JP2014177239A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve turning performance and uneven wear resistance on an ice road in a balanced manner without impairing straight advance stability.SOLUTION: The pneumatic tire, which has a pair of center main grooves 3 and 3 and a plurality of center lateral grooves 8 provided at a tread portion 2 thereof, includes a first center lateral groove 8A and a second center lateral groove 8B inclined at an angle opposite to the first center lateral groove 8A so as to section a plurality of nearly trapezoidal center blocks 9. The center blocks 9 each include: a short edge 11 that faces the center main groove 3 and has a smaller length in the tire circumferential direction; and a long edge 12 that faces the center main groove 3 on the opposite side of the short edge 11. The length in the tire circumferential direction of the short edge 11 is 0.60-0.85 times the length in the tire circumferential direction of the long edge 12. A ground contact surface being applied with a normal load includes a first block 9A and a second block 9B.

Description

  The present invention relates to a pneumatic tire in which turning performance on an icy road and uneven wear resistance are improved in a well-balanced manner without impairing straight running stability.

  A pneumatic tire having a center block provided with a center main groove extending in the tire circumferential direction on both sides of the tire equator in the tread portion and a center lateral groove connecting between the center main grooves is known. In order to improve running performance on icy and snowy roads, siping is formed in each center block.

  By the way, in the conventional pneumatic tire, in order to improve the straight running stability on an icy road, for example, the center lateral groove and the siping are both arranged in parallel with the tire axial direction. Such a pneumatic tire has a problem that the turning performance on an icy road is deteriorated.

JP 2012-86665 A

  The present invention has been devised in view of the above circumstances, and is based on improving the arrangement of the center lateral groove, the center block, and the siping. The main object is to provide a pneumatic tire with improved wear performance in a well-balanced manner.

  According to the first aspect of the present invention, the tread portion includes a pair of center main grooves extending continuously in the tire circumferential direction on both sides of the tire equator, and a plurality of center main grooves extending between the pair of center main grooves. A pneumatic tire provided with a center lateral groove, wherein the center lateral groove is a first center lateral groove that is inclined at an angle of 3 to 20 ° on one side with respect to a tire axial direction, and the first center lateral groove is A plurality of substantially trapezoidal center blocks are formed between the center main grooves by alternately including second center lateral grooves that are reverse and inclined at an angle of 3 to 20 ° with respect to the tire axial direction in the tire circumferential direction. The center block includes a first block provided with a plurality of first center sipings extending substantially parallel to the first center lateral groove, and a second center extending substantially parallel to the second center lateral groove. -A plurality of second blocks provided with a plurality of sipings are alternately included in the tire circumferential direction, and each of the first blocks and the second block extends on either one of the center main grooves and has a small length in the tire circumferential direction. A short edge and a long edge having a length in the tire circumferential direction larger than the short edge and extending on the other center main groove side, and the tire circumferential direction length of the short edge is equal to the tire circumference of the long edge. It is 0.60 to 0.85 times the length in the direction, and the normal rim is assembled to the normal rim and filled with the normal internal pressure, and the normal load is applied to the plane with a normal load and a camber angle of 0 degrees. The ground plane includes at least the first block and the second block.

  Further, the invention according to claim 2 is the pneumatic tire according to claim 1, wherein the center block has a maximum width in the tire axial direction of 8 to 15% of a tread contact width.

  In the invention according to claim 3, the maximum width of the center block in the tire axial direction is 0.8 to 1.2 times the tire circumferential direction length of the center block on the tire equator. 2. The pneumatic tire according to 2.

  According to a fourth aspect of the present invention, the tire axial length at both ends of the center block in the tire circumferential direction is greater than the tire axial length at the center of the center block in the tire circumferential direction on the tire equator. The pneumatic tire according to any one of claims 1 to 3, wherein the pneumatic tire is large.

  The center lateral groove includes a first center lateral groove inclined at a predetermined angle and a second center lateral groove inclined at an angle opposite to the first center lateral groove. Thereby, the tread part is divided into a plurality of substantially trapezoidal center blocks. The center block includes a first block provided with a first center siping extending substantially parallel to the center lateral groove and a second block provided with a plurality of second center sipings extending substantially parallel to the second center lateral groove. It is alternately included in the tire circumferential direction. Therefore, the edge component in the tire axial direction and the edge component in the tire circumferential direction increase in both the lateral groove and the siping. For this reason, the turning performance on an icy road is improved without impairing the straight running stability.

  Further, the first block and the second block are provided alternately in the tire circumferential direction and are both included in the ground contact surface. For this reason, during straight traveling, the lateral forces generated by the first block and the second block having opposite directions cancel each other, and straight traveling stability is improved.

  Each center block has a short edge extending in one of the center main grooves and having a small length in the tire circumferential direction, and a length extending in the other center main groove and having a length in the tire circumferential direction larger than the short edges. The ratio of the tire circumferential direction length of the short edge and the tire circumferential direction length of the long edge is defined within a certain range. Thereby, each of the first block and the second block has rigidity anisotropy. Such anisotropy makes a difference in how to open the siping of each block, for example, improves the followability to the road surface, and improves the grip on the icy road. Furthermore, since the anisotropy of the center block is limited to a certain range, it is possible to prevent deterioration in uneven wear resistance. Therefore, the pneumatic tire of the present invention improves the turning performance on the icy road and uneven wear resistance in a well-balanced manner without impairing the straight running stability.

It is an expanded view of the tread part which shows one Embodiment of this invention. It is an enlarged view of the center land part of FIG. It is an enlarged view of the center block of FIG. It is an expanded view of the tread part of a comparative example.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pneumatic tire of this embodiment (hereinafter, simply referred to as “tire”) can be suitably used as, for example, a studless tire. The tread portion 2 of the tire has a pair of center main grooves 3, 3 extending continuously in the tire circumferential direction on both sides of the tire equator C, and the tire axially outer side of the center main groove 3 is continuous in the tire circumferential direction. A pair of extending shoulder main grooves 4 and 4 are provided. Accordingly, the tread portion 2 of the present embodiment has a center land portion 5 divided by a pair of center main grooves 3 and 3, and a pair of middle land portions divided by the center main groove 3 and the shoulder main grooves 4. A pair of shoulder land portions 7 and 7 divided by the portions 6 and 6 and the shoulder main groove 4 and the ground contact Te are formed.

  “Grounding end” Te is a normal load applied state in which a normal load is loaded on a normal rim that is assembled with a normal rim and filled with a normal internal pressure, and a normal load is applied to a flat surface with a camber angle of 0 degrees. Is determined as the ground contact position on the outermost side in the tire axial direction. In the normal state, the distance in the tire axial direction between the ground contact ends Te and Te is determined as the tread ground contact width TW. Unless otherwise specified, the dimensions and the like of each part of the tire are values in a normal state.

  The “regular rim” is a rim determined for each tire in the standard system including the standard on which the tire is based. For example, “Standard Rim” for JATMA, “Design Rim” for TRA, ETRTO Then "Measuring Rim".

  “Regular internal pressure” is the air pressure that each standard defines for each tire in the standard system including the standard on which the tire is based. “JAMATA” is the “maximum air pressure”, TRA is the table “TIRE LOAD LIMITS” The maximum value described in “AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” if it is ETRTO, but 180 kPa if the tire is for passenger cars.

  “Regular load” is a load determined by each standard for each tire in the standard system including the standard on which the tire is based. “JATMA” is “maximum load capacity”, TRA is “TIRE LOAD” The maximum value described in “LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “LOAD CAPACITY” in the case of ETRTO, is a load corresponding to 88% of the load when the tire is for a passenger car.

  The center main groove 3 has a groove edge extending in a multiple direction with respect to the tire axial direction. In the tire axial direction, the inner edge has a trapezoidal wave shape, and the outer edge has a zigzag shape. The groove edge of the center main groove 3 thus has multidirectional edge components. Such a center main groove 3 improves straight running stability and turning performance on an icy road.

  In the present embodiment, the shoulder main groove 4 has a zigzag inner edge and an outer edge. Like the center main groove 3, such a shoulder main groove 4 has edge components in the tire circumferential direction and the tire axial direction, and can improve running performance on ice roads.

  The groove width (maximum width in the tire axial direction) W1 and W2 and the groove depth (not shown) of the main grooves 3 and 4 can be variously determined in accordance with common practice. The groove widths W1 and W2 of the main grooves 3 and 4 are preferably 3 to 10% of the tread ground contact width TW, for example. The groove depth of each of the main grooves 3 and 4 is preferably 10 to 12 mm, for example.

  FIG. 2 shows an enlarged view of the center land portion 5 of FIG. As shown in FIG. 2, the center land portion 5 is provided with a plurality of center lateral grooves 8 that connect between the pair of center main grooves 3 and 3. Thus, the center land portion 5 is a center block row in which a plurality of center blocks 9 divided by a pair of center main grooves 3 and 3 and a center lateral groove 8 are spaced apart in the tire circumferential direction.

  In the present embodiment, the center lateral groove 8 is defined as one of the first center lateral groove 8A and the first center lateral groove 8A inclined at an angle α1 of 3 to 20 ° on one side (upward in FIG. 2) with respect to the tire axial direction. And a second center lateral groove 8B inclined in the reverse direction (upward in FIG. 2) and inclined at an angle α2 of 3 to 20 ° with respect to the tire axial direction.

  In the present embodiment, each center lateral groove 8A, 8B extends linearly.

  The groove width W3 of the center lateral groove 8 is preferably 10 to 16% of the maximum width Ws of the center block 9 in the tire axial direction (shown in FIG. 3). Thereby, the ice in the center lateral groove 8 is smoothly discharged, and the turning performance on the ice road is improved. Moreover, the rigidity of the center block 9 is ensured high, and uneven wear resistance performance is improved. From the same viewpoint, the groove depth (not shown) of the center lateral groove 8 is preferably 40 to 75% of the groove depth of the center main groove 3.

  By setting the angle α1 of the first center lateral groove 8A and the angle α2 of the second center lateral groove 8B to be in the range of 3 to 20 °, an edge component in the tire circumferential direction is obtained and the turning performance on an icy road is improved. In addition, straight running stability is improved. Preferably, the angle α1 of the first center lateral groove 8A and the angle α2 of the second center lateral groove 8B are in the range of 5 to 15 °. The angle α1 of the first center lateral groove 8A and the angle α2 of the second center lateral groove 8B are defined as the angle of the straight line 8c connecting the groove width center points at both ends of each lateral groove 8.

  The first center lateral grooves 8A and the second center lateral grooves 8B are alternately arranged in the tire circumferential direction. Thereby, the center block 9 makes the substantially trapezoid shape which has an upper-bottom part and a lower-bottom part in a tire circumferential direction. The “substantially trapezoidal” block means a block having block edges whose slope directions are opposite to each other on both sides in the tire circumferential direction, and does not need to be a strict trapezoid.

  The center block 9 includes a first block 9A and a second block 9B. The first block 9A is provided with a plurality of first center sipings 10A extending substantially parallel to the first center lateral grooves 8A. The second block 9B is provided with a plurality of second center sipings 10B extending substantially parallel to the second center lateral grooves 8B. By these first block 9A and second block 9B, many edge components in the tire axial direction and edge components in the tire circumferential direction are obtained. For this reason, the straight running stability of the tire and the turning performance on an icy road are improved. Further, the first block 9A and the second block 9B are provided alternately. For this reason, during straight running, the lateral forces generated in the opposite directions generated by the respective blocks 9A and 9B are offset, and the straight running stability is improved.

  The difference between the angle α1 of the first center lateral groove 8A and the angle α3 of the first center siping 10A in the tire axial direction, and the angle α2 of the second center lateral groove 8B and the angle α4 of the second center siping 10B in the tire axial direction. The absolute value of the difference is preferably 5 ° or less.

  In the present embodiment, both the first center siping 10A and the second center siping 10B extend linearly. However, the 1st center siping 10A and the 2nd center siping 10B are not limited to such an aspect, For example, zigzag shape or a wave shape etc. may be included.

  It is desirable that 3 to 7 first center sipings 10A and second center sipings 10B are provided in each center block 9. That is, when the number of the first center siping 10A and the second center siping 10B exceeds seven, the rigidity of the center block 9 is reduced, and the uneven wear resistance may be deteriorated. Further, when the number of the first center siping 10A and the second center siping 10B is less than 3, the edge component may be small.

  In order to effectively increase the edge component while ensuring uneven wear resistance performance of the center block 9, the depths (not shown) of the first center siping 10A and the second center siping 10B are preferably center. It is 65 to 85% of the groove depth of the main groove 3. The center siping 17 may have a shallow bottom portion (not shown) having a small depth on both end sides thereof. Such a shallow bottom portion ensures high rigidity of the center block 9. The depth of the shallow bottom is preferably 15 to 20% of the depth of the center main groove 3.

  The first block 9A and the second block 9B have edges that are contour edges of the road surface. This edge includes a short edge 11 having a small length in the tire circumferential direction and a long edge 12 having a length in the tire circumferential direction larger than that of the short edge 11. In the first block 9A of the present embodiment, the short edge 11 extends to the side of one center main groove 3 (in FIG. 2, the right center main groove 3A), and the long edge 12 extends to the other center main groove 3. (In FIG. 2, the center main groove 3B on the left side) extends. In the present embodiment, the short edge 11 of the first block 9A and the long edge 12 of the second block 9B are alternately provided on the one side of the center main groove 3A. Further, the long edge 12 of the first block 9A and the short edge 11 of the second block 9B are alternately provided on the other center main groove 3B side. Therefore, as the entire center land portion 5, the rigidity anisotropy is reduced, and the uneven wear resistance performance and straight running stability are improved.

  The tire circumferential direction length La of the short edge 11 is defined as 0.60 to 0.85 times the tire circumferential direction length Lb of the long edge 12. In this way, by regulating the ratio between the short edge 11 and the long edge 12 of each block 9A, 9B, the turning performance on ice roads can be enhanced without impairing the uneven wear resistance performance. Each of the first block 9A and the second block 9B has rigidity anisotropy. Such anisotropy makes a difference in how to open the sipings 10A and 10B of the blocks 9A and 9B, improves the followability to the road surface, and improves the grip on the icy road. When the tire circumferential length La of the short edge 11 is less than 0.60 times the tire circumferential length of the long edge 12, the rigidity anisotropy in the tire circumferential direction of the center block 9 becomes remarkably large, and uneven wear resistance Performance deteriorates. When the tire circumferential direction length La of the short edge 11 exceeds 0.85 times the tire circumferential direction length Lb of the long edge 12, the edge component in the tire circumferential direction becomes small, and the turning performance on an icy road deteriorates. In particular, the tire circumferential direction length La of the short edge 11 is preferably 0.65 to 0.80 times the tire circumferential direction length Lb of the long edge 12.

  FIG. 3 shows an enlarged view of the center block 9 of FIG. As shown in FIG. 3, the center block 9 of the present embodiment is provided with a recess 14 extending from the center main grooves 3 and 3 toward the tire equator C and terminating in the center block 9. The recessed portion 14 has a depth smaller than that of the center main groove 3. Such a recess 14 gives a large edge to the short edge 11 and the long edge 12. Thereby, the grip power on an icy road is enhanced. In order to increase the grip force on the icy road while suppressing the decrease in rigidity of the center block 9, the depth of the recess 14 (not shown) is preferably 80 to 100% of the depth of the center main groove 3. is there. The depth of the recessed portion 14 of the present embodiment is the same as the depth of the center main groove 3.

  The concave portion 14 on the short edge 11 side has a gradually increasing portion 14a in which the width W4 in the tire axial direction gradually increases from one end of the short edge 11 toward the other side. The concave portion 14 on the long edge 12 side has a gradually increasing portion 14a in which the width W4 in the tire axial direction gradually increases from the other end of the long edge 12 to one side. Any of the gradually increasing portions 14 a is provided so as to include the center positions 11 c and 12 c in the tire circumferential direction of the short edge 11 or the long edge 12.

  The tire block length Lc (the lower end side in FIG. 3) and Ld (the upper end side in FIG. 3) at both ends of the center block 9 in the tire circumferential direction are the centers in the tire circumferential direction of the center block 9 on the tire equator C. It is desirable to be larger than the tire axial length Le at the position 9c. That is, the tire axial direction lengths Lc and Ld at the both ends of the center block 9 in the tire circumferential direction are larger than the tire axial direction length Le of the center position 9c in the tire circumferential direction. A large rigidity can be given to both side portions in the tire circumferential direction of the center block 9 on which a large load acts, thereby improving uneven wear resistance. In order to exhibit such an action more effectively, the tire axial direction lengths Lc and Ld at the both ends of the center block 9 in the tire circumferential direction are more preferably the tire axial length of the center position 9c in the tire circumferential direction. It is 1.20 times or more of the thickness Le, preferably 1.50 times or less, more preferably 1.45 times or less.

  The maximum width Ws of the center block 9 in the tire axial direction is desirably 0.8 to 1.2 times the tire circumferential direction length Lf on the tire equator C of the center block 9. That is, when the maximum width Ws of the center block 9 is less than 0.8 times or 1.2 times the length Lf of the center block 9 on the tire equator C, the tire axial rigidity of the center block 9 and the tire There is a possibility that the difference between the rigidity in the circumferential direction becomes large and the straight running stability and the turning performance on the icy road cannot be secured in a well-balanced manner. For this reason, the maximum width Ws of the center block 9 in the tire axial direction is more preferably 0.9 times or more, and more preferably 1.1 times or less, the length Lf of the center block 9 on the tire equator C. is there. In the present embodiment, the maximum width Ws of the center block 9 in the tire axial direction and the tire axial direction lengths Lc and Ld at both end positions in the tire circumferential direction of the center block 9 are the same length. The tire circumferential rigidity is ensured.

  The maximum width Ws of the center block 9 in the tire axial direction is desirably 8 to 15% of the tread contact width TW (shown in FIG. 1). When the maximum width Ws of the center block 9 is less than 8% of the tread contact width TW, the edge component in the tire axial direction becomes small, and the straight running stability may be deteriorated. When the maximum width Ws of the center block 9 exceeds 15% of the tread contact width TW, the rigidity in the tire axial direction of the middle land portion 6 and the shoulder land portion 7 (shown in FIG. 1) is reduced, and turning performance on an icy road May get worse. For this reason, the maximum width Ws of the center block 9 is more preferably 9 to 14% of the tread ground contact width TW.

  The center block 9 is disposed such that the maximum length Lg in the tire axial direction between the tire equator C and the short edge 11 is smaller than the maximum length Lh in the tire axial direction between the tire equator C and the long edge 12. Is desirable. Thereby, the rigidity of the tire equator C of the center block 9 on both sides in the tire axial direction is ensured in a well-balanced manner, and uneven wear resistance is further improved. In particular, the length ratio Lg / Lh is preferably 0.75 to 0.90. By setting it as such a range, the rigidity balance according to ratio of the length of the tire peripheral direction of the long edge 12 and the short edge 11 is ensured. The ratio of the maximum length Lg / Lh is more preferably 0.80 to 0.85.

  The tire according to the present embodiment has a contact surface that includes at least the first block 9A and the second block 9B in a normal load state. Accordingly, since the trapezoidal center block 9 having the opposite direction is grounded substantially at the same time, the single flow due to the rigidity anisotropy of the block is suppressed. Further, the uneven wear resistance performance is further improved.

  As shown in FIG. 1, the middle land portion 6 is provided with a middle lateral groove 16 that connects between the center main groove 3 and the shoulder main groove 4 and is spaced apart in the tire circumferential direction. Thereby, the middle land portion 6 is formed as a middle block row in which middle blocks 6A divided between the middle lateral grooves 16 and 16 are separated in the tire circumferential direction.

  The middle lateral groove 16 is linear and inclined in one direction (upward in FIG. 1) with respect to the tire axial direction.

  Each middle block 6A is provided with a middle vertical groove 17 that connects between the middle horizontal grooves 16 and 16. As a result, the middle block 6A is divided into an outer portion 18 disposed on the outer side in the tire axial direction of the middle vertical groove 17 and an inner portion 19 disposed on the inner side in the tire axial direction of the middle vertical groove 17.

  The outer portion 18 is provided with a middle outer siping 20 that is inclined in the same direction as the middle lateral groove 16. Thereby, the turning performance on the icy road and the uneven wear resistance performance of the outer portion 18 are further improved in a balanced manner. The inner portion 19 is provided with a middle inner siping 21 that is inclined in the opposite direction to the middle outer siping 20. Such a middle inner siping 21 generates a lateral force in the opposite direction to the middle outer siping 20 during straight traveling, and suppresses a decrease in straight traveling stability. For this reason, it is desirable that the middle inner siping 21 be arranged at the same angle as the angle of the middle outer siping 20.

  The middle block 6 </ b> A is provided with an elliptical dimple 22 that terminates in the middle block 6 </ b> A without communicating with the middle inner siping 21 and the grooves 3, 16, and 17. Such dimples 22 have multidirectional edge components while ensuring the rigidity of the inner portion 19. For this reason, turning performance improves.

  The shoulder land portion 7 is provided with a shoulder lateral groove 25 that connects between the shoulder main groove 4 and the ground contact end Te and is spaced in the tire circumferential direction. Thereby, the shoulder land portion 7 is formed as a shoulder block row in which the shoulder blocks 7A divided by the shoulder lateral grooves 25 are spaced in the tire circumferential direction.

  The shoulder block 7 </ b> A is provided with a shoulder siping 26 extending substantially parallel to the shoulder lateral groove 25. This further improves the turning performance on ice roads and uneven wear resistance in a well-balanced manner.

  As for the tire of this embodiment, as a studless tire for winter, it is desirable that the land ratio is set to 68 to 72%. As a result, the turning performance on the icy road and the uneven wear resistance are improved in a well-balanced manner without lowering the straight running stability. The land ratio is the total surface area Mb of the treads of all the land parts 5 to 7, all the grooves 3, 4, 8, 16, 17 and 25 of the tread part 2, the notch part 14, the dimple 22 and each siping 10 , 20, 21 and 26 are ratios (Mb / Ma) with the virtual surface area Ma of the virtual tread surface obtained.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, this invention is changed and implemented in various aspects, without being limited to said specific embodiment.

In order to confirm the effect of the present invention, a 225 / 65R17 pneumatic tire having the basic pattern of FIG. 1 and based on the specifications of Table 1 was tested. Except for the grooves described in Table 1, the groove width and angle of each groove are as shown in FIG. The main common specifications and test methods for each tire are as follows.
Tread contact width TW: 180mm
Center main groove depth: 11mm
Shoulder main groove depth: 11mm
Center lateral groove depth: 6mm
Middle lateral groove depth: 11mm
Middle vertical groove depth: 9mm
Shoulder lateral groove depth: 10mm
Center siping depth / center main groove depth: 77%
Middle block siping depth / center main groove depth: 77%
Shoulder siping depth / shoulder main groove depth: 59%
Tire circumferential direction length of ground contact surface under normal load load: Maximum tire circumferential direction length of center block × 2.2 + Tire circumferential length of center lateral groove

<Turning performance on icy road>
Each test tire was mounted on all wheels of a four-wheel drive passenger car with a displacement of 2400 cc under the following conditions. Then, the test driver drove the test course of Iceburn, and the running characteristics related to the steering wheel response, rigidity, grip, etc. at the time of turning were evaluated by the test driver's sensuality. The results are displayed as a score with the value of Example 1 being 100. The larger the value, the better.
Rim (all wheels): 17 × 6.5J
Internal pressure (all wheels): 220 kPa

<Straight running stability>
The test driver ran the test vehicle on a dry asphalt road test course, and the driving characteristics regarding the steering stability and grip during straight running at this time were evaluated by the test driver's sensuality. The results are displayed as a score with the value of Example 1 being 100. The larger the value, the better.

<Uneven wear resistance>
The test driver ran the test vehicle for 8000 km on the dry asphalt road test course. Thereafter, the amount of wear at both ends of the center block in the tire axial direction was measured at eight locations in the tire circumferential direction. Then, the reciprocal of the ratio between the maximum difference in wear amount at each of the eight locations and the groove depth of the center main groove was calculated. The results were expressed as an index with the value of Example 1 being 100. The larger the value, the better.

<Noise performance>
A test driver ran the test vehicle on a dry asphalt road surface at a speed of 100 km / H. The noise noise from the road surface at this time was evaluated by the feeling of the test driver. A result is a score which sets Example 1 to 100, and a noise sound is small and it is favorable, so that a numerical value is large.

<Drainage performance>
The test driver entered the above-mentioned test vehicle on the asphalt road surface with a radius of 100 m on a test course provided with a puddle with a depth of 6 mm while gradually increasing the speed. Then, the average lateral acceleration (lateral G) of the front wheels at a speed of 50 to 80 km / h was calculated. The results were expressed as an index with Example 1 as 100. 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 tires of the examples were significantly improved in any performance as compared with the comparative examples. Moreover, when the tire circumferential direction length of the ground contact surface in the normal load state is 1.8 to 1.9 times the maximum length in the tire circumferential direction of the center block, it can be confirmed that the uneven wear resistance performance deteriorates. It was.

3 Center main groove 4 Shoulder main groove 8A First center lateral groove 8B Second center lateral groove
9 Center block 9A First block 9B Second block 11 Short edge 12 Long edge

Claims (4)

A pneumatic tire in which a tread portion is provided with a pair of center main grooves extending continuously in the tire circumferential direction on both sides of the tire equator and a plurality of center lateral grooves connecting between the pair of center main grooves. And
The center lateral groove has a first center lateral groove that is inclined at an angle of 3 to 20 ° on one side with respect to the tire axial direction, and is opposite to the first center lateral groove and is 3 to 20 ° with respect to the tire axial direction. By alternately including second center lateral grooves inclined at an angle in the tire circumferential direction,
A plurality of substantially trapezoidal center blocks are divided between the center main grooves,
The center block includes a first block provided with a plurality of first center sipings extending substantially parallel to the first center lateral grooves, and a plurality of second center sipings extending substantially parallel to the second center lateral grooves. Including alternately provided second blocks in the tire circumferential direction,
Each of the first block and the second block has a short edge extending along one of the center main grooves and having a small length in the tire circumferential direction, and a length in the tire circumferential direction larger than the short edge, and Including a long edge extending on the other center main groove side,
The tire circumferential length of the short edge is 0.60 to 0.85 times the tire circumferential length of the long edge,
A grounding surface in a normal load state in which a normal rim is assembled and filled with a normal internal pressure and is loaded with a normal load and grounded to a flat surface with a camber angle of 0 degrees includes at least the first block and the second block. A pneumatic tire characterized by including both.   The pneumatic tire according to claim 1, wherein the center block has a maximum width in the tire axial direction of 8 to 15% of a tread contact width.   The pneumatic tire according to claim 1 or 2, wherein a maximum width in a tire axial direction of the center block is 0.8 to 1.2 times a tire circumferential direction length on the tire equator of the center block.   The tire axial direction length in the tire circumferential direction both ends position of the said center block is larger than the tire axial direction length of the center position of the tire circumferential direction of the said center block on a tire equator. Pneumatic tire described in 2.

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