Tire

Abstract

To provide a tire 2 which can achieve reduction of rolling resistance, while suppressing lowering of wet performance.SOLUTION: A tire 2 includes a tread 4. The tread 4 includes a plurality of layers 48. The plurality of layers 48 include a cap layer 50, an intermediate layer 52 and a base layer 54. The loss tangent at 30°C of the intermediate layer 52 is lower than the loss tangent at 30°C of the cap layer 50. The loss tangent at 30°C of the base layer 54 is lower than the loss tangent at 30°C of the intermediate layer 52. The tread 4 includes a first tread 60, and a second tread 62. A ratio of the thickness of the cap layer 50 in the second tread 62 to the thickness of the tread 4 is 5% or more and 25% or less. A ratio of the thickness of the cap layer 50 in the first tread 60 to the thickness of the tread 4 is 35% or more and 55% or less.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a tire. More specifically, the present invention relates to a tire mounted on a passenger car.

Background Art

[0002] The heat generation property of rubber affects the rolling resistance and the grip performance. When a low heat generation rubber is used for the tread, a tire having a low rolling resistance can be obtained. The low heat generation rubber is inferior to the high heat generation rubber in terms of grip force. Therefore, when a low heat generation rubber is used for the tread, for example, the grip performance on a wet road surface (hereinafter also referred to as wet performance) deteriorates.

[0003] The tread is usually composed of two layers arranged in the radial direction. The outermost layer is the cap layer, and the innermost layer is the base layer. The cap layer is composed of a high heat generation rubber (hereinafter referred to as cap rubber) in consideration of wet performance. The base layer is composed of a low heat generation rubber (hereinafter referred to as base rubber) in consideration of rolling resistance. Due to environmental considerations, further reduction of rolling resistance is required, and development of a tread composed of three types of rubber, in which a rubber (hereinafter referred to as intermediate rubber) having lower heat generation than the cap rubber and higher heat generation than the base rubber is added to the cap rubber and the base rubber, is underway. For example, in Patent Document 1 below, adoption of a three-layer structure tread in which a cap layer composed of cap rubber, an intermediate layer composed of intermediate rubber, and a base layer composed of base rubber are arranged in the radial direction is being considered.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By adopting the intermediate rubber, the heat generation of the entire tread is reduced. Therefore, the tire can reduce the rolling resistance. However, the grip of the intermediate rubber is inferior to that of the cap rubber. Therefore, when the tread is composed of the cap rubber, the intermediate rubber, and the base rubber, there is a concern that the wet performance will deteriorate. An object of the present invention is to provide a tire capable of achieving a reduction in rolling resistance while suppressing a decrease in wet performance.

Means for Solving the Problems

[0006] A tire according to an aspect of the present invention includes a pair of beads, a carcass bridging between the pair of beads, a tread located radially outside the carcass and in contact with the road surface, and a belt located between the carcass and the tread. The tread includes a plurality of layers arranged in the radial direction. The plurality of layers include a cap layer located on the outermost side, a base layer located on the innermost side, and an intermediate layer located between the cap layer and the base layer. The loss tangent of the intermediate layer at 30°C is lower than the loss tangent of the cap layer at 30°C. The loss tangent of the base layer at 30°C is lower than the loss tangent of the intermediate layer at 30°C. The tread includes a first tread located on the equatorial plane and a second tread located axially outside the first tread. The ratio of the thickness of the cap layer in the second tread to the thickness of the tread is 5% or more and 25% or less. The ratio of the thickness of the cap layer in the first tread to the thickness of the tread is 35% or more and 55% or less.

Advantages of the Invention

[0007] According to the present invention, a tire can be obtained that can achieve a reduction in rolling resistance while suppressing a decrease in wet performance.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0009] The tire of the present invention is assembled to a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. The tire assembled to the rim is also called a tire-rim assembly. The tire-rim assembly includes a rim and a tire assembled to this rim.

[0010] In the present invention, the state where the tire is assembled to the standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and no load is applied to this tire is called the standard state.

[0011] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the standard state. The dimensions and angles of each part in the meridian cross-section of the tire that cannot be measured in the state where the tire is assembled to the standard rim are measured on the cut surface of the tire obtained by cutting the tire along a plane including the rotation axis. In this measurement, the tire is set so that the distance between the left and right beads matches the distance between the beads in the tire assembled to the standard rim. In addition, the structure of the tire that cannot be confirmed in the state where the tire is assembled to the standard rim is confirmed on the aforementioned cut surface.

[0012] The regular rim means the rim defined in the standard that the tire relies on. The "Standard Rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are regular rims.

[0013] The regular internal pressure means the internal pressure defined in the standard that the tire relies on. The "Maximum Air Pressure" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are regular internal pressures.

[0014] The regular load means the load defined in the standard that the tire relies on. The "Maximum Load Capacity" in the JATMA standard, the "Maximum Value" published in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are regular loads.

[0015] In the present invention, the load index (LI) is, for example, an index defined in the JATMA standard and representing, by an exponent, the maximum mass, i.e., the maximum load capacity, that is allowed to be loaded on the tire under specified conditions.

[0016] In the present invention, the rubber composition is a material obtained by mixing a base rubber and chemicals in a kneader such as a Banbury mixer. The base rubber of the rubber composition is not crosslinked. The crosslinked rubber is a molded body obtained by pressurizing and heating the rubber composition. The crosslinked rubber is a crosslinked product of the rubber composition. The base rubber of the crosslinked rubber is crosslinked. The crosslinked rubber is also referred to as vulcanized rubber, and the rubber composition is also referred to as unvulcanized rubber.

[0017] Examples of the base rubber include natural rubber (NR), butadiene rubber (BR), styrene-butadiene rubber (SBR), isoprene rubber (IR), ethylene-propylene rubber (EPDM), chloroprene rubber (CR), acrylonitrile-butadiene rubber (NBR), and butyl rubber (IIR). Examples of the chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oil, fillers such as zinc oxide, lubricants such as stearic acid, anti-aging agents, processing aids, sulfur, and vulcanization accelerators. The selection of the base rubber and chemicals, the content of the selected chemicals, etc. are appropriately determined according to the specifications of each element such as the tread and sidewall to which the rubber composition is applied.

[0018] In the present invention, among the elements constituting the tire, the loss tangent (tanδ) of the element made of crosslinked rubber is measured using a viscoelastic spectrometer in accordance with the provisions of JIS K6394. The measurement conditions are as follows. Initial strain = 10% Dynamic strain = ±1% Frequency = 10 Hz Mode = elongation mode Temperature = 30°C In this measurement, the test piece (length 40 mm × width 4 mm × thickness 1 mm) is sampled from the tire. The length direction of the test piece is made to coincide with the circumferential direction of the tire. When the test piece cannot be sampled from the tire, the test piece is sampled from a sheet-like crosslinked rubber (hereinafter also referred to as a rubber sheet) obtained by pressurizing and heating the rubber composition used for forming the element to be measured at a temperature of 170°C for 12 minutes. In the present invention, the loss tangent is represented by the loss tangent at 30°C.

[0019] In the present invention, the tread portion of the tire is the portion of the tire that contacts the road surface. The bead portion is the portion of the tire that is fitted to the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. The tire includes, as parts, a tread portion, a pair of bead portions, and a pair of sidewall portions. The axially outer portion of the tread is also called the shoulder portion. The portion between the left and right shoulder portions is also called the crown portion. The crown portion intersects the equatorial plane of the tire.

[0020] [Findings underlying the present invention] When driving on a wet road surface is considered, grooves are formed in the tread. The tread wears. As a result, the groove volume decreases. Therefore, when a tire with advanced tread wear travels on a wet road surface, weak hydroplaning occurs. The heat generation property of the rubber affects the grip performance of the tire. However, when weak hydroplaning occurs, even if the rubber has high heat generation property, the contribution of the rubber to the exhibition of grip performance decreases. Therefore, the thickness of the cap layer is adjusted so that the cap layer remains until a state where weak hydroplaning occurs. Even if the tread is configured with a three-layer structure, it is necessary to ensure the thickness of the cap layer, and it is difficult to further reduce the rolling resistance. Therefore, the inventors of the present invention have earnestly studied a technique capable of achieving reduction of rolling resistance while suppressing a decrease in the wet performance of a tire by considering not only simply adjusting the thickness of each layer arranged in the radial direction but also the thickness distribution in the axial direction, and have completed the invention described below.

[0021] [Details of embodiments of the present invention] Hereinafter, the present invention will be described in detail based on preferred embodiments while appropriately referring to the drawings.

[0022] FIG. 1 shows a part of a tire 2 according to an embodiment of the present invention. This tire 2 is a pneumatic tire for a passenger car.

[0023] FIG. 1 shows a part of a cross-section of this tire 2 along a plane including the rotation axis (not shown) of the tire 2. The cross-section shown in FIG. 1 is also called a meridian cross-section. The direction indicated by the double-headed arrow AD is the axial direction of the tire 2. The axial direction of the tire 2 means a direction parallel to the rotation axis of the tire 2. The direction indicated by the double-headed arrow RD is the radial direction of the tire 2. The direction perpendicular to the paper surface of FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, the one-dot chain line CL extending in the radial direction represents the equatorial plane of the tire 2.

[0024] FIG. 1 shows a tire 2 mounted on a rim R. For example, air is filled between the tire 2 and the rim R, and the internal pressure of the tire 2 is adjusted. The rim R is a standard rim.

[0025] In FIG. 1, the position indicated by the reference sign PC is the intersection of the outer surface 2G of the tire 2 (specifically, the tread surface described later) and the equatorial plane. The intersection PC is the equator of the tire 2. When a groove is located on the equatorial plane, the equator PC is specified based on the virtual outer surface (the virtual tread surface described later) obtained by assuming that there is no groove. The equator PC is the radially outer end of the tire 2.

[0026] In FIG. 1, the position indicated by the reference sign PW is the axially outer end of the tire 2 (hereinafter, the outer end PW). When there are decorations such as patterns and letters on the outer surface, the outer end PW is specified based on the virtual outer surface obtained by assuming that there are no decorations. In FIG. 1, the length indicated by the double-headed arrow AW is the maximum width of the tire 2. The maximum width AW is represented by the axial distance from the first outer end PW to the second outer end PW. The outer end PW is the position indicating the maximum width AW and is also called the maximum width position. The maximum width AW obtained in the normal state is the cross-sectional width of the tire 2 (see JATMA, etc.).

[0027] This tire 2 includes, as elements, a tread 4, a pair of sidewalls 6, a pair of clinches 8, a pair of beads 10, a carcass 12, a belt 14, a band 16, and an inner liner 18.

[0028] The tread 4 is located radially outside the carcass 12. The tread 4 contacts the road surface at the tread surface 20. The tread 4 has a tread surface 20 that contacts the road surface. The tread surface 20 is a part of the outer surface 2G of the tire 2. The tread surface 20 includes the equator PC.

[0029] The tread 4 has grooves 22 engraved therein. Thereby, a tread pattern is formed. The grooves 22 include a plurality of circumferential grooves 24 extending continuously in the circumferential direction. The tread 4 has a tread pattern including a plurality of circumferential grooves 24. The tread pattern of the tire 2 shown in FIG. 1 includes four circumferential grooves 24 arranged axially. The groove depth of each circumferential groove 24 is 5.5 mm or more and 8.5 mm.

[0030] Of the four circumferential grooves 24, the two circumferential grooves 24 located outermost axially are shoulder circumferential grooves 24s. The two circumferential grooves 24 located axially inside the shoulder circumferential grooves 24s are middle circumferential grooves 24m. The tread pattern of this tire 2 includes a pair of shoulder circumferential grooves 24s and a pair of middle circumferential grooves 24m located between the pair of shoulder circumferential grooves 24s.

[0031] The four circumferential grooves 24 form five land portions 26 on the tread 4. The edges of the land portions 26 are also the edges of the circumferential grooves 24. Of the five land portions 26 arranged axially, the two land portions 26 located outermost are shoulder land portions 26s. The two land portions 26 located axially inside the shoulder land portions 26s are middle land portions 26m. The land portion 26 located between the two middle land portions 26m is the center land portion 26c. The center land portion 26c includes the equator PC. The five land portions 26 formed on this tread 4 are the center land portion 26c located on the equatorial plane, a pair of middle land portions 26m located axially outside the center land portion 26c, and a pair of shoulder land portions 26s located axially inside the middle land portions 26m.

[0032] Each sidewall 6 is continuous with the tread 4. The sidewall 6 is located radially inside the tread 4. The sidewall 6 is located axially outside the carcass 12. The sidewall 6 is made of crosslinked rubber considering cut resistance.

[0033] Each clinch 8 is located radially inward of the sidewall 6. The clinch 8 contacts the rim R. The clinch 8 is made of crosslinked rubber considering wear resistance.

[0034] Each bead 10 is located axially inward of the clinch 8. The bead 10 is located radially inward of the sidewall 6. The bead 10 includes a core 28 and an apex 30. The core 28 extends in the circumferential direction. Although not shown, the core 28 includes a steel wire. The apex 30 is located radially outside the core 28. The apex 30 is made of crosslinked rubber having high rigidity.

[0035] The carcass 12 is located inside the tread 4, a pair of sidewalls 6, and a pair of clinches 8. The carcass 12 spans between a pair of beads 10.

[0036] The carcass 12 includes at least one carcass ply 32. The carcass 12 of this tire 2 is composed of two carcass plies 32. Inside the tread 4 in the radial direction, the inner carcass ply 32 is the first carcass ply 34, and the carcass ply 32 located outside the first carcass ply 34 is the second carcass ply 36.

[0037] As shown in FIG. 1, the two carcass plies 32 are each folded from the axially inner side to the outer side at each bead 10.

[0038] Although not shown, the carcass ply 32 includes a number of carcass cords arranged in parallel. These carcass cords intersect the equatorial plane. The carcass 12 of this tire 2 has a radial structure. In this tire 2, a cord made of organic fiber is used as the carcass cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0039] The belt 14 is located radially inside the tread 4. The belt 14 is laminated on the carcass 12. The belt 14 is positioned between the carcass 12 and the tread 4. The aforementioned equatorial plane intersects the belt 14 at the center of the axial width of the belt 14. The axial width of the belt 14 is 65% or more and 85% or less of the cross-sectional width AW of this tire 2.

[0040] The belt 14 includes a plurality of belt plies 38 arranged radially. The plurality of belt plies 38 includes an inner belt ply 40 located innermost and an outer belt ply 42 located outermost. The belt 14 of this tire 2 is composed of two belt plies 38. Specifically, this belt 14 is composed of an inner belt ply 40 and an outer belt ply 42. The inner belt ply 40 is laminated on the carcass 12 radially inside the tread 4. The outer belt ply 42 is laminated on the inner belt ply 42.

[0041] As shown in FIG. 1, the ends of the outer belt ply 42 are located axially inside the ends of the inner belt ply 40. The outer belt ply 42 is narrower than the inner belt ply 40. The length from the end of the outer belt ply 42 to the end of the inner belt ply 40 is 3 mm or more and 10 mm or less. The aforementioned axial width of the belt 14 is represented by the axial width of the wider inner belt ply 40.

[0042] Although not shown, each of the plurality of belt plies 38 constituting the belt 14 includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equatorial plane. The material of the belt cord is steel.

[0043] The band 16 is laminated on the belt 14 inside the tread 4. The ends of the band 16 are located axially outside the ends of the belt 14. The length from the end of the belt 14 to the end of the band 16 is 3 mm or more and 7 mm or less.

[0044] The band 16 of this tire 2 includes a full band 44 and a pair of edge bands 46. The full band 44 covers the entire belt 14 from the outside in the radial direction. The aforementioned equatorial plane intersects the full band 44 at the center of the axial width of the full band 44. A pair of edge bands 46 are arranged axially spaced apart with the equatorial plane interposed therebetween. Each edge band 46 covers the end of the full band 44 from the outside in the radial direction. The band 16 may be composed of only the full band 44, or may be composed of only a pair of edge bands 46.

[0045] Although not shown, the band 16 includes a band cord wound in a spiral shape. In the band 16, the band cord extends substantially in the circumferential direction. Specifically, the angle formed by the band cord with respect to the circumferential direction is 5° or less. The band 16 has a jointless structure. A cord made of organic fiber is used as the band cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber. The band cord included in the full band 44 and the band cord included in the edge band 46 are the same. The band cord of the full band 44 and the band cord of the edge band 46 may be different.

[0046] The inner liner 18 is located inside the carcass 12. The inner liner 18 constitutes the inner surface 2N of the tire 2. The inner liner 18 is made of crosslinked rubber having excellent air barrier properties. The inner liner 18 retains the internal pressure of the tire 2.

[0047] In FIG. 1, the solid line EL is a straight line passing through the end of the belt 14 and extending in the radial direction. The position indicated by the symbol TE is the intersection of this straight line EL and the outer surface 2G of the tire 2. This intersection TE is the position on the outer surface of the tread 4 corresponding to the end of the belt 14. In the present invention, this position TE is the reference end that defines the width of the tread 4. The width TW of the tread 4 is represented by the axial distance from one reference end TE to the other reference end TE.

[0048] In the present invention, among the two reference ends TE, one reference end TE that is arranged on the inner side in the vehicle width direction when the tire 2 is mounted on a vehicle (not shown) is the first reference end TE1, and the other is the second reference end TE2. In the cross-section of the tire 2 shown in FIG. 1, the reference end TE located on the arrow AD1 side is called the first reference end TE1, and the reference end TE located on the arrow AD2 side is called the second reference end.

[0049] FIG. 2 is a developed view showing a part of the tread pattern of this tire 2. In FIG. 2, the direction indicated by both arrows AD is the axial direction of the tire 2. The direction indicated by both arrows CD is the circumferential direction of the tire 2. In this FIG. 2, for the sake of convenience of explanation, only four circumferential grooves 24 are shown as the grooves 22 constituting the tread pattern.

[0050] In this tire 2, the four circumferential grooves 24 are arranged symmetrically with respect to the equatorial plane. Therefore, the five land portions 26 are also arranged symmetrically with respect to the equatorial plane. In FIG. 2, the length indicated by both arrows WC is the width of the center land portion 26c. The width WC is represented by the axial distance from one edge of the center land portion 26c to the other edge. The width WC is 11% or more and 13% or less of the contact width CW of the standard contact surface described later. As shown in FIG. 2, at the center of the width WC of the center land portion 26c, the equatorial plane intersects the center land portion 26c.

[0051] In FIG. 2, the length indicated by both arrows WM is the width of the middle land portion 26m. The width WM is represented by the axial distance from one edge of the middle land portion 26m to the other edge. In the tread pattern shown in FIG. 2, the width WM1 of the middle land portion 26m on the first end TE1 side and the width WM2 of the middle land portion 26m on the second end TE2 side are the same. The width WM of the middle land portion 26m is 120% or more and 130% or less of the width WC of the center land portion 26c.

[0052] In FIG. 2, the length indicated by the double arrow WS is the width of the shoulder land portion 26s. The width WS is represented by the axial distance from the inner edge of the shoulder land portion 26s to the reference end TE of the tread 4. In the tread pattern shown in FIG. 2, the width WS1 of the shoulder land portion 26s on the first end TE1 side and the width WS2 of the shoulder land portion 26s on the second end TE2 side are the same. The width WS of the shoulder land portion 26s is 135% or more and 145% or less of the width WC of the center land portion 26c.

[0053] FIG. 3 shows a part of the tread portion of the tire 2 shown in FIG. 1. This FIG. 3 shows the tread portion on the first reference end TE1 side. The tread 4 of this tire 2 is composed of a plurality of layers 48 arranged in the radial direction. Each layer 48 is made of crosslinked rubber. The plurality of layers 48 include a cap layer 50, an intermediate layer 52, and a base layer 54. The cap layer 50 is located on the outermost side. The base layer 54 is located on the innermost side. The intermediate layer 52 is located between the cap layer 50 and the base layer 54. The tread 4 of this tire 2 is composed of the cap layer 50 located on the outermost side, the base layer 54 located on the innermost side, and the intermediate layer 52 located between the cap layer 50 and the base layer 54. This tread 4 has a three-layer structure.

[0054] The cap layer 50 contacts the road surface. The end 50e of the cap layer 50 is located axially inside the end 48e of the intermediate layer 52. Most of the intermediate layer 52 is covered by the cap layer 50. In a new tire 2, the intermediate layer 52 is not exposed. The end 50e of the cap layer 50 may coincide with the end 52e of the intermediate layer 52. When the cap layer 50 wears, the intermediate layer 52 contacts the road surface. The contact with the road surface is considered for the intermediate layer 52. The position of the end 54e of the base layer 54 coincides with the position of the end 52e of the intermediate layer 52 in the axial direction, or the end 54e of the base layer 54 is located axially inside the end 52e of the intermediate layer 52. The entire base layer 54 is covered by the intermediate layer 52. The base layer 54 does not contact the road surface. The contact with the road surface is not considered for the base layer 54.

[0055] In this tire 2, the loss tangent LTm of the intermediate layer 52 at 30°C is lower than the loss tangent LTc of the cap layer 50 at 30°C. The loss tangent LTb of the base layer 54 at 30°C is lower than the loss tangent LTm of the intermediate layer 52 at 30°C. The cap layer 50, the base layer 54, and the intermediate layer 52 are each made of crosslinked rubber having different heat generation properties. The cap layer 50 is the most likely to generate heat, and the base layer 54 is the least likely to generate heat. The intermediate layer 52 has a heat generation property between the heat generation property of the cap layer 50 and the heat generation property of the base layer 54.

[0056] The cap layer 50 having a high loss tangent LTc exhibits a high grip force. The cap layer 50 can contribute to the improvement of wet performance. The base layer 54 having a low loss tangent LTb is less likely to generate heat. The base layer 54 can contribute to the reduction of rolling resistance. The intermediate layer 52 has an intermediate loss tangent LTm between the loss tangent LTc and the loss tangent LTb. When wet performance is emphasized, the loss tangent LTm of the intermediate layer 52 is set to a loss tangent close to the loss tangent LTc of the cap layer 50. When rolling resistance is emphasized, the loss tangent LTm of the intermediate layer 52 is set to a loss tangent close to the loss tangent LTb of the base layer 54.

[0057] In the present invention, the thickness of the tread 4 and each layer 48 constituting the tread 4 is measured along the normal line of the outer surface 2G of the tire 2. The ratio of the thickness of each layer to the thickness of the tread 4 is expressed based on the thickness measured along the same normal line.

[0058] FIG. 4 is a cross-sectional view of the tread 4 of this tire 2. FIG. 4 schematically shows the configuration of the tread 4 shown in FIG. 1. Of the tread 4, the side on the first reference end TE1 side across the equatorial plane is called the inside tread 4u, and the side on the second reference end TE2 side across the equatorial plane is also called the outside tread 4s. The tread 4 includes an inside tread 4u located on the first reference end TE1 side across the equatorial plane and an outside tread 4s located on the second reference end TE2 side. As shown in FIG. 4, the tread 4 of this tire 2 has a layer configuration symmetric with respect to the equatorial plane.

[0059] Figure 5 is a modified example of the tread 4 shown in Figure 4. As shown in Figure 5, the tread 4 may be configured such that the cap layer 50 covers the entire intermediate layer 52. Also in the modified example shown in this Figure 5, the tread 4 has a layer configuration that is symmetric with respect to the equatorial plane.

[0060] The tread 4 of this tire 2 is divided into a first tread 60 and a second tread 62 according to the thickness TC of the cap layer 50. The first tread 60 is the part where the cap layer 50 is thick, and the second tread 62 is the part where the cap layer 50 is thin. Specifically, the first tread 60 is the part where the thickness TC of the cap layer 50 is in the range of 35% or more and 55% or less of the thickness TT of the tread 4. The second tread 62 is the part where the thickness TC of the cap layer 50 is in the range of 5% or more and 25% or less of the thickness TT of the tread 4.

[0061] The ratio TC / TT of the thickness TC of the cap layer 50 in the first tread 60 to the thickness TT of the tread 4 is also called the ratio RC1. The ratio TM / TT of the thickness TM of the intermediate layer 52 in the first tread 60 to the thickness TT of the tread 4 is also called the ratio RM1. The ratio of the thickness of the base layer 54 in the first tread 60 to the thickness TT of the tread 4 is also called the ratio RB1.

[0062] The ratio TC / TT of the thickness TC of the cap layer 50 in the second tread 62 to the thickness TT of the tread 4 is also called the ratio RC2. The ratio TM / TT of the thickness TM of the intermediate layer 52 in the second tread 62 to the thickness TT of the tread 4 is also called the ratio RM2. The ratio of the thickness of the base layer 54 in the second tread 62 to the thickness TT of the tread 4 is also called the ratio RB2.

[0063] In FIG. 4, the position indicated by reference sign P25 is the position where the thickness TC of the cap layer 50 represents 25% of the thickness TT of the tread 4. The axially outer portion of this position P25 is the second tread 62. The position indicated by reference sign P35 is the position where the thickness TC of the cap layer 50 represents 35% of the thickness TT of the tread 4. The axially inner portion of this position P35 is the first tread 60. The first tread 60 of this tire 2 intersects the equatorial plane.

[0064] When the tire 2 contacts the road surface, the shoulder portion of the tread portion is greatly deformed. Among the shoulder portions, a large compressive strain occurs near the ground contact end. Compressive strain is a factor that increases rolling resistance.

[0065] The tread 4 of this tire 2 includes a first tread 60 and a pair of second treads 62. The first tread 60 is located on the equatorial plane, and each second tread 62 is located axially outside the first tread 60. As described above, the ratio (TC / TT) of the thickness TC of the cap layer 50 in the second tread 62 to the thickness TT of the tread 4 is 5% or more and 25% or less, and the ratio (TC / TT) of the thickness TC of the cap layer 50 in the first tread 60 to the thickness TT of the tread 4 is 35% or more and 55% or less.

[0066] The cap layer 50 of the second tread 62 is thin. The second tread 62 can form a thicker intermediate layer 52 compared to the first tread 60. The second tread 62 generates less heat than the first tread 60. As described above, the second tread 62 is located axially outside the first tread 60. The second tread 62 can contribute to reducing the energy loss caused by the compressive strain in the shoulder portion. This tire 2 can achieve a reduction in rolling resistance.

[0067] The cap layer 50 of the first tread 60 is thick. As described above, the first tread 60 is located on the equatorial plane. The first tread 60 can contribute to exhibiting wet performance in the crown portion. The grounding length of the crown portion is longer than that of the shoulder portion, and the grounding area of the crown portion is wider than that of the shoulder portion. Even when the tread 4 wears and the cap layer 50 of the second tread 62 disappears, the cap layer 50 of the first tread 60 can contribute to suppressing the deterioration of wet performance. This tire 2 can achieve a reduction in rolling resistance while suppressing a deterioration in wet performance.

[0068] As described above, the ratio (TC / TT) of the thickness TC of the cap layer 50 in the first tread 60 to the thickness TT of the tread 4 is 55% or less, and the ratio (TC / TT) of the thickness TC of the cap layer 50 in the second tread 62 to the thickness TT of the tread 4 is 25% or less. From the viewpoint of reducing rolling resistance, the ratio (TC / TT) of the thickness TC of the cap layer 50 in the first tread 60 to the thickness TT of the tread 4 is preferably 50% or less, and the ratio (TC / TT) of the thickness TC of the cap layer 50 in the second tread 62 to the thickness TT of the tread 4 is preferably 20% or less.

[0069] As described above, the ratio (TC / TT) of the thickness TC of the cap layer 50 in the first tread 60 to the thickness TT of the tread 4 is 35% or more, and the ratio (TC / TT) of the thickness TC of the cap layer 50 in the second tread 62 to the thickness TT of the tread 4 is 5% or more. From the viewpoint of suppressing the deterioration of wet performance, the ratio (TC / TT) of the thickness TC of the cap layer 50 in the first tread 60 to the thickness TT of the tread 4 is preferably 40% or more, and the ratio (TC / TT) of the thickness TC of the cap layer 50 in the second tread 62 to the thickness TT of the tread 4 is preferably 10% or more.

[0070] In this tire 2, the portion between the first tread 60 and the second tread 62 is also called the boundary portion 64. In the boundary portion 64, the thickness TC of the cap layer 50 is thicker than 25% and thinner than 35% of the thickness TT of the tread 4. The boundary portion 64 is the portion between the aforementioned position P35 and position P25.

[0071] In FIG. 4, the position indicated by reference sign P30 is the position where the thickness TC of the cap layer 50 represents 30% of the thickness TT of the tread 4. The solid line LB is a straight line extending radially through this position P30. In the present invention, this straight line LB is also called a reference boundary line. The reference boundary line LB is located between the position P35 and the position P25 in the axial direction.

[0072] As shown in FIG. 4, the first tread 60 is located between the two reference boundary lines LB. The second tread 62 is located outside the reference boundary line LB in the axial direction. The reference boundary line LB is located between the first tread 60 and the second tread 62.

[0073] In FIG. 3, the length indicated by the double arrow HTW is the half-width of the tread 4. The half-width HTW of the tread 4 is the axial distance from the equatorial plane to the reference end TE of the tread 4. The half-width HTW of the tread 4 is equal to half of the width of the tread 4 described above. The length indicated by the double arrow HBW is the axial distance from the equatorial plane to the reference boundary line LB.

[0074] In this tire 2, the ratio (HBW / HTW) of the axial distance HBW to the half-width HTW of the tread 4 is preferably 70% or more and 90% or less. By setting the ratio (HBW / HTW) to 70% or more, the first tread 60 can effectively contribute to suppressing the deterioration of wet performance. From this viewpoint, the ratio (HBW / HTW) is more preferably 75% or more. By setting the ratio (HBW / HTW) to 90% or less, the second tread 62 can effectively contribute to reducing the rolling resistance. From this viewpoint, the ratio (HBW / HTW) is more preferably 85% or less.

[0075] As shown in FIG. 3, in this tire 2, the reference boundary line LB is located axially outside the circumferential groove 24s of the shoulder. Thereby, the first tread 60 can effectively contribute to suppressing the deterioration of wet performance, and the second tread 62 can effectively contribute to reducing the rolling resistance. This tire 2 can achieve a reduction in rolling resistance while suppressing the deterioration of wet performance. From this viewpoint, it is preferable that the reference boundary line LB is located axially outside the circumferential groove 24s of the shoulder.

[0076] In this tire 2, the position P35 where the thickness of the cap layer 50 is 35% of the thickness of the tread 4 is located axially outside the circumferential groove 24s of the shoulder. Thereby, the first tread 60 can effectively contribute to suppressing the deterioration of wet performance, and the second tread 62 can effectively contribute to reducing the rolling resistance. This tire 2 can achieve a reduction in rolling resistance while suppressing the deterioration of wet performance. From this viewpoint, it is preferable that the position P35 where the thickness of the cap layer 50 is 35% of the thickness of the tread 4 is located axially outside the circumferential groove 24s of the shoulder.

[0077] In FIG. 3, the length indicated by the double-headed arrow WB is the axial distance from the position P35 where the thickness TC of the cap layer 50 is 35% of the thickness TT of the tread 4 to the position P25 where the thickness TC of the cap layer 50 is 25% of the thickness TT of the tread 4. The axial distance WB is the width of the boundary portion 64.

[0078] In this tire 2, from the viewpoint that the suppression of the deterioration of wet performance and the reduction of rolling resistance can be balanced and controlled, the ratio (WB / HTW) of the width WB of the boundary portion 64 to the half-width HTW of the tread 4 is preferably 5.0% or less, more preferably 4.0% or less, and even more preferably 3.0% or less. From the viewpoint of effectively suppressing the concentration of strain at the interface between the cap layer 50 and the intermediate layer 52 in the boundary portion 64, the ratio (WB / HTW) is preferably 1.0% or more, more preferably 1.5% or more, and even more preferably 2.0% or more.

[0079] As described above, in this tire 2, the loss tangent Ltm of the intermediate layer 52 at 30°C is lower than the loss tangent LTc of the cap layer 50 at 30°C. Specifically, the ratio (LTm / LTc) of the loss tangent LTm of the intermediate layer 52 at 30°C to the loss tangent LTc of the cap layer 50 at 30°C is preferably 60% or more and 80% or less.

[0080] By setting the ratio (LTm / LTc) to 60% or more, the intermediate layer 52 can secure the required rigidity and effectively contribute to the improvement of wet performance. From this perspective, this ratio (LTm / LTc) is more preferably 65% or more.

[0081] By setting the ratio (LTm / LTc) to 80% or less, the intermediate layer 52 can effectively contribute to the reduction of rolling resistance. From this perspective, this ratio (LTm / LTc) is more preferably 75% or less.

[0082] The loss tangent LTc of the cap layer 50 at 30°C is preferably 0.15 or more. This is because the cap layer 50 can contribute to the improvement of wet performance. From this perspective, the loss tangent LTc is more preferably 0.16 or more, and even more preferably 0.17 or more. The cap layer 50 contacts the road surface. From the perspective of improving wet performance, the higher the loss tangent LTc, the more preferable. However, a high loss tangent LTc causes heat generation. There is a concern that the heat-capable cap layer 50 may increase the temperature of the intermediate layer 52 more than expected. From the perspective of maintaining the temperature state of the entire tread 4 stably and maintaining a low rolling resistance, the loss tangent LTc of the cap layer 50 at 30°C is preferably 0.30 or less, more preferably 0.28 or less, and even more preferably 0.27 or less.

[0083] In this tire 2, from the viewpoint that the intermediate layer 52 effectively contributes to reducing the rolling resistance, the loss tangent Ltm of the intermediate layer 52 at 30°C is preferably 0.15 or less, more preferably 0.14 or less, and even more preferably 0.13 or less. From the viewpoint that the intermediate layer 52 can ensure the required rigidity and effectively contribute to improving the wet performance, the loss tangent Ltm of the intermediate layer 52 at 30°C is preferably 0.10 or more, and more preferably 0.11 or more.

[0084] As described above, in this tire 2, the loss tangent LTb of the base layer 54 at 30°C is lower than the loss tangent LTm of the intermediate layer 52 at 30°C. Specifically, the loss tangent LTb of the base layer 54 at 30°C is preferably 0.10 or less. This is because the base layer 54 effectively contributes to reducing the rolling resistance. From this viewpoint, it is more preferably 0.09 or less. Since it is more preferable that the loss tangent LTb of the base layer 54 is smaller, no preferable lower limit is set.

[0085] FIG. 6 schematically shows the contact surface shape of the new tire 2. In FIG. 6, the direction indicated by the double arrow ADe corresponds to the axial direction of the tire 2. The direction indicated by the double arrow CDe corresponds to the circumferential direction of the tire 2.

[0086] The contact surface is obtained, for example, using a contact surface shape measuring device (not shown). In this device, the tire 2 is assembled on a rim (regular rim), the internal pressure of the tire 2 is adjusted, a vertical load is applied to the tire 2, and the tire 2 is brought into contact with a flat road surface (plane). Although not described in detail, an image of the contact surface formed by the tire 2 contacting the plane is obtained by a known method. Based on the obtained image, the contour of the contact surface is specified. The contour of the contact surface, that is, the contact surface shape of the contact surface, is obtained by tracing the periphery of the contact surface in the image of the contact surface.

[0087] In the present invention, the tire 2 is mounted on a standard rim, the internal pressure of the tire 2 is adjusted to 230 kPa, and a load of 70% of the load indicated by the load index of the tire 2 is applied to the tire 2 as a vertical load, and the contact surface obtained by bringing the tire 2 into contact with a road surface composed of a plane is the reference contact surface. When obtaining the reference contact surface, the tire 2 is arranged such that its axial direction is parallel to the road surface. The above-mentioned load is applied to this tire 2 in a direction perpendicular to the road surface. In other words, a vertical load is applied to the tire with the camber angle of the tire being 0°.

[0088] In FIG. 6, the dashed-dotted line LP is the center line of the axial width (that is, the contact width) of the reference contact surface. The double arrow P100 is the length of the intersection line between the plane including the straight line LP and the reference contact surface. In this tire 2, the length P100 of this intersection line is the contact length at the center of the contact width of the reference contact surface.

[0089] In FIG. 6, the position indicated by the symbol SE is the axial outer end of the reference contact surface, in other words, the contact end of the reference contact surface. The solid line LM is a straight line passing through the contact end SE and parallel to the straight line LP. The solid line L80 is located between the straight line LM and the straight line LP and is a straight line parallel to the straight line LM and the straight line LP. The double arrow A100 represents the axial distance from the straight line LP to the straight line LM. This distance A100 corresponds to half of the contact width of the reference contact surface. The double arrow A80 represents the axial distance from the straight line LP to the straight line L80. In FIG. 6, the ratio of the distance A80 to the distance A100 is set to 80%. That is, the straight line L80 represents a position corresponding to 80% of the contact width of the reference contact surface. The double arrow P80 is the length of the intersection line between the plane including the straight line L80 and the reference contact surface. In this tire 2, the length P80 of this intersection line is the contact length at the 80% width position of the contact width of the reference contact surface.

[0090] On the reference ground plane shown in FIG. 6, by specifying the grounding length P100 at the center of the grounding width of the reference ground plane and the grounding length P80 at the 80% width position of the grounding width of the reference ground plane, the ratio (P80 / P100) of the grounding length P80 to the grounding length P100 can be obtained. The smaller this ratio (P80 / P100), the more rounded the contour of the reference ground plane is.

[0091] In this tire 2, it is preferable that the aforementioned ratio (P80 / P100) is 65% or more and 95% or less. By setting the ratio (P80 / P100) to 65% or more, the shoulder portion can be sufficiently grounded to the road surface. Since the slippage of the shoulder portion with respect to the road surface is suppressed, this tire 2 can maintain good resistance to uneven wear. From this viewpoint, the ratio (P80 / P100) is more preferably 70% or more, and even more preferably 75% or more. By setting the ratio (P80 / P100) to 95% or less, the grounding length of the crown portion is longer than that of the shoulder portion, and a grounding surface with a larger grounding area of the crown portion than that of the shoulder portion is formed. Even when the tread 4 wears and the cap layer 50 of the second tread 62 disappears, the cap layer 50 of the first tread 60 can effectively contribute to suppressing the deterioration of wet performance. From this viewpoint, the ratio (P80 / P100) is more preferably 90% or less, and even more preferably 85% or less.

[0092] In FIG. 3, the solid line LS is a straight line extending in the radial direction passing through the end of the outer belt ply 42. The position indicated by the symbol SBE is the intersection of the straight line LS and the outer surface 2G of the tire 2 (specifically, the tread surface 20). The intersection SBE is the position on the tread surface 20 corresponding to the end of the outer belt ply 42. The solid line NL is the normal to the outer surface 2G of the tire 2 passing through the intersection SBE. The length indicated by the double arrow TTe is the thickness of the tread 4 measured along this normal NL. The length indicated by the double arrow TCe is the thickness of the cap layer 50 measured along this normal NL. In this tire 2, the thickness TTe is the thickness of the tread 4 at the end of the outer belt ply 42, and the thickness TCe is the thickness of the cap layer 50 at the end of the outer belt ply 42.

[0093] In this tire 2, the thickness TCe of the cap layer 50 at the end of the outer belt ply 42 is preferably 25% or less of the thickness TTe of the tread 4. Thereby, in this tire 2, the cap layer 50 in the shoulder portion can be made thin and the intermediate layer 52 can be made thick. This tire 2 can achieve a reduction in rolling resistance. From this viewpoint, the thickness TCe of the cap layer 50 at the end of the outer belt ply 42 is more preferably 10% or less of the thickness TTe of the tread 4. Particularly preferably, the thickness TCe of the cap layer 50 at the end of the outer belt ply 42 is 5% of the thickness TTe of the tread 4.

[0094] The length indicated by the double arrow WSBE in FIG. 3 is the axial distance from the end of the outer belt ply 42 to the reference boundary line LB. In this tire 2, the axial distance WSBE is preferably 50 mm. As described above, the first tread 60 is located axially inside the reference boundary line LB. Therefore, by setting the axial distance WSBE to 50 mm, the tread 4 is configured such that the thickness TC of the cap layer 50 is 35% or more of the thickness TT of the tread 4 axially inside the position 50 mm away from the end of the outer belt ply 42 in the axial direction. In this tire 2, the crown portion including the first tread 60 can effectively contribute to the exhibition of wet performance. This tire 2 can effectively suppress a decrease in wet performance.

[0095] From the viewpoint of achieving a reduction in rolling resistance while suppressing a decrease in wet performance, the thickness TC of the cap layer 50 at the end of the outer belt ply 42 is 25% or less of the thickness TT of the tread 4, and it is more preferable that the thickness of the cap layer 50 is 35% or more of the thickness of the tread 4 axially inside the position 50 mm away from the end of the outer belt ply 42 in the axial direction.

[0096] FIG. 7 shows the standard contact patch of the new tire 2. The standard contact patch is also obtained using a contact patch shape measuring device (not shown), similar to the aforementioned reference contact patch. In particular, the standard contact patch is obtained by mounting the tire 2 on the rim R, adjusting the internal pressure of the tire 2 to 230 kPa, loading a vertical load on the tire 2, and bringing the tire 2 into contact with a flat road surface. The vertical load applied to the tire 2 is 60% or more and 80% or less of the load indicated by the load index of the tire 2.

[0097] In FIG. 7, the position indicated by the reference SEs is the ground contact end of the standard contact patch. The length indicated by the double arrow CW is the ground contact width of the standard contact patch. The ground contact width CW is represented by the axial distance from one ground contact end SEs to the other ground contact end SEs. The dashed-dotted line LPs is the center line of the ground contact width of the standard contact patch. The length indicated by the double arrow CG is the ground contact length at the center of the ground contact width of the standard contact patch.

[0098] In this tire 2, it is preferable that the ground contact width CW of the standard contact patch is 70% or more and 80% or less of the cross-sectional width AW of the tire 2. Thereby, the tire 2 can contact the road surface with sufficient width. This tire 2 can exhibit good wet performance.

[0099] As shown in FIG. 7, the standard contact patch includes the contact patches corresponding to the land portions 26, specifically, the center land portion 26c, the two middle land portions 26m, and the contact patches of the two shoulder land portions 26s. The space between two adjacent contact patches corresponding to the land portions 26 corresponds to the circumferential groove 24. Therefore, the standard contact patch includes a plurality of circumferential grooves 24, specifically, two middle circumferential grooves 24m and two shoulder circumferential grooves 24s.

[0100] In FIG. 7, the double arrow CM is the groove width of the middle circumferential groove 24m in the standard contact patch. The double arrow CS is the groove width of the shoulder circumferential groove 24s in the standard contact patch. The solid line LA is a straight line extending axially through the center of the ground contact length CG. The groove width CM and the groove width CS are measured along this straight line LM.

[0101] In this tire 2, the sum of the groove widths of the plurality of circumferential grooves 24 included in the standard contact surface, that is, the sum of the groove width CM of the two middle circumferential grooves 24m and the groove width CS of the two shoulder circumferential grooves included in the standard contact surface, is adjusted. Specifically, the ratio (AT / CW) of the sum AT of the groove widths of the plurality of circumferential grooves 24 included in the standard contact surface to the contact width CW of the standard contact surface is preferably 20% or more and 30% or less. Thereby, this tire 2 can suppress the occurrence of weak hydroplaning due to the decrease in groove volume caused by the wear of the tread 4. From this viewpoint, it is more preferable that this ratio (AT / CW) is 22% or more and 28% or less.

[0102] From the viewpoint of achieving a reduction in rolling resistance while suppressing a decrease in wet performance, it is more preferable that the contact width CW of the standard contact surface is 70% or more and 80% or less of the sectional width AW of the tire 2, and the ratio (AT / CW) of the sum AT of the groove widths of the plurality of circumferential grooves 24 included in the standard contact surface to the contact width CW of the standard contact surface is 20% or more and 30% or less.

[0103] FIG. 8 shows a modified example of the tread pattern. Also in this FIG. 8, for the sake of convenience of explanation, only four circumferential grooves 24 are shown as the grooves 22 constituting the tread pattern, similar to FIG. 2. In this tread pattern, the four circumferential grooves 24 are arranged asymmetrically with respect to the equatorial plane. Therefore, the five land portions 26 are also arranged asymmetrically with respect to the equatorial plane.

[0104] In the tread pattern shown in FIG. 8, the width WC of the center land portion 26c is preferably 14% or more and 16% or less of the contact width CW of the standard contact surface. By setting the width WC to 14% or more of the contact width CW, when this tire 2 is mounted on a vehicle, a high cornering force is generated in the front tire. This tire 2 can contribute to suppressing the response delay of the front tire. When the width WC is set to 16% or less of the ground contact width CW, when this tire 2 is mounted on a vehicle, high cornering forces are generated well-balanced in the front and rear tires. This tire 2 can contribute to the improvement of linearity.

[0105] In the tread pattern shown in FIG. 8, in this tire 2, the middle land portion 26m1 on the first reference end TE1 side (hereinafter, the first middle land portion 26m1) has a groove width WM1s approximately equal to the groove width WS1 of the shoulder land portion 26s1 on the first reference end TE1 side (hereinafter, the first shoulder land portion 26s1). The center land portion 26c has a groove width WC approximately equal to the groove width WM1 of the first middle land portion 26m1 or has a groove width WC wider than the groove width WM1. The middle land portion 26m2 on the second reference end TE2 side (hereinafter, the second middle land portion 26m2) has a groove width WM2 approximately equal to the width WC of the center land portion 26c or has a groove width WM2 wider than the groove width WC. The shoulder land portion 26s2 on the second reference end TE2 side (hereinafter, the second shoulder land portion 26s2) has a groove width WS2 wider than the groove width WM2 of the second middle land portion 26m2. This tread pattern can contribute to the improvement of wet performance. Moreover, this tire 2 can increase the cornering force. When this tire 2 is mounted on a vehicle, the response delay of the front tire is suppressed and the linearity is improved. This tire 2 can enhance the handling stability of the vehicle.

[0106] The width WS1 of the first shoulder land portion 26s1 is preferably 90% or more and 100% or less of the width WC of the center land portion 26c. By setting the width WS1 to 90% or more of the width WC, this tire 2 can configure the center land portion 26c, the first middle land portion 26m1, and the second middle land portion 26m2 with appropriate widths. When this tire 2 is mounted on a vehicle, high cornering forces are generated well-balanced in the front and rear tires, so the linearity is improved. By setting the width WS1 to 100% or less of the width WC, the tire 2 can configure the center land portion 26c, the first middle land portion 26m1, and the second middle land portion 26m2 with appropriate widths. When this tire 2 is mounted on a vehicle, a high cornering force is generated in the front tire, so the response delay of the front tire is suppressed.

[0107] The width WM1 of the first middle land portion 26m1 is preferably 90% or more and 100% or less of the width WC of the center land portion 26c. By setting the width WM1 to 90% or more of the width WC, when this tire 2 is mounted on a vehicle, a high cornering force is generated in the front tire. This tire 2 can contribute to suppressing the response delay of the front tire. By setting the width WM1 to 100% or less of the width WC, when this tire 2 is mounted on a vehicle, a high cornering force is generated in a well-balanced manner in the front tire and the rear tire. This tire 2 can contribute to improving linearity.

[0108] The width WM2 of the second middle land portion 26m2 is preferably 97% or more and 107% or less of the width WC of the center land portion 26c. By setting the width WM2 to 97% or more of the width WC, when this tire 2 is mounted on a vehicle, a high cornering force is generated in the front tire. This tire 2 can contribute to suppressing the response delay of the front tire. By setting the width WM2 to 107% or less of the width WC, when this tire 2 is mounted on a vehicle, a high cornering force is generated in a well-balanced manner in the front tire and the rear tire. This tire 2 can contribute to improving linearity.

[0109] The width WS2 of the second shoulder land portion 26s2 is preferably 114% or more and 124% or less of the width WC of the center land portion 26c. By setting the width WS2 to 114% or more of the width WC, the tire 2 can configure the center land portion 26c, the first middle land portion 26m1, and the second middle land portion 26m2 with appropriate widths. When this tire 2 is mounted on a vehicle, high cornering forces are generated in a well-balanced manner in the front and rear tires, improving linearity. By setting the width WS1 to 124% or less of the width WC, the tire 2 can configure the center land portion 26c, the first middle land portion 26m1, and the second middle land portion 26m2 with appropriate widths. When this tire 2 is mounted on a vehicle, high cornering forces are generated in the front tire, suppressing the response delay of the front tire.

[0110] In the center land portion 26c shown in FIG. 8, the center of its width is arranged on the second reference end TE2 side with respect to the equatorial plane. That is, when the center land portion 26c is divided by the equatorial plane into a first portion 26c1 on the first reference end TE1 side and a second portion 26c2 on the second reference end TE2 side, the width of the second portion 26c2 is wider than the width of the first portion 26c1. Thereby, the tire 2 can increase the cornering force. When this tire 2 is mounted on a passenger car, the response delay of the front tire is suppressed and the linearity is improved. Since the handling stability is enhanced, the tire 2 can improve the wet performance.

[0111] In FIG. 8, the double-headed arrow W2 is the width of the second portion. This width W2 is represented by the axial distance from the equatorial plane to the edge of the center land portion 26c on the second reference end TE2 side. From the viewpoint of being able to suppress the response delay of the front tire and improve linearity, the ratio (W2 / WC) of the width W2 of the second portion 26c2 to the width WC of the center land portion 26c is preferably 51% or more and 55% or less.

[0112] When this tire 2 is mounted on a vehicle, from the viewpoint that the responsiveness and linearity of the front tire can be effectively improved, and the tire 2 can effectively contribute to suppressing the deterioration of wet performance and reducing the rolling resistance, when the tread pattern of the tire 2 includes four circumferential grooves 24 and five land portions 26 are formed on the tread 4, the width WC of the center land portion 26c is preferably 14% or more and 16% or less of the contact width CW of the standard contact surface. In this case, the width WS1 of the shoulder land portion 26s1 on the first reference end TE1 side is 90% or more and 100% or less of the width WC of the center land portion 26c, the width WM1 of the middle land portion 26m1 on the first reference end TE1 side is 90% or more and 100% or less of the width WC of the center land portion 26c, the width WM2 of the middle land portion 26m2 on the second reference end TE2 side is 97% or more and 107% or less of the width WC of the center land portion 26c, the width WS2 of the shoulder land portion 26s2 on the second reference end TE2 side is 114% or more and 124% or less of the width WC of the center land portion 26c, and it is more preferable that the ratio of the width W2 of the second portion 26c2 of the center land portion 26c to the width WC of the center land portion 26c is 51% or more and 55% or less. In particular, when the contact width CW of the standard contact surface is 70% or more and 80% or less of the cross-sectional width AW of the tire 2, and the ratio (AT / CW) of the total groove width AT of the plurality of circumferential grooves 24 included in the standard contact surface to the contact width CW of the standard contact surface is 20% or more and 30% or less, the tread pattern shown in FIG. 8 can effectively contribute to improving the responsiveness and linearity of the front tire when the tire 2 is mounted on a vehicle.

[0113] By adjusting the thickness and width of the intermediate layer 52, the area of the intermediate layer 52 included in the inside tread 4u and the area of the intermediate layer 52 included in the outside tread 4s of this tire 2 can be controlled. For example, by configuring only the side of the first reference end TE1 of the tread 4 with the second tread 62 and the rest with the first tread 60, the thickness TMs of the intermediate layer 52 in the outside tread 4s can be made thinner than the thickness TM of the intermediate layer 52 in the second tread 62 of the outside tread 4s of the tread 4 shown in FIG. 4. In this case, this tire 2 can make the area of the intermediate layer 52 included in the inside tread 4u larger than the area of the intermediate layer 52 included in the outside tread 4s.

[0114] By making the area of the intermediate layer 52 included in the inside tread 4u larger than the area of the intermediate layer 52 included in the outside tread 4s, this tire 2 can set the volume of the intermediate layer 52 included in the inside tread 4u to be larger than the volume of the intermediate layer 52 included in the outside tread 4s. In this case, the tread 4 is configured with an inside tread 4u that generates less heat than the outside tread 4s.

[0115] In the shoulder portion on the inside side of the tread 4, the compression strain is likely to be larger than that on the outside side shoulder portion. Therefore, by configuring an inside tread 4u that generates less heat than the outside tread 4s, this tire 2 can effectively suppress the heat generation of the entire tread 4. This tire 2 can effectively reduce the rolling resistance. From this perspective, in this tire 2, it is preferable that the area of the intermediate layer 52 included in the inside tread 4u is larger than the area of the intermediate layer 52 included in the outside tread 4s.

[0116] As is clear from the above description, according to the present invention, a tire can be obtained that can achieve a reduction in rolling resistance while suppressing a decrease in wet performance.

Example

[0117] Hereinafter, the present invention will be described in more detail by way of examples and the like, but the present invention is not limited to such examples only.

[0118] [Example 1] A tire (tire size = 255 / 50R20) having the basic configuration shown in FIG. 1 and having the specifications shown in Table 1 below was obtained. The tread of Example 1 has three layers: a cap layer, an intermediate layer, and a base layer, and has the configuration shown in FIG. 4.

[0119] [Comparative Example 1] A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that the tread was composed of two layers, a cap layer and a base layer, and the thicknesses of the respective layers were adjusted so that the ratio of the thickness of the cap layer to the thickness of the tread and the ratio of the thickness of the base layer to the thickness of the tread were uniform as a whole. The tread of Comparative Example 1 is a conventional tread having a two-layer structure.

[0120] [Comparative Examples 2-4] Tires of Comparative Examples 2-4 were obtained in the same manner as in Example 1, except that the tread was composed of three layers, a cap layer, an intermediate layer, and a base layer, and the thicknesses of the respective layers were adjusted so that the ratio of the thickness of the cap layer to the thickness of the tread, the ratio of the thickness of the intermediate layer to the thickness of the tread, and the ratio of the thickness of the base layer to the thickness of the tread were uniform as a whole. The treads of Comparative Examples 2-4 are conventional treads having a three-layer structure. In Comparative Example 2, the ratio of the thickness of the cap layer to the thickness of the tread was set to 15%, the ratio of the thickness of the intermediate layer to the thickness of the tread was set to 65%, and the ratio of the thickness of the base layer to the thickness of the tread was set to 20%. In Comparative Example 3, the ratio of the thickness of the cap layer to the thickness of the tread was set to 30%, the ratio of the thickness of the intermediate layer to the thickness of the tread was set to 50%, and the ratio of the thickness of the base layer to the thickness of the tread was set to 20%. In Comparative Example 4, the ratio of the thickness of the cap layer to the tread thickness was set to 45%, the ratio of the thickness of the intermediate layer to the tread thickness was set to 35%, and the ratio of the thickness of the base layer to the tread thickness was set to 20%.

[0121] [Example 2] The tires of Example 2 were obtained in the same manner as in Example 1, except that the ratios (AT / CW), (WS2 / WC), (WM2 / WC), (WM1 / WC), (WS1 / WC), (W2 / WC), and (WC / CW) were as shown in Table 1 below.

[0122] [Rolling Resistance (RRC)] Using a rolling resistance tester, the rolling resistance coefficient (RRC) was measured when the prototype tire traveled on a drum at a speed of 80 km / h under the following conditions. Rim width: 8.0 inches Internal pressure: 250 kPa Vertical load: 8.09 kN Based on the following formula, using the measured value RCa of the rolling resistance coefficient and the measured value RCb of the rolling resistance coefficient of Comparative Example 1, the rolling resistance index was calculated. The results are shown in the column of "RRC" in Table 1 below. The larger the numerical value, the lower the rolling resistance of the tire. Rolling resistance index = 100 + (RCb - RCa) / RCb × 100

[0123] [Wet Performance (New)] A new prototype tire was mounted on a rim (rim width = 8.0 inches), filled with air, and the internal pressure of the tire was adjusted to 220 kPa. The tire was mounted on a test vehicle (an SUV with a displacement of 2000 cc). The test vehicle was driven on a test course with a wet road surface (water film thickness = 1.4 mm). The brake was applied while the test vehicle was traveling at a speed of 100 km / h, and the traveling distance (braking distance) from when the brake was applied until it stopped was measured. The results are shown in the column of "WET (New)" in Table 1 below with Comparative Example 1 as 100. The larger the numerical value, the shorter the braking distance, and the better the wet performance of the tire.

[0124] [Wet Performance (After Wear)] A prototype tire of a new product was mounted on a rim (rim width = 8.0 inches), filled with air, and the internal pressure of the tire was adjusted to 220 kPa. The tire was mounted on a test vehicle (an SUV with a displacement of 2000 cc). The test vehicle was driven on a test course on a dry asphalt road surface to wear the tread of the tire. The tread was worn until the groove depth of the circumferential groove reached 70% of the groove depth of the new tire. Thereafter, the test vehicle was driven on a test course on a wet road surface (water film thickness = 1.4 mm). The brake was applied while the test vehicle was traveling at a speed of 100 km / h, and the traveling distance (braking distance) from when the brake was applied until it stopped was measured. The results are shown in the column of "WET (After Wear)" in Table 1 below with the index of Comparative Example 1 set to 100. The larger the numerical value, the shorter the braking distance, and the better the wet performance the tire can maintain even after wear.

[0125] [Hydroplaning] A prototype tire of a new product was mounted on a rim (rim width = 8.0 inches), filled with air, and the internal pressure of the tire was adjusted to 220 kPa. The tire was mounted on a test vehicle (an SUV with a displacement of 2000 cc). The test vehicle was driven on a test course on a wet road surface (water film thickness = 1.4 mm), and the speed at which the hydroplaning phenomenon occurred was measured. The results are shown in the column of "Hydroplaning" in Table 1 below with the index of Comparative Example 1 set to 100. The larger the numerical value, the better the hydroplaning resistance performance of the tire.

[0126] [Running Test] The prototype tire was mounted on a rim (rim width = 8.0 inches), filled with air, and the internal pressure of the tire was adjusted to 250 kPa. The tire was mounted on a test vehicle (an SUV with a displacement of 2000 cc). The test vehicle was driven on a test course on a dry road surface, and a sensory evaluation regarding responsiveness and linearity was conducted. The results are shown in the columns of "Responsiveness" and "Linearity" in Table 1 below with the index of Comparative Example 1 set to 100. The larger the numerical value, the better the tire is in terms of responsiveness or linearity.

[0127] [Quietness (Pattern Noise: P / N)] A prototype tire was mounted on a rim (rim width = 8.0 inches), filled with air, and the internal pressure of the tire was adjusted to 220 kPa. The tire was mounted on a test vehicle (an SUV with a displacement of 2000 cc). A sensory evaluation of the shushing sound was conducted when driving on a dry road test course at a speed of 100 km / h. The results are shown in the "P / N" column of Table 1 below with the index of Comparative Example 1 set to 100. The larger the numerical value, the better.

[0128] [Overall Performance] The sum of the index values obtained in each evaluation was calculated. The results are shown in the "Overall" column of Table 1 below. The larger the numerical value, the more preferable.

[0129]

Table 1

[0130] As shown in Table 1, in the examples, it has been confirmed that while suppressing the decrease in wet performance, it is possible to achieve a reduction in rolling resistance. From this evaluation result, the superiority of the present invention is clear.

Industrial Applicability

[0131] The technology described above, which can reduce rolling resistance while suppressing the decrease in wet performance, can be applied to various tires.

[0132] [Supplementary Note] The present invention includes the following aspects.

[0133] [1] A tire comprising a pair of beads, a carcass spanning between the pair of beads, a tread located radially outside of the carcass and in contact with a road surface, and a belt located between the carcass and the tread, wherein the tread comprises a plurality of layers arranged radially, the plurality of layers including a cap layer located on the outermost side, a base layer located on the innermost side, and an intermediate layer located between the cap layer and the base layer, the loss tangent of the intermediate layer at 30°C is lower than the loss tangent of the cap layer at 30°C, the loss tangent of the base layer at 30°C is lower than the loss tangent of the intermediate layer at 30°C, the tread comprises a first tread located on the equatorial plane and a second tread located axially outside of the first tread, the ratio of the thickness of the cap layer in the second tread to the thickness of the tread is 5% or more and 25% or less, and the ratio of the thickness of the cap layer in the first tread to the thickness of the tread is 35% or more and 55% or less. [2] The tire according to [1] above, wherein the ratio of the loss tangent of the intermediate layer to the loss tangent of the cap layer is 60% or more and 80% or less. [3] The tire is assembled on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, a load of 70% of the load indicated by the load index of the tire is applied to the tire as a vertical load, and the tire is brought into contact with a road surface composed of a plane. The obtained contact surface is a reference contact surface, and the ratio of the contact length at 80% of the width position of the contact width of the reference contact surface to the contact length at the center of the contact width of the reference contact surface is 65% or more and 95% or less. The tire according to [1] or [2] above. [4] The tire according to any one of [1] to [3] above, wherein the tread comprises the first tread and a pair of the second treads located axially outside of the first tread. [5] The position on the outer surface of the tread corresponding to the end of the belt is the reference end. Among the two reference ends, one reference end that is arranged on the inner side in the vehicle width direction when the tire is mounted on the vehicle is the first reference end, and the other is the second reference end. In the meridian cross-section of the tire, among the treads, the side of the first reference end across the equatorial plane of the tire is the inside tread, and the side of the second reference end is the outside tread. The area of the intermediate layer included in the inside tread is larger than the area of the intermediate layer included in the outside tread. The tire according to any one of [1] to [4] above. [6] The belt includes a plurality of belt plies arranged in the radial direction. The plurality of belt plies include an outer belt ply located on the outermost side. The thickness of the cap layer at the end of the outer belt ply is 25% or less of the thickness of the tread. Axially inside a position 50 mm away from the end of the outer belt ply in the axial direction, the thickness of the cap layer is 35% or more of the thickness of the tread. The tire according to any one of [1] to [5] above. [7] The tread includes a tread pattern including a plurality of circumferential grooves. The tire is assembled on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, a vertical load is applied to the tire, and the contact surface obtained by bringing the tire into contact with a flat road surface is the standard contact surface. The vertical load applied to the tire is 60% or more and 80% or less of the load indicated by the load index of the tire. The contact width of the standard contact surface is 70% or more and 80% or less of the cross-sectional width of the tire. The ratio of the total groove width of the plurality of circumferential grooves included in the standard contact surface to the contact width of the standard contact surface is 20% or more and 30% or less. The tire according to any one of [1] to [6] above. [8] The position on the outer surface of the tread corresponding to the end of the belt is the reference end. Among the two reference ends, when the tire is mounted on a vehicle, one reference end disposed on the inner side in the vehicle width direction is the first reference end, and the other is the second reference end. The tread pattern includes four circumferential grooves, and five land portions are formed on the tread. The five land portions are a center land portion located on the equatorial plane, a pair of middle land portions located axially outside the center land portion, and a pair of shoulder land portions located axially outside the middle land portion. The width of the shoulder land portion on the first reference end side is 90% or more and 100% or less of the width of the center land portion. The width of the middle land portion on the first reference end side is 90% or more and 100% or less of the width of the center land portion. The width of the middle land portion on the second reference end side is 97% or more and 107% or less of the width of the center land portion. The width of the shoulder land portion on the second reference end side is 114% or more and 124% or less of the width of the center land portion. When the center land portion is divided by the equatorial plane into a first portion on the first reference end side and a second portion on the second reference end side, the ratio of the width of the second portion to the width of the center land portion is 51% or more and 55% or less. The tire according to [7] described above.

Explanation of Signs

[0134] 2 ··· Tire 4 ··· Tread 4u ··· Inside Tread 4s ··· Outside Tread 10 ··· Bead 12 ··· Carcass 14 ··· Belt 20 ··· Tread Surface 22 ··· Groove 24, 24s, 24m, ··· Circumferential Groove 26, 26s, 26s1, 26s2, 26m, 26m1, 26m2, 26c ··· Land Portion 26c1 ··· First Portion 26c2 ··· Second Portion 32 ··· Carcass Ply 34 ··· First Carcass Ply 36 ··· Second Carcass Ply 38 ··· Belt ply 40 ··· Inner belt ply 42 ··· Outer belt ply 48 ··· Ply 50 ··· Cap ply 52 ··· Intermediate ply 54 ··· Base ply 60 ··· First tread 62 ··· Second tread 64 ··· Boundary

Claims

1. A tire comprising a pair of beads, a carcass spanning between the pair of beads, a tread positioned radially outside the carcass and in contact with a road surface, and a belt positioned between the carcass and the tread, wherein the tread comprises a plurality of layers arranged radially, the plurality of layers include a cap layer positioned outermost, a base layer positioned innermost, and an intermediate layer positioned between the cap layer and the base layer, a loss tangent of the intermediate layer at 30°C is lower than a loss tangent of the cap layer at 30°C, a loss tangent of the base layer at 30°C is lower than a loss tangent of the intermediate layer at 30°C, the tread comprises a first tread positioned on the equatorial plane and a second tread positioned axially outside the first tread, a ratio of a thickness of the cap layer in the second tread to a thickness of the tread is 5% or more and 25% or less, a ratio of a thickness of the cap layer in the first tread to a thickness of the tread is 35% or more and 55% or less, a tire.

2. a ratio of a loss tangent of the intermediate layer to a loss tangent of the cap layer is 60% or more and 80% or less, the tire according to Claim 1.

3. The tire is assembled on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, and a load of 70% of the load indicated by the load index of the tire is applied to the tire as a vertical load, and the tire is brought into contact with a flat road surface, and a contact surface obtained thereby is a reference contact surface, and a ratio of a contact length at an 80% width position of a contact width of the reference contact surface to a contact length at a center of the contact width of the reference contact surface is 65% or more and 95% or less, the tire according to Claim 1.

4. the tread comprises the first tread and a pair of the second treads positioned axially outside the first tread, the tire according to Claim 1.

5. a position on an outer surface of the tread corresponding to an end of the belt is a reference end, of the two reference ends, one reference end arranged on an inner side in a width direction of the vehicle when the tire is mounted on the vehicle is a first reference end, and the other is a second reference end, in a meridian cross section of the tire, of the tread, a side on the first reference end side sandwiching the equatorial plane of the tire is an inside tread, and a side on the second reference end side is an outside tread, The area of the intermediate layer included in the inside tread is larger than the area of the intermediate layer included in the outside tread. The tire according to claim 1.

6. The belt includes a plurality of belt plies arranged in the radial direction. The plurality of belt plies includes an outer belt ply located on the outermost side. At the end of the outer belt ply, the thickness of the cap layer is 25% or less of the thickness of the tread. Axially inward of a position 50 mm away in the axial direction from the end of the outer belt ply, the thickness of the cap layer is 35% or more of the thickness of the tread. The tire according to claim 1.

7. The tread has a tread pattern including a plurality of circumferential grooves. The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, a vertical load is applied to the tire, and the contact surface obtained by bringing the tire into contact with a flat road surface is a standard contact surface. The vertical load applied to the tire is 60% or more and 80% or less of the load indicated by the load index of the tire. The contact width of the standard contact surface is 70% or more and 80% or less of the section width of the tire. The ratio of the total groove width of the plurality of circumferential grooves included in the standard contact surface to the contact width of the standard contact surface is 20% or more and 30% or less. The tire according to claim 1.

8. A position on the outer surface of the tread corresponding to the end of the belt is a reference end. Of the two reference ends, when the tire is mounted on a vehicle, one reference end arranged on the inner side in the vehicle width direction is the first reference end, and the other is the second reference end. The tread pattern includes four circumferential grooves. Five land portions are formed on the tread. The five land portions are a center land portion located on the equatorial plane, a pair of middle land portions located axially outside the center land portion, and a pair of shoulder land portions located axially outside the middle land portion. The width of the shoulder land portion on the first reference end side is 90% or more and 100% or less of the width of the center land portion. The width of the middle land portion on the first reference end side is 90% or more and 100% or less of the width of the center land portion. The width of the middle land portion on the second reference end side is 97% or more and 107% or less of the width of the center land portion. The width of the shoulder land portion on the second reference end side is 114% or more and 124% or less of the width of the center land portion. When the center land portion is divided by the equatorial plane into a first portion on the first reference end side and a second portion on the second reference end side, the ratio of the width of the second portion to the width of the center land portion is 51% or more and 55% or less. The tire according to claim 7.

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