tire

Abstract

The present invention provides a tire (2) that can ensure the required wet performance and achieve reduced rolling resistance. The shape index of the reference ground contact surface of the tire (2) is not less than 1.20 and not more than 1.50. The tread (4) of the tire (2) comprises: a crown layer (38), an intermediate layer (40) whose loss tangent at 30°C is lower than the loss tangent at 30°C of the crown layer (38), and a base layer (42) whose loss tangent at 30°C is lower than the loss tangent at 30°C of the intermediate layer (40). In the radial direction, the intermediate layer (40) is located outside the base layer 42, and the crown layer (38) is located outside the intermediate layer (40). In the shoulder land portion (28s) of the tread (4), the thickness (Tm) of the crown layer (38) at the axial width center (Pm) is thinner than the thickness (Tg) of the crown layer (38) on the shoulder circumferential groove (26s) side.

Description

Technical Field

[0001] The present invention relates to a tire. Background Art

[0002] When low-heat-generating rubber is used for the tread, a tire with low rolling resistance can be obtained. However, the grip of low-heat-generating rubber is inferior to that of heat-generating rubber that can exert high grip. Therefore, when low-heat-generating rubber is used for the tread, braking performance (hereinafter also referred to as wet performance) on a wet road surface is reduced. It is difficult to strike a good balance between rolling resistance and wet performance. Various studies have been conducted to reduce rolling resistance and improve wet performance (for example, Patent Document 1 below).

[0003]

Prior art literature

[0004] Patent Literature

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-2008 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] To achieve high grip, a cap layer made of exothermic rubber is formed on the surface of the tread. Circumferential grooves are engraved on the tread to form multiple land portions. As also disclosed in the aforementioned Patent Document 1, the cap layer is typically constructed so that each land portion has approximately the same thickness.

[0008] However, depending on the tire's contact patch shape, the land portion may not wear uniformly as a whole, but rather wear only partially. Specifically, in the shoulder land portion located axially outside the tread, the sidewall portion may be virtually unworn, even in the area adjacent to the tread end. In such cases, a portion of the crown layer remains unworn on the shoulder land portion, which has worn due to running.

[0009] Considering the impact on the environment, further reduction of tire rolling resistance is required. The crown layer is formed of exothermic rubber, so it is expected that further reduction of rolling resistance can be achieved by replacing the remaining crown layer with rubber that is less susceptible to heat than the crown layer.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tire that can achieve reduced rolling resistance while ensuring necessary wet performance.

[0011] Solutions for solving problems

[0012] A tire according to one embodiment of the present invention includes a tread that contacts a road surface. The tire is assembled onto a regular rim, the internal pressure is adjusted to 230 kPa, and a longitudinal load of 70% of the regular load is applied to the tire, resulting in contact with a flat road surface. This contact patch is referred to as a reference contact patch. The tire's shape index, represented by the ratio of its equatorial contact length to its reference contact length, is 1.20 to 1.50. The equatorial contact length is measured along the equator, and the reference contact length is the reference contact length at a position corresponding to 80% of the maximum contact width. At least three circumferential grooves are engraved on the tread, forming at least four axially aligned land portions. Of the at least three circumferential grooves, the axially outer circumferential grooves are shoulder circumferential grooves. The land portion axially outward of the shoulder circumferential grooves is the shoulder land portion, while the land portion inward of the shoulder circumferential grooves is the center land portion. The tread comprises a crown layer, an intermediate layer having a loss tangent at 30°C lower than that of the crown layer, and a base layer having a loss tangent at 30°C lower than that of the intermediate layer. The intermediate layer is radially outward from the base layer, and the crown layer is radially outward from the intermediate layer. In the shoulder land portion, the thickness of the crown layer at the center of the axial width is thinner than the thickness of the crown layer on the shoulder circumferential groove side.

[0013] Preferably, in this tire, when the shape index is denoted as F and the ratio of the thickness of the crown layer at the center of the axial width of the shoulder land portion to the effective groove depth of the shoulder circumferential groove is denoted as Rm (unit: %), the ratio Rm satisfies the following formulas (1) and (2).

[0014] Rm≤33.333×F-18 (1)

[0015] Rm≥33.333×F-22 (2)

[0016] Preferably, in the tire, in the shoulder land portion, a ratio of the thickness of the crown layer on the shoulder circumferential groove side to the effective groove depth of the shoulder circumferential groove is 40% to 60%.

[0017] Preferably, in this tire, in the central land portion, a ratio of the thickness of the crown layer to the effective groove depth of the shoulder circumferential groove is 40% or more and 60% or less.

[0018] Preferably, in the tire, the axial width of the crown layer is less than or equal to the axial width of the intermediate layer.

[0019] Preferably, in this tire, a difference between an axial width of the intermediate layer and an axial width of the crown layer is not less than 10 mm and not more than 30 mm.

[0020] Preferably, in this tire, a difference between an axial width of the crown layer and a width of the tread is not less than -10 mm and not more than 10 mm.

[0021] Preferably, in this tire, a ratio of the loss tangent at 30° C. of the crown layer to the loss tangent at 30° C. of the intermediate layer is 110% or more and 250% or less.

[0022] Effects of the Invention

[0023] According to the present invention, a tire can be obtained that can achieve reduced rolling resistance while ensuring necessary wet performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention.

[0025] Figure 2 is used to indicate Figure 1 An enlarged cross-sectional view of the profile of the shoulder portion of a tire.

[0026] Figure 3 is used to indicate Figure 1 An enlarged cross-sectional view of a portion of a tire.

[0027] Figure 4 Schematic diagram illustrating a method for calculating the shape index of a reference ground plane.

[0028] Figure 5 This is a graph that plots the relationship between the shape index and the thickness ratio of the crown layer.

[0029] Figure 6 This is an enlarged cross-sectional view showing a portion of the tire of Comparative Example 1.

[0030] Marking Description

[0031] 2. Tires

[0032] 4···tread

[0033] 6···Sidewall

[0034] 12···Fetus

[0035] 14···Belt

[0036] 16···Crown layer

[0037] 26, 26s, 26m···Circumferential groove

[0038] 28, 28s, 28m···Land Department

[0039] 34, 34a, 34b···ply

[0040] 36, 36a, 36b... layers

[0041] 38···Crown layer

[0042] 40···Middle layer

[0043] 42···basal layer DETAILED DESCRIPTION

[0044] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0045] In this disclosure, a tire mounted on a regular rim, with the tire internal pressure adjusted to the regular pressure, and no load applied to the tire is referred to as a regular state. A tire mounted on a regular rim, with the tire internal pressure adjusted to 230 kPa, and no load applied to the tire is referred to as a reference state.

[0046] In this disclosure, unless otherwise specified, the dimensions and angles of various tire components are measured under normal conditions. Dimensions and angles of various components in a meridian cross-section of the tire, which cannot be measured when the tire is mounted on a normal rim, are measured by aligning the distance between the left and right beads in the cross-section of the tire, obtained by cutting the tire along a plane including the axis of rotation, with the distance between the beads aligned with the distance between the beads in the tire mounted on a normal rim.

[0047] A regular rim is a rim specified in the tire's specifications. These rims include the "standard rim" in JATMA, the "design rim" in TRA, and the "measuring rim" in ETRTO.

[0048] Normal internal pressure refers to the internal pressure specified in the tire's standards. The normal internal pressure is indicated by the "maximum air pressure" in JATMA, the "maximum value" listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA, and the "INFLATION PRESSURE" in ETRTO.

[0049] The normal load refers to the load specified in the tire's specifications. Examples include the "maximum load capacity" in JATMA, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in TRA, and the "LOADCAPACITY" in ETRTO.

[0050] In this disclosure, cross-linked rubber refers to a molded article of a rubber composition obtained by pressurizing and heating a rubber composition. A rubber composition is an uncross-linked rubber obtained by mixing a base rubber and a chemical in a mixer such as a Banbury mixer. Cross-linked rubber is also referred to as vulcanized rubber, and a rubber composition is also referred to as unvulcanized rubber.

[0051] Examples of 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 chemicals include reinforcing agents such as carbon black and silica, plasticizers such as aromatic oils, fillers such as zinc oxide, lubricants such as stearic acid, antioxidants, processing aids, sulfur, and vulcanization accelerators. The selection of base rubber and chemicals, as well as the content of the selected chemicals, can be appropriately determined based on the specifications of the tread and sidewall components to which the rubber composition is applied.

[0052] In the present disclosure, the loss tangent (also referred to as tan δ) at 30°C for elements formed from crosslinked rubber, among the elements constituting rubber, is measured in accordance with JIS K6394 using a viscoelasticity spectrometer ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) under the following conditions: initial strain = 10%, dynamic strain = 2%, frequency = 10 Hz, deformation mode = tension. For this measurement, test pieces are sampled from tires. If it is not possible to sample a test piece from a tire, the rubber composition used to form the element to be measured is pressurized and heated at 170°C for 12 minutes to obtain a sheet of crosslinked rubber (hereinafter referred to as a rubber sheet). A test piece is sampled from this crosslinked rubber.

[0053] Figure 1 A portion of a tire 2 according to one embodiment of the present invention is shown. The tire 2 is a tire for a passenger car. Figure 1 A portion of a cross section of the tire 2 (hereinafter also referred to as a meridian cross section) along a plane including the rotation axis of the tire 2 is shown. Figure 1 , the left-right direction is the axial direction of the tire 2 , and the up-down direction is the radial direction of the tire 2 . Figure 1 The direction perpendicular to the paper surface is the circumferential direction of the tire 2 .

[0054] exist Figure 1In FIG, the dot-dash line EL is the equatorial plane of the tire 2. The tire 2 is symmetrical with respect to the equatorial plane except for decorations such as tread patterns, designs, and texts engraved on its surface.

[0055] exist Figure 1 In the figure, tire 2 is assembled on rim R. Rim R is a regular rim. The interior of tire 2 is filled with air to regulate the internal pressure of tire 2. The tire 2 assembled on rim R is also called a tire-rim assembly. The tire-rim assembly includes rim R and tire 2 assembled on rim R.

[0056] exist Figure 1 In FIG, the position indicated by the symbol PW is the axial outer end of the tire 2. When a pattern, text, or other device is located on the surface, the outer end PW is determined based on an imaginary surface obtained by assuming that there is no decoration.

[0057] exist Figure 1 In the diagram, the length indicated by the symbol WA represents the maximum width of the tire 2, i.e., the cross-sectional width (see JATMA, etc.). The cross-sectional width WA of the tire 2 is the axial distance from the outer end PW on one side to the outer end PW on the other side. The outer end PW is the position indicating the maximum width of the tire 2 (hereinafter referred to as the maximum width position). The cross-sectional width WA is measured for the tire 2 in the reference state.

[0058] The tire 2 includes a tread 4 , a pair of sidewalls 6 , a pair of beadlets 8 , a pair of beads 10 , a carcass 12 , a belt 14 , a cap ply 16 , a pair of breaker layers 18 , a pair of chafers 20 , and an inner liner 22 .

[0059] The tread 4 contacts the road surface on its surface. The tread 4 is engraved with grooves 24. This constitutes a tread pattern.

[0060] In the tire 2, at least three circumferential grooves 26 extending continuously in the circumferential direction are engraved on the tread 4. Thus, at least four land portions 28 arranged in parallel in the axial direction are formed on the tread 4. Figure 1 In the tire 2 shown, three circumferential grooves 26 are engraved on the tread 4 to form four land portions 28. The circumferential grooves 26 form a part of the grooves 24 constituting the tread pattern.

[0061] exist Figure 1 In FIG, the position indicated by the symbol PE is the equator of the tire 2. The equator PE is the intersection line between the surface of the tread 4 and the equatorial plane. Figure 1 As shown, in the case where the grooves 24 are present on the equatorial plane, the equatorial PE is determined based on an imaginary surface obtained by assuming that the tread 4 does not have the grooves 24 .

[0062] Each sidewall 6 is connected to the tread 4. The sidewall 6 is located radially inside the tread 4. The sidewall 6 extends from the edge of the tread 4 along the carcass 12 toward the bead 8. The sidewall 6 is formed of a cross-linked rubber with consideration given to cut resistance.

[0063] Each bead 8 is located radially inward of the sidewall 6. The bead 8 contacts the rim R. The bead 8 is made of a cross-linked rubber that takes wear resistance into consideration.

[0064] Each bead 10 is located axially inside the nozzle 8. The bead 10 includes a bead core 30 and an apex bead 32. Although not shown, the bead core 30 includes a steel wire.

[0065] The apex bead 32 is located radially outside the bead core 30. The apex bead 32 tapers outward. The apex bead 32 is formed of a cross-linked rubber having high rigidity.

[0066] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of beads 8. The carcass 12 spans between one bead 10 and the other bead 10. The carcass 12 has a radial structure.

[0067] The carcass 12 includes at least one carcass ply 34. From the viewpoint of weight reduction, the carcass 12 of the tire 2 is composed of one carcass ply 34.

[0068] Although not shown, the carcass ply 34 includes a plurality of carcass cords arranged in parallel. These carcass cords are covered with a rubber cap. Each carcass cord intersects the equatorial plane. The carcass cords are made of organic fibers. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0069] The belt layer 14 is located radially inside the tread 4. The belt layer 14 is accumulated from the tread side to the carcass 12 in the radial direction. Figure 1 , the length indicated by symbol WR is the axial width of the belt layer 14. The axial width WR is the axial distance from one end to the other end of the belt layer 14. In this tire 2, the axial width WR of the belt layer 14 is not less than 65% and not more than 85% of the cross-sectional width WA.

[0070] The belt layer 14 is composed of at least two layers 36 stacked in the radial direction. The belt layer 14 of the tire 2 is formed by two layers 36 stacked in the radial direction. Of the two layers 36, the layer 36 located on the inner side is the inner layer 36a, and the layer 36 located on the outer side is the outer layer 36b. Figure 1 As shown, the inner layer 36a is wider than the outer layer 36b. The length from the edge of the outer layer 36b to the edge of the inner layer 36a is 3 mm to 10 mm.

[0071] Although not shown, the inner layer 36a and the outer layer 36b each include multiple belt cords arranged in parallel. These belt cords are covered with top rubber. Each belt cord is inclined relative to the equatorial plane. The belt cords are made of steel.

[0072] The cap layer 16 is located between the tread 4 and the belt layer 14 in the radial direction. The cap layer 16 is stacked on the belt layer 14 on the inner side of the tread 4.

[0073] Although not shown, the cap ply 16 includes helically wound cap ply cords. The cap ply cords extend substantially in the circumferential direction. Specifically, the cap ply cords form an angle of 5° or less with the circumferential direction. The cap ply 16 has a seamless structure. In this tire 2, cords formed from organic fibers are used as the cap ply cords. Examples of organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0074] The cap ply 16 of the tire 2 is formed of full cap plies with opposite ends sandwiching the equatorial PE. The cap ply 16 is wider than the belt 14. The length from the edge of the belt 14 to the edge of the cap ply 16 is 3 mm to 10 mm. The cap ply 16 covers the entire belt 14. The cap plies 16 are spaced apart in the axial direction and may include a pair of sidebands that cover the edges of the full cap ply and the edges of the belt 14. The cap ply 16 may consist solely of a pair of sidebands.

[0075] The breaker layers 18 are spaced apart in the axial direction. The breaker layers 18 are located between the edges of the belt layer 14 and the edge of the cap layer 16 and the layer body 34a of the carcass 12. The breaker layers 18 are formed of a cross-linked rubber having low rigidity. In this tire 2, the breaker layers 18 may not be provided.

[0076] Each chafer 20 is located radially inward of the rim 10. The chafer 20 is in contact with the rim R. The chafer 20 of the tire 2 is formed of cloth and rubber impregnated with the cloth.

[0077] Inner liner 22 is located inside carcass 12. Inner liner 22 forms the inner surface of tire 2. Inner liner 22 is made of a cross-linked rubber having a low gas permeability coefficient. Inner liner 22 maintains the internal pressure of tire 2.

[0078] exist Figure 1 , the position indicated by symbol PH is located on the surface of the tread 4. The position PH corresponds to the axially outer end of the contact surface between the tire 2 and the road surface.

[0079] The contact patch used to determine position PH is obtained using, for example, a contact patch shape measuring device (not shown). This contact patch is obtained by applying a longitudinal load of 70% of the normal load to the tire 2, with the camber angle of the tire 2 in a reference state set to 0°, and causing the tire 2 to contact a flat road surface. The contact patch thus obtained in the tire 2 serves as the reference contact patch, and the position on the surface of the tread 4 corresponding to the axially outer end of the reference contact patch is the aforementioned position PH. In the tire 2, this position PH serves as the reference contact end.

[0080] Figure 2 express Figure 1 A portion of a tire 2 is shown. Figure 2 In FIG, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. Figure 2 The direction perpendicular to the paper surface is the circumferential direction of the tire 2.

[0081] Figure 2 Indicates the outline of the shoulder portion of the tire 2 in the meridian cross section. Figure 2 The profile shown is obtained by measuring the surface shape of the tire 2 in a reference state using a displacement sensor.

[0082] In a meridian cross-section, the profile of the tire 2 surface (hereinafter referred to as tire surface TS) is formed by connecting a plurality of contour lines formed by straight lines or circular arcs. In this disclosure, contour lines formed by straight lines or circular arcs are simply referred to as contour lines. Contour lines formed by straight lines are referred to as straight contour lines, and contour lines formed by circular arcs are referred to as curved contour lines.

[0083] The tire surface TS includes a tread surface T and a pair of side surfaces S connected to the edges of the tread surface T. In a meridian cross-section, the profile of the tread surface T includes multiple curved contour lines having different radii. In this tire 2, the curved contour line with the smallest radius among the multiple curved contour lines included in the profile of the tread surface T is located at the edge of the tread surface T and connected to the side surfaces S. In a meridian cross-section, the profile of the tire surface TS includes a curved portion at the edge of the tread surface T. This curved portion is formed by an arc with the smallest radius among the multiple curved contour lines included in the profile of the tread surface T and connected to the side surfaces S. Figure 2 This curved portion is represented by symbol RS.

[0084] In the profile of the tire surface TS, the curved portion RS contacts the contour line adjacent to its axial inner side (hereinafter referred to as the inner adjacent contour line NT) at the connection point CT. The curved portion RS contacts the contour line adjacent to its axial outer side, which constitutes the profile of the side surface S (hereinafter referred to as the outer adjacent contour line NS), at the connection point CS. The profile of the tire surface TS includes the inner adjacent contour line NT, which is located axially inward of the curved portion RS and in contact with the curved portion RS, and the outer adjacent contour line NS, which is located axially outward of the curved portion RS and in contact with the curved portion RS.

[0085] exist Figure 2 In the figure, the solid line LT is a tangent to the curved portion RS at the connection point CT between the inner adjacent contour line NT and the curved portion RS. The solid line LS is a tangent to the curved portion RS at the connection point CS between the outer adjacent contour line NT and the curved portion RS. The position indicated by the symbol PT is the intersection of the tangent lines LT and LS. In this tire 2, this intersection point PT is a virtual tread end.

[0086] In the tread 4, the portion from one imaginary tread end PT to the other imaginary tread end PT is the area expected to come into contact with the road surface under normal running conditions of the tire 2 (hereinafter referred to as the normal contact area). From the perspective of effectively reinforcing the portion of the tread 4 (hereinafter referred to as the tread portion), the belt layer 14 and cap ply layer 16 are arranged in this normal contact area.

[0087] exist Figure 1 In the diagram, the length indicated by the double arrow WT is the width of the tread 4. The width of the tread 4 is the axial distance from one imaginary tread end PT to the other imaginary tread end PT. The length indicated by the double arrow WH is the axial length of the reference ground contact surface. The axial width WH is the axial distance from one reference ground contact end PH to the other reference ground contact end PH.

[0088] In this tire 2, the ratio of the tread 4 width WT to the cross-sectional width WA (WT / WA) is 70% to 90%. The imaginary tread end PT is axially outward of the reference contact patch PH. In other words, the axial width WH of the reference contact patch is narrower than the tread 4 width WT. Specifically, the ratio of the axial width WH to the tread 4 width WT (WH / WT) is 70% to 90%.

[0089] As described above, the tread 4 of the tire 2 has three circumferential grooves 26. In the tire 2, the arrangement, groove depth, and groove width of the three circumferential grooves 26 are not particularly limited. The tread 4 can be applied to the circumferential grooves of a typical tire using the same arrangement, groove depth, and groove width as those of the conventional tires.

[0090] In this tire 2, the circumferential groove 26 located on the outer side in the axial direction of the three circumferential grooves 26 is the shoulder circumferential groove 26s, and the circumferential groove 26 located on the inner side of the shoulder circumferential groove 26s is the center circumferential groove 26m.

[0091] As described above, the tread 4 of the tire 2 is formed with four land portions 28 . Of the four land portions 28 , the land portion 28 located on the equatorial plane side is the center land portion 28 m , and the land portion 28 located outside the center land portion 28 m is the shoulder land portion 28 s .

[0092] The shoulder land portion 28s is a land portion 28 located axially outward from the shoulder circumferential groove 26s. This shoulder land portion 28s includes a reference ground contact edge PH. The central land portion 28m is a land portion 28 located axially inward from the shoulder circumferential groove 26s. Ahead of the left and right central land portions 28m is the central circumferential groove 26m. In this tire 2, the central circumferential groove 26m is located on the equatorial plane. This central circumferential groove 26m is also referred to as a center circumferential groove.

[0093] Figure 3 express Figure 1 A portion of a tire 2 is shown. Figure 3 Indicates the tread 4 portion of the tire 2. Figure 3 In FIG, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. Figure 3 The direction perpendicular to the paper surface is the circumferential direction of the tire 2.

[0094] The tread 4 of the tire 2 has a crown layer 38, an intermediate layer 40, and a base layer 42. In the radial direction, the intermediate layer 40 is located outside the base layer 42, and the crown layer 38 is located outside the intermediate layer 40. Figure 3 As shown, the crown layer 38 is laminated to the intermediate layer 40 , which is laminated to the base layer 42 .

[0095] exist Figure 3 In the figure, the position indicated by the symbol PC is the outer end of the crown layer 38. The length indicated by the symbol WC is the axial width of the crown layer 38. The axial width WC is the axial distance from one outer end PC to the other outer end PC. The position indicated by the symbol PM is the outer end of the middle layer 40. The length indicated by the symbol WM is the axial width of the middle layer 40. The axial width WM is the axial distance from one outer end PM to the other outer end PM. The position indicated by the symbol PB is the outer end of the base layer 42. The length indicated by the symbol WB is the axial width of the base layer 42. The axial width WB is the axial distance from one outer end PB to the other outer end PB.

[0096] The outer end PC of the crown layer 38 is axially located inward of the outer end PM of the middle layer 40. The outer end PC of the crown layer 38 is axially located at approximately the same position as the outer end PB of the base layer 42. In this tire 2, the position of the outer end PC of the crown layer 38 can be appropriately adjusted between the reference ground contact point PH and the outer end PM of the middle layer 40, taking into account wet performance and rolling resistance.

[0097] The outer end PB of the base layer 42 is axially located inward of the outer end PM of the intermediate layer 40. In this tire 2, the difference (WB - WT) between the axial width WB of the base layer 42 and the width WT of the tread 4 is between -10 mm and 10 mm. In other words, the axial width of the base layer 42 is substantially equal to the width WT of the tread 4.

[0098] exist Figure 3 In the diagram, the position indicated by symbol Pg is the edge of the shoulder land portion 28s on the shoulder circumferential groove 26s side. The axial distance from this edge Pg to the imaginary tread end PT is the axial width of the shoulder land portion 28s. The position indicated by symbol Pm is a position on the surface of the tread 4 and is the center of the axial width of the shoulder land portion 28s. This center Pm is axially outward of the reference contact point PH.

[0099] The length indicated by the symbol Tg is the thickness of the crown layer on the shoulder circumferential groove 26s side of the shoulder land portion 28s. This thickness Tg is measured along a straight line extending radially through edge Pg of the shoulder land portion 28s on the shoulder circumferential groove 26s side. If the shape of the boundary between the crown layer 38 and the intermediate layer 40 is modified to match the shape of the shoulder circumferential groove 26s, the thickness Tg is measured along a straight line extending radially from edge Pg toward the imaginary tread end PT, passing through a position on the surface of the tread 4, and extending 1 mm from the edge Pg.

[0100] The length indicated by symbol Tm is the thickness of the crown layer 38 at the center Pm of the axial width of the shoulder land portion 28s. This thickness Tm is measured along a straight line passing through the center Pm of the axial width of the shoulder land portion 28s and extending radially.

[0101] The position indicated by the symbol Pe is the intersection of a straight line extending radially through the imaginary tread segment PT and the surface of the tread 4. This intersection Pe is also referred to as the reference end of the tread 4. When the outer end PC of the crown layer is axially outside the imaginary tread end PT, the thickness of the crown layer 38 measured along a straight line extending radially through this reference end Pe is expressed as the thickness Te of the crown layer 38 at the reference end Pe of the tread 4.

[0102] exist Figure 3In the figure, the position indicated by symbol PS is the outer end of the tread 4 on the tire surface TS. In this tire 2, the outer end PS of the tread 4 is located axially outward from the outer end PC of the crown layer 38. The portion of the tire surface TS from the outer end PC to the outer end PS is composed of the intermediate layer 40. In this tire 2, a portion of the intermediate layer 40 is exposed on the tire surface TS.

[0103] exist Figure 3 In the diagram, the length indicated by the symbol DS represents the groove depth of the shoulder circumferential groove 26s. This groove depth DS is represented by the maximum groove depth of the shoulder circumferential groove. Although not shown, a protrusion resembling a wear indicator is provided at the groove bottom of the shoulder circumferential groove 26s. In this tire 2, the effective groove depth DSe of the shoulder circumferential groove is calculated by subtracting 1.6 mm from the groove depth DS (in mm).

[0104] In this tire 2, the crown layer 38, the intermediate layer 40, and the base layer 42 are each formed from a cross-linked rubber having different heat generation properties. In this tire 2, the crown layer 38 is most susceptible to heat generation, while the base layer 42 is least susceptible to heat generation. The intermediate layer 40 has a heat generation property intermediate between the heat generation properties of the crown layer 38 and the base layer 42. In this tire 2, the loss tangent (LTm) at 30°C of the intermediate layer 40 is lower than the loss tangent (LTc) at 30°C of the crown layer 38. The loss tangent (LTb) at 30°C of the base layer 42 is lower than the loss tangent (LTm) at 30°C of the intermediate layer 40.

[0105] The loss tangent LTb of the base layer 42 at 30°C is preferably 0.11 or less. This is because it effectively contributes to reducing the rolling resistance of the base layer 42. From this perspective, the loss tangent LTb is more preferably 0.10 or less, and even more preferably 0.09 or less. A lower loss tangent LTb of the base layer 42 is preferred, so there is no preferred lower limit.

[0106] The loss tangent LTm of the intermediate layer 40 at 30°C is preferably 0.15 or less. This is because it effectively contributes to reducing the rolling resistance of the intermediate layer 40. From this perspective, the loss tangent LTm is more preferably 0.14 or less, and even more preferably 0.13 or less. The loss tangent LTm of the intermediate layer 40 at 30°C is preferably 0.11 or greater. This is because it ensures the required rigidity of the intermediate layer 40 and effectively contributes to improving wet performance. From this perspective, the loss tangent LTm is preferably 0.12 or greater.

[0107] The loss tangent LTc of the crown layer 38 at 30°C is preferably 0.15 or more. This is because the crown layer 38 can contribute to the improvement of wet performance. From this point of view, the loss tangent LTc is more preferably 0.16 or more, and further preferably 0.17 or more. The crown layer 38 is in contact with the road surface. From the viewpoint of improving wet performance, the higher the loss tangent LTc, the more preferable. However, an excessively high loss tangent LTc causes heat generation. There is a concern that the heated crown layer 38 will increase the temperature of the intermediate layer 40 to a level higher than expected. From the viewpoint of stably maintaining the temperature state of the entire tread 4 and being able to maintain low rolling resistance, the loss tangent LTc of the crown layer 38 at 30°C is preferably 0.30 or less, more preferably 0.28 or less, and further preferably 0.27 or less.

[0108] Figure 4 A model that represents the outline shape of the reference ground plane. Figure 4 , the up-down direction corresponds to the circumferential direction of the tire 2 , and the left-right direction corresponds to the axial direction of the tire 2 . Figure 4 The direction perpendicular to the paper plane corresponds to the radial direction of the tire 2 .

[0109] exist Figure 4 In the figure, the dot-dash line LP is the straight line corresponding to the equator PE of the tire 2 in the reference contact patch. If the equator PE is difficult to determine in the reference contact patch, the axial centerline of the reference contact patch is used as the straight line corresponding to the equator PE. The double-headed arrow P100 indicates the length of the intersection of the plane including the straight line LP and the reference contact patch. In this tire 2, the length P100 of this intersection is the equatorial contact length measured along the equator PE in the reference contact patch.

[0110] exist Figure 4 In the figure, solid line LM is a straight line passing through the reference contact patch end PH of the reference contact patch and parallel to line LP. Solid line L80 is located between lines LM and LP and is parallel to both lines LM and LP. Double-headed arrow A100 indicates the axial distance from line LP to line LM. This distance A100 corresponds to half the maximum contact patch width of the reference contact patch. Double-headed arrow A8 indicates the axial distance from line LP to line L80. In tire 2, the ratio of distance A80 to distance A100 is set to 80%. In other words, line L80 indicates a position corresponding to 80% of the maximum contact patch width of the reference contact patch. Double-headed arrow P80 indicates the length of the intersection of the plane including line L80 and the reference contact patch. In tire 2, length P80 of this intersection is the reference contact patch length at a position corresponding to 80% of the maximum contact patch width.

[0111] In this tire 2, the ratio of the equatorial contact patch length P100 to the reference contact patch length P80 (P100 / P80), which is expressed using the equatorial contact patch length P100 and the reference contact patch length P80, is used as a shape index for the profile shape of the reference contact patch. A larger value of this shape index indicates a more rounded profile of the reference contact patch.

[0112] As described above, the profile of the tread surface T is composed of a plurality of contour lines formed by connecting straight lines or circular arcs. Without further explanation, the shape index F of the reference contact patch can be controlled by adjusting the specifications of the contour lines that constitute the profile of the tread surface T (e.g., the length of straight contour lines and the radius and length of curved contour lines).

[0113] In this tire 2, the shape index of the reference contact patch is between 1.20 and 1.50. In this tire 2, the shoulder land portion 28s does not wear uniformly throughout its entirety, but rather tends to wear partially. In this tire 2, even the edge of the tread 4, particularly the portion on the sidewall 6 side, shows little wear. Therefore, even if the tire 2 wears with use, there is a concern that the crown layer 38 may remain in the axially outer portion of the shoulder land portion 28s.

[0114] In this tire 2, the crown layer 38 in the center land portion 28m has a substantially uniform thickness as a whole. In contrast, the crown layer 38 in the shoulder land portion 28s, on the shoulder circumferential groove 26s side, has the same thickness as the crown layer 38 in the center land portion 28m, but the thickness of the crown layer 38 gradually decreases axially outward from the shoulder circumferential groove 26s side. In the shoulder land portion 28s, the thickness Tm of the crown layer 38 at the axial center Pm is thinner than the thickness Tg of the crown layer 38 on the shoulder circumferential groove 26s side.

[0115] This tire 2 prevents the crown layer 38 from remaining unworn in the axially outer portion of the shoulder land portion 28s. In other words, a crown layer 38 of the required thickness is provided near the reference contact point PH of the shoulder land portion 28s. In this tire 2, a portion of the area where the crown layer 38 is provided in conventional tires is replaced with an intermediate layer 40 that is less susceptible to heat generation than the crown layer 38. This tire 2 ensures the required wet performance while achieving reduced rolling resistance.

[0116] As described above, in this tire 2, the shape index of the reference contact patch is 1.20 or greater and 1.50 or less. For example, if the equatorial contact patch length P100 is the same, the reference contact patch length P80 of the reference contact patch with a higher shape index is shorter than the reference contact patch length P80 of the reference contact patch with a lower shape index.

[0117] The larger the shape index, the shorter the reference contact patch length P80. Therefore, tires 2 with larger shape indices experience higher contact pressure near the reference contact patch end PH. High contact pressure promotes wear. Therefore, when the shape index of the reference contact patch is large, the thickness Tm of the crown layer 38 at the center Pm of the axial width of the shoulder land portion 28s can be increased to ensure good wet performance for the tire 2. Conversely, when the shape index of the reference contact patch is small, wear is less likely to occur in the shoulder land portion 28s. Therefore, the rolling resistance of the tire 2 can be further reduced by reducing the thickness Tm of the crown layer 38.

[0118] In this tire 2, from the perspective of ensuring wet performance and reducing rolling resistance, the ratio (Tm / DSe) of the thickness Tm of the crown layer 38 at the center Pm of the axial width of the shoulder land portion 28s to the effective groove depth DSe of the shoulder circumferential groove 26s is preferably 15% or more and 35% or less. In particular, in this tire 2, from the perspective of being able to effectively form a crown layer 38 of a desired thickness at a desired position in the shoulder land portion 28s based on the shape index of the reference contact patch, where the shape index is represented by F and the ratio (Tm / DSe) is represented by Rm (unit: %), the ratio Rm more preferably satisfies the following equations (1) and (2).

[0119] Rm≤33.333×F-18 (1)

[0120] Rm≥33.333×F-22 (2)

[0121] In the tire 2 , from the viewpoint of ensuring wet performance and reducing rolling resistance, the ratio RM further preferably satisfies the following formula (3).

[0122] Rm=33.333×F-20 (3)

[0123] exist Figure 5 In the graph, the relationship between the shape index F and the ratio Rm (hereinafter referred to as the thickness ratio Rm of the crown layer 38) is plotted, which is the ratio of the thickness Tm of the crown layer 38 at the center Pm of the axial width of the shoulder land portion 28s to the effective groove depth of the shoulder circumferential groove 26s. Figure 2 In FIG. 1 , the horizontal axis represents the shape index F, and the vertical axis represents the thickness ratio Rm of the crown layer.

[0124] exist Figure 5In the figure, the region indicated by symbol Y is a region comprising a tire 2 satisfying equations (1) and (2) above. In tire 2 encompassed by region Y, when the reference contact patch shape index F is large, the thickness Tm of crown layer 38 at center Pm of the axial width of shoulder land portion 28 is thick. Conversely, when the reference contact patch shape index F is small, the thickness Tm of crown layer 38 is thin. In this tire 2, a crown layer 38 having a desired thickness can be effectively formed at a desired location in shoulder land portion 28s according to the reference contact patch shape index. This tire 2 effectively ensures excellent wet performance and further reduces rolling resistance.

[0125] In this tire 2, the ratio (Tg / DSe) of the thickness Tg of the crown layer 38 on the shoulder circumferential groove 26s side in the shoulder land portion 28s to the effective groove depth DSe of the shoulder circumferential groove 26s is preferably 40% to 60%.

[0126] By setting the ratio (Tg / DSe) to 40% or more, the crown layer 38 can contribute to ensuring good wet performance. From this viewpoint, the ratio (Tg / DSe) is preferably 45% or more.

[0127] By setting the ratio (Tg / DSe) to 60% or less, the influence of the crown layer 38 on rolling resistance is suppressed. From this viewpoint, the ratio (Tg / DSe) is preferably 55% or less.

[0128] As described above, the crown layer 38 in the center land portion 28m has a substantially uniform thickness as a whole. Taking the thickness of the crown layer at the widthwise center of the center land portion 28m as the center land portion thickness Tm, in this tire 2, from the perspective of ensuring good wet performance and reducing rolling resistance, the ratio (TM / DSe) of the thickness TM of the crown layer 38 in the center land portion 28m to the effective groove depth DSe of the shoulder circumferential grooves 26s is preferably 40% or more and 60% or less.

[0129] By setting the ratio (TM / DSe) to 40% or more, the cap layer 38 can contribute to ensuring good wet performance. From this viewpoint, the ratio (Tg / DSe) is preferably 45% or more.

[0130] By setting the ratio (TM / DSe) to 60% or less, the influence of the crown layer 38 on rolling resistance is suppressed. From this viewpoint, the ratio (Tg / DSe) is preferably 55% or less.

[0131] In this tire 2, from the perspective of enabling the crown layer 38 to effectively contribute to wet performance, the ratio (WC / WA) of the axial width WC of the crown layer 38 to the cross-sectional width WA of the tire 2 is preferably 70% or greater, and more preferably 75% or greater. From the perspective of effectively suppressing the effect of the crown layer 38 on rolling resistance, this ratio (WC / WA) is preferably 90% or less, and more preferably 85% or less.

[0132] During braking, a large load acts on the tire 2. Consequently, the tire 2's contact patch width tends to widen. In the tire 2, the outer end PC of the crown layer 38 is axially located outward of the reference contact patch PH. This ensures sufficient contact between the crown layer 38 and the road surface even during braking. This tire 2 achieves excellent wet performance. From this perspective, the outer end PC of the crown layer 38 is preferably axially located outward of the reference contact patch PH.

[0133] In this tire 2, from the perspective of suppressing the effect of the crown layer 38 on rolling resistance, the axial width WC of the crown layer 38 is preferably less than or equal to the axial width WM of the intermediate layer 40. From the perspective of achieving further reduction in rolling resistance, the crown layer 38 is more preferably narrower than the intermediate layer 40.

[0134] As described above, in the tire 2, the outer end PC of the crown layer 38 is axially located at substantially the same position as the outer end PB of the base layer 42. The outer end PM of the intermediate layer 40 is axially located outside the outer end PC of the crown layer 38. From the perspective of the intermediate layer 40 contributing to preventing exposure of the base layer 42 during extreme driving, the difference (WM-WC) between the axial width WM of the intermediate layer 40 and the axial width WC of the crown layer 38 is preferably 10 mm or greater. From the perspective of reducing rolling resistance, this difference (WM-WC) is preferably 30 mm or less, more preferably 20 mm or less, and even more preferably 10 mm or less. In the tire 2, from the perspective of preventing exposure of the base layer 42 and effectively reducing rolling resistance, this difference (WM-WC) is particularly preferably 10 mm.

[0135] In this tire 2, the difference (WC - WT) between the axial width WC of the crown layer 38 and the width WT of the tread 4 is preferably -10 mm or more and 10 mm or less. In other words, the axial width WC of the crown layer 38 is preferably substantially equal to the width WT of the tread 4. This ensures sufficient contact between the crown layer 38 and the road surface, not only during straight-line driving but also during braking under heavy loads. This tire 2 achieves excellent wet performance. From this perspective, the difference (WC - WT) is preferably -5 mm or more and preferably 5 mm or less.

[0136] In this tire 2, the portion of the tread 4 formed by the crown layer 38 and the intermediate layer 40 corresponds to the crown layer of the tread of a conventional tire formed by the crown layer and the base layer. To ensure that the tread 4 can effectively contribute to improved wet performance and reduced rolling resistance, the ratio (LTc / LTm) of the loss tangent LTc of the crown layer 38 at 30°C to the loss tangent LTm of the intermediate layer 40 at 30°C is preferably 110% or more and 250% or less. This ratio (LTc / LTm) is more preferably 130% or more, and even more preferably 150% or more. This ratio (LTc / LTm) is more preferably 240% or less, and even more preferably 230% or less.

[0137] As described above, according to the present invention, a tire can be obtained that can achieve reduction in rolling resistance while ensuring necessary wet performance.

[0138] Example

[0139] Hereinafter, the present invention will be described in further detail with reference to Examples and the like, but the present invention is not limited to these Examples.

[0140] [Experiment 1]

[0141] [Example 1]

[0142] A pneumatic tire for a passenger car (tire size = 205 / 55R16) was obtained, which had Figure 1 The basic structure shown has the specifications shown in Table 1 below.

[0143] It uses a crown layer, an intermediate layer and a base layer, Figure 3 The tread of the structure shown has a loss tangent LTc of 0.27 at 30°C for the cap layer, a loss tangent LTm of 0.12 at 30°C for the middle layer, and a loss tangent LTb of 0.10 at 30°C for the base layer.

[0144] The difference between the axial width WC of the crown layer and the tread width WT (WC-WT) is 0 mm. The difference between the axial width WB of the base layer and the tread width WT (WB-WT) is 0 mm. The difference between the axial width WM of the intermediate layer and the axial width WB of the base layer (WM-WB) is 10 mm.

[0145] In the shoulder land portion, the ratio Rg of the thickness Tg of the crown layer on the shoulder circumferential groove side to the effective groove depth DSe of the shoulder circumferential groove is 50%. The ratio Rm of the thickness Tm of the crown layer at the center of the axial width to the effective groove depth DSe of the shoulder circumferential groove is 30%. The axial width WC of the crown layer is the same as the tread width WT, and the ratio Re of the thickness Te of the crown layer at the reference end Pe of the tread to the effective groove depth DSe of the shoulder circumferential groove is 0%.

[0146] [Comparative Example 1]

[0147] The tire of Comparative Example 1 was obtained in the same manner as in Example 1 except that the ratio Rm, the ratio Re, and the difference (WC-WT) were set as shown in Table 1 below. The tread of Comparative Example 1 was constructed as shown in Figure 6 shown.

[0148] [Example 2]

[0149] A tire of Example 2 was obtained in the same manner as in Example 1 except that the ratio Re and the difference (WC-WT) were as shown in Table 1 below.

[0150] [Example 3]

[0151] A tire of Example 3 was obtained in the same manner as in Example 1 except that the ratio RM was set as shown in Table 1 below.

[0152] Rolling resistance coefficient (RRC)

[0153] Using a rolling resistance tester, the sample tire was run on a roller at a speed of 80 km / h under the following conditions, and the rolling resistance coefficient (RRC) at this time was measured. The results are shown in Table 1 below as an index with Comparative Example 1 being 100. The smaller the value, the lower the rolling resistance of the tire. Rim: 16×6.5J Internal pressure: 210kPa Longitudinal load: 4.82kN

[0154] [Wet performance of new tires (WET)]

[0155] Assemble a new sample tire on a rim (size = 16×6.5J), fill it with air, and adjust the internal pressure of the tire to 230kPa. Install the tire on a test vehicle (passenger car). Make the test vehicle travel on a test route on a wet road surface (water film thickness = 1.4mm). Brake the test vehicle while it is traveling at a speed of 100km / h, and measure the distance traveled from the start of braking to the stop (braking distance). The results are shown in the "New" column of the following Table 1 with an index of 100 for Comparative Example 1. The larger the numerical value, the shorter the braking distance and the better the wet performance of the tire. In this evaluation, if the index is 95 or above, it is considered that good wet performance is ensured and it is qualified.

[0156] [Wet performance of worn tires (WET)]

[0157] Assemble a new sample tire on a rim (size = 16×6.5J), fill it with air, and adjust the internal pressure of the tire to 230kPa. Install the tire on a test vehicle (passenger car). Make the test vehicle travel on a test route on a dry asphalt road surface to wear the tire. When the effective groove depth reaches 50% of the effective groove depth of the new tire, evaluate the wetland performance of the worn tire in the same manner as the wetland performance of the new tire described above. The results are shown in the "Old" column of the following Table 1 with an index of 100 for Comparative Example 1. The larger the numerical value, the shorter the braking distance and the better the wetland performance of the tire. In this evaluation, if the index is 95 or above, it is considered that the tire maintains good wetland performance and is qualified.

[0158] [Comprehensive evaluation]

[0159] A comprehensive evaluation was performed based on the indices obtained from each evaluation. In this comprehensive evaluation, smaller values ​​are preferred for the rolling resistance coefficient, so the evaluation value was calculated by subtracting the index from 100. For wet performance of new and worn tires, larger values ​​are preferred, so the evaluation value was calculated by subtracting 100 from the index. The sum of the individual evaluation values ​​was calculated, and a comprehensive evaluation was performed based on this sum. The results are shown in the "Comprehensive Evaluation" column in Table 1 below. Larger values ​​are preferred.

[0160]

Table 1

[0161]

[0162] [Experiment 2]

[0163] [Examples 4-5 and Comparative Example 2]

[0164] The specifications of the contour lines constituting the contour of the tread surface were adjusted, the shape index F was set as shown in Table 2 below, and the ratio Rg, ratio Rm, ratio Re and difference (WC-WT) were set as shown in Table 2. Except for this, the same procedure as in Example 1 was carried out to obtain tires of Examples 4-5 and Comparative Example 2.

[0165] Rolling resistance coefficient (RRC)

[0166] The rolling resistance coefficient (RRC) was measured in the same manner as in Experiment 1. The results are shown in Table 2 below as indices, with Comparative Example 2 being 100. The smaller the numerical value, the lower the rolling resistance of the tire.

[0167] [Wet performance of new tires (WET)]

[0168] The wet performance of new tires was evaluated in the same manner as in Experiment 1. The results are shown in the "New" column of Table 2 below, using an index with Comparative Example 2 as 100. Larger values ​​indicate shorter braking distances and superior wet performance. In this evaluation, an index of 95 or higher indicates good wet performance and is considered acceptable.

[0169] [Wet performance of worn tires (WET)]

[0170] The wet performance of the worn tires was evaluated in the same manner as in Experiment 1. The results are shown in the "Old" column of Table 2 below, using an index with Comparative Example 2 as 100. Larger values ​​indicate shorter braking distances and superior wet performance. In this evaluation, an index of 95 or higher indicates that the tire maintains good wet performance and is considered acceptable.

[0171] [Comprehensive evaluation]

[0172] The same procedure as in Experiment 1 was followed to perform a comprehensive evaluation based on the indices obtained in each evaluation. The results are shown in the "Comprehensive Evaluation" column of Table 2 below. A larger numerical value is more preferable.

[0173]

Table 2

[0174]

[0175] [Experiment 3]

[0176] [Examples 6-7 and Comparative Example 3]

[0177] Tires of Examples 6 and 7 and Comparative Example 3 were obtained in the same manner as in Example 1, except that the specifications of the contour lines constituting the profile of the tread surface were adjusted so that the shape index F was set as shown in Table 3 below, and the ratio Tg, ratio Rm, ratio Re, and difference (WC-WT) were set as shown in Table 3. In Example 7, the outer end of the crown layer is located axially inward of the imaginary tread end PT, so the difference (WC-WT) is expressed as a negative number.

[0178] Rolling resistance coefficient (RRC)

[0179] The rolling resistance coefficient (RRC) was measured in the same manner as in Experiment 1. The results are shown in Table 3 below as indices, with Comparative Example 3 being 100. The smaller the numerical value, the lower the rolling resistance of the tire.

[0180] [Wet performance of new tires (WET)]

[0181] The wet performance of new tires was evaluated in the same manner as in Experiment 1. The results are shown in the "New" column of Table 3 below, using an index with Comparative Example 3 as 100. Larger values ​​indicate shorter braking distances and superior wet performance. In this evaluation, an index of 95 or higher indicates good wet performance and is considered acceptable.

[0182] [Wet performance of worn tires (WET)]

[0183] The wet performance of the worn tires was evaluated in the same manner as in Experiment 1. The results are shown in the "Old" column of Table 3 below, using an index with Comparative Example 3 as 100. Larger values ​​indicate shorter braking distances and superior wet performance. In this evaluation, an index of 95 or higher indicates that the tire maintains good wet performance and is considered acceptable.

[0184] [Comprehensive evaluation]

[0185] The same procedure as in Experiment 1 was followed, and comprehensive evaluation was performed based on the indices obtained in each evaluation. The results are shown in the "Comprehensive Evaluation" column of Table 3 below. A larger numerical value is more preferable.

[0186]

Table 3

[0187]

[0188] As shown in Tables 1 to 3, it was confirmed that the Examples could achieve both the required wet performance and reduced rolling resistance. The superiority of the present invention is evident from these evaluation results.

[0189] Industrial Applicability

[0190] The above-described technology capable of ensuring necessary wet performance and reducing rolling resistance can be applied to various tires.

Claims

1. A tire having a tread that contacts the ground, characterized in that: The tire is assembled on a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and a load of 70% of the regular load is applied to the tire as a longitudinal load. The ground contact surface obtained by making the tire contact a flat road surface is used as the reference ground contact surface. In the reference contact patch, the tire has a shape index represented by a ratio of an equatorial contact patch length to a reference contact patch length, the equatorial contact patch length being measured along the equator and the reference contact patch length being a reference contact patch length at a position corresponding to 80% of a maximum contact patch width, of 1.20 or greater and 1.50 or less. At least three circumferential grooves are carved on the tread to form at least four axially arranged land portions. Among the at least three circumferential grooves, the circumferential groove located on the outer side in the axial direction is the shoulder circumferential groove. In the axial direction, the land portion located outside the shoulder circumferential groove is the shoulder land portion, and the land portion located inside the shoulder circumferential groove is the center land portion. The tread comprises a crown layer, an intermediate layer having a loss tangent at 30°C lower than that of the crown layer, and a base layer having a loss tangent at 30°C lower than that of the intermediate layer. In the radial direction, the middle layer is located on the outside of the base layer, and the crown layer is located on the outside of the middle layer. In the shoulder land portion, the thickness of the crown layer at the center of the axial width is thinner than the thickness of the crown layer on the shoulder circumferential groove side. When the shape index is represented by F and the ratio of the thickness of the crown layer at the axial width center of the shoulder land portion to the effective groove depth of the shoulder circumferential groove is represented by Rm (unit: %), the ratio Rm satisfies the following equations (1) and (2): Rm≤33.333×F-18 (1) Rm≥33.333×F-22 (2) The loss tangent is measured in accordance with JIS K 6394 under the conditions of initial strain = 10%, dynamic strain = 2%, frequency = 10 Hz, and deformation mode = tension.

2. The tire according to claim 1, wherein In the shoulder land portion, a ratio of a thickness of the crown layer on the shoulder circumferential groove side to an effective groove depth of the shoulder circumferential groove is 40% or more and 60% or less.

3. The tire according to claim 1 or 2, characterized in that In the center land portion, a ratio of the thickness of the crown layer to the effective groove depth of the shoulder circumferential groove is not less than 40% and not more than 60%.

4. The tire according to claim 1 or 2, characterized in that The axial width of the crown layer is less than or equal to the axial width of the intermediate layer.

5. The tire according to claim 4, characterized in that A difference between an axial width of the intermediate layer and an axial width of the crown layer is not less than 10 mm and not more than 30 mm.

6. The tire according to claim 1 or 2, characterized in that A difference between the axial width of the crown layer and the width of the tread is not less than -10 mm and not more than 10 mm.

7. The tire according to claim 1 or 2, characterized in that A ratio of a loss tangent at 30° C. of the crown layer to a loss tangent at 30° C. of the intermediate layer is not less than 110% and not more than 250%.

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