Abstract:
To provide a motorized two-wheeled vehicle tire for traveling on uneven terrain, the block durability performance of which has been improved; and a tire vulcanization mold capable of molding said tire. A motorized two-wheeled vehicle tire for traveling on uneven terrain wherein multiple blocks are provided on the tread at intervals in the tire circumference direction. Recesses are provided on the bottom surfaces of the grooves. Multiple recesses are provided at intervals in the axial direction of the tire. Spew, which was drawn up into the vent holes of the mold during vulcanization molding, or removal marks thereof are provided between each recess and the block that is adjacent in the tire circumference direction.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a motorcycle tire for traveling on rough terrain that is improved in durability performance of blocks provided on a tread portion and a tire vulcanization mold capable of molding the tire. 
       BACKGROUND ART 
       [0002]    Motorcycle tires for traveling on rough terrain used in motocross races and others have a plurality of large blocks sparsely formed on tread portions. These tires obtain a grip from the blocks biting into the road surface. Accordingly, there is demand for improvement in durability performance of the blocks. 
         [0003]    The motorcycle tire for traveling on rough terrain described in Patent Document 1 includes a recess portion formed by recessing locally the groove bottom surface of the tread portion between adjacent blocks in a tire circumferential direction. The recess portion can reduce the concentration of stress on the basal portions of blocks to improve durability performance of the blocks. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2009-67245 
       
     
         [0005]    Unfortunately, such a tire is not sufficient in improvement of the durability performance of the blocks and is requested for further enhancement. 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    The present invention has been made in light of the foregoing circumstances. A major object of the present invention is to provide a motorcycle tire for traveling on rough terrain that improves durability performance of the blocks basically by forming a plurality of recess portions on a groove bottom surface and forming spews or their excision marks between one of recess portions and one of the blocks, and provide a tire vulcanization mold capable of molding the tire. 
       Solution to Problem 
       [0007]    The present invention provides a motorcycle tire for traveling on rough terrain, the tire including a tread portion being provided with a plurality of blocks protruding radially outwardly from a groove bottom surface and arranged in a circumferential direction of the tire with a space therebetween, a plurality of recess portions being provided on the groove bottom surface between a pair of circumferentially adjacent blocks, the recess portions arranged in an axial direction of the tire with a space therebetween, and a spew sucked up a vent hole in a mold during vulcanization molding or its excision mark being provided between each recess portion and the block adjacent to the recess portion in the circumferential direction of the tire. 
         [0008]    In another aspect of the invention, the recess portions are configured as a vertically long shape having a length in the circumferential direction of the tire greater than a length in the axial direction of the tire. 
         [0009]    In another aspect of the invention, six to ten recess portions are arranged in the axial direction of the tire. 
         [0010]    In another aspect of the invention provides a tire vulcanization mold including a tread molding surface for molding a tread portion of a motorcycle tire for traveling on rough terrain including a plurality of blocks protruding radially outwardly from a groove bottom surface and arranged in a circumferential direction of the tire with a space therebetween, the mold including the tread molding surface comprising a first portion for molding the groove bottom surface, a plurality of second portions for molding the blocks, and a plurality of projecting third portions provided between a pair of adjacent second portions in the circumferential direction of the tire for molding the recess portions on the groove bottom surface, the third portions being arranged in an axial direction of the tire with a space therebetween, and the first portion between one of the second portions and one of the third portions being provided with one end of a vent hole having the other end communicating with the outside of the mold to discharge an air to an outside of the mold during vulcanization. 
         [0011]    In another aspect of the invention, the third portions are configured as a vertically long shape having a length in the circumferential direction of the tire greater than a length in the axial direction of the tire. 
         [0012]    In another aspect of the invention, a hole diameter of the vent hole is in a range of from 0.5 to 1.5 mm. 
         [0013]    In another aspect of the invention, six to ten third portions are provided in the axial direction of the tire. 
         [0014]    In another aspect of the invention, a circumferential distance between an edge of the end of the vent hole and a circumferential end edge of the third portion is in a range of from 1 to 6 mm. 
       Advantageous Effects of Invention 
       [0015]    The motorcycle tire for traveling on rough terrain of the present invention includes the recess portions on the groove bottom surface between a pair of adjacent blocks in the circumferential direction of the tire. The recess portions are arranged in the axial direction of the tire with a space therebetween. The recess portions do not decrease excessively the rigidity of the groove bottom surface between blocks adjacent in the circumferential direction of the tire but can moderate it evenly as compared to the case where only one large recess portion is provided. This alleviates effectively the concentration of stress on the basal portions of blocks. 
         [0016]    In addition, the spew sucked up by the vent hole in the mold during vulcanization molding or its excision mark is provided between one of the recess portions and the block adjacent to the recess portion in the circumferential direction of the tire. The tire suppresses a residual gas likely to occur between blocks and recess portions when the recess portions and the blocks are vulcanized and molded on the tread portion. Accordingly, it is possible to suppress the molding failure of the basal portions of the blocks and generation of cracks causing the deterioration of durability performance of the blocks. 
         [0017]    Therefore, the motorcycle tire for traveling on rough terrain of the present invention improves durability performance of the blocks. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  is a cross-sectional view of an embodiment of a motorcycle tire for traveling on rough terrain of the present invention. 
           [0019]      FIG. 2  is a development view of a tread portion illustrated in  FIG. 1 . 
           [0020]      FIG. 3  is a cross-sectional view taken along a line B-B of  FIG. 2 . 
           [0021]      FIG. 4  is a partial perspective view of a tire vulcanization mold for molding the tire of the present invention. 
           [0022]      FIG. 5  is an illustrative view for describing vulcanization molding. 
       
    
    
     REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  Tire 
               2  Tread portion 
               9   d  Groove bottom surface 
               10  Block 
               15  Recess portion 
               17  Excision mark 
               30  Tire vulcanization mold 
           
         
       
     
       DESCRIPTION OF EMBODIMENTS 
       [0030]    An embodiment of the present invention will be described below. 
         [0031]      FIGS. 1 and 2  illustrate a tire for motocross races as a motorcycle tire for traveling on rough terrain of the embodiment (hereinafter, also referred to as simply “tire”)  1 .  FIG. 1  is a cross-sectional view of the tire  1  taken along a tire meridian including a tire rotation axis in a normal state.  FIG. 2  is a development view of a tread portion  2  of the tire  1  illustrated in  FIG. 1 .  FIG. 1  represents a cross-sectional view taken along a line A-A of  FIG. 2 . 
         [0032]    The “normal state” refers to a state in which the tire is mounted on a normal rim (not illustrated) and inflated with a normal inner pressure under no-load. Unless otherwise specified, hereinafter, the dimensions and the like of components of the tire are measured in the normal state. 
         [0033]    The term “normal rim” is a rim specified for each tire by standards in a standard system including the standards for the tire. For example, the normal rim is a “standard rim” under JATMA, a “design rim” under TRA, and a “measuring rim” under ETRTO. 
         [0034]    The term “normal inner pressure” refers to a pneumatic pressure specified for each tire by standards in a standard system including the standards for the tire. The normal inner pressure is a “maximum pneumatic pressure” under JATMA, the maximum value described in the table “Tire Load Limits at Various Cold Inflation Pressures” under TRA, and an “inflation pressure” under ETRTO. 
         [0035]    As illustrated in  FIG. 1 , the tire  1  of the embodiment includes a carcass  6  that extends from the tread portion  2  through sidewall portions  3  to bead cores  5  in bead portions  4 , a belt layer  7  that is disposed outside the carcass  6  in the tire radial direction in the tread portion  2 , and a bead apex rubber  8  that extends in a tapered manner from each bead core  5  outward in the tire radial direction. 
         [0036]    The carcass  6  comprises two carcass plies  6 A and  6 B, for example. Each of the carcass plies  6 A and  6 B includes a main portion  6   a  extending from the tread portion  2  through the sidewall portions  3  to the bead cores  5  disposed in the bead portions  4 , and turn-up portions  6   b  that connect to the main portion  6   a  and are turned up around the bead cores  5 . 
         [0037]    The carcass plies  6 A and  6 B comprise carcass cords arranged and inclined with respect to a tire equator C. The carcass cords cross each other between the carcass plies  6 A and  6 B. The carcass plies  6 A and  6 B of the embodiment have a radial structure in which the carcass cords are arranged at an angle of 65 to 90 degrees with respect to the tire equator C. The carcass plies  6 A and  6 B may have a bias structure in which the carcass cords are arranged at an angle of 15 to 45 degrees with respect to the tire equator C. 
         [0038]    The carcass cords are preferably organic fiber cords of nylon, polyester, or rayon, for example. 
         [0039]    The belt layer  7  is composed of one belt ply  7 A, for example. The belt ply  7 A has belt cords arranged and inclined with respect to the tire equator C. The belt cords are preferably formed from aramid, rayon, or the like, for example. 
         [0040]    The bead apex rubber  8  is made of a hard rubber composition. The bead apex rubber  8  is interposed between the main portion  6   a  and one of the turn-up portions  6   b . The bead apex rubber  8  reinforces the bead portions  4  and the sidewall portions  3 . 
         [0041]    The tread portion  2  includes an outer surface  2   s  curving in a convex arc shape outward in the tire radial direction between tread edges Te and Te. Accordingly, the tread portion  2  obtains a sufficient ground contact area even during cornering at a large camber angle. The tread width TW between the tread edges Te and Te in the axial direction of the tire is set to the tire maximum width. 
         [0042]    As illustrated in  FIG. 2 , the tread portion  2  of the embodiment has a specified rotational direction R. The rotational direction R is indicated by a character or a mark on the sidewall portions or the like, for example. 
         [0043]    The tread portion  2  includes blocks  10 . The blocks  10  protrude radially outwardly from a groove bottom surface  9   d  of a tread groove  9 . The blocks  10  are provided in a plurality of places with a space L 1  therebetween in the circumferential direction of the tire. The groove bottom surface  9   d  is a bottom portion of the tread groove  9  that extends smoothly along the outer surface of the carcass  6 . 
         [0044]    The space L 1  between the blocks  10  and  10  adjacent in the circumferential direction of the tire is preferably 2.0% or more, more preferably 2.5% or more, and preferably 3.0% or less, more preferably 2.8% or less of a circumferential length CL of the tire  1  on the tire equator C. This allows the blocks  10  to bite easily into the road surface and improves the grip performance in sand areas in particular. 
         [0045]    The rubber hardness of the blocks  10  is preferably 55 degrees or more, more preferably 65 degrees or more, and is preferably 95 degrees or less, more preferably 85 degrees or less. When the rubber hardness of the blocks  10  is smaller than 55 degrees, the blocks  10  may not maintain sufficient rigidity or obtain sufficient grip. In contrast, when the rubber rigidity of the blocks is larger than 95 degrees, the flexibility of the blocks  10  may become lower to deteriorate the durability performance of the blocks. The rubber hardness herein complies with JIS-K6253 and refers to a durometer type A hardness at 23 deg. C. 
         [0046]    The blocks  10  of the embodiment include center blocks  11  formed on the tire equator C, shoulder blocks  12  closest to the tread edge Te sides, and middle blocks  13  between the center blocks  11  and the shoulder blocks  12 . 
         [0047]    Each of the center blocks  11  includes a first portion  18  and a second portion  19 , for example. The first portion  18  has a landscape rectangular shape elongated in the axial direction of the tire. The first portion  18  is convex-curved to the side opposite to the rotational direction R of the tire  1 . The second portion  19  protrudes from the first portion  18  to the both ends in the circumferential direction of the tire on the tire equator C. With the first portion  18  and the second portion  19 , the tread surface of the center block  11  is formed in an almost cross shape. The center blocks  11  improve effectively the traction performance of the tire. 
         [0048]    A width W 1  of the first portion  18  in the circumferential direction of the tire is preferably 0.10 times or more, more preferably 0.15 times or more, and preferably 0.30 times or less, more preferably 0.25 times or less longer than the space L 1 . This allows the blocks  10  to bite effectively into the road surface thereby achieving further improved grip. 
         [0049]    Each of the shoulder blocks  12  includes end edges  12   e  and  12   e  extending in the circumferential direction of the tire and is formed in an almost trapezoidal shape, for example. The circumferential length W 2  of the shoulder blocks  12  increases gradually outward in the axial direction of the tire. The shoulder blocks  12  improve the stable driving performance during cornering. 
         [0050]    Each of the middle blocks  13  includes end edges  13   e  and  13   e  extending in the circumferential direction of the tire and is formed in an almost trapezoidal shape. Each of the middle blocks  13  includes an inner portion  13   a  and an outer portion  13   b . A width W 3  of the inner portion  13   a  is kept constant. A width W 3  of the outer portion  13   b  increases gradually outward in the axial direction of the tire. 
         [0051]    The land-sea ratio of the tire  1  in the embodiment is 10 to 20%, preferably 13 to 18%, for example. The land-sea ratio herein refers to the ratio of the total area of tread surfaces  10   s  of the blocks  10  to the entire area of the outer surface of the tread portion  2  based on the assumption that the entire tread grooves  9  is filled up. 
         [0052]    Recess portions  15  are provided on the groove bottom surface  9   d  between a pair of adjacent blocks  10  and  10  in the circumferential direction of the tire. In the embodiment, the recess portions  15  are provided in a tread central area where the center blocks  11  and the middle blocks  13  are formed. The recess portions  15  are arranged in the axial direction of the tire with a space therebetween. In a preferred embodiment, the recess portions  15  are arranged at equal spaces therebetween in the axial direction of the tire. These recess portions  15  do not decrease excessively rigidity of the groove bottom surface  9   d  between adjacent blocks  10  and  10  in the circumferential direction of the tire but can moderate it evenly, as compared to the case where only one large recess portion is provided. Accordingly, it is possible to alleviate effectively the concentration of stress on the basal portions of the blocks  10  when the blocks  10  are in contact with the ground. 
         [0053]    Although there is no particular limitation, number N 1  of the recess portions  15  provided in the axial direction of the tire is preferably six or more, more preferably seven or more, and is preferably ten or less, more preferably nine or less. When the number N 1  is smaller than six, the rigidity of the groove bottom surface  9   d  may not be evenly moderated. In contrast, when the number N 1  is larger than ten, the rigidity of the groove bottom surface  9   d  may decrease excessively. 
         [0054]    A spew sucked up by a vent hole in a mold during vulcanization molding or its excision mark  17  is provided between one of the recess portion  15  and one of the block  10  in the circumferential direction of the tire. The tire  1  makes it possible to suppress a residual gas prone to be generated between the block  10  and the recess portion  15  when the recess portions  15  and the blocks  10  are vulcanized and molded in the tread portion  2 . Accordingly, it is possible to suppress the molding failure of the basal portions of the blocks  10  and suppress the occurrence of cracks causing the deterioration in durability performance of the blocks  10 , between the block  10  and the recess portion  15 . 
         [0055]    In the embodiment, the recess portions  15  have edges  15   e  formed in an elongated circular shape including vertical edges  20  and  20  extending in the circumferential direction of the tire and arc portions  21 . The vertical edges  20  and  20  in a pair extend linearly in parallel to each other in the circumferential direction of the tire, for example. The arc portions  21  connect the vertical edges  20  and  20  in an arc shape. Such a recess portion  15  can suppress the occurrence of cracks from the edges  15   e.    
         [0056]    An axial length L 2  of the recess portions  15  is preferably 0.10 times or more, more preferably 0.12 times or more, and preferably 0.16 times or less, more preferably 0.14 times or less longer than a tread development width TWe. When the tire axial length L 2  of the recess portions  15  is shorter than 0.10 times the tread development width TWe, the foregoing advantages may become lessened. In contrast, when the length L 2  is longer than 0.16 times the tread development width TWe, the rigidity of the groove bottom surface  9   d  may become locally lower. 
         [0057]    A circumferential length L 3  of the recess portions  15  is desirably longer than the tire axial length L 2 . With the vertically long shaped recess portions  15 , the tread portion  2  has the rigidity in the circumferential direction of the tire higher than the rigidity in the axial direction of the tire, thereby improving the traction performance during straight-ahead driving. 
         [0058]    To produce fully the foregoing advantages, the ratio L 3 /L 2  of the tire circumferential length L 3  of the recess portions  15  to the tire axial length L 2  of the recess portions  15  is preferably 3.0 or more, more preferably 3.4 or more. When the ratio L 3 /L 2  is large, the rigidity of the tread portion  2  in the axial direction of the tire may become lower to cause deterioration in the stable driving performance when the vehicle body tilts during cornering. Accordingly, the ratio L 3 /L 2  is preferably 4.2 or less, more preferably 3.8 or less. 
         [0059]      FIG. 3  is a cross-sectional view taken along a line B-B of  FIG. 2 . As illustrated in  FIG. 3 , each of the recess portions  15  includes a bottom portion  22  and a sidewall portion  23 . The bottom portion  22  extends along a virtual surface  9   v  extended from the groove bottom surface  9   d  more inward in the tire radial direction than the virtual surface  9   v . The sidewall portions  23  connect the groove bottom surface  9   d  and the bottom portion  22 . 
         [0060]    A depth d 1  of the recess portions  15  is preferably 0.5 mm or more, more preferably 0.8 mm or more, and is preferably 1.5 mm or less, more preferably 1.2 mm or less. When the depth d 1  of the recess portions  15  is smaller than 0.5 mm, the foregoing advantages may be lessened. On the other hand, when the depth d 1  of the recess portions  15  is larger than 1.5 mm, the rigidity of the groove bottom surface  9   d  of the tread portion  2  may become lower to deteriorate the stable driving performance. 
         [0061]    As illustrated in  FIG. 2 , an axial distance W 4  between axially adjacent recess portions  15  and  15  is preferably 1.10 times or more, more preferably 1.20 times or more, and preferably 1.35 times or less, more preferably 1.30 times or less larger than the tire axial length L 2  of the recess portions  15 . When the distance W 4  is smaller than 1.10 times the length L 2 , the rigidity of the groove bottom surface  9   d  between blocks  10  and  10  may become excessively lower. On the other hand, when the distance W 4  is larger than 1.35 times the length L 2 , the concentration of stress on the basal portions of the blocks  10  may not be alleviated. 
         [0062]    Next, a tire vulcanization mold capable of molding the motorcycle tire for traveling on rough terrain as described above will be explained with reference to the drawings. 
         [0063]      FIG. 4  is a partial perspective view of a tire vulcanization mold  30 . The tire vulcanization mold  30  includes a tread molding surface  31  for molding the tread portion  2  of the tire  1  of the present invention illustrated in  FIG. 1 . For example, a range al of the tread portion  2  illustrated in  FIG. 2  is molded by the tread molding surface  31  illustrated in  FIG. 4 . 
         [0064]    As illustrated in  FIG. 4 , the tread molding surface  31  includes a first portion  32  for molding the groove bottom surface  9   d  (illustrated in  FIG. 2 ), a plurality of second portions  33  for molding the blocks  10  (illustrated in  FIG. 2 ), and a plurality of projecting third portions  34  for molding the recess portions  15  (illustrated in  FIG. 2 ). 
         [0065]    The third portions  34  are provided between second portions  33  and  33  adjacent in the circumferential direction of the tire. The third portions  34  are configured as a vertically long shape having a length in the circumferential direction of the tire greater than a length in the axial direction of the tire. The recess portions  15  (illustrated in  FIG. 2 ) recessed from the groove bottom surface  9   d  are molded by the third portions  34 . 
         [0066]    The third portions  34  are arranged in the axial direction of the tire with a space therebetween. The number N 2  of the third portions  34  provided in the axial direction of the tire is the same as the number of the recess portions  15 . That is, the number N 2  of the third portions  34  is preferably six or more, more preferably seven or more, and is preferably ten or less, more preferably nine or less. 
         [0067]    A vent hole  35  is provided in a first portion  32   m  between one of the second portions  33  and one of the third portions  34 . The vent hole  35  includes one end  36  opened on the tread molding surface  31 . The other end  37  of the vent hole  35  communicates with the outside of the mold and is connected to a vacuum device not illustrated. The vent hole  35  can eject the air between the mold and the raw cover to the outside of the mold. 
         [0068]      FIG. 5  is a cross-sectional view of the tire vulcanization mold  30  illustrated in  FIG. 4  seen from C direction. As illustrated in  FIG. 5 , at the time of vulcanization molding, the tire vulcanization mold  30  is brought into intimate contact with tread rubber  2   g . At that time, the tread rubber  2   g  forms press portions  40  pressed by the first portion  32  and the third portions  34  and suction portions  41  sucked by the second portions  33 , and moves in the directions of arrows  42 . The rubber needs to move largely in particular for the motorcycle tire for traveling on rough terrain with the large-area groove bottom surface  9   d  and the high blocks  10  (illustrated in  FIG. 1 ) as in the present invention. Accordingly, when there are no vent holes  35  between the second portions  33  and the third portions  34 , air gaps  38  are generated due to the movement failure of the rubber to cause fine vulcanization molding defects at the basal portions of the blocks  10 . However, the tire vulcanization mold  30  of the present invention includes the vent holes  35  between the second portions  33  and the third portions to suppress the occurrence of the air gaps  38 . Accordingly, it is possible to suppress the vulcanization molding defects at the basal portions of the blocks  10  and improve the durability of the blocks  10 . 
         [0069]    To produce effectively the foregoing advantages, a hole diameter L 4  of the vent holes  35  is preferably 0.5 mm or more, more preferably 0.8 mm or more, and is preferably 1.5 mm or less, more preferably 1.2 mm or less. 
         [0070]    As illustrated in  FIG. 4 , when a circumferential distance L 5  between an edge  35   e  of the vent hole  35  and an edge  34   t  of the third portion  34  is large, the gas may be likely to remain. Accordingly, the distance L 5  is preferably 6.0 mm or less, more preferably 4.0 mm or less. On the other hand, when the distance L 5  is small, spews may be formed near the end edges of the recess portions to deteriorate the external appearance of the tire. Accordingly, the distance L 5  is preferably 1.0 mm or more, more preferably 3.0 mm or more. 
         [0071]    The vent holes  35  are desirably provided between extension lines  39  and  39  extending in the circumferential direction of the tire from the both end edges  34   e  and  34   e  of the third portion  34 . The vent holes  35  suppress effectively the residual gas. 
         [0072]    The particularly preferred embodiment of the present invention has been described in detail so far. However, the present invention is not limited to the illustrated embodiment but can be modified in various manners. 
       Examples 
       [0073]    A motorcycle pneumatic tire for traveling on rough terrain having the basic structure illustrated in  FIG. 1  and having the basic tread pattern illustrated in  FIG. 2  was prototyped in accordance with the specifications in Table 1. As a comparative example 1, a tire without recess portions in the groove bottom surface was prototyped. As comparative examples 2 to 5, tires with recess portions in the groove bottom surface and without spews or their excision marks between the recess portions and the blocks were prototyped. These prototyped tires were mounted on rear wheels of a test vehicle and were tested for performance. The common specifications and test method for the test tires were as follows. 
         [0074]    Used motorcycle: Motorcycle with a displacement of 450 cc 
         [0075]    Tire size: 110/90-19 
         [0076]    Rim size: 2.50×19 
         [0077]    Inner pressure: 80 kPa 
         [0078]    Steering Stability Performance: 
         [0079]    Under the foregoing conditions, the test tires were tested for steering stability performance by sensory evaluation of a rider operating the motorcycle in a test course on an rough terrain road surface. The larger values of test results are better with a score of 100 representing the values of the comparative example 1. 
         [0080]    Block Durability Performance: 
         [0081]    After the three-hour driving on the rough terrain road surface, the number of cracks generated in the blocks was measured. The values of test results are expressed as the reciprocals of the numbers of the generated cracks with a score of 100 representing the value of the comparative example 1. The larger values of test results indicate more excellence in block durability performance. Table 1 shows the test results. 
         [0000]    
       
         
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Ref. 1 
                 Ref. 2 
                 Ref. 3 
                 Ref. 4 
                 Ref. 5 
                 Ex. 1 
                 Ex. 2 
                 Ex. 3 
                 Ex. 4 
                 Ex. 5 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Land-sea ratio (%) 
                 16.0 
                 16.0 
                 16.0 
                 24.0 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
                 16.0 
               
               
                 Block space L1/circumferential length CL (%) 
                 2.8 
                 2.8 
                 2.8 
                 14.0 
                 2.1 
                 2.8 
                 2.8 
                 2.8 
                 2.8 
                 5.0 
               
               
                 Number N1 of recess portions (unit) 
                 — 
                 8 
                 5 
                 1 
                 1 
                 8 
                 8 
                 8 
                 8 
                 12 
               
               
                 Depth d1 of recess portions (mm) 
                 — 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
                 1.0 
               
               
                 Tire circumferential length L3 of recess 
                 — 
                 4.0 
                 4.0 
                 1.0 
                 0.2 
                 4.0 
                 4.0 
                 4.0 
                 4.0 
                 6.0 
               
               
                 portions/axial length L2 of recess portions 
               
               
                 Hole diameter L4 of vent hole (mm) 
                 — 
                 — 
                 — 
                 — 
                 — 
                 0.8 
                 2.0 
                 0.5 
                 1.5 
                 0.8 
               
               
                 Distance L5 between vent hole and third 
                 — 
                 — 
                 — 
                 — 
                 — 
                 2.5 
                 2.5 
                 2.5 
                 2.5 
                 2.5 
               
               
                 portion (mm) 
               
               
                 Steering stability performance (score) 
                 100 
                 103 
                 100 
                 95 
                 102 
                 110 
                 108 
                 110 
                 113 
                 109 
               
               
                 Block durability performance (index) 
                 100 
                 102 
                 101 
                 100 
                 101 
                 112 
                 110 
                 111 
                 109 
                 109 
               
               
                   
               
             
          
         
       
     
         [0082]    As a result, it has been revealed that the tires of the example improved in the durability performance of the blocks.