JP2016084046A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of maintaining a suppression effect of a hydroplane phenomenon for a long period of time even when abrasion of a tread part advances.SOLUTION: In a pneumatic tire, a center land part 5 projects outside in a tire radial direction with respect to a first virtual tread profile P1 on a tire meridian cross section; a tread rubber G of a tread part 2 includes a cap rubber layer 10 disposed on the outermost side, and a base rubber layer 11 arranged on the inner side of the cap rubber layer 10, and made of rubber more excellent than the cap rubber layer 10 in abrasion resistance; and the base rubber layer 11 of a center land part 5 projects outside in the tire radial direction with respect to a second virtual tread profile P2 smoothly connecting between outer ends 11e in the tire radial direction of the base rubber layer 11 of a shoulder land part 6 along the first virtual tread profile P1.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a pneumatic tire that can maintain the effect of suppressing the hydroplaning phenomenon over a long period of time.

  Patent Document 1 below proposes a pneumatic tire in which a center land portion of a tread portion is protruded outward in the tire radial direction from a virtual tread profile line. Such a center land portion distributes water on the road surface to both outer sides in the tire axial direction, and shifts the occurrence of the hydroplaning phenomenon to a higher speed region.

JP 2005-31890 A

  The center land portion of the tire as described above tends to be worn earlier than other portions because a large ground pressure is likely to act. In such a case, since the protrusion amount of the center land portion with respect to the virtual tread profile is reduced, the effect of suppressing the occurrence of the hydroplaning phenomenon cannot be sufficiently exhibited.

  The present invention has been devised in view of the above circumstances, and provides a pneumatic tire capable of maintaining the effect of suppressing the hydroplane phenomenon over a long period of time even when wear of the tread portion progresses. The main purpose.

  In the present invention, the tread portion is provided with a pair of shoulder main grooves extending continuously in the tire circumferential direction, so that a center land portion between the shoulder main grooves, and between the shoulder main grooves and the tread ends. A pneumatic tire divided into a shoulder land portion, wherein the center land portion is a first virtual tread that smoothly connects the tread ends along the tire lumen surface in a tire meridian section including a tire rotation axis. The tread rubber of the tread portion protrudes outward in the tire radial direction from the profile, and the cap rubber layer arranged on the outermost side, the inner side of the cap rubber layer, and wear resistance performance than the cap rubber layer A base rubber layer made of excellent rubber, and the base rubber layer in the center land portion has the shoulder in the tire meridian cross section. Characterized in that it projects radially outward tire than the second virtual tread profile connecting the radially outer end of the base rubber layer of the land portion smoothly along the first virtual tread profile.

  In the pneumatic tire according to the present invention, it is preferable that the base rubber layer is made of rubber having a loss tangent tanδ smaller than that of the cap rubber layer.

  In the pneumatic tire according to the present invention, the base rubber layer includes a first base rubber layer and a second base rubber layer disposed outside the first base rubber layer, and the first base rubber layer. Is preferably made of rubber having higher wear resistance than the second base rubber layer.

  In the pneumatic tire according to the present invention, it is preferable that a loss tangent tan δ of the first base rubber layer is smaller than that of the second base rubber layer.

  In the pneumatic tire according to the present invention, it is desirable that the thickness of the cap rubber layer of the shoulder land portion gradually increases toward the outer side in the tire axial direction.

  In the pneumatic tire according to the present invention, the center land portion includes a ground surface that contacts the road surface, and a side wall surface that extends inward in the tire radial direction from the ground surface, and the cap rubber layer includes the side wall surface. In addition, it is desirable that the thickness is larger than the thickness at the ground contact surface.

  In the pneumatic tire according to the present invention, the center land portion includes a ground surface that contacts the road surface, and a side wall surface that extends inward in the tire radial direction from the ground surface, and the cap rubber layer includes the side wall surface. In addition, the thickness is preferably smaller than the thickness at the ground contact surface.

  In the pneumatic tire according to the present invention, the center land portion includes a ground surface that contacts the road surface, and a side wall surface that extends inward in the tire radial direction from the ground surface, and the cap rubber layer includes the side wall surface. It is desirable to extend and not be arranged at the center of the ground plane.

  The tread portion of the pneumatic tire of the present invention is provided with a pair of shoulder main grooves extending continuously in the tire circumferential direction, so that the center land portion between the shoulder main grooves, the shoulder main grooves, and the tread ends. The shoulder land between is divided. The center land portion projects outward in the tire radial direction from the first virtual tread profile that smoothly connects the tread ends along the tire lumen surface in the tire meridian cross section including the tire rotation axis. Such a center land portion effectively divides the water on the wet road surface into left and right shoulders and guides it to the shoulder main groove, which in turn suppresses the occurrence of the hydroplaning phenomenon to a higher speed range. Can do.

  On the other hand, the tread rubber of the tread portion includes a cap rubber layer disposed on the outermost side and a base rubber layer made of rubber that is disposed on the inner side of the cap rubber layer and has higher wear resistance than the cap rubber layer. Contains. In such a tread portion, the wear resistance of the center land portion and the shoulder land portion is gradually improved with the progress of wear because the base rubber layer approaches the ground contact surface as the wear of the cap rubber layer progresses.

  Further, the base rubber layer in the center land portion protrudes outward in the tire radial direction from the second virtual tread profile that smoothly connects the outer radial ends of the base rubber layer in the shoulder land portion along the first virtual tread profile. ing. Thereby, the wear resistance performance of the center land portion is maintained higher than the wear resistance performance of the shoulder land portion when the tread portion wear proceeds. Therefore, in the pneumatic tire of the present invention, the early wear of the center land portion is suppressed, and even if the wear of the tread portion progresses, the protrusion amount of the center land portion with respect to the first virtual tread profile at the time of wear can be maintained. In addition, the effect of suppressing the hydroplaning phenomenon can be maintained over a long period of time.

It is a tire meridian sectional view of a pneumatic tire of one embodiment of the present invention. FIG. 2 is a partially enlarged view on the right side of the tire of FIG. 1. It is a figure at the time of 10% abrasion of the tread part of FIG. It is a figure at the time of 20% abrasion of the tread part of FIG. It is a figure at the time of 50% abrasion of the tread part of FIG. It is an enlarged view of the center land part vicinity of FIG. It is tire meridian sectional drawing of the tread part of the pneumatic tire of other modes.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a tire meridian cross-sectional view including a tire rotation axis of a pneumatic tire (hereinafter may be simply referred to as “tire”) showing an embodiment of the present invention. The tire of this embodiment can be suitably used for, for example, a passenger car.

  The tread portion 2 of the tire is provided with a pair of shoulder main grooves 3 and 3 extending continuously in the tire circumferential direction. The shoulder main groove 3 is disposed, for example, on the most tread end Te side.

  The “tread end” Te is a position on the outermost side in the tire axial direction of the contact surface when a normal load is applied to a normal tire and contacted with a flat surface with a camber angle of 0 °. The tire axial distance between the tread ends Te and Te in the normal state is defined as the tread width TW.

  The “normal state” is a no-load state in which a tire is assembled on a normal rim (not shown) and filled with a normal internal pressure. In this specification, unless otherwise specified, the dimensions 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, For ETRTO, "Measuring Rim".

  “Regular internal pressure” is the air pressure defined by each standard for each tire in the standard system including the standard on which the tire is based. For example, “maximum air pressure” for JATMA, table “TIRE” for TRA The maximum value described in “LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”, “INFLATION PRESSURE” in the case of ETRTO.

  “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. For example, “maximum load capacity” for JATMA, “table for TRA” The maximum value described in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES”, or “LOAD CAPACITY” in the case of ETRTO.

  The tread portion 2 of the present embodiment is further provided with a center main groove 4 extending continuously between the shoulder main grooves 3 in the tire circumferential direction. The center main groove 4 is arranged on the tire equator C, for example.

  Each shoulder main groove 3 and center main groove 4 desirably extend linearly in order to improve drainage. From the same point of view, the groove volume of the shoulder main groove 3 is preferably larger than the groove volume of the center main groove 4, for example.

  FIG. 2 shows an enlarged view of the right portion of FIG. As shown in FIG. 2, the groove width W1 of the shoulder main groove 3 is preferably in the range of 2% to 13% of the tread width TW, for example, in order to ensure rigidity and drainage on the tread end Te side. . From the same viewpoint, the groove depth D1 of the shoulder main groove 3 is preferably in the range of 4.0 to 12.0 mm.

The groove width W2 of the center main groove 4 is preferably in the range of 2 to 20% of the tread width TW, for example, in order to ensure rigidity and drainage on the tire equator C side. From the same viewpoint, the groove depth D2 of the center main groove 4 is approximately the same as the groove depth D1 of the shoulder main groove 3.

  As shown in FIG. 1 or FIG. 2, by providing the shoulder main groove 3 described above, the tread portion 2 has a center land portion 5 between the shoulder main grooves 3, a shoulder main groove 3 and a tread end Te. And a shoulder land portion 6 between them. The center land portion 5 of the present embodiment is divided into a first center land portion 7 on one side of the tire equator C and a second center land portion 8 on the other side by providing the center main groove 4.

  The first center land portion 7 and the second center land portion 8 are preferably formed in, for example, a rib shape extending continuously in the tire circumferential direction in order to ensure the rigidity of the tread portion 2 on the tire equator C side. . The rib shape means a land portion that is continuous in the tire circumferential direction and does not have a transverse groove across the entire width of the land portion. The first center land portion 7 and the second center land portion 8 of the present embodiment each include a ground surface S that contacts the road surface and a pair of side wall surfaces J that extend inward in the tire radial direction from the ground surface S. .

  The ground contact surfaces S of the first center land portion 7 and the second center land portion 8 are formed so as to protrude outward in the tire radial direction. In a preferred embodiment, the ground contact surface S of the first center land portion 7 and the second center land portion 8 is formed by smoothly connecting a plurality of arcs having different curvature radii.

  A first virtual tread profile P1 is drawn on the tire meridian cross section of FIGS. The first virtual tread profile P1 smoothly connects the tread ends Te and Te along the tire cavity surface M. When the tire lumen surface M is uneven, the first virtual tread profile P1 is obtained by approximating a smooth single arc obtained by flattening the unevenness of the tire lumen surface M.

  At least a part of the first center land portion 7 and the second center land portion 8 protrudes outward in the tire radial direction from the first virtual tread profile P1. Since the first center land portion 7 and the second center land portion 8 have a high contact pressure on the wet road surface, the water on the road surface is effectively divided into left and right to the shoulder main groove 3 and the center main groove 4. As a result, the occurrence of the hydroplaning phenomenon can be suppressed by shifting to a higher speed region.

  Each shoulder land portion 6 is preferably formed in a block shape, for example, in order to drain the water in the shoulder main groove 3 outward in the tire axial direction. The block shape means a land portion in which a plurality of blocks are divided in the tire circumferential direction by providing a transverse groove across the entire width of the land portion. However, the shoulder land portion 6 may be formed as a rib.

  Each shoulder land portion 6 of the present embodiment also includes a ground surface S that contacts the road surface and a side wall surface J that extends from the ground surface S inward in the tire radial direction. The ground contact surface S of the shoulder land portion 6 is formed along the first virtual tread profile P1 in the tire meridian cross section, for example.

  The tread rubber G of the tread portion 2 includes a cap rubber layer 10 disposed on the outermost side and a base rubber layer 11 disposed on the inner side of the cap rubber layer 10. In this embodiment, the 1st center land part 7, the 2nd center land part 8, and each shoulder land part 6 are formed including the cap rubber layer 10 and the base rubber layer 11, respectively. The cap rubber layer 10 of the present embodiment extends over the ground contact surface S and the side wall surface J of the first center land portion 7, the second center land portion 8 and the shoulder land portion 6.

  The base rubber layer 11 is made of rubber that has better wear resistance than the cap rubber layer 10. The wear resistance performance can be improved, for example, by increasing the fracture characteristics of rubber. In this embodiment, the fracture characteristics of rubber are enhanced by increasing the amount of vulcanizing agent such as sulfur. In the tread rubber G as in the present embodiment, as the wear of the cap rubber layer 10 progresses, the base rubber layer 11 approaches the ground contact surface S. Therefore, as the wear progresses, the first center land portion 7 and the second center land The rigidity of the portion 8 and each shoulder land portion 6 is increased, and the wear resistance is gradually improved.

  The base rubber layer 11 is preferably formed of rubber having a loss tangent tan δ smaller than that of the cap rubber layer 10. The loss tangent tan δ is suppressed to a small value by increasing the amount of reinforcing agent such as silica or carbon black. In such a tread portion 2, the base rubber layer 11 approaches the ground contact surface S as wear of the cap rubber layer 10 progresses. Therefore, as the wear progresses, the low heat generation performance of the tread portion 2 is enhanced, and as a result, fuel consumption Performance can be improved.

  The outer surface 11a of the base rubber layer 11 of the first center land portion 7 and the second center land portion 8 is formed along each ground contact surface S of the first center land portion 7 and the second center land portion 8 in the tire meridian cross section. Has been.

  In the tire meridian cross-sectional views of FIGS. 1 and 2, a second virtual tread profile P2 is further depicted. As shown well in FIG. 1, the second virtual tread profile P2 is smooth between the tire radial direction outer ends 11e and 11e of the base rubber layer 11 of the shoulder land portion 6 along the first virtual tread profile P1. It is extended.

  At least a part of each base rubber layer 11 of the first center land portion 7 and the second center land portion 8 protrudes outward in the tire radial direction from the second virtual tread profile P2. Thereby, when the wear of the tread portion 2 proceeds, the wear resistance performance of the first center land portion 7 and the second center land portion 8 tends to be maintained higher than the wear resistance performance of the shoulder land portion 6. Therefore, in the tire according to the present embodiment, the early wear of the first center land portion 7 and the second center land portion 8 with respect to the shoulder land portion 6 is suppressed, and even if the wear of the tread portion 2 progresses, the virtual tread at the time of wear is increased. The protrusion amount of the first center land portion 7 and the second center land portion 8 with respect to the profile can be maintained, and as a result, the effect of suppressing the hydroplaning phenomenon can be maintained over a long period of time.

  FIGS. 3 to 5 are diagrams showing examples of the portion of FIG. 2 at the time of 10% wear, 20% wear, and 50% wear, respectively. The wear state of the tread portion 2 is indicated by the ratio (d / D2) between the groove depth D2 of the center main groove 4 of the tire and the reduction value d of the groove depth of the center main groove 4 during wear.

  Since the first center land portion 7 and the second center land portion 8 protrude outward in the tire radial direction from the first virtual tread profile P1 at the initial use of the tire, the ground contact pressure is larger than that of the shoulder land portion 6. Act. For this reason, as shown in FIG. 3, in the tread portion 2 at the time of 10% wear, the wear amount of each cap rubber layer 10 of the first center land portion 7 and the second center land portion 8 is that of the shoulder land portion 6. It is larger than that of the cap rubber layer 10. Therefore, the protrusion amount from the 1st virtual tread profile P1 of the 1st center land part 7 and the 2nd center land part 8 reduces. However, even at the time of 10% wear, for example, while a part of the first center land portion 7 and the second center land portion 8 protrudes outward in the tire radial direction from the first virtual tread profile P1 after wear, The suppression effect of the hydroplaning phenomenon is maintained.

  In the first center land portion 7 and the second center land portion 8, the cap rubber layer 10 wears more than the shoulder land portion 6, so that the base rubber layer 11 is brought into contact with the ground plane S earlier than the shoulder land portion 6. Get closer. Thereby, the first center land portion 7 and the second center land portion 8 have higher wear resistance than the shoulder land portion 6. For this reason, as shown in FIG. 4, the shoulder land portion 6 is worn more than the first center land portion 7 and the second center land portion 8 at the time of 20% wear. Therefore, at the time of 20% wear, the amount of protrusion of the first center land portion 7 and the second center land portion 8 from the first virtual tread profile P1 is increased again, and thus the effect of suppressing the hydroplaning phenomenon is maintained. .

  When the wear of the tread portion 2 further proceeds, the base rubber layer 11 of the first center land portion 7, the second center land portion 8, and each shoulder land portion 6 is exposed to the ground contact surface S as shown in FIG. 5. For this reason, at the time of 50% wear, the base rubber layer 11 of the first center land portion 7 and the second center land portion 8 tends to wear more than the base rubber layer 11 of the shoulder land portion 6. The suppression effect of the hydroplaning phenomenon is maintained while part of the first center land portion 7 and the second center land portion 8 protrudes outward in the tire radial direction from the first virtual tread profile P1.

  FIG. 6 shows an enlarged cross-sectional view of the first center land portion 7 at the time of 50% wear. When the first center land portion 7 and the second center land portion 8 are worn, the outer edge of the ground surface S is worn faster than the center side of the ground surface S. Thereby, the ground-contact surface S of the 1st center land part 7 and the 2nd center land part 8 can maintain the circular arc shape which protrudes on the tire radial direction outer side, and the suppression effect of a hydroplaning phenomenon is maintained by extension.

  In order to exhibit the above-described action more effectively, the cap rubber layer 10 is exposed to the ground contact surface S in the range of 5 to 40% of the ground contact surface S of the tread portion 2 in the tread portion 2 at 50% wear, for example. It is desirable to arrange so as to.

  As shown in FIG. 1 or FIG. 2, the cap rubber layer 10 of a more preferred embodiment has a thickness at the side wall surface J of the first center land portion 7 and the second center land portion 8, for example, the first center land portion. It is larger than the thickness of the contact surface S of the part 7 and the second center land part 8. Such a cap rubber layer 10 can more reliably maintain the arc shape of the ground contact surface S when the tread portion 2 is worn. From such a viewpoint, the cap rubber layer 10 extends, for example, on the side wall surface J of the first center land portion 7 and the second center land portion 8, and the first center land portion 7 and the second center land portion 8. The aspect which does not distribute to the center part of the ground-contact plane S may be sufficient. In this aspect, when the tread portion 2 is worn, the arc shape of the ground contact surface S of the first center land portion 7 and the second center land portion 8 can be maintained, and thus the effect of suppressing the hydroplaning phenomenon is maintained.

  Further, the cap rubber layer 10 of another aspect has a thickness at the side wall surface J of the first center land portion 7 and the second center land portion 8, for example, of the first center land portion 7 and the second center land portion 8. It is smaller than the thickness at the ground plane S. Such a cap rubber layer 10 can eliminate the possibility that the cap rubber layer 10 disposed on the outer side in the tire radial direction becomes thin and damaged due to the expansion of the tire during vulcanization molding.

  In order to maintain the effect of suppressing the hydroplaning phenomenon, even if the wear of the tread portion 2 progresses, the protruding amount of the first center land portion 7 and the second center land portion 8 with respect to the virtual tread profile at each wear is maintained large. It is desirable to be done. From such a viewpoint, it is desirable that the thickness of the cap rubber layer 10 on the ground contact surface S of the shoulder land portion 6 of the present embodiment gradually increases toward the outer side in the tire axial direction as shown in FIG. According to such an aspect, the progress of wear of the first center land portion 7 and the second center land portion 8 is delayed as compared with the progress of wear on the tread end Te side, and the first center with respect to the virtual tread profile. The protruding amount of the land portion 7 and the second center land portion 8 can be maintained large.

  In order to exhibit the above-mentioned operation more effectively, the thickness of the cap rubber layer 10 on the ground contact surface S of the shoulder land portion 6 is, for example, in the range of 1.0 to 6.0 mm at the end portion on the tire equator C side. Yes, at the end of the tread end Te side, the range is 1.5 to 8.0 mm.

  FIG. 7 shows an enlarged cross-sectional view of the tread portion 2 of another aspect. The base rubber layer 11 of the tread portion 2 in FIG. 7 includes a first base rubber layer 11i and a second base rubber layer 11o disposed on the outside of the first base rubber layer 11i.

  The first base rubber layer 11i is more excellent in wear resistance than the second base rubber layer 11o. In such a base rubber layer 11, when the tread portion 2 is worn, the first center land portion 7 and the second center land portion 8 are quickly worn and the shoulder land portion 6 is quickly worn. Is repeated more, and as a result, the protrusion amount of the 1st center land part 7 and the 2nd center land part 8 with respect to a virtual tread profile can be maintained more reliably.

  The base rubber layer 11 of the above-described aspect is desirably formed of rubber in which the loss tangent tan δ of the first base rubber layer 11 i is smaller than the loss tangent tan δ of the second base rubber layer 11 o. In such a base rubber layer 11, since the first base rubber layer 11i approaches the ground contact surface S as the wear of the second base rubber layer 11o progresses, the low heat generation performance of the tread portion 2 increases as the wear progresses. As a result, fuel efficiency can be further improved.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, it cannot be overemphasized that this invention can be changed into various aspects, without being limited to said specific embodiment.

A tire (195 / 65R15) having the tread profile of FIG. 1 was prototyped and tested based on the specifications in Table 1. The tire of the comparative example is not provided with a cap rubber layer.
The test method is as follows.

<Abrasion resistance>
Using an abrasion tester (Laboratory Abrasion and Skid Tester), the volume loss of each rubber composition was measured under the conditions of a load of 50 N, a speed of 20 km / h, and a slip angle of 5 degrees. Evaluation is shown by the index | exponent which makes the reciprocal number of the volume loss amount of the 2nd base rubber layer of Example 1 100, and it is excellent in abrasion resistance performance, so that a score is large.

<Low heat generation performance (1)>
Using a spectrometer (manufactured by Ueshima Seisakusho Co., Ltd.), the loss tangent tan δ of each rubber composition test piece was measured at a dynamic strain amplitude of 1%, a frequency of 10 Hz, and a temperature of 50 degrees. The evaluation is indicated by an index in which the reciprocal of the loss tangent tan δ of the second base rubber layer of Example 1 is 100. The larger the score, the better the low heat generation performance.

<Suppression effect of hydroplaning phenomenon>
A test vehicle in which each test tire is mounted on all wheels under the following conditions is a wet road surface having a 10 mm water film on which a tire on one side of the vehicle is driven, and a dry road surface on which a tire on the other side of the vehicle is driven. The vehicle speed was measured when the slip rate of the tire on one side and the tire on the other side differed by 10%. Evaluation is shown by the index | exponent which sets the speed | rate measured at the time of the initial use of Example 1 to 100, and the suppression effect of a hydroplaning phenomenon is excellent, so that a score is large.
Rims: 15 × 6.0J
Internal pressure: 220 kPa

<Low fuel consumption performance (2)>
Using a rolling resistance tester, the rolling resistance when each sample tire was run under the following conditions was measured. Evaluation is shown by the index | exponent which makes the reciprocal number of rolling resistance of Example 1 100, and it is excellent in fuel-efficient performance, so that a score is large.
Rims: 15x6JJ
Internal pressure: 230 kPa
Load: 3.43kN
Speed: 80km / h

  As a result of the test, it can be confirmed that the tire of the example has an improved hydroplaning effect and a low fuel consumption performance as compared with the comparative example.

2 tread portion 3 shoulder main groove 5 center land portion 6 shoulder land portion 10 cap rubber layer 11 base rubber layer 11e tire radial direction outer end G tread rubber C tire equator P1 first virtual tread profile P2 second virtual tread profile S ground contact surface

Claims (8)

By providing a pair of shoulder main grooves extending continuously in the tire circumferential direction in the tread portion, a center land portion between the shoulder main grooves, and a shoulder land portion between the shoulder main grooves and the tread end, Is a partitioned pneumatic tire,
The center land portion protrudes outward in the tire radial direction from the first virtual tread profile that smoothly connects the tread ends along the tire lumen surface in a tire meridian section including a tire rotation axis,
The tread rubber of the tread portion includes a cap rubber layer disposed on the outermost side, a base rubber layer made of rubber that is disposed on the inner side of the cap rubber layer and has higher wear resistance than the cap rubber layer, and Including
The base rubber layer of the center land portion is a second virtual tread that smoothly connects the outer ends in the tire radial direction of the base rubber layer of the shoulder land portion along the first virtual tread profile in the tire meridian cross section. A pneumatic tire characterized by protruding outward in the tire radial direction from the profile.   The pneumatic tire according to claim 1, wherein the base rubber layer is made of rubber having a loss tangent tan δ smaller than that of the cap rubber layer. The base rubber layer includes a first base rubber layer and a second base rubber layer disposed outside the first base rubber layer,
3. The pneumatic tire according to claim 1, wherein the first base rubber layer is made of rubber having higher wear resistance than the second base rubber layer.   The pneumatic tire according to claim 3, wherein the loss tangent tan δ of the first base rubber layer is smaller than that of the second base rubber layer.   The pneumatic tire according to any one of claims 1 to 4, wherein a thickness of the cap rubber layer of the shoulder land portion is gradually increased toward an outer side in a tire axial direction. The center land portion includes a contact surface that contacts the road surface, and a side wall surface that extends inward in the tire radial direction from the contact surface,
The pneumatic tire according to any one of claims 1 to 5, wherein the cap rubber layer extends on the side wall surface and has a thickness larger than a thickness on the ground contact surface. The center land portion includes a contact surface that contacts the road surface, and a side wall surface that extends inward in the tire radial direction from the contact surface,
The pneumatic tire according to any one of claims 1 to 5, wherein the cap rubber layer extends on the side wall surface, and a thickness thereof is smaller than a thickness on the ground contact surface. The center land portion includes a contact surface that contacts the road surface, and a side wall surface that extends inward in the tire radial direction from the contact surface,
The pneumatic tire according to any one of claims 1 to 5, wherein the cap rubber layer extends over the side wall surface and is not disposed in a central portion of the ground contact surface.

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