JP2009023601A - Pneumatic tire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of improving abrasion resistance and wet performance. <P>SOLUTION: A block 5 having a tread 7 divided by a longitudinal groove 3 and a lateral groove 4 and a parallelogram as seen in a plan view and a side wall surface 8 extending inward in the radial direction from the edge 7e of the tread is provided at a tread 2. The tread 7 of the block 5 includes a base 7a extending in an optional direction in the block linearly or in a constant width making contact with a virtual tread surface Vt formed of a curved surface separated by a distance equal to the maximum thickness H of the block and chamfering type curved surfaces 7b formed at both sides of the base 7a and positioned inside the radial direction rather than the virtual tread surface Vt and extending while gradually increasing the distance with the virtual tread surface Vt to the edge 7e of the tread from the base 7a outside the radial direction from a virtual groove bottom surface Vg continued to the deepest part 3Bt of the longitudinal groove 3. The edge 7e of the tread is formed at a position separated inside the radial direction by a distance (h) of 5-40% of the maximum thickness H of the block from the virtual tread surface Vt. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pneumatic tire that can improve wear resistance and wet performance.

  2. Description of the Related Art Conventionally, a pneumatic tire having a plurality of blocks divided into vertical grooves and horizontal grooves in a tread portion is known. Such a pneumatic tire can drain the water film on the road surface by the vertical grooves and the horizontal grooves, thereby improving the wet performance. In recent years, for the purpose of improving the wear resistance of the block, it has been proposed to provide a chamfered portion with a flat slope at the boundary portion between the tread surface and the side wall surface of the block (the following patent document). 1 to 2).

JP 2002-59711 A JP 2002-172916 A

  The inventors have conducted extensive research on pneumatic tires with blocks in the tread, and as a result, there is room for further improvement in wear resistance and wet performance in chamfered chamfers with a flat slope as in the past. I found out that there is.

  The present invention has been devised in view of the above circumstances, and the maximum thickness of the block radially outward from the virtual groove bottom surface where the deepest part of the vertical groove is connected to the tread surface of the parallelogram block in plan view. A base portion that is in contact with a virtual tread surface formed of a curved surface separated by a distance equal to the length and extends linearly or with a constant width; and provided on both sides of the base portion and located radially inward of the virtual tread surface and from the base portion The main object is to provide a pneumatic tire capable of improving wear resistance and wet performance based on the inclusion of a chamfered curved surface that gradually increases the distance from the virtual tread surface to the edge of the tread surface. .

  According to the first aspect of the present invention, the tread portion is provided with a block that is divided by a longitudinal groove and a lateral groove, and the block has a parallelogram shaped tread surface in plan view and a radial direction from the edge of the tread surface. A virtual tread surface comprising a curved surface with a distance equal to the maximum thickness of the block radially outward from a virtual groove bottom surface in which the deepest portion of the vertical groove is smoothly connected to each other. A base portion that is in contact with and extends linearly or at a constant width, and is located radially inward of the virtual tread surface and provided on both sides of the base portion, and the distance from the virtual tread surface to the edge of the tread surface from the base portion And the edge of the tread surface is provided at a position separated from the virtual tread surface by a distance h of 5 to 40% of the maximum thickness of the block inward in the radial direction. The features.

  The invention according to claim 2 is the pneumatic tire according to claim 1, wherein the distance h is substantially constant in the block.

  According to a third aspect of the present invention, the base has a linear shape extending substantially in line with the longer diagonal of the tread without having a substantial width, and the chamfered curved surfaces on both sides intersect at the diagonal. A pneumatic tire according to claim 1 or 2.

  The invention according to claim 4 is the pneumatic tire according to claim 1 or 2, wherein the base portion has a substantially constant width and includes a longer diagonal line of the tread surface.

  In the invention according to claim 5, the tread portion is provided with a plurality of block rows in which the blocks are arranged in the tire circumferential direction, and the angle of the base portion with respect to the tire circumferential direction is a block belonging to a block row far from the tire equator. The pneumatic tire according to any one of claims 1 to 4, which is larger.

  According to a sixth aspect of the present invention, in the block according to the first aspect of the present invention, a corner inclined surface including the step surface and the side wall surface is chamfered at a corner portion located on both ends of the longer diagonal of the step surface. It is a pneumatic tire in any one of thru | or 5.

  According to a seventh aspect of the present invention, in the block cross section perpendicular to the longitudinal direction of the base portion, the chamfered curved surface is an arc-shaped curve that protrudes radially outward. It is a pneumatic tire.

  The invention according to claim 8 is the block cross section perpendicular to the longitudinal direction of the base portion, wherein the chamfered curved surface is a curved main portion formed of an arcuate curve convex outward in the radial direction, the curved main portion, The pneumatic tire according to any one of claims 1 to 6, comprising a flat inclined surface portion that joins a side wall surface and descends toward the side wall surface.

  The invention according to claim 9 is the pneumatic tire according to any one of claims 1 to 8, wherein at least one block has an angle of 10 to 20 degrees with respect to a tire circumferential direction of the base.

  In the pneumatic tire of the present invention, on the tread surface of the block, by grounding the base portion to the road surface, the water film on the road surface can be pushed and discharged separately to the chamfered curved surfaces on both sides of the base portion. Further, the chamfered curved surface is a curved surface extending from the base portion to the edge of the tread surface while gradually increasing the distance from the virtual tread surface. Therefore, it is sent to the edge of the tread with less resistance guided to the chamfered curved surface and efficiently drained into the vertical and / or horizontal grooves.

  In the pneumatic tire of the present invention, the rigidity of the edge of the tread surface is improved by the chamfered curved surface, so that the steering stability is prevented from being lowered. Further, by preventing large deformation of the edge of the tread surface, deformation that reduces the groove volume is suppressed, and as a result, wet performance can be further improved. In addition, the chamfered curved surface according to the present invention makes the change in the rigidity of the block more gradual as compared to the conventional chamfered portion having a flat slope. This optimizes the contact pressure distribution and thus exhibits excellent wear resistance.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a development view of the tread portion 2 of the pneumatic tire of the present embodiment. In the pneumatic tire (not shown) of the present embodiment, a tread pattern in which a plurality of blocks 5 divided by vertical grooves 3 and horizontal grooves 4 is provided in the tread portion 2 is formed.

  The tread pattern is a so-called directional pattern created so as to obtain the most effective drainage performance in the rotational direction indicated by the arrow R in FIG. In the tread pattern, the vertical groove 3 and the horizontal groove 4 are arranged substantially symmetrically about the tire equator C, except that the distance Y is shifted in the tire circumferential direction.

  The longitudinal grooves 3 are arranged on both sides of the tire equator C and continuously extend in the tire circumferential direction, and are arranged on both outer sides in the tire axial direction and continuously in the tire circumferential direction. A pair of extending second vertical grooves 3b, third vertical grooves 3c provided on both outer sides in the tire axial direction and inclined at a relatively small angle with respect to the tire circumferential direction, and further both in the tire axial direction And a pair of fourth vertical grooves 3d that are arranged on the outer side and are inclined at a relatively small angle with respect to the tire circumferential direction.

  The first vertical groove 3a and the second vertical groove 3b extend, for example, substantially parallel to the tire circumferential direction. Further, the groove width in the tire circumferential direction is changed in the second vertical groove 3b of the present embodiment. Further, the third vertical groove 3c and the fourth vertical groove 3d are, for example, at an angle β of 5 to 15 degrees with respect to the tire circumferential direction, and the position of the groove becomes the outer side in the tire axial direction as the rotation of the tire proceeds. Be inclined to. This is useful for guiding water on the road surface from the inner side to the outer side in the tire axial direction.

  The horizontal groove 4 is a first horizontal groove 4a that connects between the first vertical groove 3a and the second vertical groove 3b, and a second that connects between the second vertical groove 3b and the third vertical groove 3c. Horizontal groove 4b, a third horizontal groove 4c connecting between the third vertical groove 3c and the fourth vertical groove 3d, and a fourth horizontal groove connecting between the fourth vertical groove 3d and the tread grounding end E 4d.

  The first, second, third and fourth lateral grooves 4a, 4b, 4c and 4d form angles θ1, θ2, θ3 and θ4 with respect to the tire axial direction, respectively. These lateral grooves 4a to 4d are all inclined so that the position of the groove is away from the tire equator C as the rotation of the tire proceeds. This is useful for guiding the water on the road surface from the tire equator C side to the tread ground contact end E side, similarly to the third to fourth vertical grooves 3c and 3d. Further, the first to fourth lateral grooves 4a to 4d are arranged so as to be substantially continuous, thereby effectively draining the drainage of the first vertical groove 3a by using the ground pressure of the tire. Can lead to.

In the present embodiment, the angles θ1 to θ4 of the first to fourth lateral grooves 4a to 4d are different from each other so as to satisfy the following relationship (1).
θ1>θ2>θ3> θ4 (1)

  Thereby, the lateral groove in the central region of the tread portion 2 is made closer to the tire circumferential direction, the drainage resistance is reduced, and the wet performance is further enhanced. In addition, the lateral groove on the tread ground contact E side is brought closer to the tire axial direction to increase block rigidity and improve steering stability.

  From such a viewpoint, the angle θ1 of the first lateral groove 4a is preferably 50 degrees or more, and more preferably 60 degrees or more. If the angle θ1 is too large, the block rigidity may be excessively lowered. Therefore, the angle θ1 is preferably 80 degrees or less, more preferably 70 degrees or less. Further, the angle θ4 of the fourth lateral groove 4d is preferably 40 degrees or less, more preferably 20 degrees or less. Since the lower limit value of the angle θ4 is not particularly defined, the angle θ4 of the fourth lateral groove 4d may be parallel to the tire axial direction.

  In addition, the groove width and the groove depth of the vertical groove 3 and the horizontal groove 4 can be appropriately determined according to the custom. As an example, the groove width is preferably 3 mm or more, more preferably 5 mm or more, and preferably 20 mm or less, more preferably 15 mm or less. Similarly, the groove depth is preferably 1.5 mm or more, more preferably 3 mm or more, and preferably 8 mm or less, more preferably 6 mm or less.

  With the vertical grooves 3 and the horizontal grooves 4 as described above, the tread portion 2 has a center rib 6 extending continuously in the tire circumferential direction between the pair of first vertical grooves 3a and 3a, and the first vertical grooves 3a. The first block 5a divided between the second vertical grooves 3b is divided between the first block row Br1 arranged in the tire circumferential direction, and the second vertical grooves 3b and the third vertical grooves 3c. The second block 5b in which the second blocks 5b formed are arranged in the tire circumferential direction, and the third block 5c partitioned between the third vertical groove 3c and the fourth vertical groove 3d is the tire circumferential direction. And a fourth block row Br4 in which the fourth block 5d divided between the fourth vertical groove 3d and the tread ground contact E is arranged in the tire circumferential direction is formed.

  As shown in FIG. 2, each of the first to third blocks 5a to 5c has a tread surface 7 having a parallelogram shape in plan view and a side wall surface 8 extending radially inward from the edge 7e of the tread surface. .

  The tread surface 7 is a radially outer surface of the block 5 that comes into contact with the road surface when traveling on a normal flat asphalt road surface. In the present embodiment, the tread surface 7 includes a base portion 7a and chamfered curved surfaces 7b and 7b on both sides thereof.

  As shown in FIG. 3, the base portion 7a extends in contact with the virtual tread surface Vt and extends across the block 5 in a linear shape. Here, “crossing” means to divide the block into two by the base portion 7a, and does not mean to extend in the tire axial direction. The “virtual tread surface” Vt is a curved surface that is spaced radially away from the virtual groove bottom surface Vg, in which the deepest portions 3Bt of the vertical grooves 3 are smoothly connected, by a distance equal to the maximum thickness H of the block 5. In this embodiment, the maximum thickness H of each block 5 is the same. Further, the deepest portion 4Bt of the lateral groove 4 is also on the virtual groove bottom surface Vg.

  As shown in FIG. 4 and FIG. 5 which is a BB cross-sectional view thereof, the base portion 7a of this embodiment is substantially the same as the longer diagonal line CL of the parallelogram-shaped tread surface 7 without having a substantial width. The line extends in line with. Such a base portion 7a may appear as a ridge line that can be observed with the naked eye on the tread surface 7, or may not appear as a ridge line.

  As shown in FIG. 5, the chamfered curved surface 7b is provided on both sides of the base portion 7a. That is, in this embodiment, the chamfered curved surfaces 7b on both sides intersect with the diagonal line CL. The chamfered curved surface 7b is located radially inward of the virtual tread surface Vt, extends from the base 7a to the tread edge 7e, and gradually increases the distance from the virtual tread surface Vt toward the tread edge 7e. It consists of a smooth three-dimensional curved surface. This three-dimensional curved surface is formed of a smooth arc-shaped curve that protrudes outward in the tire radial direction in a block cross section perpendicular to the longitudinal direction of the base portion 7a.

  The operation of the tread 7 will be described. The base portion 7a extending in contact with the virtual tread surface Vt has the maximum thickness H of the block and protrudes most radially outward from the virtual groove bottom surface Vg. Therefore, the base 7a can be grounded first on the road surface in the tread surface 7 when the tire is loaded. When the base portion 7a is grounded to the wet road surface, the water film is pushed to both sides of the base portion 7a by the pressure.

  Further, the chamfered curved surfaces 7b provided on both sides of the base portion 7a are located on the inner side of the virtual tread surface Vt, and the distance from the virtual tread surface gradually increases toward the edge 7e of the tread surface. Therefore, the waste water pushed by the base portion 7a can be effectively discharged to the vertical groove 3 and / or the horizontal groove 4 as the ground contact of the chamfered curved surface 7b proceeds. Thus, since the drainage performance of the pneumatic tire of the present invention is improved in units of blocks, the wet performance is greatly improved.

  In particular, as in the present embodiment, when the base portion 7a is formed in a linear shape having substantially no width, the contact pressure of that portion becomes larger, and an effective water film pushing action can be obtained. .

  In order to more effectively exert the above-described water film pushing action, the angle α of the base portion 7a with respect to the tire circumferential direction is preferably 50 degrees or less, more preferably 40 degrees or less, and even more preferably 30 degrees or less, most preferably It is desirable to include the block 5 of preferably 20 degrees or less. If the angle α is too small, the parallelogram shape of the tread surface 7 becomes excessively long, which may lead to deterioration in steering stability. From such a viewpoint, the angle α is preferably 10 degrees or more.

In addition, it is desirable that the angle α of the base portion 7a with respect to the tire circumferential direction is larger as the block belongs to the block row farther from the tire equator C. In the pneumatic tire of the present embodiment, when the angles of the base portion 7a of the first block 5a, the second block 5b, and the third block 5c with respect to the tire circumferential direction are α1, α2, and α3, the following relationship (2 ) Is satisfied.
α1 <α2 <α3 (2)
As a result, a more effective drainage action can be obtained on the tire equator side where the ground pressure increases during normal driving. In addition, on the tread ground contact E side, a decrease in steering stability is suppressed. Preferably, the angle α1 is 10 to 20 degrees.

  In the pneumatic tire of the present invention, the rigidity of the edge 7e of the tread is effectively enhanced by the chamfered curved surface 7b. Accordingly, during running, large deformation at the edge 7e of the tread surface, for example, deformation that reduces the groove volume can be suppressed, and the wet performance is further improved.

  Further, the chamfered curved surface 7b is a curved surface that gradually extends from the base portion 7a to the edge 7e of the tread surface while gradually increasing the distance from the virtual tread surface Vt. Such a chamfered curved surface has a gentler change in block rigidity than a conventional chamfered portion formed only of a flat slope. Therefore, the contact pressure of the chamfered curved surface 7b can be smoothly lowered toward the edge 7e of the tread. This demonstrates excellent wear resistance.

  Furthermore, in order to exhibit the above-mentioned effect, the edge 7e of the tread is provided at a position separated from the virtual tread surface Vt by a distance h of 5 to 40% of the maximum thickness H of the block 5 inward in the radial direction. That is, when the radial distance h between the tread edge 7e and the virtual tread surface Vt is less than 5% of the maximum thickness H of the block 5, the above-described drainage performance is improved and the contact pressure at the tread edge 7e is reduced. Can not be fully planned. Conversely, when the radial distance h between the tread edge 7e and the virtual tread surface Vt exceeds 40% of the maximum thickness H of the block 5, drainage performance is improved, but the ground contact area of the block 5 is significantly reduced. There is a risk of lowering the steering stability. From this point of view, the distance h is preferably 10% or more of the maximum thickness H of the block 5, preferably 30% or less, more preferably 20% or less.

  In the present embodiment, in the first to third blocks 5a to 5c, the distance h is formed substantially constant on the four circumferences of the tread edge 7e. That is, as shown in FIG. 4, the edge 7e of the tread includes a lateral edge 7e1 facing the lateral groove 4 and a longitudinal edge 7e2 facing the longitudinal groove 3 (or the tread grounding end E). The distance h at the edge 7e1 and the vertical edge 7e2 is substantially constant.

  However, as another embodiment, the distance h may be changed. For example, the distance h may be determined as a function of the distance from the base 7a. For example, as shown in FIG. 6, at the edge 7e of the tread, the distance h can be increased as the distance from the base 7a increases. In the example of FIG. 6, the radial distance h2 from the virtual tread surface at the intersection Pa between the horizontal edge 7e1 and the vertical edge 7e2 that is located farthest from the base 7a is equal to the virtual tread surface at the edges on both ends of the base 7a. It is formed to be larger than the radial distance h1.

  As still another embodiment, for example, in any block 5, the distance h may be different between the vertical edge 7e2 on the tire equator side and the vertical edge 7e2 on the tread ground contact end E side. For example, the distance h of the vertical edge 7e2 on the tread ground contact end E side can be made larger than that of the vertical edge 7e2 on the tire equator C side. Thereby, more drainage on the road surface can be guided to the vertical edge 7e2 through the chamfered curved surface 7b on the tread ground contact end E side having a large distance h. Accordingly, the drainage performance is further improved.

  Further, as shown in FIG. 4, the block 5 is a substantially drop-shaped contour plane that chamfers the tread surface 7 and the side wall surface 8 at the corner portions 7 </ b> P positioned on both ends of the longer diagonal line CL of the tread surface 7. A corner slope 9 is provided. The corner slope 9 increases the rigidity of the corner portion 7P, and mitigates the impact when the block 5 contacts the road surface. This serves to effectively prevent wear resistance, particularly heel and toe wear in which both the corner portions 7P of the block 5 are worn early.

  Furthermore, as shown in FIG. 4, the length S along the diagonal line CL of the corner slope 9 measured in plan view is the total length of the diagonal line CL (this total length is represented by Ls + 2 × S in FIG. 4). 5-25% of the If the length S of the corner slope 9 is less than 5% of the total length of the diagonal line, the above-mentioned impact mitigation ability tends to be insufficient. Conversely, if the length S exceeds 25%, the ground contact area decreases and the steering stability is reduced. May worsen.

  FIG. 7 and FIG. 8, which is a BB cross-sectional view thereof, show another embodiment of the present invention. In this embodiment, the base portion 7 a has a substantially constant width W and includes the longer diagonal line CL of the tread surface 7. The width W of the base portion 7a is not particularly limited, but is preferably 80% or less, more preferably 40% or less of the maximum width Wt of the tread surface 7 orthogonal to the base portion 7a of the block 5. That is, if the width W of the base portion 7a exceeds 80% of the maximum width Wt of the tread surface 7, the above-described effective drainage action may not be obtained.

  In each of the above embodiments, the chamfered curved surface 7b is formed only by a smooth three-dimensional curved surface that is convex outward in the tire radial direction, but is not limited to such an embodiment. For example, as shown in FIG. 9 and FIG. 10 which is a CC cross-sectional view thereof, the chamfered curved surface 7b is formed of an arcuate curve that protrudes radially outward in a block cross section perpendicular to the longitudinal direction of the base portion 7a. It may be composed of a curved main portion 7 b 1 and a flat inclined surface portion 7 b 2 that joins the curved main portion 7 b 1 and the side wall surface 8 and descends toward the side wall surface 8. In order to improve wear resistance and the like, the chamfering width Wm of the inclined surface portion 7b2 is preferably about 0.5 to 5.0 mm. As another embodiment, instead of the inclined surface portion 7b2, a curved sub-portion made of an arcuate curve having a radius of curvature different from that of the curved main portion 7b1 may be used.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the illustrated embodiment, and it is needless to say that the present invention can be modified and implemented in various modes.

  Test tires were prototyped based on the tread pattern in FIG. 1 and the specifications in Table 1, and they were tested for wear resistance and wet performance. The test method is as follows.

<Wet performance>
The average lateral G of the front wheels was calculated when the following test vehicle was used to drive on a course with a water depth of 10 mm and a length of 20 m on an asphalt road surface with a radius of 100 m. The traveling speed was 70 to 100 km / H with a step of 10 km / h. A result is shown by the index | exponent which sets the prior art example to 100. The larger the value, the better.
Vehicle: Toyota Supra Tire Size: 250/640 R18
Wheel size: 9.0J × 18

<Existence of uneven wear and steering stability>
The above test vehicle was used to drive the circuit on the road surface that was sprinkled by one driver. The driving stability was evaluated in 10 stages (10-point method) based on the driver's sensuality. The larger the value, the better. In addition, after the test run, the wear situation of each block was observed with the naked eye, and the presence or absence of uneven wear and its size were confirmed.

  Test results and the like are shown in Table 1, and a significant effect of the present invention was confirmed.

It is an expanded view of the tread part of the pneumatic tire of this embodiment. It is a fragmentary perspective view of the tread part. It is an AA expanded sectional view of FIG. It is a top view of a block. It is the BB sectional drawing. It is a perspective view of a block. It is a top view of the block which shows other embodiment which concerns on this invention. It is the BB sectional drawing. It is a top view of the block which shows other embodiment which concerns on this invention. It is the CC sectional drawing. It is sectional drawing (equivalent to BB of FIG. 4) of the block of the comparative example 1. It is sectional drawing (equivalent to BB of FIG. 4) of the block of the comparative example 2.

Explanation of symbols

2 Tread portion 3 Vertical groove 4 Horizontal groove 5 Block 7 Tread surface 7a Base portion 7b Chamfered curved surface 8 Side wall surface Vt Virtual tread surface Vg Virtual groove bottom surface H Maximum thickness h of block Radial direction between the virtual tread surface and the edge of the tread surface distance

Claims (9)

The tread part is provided with a block divided by vertical and horizontal grooves,
The block comprises a tread surface having a parallelogram shape in plan view and a side wall surface extending radially inward from an edge of the tread surface,
The tread surface is in contact with a virtual tread surface formed of a curved surface with a distance equal to the maximum thickness of the block radially outward from the virtual groove bottom surface in which the deepest portion of the vertical groove is smoothly connected and extends linearly or with a constant width. The base,
A chamfered curved surface provided on both sides of the base and positioned radially inward of the virtual tread surface and extending gradually from the base to the edge of the tread surface while gradually increasing the distance from the virtual tread surface, and The pneumatic tire is characterized in that an edge of the tread surface is provided at a position separated from the virtual tread surface by a distance h of 5 to 40% of the maximum thickness of the block inward in the radial direction.   The pneumatic tire according to claim 1, wherein the distance h is substantially constant in the block.   3. The pneumatic device according to claim 1, wherein the base portion has a linear shape extending substantially in line with a longer diagonal line of the tread surface without having a substantial width, and the chamfered curved surfaces on both sides intersect at the diagonal line. tire.   The pneumatic tire according to claim 1, wherein the base portion has a substantially constant width and includes a longer diagonal line of the tread surface. 5. The tread portion is provided with a plurality of block rows in which the blocks are arranged in the tire circumferential direction, and the angle of the base portion with respect to the tire circumferential direction is larger for blocks belonging to the block row farther from the tire equator. The pneumatic tire according to Crab.   6. The air according to claim 1, wherein the block is provided with a corner inclined surface including the step surface and the side wall surface at a corner portion located on both ends of the longer diagonal of the step surface. Enter tire.   The pneumatic tire according to any one of claims 1 to 6, wherein the chamfered curved surface is an arc-shaped curve that protrudes radially outward in a block cross section perpendicular to the longitudinal direction of the base portion.   In the block cross section perpendicular to the longitudinal direction of the base portion, the chamfered curved surface includes a curved main portion formed of an arc-shaped curve protruding outward in the radial direction, the curved main portion and the side wall surface, and the side wall surface. The pneumatic tire according to any one of claims 1 to 6, comprising a flat inclined surface portion that descends toward the front.   The pneumatic tire according to any one of claims 1 to 8, wherein at least one block has an angle of 10 to 20 degrees with respect to a tire circumferential direction of the base.

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