JP2013184606A - Pneumatic tire for irregular ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve steering response while maintaining performance of absorbing disturbance from an irregular road surface.SOLUTION: In a pneumatic tire 1 for irregular ground, a block row 3 includes a center block row 3A that consists of center blocks 4A, and a middle block row 3B that consists of middle blocks 4B. The center block 4A has a vertically long shape with a circumferential length L2a of a tread 7A larger than an axial length W2a. In the center block row 3A, a total sum Sc of the circumferential length L2a of the center block 4A is 51 to 61% of tire circumferential length L3 of the center block 4A. An expansion length L6 of an inner periphery 7Bi of a tread surface 7B of the middle block 4B, and a tire equator C, is 26 to 36% of a tread expansion half width 0.5TW.

Description

  The present invention relates to a pneumatic tire for running on rough terrain that can improve steering wheel response while maintaining the ability to absorb disturbance from uneven road surfaces.

  For example, various types of pneumatic tires for running on uneven terrain used for ATV (ALL TERRAIN VEHICLE) for running on rough terrain such as sand and muddy ground have been proposed (see, for example, Patent Document 1 below).

  In this type of pneumatic tire, for example, a block row in which a plurality of blocks are spaced apart in the tire circumferential direction is provided in a tread portion. Such a block can greatly penetrate the rough terrain surface and is useful for improving the traction performance.

  In addition, in order to improve the handle response on rough road surfaces, center blocks arranged on the tire equator or adjacent to the tire equator are arranged densely in the tire circumferential direction so that the edge component in the tire circumferential direction is reduced. It is effective to increase.

JP 2004-189193 A

  However, if the center blocks are densely arranged in the tire circumferential direction, there is a problem that the handle is easily taken due to a disturbance from an uneven road surface, and the disturbance absorbing performance is likely to be lowered.

  The present invention has been devised in view of the above circumstances, and the total sum of the circumferential lengths of the center block and the development length of the inner edge of the tread surface of the middle block in the tire axial direction and the tire equator are predetermined. The main object is to provide a pneumatic tire for running on rough terrain that can improve steering response while maintaining the ability to absorb disturbance from rough terrain.

  The invention according to claim 1 of the present invention is a pneumatic tire for running on uneven terrain, wherein the tread portion includes a block row in which a plurality of blocks are spaced apart in the tire circumferential direction. A center block row consisting of center blocks arranged on or adjacent to the tire equator, and a middle block row consisting of middle blocks arranged outside the center block in the tire axial direction, the center block comprising: A tire in which the circumferential length of the tread surface is longer than the axial length, and the center block row has a total sum of the circumferential lengths of the center blocks at a center position in the axial direction of the tread surface of the center block. 51-61% of the length of one circumference, and further, the development in the tire axial direction of the inner edge of the tread surface of the middle block in the tire axial direction and the tire equator Saga, characterized in that it is a 26 to 36% of the tread half width.

  In the invention according to claim 2, in the center block row, the center blocks are arranged via a transverse groove, and each middle block projects the transverse groove to the middle block row side in the tire axial direction. The pneumatic tire for traveling on rough terrain according to claim 1, wherein the pneumatic tire is disposed across the entire range in the tire circumferential direction of the region.

  According to a third aspect of the present invention, the block row includes at least one shoulder block row composed of shoulder blocks arranged on the outer side in the tire axial direction of the middle block, and the shoulder block extends in the tire axial direction. 3. The pneumatic tire for traveling on rough terrain according to claim 1, wherein the pneumatic tire is disposed on one side in a tire circumferential direction with respect to the adjacent middle blocks.

  According to a fourth aspect of the present invention, in the tire circumferential direction displacement amount of the shoulder block and the middle block is 5 to 20% of the circumferential length of the tread of the center block. This is a pneumatic tire for traveling on rough terrain.

  In the invention according to claim 5, the shoulder block row includes an inner shoulder block row made of an inner shoulder block arranged on the inner side in the tire axial direction, and an outer side arranged on the outer side in the tire axial direction than the inner shoulder block. An outer shoulder block row comprising shoulder blocks, the inner shoulder block having an outer recess recessed inward in the tire axial direction on an outer wall portion facing outward in the tire axial direction, and the outer shoulder block is in the tire axial direction The inner side wall portion facing inward has an inner concave portion recessed outward in the tire axial direction, and the outer concave portion of the inner shoulder block and the inner concave portion of the outer shoulder block face each other in the tire axial direction. Or it is a pneumatic tire for rough terrain travel according to 4.

  In this specification, unless otherwise specified, the dimensions of each part of the tire are values specified in an unloaded natural state in which a rim (not shown) is assembled and filled with an internal pressure of 30 kPa.

  In the pneumatic tire for traveling on rough terrain of the present invention, a block row in which a plurality of blocks are spaced apart in the tire circumferential direction is provided in the tread portion. Such a pneumatic tire can increase the amount of the block biting into the rough road surface, and can exhibit traction performance.

  The block row includes a center block row made up of center blocks arranged on or adjacent to the tire equator, and a middle block row made up of middle blocks arranged outside the center block row in the tire axial direction.

  The center block is formed in a vertically long shape in which the circumferential length of the tread surface is larger than the axial length. In the center block row, the sum of the circumferential lengths of the center blocks is limited to 51 to 61% of the circumferential length of the tire at the axial center position of the tread surface of the center block.

  Such a center block row can exhibit an edge component in the tire circumferential direction of the center block, and thus can improve steering response.

  Moreover, since the sum of the circumferential lengths of the center blocks in the center block row is limited to 61% or less of the circumferential length of the tire, the edge component in the tire circumferential direction of the center block becomes excessively large. Can be suppressed. Thereby, it can suppress that a handle | steering-wheel is taken by the disturbance from an uneven road surface, and can maintain disturbance absorption performance.

  Further, the development length in the tire axial direction between the inner edge of the tread surface of the middle block in the tire axial direction and the tire equator is limited to 26 to 36% of the half width of the tread development. Accordingly, the middle block can exhibit an edge component together with the center block at a position farther from the tire equator than the conventional tire, and the steering wheel response can be improved.

  In addition, since the developed length of the middle block is limited to 36% or less of the half width of the tread, the middle block can be disposed within the tread contact surface during straight travel, and the edge component can be reliably exhibited. Can do.

It is an expanded view of the tread part which shows the pneumatic tire for rough terrain travel of this embodiment. It is AA sectional drawing of FIG. It is an enlarged view of a center block and a middle block. It is an enlarged view of an inner side shoulder block and an outer side shoulder block.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1 and FIG. 2, traveling on rough terrain such as sand or muddy ground as a pneumatic tire (hereinafter simply referred to as “tire”) 1 for traveling on rough terrain of the present embodiment. The target tire for ATV (ALL TERRAIN VEHICLE) is exemplified.

  The tread portion 2 of the tire 1 is provided with a block row 3 in which blocks 4 divided by tread grooves 5 are spaced apart in the tire circumferential direction. Thereby, a block pattern is formed in the tread portion 2.

  Such a block 4 can increase the amount of biting into the rough terrain road surface, and can exhibit edge components in the tire circumferential direction and the tire axial direction, thereby improving traction performance and turning performance. Moreover, since the tread groove 5 separating the blocks 4 is formed wide, clogging of mud and the like can be prevented. In order to effectively exhibit such an action, the block 4 preferably has a block height H1 from the groove bottom 5b of the tread groove 5 to the tread surface 7 which is a grounding surface, for example, about 12 to 16 mm.

  The sparse arrangement of the blocks 4 is the area of the tread surface 7 of all the blocks 4 with respect to the total area Sa of the outer surface of the tread portion 2 (the total area of the outer surface of the tread portion 2 when it is assumed that all the tread grooves 5 are filled). It is grasped by the land ratio Sb / Sa which is the sum Sb.

  If the land ratio Sb / Sa is excessively small, the traction performance on a hard hard road or medium road may not be sufficiently maintained. Conversely, even if the land ratio Sb / Sa is too large, the traction performance on a soft road may not be sufficiently maintained. From such a viewpoint, the land ratio Sb / Sa is preferably 20 to 30%.

  The block row 3 of the present embodiment includes a center block row 3A composed of a center block 4A arranged on or adjacent to the tire equator C, and a middle block arranged on the outer side in the tire axial direction of the center block 4A. 4B includes a middle block row 3B, and a shoulder block row 3C including shoulder blocks 4C disposed on the outer side in the tire axial direction of the middle block 4B.

  The center block row 3A of the present embodiment is composed of a pair of center blocks 4A and 4A adjacent to each other with a center sub-groove 6A extending on the tire equator C interposed therebetween. The pair of center blocks 4A and 4A are spaced apart in the tire circumferential direction via lateral grooves 5A extending in the tire axial direction.

  As shown in FIG. 2, each center block 4 </ b> A includes a tread surface 7 </ b> A and a wall portion 8 </ b> A that extends inward in the tire radial direction from the tread surface 7 </ b> A to the groove bottom 5 b of the tread groove 5 to define a block contour. Further, as shown in FIG. 1, each center block 4A is formed in a vertically long rectangular shape in which the circumferential length L2a of the tread surface 7A is larger than the axial length W2a.

  Since each of these center blocks 4A can effectively exhibit an edge component in the tire circumferential direction, it is possible to improve steering wheel response on an uneven road surface. Further, since the center block 4A is formed in a vertically long rectangular shape, the rigidity in the tire circumferential direction can be increased, and the traction performance can be improved.

  Furthermore, in the present embodiment, the pair of center blocks 4A, 4A can compress and grip sand, soil, etc. on the rough road surface interposed in the center sub-groove 6A in the tire axial direction. Can be suppressed, and straight running stability can be improved.

  In order to effectively exhibit the above action, each center block 4A has a circumferential length L2a of about 30 to 38% of a tread deployment half width 0.5 TW from the tire equator C to the tread end 2t. The length W2a is preferably about 8 to 16% of the tread development half width 0.5 TW. Further, the center sub-groove 6A preferably has a groove width W3 of about 2 to 6% of the tread developed half width 0.5TW and a groove depth D3 (shown in FIG. 2) of about 80 to 95% of the block height H1.

  Further, in the center block row 3A of the present embodiment, the total length Sc of the circumferential length L2a of the center block 4A is one circumference of the tire at the axial center position 7Ac (shown in FIG. 3) of the tread surface 7A of the center block 4A. It is limited to 51 to 61% of the length L3.

  In such a center block row 3A, the sum Sc is limited to 51% or more of the tire circumferential length L3, so that the edge component in the tire circumferential direction by the center block 4A can be reliably increased. The handle responsiveness can be effectively improved.

  In addition, since the sum Sc is limited to 61% or less of the circumferential length L3 of the tire, the center block row 3A can suppress an excessive increase in the edge component in the tire circumferential direction due to the center block 4A. Thereby, the tire 1 can suppress the handle from being taken due to disturbance from an uneven road surface, and can reliably maintain disturbance absorbing performance.

  In order to effectively exhibit such an action, the total amount Sc is preferably 54% or more of the tire circumferential length L3, and more preferably 58% or less.

  As shown in FIG. 3, the pair of center blocks 4A, 4A has a pair of projecting corners of an inner wall portion 8Ai facing the center sub-groove 6A and a pair of end wall portions 8At, 8At on both sides in the tire circumferential direction. A pair of corner portions 9a, 9a cut out in a corner shape are provided. Such corners 9a, 9a can surely increase the edge components in the tire axial direction and the tire circumferential direction of the center blocks 4A, 4A, and can improve the steering response.

  Further, the respective corners 9a, 9a of the pair of center blocks 4A, 4A are arranged facing each other in the tire axial direction. Further, the corners 9a and 9a of the pair of center blocks 4A and 4A are arranged facing the corners 9a and 9a of the pair of center blocks 4A and 4A adjacent in the tire circumferential direction in the tire circumferential direction. .

  Accordingly, the corners 9a and 9a of the pair of center blocks 4A and 4A and the corners 9a and 9a of the pair of center blocks 4A and 4A adjacent in the tire circumferential direction are rough terrain interposed in the lateral groove 5A. Sand and soil on the road surface can be compressed and gripped, and traction performance and handle response can be effectively improved.

  In order to effectively exhibit such an action, each corner 9a has a circumferential length L4a and an axial length W4a of about 1 to 3% of the circumferential length L2a of the center block 4A. The depth (not shown) is preferably about 80 to 95% of the block height H1.

  In addition, a vertically long recess 13 extending in the tire circumferential direction is provided on the tread surface 7A of each center block 4A. Such a recess 13 can ease the rigidity of the center block 4A having a vertically long rectangular shape, and can reliably improve road surface followability with respect to uneven terrain, thereby effectively improving the traction performance and steering wheel responsiveness when traveling straight. sell. As shown in FIG. 1, the recess 13 has a circumferential length L5a of about 50 to 60% of the circumferential length L2a of the center block 4A, and an axial length W5a of the axial length W2a of the center block 4A. About 2 to 4% of is desirable.

  In the middle block row 3B, middle blocks 4B arranged on the outer side in the tire axial direction of the center block 4A are spaced apart in the tire circumferential direction. As shown in FIG. 2, the middle block 4B includes a tread surface 7B and a wall portion 8B. Further, as shown in FIG. 1, the middle block 4B is also formed in a vertically long rectangular shape in which the circumferential length L2b of the tread surface 7B is larger than the axial length W2b.

  Similar to the center block 4A, the middle block 4B can effectively increase the edge component in the tire circumferential direction and the rigidity in the tire circumferential direction, and can improve the steering response and the traction performance. In the middle block 4B, the circumferential length L2b and the axial length W2b are preferably in the same range as the center block 4A.

  As shown in FIG. 3, the middle block 4B of the present embodiment has a tread deployed half width of 0.5 TW (see FIG. 3). 1 to 26-36%.

  As described above, the development length L6 is limited to 26% or more of the tread development half-width of 0.5 TW, so that the edge component of the middle block 4B is more than the conventional tire in the tread contact surface during straight traveling. Demonstrate on the outside in the tire axial direction. Therefore, the middle block 4B can improve the handle response. In the conventional tire, the development length of the middle block is about 15 to 20% of the tread development half width 0.5 TW.

  Here, the tread contact surface is specified in a state where the tire 1 in a state where the rim is assembled to the rim and filled with the internal pressure is loaded with a load of 0.64 kN and contacted with a flat surface at a camber angle of 0 degree. Shall be.

  Moreover, since the unfolded length L6 is limited to 36% or less of the tread unfolded half width of 0.5 TW, the middle block 4B can be disposed within the tread contact surface during straight travel, and the edge component is reliably exhibited. can do.

  In order to effectively exhibit such an action, the development length L6 is preferably 28% or more of the tread development half width 0.5 TW, and more preferably 34% or less.

  Further, the middle block 4B of the present embodiment is disposed across the entire range in the tire circumferential direction of the lateral groove projection region 16 in which the lateral grooves 5A are projected on the middle block row 3B side in the tire axial direction.

  As a result, the middle block 4B can disperse the ground pressure of the middle block 4B and the ground pressure of the center blocks 4A, 4A in the tire circumferential direction. It can suppress that 4A and the middle block 4B receive simultaneously, and can further improve disturbance absorption performance.

  Further, the middle block 4B can disperse the edge component of the middle block 4B and the edge components of the center blocks 4A, 4A in the tire circumferential direction, and can reliably improve the steering response.

  In order to effectively exhibit the above action, the distance L7 in the tire circumferential direction between the end wall portions 8Bt on both sides in the tire circumferential direction of the middle block 4B and the lateral groove projection region 16 (the overlapping distance between the center block 4A and the middle block 4B). ) Is preferably 6 to 14% of the circumferential length L2b (shown in FIG. 1) of the middle block 4B.

  If the distance L7 exceeds 14% of the circumferential length L2b, the overlapping area of the middle block 4B and the center block 4A becomes excessive, and there is a possibility that the disturbance absorbing performance cannot be sufficiently improved. On the contrary, when the distance L7 is less than 6% of the circumferential length L2b, the edge component in the tire circumferential direction of the middle block 4B becomes small, and the steering response may be lowered. From such a viewpoint, the distance L7 is preferably 12% or less of the circumferential length L2b, and preferably 8% or more.

  In the middle block 4B, an inner recess 18B that is recessed outward in the tire axial direction is provided on the inner wall 8Bi facing inward in the tire axial direction. The inner concave portion 18B is formed at the center of the inner wall portion 8Bi in the tire circumferential direction, and is formed in a vertically long rectangular shape having an axial length W8b larger than the circumferential length L2b in plan view.

  Such an inner recess 18B can increase the edge component in the tire circumferential direction and the tire axial direction, and can improve the steering response. In addition, the inner concave portion 18B is disposed to face the inner concave portion 18B of the middle block 4B adjacent to the tire equator C with the tire equator C interposed therebetween. Thereby, these inner side recessed parts 18B and 18B can hold | grip the sand, earth, etc. of the rough road surface interposed in the said horizontal groove 5A with the corner 9a of the center block 4A. Therefore, the inner concave portion 18B helps to improve the traction performance and the handle response.

  In order to effectively exhibit the above action, the inner recess 18B has a circumferential length L8b of about 25 to 35% of a circumferential length L2b (shown in FIG. 1) of the middle block 4B, and an axial length. W8b is preferably about 12 to 24% of the axial length W2b (shown in FIG. 1) of the middle block 4B, and the groove depth D8b (shown in FIG. 2) is preferably about 70 to 90% of the block height H1.

  Further, the middle block 4B includes a pair of projecting corner portions formed by cutting out a pair of corners of the outer wall portion 8Bo facing outward in the tire axial direction and a pair of end wall portions 8Bt, 8Bt on both sides in the tire circumferential direction into a corner shape. Corners 9b, 9b are provided. Each of the corners 9b, 9b can increase edge components in the tire axial direction and the tire circumferential direction on the outer wall 8Bo side, and can improve steering wheel response and turning performance. The circumferential length L4b and the axial length W4b of the corner 9b are in the same range as the circumferential length L4a, the axial length W4a and the depth (not shown) of the corner 9a. It is desirable to set.

  As shown in FIG. 1, the shoulder block row 3 </ b> C of the present embodiment includes an inner shoulder block row 3 </ b> Ca composed of an inner shoulder block 4 </ b> Ca arranged on the inner side in the tire axial direction, and an outer side in the tire axial direction than the inner shoulder block 4 </ b> Ca. And outer shoulder block row 3Cb composed of outer shoulder blocks 4Cb to be arranged.

  As shown in FIG. 2, the inner shoulder block 4Ca includes a tread surface 7C and a wall portion 8C. Also, as shown in FIG. 1, the inner shoulder block 4Ca is formed in a vertically long rectangular shape in which the circumferential length L2c of the tread surface 7C is larger than the axial length W2c.

  Such an inner shoulder block 4Ca can effectively exhibit an edge component in the tire circumferential direction when turning, for example, when the ground contact pressure is relatively large from straight running, and improves steering wheel response and turning performance. Yes. The inner shoulder block 4Ca is preferably in the same range as the center block 4A and the middle block 4B in the circumferential length L2c and the axial length W2c.

  As shown in FIG. 4 in an enlarged manner, the inner shoulder block 4Ca has a pair of projecting corners of an inner wall portion 8Ci facing inward in the tire axial direction and a pair of end wall portions 8Ct, 8Ct on both sides in the tire circumferential direction. A pair of corner portions 9c, 9c cut out in a corner shape are provided.

  Such corners 9c, 9c can increase edge components in the tire axial direction and the tire circumferential direction on the inner wall 8Ci side, and can improve steering wheel response and turning performance. The circumferential length L4c, the axial length W4c, and the depth (not shown) of the corner 9c are in the same range as the corners 9a and 9b (shown in FIG. 3) of the center block 4A and the middle block 4B. It is desirable to set to.

  Further, the inner shoulder block 4Ca is provided with an outer recessed portion 18C that is recessed inward in the tire axial direction on the outer wall portion 8Co facing outward in the tire axial direction. The outer recessed portion 18C is formed at the center in the tire circumferential direction of the outer wall portion 8Co, and is formed in a vertically long rectangular shape in plan view.

  Such an outer recess 18C can increase edge components in the tire circumferential direction and the tire axial direction during turning when the contact pressure of the inner shoulder block 4Ca is relatively large, and can improve steering response and turning performance. Can improve. The circumferential length L8c, the axial length W8c, and the groove depth D8c (shown in FIG. 2) of the outer recess 18C are preferably in the same range as the inner recess 18B (shown in FIG. 3) of the middle block 4B.

  As shown in FIG. 2, the outer shoulder block 4Cb includes a tread surface 7D and a wall portion 8D. Further, as shown in FIG. 1, in the outer shoulder block 4Cb, the circumferential length L2d of the tread surface 7D is set larger than the axial length W2d.

  As shown in FIG. 4, the outer shoulder block 4Cb is configured so that the edges 7Dt on both sides in the tire circumferential direction of the tread surface 7D are directed from the inner side in the tire axial direction to the outer side and from the other side S2 in the tire circumferential direction toward the one side S1. And tilt up. Thus, the outer shoulder block 4Cb is formed in a vertically long parallelogram shape.

  Such an outer shoulder block 4Cb can effectively exhibit the edge components in the tire circumferential direction and the tire axial direction at the time of turning when the contact pressure becomes relatively large, and the steering wheel response and turning performance can be achieved. Can be improved. As shown in FIG. 1, the outer shoulder block 4Cb is preferably in the same range as the center block 4A, the middle block 4B, and the inner shoulder block 4Ca in the circumferential length L2d and the axial length W2d.

  As shown in FIG. 4, the outer shoulder block 4 </ b> Cb is provided with an inner recess 18 </ b> D that is recessed outward in the tire axial direction on the inner wall portion 8 </ b> Di that faces inward in the tire axial direction. The inner recess 18D is formed at the center in the tire circumferential direction of the inner wall portion 8Di, and is formed in a vertically long rectangular shape in plan view.

  Such an inner recess 18D can increase the edge component in the tire circumferential direction and the tire axial direction during turning when the contact pressure of the outer shoulder block 4Cb is relatively large, thereby improving steering response and turning performance. Can improve. In order to effectively exert such an action, the circumferential length L8d, the axial length W8d, and the groove depth D8d (shown in FIG. 2) of the inner recess 18D are determined by the inner recess of the middle block 4B. The same range as 18B (shown in FIG. 3) and the outer recess 18C of the inner shoulder block 4Ca is desirable.

  In addition, the inner recess 18D of the present embodiment is disposed so as to face the outer recess 18C of the inner shoulder block 4Ca in the tire axial direction. As a result, the inner concave portion 18D and the outer concave portion 18C can simultaneously exert a large edge component against sand, soil, etc. on the rough road surface interposed between the inner shoulder block 4Ca and the outer shoulder block 4Cb. In addition, steering response and turning performance can be greatly improved. In order to effectively exhibit such an action, the overlapping length L9 of the inner recess 18D and the outer recess 18C is 75% or more, more preferably 85% or more of the circumferential length L8c of the inner recess 18D. desirable.

  As shown in FIG. 1, in the present embodiment, the inner shoulder block 4Ca and the outer shoulder block 4Cb are displaced from each other on the one side S1 in the tire circumferential direction with respect to the middle block 4B adjacent in the tire axial direction. Be placed.

  Thereby, the inner shoulder block 4Ca and the outer shoulder block 4Ca can disperse the ground pressure of the inner and outer shoulder blocks 4Ca and 4Cb and the ground pressure of the middle block 4B in the tire circumferential direction, and can absorb the disturbance. Can be improved. Further, the edge components of the inner and outer shoulder blocks 4Ca and 4Cb can be displaced in the tire circumferential direction from the edge component of the middle block 4B, and the steering response and turning performance can be improved.

  Further, when the tire 1 rotates from the other side S2 toward the one side S1, the inner and outer shoulder blocks 4Ca and 4Cb are sequentially grounded next to the middle block 4B, for example, the inner and outer shoulder blocks 4Ca. , 4Cb is less affected by the moment of inertia (steering torque) around the steering wheel steering shaft than when contacting the middle block 4B, and as a result, the disturbance absorbing performance and steering wheel response can be effectively improved. .

  In order to effectively exhibit such an action, the positional deviation L10a in the tire circumferential direction between the inner shoulder block 4Ca and the middle block 4B, and the positional deviation in the tire circumferential direction between the outer shoulder block 4Cb and the middle block 4B. L10b is desirably 5 to 20% of the circumferential length L2a of the center block 4A. In addition, there exists a possibility that the said effect | action cannot fully be exhibited as the said positional offset amount L10a, L10b is less than 5% of the said circumferential direction length L2a. On the contrary, if the positional deviations L10a and L10b exceed 20% of the circumferential length L2a, the tire circumferential end edges of the inner and outer shoulder blocks 4Ca and 4Cb are detached from the tread contact surface. There is a risk that the disturbance absorbing performance will be reduced. From such a viewpoint, the positional deviation amounts L10a and L10b are more preferably 8% or more of the circumferential length L2a, and more preferably 17% or less.

  Furthermore, it is desirable that the outer shoulder block 4Cb is disposed so as to be displaced from the inner shoulder block 4Ca on one side S1 in the tire circumferential direction. Thereby, the outer side shoulder block 4Cb can further improve the said disturbance absorption performance, steering wheel responsiveness, and turning performance.

  In order to effectively exhibit such an action, the positional deviation L10c in the tire circumferential direction between the outer shoulder block 4Cb and the inner shoulder block 4Ca is preferably 3% or more of the circumferential length L2a of the center block 4A. More preferably, it is 6% or more, preferably 15% or less, more preferably 12% or less.

  As mentioned above, although especially preferable embodiment of this invention was explained in full detail, this invention is not limited to embodiment of illustration, It can deform | transform and implement in a various aspect.

Tires having the basic structure shown in FIG. 1 and the blocks shown in Table 1 were manufactured and their performance was tested. The common specifications are as follows.
tire size:
Front wheel: AT22 × 7R10
Rear wheel: AT22 × 10R9
Rim size:
Front wheel: 10 × 5.5AT
Rear wheel: 9 × 8.0AT
Tread development half width 0.5TW: 123mm
Block height H1: 12.8mm
Center block:
Circumferential length L2a: 38.3 mm
Axial length W2a: 15.3 mm
L2a / 0.5TW: 31.1%
W2a / 0.5TW: 12.4%
One tire circumference L3 at the axial center position of the tread: 1646mm
Middle block:
Circumferential length L2b: 38.3 mm
Axial length W2b: 13.3 mm
L2b / 0.5TW: 31.1%
W2b / 0.5TW: 10.8%
Inner shoulder block:
Circumferential length L2c: 37.3 mm
Axial length W2c: 12.0mm
L2c / 0.5TW: 30.3%
W2c / 0.5TW: 9.8%
Outer shoulder block:
Circumferential length L2d: 37.3 mm
Axial length W2d: 10.0mm
L2d / 0.5TW: 30.3%
W2d / 0.5TW: 8.1%
The test method is as follows.

<Handle response, disturbance absorption performance>
Each sample tire is assembled on the rim, filled with internal pressure (front wheel: 30 kPa, rear wheel: 27.5 kPa), mounted on all wheels of an ATV with a displacement of 450 cc, and circulated on the ATV competition course. “Handle response” and “disturbance absorption performance” were evaluated by a five-point method based on sensory evaluation of the driver. The larger the value, the better.
The test results are shown in Table 1.

  As a result of the test, it was confirmed that the tire of the example can improve the handle response while maintaining the disturbance absorbing performance from the rough road surface.

1 Pneumatic tire for running on rough terrain 4A Center block 4B Middle block 4C Shoulder block

Claims (5)

A pneumatic tire for traveling on rough terrain, including a row of blocks in which a plurality of blocks are spaced apart in the tire circumferential direction in the tread portion,
The block row is a center block row composed of center blocks arranged on or adjacent to the tire equator,
A middle block row consisting of middle blocks arranged on the outer side in the tire axial direction of the center block,
The center block has a vertically long shape in which the circumferential length of the tread surface is larger than the axial length,
In the center block row, the sum of the circumferential lengths of the center blocks is 51 to 61% of the circumferential length of the tire at the axial center position of the tread of the center block,
Moreover, the development length in the tire axial direction between the inner edge in the tire axial direction of the tread surface of the middle block and the tire equator is 26 to 36% of the half width of the tread development, and a pneumatic tire for running on uneven terrain. . In the center block row, the center blocks are arranged through lateral grooves,
2. The pneumatic tire for traveling on uneven terrain according to claim 1, wherein each of the middle blocks is disposed across the entire range in the tire circumferential direction of a lateral groove projection region in which the lateral grooves are projected on the middle block row side in the tire axial direction. . The block row includes at least one shoulder block row composed of shoulder blocks arranged on the outer side in the tire axial direction of the middle block,
The pneumatic tire for running on uneven terrain according to claim 1 or 2, wherein the shoulder block is arranged so as to be displaced to one side in a tire circumferential direction with respect to the middle block adjacent in the tire axial direction.   4. The pneumatic tire for running on uneven terrain according to claim 3, wherein the amount of positional deviation in the tire circumferential direction between the shoulder block and the middle block is 5 to 20% of the circumferential length of the tread surface of the center block. 5. . The shoulder block row is an inner shoulder block row composed of inner shoulder blocks arranged on the inner side in the tire axial direction,
Including an outer shoulder block row composed of outer shoulder blocks arranged on the outer side in the tire axial direction than the inner shoulder blocks,
The inner shoulder block has an outer concave portion that is recessed inward in the tire axial direction on an outer wall portion facing outward in the tire axial direction,
The outer shoulder block has an inner concave portion that is recessed outward in the tire axial direction on the inner wall portion facing inward in the tire axial direction,
The pneumatic tire for rough terrain travel according to claim 3 or 4, wherein the outer recess of the inner shoulder block and the inner recess of the outer shoulder block face each other in the tire axial direction.

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