JP5060573B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire that improves maneuvering stability and uneven wear while suppressing deterioration in drainage by improving the groove and block shape of the tread portion.

  A pneumatic tire having a block pattern in which a plurality of blocks are formed in a tread portion is known. In this type of pneumatic tire, the stability of the steering and the wear resistance are improved by increasing the rigidity of the block. In order to increase the rigidity of the block, for example, increasing the land ratio, making the wall surface of the block a gentle slope, and further decreasing the depth of the groove in the tread portion are known.

  However, each of the above methods involves a reduction in the groove volume, and thus has a problem that drainage performance, particularly hydroplaning performance, is deteriorated. Thus, the improvement in handling stability and the drainage performance due to the increase in rigidity of the block have a trade-off relationship, and it has been difficult to achieve both. Related technologies include the following.

JP-A-5-286315 JP 2009-132177 A

  The present invention has been devised in view of the above-described problems, and is based on limiting the shape of the crown block on which a large contact pressure acts, while increasing the block rigidity while suppressing a decrease in drainage performance. The main object of the present invention is to provide a pneumatic tire that can improve steering stability and uneven wear resistance.

The invention according to claim 1 of the present invention is a pneumatic tire in which the rotation direction is specified, and is substantially V-shaped toward the rear arrival side in the tire rotation direction from the tire equator to the ground contact ends on both sides in the tread portion. a main inclined grooves which are spaced in the tire circumferential direction with extending, the tire equator towards the between the main oblique grooves adjacent arranged on both sides of the tire equator and in the tire circumferential direction to the next Gikatsu tire rotation direction rear callee a pair of inner connecting grooves extending on the side, axially toward the inner joint between the main oblique grooves disposed in the tire axial direction outer side and adjacent in the tire circumferential direction splicing Gikatsu tire rotation direction rear called side groove By arranging a pair of outer joint grooves extending outward, a crown block divided by the pair of inner joint grooves between the main inclined grooves adjacent in the tire circumferential direction, the inner joint groove and the outer side With splice A maximum width position where the width in the tire axial direction of the crown block is maximum is a tire of the crown block. The crown block is formed in a first arrival side region within 1/3 of the tire circumferential length of the crown block from the end portion on the first arrival side in the rotational direction, and the outermost end in the tire axial direction of the crown block is adjacent to the crown block. The middle block protrudes 0.1 to 10.0 mm outward in the tire axial direction from the innermost end in the tire axial direction.

  According to a second aspect of the present invention, the outer edge of the first arrival side region of the crown block is formed by a single arc or a compound arc curve that protrudes toward the first arrival side in the tire rotation direction. Tire.

  According to a third aspect of the present invention, the innermost end of the middle block is formed in a region within 20% of the tire circumferential length of the middle block from an intermediate position of the middle circumferential length of the middle block. The pneumatic tire according to claim 1 or 2.

The invention according to claim 4 is the pneumatic tire according to any one of claims 1 to 5, wherein the main inclined groove has an angle of 60 to 90 degrees with respect to a tire circumferential direction at a contact end.

  In the pneumatic tire of the present invention, the main inclined grooves provided in the tire circumferential direction have a substantially V shape extending from the tire equator to the ground contact ends on both sides toward the rear arrival side in the tire rotation direction. Since such a main inclined groove guides the water film on the tire equator side to the grounding end side using the pressure at the time of grounding of the tire, the basic drainage performance is ensured.

  In addition, the maximum width position where the tire block axial width of the crown block is maximized is formed in a first arrival side region within one third of the circumferential length of the crown block in the tire circumferential direction from the end portion of the crown block in the tire rotation direction. The Such a crown block has a large area of the block tread surface in the first arrival side region and increases its rigidity, so that it can resist a large shearing force during traction or braking. Therefore, the steering stability is improved, and uneven wear such as first wear (heel wear) that tends to occur in the crown block is effectively suppressed.

  Further, the outermost end in the tire axial direction of the crown block protrudes 0.1 to 10.0 mm outward in the tire axial direction from the innermost end in the tire axial direction of the middle block adjacent to the crown block. The outer end portion including the outermost end of such a crown block has a relatively reduced ground pressure as it approaches the outer side in the tire axial direction, while the inner end portion including the innermost end of the middle block is on the tire equator side. The contact pressure increases because of For this reason, the difference in the contact pressure between the crown block and the middle block is reduced, the wear of both blocks is made uniform, and the wear resistance is improved.

  In particular, when the outer edge of the crown block's first arrival side region is formed by a single arc or a compound arc curve that protrudes toward the tire rotation direction first arrival side, the shear force during traction etc. is well balanced in the first arrival side region. Distributed with. For this reason, uneven wear resistance is remarkably improved. Further, such a crown block effectively guides the water in the vicinity of the crown block to the outside in the tire axial direction at the time of grounding, so that good drainage performance can be obtained.

It is an expanded view of the tread part of the pneumatic tire of one embodiment of the present invention. It is an enlarged view of the right half of FIG. It is an enlarged view of the crown block of this embodiment. It is an enlarged view of the crown block and middle block of this embodiment. It is an enlarged view of the shoulder block of this embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the pneumatic tire 1 of the present embodiment is a pneumatic tire in which the rotation direction is specified, and in this example, a cart tire used in a four-wheel racing cart is shown. . The tire rotation direction R is displayed by letters and / or symbols on, for example, a sidewall (not shown).

  The tread portion 2 of the pneumatic tire 1 is substantially V-shaped toward the rear side in the tire rotation direction from the tire equator C to the ground contact Te on both sides (in FIGS. 1 and 2, it is substantially V-shaped in the opposite direction). A main inclined groove 3 extending in the tire circumferential direction and a pair of inner joint grooves that are arranged on both sides of the tire equator C and that are adjacent to each other in the tire circumferential direction. 4 and a pair of outer joint grooves 5 arranged on the outer side in the tire axial direction of the inner joint groove 4 and connecting between the main inclined grooves 3 and 3 adjacent to each other in the tire circumferential direction.

  Here, the “grounding end” Te is obtained when 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. This is a position for grounding at the outermost side in the tire axial direction, and a distance in the tire axial direction between the grounding ends Te and Te is defined as a grounding width TW. Further, the dimensions and the like of each part of the tire are values in the normal state unless otherwise specified.

  The “regular rim” is a rim determined by 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. Or, if it is ETRTO, it means “Measuring Rim”, but if there is no applicable standard, the rim is recommended by the manufacturer.

  The “regular internal pressure” is an air pressure defined by the standard for each tire, and is “maximum air pressure” in the case of JATMA, and in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the case of TRA. The maximum value, ETRTO, means "INFLATION PRESSURE", but if there is no applicable standard, the internal pressure is recommended by the manufacturer. However, the normal internal pressure is 100 kPa when the tire is used for a racing cart, and 180 kPa when the tire is used for a passenger car.

  The “regular load” is a load determined by the standard for each tire, and is described in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” for JATMA and “TRAI LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” for TRA. If the maximum value of ETRTO, "LOAD CAPACITY". However, the normal load is 392 N when the tire is used for a racing cart.

  Further, the tread portion 2 includes a crown block 6 divided between the pair of inner joint grooves 4 and 4, and a pair of middle blocks 7 partitioned between the inner joint groove 4 and the outer joint groove 5. And a pair of shoulder blocks 8 formed outside the outer joint groove 5. In the present embodiment, each of the grooves 3 to 5 and the blocks 6 to 8 are formed substantially symmetrically about the tire equator C, but the present invention is not necessarily limited to such an aspect. Absent.

  The main inclined groove 3 of the present embodiment further extends from the tire equator C beyond the ground contact Te on both sides. Such a main inclined groove 3 can smoothly guide the water film near the tire equator C to the contact end Te side by using the contact pressure at the time of rotation of the tire and discharge it to the outside of the tire. Thereby, good drainage performance is ensured.

  The main inclined groove 3 of the present embodiment includes a center portion 3a having a small length extending across the tire equator C at 90 degrees with respect to the tire circumferential direction including the crown blocks 6 and 6 (that is, in the tire axial direction). A pair of middle portions 3b inclined from the both ends of the central portion 3a toward the rear side of the tire rotation direction R and at an angle α1 with respect to the tire circumferential direction and extending between the middle blocks 7 and 7; It is composed of a pair of shoulder portions 3c that are connected to the portion 3b, are inclined toward the rear side of the tire rotation direction R and inclined at an angle α2 with respect to the tire circumferential direction, and extend between the shoulder blocks 8 and 8. FIG. 1 shows a groove center line 3G of the main inclined groove 3, and the groove angle is measured by the groove center line 3G.

  Further, in the main inclined groove 3 of the present embodiment, the central portion 3a and the middle portion 3b are connected in a smooth circular arc. This is useful for reducing the resistance during drainage from the central portion 3a to the middle portion 3b.

  Further, the middle portion 3b of the present embodiment is substantially formed in a straight line shape, and drainage sent from the central portion 3a is applied to the rear arrival side and the axially outer side in the tire rotation direction using the contact pressure. Can be sent without resistance. In order to effectively exhibit such an action, the angle α1 of the middle portion 3b is preferably 30 ° or more, more preferably 45 ° or more, and preferably 80 ° or less, more preferably 60 ° or less. desirable.

  Furthermore, the shoulder portion 3c has an angle α2 larger than the angle α1 of the middle portion 3b. This can effectively increase the lateral rigidity of the shoulder block 8 to which a large lateral force acts during turning without impairing the drainage performance. In order to effectively exhibit such an action, the angle α2 of the shoulder portion 3c is preferably 60 ° or more, more preferably 75 ° or more, and preferably 90 ° or less, more preferably 85 ° or less. desirable. In particular, the angle with respect to the tire circumferential direction at the ground contact end Te of the shoulder portion 3c is preferably 60 to 90 degrees.

  Further, the angle difference α2−α1 is preferably 0 ° or more, more preferably 10 ° or more, and preferably 60 ° or less, more preferably 30 ° or less. Thereby, the drainage resistance from the middle part 3b to the shoulder part 3c can be suppressed as much as possible to further improve the drainage performance, and the lateral rigidity of the shoulder block 8 can be reliably increased to improve the steering stability.

Each of the inner joint grooves 4 is inclined in a straight line so as to incline toward the tire equator C toward the rear arrival side of the tire rotation direction R. Thereby, the crown block 6 formed between the inner joint grooves 4 and 4 has a tip-bulging shape in which the width in the tire axial direction gradually increases toward the first arrival side in the tire rotation direction R.

  The angle α3 of the inner joint groove 4 with respect to the tire circumferential direction is not particularly limited, but if it is too large, the drainage performance using the inner joint groove 4 tends to deteriorate, and conversely if too small, the crown block It is difficult to increase the rigidity of the first arrival side of 6. From such a viewpoint, the angle α3 is preferably 5 ° or more, more preferably 10 ° or more, and preferably 45 ° or less, more preferably 30 ° or less.

Each of the outer joint grooves 5 inclines outward in the tire axial direction toward the rear arrival side in the tire rotation direction R and extends linearly. For this reason, the main part of the middle block 7 divided between the outer joint groove 5 and the inner joint groove 4 has a rear bulge shape in which the width in the tire axial direction gradually increases toward the rear arrival side of the tire rotation direction R. Make.

  The angle α4 of the outer joint groove 5 with respect to the tire circumferential direction is also not particularly limited. However, if it is too large, the drainage performance using the outer joint groove 5 tends to be reduced. 8 It becomes difficult to increase the rigidity of the rear arrival side. From such a viewpoint, the angle α4 is preferably 5 ° or more, more preferably 10 ° or more, and preferably 45 ° or less, more preferably 30 ° or less.

  The groove width (the groove width perpendicular to the longitudinal direction of the groove) W and the groove depth D of the main inclined groove 3, the inner joint groove 4, and the outer joint groove 5 can be determined as appropriate according to the custom. As an example, the groove width W is desirably 3 mm or more, more preferably 4 mm or more, and preferably 20 mm or less, more preferably 10 mm or less. Further, as an example, the groove depth D is preferably 3 mm or more, more preferably 4 mm or more, and preferably 10 mm or less, more preferably 7 mm or less.

In particular, in order to maintain good drainage performance, it is desirable that the groove width W3 of the main inclined groove 3 gradually increases from the tire equator C side toward the ground contact Te. In the main inclined groove 3 of the present embodiment, the groove width W3c at the tire equator C of the central portion 3a, the groove width W3m at the middle portion 3b, and the groove width W3s of the shoulder portion 3c satisfy W3c <W3m <W3s. We are met the relationship. In addition, each groove width W3m and W3s of the middle part 3b and the shoulder part 3c are formed substantially constant. Such a main inclined groove 3 prevents overflow of drainage, and can be expected to improve drainage performance with certainty. In particular, the groove width ratios W3m / W3c and W3s / W3m are preferably 1.0 or more, more preferably 1.1 or more, and preferably 2.5 or less, more preferably 1.5 or less. Is desirable. When the groove width is not constant, the groove width W3m at the middle portion 3b indicates the groove width at the intermediate position between the tire equator C and the ground contact Te, and the groove width W3s of the shoulder portion 3c is The groove width on the ground contact Te is shown.

  As for the groove width of the joint groove, the groove width W5 of the outer joint groove 5 is preferably larger than the groove width W4 of the inner joint groove 4. As a result, the land ratio on the tire equator C side can be increased and the traction during driving can be sufficiently exerted, and the drainage performance on the ground contact end Te side can be improved, so that sufficient drainage performance can be obtained even during turning.

  As shown in FIG. 3 in an enlarged manner, the crown block 6 of the present embodiment has a bulge shape as described above. More specifically, the width in the tire axial direction of the crown block 6 is maximized. A position 6B having the maximum width BW is formed in the first arrival side region S within 1/3 of the tire circumferential direction length L1 of the crown block 6 from the end portion 6s on the first arrival side in the tire rotation direction of the crown block 6. Further, in the crown block 6 of the present embodiment, the respective tire axial widths gradually decrease from the position 6B of the maximum width BW toward the first arrival side and the rear arrival side in the tire rotation direction R. Accordingly, the contour shape of the tread surface of the crown block 6 of the present embodiment is formed in a substantially oval shape that is substantially line-symmetric with respect to the tire equator C.

  Such a crown block 6 relatively increases the shear rigidity in the tire circumferential direction of the first arrival side region S, and can particularly resist a large shear force during driving. Therefore, a large traction can be exhibited during driving. In addition, since the slip at the time of driving is reduced, the crown block 6 can effectively suppress heel wear, block chipping, and the like that tend to occur at the end 6s on the tire rotation direction first arrival side. In particular, as in the present embodiment, the position 6B having the maximum width BW is 10 to 33.3 of the length L1 from the end 6s, more preferably from the end 6s on the front side in the tire rotation direction. % Is preferably provided at a position separated by a distance of%.

  Further, in the crown block 6, the outer edge 6M1 of the first arrival side region S within one third of the tire circumferential direction length L1 of the crown block 6 from the end portion 6s on the tire rotation direction first arrival side protrudes toward the tire rotation direction first arrival side. It is desirable to be formed by a smooth curve of a single arc or a composite arc. The outer edge means the outer edge of the block tread.

  In the present embodiment, the outer edge 6M1 is formed of a compound arc curve formed by connecting two arcs. Specifically, the outer edge 6M1 includes a central arc c1 having a radius of curvature R1 passing through the end 6s and an outer arc c2 having a radius of curvature R2 that is continuous with both sides and is larger than the radius of curvature R1. It is formed in a line symmetrical shape with respect to C. In such a crown block 6, when traveling straight on a wet road surface, the end portion 6 s that first comes into contact with the road surface divides the water film on the road surface into two left and right, and the middle portion 3 b and the shoulder of the main inclined groove 3. It can be smoothly guided to the portion 3c.

  In order to maintain the rigidity of the end 6s sufficiently high and ensure the above-described drainage performance, the radius of curvature R1 of the central arc c1 is preferably 5 mm or more, more preferably 10 mm or more, and preferably 100 mm or less, more preferably 50 mm or less is desirable. In order to increase the rigidity of the entire first arrival side region S in a well-balanced manner, the radius of curvature R2 of the outer arc c2 is preferably 3 mm or more, more preferably 5 mm or more, and preferably 100 mm or less, more preferably 50 mm or less. Is desirable. Preferably, the curvature radius ratio R2 / R1 is preferably in the range of 0.1 to 1.0.

  The outer edge 6M2 including the end 6k of the crown block 6 on the rear arrival side in the tire rotation direction is configured by an arc curve c3 having a radius of curvature R3 that smoothly protrudes toward the rear arrival side in the tire rotation direction. The curvature radius R3 is larger than the curvature radii R1 and R2, preferably 7 mm or more, more preferably 10 mm or more, and preferably 1000 mm or less, more preferably 200 mm or less. The outer edge 6M2 on the rear landing side of the crown block 6 can prevent the rigidity on the rear landing side having a relatively small width in the tire axial direction from being excessively lowered and the steering stability from being deteriorated. In the crown block 6 of the present embodiment, a linear portion 6S is formed between the outer edge 6M1 on the first arrival side in the tire rotation direction R and the outer edge 6M2 on the rear arrival side.

  In addition, as for crown block 6, it is desirable for ratio L1 / BW of the said maximum width BW and the length L1 of the tire circumferential direction to be 1.0-3.0. When the ratio L1 / BW is less than 1.0, the rigidity in the circumferential direction of the crown block 6 is likely to be reduced, the amount of deformation at the time of braking and driving becomes large, and thus the braking force and driving force cannot be sufficiently obtained. Tend. On the other hand, when the ratio L1 / BW exceeds 3.0, the rigidity in the tire axial direction is lowered, so that there is a possibility that sufficient lateral force cannot be exhibited during turning.

  In particular, when the tire is for the front wheel of a racing cart, a large slip angle is given during turning, so that the ratio L1 / BW is set to 1.0-2. A range of 5 is desirable. On the other hand, when the tire is for the rear wheel of the racing cart, the tire receives a large shearing force in the tire circumferential direction with respect to the road surface. Therefore, in order to increase the tire circumferential rigidity during driving, the ratio L1 / BW is 1 A range of .5 to 3.0 is desirable.

  The middle block 7 has a substantially trapezoidal shape in which both side edges 7M1, 7M2 in the tire circumferential direction are substantially parallel and the length of the side edge 7M4 on the outer side in the tire axial direction is larger than the side edge 7M3 on the inner side in the tire axial direction. Make. Further, as described above, the main part of the middle block 7 has a rear bulge shape in which the width in the tire axial direction gradually increases toward the rear arrival side of the tire rotation direction R. Such a rear bulge shape can provide a high shear rigidity by relatively increasing the rigidity of the middle block 7 on the rear arrival side in the tire rotation direction, and thus helps to exert a large braking force during braking. In addition, the middle block 7 can suppress slip during braking to a small extent, and thus is useful for suppressing uneven wear such as toe wear over a long period of time.

  As a preferred embodiment, each corner portion of the tread surface of the middle block 7 is rounded by an arc. As a result, the drainage flowing around the middle block 7, that is, the drainage resistance at the middle portion 3 b of the main inclined groove 3, the inner joint groove 4 and the outer joint groove 5 can be reduced to improve drainage performance.

  Further, as shown in FIG. 4, the outermost end 6 e in the tire axial direction of the crown block 6 is 0.1 to less than the innermost end 7 i in the tire axial direction of the middle block 7 adjacent to the crown block 6. It is formed on the outer side of the 10.0 mm tire axial direction. That is, the difference L6-L7 between the distance L6 between the outermost end 6e of the crown block 6 and the tire equator C in the tire axial direction and the distance L7 between the innermost end 7i of the middle block 7 and the tire equator C in the tire axial direction. Is set to 0.1 to 10.0 mm.

  As the outer end portion including the outermost end 6e of the crown block 6 approaches the outer side in the tire axial direction, the ground pressure is relatively reduced. On the other hand, since the inner end portion including the innermost end 7i of the middle block 7 is closer to the tire equator C side, the contact pressure increases. For this reason, the difference in ground pressure between the crown block 6 and the middle block 7 is reduced, the wear of both blocks is made uniform, and the wear resistance is improved.

  As a result of various experiments conducted by the inventors, it has been found that when the overlap length L6 to L7 is less than 0.1 mm, the above-mentioned contact pressure equalizing action cannot be sufficiently obtained. On the contrary, when the length of the overlap exceeds 10.0 mm, the drainage performance in the inner joint groove 4 is deteriorated, and the outermost ends 6e and / or innermost ends 7i of the respective blocks 6 and 7 are sharpened. Uneven wear starting from the portion is likely to occur. From such a viewpoint, the length of the overlap is preferably 4.0 mm or more, and preferably 10.0 mm or less.

  If the position of the innermost end 7i is too biased toward the rear end, the groove width between the center block 6 and the middle block 7 (that is, the groove width of the central portion 3a and the middle portion 3b of the main inclined groove 3). May become too small, and drainage performance may be reduced. On the contrary, if the position of the innermost end 7i is too biased toward the first end, the inclination angle α3 of the inner joint groove 4 becomes too large, and the drainage performance may be deteriorated. Therefore, as shown in FIG. 2, from the viewpoint of ensuring drainage, the innermost end 7 i of the middle block 7 extends from the intermediate position 7H of the tire circumferential length L2 of the middle block 7 to the tire circumferential length. It is desirable to form in a region within 20% of L2. Thereby, especially the drainage property in the center part 3a, the middle part 3b, and the inner joint groove 4 of the main inclined groove 3 is ensured. In order to further exert such an effect, the innermost end 7i is preferably formed in a region within 10% of the length L2 from the intermediate position 7H. In the middle block 7 of the present embodiment, the position of the innermost end 7 i is the maximum width position of the middle block 7.

  4, the tire circumferential direction line 6G passing through the outermost end 6e of the crown block 6 is adjacent to the crown block 6 (adjacent between the main inclined grooves 3 and 3). 7 and two intersection points 7a and 7b. The tire circumferential direction distance L4 between the intersections 7a and 7b is preferably 0.1 mm or more, more preferably 5 mm or more, and preferably 30 mm or less, more preferably 15 mm or less. Thereby, the contact pressure between the crown block 6 and the middle block 7 is further uniformed, and the drainage of the inner joint groove 4 is ensured.

  Further, as shown in FIG. 5, the shoulder block 8 of the present embodiment includes an outer portion 8a extending from the ground contact end Te to the tire axial direction outer side, and the outer contact portion Te connected to the outer portion 8a on the inner side in the tire axial direction. The inner portion 8b is formed.

  The outer portion 8a is not substantially grounded during straight traveling, but is grounded to the road surface during turning, thereby enhancing the lateral grip and improving the steering stability. In addition, the inner portion 8b has a vertically long shape in the tire circumferential direction, and the width in the tire axial direction gradually increases toward the first arrival side in the tire rotation direction R. Such an inner portion 8b is preferable in that, like the crown block 6, it can exhibit good traction performance during driving. Further, the two corner portions of the tread surface formed on the inner portion 8b of the shoulder block 8 are also rounded by an arc.

  Further, in the pneumatic tire 1 for carts of the present embodiment, the radius of curvature of the outer surface of the tread portion 2 is preferably 100 mm or more in order to obtain a stable turning force in the tire meridian section including the tire rotation axis. The thickness is preferably 200 mm or more, and is preferably set within a range of 1000 mm or less, more preferably 500 mm or less.

  As mentioned above, although embodiment of this invention was explained in full detail, it cannot be overemphasized that this invention is not limited to illustrated embodiment, and can be deform | transformed and implemented in a various aspect.

  In order to confirm the effect of the present invention, based on the specifications in Table 1, a pneumatic tire for a racing cart having the tread portion of FIG. 1 (front wheel 10 × 4.50-5 and rear wheel 11 × 7.10-5). Was prototyped. Various performances were tested for them. Specific dimensions are as follows. All specifications are the same except for the specifications in Table 1.

(Front wheel / rear wheel)
<Main inclined groove>
Groove width W3c at the center: 3.5 to 4.5 mm / 4.0 to 5.0 mm
Middle part groove width W3m: 5.5 to 6.5 mm / 9.0 to 10.0 mm
Shoulder width W3s: 7.5 to 9.0 mm / 10.5 to 11.5 mm
Angle with respect to the tire circumferential direction at the center part: 60 to 90 degrees / 70 to 90 degrees Angle with respect to the tire circumferential direction of the middle part α1: 55 degrees / 60 degrees Angle α2 with respect to the tire circumferential direction at the contact end of the shoulder part: 80 degrees / 85 degrees <inner joint groove>
Groove width W4: 4.0 mm / 6.0 mm
Angle α3 with respect to tire circumferential direction: 10 to 20 degrees / 15 to 25 degrees <outer seam groove>
Groove width W5: 4.0 mm / 6.0 mm
Angle α4 with respect to tire circumferential direction: 10 to 20 degrees / 5 to 15 degrees <Others>
Groove depth D of each groove: 5.5 mm / 5.5 mm
Maximum width of the crown block in the tire axial direction BW: 22mm / 30mm
Crown block tire circumferential length L1: 31mm / 40mm
The test method is as follows.

<Drainage and steering stability performance>
Each test tire was mounted on a two-cycle automatic four-wheel racing cart with a displacement of 100 cc under the internal pressure conditions of a rim (front wheel 4.50 and rear wheel 8.0) and an internal pressure of 100 KPa (the front and rear are the same). Then, with this test vehicle, the test course of one lap 734 m was put into a wet asphalt state, and was run for seven laps fully open. The drainage, side grip, traction and brake performance at this time were evaluated by a five-point method based on the test driver's sensuality. The larger the value, the better. Steering stability performance is a comprehensive evaluation of side grip, traction and braking performance.

<Uneven wear resistance>
After the test run, the test driver visually confirmed the presence and state of uneven wear on the tread portion. Evaluation was made by a five-point method, where 1 was a state in which uneven wear was severe and 5 was a state in which there was no uneven wear. The larger the value, the better.
Table 1 shows the test results.

  As a result of the test, it was confirmed that in the example, the steering stability performance and the uneven wear resistance performance were improved while maintaining the drainage performance as compared with the comparative example.

DESCRIPTION OF SYMBOLS 1 Pneumatic tire 2 Tread part 3 Main inclined groove 4 A pair of inner joint groove 5 A pair of outer joint groove 6 Crown block 6B Maximum width position 6e Outermost end 6f of the crown block in the tire axial direction First arrival side of the crown block in the tire rotation direction End 6S First arrival side region 7 Middle block 7i Innermost end 8 of the middle block in the tire axial direction Shoulder block C Tire equator R Rotating direction Te Grounding end

Claims (4)

A pneumatic tire with a specified direction of rotation,
A main inclined groove extending in a substantially V shape from the tire equator to the ground contact ends on both sides toward the rear arrival side in the tire rotation direction and spaced in the tire circumferential direction on the tread portion;
A pair of inner connecting grooves extending in the tire equator side toward between said main slant grooves adjacent disposed and having the tire circumferential direction on both sides of the tire equator to the joint Gikatsu tire rotation direction rear callee,
And a pair of outer connecting grooves extending axially outwardly toward between the main oblique grooves disposed in the tire axial direction outer side and adjacent in the tire circumferential direction to the next Gikatsu tire rotation direction rear called side of the inner connecting grooves By being placed
A crown block divided by the pair of inner joint grooves between the main inclined grooves adjacent in the tire circumferential direction;
A pair of middle blocks partitioned between the inner joint groove and the outer joint groove;
A pair of shoulder blocks formed outside the outer joint groove,
The maximum width position where the tire axial direction width of the crown block is maximized is formed in a first arrival side region within one third of the circumferential length of the crown block in the tire circumferential direction from the end portion of the crown block in the tire rotation direction. As
The outermost end in the tire axial direction of the crown block protrudes 0.1 to 10.0 mm in the tire axial direction from the innermost end in the tire axial direction of the middle block adjacent to the crown block. Pneumatic tires.   2. The pneumatic tire according to claim 1, wherein an outer edge of the first arrival side region of the crown block is formed by a single arc or a compound arc curve that is convex toward the tire rotation direction first arrival side.   3. The air according to claim 1, wherein the innermost end of the middle block is formed in a region within 20% of a tire circumferential direction length of the middle block from an intermediate position of a tire circumferential length of the middle block. Enter tire. The pneumatic tire according to any one of claims 1 to 5, wherein the main inclined groove has an angle of 60 to 90 degrees with respect to a tire circumferential direction at a ground contact end.

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