Patent Publication Number: US-2018043738-A1

Title: Tire

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a tire provided with a plurality of blocks on a tread portion. 
     Related Background of the Invention 
     Conventionally, a block pattern having a plurality of blocks is formed on a tread portion of various tires such as a tire for heavy load. During running of a vehicle to which such tires are attached, strain is generated in the tread portion due to deformation of a member in the tread portion of the tire. In addition, the tread portion generates heat due to viscoelasticity of rubber, and thus a temperature of the tread portion rises. Strain and temperature of the tread portion are main factors affecting durability of the tread portion, and in order to enhance durability of the tread portion, strain and temperature rise, generated in the tread portion, are required to be coped with. 
     For coping with this, in conventional tires, generation of strain is suppressed in the tread portion mainly by adding a reinforcing member into the tread portion or by raising rigidity of the tread portion. However, in this case, along with the increase in the number of members in the tire and a weight of the tire, a cost of the tire possibly rises. Accordingly, regarding durability of the tread portion, suppression of the temperature rise by cooling the tread portion is required. In addition, cooling of the tread portion may become more important in the peripheral portion of the specific circumferential groove in the tread portion depending on the internal structure of the tread portion or the condition of use of the tire, the realization of such a demand is required, too. 
     Here, in a tire provided with a plurality of blocks, generally, the plurality of blocks is arranged between a plurality of circumferential grooves, and a plurality of lateral grooves is formed between the blocks. In such a tire, heat radiation is promoted by an air flow generated in the circumferential groove, and the tread portion is cooled. However, it is difficult to adjust heat radiation of the circumferential groove by controlling the air flow in the circumferential groove. Therefore, in a tire provided with a plurality of blocks on both sides of the specific circumferential groove in a tire width direction, increased heat radiation may sometimes occur in the circumferential groove outside the plurality of blocks in the tire width direction than in the circumferential groove between the plurality of blocks. In this case, a cooling effect of the tread portion by the circumferential groove between the plurality of blocks cannot be increased, and thus it is difficult to enhance the heat radiation of the circumferential groove. 
     Particularly, in a tread center portion, it is demanded for improvement of a wear life thereof to thick a tread rubber, and coping with a temperature rise becomes important. However, in a tire provided with a plurality of blocks on both sides of the circumferential groove in the tread center portion, increased heat radiation may sometimes occur in the circumferential groove outside the plurality of blocks in the tire width direction than in the circumferential groove on the tread center portion. In this case, a cooling effect of the tread portion by the circumferential groove in the tread center portion cannot be increased. Therefore, it is difficult to suppress the temperature rise of the tread portion on the tread center portion. 
     Moreover, a tire in which the temperature rise of the tread portion is suppressed by a block groove formed in a shoulder block row has been known (refer to Patent Literature 1). 
     However, in the conventional tire described in Patent Literature 1, a block groove is required to be formed in a tread of the block along a tire circumferential direction. Therefore, the block groove cannot be formed in some cases depending on a shape of the block or a required performance of the block. 
     PRIOR ART 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Laid-Open No. 2010-125998 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by Invention 
     The present invention was made in view of the above-described conventional problems and an object thereof is, in a tire provided with a plurality of blocks on both sides of the circumferential groove in a tire width direction, to enhance the heat radiation of the circumferential groove and to increase a cooling effect of the tread portion by the circumferential groove. 
     Means for Solving Problems 
     The present invention is a tire comprising: a first circumferential groove; two second circumferential grooves adjacent to both sides of the first circumferential groove in a tire width direction; a plurality of lateral grooves opened to the first circumferential groove and the second circumferential groove; and a plurality of blocks on a tread portion partitioned by the first circumferential groove, the second circumferential groove, and the plurality of lateral grooves. An air flow in a direction opposite to a tire rotating direction is generated in the first circumferential groove and the two second circumferential grooves during running of a vehicle. Each block of the plurality of blocks has: a first wall surface formed from a position where the lateral groove on a downstream side of the air flow is opened to the first circumferential groove, toward an upstream side of the air flow; a second wall surface formed from a position where the lateral groove on the downstream side of the air flow is opened to the second circumferential groove, toward the upstream side of the air flow; and a block corner portion formed at a position where the lateral groove on the upstream side of the air flow is opened to the second circumferential groove. When the two blocks on the upstream side and the downstream side of the air flow adjacent in a tire circumferential direction are viewed, a virtual surface obtained by extending, on the downstream side of the air flow, the second wall surface of the block on the upstream side intersects with the block corner portion of the block on the downstream side or passes through a position in the second circumferential groove which is apart from the block corner portion in the tire width direction. A groove width of the first circumferential groove gradually increases toward the downstream side of the air flow at the first wall surface of the block. 
     Effects of the Invention 
     According to the present invention, in the tire provided with the plurality of blocks on both sides of the circumferential groove in the tire width direction, heat radiation of the circumferential groove can be enhanced, and thus a cooling effect of the tread portion by the circumferential groove can be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view illustrating a tread pattern of a tire of the first embodiment; 
         FIG. 2  is a plan view illustrating a part of  FIG. 1 ; 
         FIG. 3  is a plan view illustrating a second block corner portion formed in a curved shape; 
         FIG. 4  is a plan view illustrating a block of the tire; 
         FIG. 5  is a plan view illustrating a block of the tire; 
         FIG. 6  is a plan view illustrating a block of the tire; 
         FIG. 7  is a plan view illustrating a tread pattern of a tire of the second embodiment; 
         FIG. 8  is a plan view illustrating a part of  FIG. 7 ; 
         FIG. 9  is a plan view illustrating a block of the tire; 
         FIG. 10  is a plan view illustrating a block of the tire; 
         FIG. 11  is a plan view illustrating a block of the tire; 
         FIG. 12  is a plan view illustrating a tread pattern of a conventional product; and 
         FIG. 13  is a plan view illustrating a tread pattern of a conventional product. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of a tire of the present invention will be described by referring to the attached drawings. 
     The tire of the present embodiment is a pneumatic tire for a vehicle (a tire for heavy load or a tire for passenger car, for example) and is formed so as to have a known structure by a general tire constituent member. Namely, the tire includes a pair of bead portions, a pair of side wall portions located outside the pair of bead portions in a tire radial direction, a tread portion in contact with a road surface, and a pair of shoulder portions located between the tread portion and the pair of side wall portions. Furthermore, the tire includes a pair of bead cores, a carcass arranged between the pair of bead cores, a belt arranged on an outer periphery side of the carcass, and a tread rubber having a predetermined tread pattern. 
     The First Embodiment 
       FIG. 1  is a plan view illustrating a tread pattern of a tire  1  of the first embodiment and schematically illustrates a part of a tread portion  2  in a tire circumferential direction S. 
     Note that the tire  1  is a tire for which a rotating direction during forward movement of the vehicle is designated and it rotates in the tire rotating direction R during forward movement of the vehicle. The tire rotating direction R is designated corresponding to the tread pattern of the tire  1 . The tire  1  is attached to the vehicle so that the tire rotating direction R is matched. In addition, a tread center portion  3  of the tire  1  is a center part of the tread portion  2  in a tire width direction K, and a tire equatorial plane is located on the tread center portion  3 . The shoulder portion  4  of the tire  1  is located on an outside of the tread portion  2  in the tire width direction K. 
     As illustrated, the tire  1  includes a plurality of circumferential grooves (a first circumferential groove  11 , a second circumferential groove  12 ), a plurality of lug grooves  13 , a plurality of lateral grooves  14 , and a plurality of block rows (a shoulder block row  20 , a control block row  30 ), in the tread portion  2 . Each of the circumferential groove  11  and the circumferential groove  12  is a main groove (circumferential direction main groove) extending in the tire circumferential direction S, and is continuously formed along the tire circumferential direction S. Moreover, among the plurality of circumferential grooves formed in the tread portion  2 , the first circumferential groove  11  is a circumferential groove whose heat radiation should be enhanced. Two second circumferential grooves  12  are adjacent to both sides of the first circumferential groove  11  in the tire width direction K so as to assist improvement of the heat radiation of the first circumferential groove  11 . The first circumferential groove  11  is arranged between two second circumferential grooves  12  and constitutes a group of circumferential grooves with two second circumferential grooves  12  on both sides thereof. 
     The tire  1  includes two groups of circumferential grooves each of which comprises one first circumferential groove  11  and two second circumferential grooves  12 , having two first circumferential grooves  11  and three second circumferential grooves  12 . The two first circumferential grooves  11  are formed on both sides of the tread center portion  3  in the tire width direction K, and each of the first circumferential grooves  11  is arranged between the two second circumferential grooves  12 . The one second circumferential groove  12  of the three second circumferential grooves  12  is formed on the tread center portion  3  and is arranged inside the two first circumferential grooves  11  in the tire width direction K. In addition, each of the two second circumferential grooves  12  is formed between the first circumferential groove  11  and the shoulder portion  4  (tread end) on both sides of the tread center portion  3  and is arranged outside the first circumferential groove  11  in the tire width direction K. The second circumferential groove  12  on the tread center portion  3  is arranged between the two first circumferential grooves  11  and constitutes a group of circumferential grooves with each of the two first circumferential grooves  11 . Each of the two first circumferential grooves  11  is arranged between the second circumferential groove  12  on the tread center portion  3  and the second circumferential groove  12  on the shoulder portion  4  side. 
     The tread portion  2  is partitioned by the first circumferential groove  11  and the second circumferential groove  12 , so that a plurality of the block rows (two shoulder block rows  20  and four control block rows  30 ) is formed on the tread portion  2 . The shoulder block row  20  and the control block row  30  are land portions extending along the tire circumferential direction S, and have a plurality of blocks  21  and  31 , respectively. 
     The shoulder block row  20  has a plurality of lug grooves  13  and is arranged on an outermost side in the tire width direction K in the tread portion  2 . The lug groove  13  extends in the tire width direction K and is formed from the second circumferential groove  12  to the shoulder portion  4 . The plurality of blocks  21  of the shoulder block row  20  is sequentially arranged in the tire circumferential direction S, and the lug groove  13  is formed between the blocks  21  adjacent in the tire circumferential direction S. In addition, the lug groove  13  is formed on the shoulder portion  4  side of the second circumferential groove  12  and is opened to the second circumferential groove  12 . The tire  1  includes a raised portion  15  formed within each of the lug grooves  13 . The raised portion  15  is raised from a groove bottom of the lug groove  13  and connects groove walls (wall surfaces of the block  21 ) on both sides of the lug groove  13 . Here, the raised portion  15  is a tie bar. At least a part of the lug groove  13  is shallower than the second circumferential groove  12  by the raised portion  15 . 
     The control block row  30  is a block row to control an air flow in the first circumferential groove  11  and the second circumferential groove  12  and formed between the first circumferential groove  11  and the second circumferential groove  12 . Further, the control block row  30  has a plurality of lateral grooves  14  and is arranged on both sides of the first circumferential groove  11  in the tire width direction K. The plurality of lateral grooves  14  is width direction grooves extending in the tire width direction K and is formed from the first circumferential groove  11  to the second circumferential groove  12  in each of the control block rows  30 . Furthermore, the plurality of lateral grooves  14  is formed between the first circumferential groove  11  and each of the second circumferential grooves  12  and is opened to the first circumferential groove  11  and the second circumferential groove  12 . 
     The plurality of blocks  31  of the control block row  30  is sequentially arranged in the tire circumferential direction S, and the lateral groove  14  is formed between the blocks  31  adjacent in the tire circumferential direction S. The plurality of lateral grooves  14  is formed at one side and the other side of the first circumferential groove  11  in the tire width direction K and extends in both directions in the tire width direction K from the first circumferential groove  11 . Furthermore the lateral grooves  14  at one side and the other side of the first circumferential groove  11  in the tire width direction K are alternately arranged along the tire circumferential direction S and are alternately opened to the first circumferential groove  11 . 
     As described above, the tire  1  includes the plurality of blocks  31  and the plurality of lateral grooves  14  arranged on both sides of the first circumferential groove  11  in the tire width direction K. The plurality of blocks  31  and the plurality of lateral grooves  14  are arranged between the two second circumferential grooves  12 . The plurality of lateral grooves  14  is arranged apart from each other in the tire circumferential direction S and crosses the control block row  30  between the first circumferential groove  11  and the second circumferential groove  12 . The plurality of blocks  31  is partitioned by the first circumferential groove  11 , the two second circumferential grooves  12  and the plurality of lateral grooves  14  on the tread portion  2 , and each of the blocks  31  is formed in a predetermined polygonal shape when viewed from an outside in the tire radial direction. 
     The tire  1  is attached to the vehicle and rotates in the tire rotating direction R with running (forward movement) of the vehicle. During running of the vehicle (tire rotation) by forward movement of the vehicle, an air flow in a predetermined direction is generated in the first circumferential groove  11  and the second circumferential groove  12 . The air flow is a relative flow (wind) of air generated by rotation of the tire  1  and is generated in a direction opposite to the tire rotating direction R. An arrow F illustrated in  FIG. 1  is a direction of the air flow generated in the first circumferential groove  11  and the second circumferential groove  12 . The air flow in the same direction is generated in the first circumferential groove  11  and the second circumferential groove  12 . In the tire  1  of the first embodiment, by the plurality of blocks  31  of the control block row  30  formed between the first circumferential groove  11  and each of the second circumferential grooves  12 , the air flow is controlled, and the heat radiation of the first circumferential groove  11  and the second circumferential groove  12  is adjusted. As a result, the heat radiation of the first circumferential groove  11  is enhanced. Hereinafter, the adjustment of the heat radiation will be described in detail. 
       FIG. 2  is a plan view illustrating a part of  FIG. 1  and illustrates the first circumferential groove  11  and the two second circumferential grooves  12  at one side (left side of  FIG. 1 ) in a state in which  FIG. 1  is rotated clockwise by 90°. The first circumferential groove  11  and the two second circumferential grooves  12  at the other side (right side of  FIG. 1 ) have the same constitution as the first circumferential groove  11  and the two second circumferential grooves  12  at one side, respectively, which will be described as follows. 
     As illustrated, the tire  1  includes the one first circumferential groove  11  and the two second circumferential grooves  12  arranged on both sides of the first circumferential groove  11  in the tire width direction K. Each block  31  of the plurality of blocks  31  has a first wall surface  32  on the first circumferential groove  11  side, a second wall surface  33  on the second circumferential groove  12  side, a first block corner portion  34  on the first circumferential groove  11  side, and a second block corner portion  35  on the second circumferential groove  12  side. In the first circumferential groove  11  and the second circumferential groove  12  (refer to the air flow direction F), the air flows from an upstream side G of the air flow toward the downstream side H of the air flow and cools the tread portion  2 . 
     The first wall surface  32  of the block  31  is formed from a position where the lateral groove  14  on the downstream side H of the air flow is opened to the first circumferential groove  11 , toward the upstream side G of the air flow. The second wall surface  33  of the block  31  is formed from a position where the lateral groove  14  on the downstream side H of the air flow is opened to the second circumferential groove  12 , toward the upstream side G of the air flow. The first wall surface  32  is located in the first circumferential groove  11 , and the second wall surface  33  is located in the second circumferential groove  12 . Here, the first wall surface  32  is a curved surface inclined toward an inside of the lateral groove  14  on the downstream side H of the air flow with respect to the tire circumferential direction S. The first wall surface  32  is inclined to the outside in a groove width direction of the first circumferential groove  11  with respect to the tire circumferential direction S toward the downstream side H of the air flow. In addition, the first wall surface  32  is a projecting surface curved in an arc shape and smoothly connects to the wall surface of the block  31  around it. On the first circumferential groove  11  side of the block  31 , the first wall surface  32  is curved toward the inside of the lateral groove  14  on the downstream side H of the air flow. In contrast to this, the second wall surface  33  is a plane inclined to the outside in the groove width direction of the second circumferential groove  12  with respect to the tire circumferential direction S toward the downstream side H of the air flow. The second wall surface  33  is inclined to the first circumferential groove  11  side between the two second circumferential grooves  12 . 
     The first block corner portion  34  of the block  31  is a corner portion of the block  31  formed at a position where the lateral groove  14  on the upstream side G of the air flow is opened to the first circumferential groove  11 , and is formed at a position where the wall surface of the block  31  in the lateral groove  14  and the wall surface of the block  31  in the first circumferential groove  11  intersect with each other. The second block corner portion  35  of the block  31  is a corner portion of the block  31  formed at a position where the lateral groove  14  on the upstream side G of the air flow is opened to the second circumferential groove  12 , and is formed at a position where the wall surface of the block  31  in the lateral groove  14  and the wall surface of the block  31  in the second circumferential groove  12  intersect with each other. The wall surfaces of the block  31  are formed in directions different from each other at the first block corner portion  34  and the second block corner portion  35  as boundaries. 
     The groove width W of the first circumferential groove  11  gradually increases toward the downstream side H of the air flow (lateral groove  14  on the downstream side H) at the first wall surface  32  of the block  31 . When the two blocks  31  on the upstream side G and the downstream side H of the air flow adjacent in the tire circumferential direction S are viewed, a virtual surface (first virtual surface)  36  extended from the first wall surface  32  of the block  31  on the upstream side G is extended to the outside in the groove width direction of the first circumferential groove  11 . The first virtual surface  36  is an extension surface (virtual extension surface) obtained by virtually extending the first wall surface  32  on the downstream side H of the air flow and smoothly continues from the first wall surface  32  so as to form the same plane as the first wall surface  32 . In all the blocks  31  of the control block row  30 , the first virtual surface  36  of the block  31  on the upstream side G is extended toward the inside of the lateral groove  14  (lateral groove  14  on the downstream side H) between the two blocks  31  without intersecting with the first block corner portion  34  of the block  31  on the downstream side H. The first virtual surface  36  passes through the lateral groove  14  and intersects with the block  31  (wall surface of the block  31 ) on the downstream side H in the lateral groove  14 . Alternatively, the first virtual surface  36  passes through the lateral groove  14  and is extended to the second circumferential groove  12 . 
     When the two blocks  31  on the upstream side G and the downstream side H of the air flow adjacent in the tire circumferential direction S are viewed, a virtual surface (second virtual surface)  37  extended from the second wall surface  33  of the block  31  on the upstream side G is located on the outside of the lateral groove  14  (lateral groove  14  on the downstream side H) between the two blocks  31 . The second virtual surface  37  is an extension surface (virtual extension surface) obtained by virtually extending the second wall surface  33  on the downstream side H of the air flow and smoothly continues from the second wall surface  33  so as to form the same plane as the second wall surface  33 . In addition, the second virtual surface  37  is extended toward the block  31  on the downstream side H and is arranged along the second circumferential groove  12 . In all the blocks  31  of the control block row  30 , the second virtual surface  37  of the block  31  on the upstream side G intersects with the second block corner portion  35  of the block  31  on the downstream side H. Alternatively, the second virtual surface  37  deviates from the second block corner portion  35  in the tire width direction K and passes through a position in the second circumferential groove  12  partitioning the block  31  on the downstream side H. When the second virtual surface  37  passes through the position in the second circumferential groove  12 , the second virtual surface  37  passes through the position in the second circumferential groove  12  which is apart from the second block corner portion  35  in the tire width direction K, on the downstream side H of the air flow. In addition, the second virtual surface  37  intersects with the block  31  (wall surface of the block  31 ) on the downstream side H in the second circumferential groove  12 . 
     In the tire  1  described above, the second virtual surface  37  intersects with the second block corner portion or passes through the position in the second circumferential groove  12 , and thus the air having flowed along the second wall surface  33  becomes hard to flow into the lateral groove  14  easily. Accordingly, the inflow of air from the second circumferential groove  12  to the lateral groove  14  and the first circumferential groove  11  is suppressed, and occurrences of backward flow, swirl flow, and stagnation of the air in the first circumferential groove  11  are prevented. The air in the first circumferential groove  11  is not disturbed by the air flowing in from the lateral groove  14 , and smoothly flows toward the downstream side H in the first circumferential groove  11 . Along with this, a flow rate of the air which is a cooling medium increases in the first circumferential groove  11 , and cooling of the tread portion  2  is promoted. In addition, since the air flow in the second circumferential groove  12  deviates from the second block corner portion  35 , a pressure rise of the air at the second block corner portion  35  is suppressed. 
     Since the groove width W of the first circumferential groove  11  gradually increases at the first wall surface  32 , a pressure of the air around the first wall surface  32  gradually becomes low toward the downstream side H of the air flow. Along with this, the air is drawn from the upstream side G of the first wall surface  32  toward the periphery of the first wall surface  32  in the first circumferential groove  11 , and the air flow is accelerated. In addition, since the air flow hits the first block corner portion  34 , the pressure of the air rises at the first block corner portion  34 . As a result, the pressure of the air at the first block corner portion  34  becomes higher than the pressure of the air at the second block corner portion  35  in the lateral groove  14 , and thus the air flows from the first block corner portion  34  toward the second block corner portion  35 . Accordingly, an air flow from the first circumferential groove  11  toward the lateral groove  14  is generated, and thus the inflow of air from the lateral groove  14  to the first circumferential groove  11  is suppressed. Furthermore, the air flow in the first circumferential groove  11  is further accelerated. An air flow is concentrated in the first circumferential groove  11  by the second circumferential grooves  12  and the plurality of blocks  31  located on both sides of the first circumferential groove  11  in the tire width direction K, and thus the air flow in the first circumferential groove  11  is accelerated still more. 
     As described above, in the tire  1 , heat radiation of the first circumferential groove  11  and the second circumferential groove  12  can be adjusted by controlling the air flow during running of a vehicle. Furthermore, the heat radiation can be promoted by accelerating the air flow in the first circumferential groove  11 . Therefore, the heat radiation of the first circumferential groove  11  can be enhanced, and thus the cooling effect of the tread portion  2  by the first circumferential groove  11  can be increased. Along with this, the temperature rise of the tread portion  2  can be suppressed by cooling the tread portion  2  in the first circumferential groove  11  and the peripheral portion of the first circumferential groove  11 . Durability of the tread portion  2  can also be effectively enhanced by lowering the temperature around the belt in the tread portion  2 , in which a heat generation easily occurs. Further, since the tread rubber of the tread portion  2  can be thickened, the wear life of the tire  1  can be improved. 
     When the first virtual surface  36  is extended toward the inside of the lateral groove  14 , the air flowing along the first wall surface  32  easily flows into the lateral groove  14 . In addition, the first wall surface  32  is inclined toward the inside of the lateral groove  14  on the downstream side H of the air flow, and thus the air easily flows from the first circumferential groove  11  toward the lateral groove  14 . When the first wall surface  32  is a curved surface, the air smoothly flows along the first wall surface  32 , and the air flow directed toward the lateral groove  14  is easily generated. Accordingly, the pressure of the air can be reliably lowered around the first wall surface  32 , and the air flow in the first circumferential groove  11  can be further accelerated. 
     When the groove width of the lateral groove  14  is wider than the groove width W of the first circumferential groove  11 , the inflow of air from the second circumferential groove  12  is increased, and thus backward flow of the air in the first circumferential groove  11  easily occurs. In the same way, when the groove width of the second circumferential groove  12  is wider than the groove width of the lateral groove  14 , backward flow of the air toward the first circumferential groove  11  easily occurs, and thus the cooling effect by the first circumferential groove  11  may be affected. Therefore, it is preferable for the groove width W of the first circumferential groove  11  to be wider than the groove width of the lateral groove  14 , and it is preferable for the groove width of the lateral groove  14  to be wider than the groove width of the second circumferential groove  12 . Thus, backward flow of the air can more surely be suppressed. In addition, since the groove width W of the first circumferential groove  11  is wider than the groove width of the lateral groove  14  and the groove width of the second circumferential groove  12 , the flow rate of the air in the first circumferential groove  11  is increased, and thus the cooling effect by the first circumferential groove  11  can be promoted. 
     The groove width W of the first circumferential groove  11  is permissible as long as it gradually increases toward the downstream side H of the air flow at least on the first wall surface  32 . Therefore, the groove width W of the first circumferential groove  11  may be gradually increased toward the downstream side H of the air flow at the upstream side G of the first wall surface  32 , in addition to the first wall surface  32 . In addition, between the second circumferential groove  12  and the shoulder portion  4 , ribs extending in the tire circumferential direction S may be arranged without the lug grooves  13  being formed. The first block corner portion  34  and the second block corner portion  35  may be corner portions formed in bent shapes or may be corner portions formed in curved shapes. 
       FIG. 3  is a plan view illustrating the second block corner portion  35  formed in a curved shape. 
     In this case, the second virtual surface  37  passes through, for example, a virtual intersection position  38 , and intersects with the second block corner portion  35  as illustrated. The virtual intersection position  38  is a position where virtual surfaces extended from wall surfaces  31 A and  31 B of the block  31  on the both sides of the second block corner portion  35  intersect with each other. The one wall surface  31 A is a wall surface of the block  31  in the lateral groove  14 , and the other wall surface  31 B is a wall surface of the block  31  in the second circumferential groove  12 . The air easily flows from the lateral groove  14  to the second circumferential groove  12 , by forming the second block corner portion  35  into a curved shape. 
     Subsequently, another example of the block will be described. Each of the following blocks is an example in which a part of the shape of the block  31  is changed, and an effect similar to the above-described effect is exerted. In each block, the same names as those in the block  31  are given to the same constitution as the block  31 , and detailed explanation of each constitution will be omitted. Moreover, in the following description, explanation for the same matters as the already-described matters will be omitted. 
       FIGS. 4 to 6  are plan views illustrating blocks  41 ,  51  and  61  of the tire  1  and illustrate a part of tread patterns including the blocks  41 ,  51  and  61  similarly to  FIG. 2 . 
     The block  41  illustrated in  FIG. 4  has a first wall surface  42 , a second wall surface  43 , a first block corner portion  44 , and a second block corner portion  45 . A first virtual surface  46  is an extension surface extended from the first wall surface  42 , and a second virtual surface  47  is an extension surface extended from the second wall surface  43 . Here, only the first wall surface  42  is different from the first wall surface  32  of the block  31 . The first wall surface  42  of the block  41  is a plane inclined toward the inside of the lateral groove  14  on the downstream side H of the air flow with respect to the tire circumferential direction S. The first wall surface  42  is inclined to the outside in the groove width direction of the first circumferential groove  11  with respect to the tire circumferential direction S toward the downstream side H of the air flow. In this first wall surface  42 , the air can easily flow from the first circumferential groove  11  toward the lateral groove  14 . Therefore, the pressure of the air can be reliably lowered around the first wall surface  42 , and the air flow in the first circumferential groove  11  can be further accelerated. 
     In the block  51  illustrated in  FIG. 5 , in a plan view where the block  51  is viewed from an outside in the tire radial direction, the block  51  is formed line-symmetrically with respect to a center line  58  passing through the center in the tire circumferential direction S. Therefore, the block  51  has a first wall surface  52 , a second wall surface  53 , a first block corner portion  54 , and a second block corner portion  55 , on each of both sides of the center line  58 . In addition, a first virtual surface  56  is an extension surface extended from each of the first wall surfaces  52  on the both sides of the center line  58 , and a second virtual surface  57  is an extension surface extended from each of the second wall surfaces  53  on the both sides of the center line  58 . The second wall surface  53  is a plane inclined to the inside in the groove width direction of the second circumferential groove  12  with respect to the tire circumferential direction S toward the downstream side H of the air flow. The two second wall surfaces  53  intersect with each other on the centerline  58 . In this block  51 , the tire rotating direction R can be set in both directions of the tire circumferential direction S. Namely, even if the air flow direction F becomes an opposite direction, the block  51  satisfies the conditions similar to those of the block  31  and acts in the same way as the block  31 . Therefore, it is not necessary to designate the tire rotating direction R when the tire is to be attached, and convenience of a user is improved. 
     In the block  61  illustrated in  FIG. 6 , in the same way as the block  51 , the block  61  is formed line-symmetrically with respect to a center line  68  passing through the center in the tire circumferential direction S, in a plan view where the block  61  is viewed from the outside in the tire radial direction. Accordingly, the block  61  has a first wall surface  62 , a second wall surface  63 , a first block corner portion  64 , and a second block corner portion  65  on each of both sides of the center line  68 . Moreover, a first virtual surface  66  is an extension surface extended from each of the first wall surfaces  62  on both sides of the center line  68 , and a second virtual surface  67  is an extension surface extended from each of the second wall surfaces  63  on the both sides of the center line  68 . The first wall surface  62  of the block  61  is a plane inclined toward the inside of the lateral groove  14  on the downstream side H of the air flow with respect to the tire circumferential direction S in the same way as the first wall surface  42  of the block  41 . The second wall surface  63  is a plane inclined to the inside in the groove width direction of the second circumferential groove  12  with respect to the tire circumferential direction S toward the downstream side H of the air flow. The two second wall surfaces  63  intersect with each other on the center line  68 . In this block  61 , in the same way as the block  51 , the tire rotating direction R can be set in both directions of the tire circumferential direction S. Namely, even if the air flow direction F becomes an opposite direction, the block  61  satisfies the conditions similar to those of the block  31 , and the effect similar to that of the block  31  is exerted. Therefore, it is not necessary to designate the tire rotating direction R when the tire is to be attached, and convenience of a user is improved. 
     The first embodiment described above is an example of the tire  1  including two groups of circumferential grooves each of which comprises one first circumferential groove  11  and two second circumferential grooves  12 . The tire  1  has only to include at least one group of circumferential grooves. Accordingly, one group of circumferential grooves may be formed on the tire  1 , or more than one group of circumferential grooves may be formed on the tire  1 . 
     The Second Embodiment 
       FIG. 7  is a plan view illustrating a tread pattern of a tire  5  of the second embodiment and schematically illustrates a part of a tread portion  2  in a tire circumferential direction S similarly to  FIG. 1 .  FIG. 8  is a plan view illustrating a part of  FIG. 7  and illustrates a part between the two second circumferential grooves  12  in a state in which  FIG. 7  is rotated clockwise by 90°. 
     The tire  5  of the second embodiment is an example in which apart of the tire  1  of the first embodiment is changed, and an effect similar to that of the tire  1  is exerted. In the tire  5 , the same names as those in the tire  1  are given to the same constitution as the tire  1 , and detailed explanation of each constitution will be omitted. Moreover, in the following description, explanation for the same matters as the already-described matters will be omitted. 
     As illustrated, the tire  5  includes the one circumferential groove  11 , the two second circumferential grooves  12 , a plurality of lug grooves  13 , a plurality of lateral grooves  14 , the two shoulder block rows  20 , and the two control block rows  30 , in the tread portion  2 . The first circumferential groove  11  is arranged on the tread center portion  3 , and the two second circumferential grooves  12  are adjacent to both sides of the first circumferential groove  11  in the tire width direction K. The first circumferential groove  11  is a center circumferential groove of the tread portion  2 , and is arranged between the two circumferential grooves  12 . The second circumferential groove  12  is an outside circumferential groove formed outside the first circumferential grooves  11  in the tire width direction K, and is arranged between the first circumferential groove  11  and the shoulder portion  4  (tread end). The two second circumferential grooves  12  are arranged on both sides of the tread center portion  3  and the first circumferential groove  11  in the tire width direction K, respectively, and are arranged between the tread center portion  3  and the shoulder portions  4 , respectively. 
     The shoulder block row  20  has a plurality of lug grooves  13  and a plurality of blocks  21 . The control block row  30  has a plurality of lateral grooves  14  and a plurality of blocks  31 . Here, the control block row  30  is a center block row and is arranged on a center area of the tread portion  2  which includes the tread center portion  3 . The two control block rows  30  are arranged on both sides of the tread center portion  3  and the first circumferential groove  11  in the tire width direction K, respectively. The plurality of lateral grooves  14  extends from the first circumferential groove  11  toward both outsides in the tire width direction K thereof. The first circumferential groove  11  extends along the wall surfaces on the tread center portion  3  side of the plurality of blocks  31 . The second circumferential groove  12  extends along the wall surfaces on the shoulder portion  4  side of the plurality of blocks  31 . 
     The block  31  of the tire  5  has the same constitution as the block  31  of the tire  1  as shown in  FIG. 2 . Each block  31  of the plurality of blocks  31  has a first wall surface  32  on the tread center portion  3  side (inside in the tire width direction K), a second wall surface  33  on the shoulder portion  4  side (outside in the tire width direction K), a first block corner portion  34  on the tread center portion  3  side, and a second block corner portion  35  on the shoulder portion  4  side. A first virtual surface  36  is an extension surface extended from the first wall surface  32 , and a second virtual surface  37  is an extension surface extended from the second wall surface  33 . The first wall surface  32  is a curved surface inclined to the outside in the tire width direction K (shoulder portion  4  side) with respect to the tire circumferential direction S toward the downstream side H of the air flow. The groove width W of the first circumferential groove  11  gradually increases toward the downstream side H of the air flow at the first wall surface  32  of the block  31 . 
     On the tread center portion  3  side of the block  31 , the first wall surface  32  is curved toward the inside of the lateral groove  14  on the downstream side H of the air flow. The second wall surface  33  is a plane inclined to the inside in the tire width direction K (tread center portion  3  side) with respect to the tire circumferential direction S toward the downstream side H of the air flow. When the two blocks  31  on the upstream side G and the downstream side H of the air flow adjacent in the tire circumferential direction S are viewed, the first virtual surface  36  of the block  31  on the upstream side G is extended to the outside in the tire width direction K. In all the blocks  31  of the control block row  30 , the first virtual surface  36  is extended toward the inside of the lateral groove  14  between the two blocks  31 . The second virtual surface  37  of the block  31  on the upstream side G intersects with the second block corner portion  35  of the block  31  on the downstream side H, or passes through a position in the second circumferential groove  12  on the outside (shoulder portion  4  side) of the second block corner portion  35  in the tire width direction K. When the second virtual surface  37  passes through a position in the second circumferential groove  12 , the second virtual surface  37  passes through a position in the second circumferential groove  12  which is apart from the second block corner portion  35  in the tire width direction K. 
     In the tire  5 , the heat radiation of the first circumferential groove  11  located on the tread center portion  3  can be enhanced, and thus the cooling effect of the tread portion  2  by the first circumferential groove  11  can be increased. Along with this, the temperature rise of the tread portion  2  can be suppressed by cooling the tread portion  2  in the tread center portion  3  and the peripheral portion of the tread center portion  3 . Regarding durability of the tread portion  2 , for example, since an occurrence of separation in the tread portion  2  can be suppressed, the separation-resistance of the tread portion  2  can be improved. 
     One or more circumferential grooves may be formed between the second circumferential groove  12  and the shoulder portion  4  in addition to the first circumferential groove  11  and the two second circumferential grooves  12 . In this case, a plurality of block rows or ribs is arranged between the second circumferential groove  12  and the shoulder portion  4 . Further, the blocks  41 ,  51  and  61  as shown in  FIGS. 4 to 6  may be arranged in the control block row  30  of the tire  5  instead of the blocks  31 . 
     Subsequently, other examples of the block will be described. Each of the following blocks is an example in which a part of the shape of the block  31  is changed, and an effect similar to the above-described effect is exerted. In each block, the same names as those in the block  31  are given to the same constitution as the block  31 , and detailed explanation of each constitution will be omitted. Moreover, in the following description, explanation for the same matters as the already-described matters will be omitted. 
       FIGS. 9 to 11  are plan views illustrating blocks  41 ,  71  and  81  of the tire  5  and illustrate apart of tread patterns including the blocks  41 ,  71  and  81  similarly to  FIG. 8 . 
     The block  41  illustrated in  FIG. 9  has the same constitution as the block  41  as shown in  FIG. 4 . The block  41  has a first wall surface  42 , a second wall surface  43 , a first block corner portion  44 , and a second block corner portion  45 . A first virtual surface  46  is an extension surface extended from the first wall surface  42 , and a second virtual surface  47  is an extension surface extended from the second wall surface  43 . The first wall surface  42  of the block  41  is a plane inclined to the outside in the tire width direction K (shoulder portion  4  side) with respect to the tire circumferential direction S toward the downstream side H of the air flow. The first wall surface  42  is inclined toward the inside of the lateral groove  14  on the downstream side H of the air flow. In this first wall surface  42 , the air can easily flow from the first circumferential groove  11  toward the lateral groove  14 . Therefore, the pressure of the air can be reliably lowered around the first wall surface  42 , and the air flow in the first circumferential groove  11  can be further accelerated. 
     In the block  71  illustrated in  FIG. 10 , in a plan view where the block  71  is viewed from an outside in the tire radial direction, the block  71  is formed line-symmetrically with respect to a center line  78  passing through the center in the tire circumferential direction S. Therefore, the block  71  has a first wall surface  72 , a second wall surface  73 , a first block corner portion  74 , and a second block corner portion  75 , on each of both sides of the center line  78 . In addition, a first virtual surface  76  is an extension surface extended from each of the first wall surfaces  72  on the both sides of the center line  78 , and a second virtual surface  77  is an extension surface extended from each of the second wall surfaces  73  on the both sides of the center line  78 . The second wall surface  73  is a curved surface recessed in the block  71 , and the two second wall surfaces  73  intersect with each other on the center line  78 . In this block  71 , the tire rotating direction R can be set in both directions of the tire circumferential direction S. Namely, even if the air flow direction F becomes an opposite direction, the block  71  satisfies the conditions similar to those of the block  31  and acts in the same way as the block  31 . Therefore, it is not necessary to designate the tire rotating direction R when the tire is to be attached, and convenience of a user is improved. 
     In the block  81  illustrated in  FIG. 11 , in the same way as the block  71 , the block  81  is formed line-symmetrically with respect to a center line  88  passing through the center in the tire circumferential direction S, in a plan view where the block  81  is viewed from the outside in the tire radial direction. Accordingly, the block  81  has a first wall surface  82 , a second wall surface  83 , a first block corner portion  84 , and a second block corner portion  85  on each of both sides of the center line  88 . Moreover, a first virtual surface  86  is an extension surface extended from each of the first wall surfaces  82  on both sides of the center line  88 , and a second virtual surface  87  is an extension surface extended from each of the second wall surfaces  83  on the both sides of the center line  88 . The second wall surface  83  is a curved surface recessed in the block  81 , and the two second wall surfaces  83  intersect with each other on the centerline  88 . The first wall surface  82  of the block  81  is a plane inclined to the outside in the tire width direction K with respect to the tire circumferential direction S toward the downstream side H of the air flow in the same way as the first wall surface  42  of the block  41 . The first wall surface  82  is inclined toward the inside of the lateral groove  14  on the downstream side H of the air flow. In this block  81 , in the same way as the block  71 , the tire rotating direction R can be set in both directions of the tire circumferential direction S. Namely, even if the air flow direction F becomes an opposite direction, the block  81  satisfies the conditions similar to those of the block  31 , and the effect similar to that of the block  31  is exerted. Therefore, it is not necessary to designate the tire rotating direction R when the tire is to be attached, and convenience of a user is improved. 
     When the tire  1  is a tire for heavy load (such as a tire for truck/bus, for example), a heat generation amount of the tread portion  2  tends to be larger. Therefore, the present invention is suitable for the tire for heavy load. However, the present invention can be applied to various tires other than the tire for heavy load. 
     (Tire Test) 
     In order to confirm the effects of the tire  1  of the first embodiment, tires of two practical examples (referred to as embodied products 1, 2) and a tire of the conventional example (referred to as a conventional product 1) were produced, and their performances were evaluated. Each of the embodied products 1, 2 includes a plurality of blocks  51  illustrated in  FIG. 5  in the control block row  30 . In the embodied product 2, the groove width W of the first circumferential groove  11  is wider than the groove width of the lateral groove  14 , and the groove width of the lateral groove  14  is wider than the groove width of the second circumferential groove  12 . That is, in the embodied product 2, the whole of the first circumferential groove  11  is wider than the widest part of the lateral groove  14 , and the whole of the lateral groove  14  is wider than the widest part of the second circumferential groove  12 . The condition of the groove width of the embodied product 1 differs from the condition of the groove width of the embodied product 2. In particular, in the embodied product 1, the widest part of the first circumferential groove  11  is wider than the lateral groove  14  and the second circumferential groove  12 , and the lateral groove  14  and the second circumferential groove  12  are formed so as to have the equivalent groove width. The conventional product 1 is different from the embodied product 1 in the plurality of blocks of the control block row  30 . 
       FIG. 12  is a plan view illustrating a tread pattern of the conventional product 1 and illustrates a part of the tread pattern similarly to  FIG. 5 . 
     As illustrated, in a tire  90 A of the conventional product 1, a block  91  is formed line-symmetrically with respect to a center line  98  passing through the center in the tire circumferential direction S, in a plan view of the block  91  of the control block row  30  when viewed from the outside in the tire radial direction. Furthermore, the block  91  has a first wall surface  92 , a second wall surface  93 , a first block corner portion  94 , and a second block corner portion  95 , on each of both sides of the center line  98 . A second virtual surface  97  is an extension surface extended from each of the second wall surfaces  93  on both sides of the center line  98 . When the two blocks  91  on the upstream side G and the downstream side H of the air flow adjacent in the tire circumferential direction S are viewed, the second virtual surface  97  of the block  91  on the upstream side G is extended toward the inside of the lateral groove  14  between the two blocks  91  and intersects with the block  91  on the downstream side H in the lateral groove  14 . The groove width W of the first circumferential groove  11  is a constant width at the first wall surface  92 . 
     A drum durability test was conducted using the embodied products 1, 2 and the conventional product 1, under the following conditions: 
     Tire size: 11R22.5 
     Rim width: 7.50 
     Tire load: 2740 kgf (=26.9 kN) 
     Tire internal pressure: 700 kPa 
     Drum speed: 65 km/h 
     Temperature during test: 38° C. 
     In the test, the embodied products 1, 2 and the conventional product 1 were brought into contact with an outer circumferential surface of a drum, and the same load was applied to the embodied products 1, 2 and the conventional product 1. In that state, the drum was rotated, and the embodied products 1, 2 and the conventional product 1 were rotated (made to run) by the drum. Thereby, traveling distances sufficient for belts of the embodied products 1, 2 and the conventional product 1 to endure were measured, and belt durability of the embodied products 1, 2 and the conventional product 1 was evaluated. Furthermore, heat transfer rate at the groove bottom of the first circumferential groove  11  was measured in the embodied products 1, 2 and the conventional product 1, and heat radiation of the first circumferential groove  11  was evaluated. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 EMBODIED 
                 EMBODIED 
                 CONVENTIONAL  
               
               
                   
                 PRODUCT 
                 PRODUCT 
                 PRODUCT 
               
               
                   
                 1 
                 2 
                 1 
               
               
                   
               
             
            
               
                 HEAT TRANSFER  
                 150 
                 153 
                 100 
               
               
                 RATE AT 
                   
                   
                   
               
               
                 GROOVE BOTTOM  
                   
                   
                   
               
               
                 OF FIRST 
                   
                   
                   
               
               
                 CIRCUMFERENTIAL  
                   
                   
                   
               
               
                 GROOVE 
                   
                   
                   
               
               
                 BELT DURABILITY 
                   
                   
                   
               
               
                 INDICATED BY  
                 115 
                 120 
                 100 
               
               
                 TRAVELING 
                   
                   
                   
               
               
                 DISTANCE 
               
               
                   
               
            
           
         
       
     
     Table 1 shows test results of the embodied products 1, 2 and the conventional product 1. The test results are expressed by index with the conventional product 1 at 100 and indicate that the larger the numerical value is, the higher the performances. 
     As shown in Table 1, the heat transfer rate (150) of the embodied product 1 and the heat transfer rate (153) of the embodied product 2 are remarkably higher than the heat transfer rate of the conventional product 1. As a result, it is known that in the embodied products 1, 2, the heat radiation of the first circumferential groove  11  is enhanced. Furthermore, the belt durability (115) of the embodied product 1 and the belt durability (120) of the embodied product 2 are higher than the belt durability of the conventional product 1. It is known that in the embodied products 1, 2, the cooling effect by the first circumferential groove  11  becomes higher, and the belt durability is enhanced. The heat transfer rate of the embodied product 2 is higher than the heat transfer rate of the embodied product 1 and the belt durability of the embodied product 2 is higher than the belt durability of the embodied product 1. From these, it is known that in the embodied product 2, the heat radiation of the first circumferential groove  11  is enhanced, and thus the cooling effect by the first circumferential groove  11  becomes higher. 
     In order to confirm the effects of the tire  5  of the second embodiment, tires of two practical examples (referred to as embodied products 3, 4) and a tire of the conventional example (referred to as a conventional product 2) were produced, and their performances were evaluated. Each of the embodied products 3, 4 includes a plurality of blocks  71  illustrated in  FIG. 10  in the control block row  30 . In the embodied product 4, the groove width W of the first circumferential groove  11  is wider than the groove width of the lateral groove  14 , and the groove width of the lateral groove  14  is wider than the groove width of the second circumferential groove  12 . That is, in the embodied product 4, the whole of the first circumferential groove  11  is wider than the widest part of the lateral groove  14 , and the whole of the lateral groove  14  is wider than the widest part of the second circumferential groove  12 . The condition of the groove width of the embodied product 3 differs from the condition of the groove width of the embodied product 4. In particular, in the embodied product 3, the widest part of the first circumferential groove  11  is wider than the lateral groove  14  and the second circumferential groove  12 , and the lateral groove  14  and the second circumferential groove  12  are formed so as to have the equivalent groove width. The conventional product 2 is different from the embodied product 3 in the plurality of blocks of the control block row  30 . 
       FIG. 13  is a plan view illustrating a tread pattern of the conventional product 2 and illustrates a part of the tread pattern similarly to  FIG. 10 . 
     As illustrated, in a tire  90 B of the conventional product 2, the block  91  has the same constitution as the block  91  of the tire  90 A as shown in  FIG. 12 . 
     A drum durability test was conducted using the embodied products 3, 4 and the conventional product 2, under the same conditions of the embodied products 1, 2 and the conventional product 1 described above. In the test, traveling distances sufficient for belts of the embodied products 3, 4 and the conventional product 2 to endure were measured, and belt durability of the embodied products 3, 4 and the conventional product 2 was evaluated. Further, traveling distances to occur the separation in the tread portion  2  of the embodied products 3, 4 and the conventional product 2 were measured, and the separation-resistance of the tread portion  2  of the embodied products 3, 4 and the conventional product 2 was evaluated. Furthermore, heat transfer rate at the groove bottom of the first circumferential groove  11  was measured in the embodied products 3, 4 and the conventional product 2, and heat radiation of the first circumferential groove  11  was evaluated. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 EMBODIED 
                 EMBODIED 
                 CONVENTIONAL  
               
               
                   
                 PRODUCT 
                 PRODUCT 
                 PRODUCT 
               
               
                   
                 3 
                 4 
                 2 
               
               
                   
               
             
            
               
                 HEAT TRANSFER  
                 150 
                 153 
                 100 
               
               
                 RATE AT 
                   
                   
                   
               
               
                 GROOVE BOTTOM  
                   
                   
                   
               
               
                 OF FIRST 
                   
                   
                   
               
               
                 CIRCUMFERENTIAL  
                   
                   
                   
               
               
                 GROOVE 
                   
                   
                   
               
               
                 SEPARATION- 
                 120 
                 130 
                 100 
               
               
                 RESISTANCE 
                   
                   
                   
               
               
                 INDICATED BY  
                   
                   
                   
               
               
                 TRAVELING 
                   
                   
                   
               
               
                 DISTANCE 
                   
                   
                   
               
               
                 BELT DURABILITY 
                 112 
                 112 
                 100 
               
               
                 INDICATED  
                   
                   
                   
               
               
                 BY TRAVELING 
                   
                   
                   
               
               
                 DISTANCE 
               
               
                   
               
            
           
         
       
     
     Table 2 shows test results of the embodied products 3, 4 and the conventional product 2. The test results are expressed by index with the conventional product 2 at 100 and indicate that the larger the numerical value is, the higher the performances. 
     As shown in Table 2, the heat transfer rate (150) of the embodied product 3 and the heat transfer rate (153) of the embodied product 4 are remarkably higher than the heat transfer rate of the conventional product 2. As a result, it is known that in the embodied products 3, 4, the heat radiation of the first circumferential groove  11  is enhanced. Further, the separation-resistance (120) of the embodied product 3 and the separation-resistance (130) of the embodied product 4 are higher than the separation-resistance of the conventional product 2. Furthermore, the belt durability (112) of the embodied product 3 and the belt durability (112) of the embodied product 4 are higher than the belt durability of the conventional product 2. It is known that in the embodied products 3, 4, the cooling effect by the first circumferential groove  11  becomes higher, and the separation-resistance and the belt durability is enhanced. 
     The heat transfer rate of the embodied product 4 is higher than the heat transfer rate of the embodied product 3. Further, the separation-resistance of the embodied product 4 is higher than the separation-resistance of the embodied product 3 and the belt durability of the embodied product 4 is equal to the belt durability of the embodied product 3. From these, it is known that in the embodied product 4, the heat radiation of the first circumferential groove  11  is enhanced, and thus the cooling effect by the first circumferential groove  11  becomes higher. 
     REFERENCE SIGNS LIST 
     
         
           1  . . . tire 
           2  . . . tread portion 
           3  . . . tread center portion 
           4  . . . shoulder portion 
           5  . . . tire 
           11  . . . first circumferential groove 
           12  . . . second circumferential groove 
           13  . . . lug groove 
           14  . . . lateral groove 
           15  . . . raised portion 
           20  . . . shoulder block row 
           21  . . . block 
           30  . . . control block row 
           31  . . . block 
           32  . . . first wall surface 
           33  . . . second wall surface 
           34  . . . first block corner portion 
           35  . . . second block corner portion 
           36  . . . first virtual surface 
           37  . . . second virtual surface 
           38  . . . virtual intersection position 
           41  . . . block 
           42  . . . first wall surface 
           43  . . . second wall surface 
           44  . . . first block corner portion 
           45  . . . second block corner portion 
           46  . . . first virtual surface 
           47  . . . second virtual surface 
           51  . . . block 
           52  . . . first wall surface 
           53  . . . second wall surface 
           54  . . . first block corner portion 
           55  . . . second block corner portion 
           56  . . . first virtual surface 
           57  . . . second virtual surface 
           58  . . . center line 
           61  . . . block 
           62  . . . first wall surface 
           63  . . . second wall surface 
           64  . . . first block corner portion 
           65  . . . second block corner portion 
           66  . . . first virtual surface 
           67  . . . second virtual surface 
           68  . . . center line 
           71  . . . block 
           72  . . . first wall surface 
           73  . . . second wall surface 
           74  . . . first block corner portion 
           75  . . . second block corner portion 
           76  . . . first virtual surface 
           77  . . . second virtual surface 
           78  . . . center line 
           81  . . . block 
           82  . . . first wall surface 
           83  . . . second wall surface 
           84  . . . first block corner portion 
           85  . . . second block corner portion 
           86  . . . first virtual surface 
           87  . . . second virtual surface 
           88  . . . center line 
         F . . . air flow direction 
         G . . . upstream side 
         H . . . downstream side 
         K . . . tire width direction 
         R . . . tire rotating direction 
         S . . . tire circumferential direction 
         W . . . groove width