JP2016159852A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire capable of improving wear resistance performance of a center main groove.SOLUTION: A pneumatic tire 1 is configured so that: a tread rubber 15 comprises a first cap tread 151 for forming one center land part 32, a second cap tread 152 for forming the other center land part 33, and a surface rubber layer 153 disposed on an outer periphery of the first cap tread 151 and the second cap tread 152 and exposed to a tread surface. A rubber hardness Hs1 of the first cap tread 151 and a rubber hardness Hs2 of the second cap tread 152 have a relationship of Hs1<Hs2. A tanδ value T1 of the first cap tread 151, a tanδ value T2 of the second cap tread 152, and a tanδ value T3c of the surface rubber layer 153 on a ground contact surface of the center land parts 32, 33 have relationships of T3c<T1 and T3c<T2.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire capable of improving the wear resistance performance of a center main groove.

  A circuit tire for motor sports employs a structure in which a thin surface rubber layer having a small tan δ value is formed on the outer layer of the cap tread in order to improve the grip characteristics of the road surface. As a conventional pneumatic tire employing such a structure, a technique described in Patent Document 1 is known.

JP-A-1-127401

  On the other hand, for circuit tires, there is a demand to increase the wear resistance of the center main groove so that the slip sign of the center main groove is not exposed at an early stage based on the regulation of competition.

  Therefore, the present invention has been made in view of the above, and an object thereof is to provide a pneumatic tire capable of improving the wear resistance performance of the center main groove.

  In order to achieve the above object, a pneumatic tire according to the present invention includes a tread rubber, a center main groove that is disposed in the tread portion center region and extends in the tire circumferential direction, and left and right compartments partitioned by the center main groove. A pneumatic tire including a center land portion, wherein the tread rubber includes a first cap tread constituting one center land portion, a second cap tread constituting the other center land portion, and the first A surface rubber layer disposed on the outer periphery of the cap tread and the second cap tread and exposed to the tread surface; and a rubber hardness Hs1 of the first cap tread and a rubber hardness Hs2 of the second cap tread. Hs1 <Hs2, and the tan δ value T1 of the first cap tread and the tan δ value T2 of the second cap tread The tan δ value T3c of the surface rubber layer on the ground contact surface of the center land portion has a relationship of T3c <T1 and T3c <T2.

  In the pneumatic tire according to the present invention, since the rubber hardness Hs2 of the second cap tread on the inner side in the vehicle width direction is large (Hs1 <Hs2), early wear of the edge portion on the inner side in the vehicle width direction is suppressed. Accordingly, there is an advantage that the left and right edge portions are evenly worn at the initial stage of wear, and uneven wear of the edge portion on the inner side in the vehicle width direction is suppressed.

FIG. 1 is a sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment of the present invention. FIG. 2 is an explanatory diagram illustrating a center land portion of the pneumatic tire illustrated in FIG. 1. FIG. 3 is an enlarged view showing an edge portion of the center land portion described in FIG. 2. FIG. 4 is an enlarged view showing an edge portion of the center land portion shown in FIG. FIG. 5 is an explanatory view showing a modified example of the pneumatic tire shown in FIG. 1. FIG. 6 is an explanatory view showing a modified example of the pneumatic tire shown in FIG. 1. FIG. 7 is an explanatory view showing a modified example of the pneumatic tire shown in FIG. 1. FIG. 8 is a chart showing the results of the performance test of the pneumatic tire according to the embodiment of the present invention.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Further, the constituent elements of this embodiment include those that can be replaced while maintaining the identity of the invention and that are obvious for replacement. In addition, a plurality of modifications described in this embodiment can be arbitrarily combined within a range obvious to those skilled in the art.

[Pneumatic tire]
FIG. 1 is a sectional view in the tire meridian direction showing a pneumatic tire according to an embodiment of the present invention. The same figure has shown sectional drawing of the one-side area | region of a tire radial direction. The figure shows a circuit tire for motor sports as an example of a pneumatic tire. Moreover, the code | symbol T is a tire grounding end.

  In the figure, the cross section in the tire meridian direction means a cross section when the tire is cut along a plane including a tire rotation axis (not shown). Reference sign CL denotes a tire equator plane, which is a plane that passes through the center point of the tire in the tire rotation axis direction and is perpendicular to the tire rotation axis. Further, the tire width direction means a direction parallel to the tire rotation axis, and the tire radial direction means a direction perpendicular to the tire rotation axis. Further, the inside in the vehicle width direction and the outside in the vehicle width direction indicate directions with respect to the vehicle width direction when the tire is mounted on the vehicle. Here, of the left and right regions having the tire equator plane CL as a boundary, a region on the outer side in the vehicle width direction when the tire is mounted on the vehicle is referred to as an outer region, and a region on the inner side in the vehicle width direction is referred to as an inner region.

  The pneumatic tire 1 has an annular structure centered on the tire rotation axis, and includes a pair of bead cores 11, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, and a tread rubber 15. And a pair of side wall rubbers 16 and 16, a pair of rim cushion rubbers 17 and 17, and an inner liner 18 (see FIG. 1).

  The pair of bead cores 11 and 11 is an annular member formed by bundling a plurality of bead wires, and constitutes the core of the left and right bead portions. The pair of bead fillers 12 and 12 are disposed on the outer circumference in the tire radial direction of the pair of bead cores 11 and 11 to constitute a bead portion.

  The carcass layer 13 has a single layer structure composed of a single carcass ply or a multilayer structure formed by laminating a plurality of carcass plies, and is bridged in a toroidal shape between the left and right bead cores 11 and 11 to form a tire skeleton. Configure. Further, both end portions of the carcass layer 13 are wound and locked outward in the tire width direction so as to wrap the bead core 11 and the bead filler 12. The carcass ply of the carcass layer 13 is formed by rolling a plurality of carcass cords made of steel or an organic fiber material (for example, aramid, nylon, polyester, rayon, etc.) with a coat rubber, and has an absolute value of 70. It has a carcass angle (inclination angle in the longitudinal direction of the carcass cord with respect to the tire circumferential direction) of [deg] or more and 95 [deg] or less.

  For example, in the configuration of FIG. 1, the carcass layer 13 has a multilayer structure formed by stacking a pair of carcass plies 131 and 132, and the carcass plies 131 and 132 wrap around the bead core 11 and the bead filler 12 in the tire width direction. It is rolled back to the outside. Further, the winding end portion of one carcass ply 131 is sandwiched between the belt layer 14 and the main body portion of the carcass layer 13, and the winding end portion of the other carcass ply 132 is located at the bead portion.

  The belt layer 14 is formed by laminating a pair of cross belts 141, 142, a belt cover 143, and a pair of belt edge covers 144, and is arranged around the outer periphery of the carcass layer 13. The pair of cross belts 141 and 142 is formed by rolling a plurality of belt cords made of steel or organic fiber material with a coating rubber, and has an absolute value of a belt angle of 20 [deg] or more and 55 [deg] or less. Have. The pair of cross belts 141 and 142 have belt angles with different signs (inclination angles in the longitudinal direction of the belt cord with respect to the tire circumferential direction) and are laminated with the longitudinal directions of the belt cords intersecting each other. (Cross ply structure). The belt cover 143 and the pair of belt edge covers 144 are configured by coating a belt cord made of steel or an organic fiber material with a coat rubber, and have a belt angle of 0 [deg] or more and 10 [deg] or less in absolute value. Further, the belt cover 143 and the pair of belt edge covers 144 are strip materials formed by coating one or a plurality of belt cords with a coat rubber, and the strip materials are arranged on the outer side in the tire radial direction of the cross belts 141 and 142 and on the tire. It is configured by winding a plurality of times in the circumferential direction and spirally. The belt cover 143 is disposed over the entire area of the cross belts 141 and 142, and the pair of belt edge covers 144 are disposed only at the left and right edge portions of the cross belts 141 and 142.

  The tread rubber 15 is disposed on the outer circumference in the tire radial direction of the carcass layer 13 and the belt layer 14 to constitute a tread portion of the tire. The pair of side wall rubbers 16 and 16 are respectively arranged on the outer side in the tire width direction of the carcass layer 13 to constitute left and right side wall portions. The pair of rim cushion rubbers 17, 17 are respectively disposed on the inner side in the tire radial direction of the wound portions of the left and right bead cores 11, 11 and the carcass layer 13, and constitute the contact surfaces of the left and right bead portions with respect to the rim flange.

  The inner liner 18 is an air permeation preventive layer that is disposed on the tire cavity surface and covers the carcass layer 13, and is composed of, for example, a belt-shaped rubber sheet. The inner liner 18 suppresses oxidation due to the exposure of the carcass layer 13 and prevents leakage of air filled in the tire.

  The pneumatic tire 1 includes a plurality of circumferential grooves 21 to 23 extending in the tire circumferential direction and a plurality of land portions 31 to 34 partitioned by the circumferential grooves 21 to 23 in the tread portion. .

  For example, in the configuration of FIG. 1, the pneumatic tire 1 includes three circumferential grooves 21 to 23, and these circumferential grooves 21 to 23 are arranged symmetrically about the tire equatorial plane CL. Moreover, the 1st circumferential groove | channel 21 is a circumferential narrow groove, and is arrange | positioned in the area | region of the vehicle width direction outer side. The second circumferential groove 22 is a circumferential main groove and is disposed on the tire equatorial plane CL. The third circumferential groove 23 is a circumferential main groove, and is disposed in an inner region in the vehicle width direction. Moreover, four rows of land portions 31 to 34 are defined by these circumferential grooves 21 to 23. The land portions 31 to 34 are ribs continuous in the tire circumferential direction, and include a plurality of non-through lug grooves (not shown).

  However, the present invention is not limited to this, and four or more circumferential grooves may be arranged (not shown). Further, the circumferential grooves may be arranged asymmetrically about the tire equatorial plane CL (not shown). Further, the circumferential main groove 22 may be disposed at a position deviated from the tire equatorial plane CL (not shown). For this reason, a land part may be arrange | positioned on the tire equator surface CL.

  The circumferential main groove is a circumferential groove having a wear indicator indicating the end of wear, and generally has a groove width of 5.0 [mm] or more and a groove depth of 7.5 [mm] or more. The lug groove means a lateral groove having a groove width of 2.0 [mm] or more and a groove depth of 3.0 [mm] or more.

  The groove width is measured as the maximum value of the distance between the left and right groove walls at the groove opening in a no-load state in which the tire is mounted on the prescribed rim and filled with the prescribed internal pressure. In the configuration where the land part has a notch part or a chamfered part at the edge part, the groove width is based on the intersection of the tread surface and the extension line of the groove wall in a cross-sectional view in which the groove length direction is a normal direction. Measured. In the configuration in which the groove extends in a zigzag shape or a wave shape in the tire circumferential direction, the groove width is measured with reference to the center line of the amplitude of the groove wall.

  The groove depth is measured as the maximum value of the distance from the tread surface to the groove bottom in an unloaded state in which the tire is mounted on the specified rim and filled with the specified internal pressure. Moreover, in the structure which a groove | channel has a partial uneven | corrugated | grooved part and a sipe in a groove bottom, groove depth is measured except these.

  The specified rim refers to an “applied rim” defined in JATMA, a “Design Rim” defined in TRA, or a “Measuring Rim” defined in ETRTO. The specified internal pressure means “maximum air pressure” defined by JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. The specified load means “maximum load capacity” defined in JATMA, the maximum value of “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined in TRA, or “LOAD CAPACITY” defined in ETRTO. However, in JATMA, in the case of tires for passenger cars, the specified internal pressure is air pressure 180 [kPa], and the specified load is 88 [%] of the maximum load capacity.

  In this embodiment, the circumferential main groove in the region of 20 [%] of the tire ground contact width TW centering on the tire equatorial plane CL is referred to as a center main groove. In addition, the left and right land portions partitioned by the center main groove are called center land portions.

  The tire ground contact width TW is the contact surface between the tire and the flat plate when the tire is mounted on the specified rim to apply the specified internal pressure and is placed perpendicular to the flat plate in a stationary state and applied with a load corresponding to the specified load. It is measured as the maximum linear distance in the tire axial direction.

[Dual tread structure]
FIG. 2 is an explanatory diagram illustrating a center land portion of the pneumatic tire illustrated in FIG. 1. This figure shows an enlarged cross-sectional view of a pair of center land portions 32 and 33 adjacent to each other with the center main groove 22 interposed therebetween.

  As shown in FIG. 1, the pneumatic tire 1 includes a single center main groove 22 and left and right center land portions 32 and 33 defined by the center main groove 22. Further, the tread rubber 15 has a first cap tread 151 and a second cap tread 152.

  The first cap tread 151 and the second cap tread 152 are disposed adjacent to each other in the tire width direction with the center main groove 22 as a boundary. The first cap tread 151 constitutes the center land portion 32 and the shoulder land portion 31 on the outer side in the vehicle width direction, and the second cap tread 152 constitutes the center land portion 33 and the shoulder land portion 34 on the inner side in the vehicle width direction. To do. The first cap tread 151 and the second cap tread 152 are made of rubber materials having different physical property values. Thereby, a dual tread structure is configured.

  That is, the rubber hardness Hs1 of the first cap tread 151 and the rubber hardness Hs2 of the second cap tread 152 have a relationship of Hs1 <Hs2. Moreover, it is preferable that these rubber hardness Hs1 and Hs2 have the relationship of 5 <= Hs2-Hs1 <= 15. Moreover, it is preferable that these rubber hardness Hs1 and Hs2 exist in the range of 60 <= Hs1 <= 75 and 65 <= Hs2 <= 80. Thereby, the rubber hardness Hs1, Hs2 of the first cap tread 151 and the second cap tread 152 is optimized.

  Rubber hardness is measured as JIS-A hardness based on JIS-K6253.

  In such a configuration, the rubber hardness Hs1 of the first cap tread 151 on the outer side in the vehicle width direction is smaller than the rubber hardness Hs2 of the second cap tread 152 on the inner side in the vehicle width direction (Hs1 <Hs2). Then, since the rubber hardness Hs1 on the outer side in the vehicle width direction is small, the grip action in the outer region in the vehicle width direction that becomes a heavy load at the time of cornering increases, and the steering stability performance on the dry road is improved. Further, since the rubber hardness Hs2 on the inner side in the vehicle width direction is large, wear in the inner region in the vehicle width direction is suppressed, the drainage action by the groove is ensured, and the steering stability performance on the wet road is ensured. Thereby, the steering stability performance on the dry road and the wet road is compatible.

  Further, the tan δ value T1 of the first cap tread 151 and the tan δ value T2 of the second cap tread 152 may be in the ranges of 0.35 ≦ T1 ≦ 0.65 and 0.15 ≦ T2 ≦ 0.45. preferable. As a result, the tan δ values T1 and T2 of the first cap tread 151 and the second cap tread 152 are optimized.

  The tan δ value (loss tangent) was measured using a viscoelastic spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. at a temperature of 60 [° C.], a shear strain of 10 [%], an amplitude of ± 0.5 [%], and a frequency of 20 [Hz. ] Measured under the conditions.

  In the configuration of FIG. 1, the first cap tread 151 and the second cap tread 152 are arranged adjacent to the outer periphery of the belt layer 14. However, the present invention is not limited thereto, and the tread rubber 15 may include a rubber layer such as an under tread (not shown) between the first cap tread 151 and the second cap tread 152 and the belt layer 14.

  In the configuration of FIG. 1, the first cap tread 151 and the second cap tread 152 extend from the tire equatorial plane CL to the left and right tread ends. However, the present invention is not limited to this, and the tread rubber 15 may include, for example, a rubber layer such as a wing tip in a non-grounding region outside the first cap tread 151 and the second cap tread 152 in the tire width direction (not shown). ).

  In the configuration of FIG. 1, the boundary between the first cap tread 151 and the second cap tread 152 is located at the center of the center main groove 22. Such a configuration is preferable in that the occurrence of groove cracks starting from the boundary between the first cap tread 151 and the second cap tread 152 is suppressed. However, the present invention is not limited to this, and the boundary between the first cap tread 151 and the second cap tread 152 may be positioned on the groove wall (not shown).

[Surface rubber layer]
As shown in FIG. 2, the tread rubber 15 includes a surface rubber layer 153. The surface rubber layer 153 is disposed on the outer periphery of the first cap tread 151 and the second cap tread 152 and exposed to the tread surface. For this reason, the surface rubber layer 153 constitutes the outermost layer of the tread rubber 15 and contacts the road surface when the tire contacts the ground.

  Further, the surface rubber layer 153 is thinner than the first cap tread 151 and the second cap tread 152. Specifically, the gauge G3c of the surface rubber layer 153 on the ground contact surfaces of the center land portions 32 and 33 is preferably in the range of 0.5 [mm] ≦ G3c ≦ 1.0 [mm].

  The gauge G3c of the surface rubber layer 153 on the ground contact surface is measured as the thickness of the surface rubber layer 153 on the ground contact surface of the center land portions 32 and 33. Conceptually, the distance between the profile of the center land portions 32 and 33 and the outer peripheral surfaces of the first cap tread 151 and the second cap tread 152 is the gauge G3c of the surface rubber layer 153. However, for example, a reinforcing rubber material (for example, edge rubber 1531 described later) partially disposed on the edge portions of the center land portions 32 and 33, and unevenness partially formed on the treads of the center land portions 32 and 33 Arrangement positions such as parts are excluded from measurement points.

  Further, the tan δ value T3c of the surface rubber layer 153 on the ground contact surfaces of the center land portions 32 and 33 is T3c <T1 and T3c with respect to the tan δ value T1 of the first cap tread 151 and the tan δ value T2 of the second cap tread 152. <T2 relationship. The tan δ value T3c is preferably in the range of 0.06 ≦ T3c ≦ 0.15, and the tan δ value T3c is more preferably in the range of 0.08 ≦ T3c ≦ 0.13.

  The tan δ value T3c of the surface rubber layer 153 on the ground contact surface is measured as the tan δ value of the surface rubber layer 153 on the ground contact surfaces of the center land portions 32 and 33. In the configuration in which the surface rubber layer 153 is made of a plurality of types of rubber materials having different physical properties, the tan δ value T3c is calculated as an average value using the area ratio of each rubber material in the tire contact surface. However, for example, a reinforcing rubber material (for example, edge rubber 1531 described later) partially disposed at the edge portions of the center land portions 32 and 33, and a rubber material disposed at a non-grounding portion such as a groove bottom portion or a notch portion. Are excluded from the calculation of the tan δ value T3c.

  The tire ground contact surface is a contact surface between the tire and the flat plate when the tire is mounted on the predetermined rim and applied with a predetermined internal pressure, and is placed perpendicular to the flat plate in a stationary state and a load corresponding to the predetermined load is applied. Defined.

  In such a configuration, the tan δ value T3c of the surface rubber layer 153 exposed on the tire contact surface is smaller than the tan δ values T1 and T2 of the first cap tread 151 and the second cap tread 152 in the lower layer (T3c <T1 and T3c < Therefore, the rolling resistance of the tire at the initial stage of wear is reduced as compared with the configuration in which the first cap tread 151 and the second cap tread 152 are exposed on the tire contact surface.

  Further, the rubber hardness Hs3c of the surface rubber layer 153 on the ground contact surfaces of the center land portions 32 and 33 is Hs3c <Hs1 <Hs2 with respect to the rubber hardness Hs1 of the first cap tread 151 and the rubber hardness Hs2 of the second cap tread 152. Have the relationship. Further, it is preferable that the rubber hardness Hs1 and Hs3c have a relationship of 1 ≦ Hs1−Hs3c ≦ 10. The rubber hardness Hs3c is preferably in the range of 45 ≦ Hs3c ≦ 60, and more preferably in the range of 50 ≦ Hs3c ≦ 55.

  The rubber hardness Hs3c of the surface rubber layer 153 on the ground contact surface is measured as the rubber hardness of the surface rubber layer 153 on the ground contact surface of the center land portions 32 and 33. In the configuration in which the surface rubber layer 153 is made of a plurality of types of rubber materials having different physical properties, the rubber hardness Hs3c is calculated as an average value using the area ratio of each rubber material in the tire contact surface. However, for example, a reinforcing rubber material (for example, edge rubber 1531 described later) partially disposed at the edge portions of the center land portions 32 and 33, and a rubber material disposed at a non-grounding portion such as a groove bottom portion or a notch portion. Are excluded from the calculation of the rubber hardness Hs3c.

  In such a configuration, the rubber hardness Hs3c of the surface rubber layer 153 is set smaller than the rubber hardness Hs1 and Hs2 of the first cap tread 151 and the second cap tread 152 in the lower layer. Thereby, the followability with respect to the road surface of the tread surface at the time of tire contact is improved, and the grip force is increased. Thereby, the steering stability performance on the dry road surface is improved.

[Edge rubber of surface rubber layer]
In the configuration of FIG. 2, the surface rubber layer 153 includes two types of rubber members 1531 and 1532. Specifically, in the green tire molding process, two types of rubber members 1531 and 1532 are integrally molded by extrusion and wound around the outer circumferences of the first cap tread 151 and the second cap tread 152. Thereafter, the green tire is filled into a tire vulcanization mold (not shown), and the green tire is heated to vulcanize the tire. At this time, the shape of the tire molding die is transferred to the tread surface of the green tire, and the circumferential grooves 21 to 23 and the land portions 31 to 34 of the tread portion are molded.

  Here, of the rubber members 1531 and 1532 of the surface rubber layer 153, the rubber member 1531 disposed at the edge portion on the center main groove 22 side of the center land portion 33 on the inner side in the vehicle width direction is referred to as edge rubber. In the drawing, hatching is attached to the edge rubber 1531. A specific configuration of the edge rubber 1531 will be described later.

  Further, the portion other than the edge rubber 1531 of the surface rubber layer 153 is denoted by reference numeral 1532 for convenience. The other portion 1532 of the surface rubber layer 153 may be composed of a single rubber material or a plurality of rubber materials.

  3 and 4 are enlarged views showing an edge portion of the center land portion shown in FIG. In these drawings, FIG. 3 shows an enlarged cross-sectional view of an edge portion on the center main groove 22 side of a pair of adjacent center land portions 32, 33, and FIG. 4 shows the center land portion 33 on the inner side in the vehicle width direction. The enlarged view cross section of the edge part is shown.

  3, in the surface rubber layer 153, the rubber hardness Hs3e of the edge rubber 1531 at the edge portion of the center land portion 33 on the inner side in the vehicle width direction and the portion of the surface rubber layer 153 at the edge portion of the center land portion 32 on the outer side in the vehicle width direction. The rubber hardness Hs3e ′ of 1532 has a relationship of Hs3e ′ <Hs3e. Further, it is preferable that these rubber hardnesses Hs3e and Hs3e ′ have a relationship of 1 ≦ Hs3e−Hs3e ′ ≦ 15. Further, the rubber hardness Hs3e of the edge rubber 1531 is preferably in the range of 60 ≦ Hs3e ≦ 75, and more preferably in the range of 64 ≦ Hs3e ≦ 71. Further, the rubber hardness Hs3e ′ of the portion 1532 of the surface rubber layer 153 on the ground contact surface is preferably in the range of 45 ≦ Hs3e ′ ≦ 60, and more preferably in the range of 50 ≦ Hs3e ′ ≦ 55.

  Further, the width We of the edge rubber 1531 on the tread surface of the center land portion 33 on the inner side in the vehicle width direction is preferably in the range of 5 [mm] ≦ We ≦ 15 [mm], and 8 [mm] ≦ We ≦ 12 [mm]. ] Is more preferable. Further, the width We of the edge rubber 1531 and the width Wr of the tread surface of the center land portion 33 (see FIG. 2) preferably have a relationship of 0.1 ≦ We / Wr ≦ 0.4, and 0.2 ≦ We It is more preferable to have a relationship of /Wr≦0.3.

  The width We of the edge rubber 1531 is the distance in the tire width direction between the edge portion of the center land portion 33 and the end portion of the edge rubber 1531 on the tread surface of the center land portion 33. The tire is attached to the specified rim to apply the specified internal pressure. And measured as an unloaded condition. As shown in FIG. 4, when the edge portion of the center land portion 33 has a chamfered portion, the extension line of the tread surface of the center land portion 33 and the groove wall of the center main groove 22 in a sectional view in the tire meridian direction. The width We of the edge rubber 1531 is measured on the basis of the intersection point P with the extension line.

  The width Wr of the tread surface of the center land portion 33 is a distance in the tire width direction of the left and right edge portions of the center land portion 33, and is measured as a no-load state while attaching a tire to a specified rim and applying a specified internal pressure. . Further, as shown in FIG. 4, when the edge portion of the center land portion 33 has a chamfered portion, the width Wr of the tread surface of the center land portion 33 is measured with the intersection point P as a reference.

  In the above configuration, the rubber hardness Hs3e at the edge portion of the center land portion 33 on the inner side in the vehicle width direction is higher than the rubber hardness Hs3e ′ at the edge portion of the center land portion 32 on the outer side in the vehicle width direction (Hs3e ′ <Hs3e). In addition, early wear of the edge portion on the inner side in the vehicle width direction is suppressed. Thereby, at the initial stage of wear, the left and right edge portions are evenly worn, and uneven wear of the inner edge portion in the vehicle width direction is suppressed.

  In particular, in the circuit tire for motor sports, the edge portion on the center main groove 22 side of the center land portion 33 on the inner side in the vehicle width direction is significantly worn compared to the edge portion of the center land portion 32 on the outer side in the vehicle width direction. There is a problem that it is easy to do. In this respect, in the above configuration, since the rubber hardness Hs2 of the second cap tread 152 on the inner side in the vehicle width direction is large (Hs1 <Hs2), early wear of the edge portion on the inner side in the vehicle width direction is suppressed. Thereby, at the initial stage of wear, the left and right edge portions are evenly worn, and uneven wear of the inner edge portion in the vehicle width direction is suppressed.

  3, the gauge G3e of the surface rubber layer 153 at the edge portion on the center main groove 22 side of the center land portion 33 on the inner side in the vehicle width direction and the center main groove 22 of the center land portion 32 on the outer side in the vehicle width direction. The gauge G3e ′ of the surface rubber layer 153 at the side edge portion has a relationship of G3e ′ <G3e. Moreover, it is preferable that the gauges G3e and G3e ′ have a relationship of 0.3 [mm] ≦ G3e−G3e ′ ≦ 2.0 [mm]. Moreover, it is preferable that the gauge G3e of the edge part inside a vehicle width direction exists in the range of 1.0 [mm] <= G3e <= 1.5 [mm]. Further, it is preferable that the gauge G3e ′ at the edge portion on the outer side in the vehicle width direction is in the range of 0.5 [mm] ≦ G3e ′ ≦ 1.0 [mm].

  The gauge G3e (G3e ′) of the surface rubber layer 153 is the thickness of the surface rubber layer 153 on the vertical line that is lowered from the edge portion of the center land portion 33 (32) to the second cap tread 152 (first cap tread 151). Yes, the tire is mounted on a specified rim to apply a specified internal pressure, and is measured as a no-load state. Further, when the edge portion of the center land portion 33 (32) has a chamfered portion, the surface rubber layer 153 on the perpendicular line extending from the intersection point P to the second cap tread 152 (first cap tread 151). The thickness is measured as a gauge G3e (G3e ′) of the surface rubber layer 153.

  For example, in the configuration of FIG. 3, the center main groove 22 has a symmetrical structure with respect to the groove center line in a sectional view in the tire meridian direction. On the other hand, the C chamfered portion 1521 formed on the edge portion on the center main groove 22 side of the second cap tread 152 on the inner side in the vehicle width direction is the center main groove 22 of the first cap tread 151 on the outer side in the vehicle width direction. It is larger than the R chamfered portion 1511 formed on the side edge portion. Therefore, the gauge G3e of the surface rubber layer 153 at the edge portion of the center land portion 33 on the inner side in the vehicle width direction is thicker than the gauge G3e ′ of the surface rubber layer 153 at the edge portion of the center land portion 32 on the outer side in the vehicle width direction. ing.

  In the configuration of FIG. 3, the gauge G3b of the surface rubber layer 153 at the groove bottom of the center main groove 22 and the gauge G3c of the surface rubber layer 153 at the ground contact surface of the center land portions 32 and 33 have a relationship of G3c <G3b. Have Moreover, it is preferable that the gauges G3b and G3c have a relationship of 0.5 [mm] ≦ G3b−G3c ≦ 3.0 [mm]. The groove bottom gauge G3b is preferably in the range of 1.0 [mm] ≦ G3b ≦ 2.0 [mm].

  The gauge G3b at the groove bottom is the thickness of the surface rubber layer 153 at the maximum groove depth position of the center main groove 22. The gauge G3b is measured in a state where a tire is mounted on a specified rim to apply a specified internal pressure and no load is applied.

  For example, in the configuration of FIG. 3, the gauge of the edge rubber 1531 is thicker than the gauge of the other portion 1532 of the surface rubber layer 153. Specifically, the gauge of the edge rubber 1531 is the surface rubber of the surface rubber layer 153 portion 1532 on the ground contact surface of the center land portion 33 on the inner side in the vehicle width direction, the edge portion of the center land portion 32 on the outer side in the vehicle width direction Thicker than the gauge of portion 1532 of layer 153. Further, the edge rubber 1531 extends from the edge portion of the center land portion 33 on the inner side in the vehicle width direction to the groove bottom of the center main groove 22. Thereby, the gauges G3e and G3b of the surface rubber layer 153 at the edge portion of the center land portion 33 and the groove bottom of the center main groove 22 are set thick.

[Modification]
5-7 is explanatory drawing which shows the modification of the pneumatic tire described in FIG. These drawings show enlarged cross-sectional views of edge portions on the center main groove 22 side of a pair of adjacent center land portions 32 and 33.

  In the configuration of FIG. 3, the rubber hardness Hs3e at the edge portion of the center land portion 33 on the inner side in the vehicle width direction is higher than the rubber hardness Hs3e ′ at the edge portion of the center land portion 32 on the outer side in the vehicle width direction (Hs3e ′ <Hs3e). The rubber gauge G3e of the surface rubber layer 153 at the edge portion of the center land portion 33 on the inner side in the vehicle width direction is thicker than the rubber gauge G3e ′ of the surface rubber layer 153 at the edge portion of the center land portion 32 on the outer side in the vehicle width direction. G3e '<G3e). Such a configuration is preferable in that early wear of the edge portion on the inner side in the vehicle width direction is effectively suppressed, and uneven wear on the edge portion on the inner side in the vehicle width direction is suppressed.

  In contrast, in the configuration of FIG. 5, the rubber hardness Hs3e at the edge of the center land portion 33 on the inner side in the vehicle width direction is higher than the rubber hardness Hs3e ′ at the edge portion of the center land portion 32 on the outer side in the vehicle width direction ( Hs3e ′ <Hs3e), and the gauges of the surface rubber layer 153 at the left and right edge portions of the center main groove 22 are equal. Specifically, the edge rubber 1531 and the other portion 1532 of the surface rubber layer 153 have the same gauge, so that the entire surface rubber layer 153 has a constant gauge. Even in such a configuration, the rubber hardness Hs3e at the edge portion on the inner side in the vehicle width direction of the center main groove 22 is large, so that early wear of the edge portion on the inner side in the vehicle width direction is effectively suppressed.

  In the configuration of FIG. 6, the edge rubber 1531 has the same gauge as the other portion 1532 of the surface rubber layer 153 in the configuration of FIG. 5, and the left and right center land portions 32 cross the center main groove 22. It is arranged across 33 edge portions. For this reason, the rubber hardness of the surface rubber layer 153 at the left and right edge portions of the center main groove 22 is equal, and the gauge of the surface rubber layer 153 at the left and right edge portions of the center main groove 22 is equal. Even in this configuration, the rubber hardness Hs1 of the first cap tread 151 on the outer side in the vehicle width direction is smaller than the rubber hardness Hs2 of the second cap tread 152 on the inner side in the vehicle width direction (Hs1 <Hs2). Early wear of the portion is suppressed, and uneven wear of the edge portion on the inner side in the vehicle width direction is suppressed. Further, the configuration of FIG. 6 is easier to manufacture than the configuration of FIG.

  In the configuration of FIG. 7, the surface rubber layer 153 does not include the edge rubber 1531, and has a certain rubber hardness and gauge in the tread portion center region. For this reason, the rubber hardness of the surface rubber layer 153 at the left and right edge portions of the center main groove 22 is equal, and the gauge of the surface rubber layer 153 at the left and right edge portions of the center main groove 22 is equal. Even in this configuration, the rubber hardness Hs1 of the first cap tread 151 on the outer side in the vehicle width direction is smaller than the rubber hardness Hs2 of the second cap tread 152 on the inner side in the vehicle width direction (Hs1 <Hs2). Early wear of the portion is suppressed, and uneven wear of the edge portion on the inner side in the vehicle width direction is suppressed. Further, the configuration of FIG. 7 is easier to manufacture than the configuration of FIG.

[effect]
As described above, the pneumatic tire 1 includes the tread rubber 15, the center main groove 22 disposed in the center area of the tread portion and extending in the tire circumferential direction, and the left and right centers partitioned by the center main groove 22. And land portions 32 and 33 (see FIG. 1). Further, the tread rubber 15 includes a first cap tread 151 constituting one center land portion 32, a second cap tread 152 constituting the other center land portion 33, the first cap tread 151 and the second cap tread 152. And a surface rubber layer 153 exposed on the tread surface (see FIG. 2). Further, the rubber hardness Hs1 of the first cap tread 151 and the rubber hardness Hs2 of the second cap tread 152 have a relationship of Hs1 <Hs2 (dual tread structure). Further, the tan δ value T1 of the first cap tread 151, the tan δ value T2 of the second cap tread 152, and the tan δ value T3c of the surface rubber layer 153 on the ground contact surfaces of the center land portions 32 and 33 are T3c <T1 and T3c. <T2 relationship.

  In this configuration, (1) the rubber hardness Hs1 of the first cap tread 151 on the outer side in the vehicle width direction is the vehicle width in a state where the tire is mounted on the vehicle with the other center land portion 33 side on the inner side in the vehicle width direction. Since the rubber hardness Hs2 of the second cap tread 152 on the inner side in the direction is smaller (Hs1 <Hs2), there is an advantage that the steering stability performance on the dry road and the wet road is compatible.

  (2) In particular, in circuit sports tires for motor sports, there is a request to increase the wear resistance of the center main groove 22 so that the slip sign of the center main groove 22 is not exposed early based on the regulations of competition. . Specifically, since the edge portion on the center main groove 22 side of the center land portion 33 on the inner side in the vehicle width direction is more easily worn than the edge portion on the center land portion 32 on the outer side in the vehicle width direction, There is a problem that uneven wear of the groove 22 should be suppressed. In this respect, in the above configuration, since the rubber hardness Hs2 of the second cap tread 152 on the inner side in the vehicle width direction is large (Hs1 <Hs2), early wear of the edge portion on the inner side in the vehicle width direction is suppressed. Accordingly, there is an advantage that the left and right edge portions are evenly worn at the initial stage of wear, and uneven wear of the edge portion on the inner side in the vehicle width direction is suppressed.

  (3) The tan δ value T3c of the surface rubber layer 153 exposed on the tire contact surface is smaller than the tan δ values T1 and T2 of the first cap tread 151 and the second cap tread 152 in the lower layer (T3c <T1 and T3c). Since <T2), there is an advantage that the rolling resistance of the tire in the initial stage of wear is reduced.

  Further, in the pneumatic tire 1, the gauge G3c of the surface rubber layer 153 on the ground contact surfaces of the center land portions 32 and 33 is in a range of 0.5 [mm] ≦ G3c ≦ 1.0 [mm]. In such a configuration, the gauge G3c of the surface rubber layer 153 on the ground contact surface is optimized, so that the function of the surface rubber layer 153 is appropriately ensured.

  Further, in the pneumatic tire 1, the tan δ value T3c of the surface rubber layer 153 is in the range of 0.06 ≦ T3c ≦ 0.15. Accordingly, there is an advantage that the tan δ value T3c of the surface rubber layer 153 is optimized and the function of the surface rubber layer 153 is optimized. Specifically, the rolling resistance of the tire can be reduced.

  Further, in the pneumatic tire 1, the rubber hardness Hs1 of the first cap tread 151, the rubber hardness Hs2 of the second cap tread 152, and the rubber hardness Hs3c of the surface rubber layer 153 on the ground contact surfaces of the center land portions 32 and 33, Have a relationship of Hs3c <Hs1 <Hs2. In such a configuration, the rubber hardness Hs3c of the surface rubber layer 153 is set smaller than the rubber hardness Hs1 and Hs2 of the first cap tread 151 and the second cap tread 152 in the lower layer. Thereby, there exists an advantage which the steering stability performance on a dry road surface improves.

  Further, in the pneumatic tire 1, the rubber hardness Hs3c of the surface rubber layer 153 is in the range of 45 ≦ Hs3c ≦ 60. Thereby, there exists an advantage by which the rubber hardness Hs3c of the surface rubber layer 153 is optimized. That is, by satisfying 45 ≦ Hs3c, the rubber hardness Hs3c of the surface rubber layer 153 is ensured, and the acceleration of wear accompanying the initial wear is reduced. Further, since Hs3c ≦ 60, the surface rubber layer 153 is appropriately worn at the initial stage of wear.

  Further, in the pneumatic tire 1, the center line of the center main groove 22 is in the region of 20 [%] of the tire ground contact width TW centering on the tire equator plane CL (see FIG. 1). As a result, the position of the center main groove 22 that becomes the boundary between the first cap tread 151 and the second cap tread 152 is optimized, and the operation of the dual tread structure including the first cap tread 151 and the second cap tread 152 is achieved. There is an advantage to be secured.

  Further, the pneumatic tire 1 includes an edge rubber 1531 in which the surface rubber layer 153 is disposed at the edge portion on the center main groove 22 side of the other center land portion 33 (see FIG. 3). Further, the rubber hardness Hs3e of the edge rubber 1531 and the rubber hardness Hs3e 'of the portion 1532 of the surface rubber layer 153 at the edge portion on the center main groove 22 side of one center land portion 32 have a relationship of Hs3e' <Hs3e. In such a configuration, the rubber hardness Hs3e of the edge portion of the center land portion 33 on the inner side in the vehicle width direction is such that the tire is mounted on the vehicle with the other center land portion 33 side on the inner side in the vehicle width direction. The rubber hardness Hs3e ′ at the edge of the outer center land portion 32 is higher (Hs3e ′ <Hs3e). Then, the early wear of the edge portion on the inner side in the vehicle width direction is suppressed, and the left and right edge portions are evenly worn at the initial stage of wear. Thereby, there is an advantage that uneven wear of the edge portion on the inner side in the vehicle width direction is suppressed.

  In the pneumatic tire 1, the rubber hardness Hs 1 of the first cap tread 151, the rubber hardness Hs 2 of the second cap tread 152, the rubber hardness Hs 3 e of the edge rubber 1531, and the surface at the edge portion of one center land portion 32. The rubber hardness Hs3e ′ of the portion 1532 of the rubber layer 153 has a relationship of Hs3e ′ <Hs1 <Hs2 <Hs3e (see FIG. 3). Thereby, the relationship between the rubber hardness Hs3e and Hs3e ′ of the surface rubber layer 153 at the left and right edge portions of the center main groove 22 and the rubber hardness Hs1 and rubber hardness Hs2 of the left and right cap treads 151 and 152 is optimized. There is an advantage that uneven wear of the edge portion on the inner side in the vehicle width direction is suppressed, and that steering stability performance on a dry road and a wet road is compatible.

  Further, in the pneumatic tire 1, the width We of the edge rubber 1531 on the tread surface of the other center land portion 33 is in the range of 5 [mm] ≦ We ≦ 15 [mm] (see FIG. 4). Accordingly, there is an advantage that the width We of the edge rubber 1531 is optimized. That is, when 5 [mm] ≦ We, the function of the edge rubber 1531 is ensured, and early wear of the edge portion on the inner side in the vehicle width direction is suppressed. Further, when We ≦ 15 [mm], uneven wear due to excessive edge rubber 1531 is suppressed.

  Moreover, in this pneumatic tire 1, the gauge G3e of the surface rubber layer 153 in the edge part by the side of the center main groove 22 of the other center land part 33, and the edge part by the side of the center main groove 22 of the one center land part 32 are provided. The gauge G3e ′ of the surface rubber layer 153 has a relationship of G3e ′ <G3e (see FIG. 3). In such a configuration, the gauge G3e of the center land portion 33 on the inner side in the vehicle width direction is connected to the center land on the outer side in the vehicle width direction with the tire mounted on the vehicle with the other center land portion 33 side on the inner side in the vehicle width direction. It is thicker than the gauge G3e ′ at the edge portion of the portion 32 (G3e ′ <G3e). As a result, early wear of the edge portion on the inner side in the vehicle width direction is suppressed, and there is an advantage that the left and right edge portions are evenly worn in the early stage of wear.

  In the pneumatic tire 1, the chamfered portion 1521 formed at the edge portion on the center main groove 22 side of the second cap tread 152 is formed on the edge portion on the center main groove 22 side of the first cap tread 151. It is larger than the chamfered portion 1511 (see FIG. 3). In such a configuration, there is an advantage that the gauge G3e of the surface rubber layer 153 at the edge portion on the inner side in the vehicle width direction can be increased while maintaining the shape of the left and right edge portions of the center main groove 22.

  In the pneumatic tire 1, the gauge G3b of the surface rubber layer 153 at the groove bottom of the center main groove 22 and the gauge G3c of the surface rubber layer 153 at the ground contact surfaces of the center land portions 32 and 33 satisfy G3c <G3b. There is a relationship (see FIGS. 3 and 4). Thereby, there exists an advantage by which generation | occurrence | production of the groove crack in the groove bottom of the center main groove 22 is suppressed.

[Indication of vehicle mounting direction]
The pneumatic tire 1 has a mounting direction display unit (not shown) that indicates a mounting direction with respect to the vehicle. The mounting direction display part is configured by, for example, marks or irregularities attached to the sidewall part of the tire. For example, ECER30 (European Economic Commission Regulation Article 30) obligates the installation of a mounting direction display section on the side wall that is on the outer side in the vehicle width direction when the vehicle is mounted.

  FIG. 8 is a chart showing the results of the performance test of the pneumatic tire according to the embodiment of the present invention.

  In this performance test, evaluations on (1) dry handling stability, (2) wet handling stability, (3) wear resistance, and (4) rolling resistance were performed on a plurality of types of test tires. Further, a test tire having a tire size of 205 / 55R16 is assembled to a rim having a rim size of 16 × 7.0J, and a maximum air pressure and a maximum load specified by JATMA are applied to the test tire.

  (1) In the dry steering stability evaluation, a test vehicle equipped with test tires runs on a dry road test course, and a specialized test driver performs a feeling evaluation on lane change performance and cornering performance. This evaluation is performed by index evaluation using Conventional Example 1 as a reference (100), and the larger the value, the better.

  (2) In the wet steering stability evaluation, a test vehicle equipped with test tires traveled on an asphalt road sprinkled at a water depth of 1 [mm] at a speed of 40 [km / h], and the test driver performed a sensory evaluation on the steering stability. I do. This evaluation is performed by index evaluation using the conventional example as a reference (100), and the larger the value, the better.

  (3) In the evaluation regarding the wear resistance performance, after the test vehicle equipped with the test tire travels 5000 km on the general pavement, the remaining groove amount and uneven wear of the center main groove are observed. This evaluation is performed by index evaluation using the conventional example as a reference (100), and the larger the value, the better.

  (4) In the evaluation regarding rolling resistance, a drum testing machine having a drum diameter of 854 [mm] was used, and a preliminary test for 30 minutes at an air pressure of 210 [kPa], a load of 4.82 [kN] and a speed of 80 [km / h]. Traveling is performed, after which the resistance is measured and evaluated. This evaluation is performed by index evaluation using the conventional example as a reference (100), and the larger the value, the better.

  The test tires of Examples 1 to 9 include a dual tread in which the tread rubber 15 includes the first cap tread 151 and the second cap tread 152 and the surface rubber layer 153 based on the structure of FIGS. However, in Example 1, the surface rubber layer 153 does not have the edge rubber 1531 (see FIG. 7). In Examples 2 to 4, the edge rubber 1531 is thin and the surface rubber layer 153 has a constant gauge. The tan δ values T1 and T2 of the first cap tread 151 and the second cap tread 152 are T1 = 0.55 and T2 = 0.30, and the tan δ value T3e of the edge rubber 1531 of the surface rubber layer 153 and other portions. The tan δ value T3c of 1532 is T3e = 0.25 and T3c = 0.10.

  In the test tire of Conventional Example 1, in the configuration of FIG. 1, the tread rubber has a single tread structure including a single cap tread, and the surface rubber layer 153 is not provided. In the test tire of Conventional Example 2, the surface rubber layer 153 has a rubber hardness higher than that of the lower layer cap tread in the configuration of FIG.

  As shown in the test results, it can be seen that in the test tires of Examples 1 to 9, the dry steering stability performance, the wet steering stability performance, the wear resistance performance, and the rolling resistance are improved as compared with the conventional example.

  1: pneumatic tire, 11: bead core, 12: bead filler, 13: carcass layer, 131, 132: carcass ply, 14: belt layer, 141, 142: cross belt, 143: belt cover, 144: belt edge cover, 15: tread rubber, 151: first cap tread, 152: second cap tread, 153: surface rubber layer, 1511: chamfered portion, 1521: chamfered portion, 1531: edge rubber, 16: sidewall rubber, 17: rim Cushion rubber, 18: inner liner, 21-23: circumferential groove, 31, 34: shoulder land portion, 32, 33: center land portion

Claims (13)

A pneumatic tire comprising a tread rubber, a center main groove disposed in the tread portion center region and extending in the tire circumferential direction, and left and right center land portions defined in the center main groove,
The tread rubber is disposed on the outer periphery of the first cap tread constituting one of the center land portions, the second cap tread constituting the other center land portion, and the first cap tread and the second cap tread. A surface rubber layer exposed on the tread surface,
The rubber hardness Hs1 of the first cap tread and the rubber hardness Hs2 of the second cap tread have a relationship of Hs1 <Hs2, and
The relationship between the tan δ value T1 of the first cap tread, the tan δ value T2 of the second cap tread, and the tan δ value T3c of the surface rubber layer on the ground contact surface of the center land portion is T3c <T1 and T3c <T2. A pneumatic tire characterized by comprising:   The pneumatic tire according to claim 1, wherein a gauge G3c of the surface rubber layer on the ground contact surface of the center land portion is in a range of 0.5 [mm] ≤ G3c ≤ 1.0 [mm].   The pneumatic tire according to claim 1 or 2, wherein a tan δ value T3c of the surface rubber layer is in a range of 0.06 ≦ T3c ≦ 0.15.   The rubber hardness Hs1 of the first cap tread, the rubber hardness Hs2 of the second cap tread, and the rubber hardness Hs3c of the surface rubber layer on the ground contact surface of the center land portion have a relationship of Hs3c <Hs1 <Hs2. The pneumatic tire according to any one of claims 1 to 3.   The pneumatic tire according to claim 4, wherein the rubber hardness Hs3c of the surface rubber layer is in a range of 45 ≦ Hs3c ≦ 60.   The pneumatic tire according to any one of claims 1 to 5, wherein a groove center line of the center main groove is in a region of 20% of a tire ground contact width centering on a tire equator plane. The surface rubber layer comprises an edge rubber disposed on an edge portion on the center main groove side of the other center land portion; and
The rubber hardness Hs3e of the edge rubber and the rubber hardness Hs3e 'of the surface rubber layer portion at the edge portion on the center main groove side of the one center land portion have a relationship of Hs3e'<Hs3e. The pneumatic tire according to any one of 6.   The rubber hardness Hs1 of the first cap tread, the rubber hardness Hs2 of the second cap tread, the rubber hardness Hs3e of the edge rubber, and the rubber hardness Hs3e of the surface rubber layer at the edge portion of the one center land portion. The pneumatic tire according to claim 7, wherein “and Hs3e” <Hs1 <Hs2 <Hs3e.   The pneumatic tire according to claim 7 or 8, wherein the width We of the edge rubber on the tread of the other center land portion is in a range of 5 [mm] ≤ We ≤ 15 [mm].   Gauge G3e of the surface rubber layer at the edge portion on the center main groove side of the other center land portion, and Gauge G3e ′ of the surface rubber layer at the edge portion on the center main groove side of the one center land portion. The pneumatic tire according to claim 1, wherein G3e ′ <G3e.   The chamfered portion formed on the edge portion of the second cap tread on the center main groove side is larger than the chamfered portion formed on the edge portion of the first cap tread on the center main groove side. Pneumatic tire described in 2.   The gauge G3b of the surface rubber layer at the groove bottom of the center main groove and the gauge G3c of the surface rubber layer at the ground contact surface of the center land portion have a relationship of G3c <G3b. The pneumatic tire according to one.   The pneumatic tire according to any one of claims 1 to 12, further comprising a mounting direction display unit that specifies that the other center land portion side is mounted on the vehicle with a vehicle width direction inside.