comprising: a tread including: a circumferential groove; and a lug groove which is connected to the circumferential groove and which extends from a first side in a tire width direction to a second side; two first raised portions formed in the circumferential groove, on a groove bottom at positions either side of an end of the lug groove on a side near the circumferential groove; a second raised portion formed on a groove bottom at a portion of the lug groove on a side near the circumferential groove; and a third raised portion formed at an intersection of the circumferential groove with an extension of the lug groove, on at least a part of a groove bottom of a portion surrounded in three directions by the two first raised portions and the second raised portion. 
     According to the pneumatic tire described above, in the circumferential groove, two first raised portions are formed on a groove bottom at positions either side of an end of the lug groove on the side near the circumferential groove, and the second raised portion is formed on a groove bottom at a portion of the lug groove on the side near the circumferential groove. With this configuration, rigidities of a land portion adjacent to the first raising portion of the circumferential groove, and a land portion adjacent to the second raising portion of the lug groove, can be improved. Thus, energy loss due to deformation of the land portions during travel of the vehicle can be reduced, and the rolling resistance of the tire can be reduced. Further, with a shearing force acting on snow which is pressurized and hardened in the groove during the travel on a snowy road surface, the resistance between the tire and the road surface can be increased and the snow traction performance can be improved. Further, the third raised portion is formed in an intersection of the circumferential groove with the extension of the lug groove, on a groove bottom on a portion surrounded in three directions by the two first raised portions and the second raised portion. With this configuration, an amount of air accumulation at the intersection can be reduced, and the air pumping sound during travel can be reduced. 
     According to a pneumatic tire of an aspect of the present disclosure, the snow traction performance can be improved, the rolling resistance can be reduced, and the air pumping sound can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Embodiment(s) of the present disclosure will be described based on the following figures, wherein: 
         FIG.  1    is a perspective diagram of a pneumatic tire according to an embodiment of the present disclosure; 
         FIG.  2    is a plan view of a pneumatic tire according to an embodiment of the present disclosure, showing a part of a tread; 
         FIG.  3    is a plan view showing in an enlarged manner a part of a center region of a tread; 
         FIG.  4    is an enlarged perspective view of a recess on a slanted circumferential groove of  FIG.  3   ; 
         FIG.  5    is a plan view showing an enlarged manner the recess shown in  FIG.  4   ; 
         FIG.  6    is a diagram showing a cross section along a line A 1 -A 1  in  FIG.  5   ; 
         FIG.  7 A  is a diagram showing another configuration of the recess, and corresponding to  FIG.  6   ; 
         FIG.  7 B  is a diagram showing another configuration of the recess, and corresponding to  FIG.  6   ; 
         FIG.  8    is a diagram showing another configuration of the recess, and corresponding to  FIG.  4   : 
         FIG.  9    is a plan view showing in an enlarged manner a part of a center region of a tread in an embodiment of the present disclosure; 
         FIG.  10    is a perspective diagram showing in an enlarged manner a connection portion between a first circumferential groove and a lug groove between center blocks which are first land portions of  FIG.  9   ; 
         FIG.  11    is an enlarged perspective diagram cutting  FIG.  9    along a line B-B; 
         FIG.  12    is a plan view showing in an enlarged manner a C part of  FIG.  9   : 
         FIG.  13    is a diagram showing a cross section along a line D-D of  FIG.  12   ; 
         FIG.  14    is an enlarged view of a cross section along a line E-E of  FIG.  9   ; 
         FIG.  15    is an enlarged perspective diagram of an embodiment of the present disclosure, cutting  FIG.  9    along a line F-F; 
         FIG.  16    is an enlarged cross-sectional view showing a bridge which corresponds to a second raised portion in a G part of  FIG.  9   ; 
         FIG.  17    is an enlarged view of a cross section along a line H-H of  FIG.  15   ; 
         FIG.  18    is an enlarged cross-sectional view of a third raised portion on a third circumferential groove of  FIG.  9   ; 
         FIG.  19    is a diagram corresponding to an I part of  FIG.  9   , showing another configuration of the third raised portion; 
         FIG.  20    is a diagram showing in an enlarged manner a part of a shoulder block which is a fifth land portion at an outer side in a vehicle width direction of  FIG.  2   ; 
         FIG.  21    is an enlarged perspective diagram of an end, of the shoulder block of  FIG.  20   , at an outer side in a tire width direction; and 
         FIG.  22    is a perspective diagram showing the shoulder block of  FIG.  20   , cut in a plane including a ground-contacting end. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A pneumatic tire according to an embodiment of the present disclosure will now be described in detail with reference to the drawings. The embodiment described below is merely exemplary, and the present disclosure is not limited to the embodiment described below. Further, selective combination of various constituent elements of a plurality of embodiments and alternative configurations described below is within the scope of the present disclosure. 
     In the present disclosure, terms are used such as a wet road surface, a snowy road surface, and a dry road surface. The wet road surface refers to a road surface which is wet due to rain water or the like, and a road surface which is wet due to melting of snow and ice. The snowy road surface refers to a road surface covered with snow. The dry road surface refers to a dry road surface without snow or ice. In the following, for convenience of explanation, the wet road surface and the snowy road surface may be collectively called “snow-ice road surface”. In addition, in the following description, a traveling performance on an icy road surface (ice performance) will not be particularly described, but the pneumatic tire according to an embodiment of the present disclosure has superior ice performance, in addition to superior wet performance, superior snow performance, and superior dry performance. 
       FIG.  1    is a perspective diagram of a pneumatic tire  1  according to an embodiment of the present disclosure.  FIG.  2    is a plan view of the pneumatic tire  1 , and shows a part of a tread. As shown in  FIGS.  1  and  2   , the pneumatic tire  1  has a tread  10  which is a portion which contacts the road surface. In the following, the “pneumatic tire  1 ” will also be called a “tire  1 ”. The tread  10  has a tread pattern including a plurality of blocks, and is formed in an annular shape along a tire circumferential direction. While a “primary rotation direction” of the tire  1 , which is a rotational direction of the tire  1  during forward travel of a vehicle on which the tire  1  is fitted, is not limited, in the following, primarily, a case will be described in which a direction of an arrow α of  FIG.  1    is the primary rotation direction. 
     In the present disclosure, for the tire  1  and the constituent elements thereof, the terms “left” and“right” will be used for convenience of the description. A “right side” of the tire  1  refers to a right side when the tire  1  in a state of being fitted on the vehicle is viewed from the front side of the vehicle, and a “left side” refers to a left side when the tire  1  in the state of being fitted on the vehicle is viewed from the front side of the vehicle. 
     In the tire  1  according to an embodiment of the present disclosure, a direction of fitting of a front side and a back side of the tire  1  with respect to the vehicle is designated. That is, in the tire  1 , a side which becomes an outer side in a vehicle width direction and a side which becomes an inner side in the vehicle width direction are respectively designated. In  FIG.  1   , the tire  1  is fitted to the vehicle so that the right side is at the outer side in the width direction of the vehicle (OUT-SIDE), and the left side is at the inner side in the width direction of the vehicle (IN-SIDE). Tires  1  of a common structure may be used for the left and right wheels by reversing the primary rotation direction and the left-and-right direction of the tire  1  between the tire  1  used for the right wheel of the vehicle and the tire  1  used for the left wheel. 
     The tread  10  has a plurality of circumferential grooves  20 ,  21 , and  22 , and a plurality of lug grooves  25  and  26  which extend while being curved from a left side, which is a first side, in the tire width direction to a right side, which is a second side, in the tire width direction. The tread  10  is partitioned by the plurality of circumferential grooves  20 ,  21 , and  22 , and a plurality of lug grooves  25 , and  26 , so as to include a plurality of blocks which are separated in the tire circumferential direction and also separated in the tire width direction. 
     The block is a land-like region bulged toward an outer side in a tire radial direction. As shown in  FIG.  2   , the tread  10  includes, as the blocks, a plurality of center blocks  50 , a plurality of mediate blocks  60  and  70 , and a plurality of shoulder blocks  80  and  90 , all of which will be described below. A tire equator CL to be described below passes through the center block  50 . The mediate block  60  and the shoulder block  80  are placed at a left side in a width direction of the tread  10 , and the mediate block  70  and the shoulder block  90  are placed at a right side in the width direction of the tread  10 . 
     The circumferential grooves  20 ,  21 , and  22  include a first circumferential groove  20  formed near the center in the width direction of the tread  10 , and a second circumferential groove  21  and a third circumferential groove  22  provided respectively on the left and right sides of the first circumferential groove  20 . Further, a plurality of slanted circumferential grooves  31  which will be described later are formed between the first circumferential groove  20  and the second circumferential groove  21  of the tread  10 . The “tire width direction” and the “width direction of the tread  10 ” are the same direction, and these terms will hereinafter be used appropriately. The first circumferential groove  20  and the second circumferential groove  21  are provided either side of the center in the tire width direction. The first circumferential groove  20  is provided closest to the tire equator at the center in the tire width direction, among the circumferential grooves  20 ,  21 , and  22 . The tire equator CL refers to a line passing through the center in the tire width direction and extending along the tire circumferential direction. 
     Further, on the tread  10 , a center region  40  is provided, which is a predetermined region in the tire width direction partitioned by the first circumferential groove  20  and the second circumferential groove  21 . The center region  40  is divided into the center block  50  and the mediate block  60  which are separated to the right and left at each of a plurality of positions in the tire circumferential direction, by the plurality of slanted circumferential grooves  31  to be described later. The center block  50  is placed adjacent to the first circumferential groove  20  on the side near the center in the tire width direction. The center block  50  corresponds to a first land portion serving as a center land portion. A row of center blocks  41  is formed by the plurality of center blocks  50  arranged along the tire circumferential direction. 
     The mediate block  60  corresponds to a second land portion. A row of mediate blocks  44  is formed by the plurality of mediate blocks  60  arranged along the tire circumferential direction. 
     Further, a row of shoulder blocks  45 , including a plurality of shoulder blocks  80  having an inner end in the tire width direction determined by the second circumferential groove  21 , is formed on the tread  10 . In addition, a row of mediate blocks  46 , including a plurality of mediate blocks  70  partitioned by the first circumferential groove  20  and the third circumferential groove  22 , is formed on the tread  10 . Moreover, a row of shoulder blocks  47  including a plurality of shoulder blocks  90  having an inner end in the tire width direction determined by the third circumferential groove  22  is formed on the tread  10 . The shoulder block  80  corresponds to a third land portion serving as a shoulder land portion. The mediate block  70  corresponds to a fourth land portion. The shoulder block  90  corresponds to a fifth land portion serving as a shoulder land portion. The circumferential grooves  20 ,  21 , and  22  extend along the tire circumferential direction, and have approximately the same width as each other. 
     The plurality of lug grooves  25  and  26  extend while being curved from the left side in the tire width direction to the right side, and are placed with a spacing therebetween in the tire circumferential direction. The plurality of lug grooves  25  and  26  are inclined to the same side with respect to the tire width direction on each of the plurality of rows of blocks  41  and  44  to  47 , and between blocks that are adjacent to each other in the tire circumferential direction. The lug grooves  25  and  26  in the row of center blocks  41  and the row of mediate blocks  44  are inclined more significantly with respect to the tire width direction than the lug grooves  25  and  26  in the other rows of blocks  45  to  47 . With this configuration, it becomes easier to improve snow traction performance in a lateral direction at the center portion in the tire width direction. In addition, the plurality of lug grooves  25  and  26  have shallower depths than the plurality of circumferential grooves  20  to  22 . 
     The plurality of lug grooves  25  and  26  include a plurality of first lug grooves  25  and a plurality of second lug grooves  26 , distanced from each other in the tire circumferential direction. On the tread  10 , one or more first lug grooves  25  and one or more second lug grooves  26  are alternately placed in the tire circumferential direction. In the following description, a case will be exemplified in which one first lug groove  25  and one second lug groove  26  are alternately placed along the tire circumferential direction on the tread  10 . Alternatively, a configuration may be employed in which a plurality of first lug grooves  25  and one second lug groove  26  are alternately placed. The first lug groove  25  is a lug groove across which an intermediate portion of the slanted circumferential groove  31  to be described below extends in the tire circumferential direction in the center region  40 . On the other hand, the second lug grooves  26  are lug grooves that are connected by respective ends of a slanted circumferential groove  31 . The widths of the lug grooves  25  and  26  are basically approximately equal to each other, but ends of the lug grooves  25  and  26  near the first circumferential groove  20  in the row of mediate blocks  46  are narrower than those in the other portions. 
     In the present embodiment, blocks of the same type and assigned the same reference numeral are placed along the tire circumferential direction, arranged in one row. In addition, a plurality of blocks of the same number are arrange and placed, in a separated manner at a plurality of positions in the tire circumferential direction and along the plurality of lug grooves  25  and  26  of the tread  10 . That is, on the tread  10 , the same numbers of the center blocks  50 , the mediate blocks  60  and  70 , and the shoulder blocks  80  and  90  are formed. 
     On a ground-contacting surface of each block, a plurality of sipes of a narrow line shape are formed, which extend approximately along the tire width direction or approximately along the tire circumferential direction. Each sipe is a groove of a narrow line shape, having a narrower width than the circumferential grooves  20  to  22  and the lug grooves  25  and  26 , and improves an edge effect to dig into snow and ice, to thereby realize superior braking and driving performance, and superior maneuver stability on the snow-ice road surface. The tire  1  having such a tread pattern is suited, for example, for an all-season tire. 
     The tire  1  has, on respective sides in the width direction of the tread  10 , side walls  12  formed in an annular shape along the tire circumferential direction, similar to the tread  10 . 
     On the other hand, the shoulder blocks  80  and  90  placed on respective ends in the width direction of the tread  10  include ground-contacting ends T ( FIG.  2   ) which are ends of the ground-contacting surface on the outer side in the tire width direction. End portions of the shoulder blocks  80  and  90  in the tire width direction protrude from the ground-contacting ends T toward an outer side in the tire width direction, and are gradually curved toward the inner side in the tire radial direction such that outer circumferential surfaces are convex toward the outer side. The portion, of each of the shoulder blocks  80  and  90 , protruding from the ground-contacting end T toward the outer side in the tire width direction is called a buttress. 
     In the present disclosure, the ground contacting ends T refer to respective ends, in the tire width direction, of a region contacting a flat road surface when a load which is 70% of a regular load (maximum load capability) at a regular internal pressure is applied in a state in which the tire  1  which is yet to be used is fitted on a regular rim, and filled with air to achieve the regular internal pressure. 
     Here, the “regular rim” refers to a rim determined by a tire standard, and is defined as a “standard rim” in JATMA, a “Design Rim” in TRA, and a “Measuring Rim” in ETRTO. The “regular internal pressure” is defined as a “maximum pneumatic pressure” in JATMA, a maximum value described in the table. “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA, and an “INFLATION PRESSURE” in ETRTO. The “regular load” is defined as a “maximum load capability” in JATMA, a maximum value described in the table, “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA, and a “LOAD CAPACITY” in ETRTO. 
     On an inner circumferential side of the tire  1 , a reinforcement structure is provided, illustration of which is omitted. The reinforcement structure includes a carcass which is a cord layer covered with rubber, and a belt placed between the tread pattern and the carcass. The carcass is formed from, for example, two carcass plies, and forms a tire skeleton which endures load, shock, pneumatic pressure, and the like. The belt is a reinforcement band stretched in the tire circumferential direction, and firmly fastens the carcass, to thereby improve rigidity of the tread  10 . On an inner circumferential surface of the carcass, an inner liner which is a rubber layer for maintaining the pneumatic pressure is attached. 
     In addition, on the tire  1 , a bead  13  is provided which is provided to be continuous from an inner circumferential end of the side wall  12 , which extends to an inner side in the tire radial direction, the bead  13  being curved to be convex toward the inner side of the tire  1 . The bead  13  is positioned at an inner side in the width direction of the tire  1  (side nearer to the tire equator CL) than the side wall  12 . The bead  13  is a portion fixed on the rim of the wheel, and a bead core and a bead filler are provided in the bead  13 . 
     Further, in the present embodiment, the slanted circumferential grooves  31  are formed at a plurality of positions of the center region  40  in the tire circumferential direction. With the slanted circumferential groove  31 , the snow traction performance of the tire  1  can be improved. The slanted circumferential groove  31  will be described later in detail. 
     In addition, as shown in  FIG.  2   , in the row of center blocks  41 , bridges  100  and  101  serving as raised portions are formed in the lug grooves  25  and  26  between the center blocks  50 . With these bridges  100  and  101 , the rigidity of the center blocks  50  that are adjacent in the tire circumferential direction can be improved. Similarly, raised portions  102 ,  103 ,  104 , and  105  are provided respectively in the lug grooves  25  and  26  between the blocks in the row of mediate blocks  44 , the row of shoulder blocks  45 , the row of mediate blocks  46 , and the row of shoulder blocks  47 . With the raised portions  102  to  105 , the rigidities of respective blocks adjacent in the tire circumferential direction can be improved. 
     At respective ends of the bridge  100  formed in the second lug groove  26  between the center blocks  50 , inclined tapered surfaces are formed having heights which are reduced toward corresponding ends. With this configuration, as will be described below, reduction of water drainage performance at the center portion in the tire width direction can be suppressed while the rigidity of the center block  50  can be improved and dependence on the tire rotational direction can be suppressed. 
     In the second circumferential groove  21 , raised portions  106  and  107  are formed as two first raised portions at groove bottoms at positions either side of ends of the lug grooves  25  and  26  near the second circumferential groove  21 , between the shoulder blocks  80  of the row of shoulder blocks  45 . In the second circumferential groove  21 , at an intersection with extensions of the lug grooves  25  and  26 , a raised portion  108  serving as a third raised portion is formed at the groove bottom in a portion surrounded in three directions by the two raised portions  106  and  107  and the raised portion  103  serving as a second raised portion. With this configuration, as will be described below, the snow traction performance can be improved and rolling resistance can be reduced, and in addition, an air pumping sound, which is tire noise, can be reduced. 
     Further, narrow grooves  109  and  110  to be described below which are inclined with respect to the tire circumferential direction are formed on portions of the shoulder block  90  at outer sides in the tire width direction than the ground-contacting ends T. With this configuration, the snow traction performance can be improved. In addition, the narrow grooves  109  and  110  are connected to sipes  81  and  82  serving as lateral sipes, and are not connected to the lug grooves  25  and  26 , so that the water drainage performance can be improved and the rigidity of the shoulder block  90  can be improved. 
     Next, structures for the slanted circumferential groove  31 , a portion of the second lug groove  26  near the first circumferential groove  20  and the first circumferential groove  20 , connection portions between the second and third circumferential grooves  21  and  22  and the lug grooves  25  and  26 , and the narrow grooves  109  and  110  of the shoulder block  90 , will be described in detail. First, with reference to  FIGS.  3  to  6   , the slanted circumferential groove  31  will be described. 
       FIG.  3    is a plan view showing in an enlarged manner a part of the center region  40  of the tread  10 .  FIG.  4    is an enlarged perspective diagram of a recess  31   a  in the slanted circumferential groove  31  of  FIG.  3   .  FIG.  5    is a plan view showing in an enlarged manner the recess  31   a .  FIG.  6    is a diagram showing a cross section along a line A 1 -A 1  of  FIG.  5   . 
     The slanted circumferential groove  31  is provided at a plurality of positions in the tire circumferential direction on the center region  40 . Each slanted circumferential groove  31  is a groove which extends across the first lug groove  25  in the tire circumferential direction, and is inclined with respect to the tire circumferential direction such that a first end K 1  in a longitudinal direction is closer to the tire equator CL at the center in the tire width direction than a second end K 2  in the longitudinal direction. The slanted circumferential groove  31  extends across the first lug groove  25 , and connects two second lug grooves  26 . 
     As a position where the first end K 1  of the slanted circumferential groove  31  penetrates through the second lug groove  26 , the recess  31   a  which extends into a wall surface  50   a  ( FIG.  5   ) of the center block  50  is formed on the first end K 1 . The recess  31   a  extends along the second lug groove  26 , and is a portion recessed from the ground-contacting surface of the center block  40  in a shape when viewed from the outer side in the tire radial direction, that is, in plan view, of an approximate isosceles triangle, as shown in  FIG.  5   . 
     More specifically, the shape of the recess  31   a  in plan view is an isosceles triangle with three vertices P 1 , P 2 , and P 3 , and a first long side L 1 , a second long side L 2 , and a short side L 3 , with one corner corresponding to the vertex P 1  rounded. Lengths of the first long side L 1  and the second long side L 2  are approximately equal to each other, and are longer than a length of the short side L 3 . The first long side L 1  extends along a longitudinal direction of the second lug groove  26 . The vertex P 1  of the isosceles triangle which is an intersection of the second long side L 2  and the short side L 3  goes inside the wall surface  50   a . The vertices P 1 , P 3  are positioned at a position farther away from the tire equator CL at the center in the tire width direction than the vertex P 2  of the isosceles triangle which is an intersection of the first long side L 1  and the second long side L 2 . The corner corresponding to the vertex P 1  of the isosceles triangle is an intersection of the second long side L 2  and the short side L 3 . 
     On a bottom surface of the recess  31   a , an inclined surface  31   b  is formed which becomes closer to the ground-contacting surface  50   a  of the center block  50  toward an inner side of the center block  50 . Specifically, as shown in  FIG.  4   , a region near a left end of a lower edge DL of a bottom surface of the recess  31   a  adjacent to the second lug groove  26  is inclined such that the region becomes closer to the ground-contacting surface toward a left end of the recess  31   a . The left end of the recess  31   a  is slightly recessed toward an inner side of the center block  50 , and the inclined surface  31   b  is formed connecting an upper edge UL and the lower edge DL on the ground-contacting surface  50   b . With this configuration, as shown in the cross-sectional diagram of  FIG.  6   , the cross section of the bottom surface of the recess  31   a  is a straight line form inclined in a straight line shape which becomes closer to the ground-contacting surface  50   b  of the center block  50  toward the inner side of the center block  50  (left side of  FIG.  6   ) on which the recess  31   a  is formed. Because of this, a relatively large space is formed at the inner side of the recess  31   a  extending into the wall surface  50   a  of the center block  50 , into which water from the second lug groove  26  and the slanted circumferential groove  31  can enter. In the present disclosure, when the terms of “upper” and “lower” are used, with a side in which the heights in the bulging directions of the bulging portions such as the block, a protrusion, and the like are increased being referred to as the “upper” side, and a side in which the heights are reduced being referred to as the “lower” side”. 
     Although not shown in the figures, in the cross section along a line A 2 -A 2  and the cross section along a line A 3 -A 3  in  FIG.  5    also, similar to  FIG.  6   , the cross section of the bottom surface of the recess  31   a  is the straight line form inclined in the straight line shape which becomes closer to the ground-contacting surface  50   b  of the center block  50  toward the inner side of the center block  50 . 
     As shown in  FIG.  2   , the plurality of slanted circumferential grooves  31  are connected over the entire circumference via a portion of the second lug grooves  26  formed at the plurality of positions in the tire circumferential direction, so that the slanted circumferential grooves  31  are formed in a zigzag shape. As shown in  FIG.  4   , portions of each of the slanted circumferential grooves  31  other than the recess  31   a  are deeper than portions of each of the lug groves  25  and  26  other than the intersection with the slanted circumferential groove  31 . The depths of the portions of the slanted circumferential groove  31  other than the recess  31   a  may be approximately equal to the depth of each of the lug grooves  25  and  26 . 
     With this configuration, the slanted circumferential groove  31  which is inclined with respect to the tire circumferential direction is formed, extending across the first lug groove  25  provided on the center region  40  of the tread  10 . The recess  31   a  provided on the first end K 1  of the slanted circumferential groove  31  extends into the center block  50 , and the first end K 1  is closer to the tire equator CL at the center in the tire width direction than the second end K 2 . Because of this, maneuver stability and turning performance of the vehicle on snow can be improved. For example, in portions of the slanted circumferential groove  31  other than the recess  31   a , because the slanted circumferential groove  31  is inclined with respect to the tire circumferential direction, it becomes easier to dig into and grip snow and ice in the circumferential direction and the lateral direction of the tire. In addition, at the portion of the slanted circumferential groove  31  recessed at the left end of the recess  31   a  near the center in the tire width direction, it becomes easier to dig into and grip the snow and ice in the lateral direction of the tire  1 . With this configuration, the snow traction performance in the circumferential direction and the lateral direction of the tire  1  can be improved. Moreover, because the first end K 1  of the slanted circumferential groove  31  on which the recess  31   a  is provided is closer to the center in the tire width direction than the second end K 2 , the maneuver stability and the turning performance on snow can be improved to a higher degree than a configuration in which the recess is separated with a larger distance in the outer side in the tire width direction. 
     Further, the recess  31   a  provided on the first end K 1  of the slanted circumferential groove  31  extends along the second lug groove  26 . With this configuration, during traveling of the vehicle on the wet road surface, when the tire  1  rotates in such a manner that water flows from the side of the second end K 2  to the side of the first end K 1  in the slanted circumferential groove  31 , the space between the recess  31   a  and the road surface can be widened, and it becomes possible to suppress a phenomenon in which the wall surface or the bottom surface of the recess  31   a  becomes a resistance to the flow of water. In addition, on the bottom surface of the recess  31   a , the inclined surface  31   b  is formed which becomes closer to the ground-contacting surface  50   b  of the center block  50  toward the inner side of the center block  50 . Thus, it becomes possible to suppress retention of water in the recess  31   a . Further, unlike a structure in which a deeper side of a recess  31   c  is formed as a corner of a right angle as shown by a two-dots-and-chain line in  FIG.  6   , reduction of rigidity of the center block  50  can be suppressed. With such a configuration, superior water drainage performance from the groove of the tire  1  can be achieved, and thus, the tire  1  can be realized having an advantage of superior hydroplaning suppression, and which can suppress the reduction of rigidity of the center block  50 . 
     For example, when the tire  1  rotates in a direction of an arrow a of  FIG.  3    during the traveling of the vehicle, a case may be considered in which a water flow shown by an arrow β of  FIG.  3   , from the center in the tire width direction toward the outer side in the tire width direction along the second lug groove  26 , merges with a water flow shown by an arrow γ of  FIG.  3   , toward a rear side in the rotational direction of the tire  1  along the slanted circumferential groove  31 . In this case, a volume of a space can be widened at a merging portion by the recess  31   a , and thus, resistance of the water flow can be suppressed and the water drainage performance can be improved. 
     Moreover, in the tire  1 , the shape in plan view of the recess  31   a  is an isosceles triangle with a corner corresponding to the vertex P 1  rounded. Thus, generation of a turbulent flow in the water flow at the deeper side of the recess  31   a  can be suppressed, the water flow in the groove in communication with the recess  31   a  can be smoothed, and the water drainage performance can be improved. Unlike the structure in which the shape of the recess  31   a  in plan view is set to a quadrangular shape, excessive enlargement of the recess  31   a  can be prevented while suppressing resistance to the water flow at the merging portion of the water flows, and therefore, the reduction of rigidity of the center block  50  can be suppressed. 
       FIG.  7 A  shows a first alternative configuration of the recess. In the structure shown in  FIG.  7 A , a position of an upper end of an inclined surface  31   e  formed on a bottom surface of a recess  31   d  is at a position going into the inner side in the tire radial direction (lower side in  FIG.  7 A ) than the ground-contacting surface  50   b . In this structure, in comparison to the structure shown in  FIGS.  3  to  6   , the rigidity of the center block  50  may be slightly reduced, but the space in the recess  31   a  can be widened. Thus, the advantage of suppression of hydroplaning can be further improved. 
       FIG.  7 B  shows a second alternative configuration of the recess. In the structure shown in  FIG.  7 B , on a bottom surface of a recess  31   f , there are formed a convex surface  31   g  having a cross section of a curved line and which is convex toward the outer side such that the surface becomes closer to the ground-contacting surface  50   b  of the center block  50  toward the inner side of the center block  50 , and a concave surface  31   h  having a cross section of an are shape in which a corner portion is continuously rounded from a deep end of the convex surface  31   g . In this configuration also, in comparison to the structure shown in  FIGS.  3  to  6   , the rigidity of the center block  50  may be slightly reduced, but the space in the recess  31   a  can be widened. Therefore, the advantage of suppression of hydroplaning can be improved. Further, the water flow between the recess  31   a  and the groove can be smoothed, and the water drainage performance can be improved. 
       FIG.  8    shows a third alternative configuration of the recess. In the structure shown in  FIG.  8   , unlike the structure shown in  FIGS.  3  to  6   , a shape of a recess  31   i  in plan view is an isosceles triangle without the corners rounded. An inclined surface  31   j  is formed at a bottom surface of the recess  31   a , which has the second long side L 2  connecting the vertex P 1  and the vertex P 2  as an upper edge UL, and which connects the upper edge UL and a lower edge DL at the side of the bottom surface of the groove. In the case of this structure, because the area of a wall surface  31   k  at a left end of the recess  31   i  can be widened, the snow traction performance in the lateral direction can be further improved. 
     Next, structures of a portion of the second lug groove  26  near the first circumferential groove  20 , and the first circumferential groove  20  will be described in detail with reference to  FIGS.  9  to  14   .  FIG.  9    is a plan view showing in an enlarged manner apart of the center region  40  of the tread  10 .  FIG.  10    is a perspective view showing in an enlarged manner a connection portion between the first circumferential groove  20  and the second lug groove  26  between the center blocks  50  shown in  FIG.  9   .  FIG.  11    is an enlarged perspective diagram showing  FIG.  9   , which is cut along a line B-B.  FIG.  12    is a plan view showing in an enlarged manner a C part of  FIG.  9   .  FIG.  13    is a diagram showing a cross section along a line D-D of  FIG.  12   .  FIG.  14    is an enlarged view of a cross section along a line E-E of  FIG.  9   . 
     As shown in  FIGS.  9  to  14   , a plurality of the center blocks  50  are placed adjacent to the first circumferential groove  20  at a side near the center in the tire width direction. The lug grooves  25  and  26  between the center blocks  50  extend to a right side in the tire width direction and open to the side near the first circumferential groove  20 . On the portion of the second lug groove  26  between the center blocks  50 , near the first circumferential groove  20 , the bridge  100  having a bottom surface which is bulged is formed.  FIG.  12    shows the bridge  100  with a portion shaded with fine dots. 
     The bridge  100  is provided in order to improve the rigidity of adjacent center blocks  50 . As shown in  FIGS.  12  and  13   , the bridge has a cross-sectional shape of an approximate trapezoid. Specifically, the bridge has an upper surface  100   a  which is approximately planar along the tire circumferential direction, and has tapered surfaces  100   b  and  100   c  in which side surfaces on an end of the second lug groove  26  near the center in the longitudinal direction and an end of the second lug groove  26  near the first circumferential groove  20  are inclined so that heights thereof are reduced toward the corresponding ends of the bridge  100  in the longitudinal direction. In  FIG.  12   , each of arrows J 1  and J 2  shown on side surfaces on both sides of the bridge  100  show that a corresponding side surface is inclined in a direction of reducing the height, from an upper surface toward a tip of the arrow. 
     In the second lug groove  26 , a wide-width portion  111  which is a space of an approximate triangular shape in plan view is formed, on the end near the first circumferential groove  20 , in a range W in the tire circumferential direction of  FIG.  12   , in which the width in the tire circumferential direction is larger on the side near the first circumferential groove  20  than the side near the center of the lug groove. The tapered surface  100   c  of the bridge  100  on the side near the first circumferential groove  20  is provided in this wide-width portion  111 . 
     As shown in  FIG.  10   , an end of the bridge  100  in the width direction is connected to a wall surface of the center block  50  via an R portion  123  having a cross section of an arc shape. Alternatively, a configuration may be employed in which the end in the width direction of the bridge  100  is directly connected to the wall surface, without the intervention of the R portion. As shown in  FIG.  13   , a maximum height HB of the bridge HB may be set, for example, in a range of greater than or equal to 30% and less than or equal to 40% of a depth HL of the second lug groove  26 . 
     Although not described in detail, as shown in  FIG.  9   , the bridge  101  having the bottom surface which is bulged is formed at an intermediate portion of the first lug groove  25  between the center blocks  50 , which is adjacent to the second lug groove  26 . Similar to the bridge  100 , the bridge  101  has a cross-sectional shape of a trapezoid, with tapered surfaces in which side surfaces on respective ends are inclined so that the heights are reduced toward the corresponding ends of the bridge  101  in the longitudinal direction. 
     As shown in  FIGS.  9  to  11  and  14   , on the bottom surface of the first circumferential groove  20 , a tapered protrusion  112  is formed adjacent to the wide-width portion  111  at a first side in the tire circumferential direction (lower side of  FIG.  9    and left side of  FIG.  10   ). The tapered protrusion  112  has an approximate triangular shape in plan view, and is formed to bulge toward the outer side in the tire radial direction. In addition, as shown in  FIGS.  11  and  14   , on an upper surface of the tapered protrusion  112 , a first inclined surface  113  is provided in which a left side, which is a side near the lug grooves  25  and  26  between the center blocks, is higher than a right side, which is a side near the mediate block  70 . 
     Moreover, as shown in  FIGS.  9  and  10   , a second inclined surface  114  which is inclined toward a second side in the tire circumferential direction (upper side of  FIG.  9    and right side of  FIG.  10   ) toward the wide-width portion  111  with respect to the tire width direction is formed over the entirety of a side surface of the tapered protrusion  112  on the second side in the tire circumferential direction. As shown in  FIG.  9   , the second inclined surface  114  extends approximately along a wall surface  111   a  of the wide-width portion  111  on the side near the tapered protrusion  112 . 
     Further, in the tapered protrusion  112 , a third inclined surface  115  which is inclined in the second side in the tire circumferential direction toward the center block  50  with respect to the tire width direction is formed over the entirety of a side surface on the first side in the tire circumferential direction (lower side of  FIG.  9    and left side of  FIG.  10   ). The third inclined surface  115  is placed nearer to the second side in the tire circumferential direction than an opening of the first lug groove  25  on the side near the first circumferential groove  20 . The third inclined surface  115  is inclined with respect to the tire circumferential direction so as to extend approximately along the longitudinal direction of the first lug groove  25 . 
     According to the above-described structure, because bridges  100  and  101  are provided in the lug grooves  25  and  26  between the center blocks  50 , the rigidity of the center block  50  can be improved. In addition, during travel of the vehicle on the wet road surface, even when the tire rotates in a direction such that water flows from the first circumferential groove  20  near the center in the tire width direction toward the lug grooves  25  and  26  between the center blocks  50 , the water can be easily caused to flow from the first circumferential groove  20  to the lug grooves  25  and  26 , by the tapered surface  100   c  of each of the bridges  100  and  101 . 
     More specifically, when the tire  1  rotates in the direction of the arrow α in  FIG.  9   , the water tends to be easily caused to flow from the first circumferential groove  20  to the second lug groove  26  along the direction shown by an arrow M 1  in  FIG.  9   , due to the tapered surface  100   c  ( FIG.  12   ) of the bridge  100 . On the other hand, when the tire  1  rotates in a direction opposite to the direction of the arrow a in  FIG.  9   , the water tends to be easily caused to flow from the second lug groove  26  to the first circumferential groove  20 , that is, in a direction shown by an arrow M 2  in  FIG.  9   , due to the tapered surface  100   b  ( FIG.  12   ) of the bridge  100 . With this configuration, the tire  1  can be realized in which reduction in the water drainage performance at the center portion in the tire width direction is suppressed while the rigidity of the center block  50  is improved and the dependence on the tire rotational direction are suppressed. 
     In addition, the tapered protrusion  112  having, as the upper surface, the first inclined surface  113  which is higher on the side near the lug grooves  25  and  26  between the center blocks  50 , is formed on the bottom surface of the first circumferential groove  20 . Thus, when the tire  1  rotates in the direction of the arrow α in  FIG.  9   , the water tends to be more easily caused to flow along the first inclined surface  113 , from the first circumferential groove  20  to the second lug groove  26  between the center blocks  50 . With this configuration, the reduction of the water drainage performance at the center portion in the tire width direction can be further suppressed. 
     Moreover, the wide-width portion  111  is formed on the end of the second lug groove  26  near the first circumferential groove  20 , the tapered protrusion  112  is placed adjacent to the first side of the wide-width portion  111  in the tire circumferential direction, and the second inclined surface  114  is formed on the side surface of the tapered protrusion  112  on the second side in the tire circumferential direction. With this configuration, when the tire rotates in a direction opposite to the direction of the arrow a in  FIG.  9   , because of the inclination of the first inclined surface  113  of the tapered protrusion  112  and the inclination of the second inclined surface  114 , even with the presence of the tapered protrusion  112 , the water flowing from the second lug groove  26  into the first circumferential groove  20  can flow through the right side of the first circumferential groove  20  in the tire width direction to the first circumferential groove  20  in a larger amount, and can be drained. 
     Further, the third inclined surface  115  is formed on the side surface of the tapered protrusion  112  on the first side in the tire circumferential direction. The third inclined surface  115  is inclined with respect to the tire circumferential direction, so as to extend along the longitudinal direction of the first lug groove  25 . With this configuration, when the tire  1  rotates in the direction of the arrow α in  FIG.  9   , due to the third inclined surface  115  of the tapered protrusion  112 , the water can be easily caused to flow from the first circumferential groove  20  to the first lug groove  25 . Because of this, the reduction of the water drainage performance at the center portion in the tire width direction can be further suppressed. 
     In the case of the present embodiment, because of the bridge  101  having the trapezoidal cross section, provided at the intermediate portion of the first lug groove  25  between the center blocks  50 , the rigidity of the center blocks  50  at both sides in the tire circumferential direction can be improved. Further, similar to the bridge  100 , the water drainage performance from the first circumferential groove  20  to the first lug groove  25  can be improved. 
     Next, the structure of the connection portion between each of the second and third circumferential grooves  21  and  22  and the lug groove will be described in detail.  FIG.  15    is an enlarged perspective diagram showing an embodiment of the present disclosure, cutting  FIG.  9    along a line F-F.  FIG.  16    is an enlarged cross-sectional diagram showing the raised portion  103  which is the second raised portion at a G part in  FIG.  9   .  FIG.  17    is an enlarged view of a cross section along a line H-H of  FIG.  15   . 
     With reference to  FIGS.  9  and  15    described above, in the second circumferential groove  21 , the raised portions  106  and  107  serving as the two first raised portions are formed respectively corresponding to the lug grooves  25  and  26 , on the groove bottom at positions either side of the ends of the lug grooves  25  and  26  near the second circumferential groove  21 . Each of the raised portions  106  and  107  is formed to bulge to an outer side in the tire radial direction. As shown in  FIG.  9   , a shape of the raised portions  106  and  107  in plan view is an approximate triangle with a bottom side connected to a wall surface of the shoulder block  80  and a vertex connected to a wall surface on the side near the mediate block  60 . 
     Further, as shown in  FIGS.  15  and  16   , upper surfaces of the raised portions  106  and  107  are inclined surfaces S which are inclined such that heights thereof are increased in the outer side in the tire radial direction toward the shoulder block  80 . With this configuration, during travel of the vehicle on the wet road surface, when the tire  1  rotates in the direction of the arrow a in  FIG.  9    or in a direction opposite to the direction of the arrow α, due to the inclined surfaces S of the raised portions  106  and  107 , water tends to be easily caused to flow from the second circumferential groove  21  to the lug grooves  25  and  26  between the shoulder blocks  80 . Thus, as will be described below, even when the raised portion  103  serving as the second raised portion is provided in the lug grooves  25  and  26 , the water drainage performance can be improved. 
     More specifically, as shown in  FIGS.  9  and  16   , the raised portion  103  which is bulged to the outer side in the tire radial direction is formed on the groove bottom of the portions, of the lug grooves  25  and  26  between the shoulder blocks  80 , near the second circumferential groove  21 . Similar to the bridges  100  and  101  provided on the lug grooves  25  and  26  between the center blocks  50 , the raised portion  103  has a cross-sectional shape of an approximate trapezoid. Specifically, the raised portion  103  has an upper surface which is approximately planar along the tire circumferential direction, and two tapered surfaces  103   a  and  103   b  in which side surfaces on respective sides in the longitudinal direction of the lug grooves  25  and  26  are inclined such that the heights thereof are reduced toward corresponding ends of the raised portion  103 . The raised portion  103  is provided for improving the rigidity of the shoulder block  80 , and respective ends in the width direction are connected to the wall surfaces of the shoulder blocks  80  that are adjacent in the tire circumferential direction. 
     As described above, the inclined surface S is formed on the upper surface of each of the raised portions  106  and  107  in the second circumferential groove  21 . With this configuration, when the vehicle travels on the wet road surface, even with the presence of the bridge  100 , the water can be easily caused to flow from the second circumferential groove  21  to the lug grooves  25  and  26  so that the water drainage performance can be improved. 
     On the other hand, in such a configuration in which the two raised portions  106  and  107  are formed in the second circumferential groove  21  and the raised portion  103  is provided in the lug grooves  25  and  26 , when the space of intersections with extensions of the lug grooves  25  and  26  in the second circumferential groove  21  is relatively wide, air tends to accumulate in this space. With this configuration, during travel on the dry road surface by the vehicle on which the tire  1  is fitted, an air pumping sound tends to be generated due to the air accumulated in the space of the intersection. 
     In the present embodiment, in order to resolve such a disadvantage, as shown in  FIGS.  9 ,  15 , and  17   , in the second circumferential groove  21 , at the intersections with the extensions of the lug grooves  25  and  26 , the raised portion  108  serving as the third raised portion is formed on the groove bottom of a portion surrounded in three directions by the two raised portions  106  and  107  and the raised portion  103 . The raised portion  108  bulges to the outer side in the radial direction, to have a height higher than a reference surface  21   a , which is the lowest portion of the second circumferential groove  21  ( FIGS.  15  and  17   ). 
     In  FIG.  9   , the raised portion  108  is shown as a portion shaded with fine dots in the second circumferential groove  21 . As shown in  FIG.  9   , the raised portion  108  has an approximate trapezoidal shape in plan view, and respective end edges in the tire circumferential direction are connected to wall surfaces of the ends, of the two raised portions  106  and  107  on both sides, in the tire circumferential direction. 
     As shown in  FIG.  17   , an upper surface of the raised portion  108  is approximately planar, with the height in the up-and-down direction from the reference surface  21   a  being constant. Respective end edges of the raised portion  108  in the tire width direction are connected to wall surfaces of the second circumferential groove  21 . As shown in  FIG.  15   , the upper surface of the raised portion  108  has a height lower than those of the upper surfaces of the raised portions  106  and  107 . In the present embodiment, the lowest ends of the inclined surfaces S of the raised portions  106  and  107  have a height position approximately equal to that of the upper surface of the raised portion  108 . 
     As shown in  FIG.  9   , the ends of the lug grooves  25  and  26  between the shoulder blocks  80 , near the second circumferential groove  21 , oppose the wall surface of the ends in the tire width direction of the mediate block  60  via a portion, in the second circumferential groove  21  on lines of extension of the lug grooves  25  and  26 , in which the raised portion  108  is provided on the groove bottom. 
     According to the configuration described above, in the second circumferential groove  21 , the two raised portions  106  and  107  are formed on the groove bottom at positions either side of the ends, of the lug grooves  25  and  26 , near the second circumferential groove  21 . Further, the raised portion  103  is formed on the groove bottom of the portions, of the lug grooves  25  and  26 , near the second circumferential groove  21 . With this configuration, the rigidities of the shoulder blocks  80  adjacent to the raised portions  106  and  107  of the second circumferential groove  21  and of the shoulder blocks  80  adjacent to the raised portions  103  of the lug grooves  25  and  26  can be improved. Because of this, the rigidity of the shoulder block  80  is improved by one of the raised portions  106  and  107  and the raised portion  103 . Therefore, energy loss caused by deformation of the block during the travel of the vehicle can be reduced, and rolling resistance of the tire  1  can be reduced. Further, during travel on the snowy road surface, the resistance between the tire  1  and the road surface can be increased by a shearing force acting on the snow that has been pressurized and hardened in the groove, and the snow traction performance can thus be improved. 
     Moreover, in the second circumferential groove  21 , at the intersections with the extensions of the lug grooves  25  and  26  between the shoulder blocks  80 , the raised portion  108  is formed on the groove bottom in the portion surrounded in three directions by the two raised portions  106  and  107  and the raised portion  103 . With this configuration, the volume of the space at the intersection can be reduced, and the amount of air accumulation can be reduced. Thus, the air pumping sound during travel can be reduced. 
     Further, the ends of the lug grooves  25  and  26  between the shoulder blocks  80 , near the second circumferential groove  21 , oppose the wall surface of the mediate block  60  via the portion, in the second circumferential groove  21  on the lines of extension of the lug grooves  25  and  26 , on which the raised portion  108  is provided on the groove bottom. With this configuration, the intersection of the second circumferential groove  21  described above is surrounded in four directions by the three raised portions  106 ,  107 , and  108 , and the wall surface of the mediate block  60 . Because of this, the air tends to not be easily discharged from the intersection during travel of the vehicle, but the amount of air accumulation can be reduced by the raised portion  108 . Thus, the advantage of providing the raised portion  108  can be made more significant. 
     In the present embodiment, as shown in  FIG.  9   , in the third circumferential groove  22 , two raised portions  116  and  117  having an approximate triangular shape in plan view are also formed on the groove bottom at positions either side of ends, of the lug grooves  25  and  26  between the shoulder blocks  90 , near the third circumferential groove  22 . In addition, the raised portion  105  is formed on the groove bottom on the side, of the lug grooves  25  and  26  between the shoulder blocks  90 , near the third circumferential groove  22 . In the raised portion  105 , a tapered surface having a height which is lowered toward an end is formed only on a side surface at ends, of the lug grooves  25  and  26 , near the center in the longitudinal direction. An end near the third circumferential groove  22  is matched with a wall surface of the third circumferential groove  22 , and no tapered surface is formed. 
     In the third circumferential groove  22 , at intersections with the extensions of the lug grooves  25  and  26  between the shoulder blocks  90 , a raised portion  118  is formed on the groove bottom of a portion surrounded in three directions by the three raised portions  116 ,  117 , and  105 . In  FIG.  9   , the raised portion  118  is shown as a portion in the third circumferential groove  22 , shaded with fine dots. 
       FIG.  18    is an enlarged cross-sectional diagram of the raised portion  118  in the third circumferential groove  22 . As shown in  FIG.  18   , similar to the raised portion  108  in the second circumferential groove  21 , an upper surface of the raised portion  118  has an approximate planar shape in which a height in the up-and-down direction from the reference surface  22   a  of the third circumferential groove  22  is constant. Respective end edges in the tire width direction of the raised portion  118  are connected to the wall surface of the second circumferential groove  21 . 
     With this configuration also, in the third circumferential groove  22 , an amount of air accumulation at the intersection with the extension of the lug groove between the shoulder blocks  90  can be reduced. Because of this, the air pumping sound during travel can be reduced. As shown in  FIG.  9   , in this intersection, unlike the intersection of the second circumferential groove  21 , the end of the lug groove between the shoulder blocks  90 , near the second circumferential groove  21 , opposes an end, of the lug groove between the mediate blocks  70  near the second circumferential groove  21 , on the lines of extension of the lug grooves. Because of this, in the intersection of the third circumferential groove  22 , the air tends to be more easily caused to be discharged in comparison to the intersection of the second circumferential groove  21 . The advantage of providing the raised portion  108  is higher for the intersection of the second circumferential groove  21 . 
       FIG.  19    is a diagram showing another configuration of the third raised portion, corresponding to an I part of  FIG.  9   . A raised portion  119  serving as the third raised portion shown in  FIG.  19    has a shape in plan view of a narrow line extending in the tire width direction, and respective ends in the tire circumferential direction are not connected to the wall surfaces of two raised portions  106  and  107 . Because of this, although the advantage is inferior in comparison to the raised portion  108  of  FIG.  9   , the structure can achieve an advantage of reducing the volume of a space, in the second circumferential groove  21 , at the intersections with the extensions of the lug grooves  25  and  26  between the shoulder blocks  80 . Thus, the advantage of reduction in the air pumping sound during traveling can be achieved. In this manner, a structure may be employed in which the third raised portion is formed only at a part of the groove bottom surrounded in three directions by the two first raised portions and the second raised portion, at the intersection with the extension of the lug groove in the circumferential groove. 
     Next, narrow grooves  109  and  110  of the shoulder block  90  will be described with reference to  FIGS.  20  to  22   .  FIG.  20    is a diagram showing in an enlarged manner a part of the shoulder block  90  shown in  FIG.  2   .  FIG.  21    is an enlarged perspective diagram of an end of the shoulder block  90  at the outer side in the tire width direction.  FIG.  22    is a perspective diagram showing the shoulder block  90 , in a cut manner along a plane including the ground-contacting end T. 
     Between a plurality of shoulder blocks  90  of the row of shoulder blocks  47 , a plurality of lug grooves  25  and  26  are formed separately in the tire circumferential direction, and extending from the left side in the tire width direction to the right side. The plurality of shoulder blocks  90  are divided in the tire circumferential direction by the lug grooves  25  and  26 . The shoulder block  90  is provided at an end positioned at the outer side in the vehicle width direction when the tire  1  is fitted on the vehicle. 
     On the ground-contacting surfaces of the shoulder blocks  90 , sipes  81  and  82  which are two lateral sipes are formed extending from the left side in the tire width direction to the right side. Each of the sipes  81  and  82  is provided between two lug grooves  25  and  26  adjacent in the tire circumferential direction. In the shoulder block  90 , the sipes  81  and  82  have an equal width over the entire lengths in the longitudinal direction, and are narrower than a maximum width of the two lug grooves  25  and  26  provided at positions either side of the sipes  81  and  82 . 
     Ends  81   a  and  82   a  which are inner ends in the tire width direction of the sipes  81  and  82  open to a wall surface of an inner end in the tire width direction of the shoulder block  90 . Ends  81   b  and  82   b  which are outer ends in the tire width direction of the sipes  81  and  82  end in the shoulder block  90 , and do not open to the wall surface of the shoulder block  90 . A serpentine portion is provided at a part of the sipes  81  and  82 , but alternatively, the serpentine portion may be omitted. 
     Further, in the row of shoulder blocks  47 , between the two lug grooves  25  and  26  sandwiching the sipes  81  and  82 , that is, at the side, of the upper surface of the shoulder block  90 , that is further out in the tire width direction than the ground-contacting end T, two narrow grooves  109  and  110  inclined on the same side are formed over the entire length with respect to the tire circumferential direction. The narrow groove  109  is longer than the narrow groove  110 , and an inner end in the tire width direction of the narrow groove  109  is connected to the end  81   b  of the sipe  81 . 
     The narrow groove  110  is inclined on the same side as the narrow groove  109  with respect to the tire circumferential direction, toward the outer side in the tire width direction. In the narrow groove  110 , an inner end in the tire width direction of the narrow groove  110  is connected to the sipe  82  in a manner to branch from the sipe  82  from a region near the outer end in the tire width direction. 
     The narrow grooves  109  and  110  have shallower depths than the sipes  81  and  82 , and have, for example, a cross section of an arc shape and widths widened toward opening ends. The shape of the narrow groove is not limited to such a configuration, and the narrow groove may have a cross-sectional shape of an approximate quadrangle with an upper end opened, or a shape in which the wall surfaces on respective sides in the width direction are inclined with respect to the bottom surface such that the width is widened from the bottom surface which is approximately planar toward the opening end. 
     In addition, the narrow grooves  109  and  110  are distanced from the two lug grooves  25  and  26  which partition the respective ends of the shoulder block  90  in the tire circumferential direction over the entire length in the shoulder block  90 . With this configuration, the narrow grooves  109  and  110  are not connected to the lug grooves  25  and  26  between the shoulder blocks  90 . 
     Moreover, the outer ends in the tire width direction of the narrow grooves  109  and  110  do not open to the wall surface of the shoulder block  90 , and end in the shoulder block  90 . Because of this, the narrow grooves  109  and  110  do not open to the wall surface of the shoulder block  90 . 
     Furthermore, a shallow groove  120  having a J shape in plan view is formed at a portion, at the side of the upper surface of the shoulder block  90  that is further out, in the tire width direction, than the ground-contacting end T, and positioned at the side that is further out in the tire width direction than the narrow grooves  109  and  110 . The shallow groove  120  has a straight portion  121  which is positioned at the outer side in the tire width direction than a curved portion  122 , and extends along the tire circumferential direction. The shallow groove  120  has approximately the same depth as the narrow grooves  109  and  110 . A width of the shallow groove  120  is widened from an end, among the ends in the longitudinal direction, near the curved portion  122  toward an end near the straight portion  121 . 
     According to the above-described structure, the narrow grooves  109  and  110  that are inclined with respect to the tire circumferential direction are formed in a region called a buttress, at the side of the shoulder block  90  that is further out in the tire width direction than the ground-contacting end T. The narrow grooves  109  and  110  are not connected to the two lug grooves  25  and  26  either side of the sipes  81  and  82  and the narrow grooves  109  and  110 . With this configuration, the rigidity of the buttress can be improved, and the snow traction performance can thus be improved. 
     Because the narrow grooves  109  and  110  are connected to the sipes  81  and  82 , the water drainage performance can be improved. In addition, because the narrow grooves  109  and  110  are inclined on the same side with respect to the tire circumferential direction over their entire lengths, lengths of the sipes  81  and  82 , the depths of which can be easily enlarged, can be increased while the water drainage performance is improved by the narrow grooves  109  and  110 . With this configuration, the water drainage performance of the shoulder block  90  can be improved. 
     In addition, because the narrow grooves  109  and  110  have shallower depths than the sipes  81  and  82 , although the thickness of a rubber portion of the tire is reduced by the buttress at the outer end in the tire width direction, excessive reduction of the thickness of the bottom portions of the narrow grooves  109  and  110  can be prevented, by forming the narrow grooves  109  and  110  shallow. With this configuration, generation of cracks at the groove bottom of the narrow grooves  109  and  110  can be suppressed. In particular, the buttress tends to be exposed to sunlight, and the rubber tends to become hardened. However, even in such cases, the generation of the cracks can be easily suppressed. With this configuration, the advantages of forming the narrow grooves  109  and  110  shallow can be made more significant. 
     In the embodiment described above, two narrow grooves are formed in each shoulder block  90 , but alternatively, only one narrow groove or three or more narrow grooves may be formed on each shoulder block. 
     Further, in the embodiment described above, a case has been described in which the shoulder land portion is a plurality of blocks divided by the lug grooves in the tire circumferential direction. Alternatively, a structure may be employed in which, in the shoulder land portion, the lug groove is not formed over the entire length in the tire width direction, and the shoulder land portion is not divided into a plurality of blocks in the tire circumferential direction. In this case also, a narrow groove which is inclined with respect to the tire circumferential direction over the entire length, which is connected to the lateral sipe, and which is not connected to the lug groove, may be formed at the side that is further out in the tire width direction than the ground-contacting end.