JP2002264612A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance both the drainage performance and the on-snow performance of a winter tire. SOLUTION: A pair of linear grooves 3, zigzag grooves 5 and inclined main grooves 6 are provided. Each of the zigzag grooves 5 is formed of long side portions 5a and short side portions 5b. At least some of the long side portions and the inclined main grooves 6 share common sections. The long side portions 5a extend away from one another from bottom to top and the short side portions 5b extend toward one another from bottom to top. The long side portions 5a and the short side portions 5b are at acute angles to the circumferential direction of the tire. The distance of each zigzag groove 5 from the tread center C is 17 to 35% of the width T of the tread.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic tire, and more particularly to a winter tire, and particularly to a technique for improving drainage performance together with performance on ice and snow.

[0002]

2. Description of the Related Art As a conventional tire capable of exerting good performance on ice and snow in a well-balanced manner, there is a tire having a tread pattern as exemplified in a development view in FIG. 3, and a snow tire is continuous in a circumferential direction. Conventionally, a combination of a zigzag groove and a linear groove and a block having a lateral groove extending in the tire width direction is used.

[0003]

However, all of such conventional tires have a point-symmetric tread pattern, and the extending angle of the lateral groove with respect to the tread center is naturally limited. Since the circumferential zigzag grooves are unavoidable in order to ensure the driving performance and braking performance of the vehicle, there is a problem that it is difficult to ensure high drainage performance on wet road surfaces.

An object of the present invention is to solve such problems of the prior art, and an object of the present invention is to adopt a so-called directional pattern to achieve high drainage performance. It is still another object of the present invention to provide a pneumatic tire capable of further improving performance on ice and snow.

[0005]

According to the pneumatic tire of the present invention, a pair of straight grooves defining a center block row are formed in the center region in the tire width direction in the tire circumferential direction when the tire is mounted on a vehicle when viewed from the front. The zigzag grooves are extended in the tire circumferential direction, and the zigzag grooves are respectively extended in the tire circumferential direction, and the second block rows are arranged between the linear grooves and the zigzag grooves. Each of the inclined main grooves that define the shoulder block row along with the linear grooves and the zigzag grooves on the outer side in the tire width direction is opened from each linear groove to the tread tread edge, in a direction away from the tread center upward from below. Extend, the zigzag groove and the inclined main groove have a common portion, and the angle between the inclined main groove and the tire circumferential direction in the vicinity of the opening edge of each inclined main groove to the linear groove is 10 °. Along with 40 °, a plurality of sipes are provided in each of the blocks constituting each block row, and each of the zigzag grooves is formed from a long side and a short side, and at least a part of the long side is formed. A common portion is provided with the inclined main groove, and the long side portion extends in a direction away from each other upward from below, and the short side portion,
Extending in a direction approaching each other from below to above,
The angles of the long side and the short side with respect to the tire circumferential direction are both acute angles, and the distance of each zigzag groove from the tread center is 17 to 35% of the tread tread width. Here, the tread tread width refers to the tread tread width, in other words, the maximum width in the width direction of the tread when the load, tire pressure, and rim satisfy the following conditions. That is, the applied load refers to the maximum load (maximum load capacity) of a single wheel in the applicable size described in the JATMA Year Book, and the tire pressure refers to the maximum value of the single wheel in the applicable size described in the above standard. The rim refers to the air pressure corresponding to the load (maximum load capacity), and the rim refers to the standard rim in the applicable size described in the above standard.

In the pneumatic tire according to the present invention, a pair of linear grooves are provided in the center area in the tire width direction to form the center block row, so that the center block row has a sufficient ground contact area in the center area in the tire width direction. As a result, the center block row also serves to separate the left and right treads in the tire width direction, as well as exhibiting excellent braking and driving performance on dry road surfaces, especially on road surfaces with low friction coefficients. Therefore, water can be diverted right and left on a wet road surface, and excellent drainage performance can be exhibited.

[0007] Further, zigzag grooves extending in the tire circumferential direction are provided on the outer side in the tire width direction of the respective linear grooves, and openings are formed on the tread tread edges extending from the respective linear grooves and positioned on the outer side in the tire width direction. By providing an inclined main groove extending in a direction away from the tread center upward from below and sharing a part of the zigzag groove, the second divided by the linear groove, the zigzag groove and the inclined main groove is provided. Each block of the block row, and each block of the shoulder block row divided by the zigzag groove and the inclined main groove, can have a block edge component in the tire width direction, braking performance and driving performance on ice and snow, That is, the performance on ice and snow can be improved.

By providing the inclined main grooves, water in the central region in the tire width direction can be discharged more efficiently to the outer side in the tire width direction of the tread tread edge. In the case where the angle formed by the inclined main groove and the tire circumferential direction in the vicinity of the opening edge of the tire is 10 ° to 40 °,
Excellent drainage performance can be secured.

In addition, each block constituting the center block sequence, each block constituting the second block sequence,
By providing a plurality of sipes in each of the blocks constituting the shoulder block row, not only can the block edge component in the tire width direction of each of the above blocks be increased, but also the optimization of the block rigidity can be achieved. This makes it possible to exhibit the basic performance on ice and snow as a winter tire.

On the premise of the above configuration, each of the zigzag grooves is formed from a long side portion and a short side portion, and at least a part of the long side portion and the inclined main groove have a common portion. By extending the long sides in the direction away from each other upward from below and the short sides in the direction approaching each other upward from below, the long sides are: Based on the extending direction, it is possible to contribute to securing high drainage performance, which was difficult with the conventional zigzag groove and the lateral groove, and the short side portion is provided in each block located on both sides in the width direction. Since a block edge component in the tire width direction can be provided, it is possible to contribute to securing high performance on ice and snow.

The rigidity of each block is increased by setting the angles of the long side and the short side with respect to the tire circumferential direction to acute angles, and making each of the inner angles of the blocks adjacent to the zigzag groove at 40 ° or more. Level, and the performance on ice and snow, the kinetic performance on dry road surfaces, and the wear resistance performance can be respectively improved.

The distance of each of the zigzag grooves from the tread center is set to 17 to 35% of the tread tread width.
The long and short sides of the zigzag groove can exhibit both high performance on ice and snow and high drainage performance at a high level. Conversely, when the distance of each of the zigzag grooves from the tread center is set to less than 17% of the tread tread width, the zigzag grooves are biased toward the tread center side, thereby reducing the drainage performance in the tire width direction outside. If it cannot be set to a high level, and if it exceeds 35%, the zigzag grooves are offset to the tread tread edge side, so that the rigidity of each block constituting the shoulder block row is reduced and each block may be unevenly worn. . Here, the distance of each of the zigzag grooves from the tread center refers to the distance from the midpoint of the center line to the tread center on the long side of the zigzag groove.

Preferably, in such a pneumatic tire, the center block row is preferably partitioned by providing an upwardly convex sub-groove having a substantially mountain shape, and each block constituting the center block row is shaped like an arrow that tapers downward. Block. According to this, since the sub-groove can be set substantially in parallel with the tread-side shape of the tread contact surface, it is possible to improve both the driving performance and the braking performance on ice and snow road surfaces, that is, the performance on ice and snow is at a high level. Can be secured.

Preferably, the width of the arrow-shaped block is gradually reduced from above to below, and the width of the lower side is set to be 80 to 90% of the width of the upper side. The lower width,
If the width is less than 80% of the width on the upper side, not only the block edge component in the tire width direction on the lower side of the block cannot be sufficiently secured, but also the arrow-shaped block due to its shape. If it exceeds 90%, it is not possible to secure a sufficient block edge component in the tire width direction at the portion where the block width gradually decreases. According to this, it is possible to sufficiently secure the block edge component in the tire width direction as a whole block without fear of uneven wear of the arrow-shaped block, and thus it is possible to secure a high level of performance on ice and snow.

[0015] Preferably, the length of the long side of the zigzag groove is 1.3 to 2 times the length of the short side. If the length of the long side of the zigzag groove is less than 1.3 times the length of the short side, the length of the long side cannot be sufficiently secured, and it is difficult to secure drainage performance at a high level. If it exceeds 2.0 times, it is difficult to secure a sufficient block edge component in the tire width direction for blocks located on the left and right of the zigzag groove, and it is difficult to secure a high level of performance on ice and snow. According to such a pneumatic tire, both drainage performance and performance on ice and snow can be ensured at a high level.

Here, a branch groove for further dividing each block of the shoulder block row into sub-blocks is provided substantially at the center of each block constituting the shoulder block row in the tire circumferential direction from the outer side of the tread tread edge in the tire width direction. In the case of extending in the direction inside, if the sub-block constituting each block of the shoulder block row can have a block edge component in the tire width direction, and if the performance on ice and snow can only be further improved, Instead, the drainage performance can be enhanced by the branch groove itself, and the short side of the zigzag groove can be improved by setting the block pitch length of the sub-blocks of the shoulder block row to almost half the groove pitch length of the zigzag groove. The long side portion extending relatively in the circumferential direction of the tire can be set relatively long with respect to the portion, thereby eliminating the zigzag groove. It is possible to further increase the contribution to the performance.

Here, the branch groove is further branched into two branch grooves before being opened to the zigzag groove. One of the branch grooves extends at least to the long side of the zigzag groove, and the other branch groove has a shorter length. By extending to the side, a new sub-block can be further formed in each block of the shoulder block row by the zigzag groove and the two branch grooves, so that the new sub-block has a tire width. Since it is possible to have a block edge component in the direction, not only the performance on ice and snow can be further improved, but also the drainage performance can be further improved by the branch groove itself. The block is further divided into sub-blocks by opening branch grooves extending at least to the long sides of the zigzag grooves into straight grooves. Since the sub-blocks constituting each block of the second block row can have a block edge component in the tire width direction, not only can the performance on ice and snow be further improved, but also the drainage performance can be improved by the grooves themselves. Can also be increased.

On the other hand, an inclined sub-groove for further dividing each block of the shoulder block row into sub-blocks is provided substantially at the center of each block constituting the shoulder block row in the tire circumferential direction from the outer side in the tire width direction of the tread tread edge. In the case of extending inward in the tire width direction, sub-blocks constituting each block of the shoulder block row have a block edge component in the tire width direction, so that performance on ice and snow can be further improved. Instead, the drainage performance can be enhanced by the inclined sub-groove itself,
By making the block pitch length of the sub-blocks constituting each block of the shoulder block row substantially equal to the groove pitch length of the zigzag groove, it is possible to provide more short side portions of the zigzag groove on the tire circumference, With respect to blocks located on both sides in the width direction of the short side, more block edge components in the tire width direction can be secured, so that the performance on ice and snow can be further improved.

Here, the inclined sub-groove is further extended from the tread tread edge to at least the zigzag groove,
By making the inclined sub-groove and the long side of the zigzag groove have a common portion, the long side extending relatively in the tire circumferential direction to the short side of the zigzag groove smoothly communicates with the inclined sub-groove. In addition, it is possible to realize more excellent drainage performance, and to further divide each block constituting the second block row into sub-blocks by opening the inclined sub-grooves into straight grooves, thereby forming the second block row. Since the sub-blocks constituting each block can have a block edge component in the tire width direction, not only the performance on ice and snow can be further improved, but also the drainage performance can be enhanced by the inclined sub-groove itself. Can also.

In this case, when the inclined sub-groove extends substantially parallel to the inclined main groove, each sub-block divided by the linear groove, the zigzag groove, the inclined main groove and the inclined sub-groove,
The shape of each sub-block defined by the zigzag groove, the inclined main groove, and the inclined sub-groove can be substantially rectangular, thereby increasing the block rigidity of the sub-block and further improving the performance on ice and snow. Can be improved.

The width of the inclined sub-groove is made different from the width of the inclined main groove, and each of the sub blocks defined by the inclined sub-groove of each block constituting the second block row is extended by the extension of the inclined main groove. When the slender blocks whose direction is the longitudinal direction are formed, and the slender block pairs sandwiching each inclined sub-groove are formed, the disposing intervals of the slender blocks are not made equal, so that the disposing intervals are made equal. The rigidity of the entire second block row can be improved in comparison with the above, and since a large number of sipes can be formed in each sub-block, the performance on ice and snow can be further improved.

In addition, the inclined sub-groove can be set substantially parallel to the tread-side shape of the contact patch by bending the inclined sub-groove upward before opening the straight groove. The performance can be further improved.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an exploded view of a tire tread showing an embodiment of the present invention in a tire front view in a mounting posture on a vehicle. When the vehicle is running forward, as shown by arrows in FIG. It rotates downward.

Here, a pair of straight grooves 3 extending substantially linearly in the tire circumferential direction are provided on the tread surface 2 of the tread 1 with a tread center C therebetween in the center area in the tire width direction. Each zigzag groove 5 extending in the tire circumferential direction is provided on the outer side in the tire width direction of each straight groove 3, and the tread tread edge E extending from each straight groove 3 and located on the outer side in the tire width direction is provided. Each of the zigzag grooves 5 and the inclined main grooves 6 has a common portion that is open and extends in a direction away from the tread center C from below to above and extends away from the tread center C. A second block row 7 is defined between the zigzag grooves 5 located outside the tire width direction, and a shoulder block row 8 is defined outside the zigzag grooves 5 in the tire width direction. At the opening near the edge of the inclined main grooves 6
The angle between the tire and the tire circumferential direction is set to 10 ° to 40 °, and the blocks 4 forming the respective block rows 4, 7, 8
a, 7a, and 8a are provided with a plurality of sipes.

Assuming the above configuration, each of the zigzag grooves 5 is formed of a long side portion 5a and a short side portion 5b, and the long side portion 5a and the inclined main groove 6 have a common portion.
The long sides 5a extend in a direction away from each other from below upward, and the short sides 5b extend in a direction approaching each other from below upward, and the long side 5a and The angles of the short sides 5b with respect to the tire circumferential direction are both acute angles, and the distance of each zigzag groove 5 from the tread center C is 17 to 35% of the tread tread width T. The distance of each of the zigzag grooves 5 from the tread center C is the distance from the midpoint of the long and short dash line in the drawing to the tread center C.

In this case, the center block row 4 is
An approximately chevron-shaped sub-groove 9 that is convex upward is provided and partitioned,
Each block 4a constituting the center block row 4 is an arrow-shaped block tapering downward, and the width of the arrow-shaped block 4a is gradually reduced from the upper side to the lower side. 80 to 90% of the width H, and the length of the long side 5a of the zigzag groove 5 is set to the short side 5b.
1.3 to 2 times the length of

Here, the shoulder block row 8
At approximately the center in the tire circumferential direction of each block 8a constituting
A branch groove 10 that further divides each block 8a of the shoulder block row 8 into sub-blocks 8b and 8c extends from the outer side of the tread tread edge E in the tire width direction to the inner side in the tire width direction, and before the zigzag groove 5 is opened. To form two branch grooves 10a and 10b, one of the branch grooves 10a intersects the long side 5a of the zigzag groove 5 and extends to the straight groove 3, and the other side 10b extends to the short side of the zigzag groove 5. 5b, and the block pitch length of the sub-blocks 8b and 8c constituting each block 8a of the shoulder block row 8 is set to be approximately 1/2 the groove pitch length of the zigzag groove 5. Here, each block 7a constituting the second block row 7 is further divided into sub-blocks 7b and 7c by the branch grooves 10a.

According to the pneumatic tire configured as described above, by employing a so-called directional pattern, it is possible to realize a high drainage performance, which is difficult with the conventional zigzag groove and lateral groove. , Each sub-block 4
By providing a, 7b, 7c, 8b, 8c with a sufficient block edge component in the tire width direction, it is possible to realize high performance on ice and snow.

FIG. 2 is a development view of a tire tread showing another embodiment of the present invention in a front view of a tire in a mounting posture to a vehicle.
As shown by the arrow in the figure, it rotates downward from above.

The tire tread pattern shown in FIG. 2 has the same basic structure as that shown in FIG. 1 for ensuring a high level of both drainage performance and performance on ice and snow, and the tread shown in FIG. The difference from the pan is that the inclined sub-groove 11 that further divides each block 8a of the shoulder block array 8 into sub-blocks 8b and 8c is provided substantially at the center of each block 8a that constitutes the shoulder block array 8 in the tire circumferential direction. The sub-blocks 8 extend from the outer side in the tire width direction of the tread edge E to the inner side in the tire width direction, and constitute each block 8 a of the shoulder block row 8.
The point that the block pitch length of b, 8c is substantially equal to the groove pitch length of the zigzag groove 5, the inclined sub-groove 11 is extended from the tread surface edge E to at least the zigzag groove 5, and The point where a common portion is provided with the long side portion 5a of the groove 5 and each block 7a constituting the second block row 7 is formed into the sub-blocks 7b and 7c by opening the inclined sub-groove 11 in the linear groove 3. The point is that it is further divided.

Here, the inclined sub-groove 11 extends substantially parallel to the inclined main groove 6, the width of the inclined sub-groove 11 is made different from the width of the inclined main groove 6, and each block constituting the second block row 7 is formed. 7a, the sub-blocks 7b and 7c defined by the inclined sub-grooves 11 are elongated blocks whose longitudinal direction is the extension direction of the inclined main groove 6, and a pair of elongated sub-blocks sandwiching each inclined sub-groove 11 is formed. Insert the inclined sub-groove 11 into the straight groove 3
Bending upward just before opening to

According to the embodiment shown in FIG. 2, by adopting a so-called directional pattern, it is possible to realize a high drainage performance, which is difficult with the conventional zigzag groove and the lateral groove, and to realize each sub-type. Blocks 4a, 7b, 7
By providing c, 8b, and 8c with a sufficient block edge component in the tire width direction, it is possible to achieve high performance on ice and snow. In this example, as compared with the example shown in FIG. 1, the short side portion 5b of the zigzag groove 5 is set more on the circumference of the tire, so that each of the sub blocks 7b, 7c, 8b, and 8c can further have a block edge component in the tire width direction, and can exhibit higher performance on ice and snow.

[0033]

EXAMPLES Next, a pneumatic tire according to the present invention was prototyped, and its driving performance, braking performance, performance on ice and snow, and drainage performance were evaluated.
Example tires 1 and 2 and the conventional tire have the configurations shown in FIGS. 1, 2 and 3, respectively.
Have the following specifications.

[0034]

[Table 1] * Here, the angle of the inclined main groove with respect to the tire circumferential direction is
In the vicinity of the opening edge of each inclined main groove 6 to the straight groove 3, the angle formed by the inclined main groove 6 with the tire circumferential direction is referred to as the distance between the zigzag groove 5 and the tread center C. 2, the distance from the midpoint of the dashed line of the long side 5a to the tread center C, and the minimum unit blocks 4a, 7b,
The main sipe in 7c, 8b, 8c means the sipe shown by the bold line shown in FIGS. 1 and 2, which means that the width of these sipe is larger than the width of other sipe. is not. The width on the lower side and the width on the upper side are the widths indicated by h and H in FIGS.

Each of the test tires is filled with a predetermined air pressure,
Mounted on a four-wheeled vehicle,
Driving performance, braking performance, on-snow performance and drainage performance were each evaluated by the rider's feeling. Here, the driving performance is evaluated based on a lap time when a distance of 50 m is accelerated from a stationary state, and the braking performance is 40 km / h.
From snow, the braking performance when fully braking from is measured, the performance on ice and snow is comprehensively evaluated for driving performance, braking performance, straight running performance, and cornering performance, and the drainage performance is for passing a wet road surface at a depth of 5 mm. Evaluation was made by measuring the critical speed at which the so-called hydroplaning phenomenon occurred. In addition, all the evaluation results used the conventional tire as a control, and the larger the value, the better the result. Table 2 shows the results.

[0036]

[Table 2]

As a result of the above evaluation, both the tires of Examples 1 and 2 showed excellent results in both the performance on ice and snow and the drainage performance as compared with the conventional tires. However, it can be seen that the tire 2 of the example has particularly excellent performance on ice and snow.

[0038]

Thus, according to the present invention, it is possible to propose a technique for improving the drainage performance and the performance on ice and snow, particularly for winter tires.

[Brief description of the drawings]

FIG. 1 is an expanded view of a tire tread showing an embodiment of the present invention in a tire front view in a mounting posture of a vehicle.

FIG. 2 is a developed view of a tire tread showing another embodiment of the present invention in a tire front view in a mounting posture to a vehicle.

FIG. 3 is a development view of a tire tread showing a conventional embodiment in a tire front view in a mounting posture to a vehicle.

[Explanation of symbols]

 Reference Signs List 1 tread 2 tread tread 3 straight groove 4 center block row 4a arrow-shaped block 5 zigzag groove 5a long side 5b short side 6 inclined main groove 7 second block row 7a block 7b, 7c sub-block (elongated block) 8 shoulder block Row 8a Block 8b, 8c Sub-block 9 Sub-groove 10 Branch groove 10a, 10b Branch groove 11 Inclined sub-groove C Tread center E Tread tread edge H Upper width h Lower width T Tread tread width

Claims (13)

[Claims] 1. A pair of straight grooves that define a center block row in the center area in the tire width direction and extend substantially linearly in the tire circumferential direction when the tire is mounted on a vehicle when viewed from the front of the tire. On the outer side in the tire width direction, the zigzag grooves are respectively extended in the tire circumferential direction, and a second block row is provided between each straight groove and the zigzag groove.
In addition, each of the inclined main grooves that define the shoulder block row along with each linear groove and the zigzag groove on the outer side in the tire width direction of each zigzag groove is opened from each linear groove to the tread tread edge, and the tread is directed upward from below. Extending in the direction away from the center, the angle between the inclined main groove and the tire circumferential direction in the vicinity of the opening edge of each inclined main groove to the linear groove is set to 10 ° to 40 °, and each block row is In a pneumatic tire in which a plurality of sipes are provided in each of the constituent blocks, each of the zigzag grooves is formed from a long side and a short side, and at least a part of the long side and the inclined main groove are formed. And a long side portion extending in a direction away from each other from below upward, and a short side portion in a direction approaching each other from below upward. Zaisa allowed, the long side portions and short side portions, both an acute angle with respect to the tire circumferential direction, wherein each zigzag groove, the distance from the tread center, a pneumatic tire comprising a 17 to 35% of the tread surface width. 2. The center block row is partitioned by providing an upwardly convex sub-groove having a substantially mountain shape, and each block constituting the center block row is an arrow-shaped block tapering downward. 2. The pneumatic tire according to 1. 3. The pneumatic tire according to claim 1, wherein the width of the arrow-shaped block is gradually reduced from above to below, and the width of the lower side is 80 to 90% of the width of the upper side. . 4. The pneumatic tire according to claim 1, wherein the length of the long side of the zigzag groove is 1.3 to 2 times the length of the short side. 5. A branch groove for further dividing each block of the shoulder block row into sub-blocks is provided substantially at the center of each block constituting the shoulder block row in the tire circumferential direction from the outside of the tread tread edge in the tire width direction. The block pitch length of the sub-blocks constituting each block of the shoulder block row is set to be approximately 倍 times the groove pitch length of the zigzag groove while extending inward in the direction. Pneumatic tire. 6. The branch groove is branched into two branch grooves before opening to the zigzag groove, one of the branch grooves extends at least to the long side of the zigzag groove, and the other branch groove has a shorter length. The pneumatic tire according to claim 5, which extends to a side. 7. Each of the blocks constituting the second block row is further divided into sub-blocks by opening branch grooves extending to at least long sides of the zigzag grooves into straight grooves. 7. The pneumatic tire according to 6. 8. An inclined sub-groove for further dividing each block of the shoulder block row into sub-blocks at substantially the center of each block constituting the shoulder block row in the tire circumferential direction from the tire width direction outer side of the tread tread edge. The pneumatic pump according to any one of claims 1 to 4, wherein the block pitch length is extended inward in the width direction, and a block pitch length of a sub-block constituting each block of the shoulder block row is substantially equal to a groove pitch length of the zigzag groove. tire. 9. The air according to claim 8, wherein the inclined sub-groove extends from the edge of the tread surface to at least the zigzag groove, and the inclined sub-groove and the long side of the zigzag groove have a common portion. Containing tires. 10. The pneumatic tire according to claim 8, wherein each of the blocks forming the second block row is further divided into sub-blocks by opening inclined sub-grooves into linear grooves. 11. The pneumatic tire according to claim 8, wherein the inclined sub-groove extends substantially parallel to the inclined main groove. 12. The width of the inclined sub-groove is made different from the width of the inclined main groove, and each of the sub blocks defined by the inclined sub-groove of each block constituting the second block row is extended by the inclined main groove. The pneumatic tire according to any one of claims 8 to 11, wherein the pneumatic tire is formed as an elongated block whose longitudinal direction is the existing direction and a pair of elongated blocks sandwiching each inclined sub-groove. 13. The pneumatic tire according to claim 8, wherein the inclined sub-groove is bent upward before opening the straight sub-groove.