tire

Abstract

To provide a tire 2 capable of achieving reduction of rolling resistance without deteriorating grip performance on a wet road surface.SOLUTION: A tire 2 has a tread 4.The tread 4 includes a cap layer 46, a base layer 50, and an intermediate layer 48. The loss tangent of the intermediate layer 48 at 30°C is lower than that of the cap layer 46 at 30°C. The loss tangent of the base layer 50 at 30°C is lower than that of the intermediate layer 48 at 30°C. The boundary between a shoulder circular arc and a corner arc included in the contour line of the tread surface 24 is a reference boundary point. The reference boundary point is positioned outside in an axial direction, of the reference ground position of the tire 2. When a shoulder land portion 32 s is divided into an axial inner portion and an axial outer portion by a ground reference line LG passing through the reference ground position of the tire 2, the thickness ratio of the intermediate layer 48 in the axial outer portion is larger than that of the intermediate layer 48 in the axial inner portion.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tire, and more particularly to a tire for use on a passenger vehicle. [Background technology]

[0002] In consideration of the environment, there is a demand for reduced rolling resistance in tires mounted on vehicles.To this end, measures such as reducing the number of elements constituting the tire, reducing the thickness of the elements, and using materials with low energy loss for the materials constituting the elements, specifically rubber with a low loss tangent (hereinafter, low-loss rubber), are being considered (for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2021-120242 A Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a tire that can achieve a reduction in rolling resistance without deteriorating grip performance on wet road surfaces. [Means for solving the problem]

[0005] A tire according to one aspect of the present invention includes a pair of beads, a carcass spanning between the pair of beads, a pair of sidewalls located axially outside the carcass, a tread located radially outside the carcass, and a belt located between the carcass and the tread. The tread is composed of a plurality of layers aligned in the radial direction. The plurality of layers includes a cap layer located at the outermost position, a base layer located at the innermost position, and an intermediate layer located between the cap layer and the base layer. The loss tangent at 30°C of the intermediate layer is lower than the loss tangent at 30°C of the cap layer. The loss tangent at 30°C of the base layer is lower than the loss tangent at 30°C of the intermediate layer. The outer surface of the tire includes a tread surface including the equator of the tire, and a pair of side surfaces that are connected to the tread surface and include a maximum width position of the tire. In a meridian cross section of the tire, the contour line of the tread surface includes a plurality of arcs aligned in the axial direction. The plurality of circular arcs include a center arc including the equator, a pair of middle arcs connected to the center arc, a pair of shoulder arcs connected to the middle arc, and a pair of corner arcs located on the outermost sides and connected to the shoulder arcs. The intersection of a first tangent to the corner arc at a first end on the equator side of each of the corner arcs and a second tangent to the corner arc at a second end on the side surface side of the corner arc is the tread reference edge. The boundary between the shoulder arc and the corner arc is the reference boundary point. The tire is mounted on a regular rim, the internal pressure of the tire is adjusted to the regular internal pressure, and a load of 80% of the regular load is applied to the tire as a vertical load, and the tire is brought into contact with a flat road surface to obtain a contact edge that is the reference contact edge, and a position on the outer surface of the tire corresponding to the reference contact edge is the reference contact position. The reference boundary point is located axially outward of the reference contact position. At least three circumferential grooves including the two outermost shoulder circumferential grooves form at least four land portions in the tread including the two outermost shoulder land portions. Each of the shoulder land portions includes the reference contact position.When a normal to the inner surface of the tire that passes through the reference contact position is defined as a contact reference line, the shoulder land portion is divided into an axially inner portion and an axially outer portion by the contact reference line, the ratio of the thickness of the cap layer at the axially outer portion to the thickness of the tread is defined as the outer thickness ratio of the cap layer, the ratio of the thickness of the intermediate layer at the axially outer portion to the thickness of the tread is defined as the outer thickness ratio of the intermediate layer, the ratio of the thickness of the cap layer at the axially inner portion to the thickness of the tread is defined as the inner thickness ratio of the cap layer, and the ratio of the thickness of the intermediate layer at the axially inner portion to the thickness of the tread is defined as the inner thickness ratio of the intermediate layer, the outer thickness ratio of the cap layer is smaller than the inner thickness ratio of the cap layer and the outer thickness ratio of the intermediate layer is greater than the inner thickness ratio of the intermediate layer. Effect of the Invention

[0006] According to the present invention, a tire can be obtained that can achieve reduced rolling resistance without deteriorating grip performance on wet road surfaces. [Brief description of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing a portion of a tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing a part of the tread portion. [Diagram 3] FIG. 2 is a cross-sectional view illustrating the contour line of the tread surface. [Figure 4] FIG. 2 is a schematic diagram showing the shape of a contact patch of a tire. [Diagram 5] 1 is a cross-sectional view illustrating the positional relationship between a reference boundary and a reference ground end. [Figure 6] FIG. [Figure 7] FIG. 2 is an enlarged cross-sectional view showing a shoulder land portion. [Figure 8] FIG. 4 is an enlarged cross-sectional view showing a modified example of the tread. [Figure 9] FIG. 11 is an enlarged cross-sectional view showing another modified example of the tread. [Figure 10] FIG. 2 is an enlarged cross-sectional view showing a portion of the tire of Comparative Example 1. [Figure 11] FIG. 1 is a cross-sectional view illustrating a contour line of a conventional tread surface. [Figure 12] 3A to 3C are schematic diagrams illustrating deformation of a tread portion due to contact with a road surface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The tire of the present invention is mounted on a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. The tire mounted on the rim is also called a tire-rim assembly. The tire-rim assembly includes a rim and a tire mounted on the rim.

[0009] In the present invention, a state in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to a standard internal pressure, and no load is applied to the tire is called a standard state.

[0010] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. The dimensions and angles of each part in the meridian section of the tire, which cannot be measured when the tire is mounted on a regular rim, are measured on the cut surface of the tire obtained by cutting the tire along a plane including the axis of rotation. In this measurement, the tire is set so that the distance between the left and right beads is the same as the distance between the beads of the tire mounted on a regular rim. The tire configuration that cannot be confirmed when the tire is mounted on a regular rim is confirmed on the aforementioned cut surface.

[0011] A genuine rim is a rim that is specified in the standard on which the tire is based. The "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, and the "Measuring Rim" in the ETRTO standard are genuine rims.

[0012] Normal tire pressure means the internal pressure specified in the standard on which the tire is based. The "maximum air pressure" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "INFLATION PRESSURE" in the ETRTO standard are normal tire pressures.

[0013] Normal load refers to the load specified in the standard on which the tire is based. The "maximum load capacity" in the JATMA standard, the "maximum value" listed in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, and the "LOAD CAPACITY" in the ETRTO standard are normal loads.

[0014] 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 product 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 called vulcanized rubber, and the rubber composition is also called unvulcanized rubber.

[0015] 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, antioxidants, processing aids, sulfur, and vulcanization accelerators. The selection of the base rubber and chemicals, the content of the selected chemicals, etc. are appropriately determined depending on the specifications of each element such as the tread and sidewall to which the rubber composition is applied.

[0016] In the present invention, the loss tangent (tan δ) of an element made of crosslinked rubber among elements constituting a tire is measured using a viscoelasticity spectrometer in accordance with the provisions of JIS K 6394. The measurement conditions are as follows. Initial distortion = 10% Dynamic distortion = ±1% Frequency = 10Hz Mode = Decompression mode Temperature = 0℃ or 30℃ In this measurement, a test piece (length 40 mm x width 4 mm x thickness 1 mm) is sampled from the tire. The length direction of the test piece is aligned with the circumferential direction of the tire. If it is not possible to sample a test piece from the tire, the test piece is sampled from a sheet-like crosslinked rubber (hereinafter also referred to as a rubber sheet) obtained by pressing and heating the rubber composition used to form 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 0°C or the loss tangent at 30°C.

[0017] In the present invention, the LAT abrasion index is an index for evaluating the abrasion resistance of an element made of crosslinked rubber among elements constituting a tire. The larger the LAT abrasion index, the more excellent the abrasion resistance of the element being evaluated. The LAT abrasion index is measured using a friction tester, such as an LAT tester (Laboratory Abration and Skid Tester) such as LAT100 (manufactured by VMI) in accordance with the provisions of JIS K6264-1 (LAT100 abrasion test). In this measurement, a rubber composition used to form the element to be measured is vulcanized and molded in a mold for the test piece at 170°C for 20 minutes to prepare a test piece. Using this test piece, the volume loss of this test piece (volume loss of the evaluation object) is measured under conditions of a load of 50N, a speed of 20km / h, and a slip angle of 5°. The volume loss of the reference rubber composition (reference volume loss) is also measured in the same manner. Using the volume loss of the evaluation object and the reference volume loss, the LAT abrasion index of the evaluation object element is obtained by the following formula. LAT wear index = (reference volume loss amount / evaluation target volume loss amount) x 100 The LAT abrasion index is the volume loss of the object to be evaluated, expressed as an index with the reference volume loss being 100. There is no particular limitation on the reference rubber composition. For example, when obtaining the LAT abrasion index of a tread component, a rubber composition for a cap layer of a conventional tread composed of two layers, a cap layer and a base layer, is used as the reference rubber composition.

[0018] In the present invention, the tread portion of a tire is the portion of the tire that comes into contact with the road surface. The bead portion is the portion of the tire that fits onto the rim. The sidewall portion is the portion of the tire that bridges between the tread portion and the bead portion. A tire has the following portions: a tread portion, a pair of bead portions, and a pair of sidewall portions. The end portions of the tread are also called shoulder portions. The portion consisting of the bead portion and the sidewall portion is also called a side portion.

[0019] [Foundations underlying the present invention] A tire tread is usually made up of a cap layer and a base layer aligned in the radial direction. The cap layer, which comes into contact with the road surface, is made of rubber that takes into consideration grip performance and abrasion resistance. The base layer is covered by the cap layer and does not come into contact with the road surface. Low-loss rubber is used for the base layer to reduce rolling resistance.

[0020] In recent years, the level of requirements for reducing rolling resistance is high, and in order to reduce rolling resistance, it has been considered to replace part of the cap layer with an intermediate layer that has a lower loss tangent than the cap layer, but has a lower grip performance than the cap layer. However, in order to meet the required level, it is not enough to simply configure the tread with three layers using the cap layer, intermediate layer, and base layer, and various approaches are being attempted to further reduce rolling resistance.

[0021] FIG. 9 shows the contour line of the tread surface TS in a meridian cross section of a conventional tire. The contour line of the tread surface TS is formed by combining multiple arcs in the axial direction. The contour line shown in FIG. 9 includes a center arc, a middle arc, a shoulder arc, and a corner arc. The center arc located in the center has the largest radius Rc. The middle arc located next to the center arc has the next largest radius Rm. The shoulder arc located next to the middle arc has the next largest radius Rs. The corner arc located next to the shoulder arc has the smallest radius Rk. The corner arc is the arc located on the outermost side, and the contour line of the side surface is connected to this corner arc.

[0022] The radius of curvature of the contour line of the tread surface TS changes at the boundary between adjacent arcs. The boundary where the rate of change of the radius of curvature is greatest is the boundary between the shoulder arc and the corner arc (hereinafter referred to as the reference boundary point SHc).

[0023] 10, the solid line shows a schematic diagram of the state of the tread portion in contact with the road surface, and the dotted line shows the state of the tread portion before (or after) contact with the road surface. As shown in Figure 10, the shoulders of the tread are significantly deformed when the tyre comes into contact with the road surface. This causes compressive strain in the surface layer of the shoulders, indicated by the symbol CS. Compressive strain is a factor that increases rolling resistance. If the generation of compressive strain can be suppressed, it is expected that rolling resistance can be further reduced. Therefore, the inventors conducted extensive research into the mechanism by which compressive strain occurs and discovered that when the aforementioned reference boundary point SHc is included in the contact surface, the occurrence of compressive strain tends to be promoted, leading to the completion of the invention described below.

[0024] [Details of the embodiment of the present invention] Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

[0025] 1 shows a portion of a tire 2 according to one embodiment of the present invention. The tire 2 is a pneumatic tire for passenger cars.

[0026] FIG. 1 shows a portion of a cross section of a tire 2 taken 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 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 arrow RD is the radial direction of the tire 2. The direction perpendicular to the plane of FIG. 1 is the circumferential direction of the tire 2. In FIG. 1, a dashed dotted line CL extending in the radial direction represents the equatorial plane of the tire 2.

[0027] The tire 2 is mounted on a rim R. The inside of the tire 2 is filled with air, for example, and the internal pressure is adjusted. Although not described in detail, the rim R is a regular rim.

[0028] In Fig. 1, the solid line BBL extending in the axial direction is the bead base line. This bead base line is a line that defines the rim diameter of the rim R (see JATMA, etc.).

[0029] The position indicated by the symbol PC in Fig. 1 is the intersection point between the outer surface 2G of the tire 2 (specifically, the tread surface described later) and the equatorial plane. The intersection point PC is the equator of the tire 2. When a groove is located on the equatorial plane, the equator PC is determined based on a virtual outer surface (a 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.

[0030] 1, the position indicated by the symbol PW is the axial outer end (hereinafter, the outer end PW) of the tire 2. When the outer surface has decoration such as a pattern or letters, the outer end PW is identified based on a virtual outer surface obtained by assuming that there is no decoration. The axial distance from the first outer end PW to the second outer end PW obtained in the normal state is the maximum width of the tire 2. The outer end PW is also referred to as the maximum width position. The maximum width position is the position where the tire 2 shows the maximum width. The maximum width obtained in the normal state is the cross-sectional width of the tire 2 (see JATMA, etc.).

[0031] 1, the position indicated by the symbol PT is the toe of the tire 2. The toe PT is the boundary between the outer surface 2G and the inner surface 2N of the tire 2.

[0032] The 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, an inner liner 18, a pair of cushions 20, and a pair of insulations 22.

[0033] The tread 4 is located radially outward of the carcass 12. The tread 4 comes into contact with the road surface at a tread surface 24. The tread 4 has a tread surface 24 that comes into contact with the road surface. The tread surface 24 is a part of an outer surface 2G of the tire 2. Side surfaces 26 are continuous to the tread surface 24. The outer surface 2G of the tire 2 includes the tread surface 24 and a pair of side surfaces 26. The tread surface 24 includes an equator PC and each side surface 26 includes a maximum width position PW.

[0034] Grooves 28 are cut into the tread 4. This forms a tread pattern. The grooves 28 include circumferential grooves 30 that extend continuously in the circumferential direction. At least three circumferential grooves 30 are formed in the tread 4 of the tire 2. As a result, at least four land portions 32 are formed.

[0035] The tread 4 shown in Fig. 1 is formed with four circumferential grooves 30 aligned in the axial direction. Of the four circumferential grooves 30, the circumferential groove 30 located on the outermost side is a shoulder circumferential groove 30s. The circumferential groove 30 located axially inside the shoulder circumferential groove 30s is a middle circumferential groove 30m. The tread 4 is formed with two shoulder circumferential grooves 30s located on the outermost side and two middle circumferential grooves 30m located between the two shoulder circumferential grooves 30s.

[0036] In this tread 4, five land portions 32 are formed by four circumferential grooves 30. Of the five land portions 32 arranged in the axial direction, the land portion 32 located on the outermost side is the shoulder land portion 32s. The land portion 32 located on the axially inner side of the shoulder land portion 32s is the middle land portion 32m. The land portion 32 located on the axially inner side of the middle land portion 32m is the center land portion 32c. In this tread, two shoulder land portions 32s located on the outermost side, two middle land portions 32m located between the two shoulder land portions 32s, and one center land portion 32c located between the two middle land portions 32m are formed. The center land portion 32c includes the equator PC.

[0037] Each sidewall 6 is continuous with the tread 4. The sidewall 6 is located radially inward of the tread 4. The sidewall 6 is located axially outward of the carcass 12. The sidewall 6 is made of crosslinked rubber in consideration of cut resistance. The sidewall 6 constitutes a part of the side surface 26.

[0038] Each clinch 8 is located radially inside the sidewall 6. The clinch 8 contacts the rim R. The clinch 8 is made of crosslinked rubber that takes into account wear resistance.

[0039] Each bead 10 is located axially inward of the clinch 8. The beads 10 are located radially inward of the sidewall 6. When one bead 10 of a pair of beads 10 is a first bead 10, the other bead 10 is a second bead 10. The bead 10 includes a core 34 and an apex 36. The core 34 extends in the circumferential direction. Although not shown, the core 34 includes a steel wire. The apex 36 is located radially outward of the core 34. The apex 36 is made of crosslinked rubber having high rigidity.

[0040] The carcass 12 is located inside the tread 4, the pair of sidewalls 6, and the pair of clinches 8. The carcass 12 bridges between the pair of beads 10.

[0041] The carcass 12 includes at least one carcass ply 38. The carcass 12 of the tire 2 is composed of one carcass ply 38.

[0042] Although not shown, the carcass ply 38 includes a number of carcass cords arranged in parallel. These carcass cords intersect with the equatorial plane. The carcass 12 of the tire 2 has a radial structure. In the tire 2, cords made of organic fibers are used as the carcass cords. Examples of the organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0043] The carcass ply 38 includes a ply body 38a and a pair of turned-up portions 38b. The ply body 38a spans between the first bead 10 and the second bead 10. Each turned-up portion 38b is continuous with the ply body 38a and is turned up at each bead 10 from the inside toward the outside in the axial direction.

[0044] The belt 14 is located radially inward of the tread 4. The belt 14 is laminated on the carcass 12. The belt 14 is located between the carcass 12 and the tread 4. The above-mentioned equatorial plane intersects with the belt 14 at the center of the axial width of the belt 14. The axial width of the belt 14 is equal to or greater than 85% and equal to or less than 100% of the width of the tread 4.

[0045] The belt 14 includes an inner layer 40 and an outer layer 42. The inner layer 40 is located radially outward of the ply body 38a and is laminated to the ply 38a. The outer layer 42 is located radially outward of the inner layer 40 and is laminated to the inner layer 40.

[0046] 1, an end of the outer layer 42 is located axially inward of an end of the inner layer 40. The outer layer 42 is narrower than the inner layer 40. The length from the end of the outer layer 42 to the end of the inner layer 40 is 3 mm or more and 10 mm or less. The axial width of the belt 14 described above is represented by the axial width of the wider inner layer 40.

[0047] Although not shown, each of the inner layer 40 and the outer layer 42 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.

[0048] The band 16 is laminated on the belt 14 on the inside of the tread 4. An end of the band 16 is located axially outward of an end 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. The above-mentioned equatorial plane intersects with the band 16 at the center of the axial width of the band 16. Both ends of the band 16 are arranged to face each other across the equatorial plane. This band 16 is a full band. This band 16 may be a pair of edge bands arranged axially apart from each other across the equatorial plane and configured to cover end portions of the belt 14. This band 16 may be configured with a full band and a pair of edge bands.

[0049] 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 that the band cord makes with the circumferential direction is 5° or less. The band 16 has a jointless structure. A cord made of an organic fiber is used as the band cord. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0050] The inner liner 18 is positioned 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 maintains the internal pressure of the tire 2.

[0051] The cushions 20 are spaced apart from each other in the axial direction. The cushions 20 are located between the ends of the belt 14 and the band 16 and the carcass 12. The cushions 20 are made of crosslinked rubber having low rigidity. The cushions 20 are not essential elements in the tire 2. Depending on the specifications of the tire 2, the cushions 20 may not be provided.

[0052] Each insulation 22 is positioned between the carcass 12 and the inner liner 18. A first end of the insulation 22 is positioned axially inward of the end of the belt 14. A second end of the insulation 22 is positioned radially between the maximum width position PW and the bead 10.

[0053] FIG. 2 shows a portion of the tread portion of the tire 2 shown in FIG. The tread 4 of the tire 2 is composed of a plurality of layers 44 arranged in the radial direction. Each layer 44 is made of crosslinked rubber. The multiple layers 44 include a cap layer 46, an intermediate layer 48, and a base layer 50. The cap layer 46 is located on the outermost side. The base layer 50 is located on the innermost side. The intermediate layer 48 is located between the cap layer 46 and the base layer 50. The tread 4 of the tire 2 is composed of the cap layer 46 located on the outermost side, the base layer 50 located on the innermost side, and the intermediate layer 48 located between the cap layer 46 and the base layer 50. The tread 4 has a three-layer structure.

[0054] The cap layer 46 comes into contact with the road surface. An end 46e of the cap layer 46 is located axially inward of an end 48e of the intermediate layer 48. Most of the intermediate layer 48 is covered by the cap layer 46. When the cap layer 46 wears, the intermediate layer 48 comes into contact with the road surface. Contact with the road surface is taken into consideration for the intermediate layer 48. The position of the end 50e of the base layer 50 coincides with the position of the end 48e of the intermediate layer 48 in the axial direction, or the end 50e of the base layer 50 is located axially inward of the end 48e of the intermediate layer 48. The base layer 50 is entirely covered by the intermediate layer 48. The base layer 50 does not come into contact with the road surface. Contact with the road surface is not taken into consideration for the base layer 50.

[0055] In this tire 2, the loss tangent LTm of the intermediate layer 48 at 30°C is lower than the loss tangent LTc of the cap layer 46 at 30°C. The loss tangent LTb of the base layer 50 at 30°C is lower than the loss tangent LTm of the intermediate layer 48 at 30°C. The cap layer 46, the base layer 50, and the intermediate layer 48 are each made of a crosslinked rubber having a different heat buildup property. The cap layer 46 is most susceptible to heat buildup, and the base layer 50 is least susceptible to heat buildup. The intermediate layer 48 has heat buildup property between that of the cap layer 46 and that of the base layer 50.

[0056] The cap layer 46 having a high loss tangent LTc exhibits high grip. The cap layer 46 can contribute to improving wet performance. The base layer 50 having a low loss tangent LTb is less likely to generate heat. The base layer 50 can contribute to reducing rolling resistance. The intermediate layer 48 has an intermediate loss tangent LTm between the loss tangent LTc and the loss tangent LTb. When emphasis is placed on wet performance, the loss tangent LTm of the intermediate layer 48 is set to a loss tangent close to the loss tangent LTc of the cap layer 46. When emphasis is placed on rolling resistance, the loss tangent LTm of the intermediate layer 48 is set to a loss tangent close to the loss tangent LTb of the base layer 50.

[0057] As described above, the tread 4 of the tire 2 is configured with five land portions 32, including the center land portion 32c, a pair of middle land portions 32m, and a pair of shoulder land portions 32s. Each land portion 32 includes a cap layer 46, an intermediate layer 48, and a base layer 50.

[0058] 3 shows a part of the contour of the outer surface 2G of the tire 2 in a meridian cross section. The contour of the outer surface 2G is represented by a virtual outer surface obtained by assuming that there is no decoration such as grooves, patterns, letters, etc. Although not described in detail, in the present invention, the contour of the outer surface 2G is obtained by measuring the outer surface shape of the tire 2 in a normal state using, for example, a displacement sensor.

[0059] In the meridian cross section, the contour line of the tread surface 24 includes a plurality of circular arcs aligned in the axial direction. In detail, the contour line of the tread surface 24 is composed of a plurality of circular arcs aligned in the axial direction. The plurality of arcs include a center arc, a pair of middle arcs, a pair of shoulder arcs, and a pair of corner arcs. The center arc is an arc located at the axial center of the multiple arcs. The arrow indicated by the symbol Rc in FIG. 3 indicates the radius of the center arc. The center arc includes an equator PC. Although not shown, the center of the center arc is located on the equatorial plane. The center arc has the largest radius Rc among the multiple arcs that make up the contour line of the tread surface 24. Each middle arc is an arc located axially outward of the center arc. The arrow indicated by the symbol Rm in Fig. 3 indicates the radius of the middle arc. The middle arc has a radius Rm that is next to the radius Rc of the center arc. Each shoulder arc is an arc located axially outward of the middle arc. The arrows indicated with the symbol Rs in Fig. 3 indicate the radii of the shoulder arcs. The shoulder arcs have a radius Rs that is next to the radius Rm of the middle arc. Each corner arc is an arc located axially outward of the shoulder arc. The arrow indicated by the symbol Rk in FIG. 3 indicates the radius of the corner arc. The corner arc has a radius Rk that is the second largest after the radius Rs of the shoulder arc. The corner arc is the outermost arc among the multiple arcs arranged in the axial direction. The corner arc has the smallest radius Rk among the multiple arcs that make up the contour line of the tread surface 24.

[0060] The first end of the middle arc on the equator side is connected to the end of the center arc. The position indicated by the symbol CM in Figure 3 is the boundary between the center arc and the middle arc. The middle arc is in contact with the center arc at the boundary CM. The boundary CM is also the end of the center arc and the first end of the middle arc. A first end of the shoulder arc on the equator side is connected to a second end of the middle arc on the side surface side. The position indicated by the symbol MS in FIG. 2 is the boundary between the middle arc and the shoulder arc. The shoulder arc is in contact with the middle arc at the boundary MS. The boundary MS is also the second end of the middle arc and the first end of the shoulder arc. A first end of the corner arc on the equator side is connected to a second end of the shoulder arc on the side surface side. The position indicated by the symbol SH in Fig. 3 is the boundary between the shoulder arc and the corner arc. The corner arc is in contact with the shoulder arc at the boundary SH. The boundary SH is also the second end of the shoulder arc and the first end of the corner arc. The contour line of the tread surface 24 of this tire 2 is made up of seven arcs: a center arc, a pair of middle arcs, a pair of shoulder arcs, and a pair of corner arcs.

[0061] In the present invention, among the arcs having a center on the equatorial plane and including the equator PC, the arc having the maximum overlap length with the contour line of the tread surface 24 may be specified as the center arc, and the end of this arc may be specified as the boundary CM, and the radius of this arc may be used as the radius Rc of the center arc. Among the arcs having a center on a line passing through the boundary CM and the center of the center arc and including the boundary CM, the arc having the maximum overlap length with the contour line of the tread surface 24 may be specified as the middle arc, and the outer end of this arc may be specified as the boundary MS, and the radius of this arc may be used as the radius Rm of the middle arc. Among the arcs having a center on a line passing through the boundary MS and the center of the middle arc and including the boundary MS, the arc having the maximum overlap length with the contour line of the tread surface 24 may be specified as the shoulder arc, and the outer end of this arc may be specified as the boundary SH, and the radius of this arc may be used as the radius Rs of the shoulder arc. Of the arcs that have their center on a straight line passing through this boundary SH and the center of the shoulder arc, and that include the boundary SH, the arc that has the longest overlap length with the contour line of the tread surface 24 is identified as the corner arc, and the outer end of this arc is identified as the boundary HU described below, and the radius of this arc may be used as the radius Rk of the corner arc.

[0062] In this tire 2, the contour line of the side surface 26 is continuous with the second end of the corner arc. The position indicated by the symbol HU in FIG. 3 is the boundary between the corner arc and the contour line of the side surface 26. The contour line of the side surface 26 is in contact with the corner arc at the boundary HU. The boundary HU is also the second end of the corner arc and the first end of the contour line of the side surface 26. The second end of the contour line of the side surface 26 is the toe PT of the tire 2.

[0063] In Fig. 3, the straight line indicated by the symbol LSH is a first tangent to the corner arc at a first end SH of the corner arc. The straight line indicated by the symbol LHU is a second tangent to the corner arc at a second end HU of the corner arc. The position indicated by the symbol TE is the intersection point between the first tangent LSH and the second tangent LHU. In the present invention, the intersection point TE is the tread reference edge.

[0064] In FIG. 3, the length indicated by the double-headed arrow HTW is the axial distance from the equator to the tread reference edge TE. In the present invention, the axial distance HTW is the reference width of the tread 4. Twice this reference width HTW is the width of the tread 4 described above. The length indicated by the double-headed arrow HXW is the axial distance from the equator to the maximum width position PW. In the present invention, the axial distance HXW is the reference section width. Twice the reference section width HXW is the section width of the tire 2 described above. In the tire 2, the ratio (HTW / HXW) of the reference width HTW of the tread 4 to the reference section width HXW is equal to or greater than 70% and equal to or less than 80%.

[0065] 3, the length indicated by the double arrow HCM is the axial distance from the equator PC to the boundary CM, and the length indicated by the double arrow HMS is the axial distance from the equator PC to the boundary MS. In the tire 2, the ratio (HCM / HTW) of the axial distance HCM to the reference width HTW of the tread 4 is preferably 0.25 or greater and 0.35 or less. The ratio (HMS / HTW) of the axial distance HMS to the reference width HTW of the tread 4 is preferably 0.65 or greater and 0.75 or less.

[0066] The contour line of the side surface 26 includes at least one arc. The contour line of the side surface 26 includes an upper arc. The upper arc includes the maximum width position PW and extends from the maximum width position PW toward the tread reference edge TE. The upper arc is an outwardly convex arc, and its center is located on a straight line that passes through the maximum width position PW and extends in the axial direction. The position indicated by the symbol UG in FIG. 3 is the outer end of the upper arc. The arrow indicated by the symbol Ru in FIG. 3 is the radius of the upper arc.

[0067] In this tire 2, the boundary HU and the outer end UG are connected by a straight line. This straight line is tangent to the corner arc at the boundary HU and is tangent to the upper arc at the outer end UG. The position of the boundary HU and the position of the outer end UG may coincide. In this case, the upper arc is directly connected to the corner arc. The farther the outer end UG of the upper circular arc is located from the boundary HU, the more the volume of rubber in the shoulder portion can be reduced. Reducing the rubber volume contributes to reducing rolling resistance. From this perspective, it is preferable that the boundary HU and the outer end UG are connected by a straight line on the contour of the outer surface 2G.

[0068] 4 is a schematic diagram showing the contact patch shape of the tire 2. In FIG. 4, the direction indicated by the double-headed arrow ADe corresponds to the axial direction of the tire 2. The direction indicated by the double-headed arrow CDe corresponds to the circumferential direction of the tire 2.

[0069] The contact patch is obtained by applying a predetermined load to the tire 2 in a normal state using a tire contact patch shape measuring device (not shown) and bringing the tire 2 into contact with a flat surface. The contours of each land portion 32 included in the contact patch are traced to obtain the contact patch shape shown in FIG. 4. To obtain the contact patch, the tire 2 is placed so that its axial direction is parallel to the road surface. The aforementioned load is applied to the tire 2 in a direction perpendicular to the road surface. In other words, a longitudinal load is applied to the tire with the camber angle of the tire set to 0°.

[0070] The position indicated by the symbol GE in Fig. 4 is the axially outer end (also referred to as the ground contact edge) of the ground contact surface. In the present invention, the axially outer end GE of the ground contact surface of the tire 2 obtained by applying a vertical load of 80% of the normal load to the tire 2 in a normal state and bringing the tire 2 into contact with a flat road surface is the reference ground contact edge. The position on the outer surface 2G of the tire 2 corresponding to the reference ground contact edge GE is the reference ground contact position. In Figs. 2 and 3, the position indicated by the symbol PG is the reference ground contact position. The reference ground contact position PG is included in the shoulder land portion 32s.

[0071] 3, the length indicated by the double-headed arrow HGW is the axial distance from the equator PC to the reference ground contact position PG. In the tire 2, the ratio of the axial distance HGW to the reference width HTW of the tread 4 is set in the range of 0.88 to 0.92.

[0072] In the tire 2, a plurality of arcs constituting the contour line of the tread surface 24 have different radii. The radius of curvature of the contour line of the tread surface 24 changes at the boundary between adjacent arcs. As described above, the corner arc is the arc located axially outermost among the multiple arcs constituting the contour line of the tread surface 24, and has the smallest radius Rk. The contour line of the side surface 26 is continuous with this corner arc. The radius of curvature of the contour line of the tread surface 24 shows the greatest rate of change at the boundary SH between the shoulder arc and the corner arc. In the present invention, the boundary SH between the shoulder arc and the corner arc is the reference boundary point. The length indicated by the double arrow L in FIG. 3 is the axial distance from the equator PC to the reference boundary point SH.

[0073] The contour line of the tread surface is closely related to the contact state of the tread with the road surface. Therefore, the inventors of the present invention have conducted extensive research into the relationship between the contour line of the tread surface and the occurrence of compressive strain. As a result, the inventors have found that the position of the reference boundary point relative to the reference contact position is involved in the occurrence of compressive strain, and more specifically, that when the reference boundary point is located axially inside the reference contact position, the occurrence of compressive strain in the surface layer of the shoulder portion tends to be promoted, which has led to the completion of the present invention.

[0074] Fig. 5 shows the positional relationship between the reference boundary point SH and the reference ground contact position PG. In Fig. 5, the solid line is the contour line of the tread surface 24, and the dotted line is the contour line of the conventional tread surface TS. The position indicated by the symbol SHc on the contour line of the conventional tread surface TS is the reference boundary point on the conventional tread surface TS. The position indicated by the symbol PGc is the reference ground contact position on the conventional tread surface TS.

[0075] As shown in Figure 5, in the conventional tread surface TS, the reference boundary point SHc is located axially inside the reference contact position PGc. In contrast, in the tread surface 24 of the tire 2, the reference boundary point SH is located axially outside the reference contact position PG. In the tread surface 24, the reference boundary point SH, where the curvature change of the contour line is large, is not included in the contact surface. In the tire 2, the occurrence of compressive strain in the surface layer of the shoulder portion, which is observed in conventional tires, is suppressed. Positioning the reference boundary point SH axially outside the reference contact position PG can contribute to reducing the rolling resistance of the tire 2.

[0076] In this tire 2, the thickness of each layer constituting the tread 4 is expressed as a length along a normal line to the inner surface 2N of this tire 2 in a meridian cross section of this tire 2. This normal line is also called a thickness reference line. The ratio (TC / TA) of the thickness of the cap layer 46 (hereinafter, cap layer thickness TC) to the thickness of the tread 4 (hereinafter, tread thickness TA) is the thickness ratio RC of the cap layer 46. If the cap layer 46 is not included in the tread 4 at the thickness measurement position, the thickness ratio RC is 0 (zero)%. The ratio (TM / TA) of the thickness of the intermediate layer 48 (hereinafter, intermediate layer thickness TM) to the thickness of the tread 4 (hereinafter, tread thickness TA) is the thickness ratio RM of the intermediate layer 50. When the tread 4 at the thickness measurement position is composed of only the intermediate layer 48, the thickness ratio RM is 100%.

[0077] Fig. 6 shows a part of the tread portion shown in Fig. 2. Fig. 6 shows a cross section of the middle land portion 32m. The middle land portion 32m is a land portion 32 (hereinafter also referred to as a main land portion 32M) located between two circumferential grooves 30. The thickness of each layer in the main land portion 32M will be explained using the middle land portion 32m as an example.

[0078] 6, straight lines Lm1, Lm2, and Lm3 are thickness reference lines in the main land portion 32M. Symbols Pm1, Pm2, and Pm3 are positions that divide a line segment connecting one edge and the other edge of the main land portion 32M into four equal parts. The thickness reference line Lm1 passes through position Pm1, the thickness reference line Lm2 passes through position Pm2, and the thickness reference line Lm3 passes through position Pm3.

[0079] The length indicated by the double arrow TAm1 is the tread thickness at the position Pm1. The length indicated by the double arrow TCm1 is the cap layer thickness at the position Pm1. The length indicated by the double arrow TMm1 is the intermediate layer thickness at the position Pm1. The ratio (TCm1 / TAm1) of the cap layer thickness TCm1 to the tread thickness TAm1 is the thickness ratio RCm1 of the cap layer 46 at the position Pm1. The ratio (TMm1 / TAm1) of the intermediate layer thickness TMm1 to the tread thickness TAm1 is the thickness ratio RMm1 of the intermediate layer 48 at the position Pm1.

[0080] The length indicated by the double arrow TAm2 is the tread thickness at the position Pm2. The length indicated by the double arrow TCm2 is the cap layer thickness at the position Pm2. The length indicated by the double arrow TMm2 is the intermediate layer thickness at the position Pm2. The ratio (TCm2 / TAm2) of the cap layer thickness TCm2 to the tread thickness TAm2 is the thickness ratio RCm2 of the cap layer 46 at the position Pm2. The ratio (TMm2 / TAm2) of the intermediate layer thickness TMm2 to the tread thickness TAm2 is the thickness ratio RMm2 of the intermediate layer 48 at the position Pm2.

[0081] The length indicated by the double arrow TAm3 is the tread thickness at the position Pm3. The length indicated by the double arrow TCm3 is the cap layer thickness at the position Pm3. The length indicated by the double arrow TMm3 is the intermediate layer thickness at the position Pm3. The ratio (TCm3 / TAm3) of the cap layer thickness TCm3 to the tread thickness TAm3 is the thickness ratio RCm3 of the cap layer 46 at the position Pm3. The ratio (TMm3 / TAm3) of the intermediate layer thickness TMm3 to the tread thickness TAm3 is the thickness ratio RMm3 of the intermediate layer 48 at the position Pm3.

[0082] In the tire 2, the ratio RCm of the thickness of the cap layer 46 in the main land portion 32M to the thickness of the tread 4 is represented by the average value of the cap layer thickness ratio RCm1, the cap layer thickness ratio RCm2, and the cap layer thickness ratio RCm3. This ratio RCm is the thickness ratio RCm of the cap layer 46 in the main land portion 32M.

[0083] 1, the cap layer 46 has a uniform thickness in the main land portion 32M. In detail, the absolute value of the difference (RCm-RCm1) between the cap layer thickness ratio RCm in the main land portion 32M and the cap layer thickness ratio RCm1 at the position Pm1 is 3% or less, the absolute value of the difference (RCm-RCm2) between the thickness ratio RCm and the thickness ratio RCm2 is 3% or less, and the absolute value of the difference (RCm-RCm3) between the thickness ratio RCm and the thickness ratio RCm3 is 3% or less. The cap layer thickness ratio RCm in the main land portion 32M is not less than 20% and not more than 30%.

[0084] In the tire 2, the average value of the intermediate layer thickness ratio RMm1, the intermediate layer thickness ratio RMm2, and the intermediate layer thickness ratio RCm3 represents the ratio RMm of the thickness of the intermediate layer 48 in the main land portion 32M to the thickness of the tread 4. This ratio RMm is the thickness ratio of the intermediate layer 48 in the main land portion 36M.

[0085] 1, the intermediate layer 48 has a uniform thickness in the main land portion 32M. In detail, the absolute value of the difference (RMm-RMm1) between the intermediate layer thickness ratio RMm in the middle land portion 32m and the intermediate layer thickness ratio RMm1 at the position Pm1 is 3% or less, the absolute value of the difference (RMm-RMm2) between the thickness ratio RMm and the thickness ratio RMm2 is 3% or less, and the absolute value of the difference (RMm-RMm3) between the thickness ratio RMm and the thickness ratio RMm3 is 3% or less. The intermediate layer thickness ratio RMm in the middle land area of ​​32 m is between 40% and 50%.

[0086] The center land portion 32c, like the middle land portion 32m, is a main land portion 32. Although not described in detail, the thickness of each layer in the center land portion 32c is expressed in the same manner as in the middle land portion 32m. The cap layer 46 and the intermediate layer 48 in the center land portion 32c each have a uniform thickness. In the tire 2, the land portion 32 located between the two circumferential grooves 30, that is, the cap layer 46 and the intermediate layer 48 in the main land portion 32, each have a uniform thickness. The thickness ratio RC of the cap layer 46 in the main land portion 32 is 20% or more and 30% or less. The thickness ratio RM of the intermediate layer 48 in the main land portion 32 is 40% or more and 50% or less. In contrast, the thickness of the cap layer 46 (or the thickness of the intermediate layer 48) in the shoulder land portion 32s is not uniform in the axial direction. The thickness of the cap layer 46 (or the thickness of the intermediate layer 48) varies in the axial direction.

[0087] As described above, the shoulder land portion 32s of the tire 2 includes the reference contact position PG. Of the shoulder land portion 32s, the axially outer portion of the reference contact position PG comes into contact with the road surface less frequently than the axially inner portion of the shoulder land portion 32s comes into contact with the road surface. As described above, the reference boundary point SH is located axially outward from the reference boundary position PG. The reference boundary point SH is included in the outer portion of the shoulder land portion 32s that comes into contact with the road surface less frequently. In the tire 2, the cap layer thickness TC and the intermediate layer thickness TM in the shoulder land portion 32s are controlled in consideration of these points.

[0088] 7 shows a cross section of the shoulder land portion 32s. The cross section of the shoulder land portion 32s shown in FIG. 7 is a part of the cross section of the tread portion shown in FIG.

[0089] 7, a straight line LG is a ground contact reference line. The ground contact reference line LG is a normal line to the inner surface 2N of the tire 2 that passes through the reference ground contact position PG. The part of the shoulder land portion 32s on the equatorial plane side from the ground contact reference line LG is the axially inner part. The part of the shoulder land portion 32s on the sidewall side from the ground contact reference line LG is the axially outer part. The ground contact reference line LG divides the shoulder land portion 32c into the axially inner part and the axially outer part.

[0090] 7, straight lines Lu1, Lu2, and Lu3 are thickness reference lines at the axially inner portion of the shoulder land portion 32s. Symbols Pu1, Pu2, and Pu3 are positions that divide a line segment connecting the equatorial edge of the shoulder land portion 32s and the reference ground position PG into four equal parts. The thickness reference line Lu1 passes through position Pu1, the thickness reference line Lu2 passes through position Pu2, and the thickness reference line Lu3 passes through position Pu3.

[0091] The length indicated by the double arrow TAu1 is the tread thickness at the position Pu1. The length indicated by the double arrow TCu1 is the cap layer thickness at the position Pu1. The length indicated by the double arrow TMu1 is the intermediate layer thickness at the position Pu1. The ratio (TCu1 / TAu1) of the cap layer thickness TCu1 to the tread thickness TAu1 is the thickness ratio RCu1 of the cap layer 46 at the position Pu1. The ratio (TMu1 / TAu1) of the intermediate layer thickness TMu1 to the tread thickness TAu1 is the thickness ratio RMu1 of the intermediate layer 48 at the position Pu1.

[0092] The length indicated by the double arrow TAu2 is the tread thickness at the position Pu2. The length indicated by the double arrow TCu2 is the cap layer thickness at the position Pu2. The length indicated by the double arrow TMu2 is the intermediate layer thickness at the position Pu2. The ratio (TCu2 / TAu2) of the cap layer thickness TCu2 to the tread thickness TAu2 is the thickness ratio RCu2 of the cap layer 46 at the position Pu2. The ratio (TMu2 / TAu2) of the intermediate layer thickness TMu2 to the tread thickness TAu2 is the thickness ratio RMu2 of the intermediate layer 48 at the position Pu2.

[0093] The length indicated by the double arrow TAu3 is the tread thickness at the position Pu3. The length indicated by the double arrow TCu3 is the cap layer thickness at the position Pu3. The length indicated by the double arrow TMu3 is the intermediate layer thickness at the position Pu3. The ratio (TCu3 / TAu3) of the cap layer thickness TCu3 to the tread thickness TAu3 is the thickness ratio RCu of the cap layer 46 at the position Pu3. The ratio (TMu3 / TAu3) of the intermediate layer thickness TMu3 to the tread thickness TAu3 is the thickness ratio RMu3 of the intermediate layer 48 at the position Pu3.

[0094] In the tire 2, the ratio RCu of the thickness of the cap layer 46 in the axially inner portion of the shoulder land portion 32s to the thickness of the tread 4 is represented by the average value of the cap layer thickness ratio RCu1, the cap layer thickness ratio RCu2, and the cap layer thickness ratio RCu3. This ratio RCu is the inner thickness ratio RCu of the cap layer 46 in the axially inner portion of the shoulder land portion 32s. The ratio RMu of the thickness of the intermediate layer 48 in the axially inner portion of the shoulder land portion 32s to the thickness of the tread 4 is represented by the average value of the intermediate layer thickness ratio RMu1, the intermediate layer thickness ratio RMu2, and the intermediate layer thickness ratio RMu3. This ratio RMu is the inner thickness ratio RMu of the intermediate layer 48 in the axially inner portion of the shoulder land portion 32s.

[0095] 7, straight lines Ls1, Ls2, and Ls3 are thickness reference lines in the axially outer portion of the shoulder land portion 32s. Symbols Ps1, Ps2, and Ps3 are positions that divide into four equal parts a line segment connecting the reference ground contact position PG and the end 4e of the tread 4. The thickness reference line Ls1 passes through the position Ps1, the thickness reference line Ls2 passes through the position Ps2, and the thickness reference line Ls3 passes through the position Ps3.

[0096] The length indicated by the double-headed arrow TAs1 is the tread thickness at the position Ps1. In the shoulder land portion 32s shown in FIG. 7, the tread 4 at the position Ps1 does not include the cap layer 46. However, if the tread 4 at the position Ps1 includes the cap layer 46, the cap layer thickness at the position Ps1 is represented by a thickness TCs1. The length indicated by the double-headed arrow TMs1 is the intermediate layer thickness at the position Ps1. The ratio (TCs1 / TAs1) of the cap layer thickness TCs1 to the tread thickness TAs1 is the thickness ratio RCs1 of the cap layer 46 at the position Ps1. The ratio (TMs1 / TAs1) of the intermediate layer thickness TMs1 to the tread thickness TAs1 is the thickness ratio RMs1 of the intermediate layer 48 at the position Ps1. As described above, in the shoulder land portion 32s shown in Fig. 7, the tread 4 at the position Ps1 does not include the cap layer 46. Therefore, in the shoulder land portion 32s shown in Fig. 7, the cap layer thickness ratio RCs1 at the position Ps1 is 0 (zero)%.

[0097] The length indicated by the double-headed arrow TAs2 is the tread thickness at the position Ps2. In the shoulder land portion 32s shown in FIG. 7, the tread 4 at the position Ps2 does not include the cap layer 46. However, if the tread 4 at the position Ps2 includes the cap layer 46, the cap layer thickness at the position Ps2 is represented by the thickness TCs2. The length indicated by the double-headed arrow TMs2 is the intermediate layer thickness at the position Ps2. The ratio (TCs2 / TAs2) of the cap layer thickness TCs2 to the tread thickness TAs2 is the thickness ratio RCs2 of the cap layer 46 at the position Ps2. The ratio (TMs2 / TAs2) of the intermediate layer thickness TMs2 to the tread thickness TAs2 is the thickness ratio RMs2 of the intermediate layer 48 at the position Ps2. As described above, in the shoulder land portion 32s shown in Fig. 7, the tread 4 at the position Ps2 does not include the cap layer 46. Therefore, in the shoulder land portion 32s shown in Fig. 7, the cap layer thickness ratio RCs2 at the position Ps2 is 0 (zero)%.

[0098] The length indicated by the double-headed arrow TAs3 is the tread thickness at the position Ps3. In the shoulder land portion 32s shown in FIG. 7, the tread 4 at the position Ps3 does not include the cap layer 46. However, if the tread 4 at the position Ps3 includes the cap layer 46, the cap layer thickness at the position Ps3 is represented by a thickness TCs3. The length indicated by the double-headed arrow TMs3 is the intermediate layer thickness at the position Ps3. The ratio (TCs3 / TAs3) of the cap layer thickness TCs3 to the tread thickness TAs3 is the thickness ratio RCs3 of the cap layer 46 at the position Ps3. The ratio (TMs3 / TAs3) of the intermediate layer thickness TMs3 to the tread thickness TAs3 is the thickness ratio RMs3 of the intermediate layer 48 at the position Ps3. As described above, in the shoulder land portion 32s shown in Fig. 7, the tread 4 at the position Ps3 does not include the cap layer 46. Therefore, in the shoulder land portion 32s shown in Fig. 7, the cap layer thickness ratio RCs3 at the position Ps3 is 0 (zero)%.

[0099] In the tire 2, the ratio RCs of the thickness of the cap layer 46 in the axially outer portion of the shoulder land portion 32s to the thickness of the tread 4 is represented by the average value of the cap layer thickness ratio RCs1, the cap layer thickness ratio RCs2, and the cap layer thickness ratio RCs3. This ratio RCs is the outer thickness ratio RCs of the cap layer 46 in the axially outer portion of the shoulder land portion 32s. The ratio RMs of the thickness of the intermediate layer 48 in the axially outer portion of the shoulder land portion 32s to the thickness of the tread 4 is represented by the average value of the intermediate layer thickness ratio RMs1, the intermediate layer thickness ratio RMs2, and the intermediate layer thickness ratio RMs3. This ratio RMs is the outer thickness ratio RMs of the intermediate layer 48 in the axially outer portion of the shoulder land portion 32s. As described above, in the shoulder land portion 32s shown in Fig. 7, the cap layer thickness ratio RCs1, the cap layer thickness ratio RCs2, and the cap layer thickness ratio RCs3 are 0%. The outer thickness ratio RCs of the cap layer 46 in the axially outer portion of the shoulder land portion 32s is 0%.

[0100] In the shoulder land portion 32s of the tire 2, the outer thickness ratio RCs of the cap layer 46 is smaller than the inner thickness ratio RCu of the cap layer 46. In contrast, the outer thickness ratio RMs of the intermediate layer 48 is larger than the inner thickness ratio RMu of the intermediate layer 48. In the axially outer portion of the reference ground position PG, the thickness ratio of the cap layer 46 is smaller and the thickness ratio of the intermediate layer 48 is larger than in the axially inner portion thereof.

[0101] In the tire 2, the intermediate layer 48 included in the shoulder land portion 32s can effectively contribute to reducing rolling resistance. By locating the reference boundary point SH axially outward of the reference contact position PG, the occurrence of compressive strain in the surface layer of the shoulder portion is suppressed, so that the intermediate layer 48 included in the shoulder land portion 32s can more effectively contribute to reducing rolling resistance. In the tread surface 24, the axially outer portion of the reference contact position PG does not frequently come into contact with the road surface, so even if the shoulder land portion 32s is configured so that the outer thickness ratio RCs of the cap layer 46 in the axially outer portion of the shoulder land portion 32s is smaller than the inner thickness ratio RCu of the cap layer 46 in the axially inner portion, the impact on the grip performance on wet road surfaces (wet grip performance) is small. In this tire 2, the deterioration of wet grip performance is suppressed. Even if the axially outer portion of the reference contact position PG comes into contact with the road surface, the intermediate layer 48 can contribute to exhibiting grip performance. The tire 2 can achieve a reduction in rolling resistance without deteriorating the wet grip performance.

[0102] As shown in Fig. 2, the cross-sectional shape of the cap layer 46 in the shoulder land portion 32s tapers outward in the axial direction. This cross-sectional shape of the cap layer 46 may be adjusted so that the end 46e of the cap layer 46 has a thickness as shown in Fig. 8. In this case, the effect of the cap layer 46 is sustained even if the tread 4 wears. This tire 2 can suppress a decrease in grip performance on wet roads due to wear while reducing rolling resistance. As shown in FIG. 9, the end 50e of the base layer 50 may be disposed axially inside the end 14e of the belt 14. In this case, exposure of the base layer 50 at the end of the tread 4 can be effectively suppressed. Damage caused by exposure of the base layer 50 is prevented. By disposing the end 50e of the base layer 50 axially inside the end 14e of the belt 14, the volume of the base layer 50 is reduced. However, since disposing the reference boundary point SH axially outside the reference ground contact position PG suppresses the occurrence of compressive strain in the surface layer of the shoulder portion, the tire 2 can reduce the rolling resistance even if the volume of the base layer 50 is reduced. The tire 2 can achieve reduced rolling resistance while improving durability and without deteriorating grip performance on wet roads.

[0103] As described above, the outer thickness ratio RCs of the cap layer 46 at the axially outer portion of the shoulder land portion 32s is smaller than the inner thickness ratio RCu of the cap layer 46 at the axially inner portion thereof. Specifically, the ratio (RCs / RCu) of the outer thickness ratio RCs of the cap layer 46 to the inner thickness ratio RCu of the cap layer 46 is preferably 0.9 or less. This allows the tire 2 to effectively reduce the rolling resistance. It is particularly preferable that the ratio (RCs / RCu) is 0 (zero).

[0104] As described above, the outer thickness ratio RMs of the intermediate layer 48 in the axially outer portion of the shoulder land portion 32s is greater than the inner thickness ratio RMu of the intermediate layer 48 in the axially inner portion thereof. Specifically, the ratio (RMs / RMu) of the outer thickness ratio RMs of the intermediate layer 48 to the inner thickness ratio RMu of the intermediate layer 48 is preferably 1.1 or greater and 2.0 or less. By setting the ratio (RMs / RMu) to be equal to or greater than 1.1, the mid layer 48 can effectively contribute to reducing rolling resistance. By setting the ratio (RMs / RMu) to 2.0 or less, the cap layer 46 can contribute to exhibiting grip performance on wet road surfaces (hereinafter, wet grip performance).

[0105] In the tire 2, the inner thickness ratio RCu of the cap layer 46 in the axially inner portion of the shoulder land portion 32s is preferably 20% or more and 30% or less. By setting the inner thickness ratio RCu of the cap layer 46 to 20% or more, the tire 2 can maintain good wet grip performance. By setting the inner thickness ratio RCu of the cap layer 46 to 30% or less, the tire 2 can effectively reduce the rolling resistance.

[0106] In the tire 2, the inner thickness ratio RMa of the intermediate layer 48 in the axially inner portion of the shoulder land portion 32s is preferably 40% or greater and 50% or less. By setting the inner thickness ratio RMa of the intermediate layer 48 to 50% or less, the tire 2 can maintain good wet grip performance. By setting the inner thickness ratio RMa of the intermediate layer 48 to 40% or more, the tire 2 can effectively reduce the rolling resistance.

[0107] 2, the length indicated by the double arrow HCW is the axial distance from the equator PC to the end 46e of the cap layer 46. The length indicated by the double arrow HBW is the axial distance from the equator PC to the end 50e of the base layer 50. The length indicated by the double arrow HVW is the axial distance from the equator PC to the end 14e of the belt 14. Twice this width HVW is the axial width of the belt 14 described above.

[0108] In the tire 2, the ratio (HCW / L) of the axial distance HCW from the equator PC to the end 46e of the cap layer 46 to the axial distance L from the equator PC to the reference boundary point SH is preferably 0.9 or greater and 1.0 or less. By setting the ratio (HCW / L) to be equal to or greater than 0.9, the cap layer 46 can effectively contribute to improving the wet grip performance. From this viewpoint, the ratio (HCW / L) is more preferably equal to or greater than 0.93. By setting the ratio (HCW / L) to 1.0 or less, the intermediate layer 48 has sufficient volume. This intermediate layer 48 can effectively contribute to reducing rolling resistance. From this viewpoint, the ratio (HCW / L) is more preferably 0.97 or less.

[0109] In the tire 2, the ratio (HBW / HVW) of the axial distance HBW from the equator PC to the end 50e of the base layer 50 to the axial distance HVW from the equator PC to the end 14e of the belt 14 is preferably 0.8 or greater and 1.2 or less. Setting the ratio (HBW / HVW) to be equal to or greater than 0.8 allows the base layer 50 to contribute to reducing rolling resistance. From this viewpoint, it is more preferable that the ratio (HBW / HVW) be equal to or greater than 0.9. By setting the ratio (HBW / HVW) to 1.2 or less, exposure of the base layer 50 is effectively suppressed. The tire 2 can reduce rolling resistance without deteriorating grip performance on wet road surfaces while improving durability. From this viewpoint, it is more preferable that the ratio (HBW / HVW) is 1.1 or less.

[0110] As described above, in the tire 2, the loss tangent Ltm of the intermediate layer 48 at 30° C. is lower than the loss tangent LTc of the cap layer 46 at 30° C. Specifically, the ratio (LTm / LTc) of the loss tangent LTm of the intermediate layer 48 at 30° C. to the loss tangent LTc of the cap layer 46 at 30° C. is preferably 40% or more and 90% or less.

[0111] By setting the ratio (LTm / LTc) to 40% or greater, the intermediate layer 48 can ensure the necessary rigidity and effectively contribute to improving the wet performance. From this viewpoint, the ratio (LTm / LTc) is more preferably 50% or greater, and further preferably 60% or greater.

[0112] Setting the ratio (LTm / LTc) to 90% or less allows the mid layer 48 to effectively contribute to reducing rolling resistance. From this viewpoint, the ratio (LTm / LTc) is more preferably 80% or less, and further preferably 70% or less.

[0113] The loss tangent LTc of the cap layer 46 at 30°C is preferably 0.15 or more. This is because the cap layer 46 can contribute to improving wet performance. From this viewpoint, the loss tangent LTc is more preferably 0.16 or more, and even more preferably 0.17 or more. The cap layer 46 contacts the road surface. From the viewpoint of improving wet performance, the higher the loss tangent LTc, the better. However, a high loss tangent LTc leads to heat generation. There is a concern that the heated cap layer 46 will increase the temperature of the intermediate layer 48 more than expected. From the viewpoint of keeping the temperature state of the entire tread 4 stable and maintaining low rolling resistance, the loss tangent LTc of the cap layer 46 at 30°C is preferably 0.30 or less, more preferably 0.28 or less, and even more preferably 0.27 or less.

[0114] From the standpoint of enabling the cap layer 46 to effectively contribute to improving wet grip performance, the loss tangent LTcw of the cap layer 46 at 0° C. is preferably 0.80 or greater.

[0115] In this tire 2, from the viewpoint of the intermediate layer 48 effectively contributing to reducing rolling resistance, the loss tangent Ltm of the intermediate layer 48 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 of the intermediate layer 48 being able to ensure necessary rigidity and effectively contributing to improving wet performance, the loss tangent Ltm of the intermediate layer 48 at 30° C. is preferably 0.10 or more, and more preferably 0.11 or more.

[0116] As described above, in the tire 2, the loss tangent LTb of the base layer 50 at 30° C. is lower than the loss tangent LTm of the intermediate layer 48 at 30° C. Specifically, the loss tangent LTb of the base layer 50 at 30° C. is preferably 0.10 or less. This is because the base layer 50 effectively contributes to reducing rolling resistance. From this viewpoint, the loss tangent LTb is more preferably 0.09 or less. The smaller the loss tangent LTb of the base layer 50, the more preferable it is, and therefore no preferred lower limit is set.

[0117] In this tire 2, the cap layer 46 and the intermediate layer 48 coexist in each land portion 32. If there is a discrepancy between the wear resistance of the cap layer 46 and the wear resistance of the intermediate layer 48, there is a concern that the wear amounts of the two will differ. In this case, a step will be generated near the boundary between the cap layer 46 and the intermediate layer 48, which may impair the appearance of the tire 2. From the viewpoint of maintaining a good appearance, it is preferable that the LAT wear index LATc of the cap layer 46 and the LAT wear index LATm of the intermediate layer 48 are approximately the same. Specifically, the difference (LATc-LATm) between the LAT wear index LATc of the cap layer 46 and the LAT wear index LATm of the intermediate layer 48 is preferably -10 or more and 10 or less. It is more preferable that this difference (LATc-LATm) is -5 or more and 5 or less. It is even more preferable that this difference (LATc-LATm) is 0.

[0118] From the viewpoint of exhibiting good abrasion resistance, the LAT abrasion index LATc of the cap layer 46 is preferably equal to or greater than 130. From the same viewpoint, the LAT abrasion index LATm of the intermediate layer 48 is preferably equal to or greater than 130.

[0119] As described above, in the tire 2, the reference boundary point SH is located axially outward from the reference ground contact position PG. However, if the reference boundary point SH is located axially outward from the reference ground contact position PG, there is a concern that the thickness of the tread 4 in the shoulder portion will increase. Since an increase in the thickness of the tread 4 increases the rolling resistance, in this case, the effect of reducing the rolling resistance brought about by suppressing the occurrence of compressive strain is canceled out. Therefore, the reference boundary point SH relative to the reference ground contact position PG is preferably precisely controlled in the tire 2. Specifically, the ratio (L / HTW) of the axial distance L from the equator PC to the reference boundary point SH to the axial distance HTW from the equator PC to the tread reference end TE is preferably 0.94 or more and 0.99 or less.

[0120] By setting the ratio (L / HTW) to 0.99 or less, the reference boundary point SH is positioned without being too far away from the reference ground contact position PG. Since the distance between the reference boundary SH and the reference ground contact position PG is appropriately maintained, the tread 4 in the shoulder portion is configured with an appropriate thickness. This tire 2 can suppress an increase in rolling resistance due to an increase in thickness. In this tire 2, the effect of reducing rolling resistance brought about by suppressing the occurrence of compression strain is fully exhibited. From this viewpoint, it is more preferable that the ratio (L / HTW) is 0.97 or less. By setting the ratio (L / HTW) to 0.94 or more, the reference boundary point SH is located axially outward of the reference ground contact position PG, which can effectively contribute to suppressing the occurrence of compressive strain. In the tire 2, rolling resistance caused by compressive strain is reduced. From this viewpoint, it is more preferable that the ratio (L / HTW) is 0.95 or more.

[0121] 2, the end 48e of the intermediate layer 48 is located axially outward of the reference boundary point SH. From the viewpoint of allowing the intermediate layer 48 to effectively contribute to reducing rolling resistance without reducing grip performance on wet road surfaces, it is more preferable that the end 48e of the intermediate layer 48 is located axially outward of the reference boundary point SH, and that the ratio (L / HTW) of the axial distance L from the equator PC to the reference boundary point SH to the axial distance HTW from the equator PC to the tread reference end TE is preferably 0.94 or more and 0.99 or less.

[0122] In FIG. 3, the length indicated by the double-headed arrow t is the radial distance from the equator PC to the reference ground position PG. In the tire 2, a ratio (t / HTW) of a radial distance t from the equator PC to the reference ground contact position PG to an axial distance HTW from the equator PC to the tread reference edge TE is preferably 0.06 or greater and 0.15 or less. By setting the ratio (t / HTW) to 0.06 or more, the tread surface 24 does not become too flat, and the tread 4 in the shoulder portion of the tire 2 can be configured with an appropriate thickness. Since a local increase in ground pressure is suppressed, the occurrence of uneven wear is suppressed. The tire 2 maintains good uneven wear resistance. From this viewpoint, it is more preferable that the ratio (t / HTW) is 0.10 or more. By setting the ratio (t / HTW) to be equal to or less than 0.15, the occurrence of compressive strain is effectively suppressed. The tire 2 can achieve a further reduction in rolling resistance. From this viewpoint, the ratio (t / HTW) is more preferably equal to or less than 0.12.

[0123] From the standpoint of reducing rolling resistance without degrading grip performance on wet roads, the ratio (L / HTW) of the axial distance L from the equator PC to the reference boundary point SH to the axial distance HTW from the equator PC to the tread reference end TE is preferably 0.94 or more and 0.98 or less, and it is more preferable that the ratio (t / HTW) of the radial distance t from the equator PC to the reference ground contact position PG to the axial distance HTW from the equator PC to the tread reference end TE is 0.06 or more and 0.15 or less.

[0124] In the tire 2, a ratio (Rm / Rs) of the radius Rm of the middle circular arc to the radius Rs of the shoulder circular arc is preferably equal to or greater than 2.1 and equal to or less than 2.7. By setting the ratio (Rm / Rs) to be equal to or greater than 2.1, the occurrence of compressive strain is effectively suppressed. The tire 2 can achieve a further reduction in rolling resistance. From this viewpoint, the ratio (Rm / Rs) is more preferably equal to or greater than 2.3. By setting the ratio (Rm / Rs) to 2.7 or less, slippage of the tread surface 24 on the road surface is suppressed, and the tread 4 in the shoulder portion is configured to have an appropriate thickness. In this tire 2, good resistance to uneven wear is maintained. From this viewpoint, it is more preferable that the ratio (Rm / Rs) is 2.5 or less.

[0125] In the tire 2, a ratio (Rc / Rm) of the radius Rc of the center arc to the radius Rm of the middle arc is preferably equal to or greater than 4.0 and equal to or less than 5.5. By setting the ratio (Rc / Rm) to be equal to or greater than 4.0, the occurrence of compressive strain is effectively suppressed. The tire 2 can achieve a further reduction in rolling resistance. From this viewpoint, the ratio (Rc / Rm) is more preferably equal to or greater than 4.2. By setting the ratio (Rc / Rm) to 5.5 or less, slippage of the tread surface 24 on the road surface is suppressed, and the tread 4 in the shoulder portion is configured to have an appropriate thickness. In this tire 2, good resistance to uneven wear is maintained. From this viewpoint, it is more preferable that the ratio (Rm / Rs) is 5.3 or less.

[0126] In the tire 2, the ratio (Rs / Rk) of the shoulder arc radius Rs to the corner arc radius Rk is preferably 10 or greater and 20 or less. The occurrence of compressive strain is effectively suppressed by setting the ratio (Rs / Rk) to be equal to or greater than 10. The rolling resistance of the tire 2 can be further reduced. From this viewpoint, it is more preferable that the ratio (Rs / Rk) be equal to or greater than 13. By setting the ratio (Rs / Rk) to 20 or less, slippage of the tread surface 24 on the road surface is suppressed, and the tread 4 in the shoulder portion is configured to have an appropriate thickness. In this tire 2, good resistance to uneven wear is maintained. From this viewpoint, it is more preferable that the ratio (Rs / Rk) is 17 or less.

[0127] 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 without deteriorating grip performance on wet road surfaces. EXAMPLES

[0128] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0129] [Example 1] A pneumatic tire for a passenger car (tire size: 205 / 55R19) having the basic structure shown in FIG. 1 was obtained. By adjusting the tread surface profile, the ratio (L / HTW), ratio (t / HTW) and ratio (Rm / Rs) were set as shown in Table 1 below. The ratio (HGW / HTW) of the axial distance HGW from the equator to the reference ground contact position PG to the reference tread width HTW was 0.88. The reference boundary point SH was located axially outboard of the reference ground contact position PG. The loss tangent LTcw of the cap layer at 0° C. was 0.80. The LAT index LATc of the cap layer was 130. In the shoulder land area, the ratio (RMs / RMu) of the outer thickness ratio RMs of the intermediate layer to the inner thickness ratio RMu of the intermediate layer was 1.2. The ratio (RCs / RCu) of the outer thickness ratio RCs of the cap layer to the inner thickness ratio RCu of the cap layer was 0 (zero).

[0130] [Comparative Example 1] A tire of Comparative Example 1 was obtained in the same manner as in Example 1, except that the tread structure was changed to the structure shown in FIG. 10 and the ratio (RMs / RMu) and ratio (RCs / RCu) were as shown in Table 1 below.

[0131] [Wet grip] A new prototype tire was mounted on a rim (size = 16 x 7J) and air was filled to adjust the tire's internal pressure to 250 kPa. The tire was mounted on a test vehicle (passenger car). The test vehicle was run on a test course with a wet road surface (water film thickness = 1.4 mm). The test vehicle was braked while running at a speed of 100 km / h, and the running distance (braking distance) from braking to stopping was measured. The results are shown in Table 1 below as an index, with Comparative Example 1 set to 100. The higher the value, the shorter the braking distance and the better the tire's wet performance.

[0132] [Rolling resistance (RRC)] Using a rolling resistance tester, the rolling resistance coefficient (RRC) was measured when the prototype tire ran on a drum at a speed of 80 km / h under the following conditions. The results are shown in Table 1 below as an index, with Comparative Example 1 being set at 100. The higher the value, the lower the rolling resistance of the tire. Rim: 16×6.5J Internal pressure: 210kPa Vertical load: 4.82kN

[0133] [Resistant to uneven wear] The prototype tire was mounted on a rim (size = 16 x 7.0J) and filled with air to adjust the internal pressure to 250 kPa. This tire was mounted on a wear energy measuring device. The camber angle was set to 0° and the slip angle to 0°, and the wear energy of the tire was measured. The ratio (Ec / Es) was calculated as an index of uneven wear resistance from the wear energy Ec at the equatorial plane and the wear energy Es at the contact edge. The results are shown in Table 1 below as an index, with Comparative Example 1 set to 100. The smaller the value, the better the uneven wear resistance.

[0134] [Table 1]

[0135] As shown in Table 1, it has been confirmed that the rolling resistance is reduced without deteriorating the grip performance on wet road surfaces in the examples. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0136] The above-described technology capable of reducing rolling resistance without deteriorating grip performance on wet road surfaces can be applied to various tires.

[0137] [Note] The present invention includes the following aspects.

[0138] [1] A tire comprising a pair of beads, a carcass spanning the pair of beads, a pair of sidewalls positioned axially outward of the carcass, a tread positioned radially outward of the carcass, and a belt positioned between the carcass and the tread, wherein the tread is composed of a plurality of layers aligned radially, the plurality of layers including a cap layer positioned at the outermost position, a base layer positioned at the innermost position, and an intermediate layer positioned between the cap layer and the base layer, and the loss tangent at 30°C of the intermediate layer is lower than the loss tangent at 30°C of the cap layer. a loss tangent at 30°C of the base layer is lower than a loss tangent at 30°C of the intermediate layer, an outer surface of the tire comprises a tread surface including the equator of the tire, and a pair of side surfaces that are connected to the tread surface and include a maximum width position of the tire, and in a meridian cross section of the tire, a contour line of the tread surface includes a plurality of arcs that are arranged in an axial direction, the plurality of arcs including a center arc that includes the equator, a pair of middle arcs that are connected to the center arc, a pair of shoulder arcs that are connected to the middle arc, and a pair of corner arcs that are located on the outermost sides and are connected to the shoulder arcs a shoulder arc and a corner arc, an intersection point of a first tangent to the corner arc at a first end on the equator side and a second tangent to the corner arc at a second end on the side surface side of the shoulder arc is a tread reference edge, a boundary between the shoulder arc and the corner arc is a reference boundary point, the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to a regular internal pressure, a load of 80% of the regular load is applied to the tire as a vertical load, and the tire is brought into contact with a flat road surface to obtain a contact edge that is a reference contact edge, and a position on the outer surface of the tire that corresponds to the reference contact edge is a reference contact edge. At least three circumferential grooves, including two shoulder circumferential grooves located axially outward of the reference contact position, form at least four land portions in the tread, including the two shoulder land portions located outermost, and each shoulder land portion includes the reference contact position. A ground contact reference line is a normal to the inner surface of the tire that passes through the reference contact position, and the shoulder land portion is divided into an axially inner portion and an axially outer portion by the ground contact reference line. The thickness of the cap layer in the axially outer portion is,a ratio to the thickness of the tread is defined as an outer thickness ratio of the cap layer, a ratio of the thickness of the intermediate layer at the axially outer portion to the thickness of the tread is defined as an outer thickness ratio of the intermediate layer, a ratio of the thickness of the cap layer at the axially inner portion to the thickness of the tread is defined as an inner thickness ratio of the cap layer, and a ratio of the thickness of the intermediate layer at the axially inner portion to the thickness of the tread is defined as an inner thickness ratio of the intermediate layer, wherein the outer thickness ratio of the cap layer is smaller than the inner thickness ratio of the cap layer and the outer thickness ratio of the intermediate layer is greater than the inner thickness ratio of the intermediate layer. [2] The tire described in [1] above, wherein a ratio of an outer thickness ratio of the intermediate layer to an inner thickness ratio of the intermediate layer is 1.1 or more and 2.0 or less. [3] A tire as described in [1] or [2] above, wherein a ratio of the axial distance from the tire equator to the end of the cap layer to the axial distance from the equator to the reference boundary point is 0.9 or greater and 1.0 or less. [4] A tire described in any one of [1] to [3] above, wherein the inner thickness ratio of the cap layer is 20% or more and 30% or less, and the inner thickness ratio of the intermediate layer is 40% or more and 50% or less. [5] A tire as described in any of [1] to [4] above, wherein a ratio of the axial distance from the equator of the tire to an end of the base layer to the axial distance from the equator to an end of the belt is 0.8 or greater and 1.2 or less. [6] The tire according to any one of [1] to [5] above, wherein a ratio of a loss tangent at 30°C of the intermediate layer to a loss tangent at 30°C of the cap layer is 40% or more and 90% or less. [7] A tire described in any of [1] to [6] above, wherein the ratio of the axial distance from the equator to the reference boundary point to the axial distance from the equator to the tread reference end is 0.94 or greater and 0.99 or less. [8] The tire described in [7] above, wherein a ratio of the radial distance from the equator to the reference ground contact position to the axial distance from the equator to the tread reference end is 0.06 or greater and 0.15 or less. [9] The tire described in [8] above, wherein a ratio of the radius of the middle arc to the radius of the shoulder arc is 2.1 or greater and 2.7 or less. [Explanation of symbols]

[0139] 2. Tires 4. Tread 6. Sidewall 10 Bead 12. Carcass 14. Belt 24 Tread surface 26 Side surface 30, 30s, 30m...Circumferential groove 32, 32s, 32m, 32c...Land 38···Carcass ply 44...layer 46 Cap layer 48. Middle class 50···Base layer

Claims

1. A tire comprising: a pair of beads; a carcass extending between the pair of beads; a pair of sidewalls positioned axially outward of the carcass; a tread positioned radially outward of the carcass; and a belt positioned between the carcass and the tread, The tread is composed of a plurality of radially aligned layers, the plurality of layers includes a cap layer located at an outermost position, a base layer located at an innermost position, and an intermediate layer located between the cap layer and the base layer; a loss tangent at 30° C. of the intermediate layer is lower than a loss tangent at 30° C. of the cap layer, and a loss tangent at 30° C. of the base layer is lower than a loss tangent at 30° C. of the intermediate layer; The outer surface of the tire includes a tread surface including an equator of the tire, and a pair of side surfaces that are continuous with the tread surface and include a maximum width position of the tire, In a meridian section of the tire, The contour line of the tread surface includes a plurality of arcs aligned in the axial direction, the plurality of arcs include a center arc including the equator, a pair of middle arcs connected to the center arc, a pair of shoulder arcs connected to the middle arc, and a pair of corner arcs located on the outermost sides and connected to the shoulder arcs, an intersection of a first tangent to the corner arc at a first end on the equator side and a second tangent to the corner arc at a second end on a side surface side of the corner arc is a tread reference edge, a boundary between the shoulder arc and the corner arc is a reference boundary point; The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and a load of 80% of the standard load is applied to the tire as a vertical load. The tire is brought into contact with a flat road surface, and the resulting ground contact edge is the reference ground contact edge, and a position on the outer surface of the tire that corresponds to the reference ground contact edge is the reference ground contact position, the reference boundary point is located axially outward of the reference ground position; At least three circumferential grooves including two outermost shoulder circumferential grooves form at least four land portions in the tread including two outermost shoulder land portions; Each shoulder land portion includes the reference contact position, In a meridian cross section of the tire, a normal to the inner surface of the tire that passes through the reference contact position is defined as a ground contact reference line, the shoulder land portion is divided into an axially inner portion and an axially outer portion by the ground contact reference line, the ratio of the thickness of the cap layer at the axially outer portion to the thickness of the tread is defined as an outer thickness ratio of the cap layer, the ratio of the thickness of the intermediate layer at the axially outer portion to the thickness of the tread is defined as an outer thickness ratio of the intermediate layer, the ratio of the thickness of the cap layer at the axially inner portion to the thickness of the tread is defined as an inner thickness ratio of the cap layer, and the ratio of the thickness of the intermediate layer at the axially inner portion to the thickness of the tread is defined as an inner thickness ratio of the intermediate layer, an outer thickness ratio of the cap layer is smaller than an inner thickness ratio of the cap layer; an outer thickness ratio of the intermediate layer is greater than an inner thickness ratio of the intermediate layer; tire.

2. The ratio of the outer thickness ratio of the intermediate layer to the inner thickness ratio of the intermediate layer is 1.1 or more and 2.0 or less.

2. The tire of claim 1.

3. a ratio of an axial distance from an equator of the tire to an end of the cap layer to an axial distance from the equator to the reference boundary point is 0.9 or more and 1.0 or less; 3. A tire according to claim 1 or 2.

4. The inner thickness ratio of the cap layer is 20% or more and 30% or less, The inner thickness ratio of the intermediate layer is 40% or more and 50% or less.

2. The tire of claim 1.

5. a ratio of an axial distance from an equator of the tire to an end of the base layer to an axial distance from the equator to an end of the belt is 0.8 or more and 1.2 or less; 2. The tire of claim 1.

6. a ratio of a loss tangent at 30° C. of the intermediate layer to a loss tangent at 30° C. of the cap layer is 40% or more and 90% or less; 2. The tire of claim 1.

7. a ratio of an axial distance from the equator to the reference boundary point to an axial distance from the equator to the tread reference end is 0.94 or more and 0.99 or less; 2. The tire of claim 1.

8. a ratio of a radial distance from the equator to the reference ground contact position to an axial distance from the equator to the tread reference end is 0.06 or more and 0.15 or less; 8. The tire of claim 7.

9. a ratio of a radius of the middle arc to a radius of the shoulder arc is 2.1 or more and 2.7 or less; 9. The tire of claim 8.

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