tire

Abstract

To provide a tire 2 which can improve wet performance while reducing rolling resistance.SOLUTION: A tread 4 of a tire 2 includes a base layer 44, an intermediate layer 46 covering the base layer 44, and a cap layer 48 covering the intermediate layer 46. The cap layer 48 includes a tread surface T. A loss tangent at 30°C of the intermediate layer 46 is lower than a loss tangent at 30°C of the cap layer 48, and a loss tangent at 30°C of the base layer 44 is lower than a loss tangent at 30°C of the intermediate layer 46. On a reference ground contact area, a land part 26 having a longest ground contact length is a longest land part 26w, a land part 26 having a shortest ground contact length is a shortest land part 26n, and a ratio (TL / TS) of a thickness TL of the intermediate layer 46 in the longest land part 26w to a thickness TS of the intermediate layer 46 in the shortest land part 26n is more than 1.0 and 3.5 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] When low heat generation rubber is used in the tread, a tire with low rolling resistance is obtained. Low heat generation rubber is inferior to high heat generation rubber in terms of grip. Therefore, when low heat generation rubber is used in the tread, for example, braking performance on wet road surfaces (hereinafter also referred to as wet performance) decreases. It is difficult to achieve a good balance between rolling resistance and wet performance. Various studies have been conducted with the aim of reducing rolling resistance and improving wet performance (for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-2008 A Summary of the Invention [Problem to be solved by the invention]

[0004] Due to environmental considerations, there is a demand for further reduction in tire rolling resistance. Usually, tires mounted on a vehicle are given a negative camber. Therefore, the tire's contact length is longer on the inside in the width direction of the vehicle and shorter on the outside. By taking into consideration the contact shape of the tire mounted on the vehicle, it is expected that the rolling resistance can be further reduced and the wet performance can be further improved.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a tire that can achieve improved wet performance while reducing rolling resistance. [Means for solving the problem]

[0006] The inventors have found that the contribution of the outside tread, which is a portion of the tread arranged on the outside of a passenger vehicle (hereinafter also referred to as a vehicle), to the exertion of gripping force is greater than that of the inside tread, which is a portion arranged on the inside of the passenger vehicle (hereinafter also referred to as a vehicle), and have completed the present invention. That is, a tire according to one aspect of the present invention has a tread forming a tread surface. In this tire, the orientation of the tread with respect to the vehicle is specified, and of both ends of the tread, the end arranged on the inside in the width direction of the vehicle is a first end, and the end arranged on the outside is a second end. The tread has a base layer, an intermediate layer located on the outside of the base layer in the radial direction and covering the base layer, and a cap layer located on the outside of the intermediate layer in the radial direction and covering the intermediate layer. The cap layer includes the tread surface. The loss tangent of the intermediate layer at 30° C. is lower than the loss tangent of the cap layer at 30° C., and the loss tangent of the base layer at 30° C. is lower than the loss tangent of the intermediate layer at 30° C. At least four land portions are formed by carving at least three circumferential grooves in the tread. The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and the camber angle of the tire is set to -1°. A load of 50% of the standard load is applied to the tire, and the tire is brought into contact with a flat road surface to obtain a contact surface which is a reference contact surface. In the reference contact surface, the land portion with the longest contact length is the longest land portion, and the land portion with the shortest contact length is the shortest land portion, and the ratio of the thickness of the intermediate layer at the longest land portion to the thickness of the intermediate layer at the shortest land portion is greater than 1.0 and not greater than 3.5.

[0007] Preferably, in the tire, the intermediate layer is thicker on the first end side and thinner on the second end side.

[0008] Preferably, in this tire, the tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, the camber angle of the tire is set to 0°, a load of 70% of the standard load is applied to the tire, and the tire is brought into contact with a flat road surface, resulting in a contact surface that is a reference contact surface, and within the reference contact surface, the ratio of the axial width of the thick zone of the intermediate layer to the contact width of the reference contact surface is equal to or greater than 40% and equal to or less than 100%.

[0009] Preferably, in the tire, in a meridian cross section of the tire with the tire mounted on a regular rim, the internal pressure of the tire adjusted to 230 kPa, and no load applied to the tire, the contour of the tread surface is represented by a plurality of curved contour lines consisting of circular arcs and arranged in parallel in the axial direction, the curved contour line located in the middle of the plurality of curved contour lines is a center curved contour line, and the radius of the center curved contour line is 500 mm or more and 1000 mm or less.

[0010] Preferably, in the tire, a ratio of a loss tangent at 30° C. of the cap layer to a loss tangent at 30° C. of the intermediate layer is 125% or greater and 200% or less. Effect of the Invention

[0011] According to the present invention, a tire can be obtained that can achieve improved wet performance while reducing rolling resistance. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing a part of a tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing the contour of a shoulder portion of a tire. [Diagram 3] FIG. 3 is an image diagram explaining the camber angle of a tire. [Figure 4] FIG. 4 is an image diagram illustrating the reference ground plane. [Diagram 5] FIG. 5 is a cross-sectional view showing the contour of the tread surface. [Figure 6] FIG. 6 is a cross-sectional view showing a part of the tire of Comparative Example 2. As shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view showing a part of the tire of Comparative Example 3. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the present invention will be described in detail based on preferred embodiments with reference to the drawings as appropriate.

[0014] In this disclosure, 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 referred to as a standard state. The condition in which a tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, and no load is applied to the tire is called the standard condition.

[0015] In this disclosure, unless otherwise specified, the dimensions and angles of each part of the tire are measured in a normal state. Dimensions and angles that cannot be measured when the tire is mounted on a normal rim are measured by matching the distance between the left and right beads in a cross section of the tire obtained by cutting the tire along a plane including the rotation axis to the distance between the beads of the tire mounted on a normal rim.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] In the present disclosure, the crosslinked rubber is a molded product of the rubber composition obtained by pressurizing and heating the rubber composition. The rubber composition is an uncrosslinked rubber obtained by mixing a base rubber and chemicals in a kneader such as a Banbury mixer. The crosslinked rubber is also called vulcanized rubber, and the rubber composition is also called unvulcanized rubber.

[0020] 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.

[0021] In the present disclosure, the loss tangent (also referred to as tan δ) at a temperature of 30°C of an element made of crosslinked rubber among the elements constituting a tire is measured in accordance with the provisions of JIS K6394 using a viscoelasticity spectrometer ("VES" manufactured by Iwamoto Seisakusho Co., Ltd.) under the following conditions. Initial distortion = 10% Dynamic strain = 2% Frequency = 10Hz Deformation mode = tension In this measurement, the test specimen is sampled from a tire. If it is not possible to sample the test specimen from a tire, the test specimen 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.

[0022] Fig. 1 shows a portion of a tire 2 according to one embodiment of the present invention. This tire 2 is a tire for passenger cars. Fig. 1 shows a portion of a cross section (hereinafter also referred to as a meridian cross section) of the tire 2 along a plane including the rotation axis of the tire 2. In Fig. 1, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of Fig. 1 is the circumferential direction of the tire 2.

[0023] 1, the dashed dotted line CL is the equatorial plane of the tire 2. The tire 2 is symmetrical with respect to the equatorial plane, except for the tread pattern, decorations such as designs and letters engraved on the outer surface, and the internal configuration of the tread, which will be described later.

[0024] The tire 2 is mounted on a rim R. The rim R is a regular rim. Air is filled inside the tire 2, and the internal pressure of the tire 2 is adjusted. The tire 2 mounted on the rim R is also called a tire-rim assembly. The tire-rim assembly includes the rim R and the tire 2 mounted on the rim R.

[0025] 1, the position indicated by the symbol PW is the axially outer end of the tire 2. If there is a decoration such as a pattern or lettering on the outer surface, the outer end PW is identified based on a virtual outer surface obtained by assuming that there is no decoration.

[0026] In Fig. 1, the length indicated by the symbol WA is the maximum width of the tire 2, i.e., the section width (see JATMA, etc.). The section width WA of the tire 2 is the axial distance from one outer end PW to the other outer end PW. The outer end PW is the position where the tire 2 shows the maximum width (hereinafter, the maximum width position). The section width WA is measured with the tire 2 in a standard state.

[0027] The tire 2 includes 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 , a pair of chafers 18 , and an inner liner 20 .

[0028] The tread 4 forms a tread surface T. The tire 2 comes into contact with the road surface at the tread surface T. Grooves 22 are cut into the tread 4. This forms a tread pattern.

[0029] The grooves 22 constituting the tread pattern include circumferential grooves 24 that extend continuously in the circumferential direction. In this tire 2, at least three circumferential grooves 24 are cut into the tread 4. As a result, at least four land portions 26 are formed in the tread 4. In the tire 2 shown in FIG. 1, five land portions 26 are formed by cutting the four circumferential grooves 24 into the tread 4.

[0030] The tread 4 of this tire 2 includes a tread body 28 and a pair of wings 30. Each of the wings 30 is located axially outward of the tread body 28. The wings 30 join the tread body 28 and the sidewall 6. The wings 30 are made of crosslinked rubber with adhesive properties taken into consideration.

[0031] In FIG. 1, the position indicated by the symbol TE is an end of the tread 4. In this tire 2, the orientation of the tread 4 with respect to the vehicle is specified. The end TE of the tread 4 located on the right side of the paper in FIG. 1 is the first end TE1, and the end TE of the tread 4 located on the left side is the second end TE2. When this tire 2 is mounted on a vehicle, of both ends TE of the tread 4, the first end TE1 of the tread 4 is positioned on the inside in the width direction of the vehicle. The second end TE2 of the tread 4 is positioned on the outside in the width direction of the vehicle.

[0032] 1, the position indicated by the symbol PE is the equator of the tire 2. The equator PE is the intersection point between the tread surface T and the equatorial plane. When a groove 22 is present on the equatorial plane, the equator PE is determined based on a virtual tread surface obtained by assuming that the groove 22 does not exist. In the tire 2, the portion of the tread 4 from the equator PE to the first end TE1 is also referred to as an inside tread 4a, and the portion from the equator PE to the second end TE2 is also referred to as an outside tread 4b.

[0033] 1, the position indicated by the symbol PH is a position on the tread surface T. The position PH corresponds to the axially outer end of the contact surface of the tire 2 with the road surface.

[0034] The contact patch for identifying the position PH is obtained, for example, by using a contact patch shape measuring device (not shown). This contact patch is obtained by applying a load of 70% of the normal load as a vertical load to the tire 2 in a state where the camber angle of the tire 2 in a standard state is set to 0°, and bringing the tire 2 into contact with a flat road surface. In the tire 2, the contact patch obtained in this manner is the reference contact patch, and the position on the tread surface T corresponding to the axial outer end of this reference contact patch is the above-mentioned position PH. In the tire 2, this position PH is the reference contact edge. In FIG. 1, the length indicated by the symbol WH is the contact width of the reference contact patch. The contact width WH is the axial distance from one reference contact edge PH to the other reference contact edge PH. The contact width WH is measured in the tire 2 in a standard state.

[0035] Each sidewall 6 is continuous with an end TE of the tread 4. The sidewall 6 is located radially inside the tread 4. The sidewall 6 extends from the end TE of the tread 4 toward the clinch 8 along the carcass 12. The sidewall 6 is made of crosslinked rubber in consideration of cut resistance.

[0036] 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 in consideration of wear resistance.

[0037] Each bead 10 is located axially inside the clinch 8. The bead 10 includes a core 32 and an apex 34. Although not shown, the core 32 includes a steel wire.

[0038] The apex 34 is located radially outward of the core 32. The apex 34 tapers outward. The apex 34 is made of crosslinked rubber having high rigidity.

[0039] 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 one bead 10 and the other bead 10. This carcass 12 has a radial structure.

[0040] The carcass 12 includes at least one carcass ply 36. The carcass 12 of the tire 2 is composed of two carcass plies 36. The carcass ply 36 located radially inward on the inner side of the tread 4 is a first carcass ply 38, and the carcass ply 36 located outward of the first carcass ply 38 is a second carcass ply 40. From the viewpoint of weight reduction, the carcass 12 may be composed of one carcass ply 36.

[0041] The first carcass ply 38 includes a first ply body 38a that spans between one core 32 and the other core 32, and a pair of first turn-up portions 38b that are connected to the first ply body 38a and are turned back from the axial inside to the axial outside around each core 32.

[0042] The second carcass ply 40 includes a second ply body 40a that spans between one core 32 and the other core 32, and a pair of second turn-up portions 40b that are connected to the second ply body 40a and are turned up from the axially inner side to the axially outer side around each core 32.

[0043] Although not shown, the carcass ply 36 includes a number of carcass cords arranged in parallel. Each carcass cord crosses the equator plane. The carcass cord is a cord made of an organic fiber. Examples of the organic fiber include nylon fiber, rayon fiber, polyester fiber, and aramid fiber.

[0044] The belt 14 is located on the inside of the tread 4 in the radial direction. The belt 14 is layered on the carcass 12 from the outside in the radial direction. In FIG. 1, the length indicated by the symbol WR is the axial width of the belt 14. The axial width WR is the axial distance from one end of the belt 14 to the other end. In this tire 2, the axial width WR of the belt 14 is 65% or more and 85% or less of the cross-sectional width WA.

[0045] The belt 14 is composed of at least two layers 42 laminated in the radial direction. The belt 14 of the tire 2 is composed of two layers 42 laminated in the radial direction. Of the two layers 42, the layer 42 located on the inner side is the inner layer 42a, and the layer 42 located on the outer side is the outer layer 42b. As shown in FIG. 1, the inner layer 42a is wider than the outer layer 42b. The length from an end of the outer layer 42b to an end of the inner layer 42a is 3 mm or more and 10 mm or less.

[0046] Although not shown, each of the inner layer 42a and the outer layer 42b includes a number of belt cords arranged in parallel. Each belt cord is inclined with respect to the equator plane. The material of the belt cord is steel.

[0047] The band 16 is located radially between the tread 4 and the belt 14. The band 16 is laminated to the belt 14 on the inside of the tread 4. The band 16 has a jointless structure.

[0048] Although not shown, the band 16 includes a band cord wound in a spiral shape. The band cord extends substantially in the circumferential direction. Specifically, the angle that the band cord forms with the circumferential direction is 5° or less. In the tire 2, 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.

[0049] The band 16 of the tire 2 is composed of a full band whose two ends face each other across the equator PE. The band 16 is wider than 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 band 16 covers the belt 14 from the outside in the radial direction. The band 16 may include a pair of edge bands that are arranged spaced apart in the axial direction and cover the ends of the full band and the ends of the belt 14. The band 16 may be composed of only a pair of edge bands.

[0050] Each chafer 18 is located radially inside the bead 10. The chafers 18 contact the rim R. The chafers 18 of the tire 2 are made of cloth and rubber impregnated into the cloth.

[0051] The inner liner 20 is positioned inside the carcass 12. The inner liner 20 constitutes the inner surface of the tire 2. The inner liner 20 is made of a crosslinked rubber having a low gas permeability coefficient. The inner liner 20 maintains the internal pressure of the tire 2.

[0052] Fig. 2 shows a part of the tire 2 shown in Fig. 1. In Fig. 2, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of Fig. 2 is the circumferential direction of the tire 2.

[0053] Fig. 2 shows the outline of the shoulder portion of the tire 2 in a meridian cross section. The outline shown in Fig. 2 is obtained by measuring the outer surface shape of the tire 2 in a standard state with a displacement sensor. Fig. 2 shows the outline of the outer surface of the tire 2 in a meridian cross section of the tire 2 in a standard state.

[0054] For example, grooves 22 are formed in the tread 4. Decorations such as patterns and letters are provided on the sidewalls 6. Therefore, the outer surface shape of the tire 2 obtained by measurement includes irregularities corresponding to the grooves 22 and decorations such as patterns and letters. The contour of the outer surface of the tire 2 is represented by a virtual outer surface obtained by assuming that such irregularities do not exist.

[0055] In a meridian cross section, the contour of the outer surface of the tire 2 (hereinafter, tire outer surface TS) is formed by connecting multiple contour lines consisting of straight lines or circular arcs. In this disclosure, a contour line consisting of a straight line or a circular arc is simply referred to as a contour line. A contour line consisting of a straight line is referred to as a straight contour line, and a contour line consisting of a circular arc is referred to as a curved contour line.

[0056] The tire outer surface TS includes a tread surface T and a pair of side surfaces S connected to the ends of the tread surface T. In a meridian cross section, the contour of the tread surface T includes a plurality of curved contour lines having different radii. In this tire 2, the curved contour line having the smallest radius among the plurality of curved contour lines included in the contour of the tread surface T is located at the end portion of the tread surface T and connected to the side surface S. In a meridian cross section, the contour of the tire outer surface TS includes a curved portion, which is a curved contour line consisting of an arc having the smallest radius among the plurality of curved contour lines included in the contour of the tread surface T and connected to the side surface S, at the end portion of the tread surface T. In FIG. 2, this curved portion is indicated by the symbol RS.

[0057] In the contour of the tire outer surface TS, the curved portion RS is tangent to a contour line adjacent to the axially inner side (hereinafter, referred to as an inner adjacent contour line NT) at a tangent point CT. This curved portion RS is tangent to a contour line constituting the contour of the side surface S adjacent to the axially outer side (hereinafter, referred to as an outer adjacent contour line NS) at a tangent point CS. This contour of the tire outer surface TS includes an inner adjacent contour line NT located axially inside the curved portion RS and tangent to the curved portion RS, and an outer adjacent contour line NS located axially outside the curved portion RS and tangent to the curved portion RS.

[0058] In Fig. 2, a solid line LT is a tangent to the curved portion RS at a contact point CT between the inner adjacent contour line NT and the curved portion RS. A solid line LS is a tangent to the curved portion RS at a contact point CS between the outer adjacent contour line NS and the curved portion RS. The position indicated by the symbol PT is the intersection point between the tangent line LT and the tangent line LS. In this tire 2, this intersection point PT is the tread reference edge.

[0059] In Fig. 1, the length indicated by the double-headed arrow WT is the tread width. This tread width WT is the axial distance from one tread reference end PT to the other tread reference end PT. In this tire 2, the ratio (WT / WA) of the tread width WT to the cross-sectional width WA is 70% or more and 90% or less. The ratio (WH / WT) of the contact width WH of the reference contact surface to the tread width WT is 70% or more and 90% or less.

[0060] As described above, the four circumferential grooves 24 are formed in the tread 4 of the tire 2. There are no particular limitations on the arrangement, groove depth, and groove width of the four circumferential grooves 24 in the tire 2. The arrangement, groove depth, and groove width of the circumferential grooves of a tire are generally applied to the tread 4.

[0061] In the tire 2, the circumferential groove 24 located on the outer side in the axial direction among the four circumferential grooves 24 is a shoulder circumferential groove 24s. The circumferential groove 24 located on the inner side of the shoulder circumferential groove 24s is a middle circumferential groove 24m.

[0062] As described above, the tread 4 of the tire 2 is formed with five land portions 26. Of the five land portions 26, the land portion 26 located on the outer side in the axial direction is the shoulder land portion 26s. The land portion 26 located on the inner side of the shoulder land portion 26s in the axial direction is the middle land portion 26m. The land portion 26 located between the left and right middle land portions 26m is the center land portion 26c. This center land portion 26c is located on the equatorial plane. In the tire 2, the shoulder land portion 26s on the first end TE1 side of the tread 4 is a first shoulder land portion 26s1, and the shoulder land portion 26s on the second end TE2 side is a second shoulder land portion 26s2. The middle land portion 26m on the first end TE1 side of the tread 4 is a first middle land portion 26m1, and the middle land portion 26m on the second end TE2 side is a second middle land portion 26m2.

[0063] Fig. 3 shows a state of the tire 2 mounted on a vehicle (not shown). In Fig. 3, the right side is the inside in the width direction of the vehicle, and the left side is the outside in the width direction of the vehicle.

[0064] As shown in FIG. 3, the tire 2 is usually mounted on a vehicle so that its equatorial plane CL is inclined with respect to the road surface. In FIG. 3, the solid line indicated by the symbol BL is a straight line perpendicular to the flat road surface on which the tire 2 is in contact. When the road surface spreads horizontally, this straight line CL is also called a vertical line. The angle θ is the angle that the equatorial plane CL makes with this straight line BL. This angle θ is also called a camber angle. The tire 2 shown in FIG. 3 is mounted on a vehicle so that the upper part of the equatorial plane CL is located more inward than the lower part in the width direction of the vehicle. The camber angle of the tire 2 mounted in this way is also called negative camber and is expressed as a negative angle. The tire 2 shown in FIG. 3 is in a state in which a negative camber is applied.

[0065] Fig. 4 shows an image of the contact surface of the tire 2. In Fig. 4, the up-down direction corresponds to the circumferential direction of the tire 2, and the left-right direction corresponds to the axial direction of the tire 2. The right side of Fig. 4 is the inside in the width direction of the vehicle, in other words, the first end TE1 side of the tread 4. The left side of the paper is the outside in the width direction of the vehicle, in other words, the second end TE2 side of the tread 4.

[0066] This contact patch is obtained, for example, by using the above-mentioned contact patch shape measuring device (not shown). This contact patch is obtained by applying a load of 50% of the normal load as a vertical load to the tire 2 with the camber angle θ of the tire 2 in the normal state set to -1° and bringing the tire 2 into contact with a flat road surface. In the present disclosure, this contact patch is the reference contact patch. A negative camber is usually imparted to tires mounted on a vehicle (specifically, a passenger car). The reference contact patch is a contact patch that takes into account the contact state of the tire mounted on the vehicle.

[0067] As described above, the tread 4 of the tire 2 is formed with five land portions 26. The reference ground contact surface includes ground contact surfaces CA corresponding to the five land portions 26. In Fig. 4, from the right side of the page, the ground contact surface CA1 of the first shoulder land portion 26s1, the ground contact surface CA2 of the first middle land portion 26m1, the ground contact surface CA3 of the center land portion 26c, the ground contact surface CA4 of the second middle land portion 26m2, and the ground contact surface CA5 of the second shoulder land portion 26s2 are shown. 4, the length indicated by the reference symbol LM1 is the contact length of the contact surface CA2 of the first middle land portion 26m1, and the length indicated by the reference symbol LS2 is the contact length of the contact surface CA5 of the second shoulder land portion 26s2.

[0068] In this tire 2, of the five land portions 26 included in the reference contact surface, the contact surface CA2 of the first middle land portion 26m1 has the longest contact length. The contact surface CA5 of the second shoulder land portion 26s2 has the shortest contact length. In the present disclosure, of the land portions 26 included in the reference contact surface, the land portion 26 showing the longest contact length is the longest land portion 26w, and the land portion 26 having the shortest contact length is the shortest land portion 26n. In this tire 2, the first middle land portion 26m1 is the longest land portion 26w, and the second shoulder land portion 26s2 is the shortest land portion 26n.

[0069] As shown in FIG. 1, the tread 4 of the tire 2 (more specifically, the tread body 28 ) includes a base layer 44 , an intermediate layer 46 , and a cap layer 48 . The base layer 44 is located radially inward of the intermediate layer 46 and the cap layer 48. The base layer 44 is located radially outward of the band 16. The base layer 44 is laminated on the band 16. The base layer 44 covers the band 16 from the outside in the radial direction. The intermediate layer 46 is located between the base layer 44 and the cap layer 48 in the radial direction. The intermediate layer 46 is located outside the base layer 44 in the radial direction. The intermediate layer 46 is laminated on the base layer 44. The intermediate layer 46 covers the base layer 44 from the outside in the radial direction. The cap layer 48 is located radially outward of the base layer 44 and the intermediate layer 46. The cap layer 48 includes a tread surface T. The cap layer 48 is located radially outward of the intermediate layer 46. The cap layer 48 is laminated on the intermediate layer 46. The cap layer 48 covers the intermediate layer 46 from the outside in the radial direction.

[0070] The base layer 44, the intermediate layer 46, and the cap layer 48 are each made of a crosslinked rubber having a different heat buildup property. In the tire 2, the loss tangent LTm of the intermediate layer 46 at 30° C. is lower than the loss tangent LTc of the cap layer 48 at 30° C. The loss tangent LTb of the base layer 44 at 30° C. is lower than the loss tangent LTm of the intermediate layer 46 at 30° C. In this tire 2, the cap layer 48 generates heat most easily and contributes to exerting grip force of the tire 2. The base layer 44 generates heat least easily and contributes to reducing the rolling resistance of the tire 2. The intermediate layer 46 generates heat less easily than the cap layer 48 and more easily than the base layer 44. The intermediate layer 46 contributes to reducing rolling resistance more than the cap layer 48 and contributes to exerting grip force more than the base layer 44.

[0071] Each land portion 26 in the tread 4 is composed of three layers: a base layer 44, an intermediate layer 46, and a cap layer 48. As shown in Fig. 4, the contact length of the land portion 26 varies depending on the position on the reference contact surface. As described above, the reference contact surface is a contact surface that takes into account the contact state of the tire mounted on a vehicle.

[0072] The inventors have thoroughly studied treads, taking into consideration the contact shape of a tire mounted on a vehicle, and have discovered that the outside tread, which is located on the outside of a passenger vehicle (hereinafter also referred to as the vehicle), contributes more to gripping power than the inside tread, which is located on the inside of the vehicle. In order to reduce rolling resistance while ensuring wet performance, the inventors focused on the thickness of the intermediate layer in the land portion and considered constructing the outside tread mainly from heat-generating rubber and the inside tread mainly from low-heat-generating rubber, and have thus completed the present invention.

[0073] In the present disclosure, the thickness of the intermediate layer 46 in the shoulder land portion 26s is expressed as the thickness of the intermediate layer 46 measured along a normal line to the interface between the intermediate layer 46 and the base layer 44, which passes through a boundary between the shoulder land portion 26s and the shoulder circumferential groove 24s on the tread surface T, i.e., a position on the tread surface T 5 mm away from the edge of the shoulder land portion 26s, as a reference position. In FIG. 1, the straight line indicated by the symbol SN is a normal line to the interface between the intermediate layer 46 and the base layer 44, which passes through a position 5 mm away from the edge of the second shoulder land portion 26s2. The thickness of the intermediate layer 46 in the second shoulder land portion 26s2 is measured along this normal line SN.

[0074] In the present disclosure, the thickness of the intermediate layer 46 in the land portions 26 other than the shoulder land portions 26s is expressed as the thickness of the intermediate layer 46 measured along a normal line to the interface between the intermediate layer 46 and the base layer 44, which passes through the width center of the land portion 26 on the tread surface T and passes through this reference position. In FIG. 1, the straight line indicated by the symbol LN is the normal line to the interface between the intermediate layer 46 and the base layer 44, which passes through the width center of the first middle land portion 26m1. The thickness of the intermediate layer 46 in the first middle land portion 26m1 is measured along this normal line LN.

[0075] As described above, in the tire 2, the first middle land portion 26m1 is the longest land portion 26w, and the second shoulder land portion 26s2 is the shortest land portion 26n. 1, the length indicated by the symbol TL is the thickness of the intermediate layer 46 in the first middle land portion 26m1, which is the longest land portion 26w. The length indicated by the symbol TS is the thickness of the intermediate layer 46 in the second shoulder land portion 26s2, which is the shortest land portion 26n.

[0076] In the present disclosure, when the thickness of the intermediate layer 46 in the longest land portion 26w varies, the thickness TL of the intermediate layer 46 in the longest land portion 26w is represented by the maximum thickness, not the thickness at the aforementioned reference position. When the thickness of the intermediate layer 46 in the shortest land portion 26n varies, the thickness TS of the intermediate layer 46 in the shortest land portion 26n is represented by the minimum thickness, not the thickness at the aforementioned reference position. When the shoulder land portion 26s is the shortest land portion 26n, the minimum thickness is specified in the portion that overlaps with the reference ground surface in the radial direction.

[0077] In this tire 2, the cap layer 48, which has excellent wear resistance, covers the entire intermediate layer 46 from the outside in the radial direction. Since the intermediate layer 46, which has poor wear resistance, is not exposed to the tread surface T, the occurrence of unusual wear in the tread 4 is prevented. In this tire 2, uneven wear is unlikely to occur.

[0078] In this tire 2, the longest land portion 26w is configured in the inside tread 4a arranged on the inside when mounted on a vehicle, and the shortest land portion 26n is configured in the outside tread 4b arranged on the outside. The ratio (TL / TS) of the thickness TL of the intermediate layer 46 in the longest land portion 26w to the thickness TS of the intermediate layer 46 in the shortest land portion 26n is greater than 1.0 and equal to or less than 3.5. In the tire 2, the intermediate layer 46, which contributes more to the rolling resistance than the cap layer 48, is thick in the longest land portion 26w. The tread 4 effectively contributes to reducing the rolling resistance. Since the intermediate layer 46 is thin in the shortest land portion 26n, the tire 2 can have a thick cap layer 48 in the outside tread 4b, which contributes to gripping force. Since the cap layer 48 contributes to gripping force more than the intermediate layer 46, the tread 4 can contribute to improving gripping force. Since the ratio (TL / TS) is 3.5 or less, a cap layer 48 having an appropriate thickness is formed in the inside tread 4a, and an intermediate layer 46 having an appropriate thickness is formed in the outside tread 4b. The tire 2 can achieve improved wet performance while reducing rolling resistance.

[0079] As described above, in the tire 2, the ratio (TL / TS) is greater than 1.0 and equal to or less than 3.5. From the viewpoint of effectively contributing to reducing rolling resistance and improving wet performance, the ratio (TL / TS) is preferably equal to or greater than 1.1, more preferably equal to or greater than 1.2, even more preferably equal to or greater than 1.3, and particularly preferably equal to or greater than 1.4. From the same viewpoint, the ratio (TL / TS) is preferably equal to or less than 3.3, more preferably equal to or less than 3.1, even more preferably equal to or less than 2.9, and particularly preferably equal to or less than 2.7.

[0080] As shown in FIG. 1, in the tire 2, the intermediate layer 46 is thicker on the first end TE1 side of the tread 4 and is thinner on the second end TE2 side.

[0081] In this tire 2, the inside tread 4a effectively contributes to reducing rolling resistance, and the outside tread 4b effectively contributes to exerting grip force. This tire 2 can achieve improved wet performance while reducing rolling resistance. From this viewpoint, it is preferable that the intermediate layer 46 is thicker on the first end TE1 side of the tread 4 and thinner on the second end TE2 side. In this tire 2, it is more preferable that the intermediate layer 46 is thicker than the cap layer 48 on the first end TE1 side of the tread 4 and thinner than the cap layer 48 on the second end TE2 side.

[0082] As described above, the intermediate layer 46 of the tire 2 is thicker on the first end TE1 side of the tread 4 and is thinner on the second end TE2 side. From the viewpoint of forming an intermediate layer 46 that can effectively contribute to reducing rolling resistance and improving grip, it is preferable that, at the first end TE1 side, the ratio of the thickness of the intermediate layer 46 to the total thickness of the intermediate layer 46 and the cap layer 48 is set to 50% or more, and, at the second end TE2 side, the ratio of the thickness of the intermediate layer 46 to the total thickness of the intermediate layer 46 and the cap layer 48 is set to 50% or less.

[0083] 1, the position indicated by the symbol PB represents the position where the ratio of the thickness of the intermediate layer 46 to the total thickness of the intermediate layer 46 and the cap layer 48 is 50%. In this tire 2, this position PB is the boundary between a thick zone of the intermediate layer on the first end TE1 side and a thin zone of the intermediate layer on the second end TE2 side. In this tire 2, it is preferable that the boundary PB is formed between the longest land portion 26w and the shortest land portion 26n described above. 1, the length indicated by the symbol WM is the axial width of the thick zone of the intermediate layer 46 configured on the first end TE1 side. This axial width is represented as the axial distance from the aforementioned boundary PB to the reference ground end PH (hereinafter, the first reference ground end PH1) on the first end TE1 side.

[0084] In the tire 2, the ratio (WM / WH) of the axial width WM of the thick zone of the intermediate layer 46 within the reference contact patch to the contact width WH of the reference contact patch is preferably 40% or more and 100% or less.

[0085] By setting the ratio (WM / WH) to 40% or more, the inside tread 4a can effectively contribute to reducing rolling resistance. From this viewpoint, the ratio (WM / WH) is more preferably 50% or more, and further preferably 60% or more.

[0086] By setting the ratio (WM / WH) to 100% or less, the outside tread 4b can contribute to ensuring gripping force. From this viewpoint, the ratio (WM / WH) is more preferably 85% or less, and further preferably 75% or less.

[0087] 1, the length indicated by the symbol AL is the total thickness of the cap layer 48 and the intermediate layer 46 in the longest land portion 26w. This total thickness AL is measured along the normal line LN.

[0088] In the tire 2, from the viewpoint of allowing the longest land portion 26w to effectively contribute to reducing rolling resistance, the ratio (TL / AL) of the thickness TL of the intermediate layer 46 to the total thickness AL of the cap layer 48 and the intermediate layer 46 in the longest land portion 26w is preferably 50% or more, and more preferably 60% or more. From the viewpoint of configuring a cap layer 48 having an appropriate thickness in the longest land portion 26w, the ratio (TL / AL) is preferably 75% or less, more preferably 70% or less, and even more preferably 65% ​​or less.

[0089] 1, the length indicated by the symbol AS is the total thickness of the cap layer 48 and the intermediate layer 46 in the shortest land portion 26n. This total thickness AS is measured along the normal line SN.

[0090] In the tire 2, from the viewpoint of allowing the shortest land portion 26n to effectively contribute to improving grip, the ratio (TS / AS) of the thickness TS of the intermediate layer 46 to the total thickness AS of the cap layer 48 and the intermediate layer 46 in the shortest land portion 26n is preferably 50% or less, and more preferably 40% or less. From the viewpoint of forming an intermediate layer 46 having an appropriate thickness in the shortest land portion 26n, the ratio (TS / AS) is preferably 20% or more, and more preferably 25% or more.

[0091] Fig. 5 shows a part of the tire 2 shown in Fig. 1. In Fig. 5, the left-right direction is the axial direction of the tire 2, and the up-down direction is the radial direction of the tire 2. The direction perpendicular to the paper surface of Fig. 5 is the circumferential direction of the tire 2.

[0092] Fig. 5 shows the contour of the tread surface T of the tire 2 in a meridian cross section. The contour shown in Fig. 5, like the contour shown in Fig. 2, is obtained by measuring the outer surface shape of the tire 2 in a standard state with a displacement sensor. Fig. 5 shows the contour of the tread surface T of the tire 2 in a meridian cross section of the tire 2 in a standard state.

[0093] The tread surface T of the tire 2 is divided into a plurality of regions arranged in parallel in the axial direction in a meridian cross section. The plurality of regions include a crown region Cr, a pair of middle regions Mi, and a pair of side regions Sd. The crown region Cr is located at the center in the axial direction. The crown region Cr includes an equator PE. Each middle region Mi is located outside the crown region Cr in the axial direction. Each side region Sd is located outside the middle region Mi in the axial direction.

[0094] 5, the position indicated by the symbol CM is the boundary between the crown region Cr and the middle region Mi. The position indicated by the symbol MS is the boundary between the middle region Mi and the side region Sd. The symbol SE is the outer end of the side region Sd. The outer end SE is also the aforementioned contact point CT.

[0095] As described above, the contour of the tread surface T includes a plurality of curved contours having different radii. The contour of each region is represented by a curved contour. In the tire 2, the curved contour representing the contour of the crown region Cr is also referred to as a center contour. The curved contour representing the contour of the middle region Mi is also referred to as a middle contour. The curved contour representing the contour of the side region Sd is also referred to as a side contour. The plurality of curved contours included in the contour of the tread surface T include a center contour, a pair of middle contours, and a pair of side contours. The center contour is the curved contour located in the center among the plurality of curved contours representing the contour of the tread surface T.

[0096] Although not shown, the center of the center contour is located on the equatorial plane. In FIG. 5, the single arrow indicated by the symbol Rc is the radius of the center contour. The middle contour meets the center contour at the boundary CM. In FIG. 5, the single arrow indicated by the symbol Rm is the radius of the middle contour. The side contour meets the middle contour at the boundary MS. In FIG. 5, the single arrow indicated by the symbol Rd is the radius of the side contour.

[0097] In this tire 2, the radius Rc of the center contour line is preferably 500 mm or more and 1000 mm or less. This allows the tread 4 to fully exert its function. In this tire 2, the longest land portion 26w is configured axially outward from a position where the axial distance from the first reference ground edge PH1 is 40% of the ground contact width WH of the reference ground surface, and the shortest land portion 26n is configured axially outward from a position where the axial distance from the first reference ground edge PH1 is 75% of the ground contact width WH of the reference ground surface. This tire 2 can achieve improved wet performance while reducing rolling resistance. From this viewpoint, the radius Rc of this center contour line is more preferably 600 mm or more, and more preferably 700 mm or more. The radius Rc of this center contour line is more preferably 900 mm or less, and more preferably 800 mm or less.

[0098] In the present disclosure, the radius of a circular arc having a center on the equatorial plane and passing through the left and right edges of the central land portion 26c and the equator PE is used as the radius Rc of this center contour line. In a tread having circumferential grooves on the equatorial plane, the radius of a circular arc having a center on the equatorial plane and passing through the edges of the land portions located on both sides of the circumferential groove is used as the radius Rc of this center contour line.

[0099] In this tire 2, the radius Rm of the middle contour line is smaller than the radius Rc of the center contour line, and the radius Rs of the side contour line is smaller than the radius Rm of the middle contour line. This allows each contour line to be smoothly connected to form a tread 4 that can fully exhibit its functions. In this tire, cornering stability and straight-line stability are well balanced. From this viewpoint, the ratio (Rm / Rc) of the radius Rm of the middle contour line to the radius Rc of the center contour line is preferably 0.50 or more and preferably 0.54 or less. The ratio (Rd / Rc) of the radius Rd of the side contour line to the radius Rc of the center contour line is preferably 0.20 or more and preferably 0.24 or less.

[0100] In this tire 2, the loss tangent LTc of the cap layer 48 at 30° C. is higher than the loss tangent LTm of the intermediate layer 46 at 30° C. The cap layer 48 is prone to heat generation, while the intermediate layer 46 is not prone to heat generation. In this tire 2, the ratio (LTc / LTm) of the loss tangent LTc of the cap layer 48 at 30° C. to the loss tangent LTm of the intermediate layer 46 at 30° C. is preferably 125% or more and 200% or less.

[0101] By setting the ratio (LTc / LTm) to 125% or greater, the cap layer 48 effectively contributes to exerting the clipping force, and the intermediate layer 46 effectively contributes to reducing the rolling resistance. From this viewpoint, the ratio (LTc / LTm) is more preferably 140% or greater, and further preferably 155% or greater.

[0102] Setting the ratio (LTc / LTm) to 200% or less suppresses the effect of the cap layer 48 on rolling resistance. The difference between the heat generation amount of the cap layer 48 and the heat generation amount of the intermediate layer 46 is appropriately maintained, thereby preventing the occurrence of damage caused by the difference in the heat generation amount. From this viewpoint, the ratio (LTc / LTm) is more preferably 185% or less, and even more preferably 175% or less.

[0103] In this tire 2, the loss tangent LTb of the base layer 44 at 30° C. is preferably 0.11 or less. This is because the base layer 44 effectively contributes to reducing rolling resistance. From this viewpoint, the loss tangent LTb is more preferably 0.10 or less, and further preferably 0.09 or less. In this tire 2, the smaller the loss tangent LTb of the base layer 44, the more preferable it is, and therefore no preferable lower limit is set.

[0104] The loss tangent Ltm of the intermediate layer 46 at 30°C is preferably 0.15 or less. This is because the intermediate layer 46 effectively contributes to reducing rolling resistance. From this viewpoint, the loss tangent Ltm is more preferably 0.14 or less, and even more preferably 0.13 or less. The loss tangent Ltm of the intermediate layer 46 at 30°C is preferably 0.11 or more. This is because the intermediate layer 46 can ensure the necessary rigidity and can effectively contribute to improving wet performance. From this viewpoint, the loss tangent LTm is more preferably 0.12 or more.

[0105] The loss tangent LTc of the cap layer 48 at 30°C is preferably 0.15 or more. This is because the cap layer 48 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 48 contacts the road surface. From the viewpoint of improving wet performance, the higher the loss tangent LTc, the more preferable. However, a high loss tangent LTc leads to heat generation. There is a concern that the heated cap layer 48 will increase the temperature of the intermediate layer 46 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 48 at 30°C is preferably 0.30 or less, more preferably 0.28 or less, and even more preferably 0.27 or less.

[0106] As described above, according to the present invention, a tire can be obtained that can achieve improved wet performance while reducing rolling resistance. EXAMPLES

[0107] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0108] [Example 1] A pneumatic tire for passenger cars (tire size=225 / 55R19) having the basic structure shown in FIG. 1 and the specifications shown in Table 1 below was obtained. The radius Rc of the center curve contour line constituting the contour of the tread surface was 750 mm. Within the reference contact patch, the ratio of the axial width WM of the thick zone of the intermediate layer to the contact width WH of the reference contact patch (WM / WH) was 68%. In this Example 1, the total thickness AL in the longest land portion was the same as the total thickness AS in the shortest land portion, and the ratio (TL / TS) of the intermediate layer thickness TL in the longest land portion to the intermediate layer thickness TS in the shortest land portion was 1.50. The loss tangent LTc of the cap layer at 30°C was 0.24. The loss tangent LTm of the intermediate layer at 30°C was 0.15. The ratio of the loss tangent LTc to the loss tangent LTm (LTc / LTm) was 160%. The loss tangent LTb of the base layer at 30°C was 0.10.

[0109] [Comparative Example 1] Comparative Example 1 is a conventional tire having a tread composed of two layers, a cap layer and a base layer. In this Comparative Example 1, the radius Rc of the center contour line is set to 450 mm. The configuration of the base layer is the same as that of Example 1. In this Comparative Example 1, the loss tangent LTc of the cap layer at 30° C. was 0.22. The configuration other than the tread is the same as that of the first embodiment.

[0110] [Example 2] A tire of Example 2 was obtained in the same manner as in Example 1, except that the radius Rc of the center curved contour line was set as shown in Table 2 below. In Example 2, similarly to Example 1, the first middle land portion was the longest land portion, and the second shoulder land portion was the shortest land portion.

[0111] [Comparative Example 2] A tire of Comparative Example 2 was obtained in the same manner as in Example 2, except that a tread having the configuration shown in Fig. 6 was used. The tread of Comparative Example 2 includes a cap layer C, an intermediate layer M, and a base layer B. The materials of the cap layer C, the intermediate layer M, and the base layer B are the same as the materials of the cap layer, the intermediate layer, and the base layer of Example 1. In this comparative example 2, the intermediate layer M was laminated on the base layer B on the first end TE1 side, and the cap layer C was laminated on the base layer B on the second end TE2 side. The ratio (Wa / WH) of the axial distance Wa from the reference ground edge PH on the first end TE1 side to the boundary between the cap layer and the intermediate layer to the contact width WH of the reference ground surface was 68%. The ratio (Wa / WH) is shown in the "WM / WH" column in Table 1 below.

[0112] [Comparative Example 3] A tire of Comparative Example 3 was obtained in the same manner as in Example 2, except that a tread having the configuration shown in FIG. In this Comparative Example 3, the intermediate layer M was laminated on the base layer B. The first end TE1 side of this tread was composed of two layers, the intermediate layer M and the base layer B, and the second end TE2 side was composed of three layers, the cap layer C, the intermediate layer M, and the base layer B. The ratio (Wa / WH) of the axial distance Wa from the reference ground edge PH on the first end TE1 side to the boundary between the cap layer and the intermediate layer to the contact width WH of the reference ground surface was 68%. The ratio (Wa / WH) is shown in the "WM / WH" column in Table 1 below. In this Comparative Example 3, the first middle land portion was the longest land portion, and the second shoulder land portion was the shortest land portion, as in Example 2. The ratio of the thickness of the intermediate layer in the shortest land portion to the total thickness of the cap layer and the intermediate layer was the same as that in Example 2.

[0113] [Example 3] A tire of Example 3 was obtained in the same manner as in Example 1, except that the ratio (WM / WH) was set as shown in Table 2 below.

[0114] [Example 4-5] Tires of Examples 4 and 5 were obtained in the same manner as in Example 1, except that the thickness TL and the thickness TS were changed to make the ratio (TL / TS) as shown in Table 2 below.

[0115] [Rolling resistance coefficient (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 Tables 1 and 2 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: 19×7J Internal pressure: 210kPa Vertical load: 6.08kN

[0116] [Wet performance of new tires (WET-NEW)] A new prototype tire was mounted on a rim (size = 19 x 7J) and air was filled to adjust the internal pressure of the tire to 230 kPa. The tire was mounted on a test vehicle (a domestic SUV). The test vehicle was made to make a steady turn on a test course with a wet road surface (water film thickness = 1.4 mm), and the limit speed was measured. The results are shown in the "WET (NEW)" column of Tables 1 and 2 below, as an index with Comparative Example 1 set to 100. The higher the value, the higher the limit speed and the better the wet performance of the tire.

[0117] [Wet performance of worn tires (WET-OLD)] A new prototype tire was mounted on a rim (size = 19 x 7J), and air was filled to adjust the tire internal pressure to 230 kPa. The tire was mounted on a test vehicle (a domestic SUV). The test vehicle was driven on a test course with a dry asphalt road surface to wear down the tire tread. The tread was worn down until the groove depth of the circumferential groove reached 50% of the groove depth of the new tire. After that, the test vehicle was driven on a test course with a wet road surface (water film thickness = 1.4 mm) to make a steady turn and measure the limit speed. The results are shown in the "WET (OLD)" column of Tables 1 and 2 below, with Comparative Example 1 set to 100 as an index. The higher the value, the higher the limit speed and the better the wet performance of the tire.

[0118] [Table 1]

[0119] [Table 2]

[0120] As shown in Table 1-2, it has been confirmed that the examples can achieve improved wet performance while reducing rolling resistance. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0121] The technology described above that can achieve improved wet performance while reducing rolling resistance can be applied to various types of tires. [Explanation of symbols]

[0122] 2. Tires 4. Tread 6. Sidewall 24, 24s, 24m...Circumferential groove 26, 26s, 26m, 26c...Land 44 Cap layer 46. ​​Middle class 48...Base layer

Claims

1. A tire having a tread forming a tread surface, an orientation of the tread relative to a vehicle is specified; Of both ends of the tread, an end disposed on an inner side in a width direction of the vehicle is a first end, and an end disposed on an outer side is a second end, The tread includes a base layer, an intermediate layer located radially outwardly of the base layer and covering the base layer, and a cap layer located radially outwardly of the intermediate layer and covering the intermediate layer, the cap layer includes the tread surface, 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; At least three circumferential grooves are formed in the tread to define at least four land portions; the tire is mounted on a standard rim, the internal pressure of the tire is adjusted to the standard internal pressure, and the camber angle of the tire is set to −1°. A load of 50% of a standard load is applied to the tire, and the tire is brought into contact with a flat road surface, the contact surface being the reference contact surface; In the reference ground contact surface, the land portion with the longest contact length is the longest land portion, and the land portion with the shortest contact length is the shortest land portion, a ratio of a thickness of the intermediate layer at the longest land portion to a thickness of the intermediate layer at the shortest land portion is greater than 1.0 and is not greater than 3.5; tire.

2. The intermediate layer is thicker at the first end side and thinner at the second end side.

2. The tire of claim 1.

3. The tire is mounted on a standard rim, the internal pressure of the tire is adjusted to 230 kPa, and the camber angle of the tire is set to 0°. A load of 70% of a standard load is applied to the tire, and the tire is brought into contact with a flat road surface, and the contact surface obtained is the reference contact surface. Within the reference ground plane, the ratio of the axial width of the thick zone of the intermediate layer to the ground width of the reference ground plane is 40% or more and 100% or less.

3. The tire of claim 2.

4. In a meridian cross section of the tire in a state in which the tire is mounted on a regular rim, the internal pressure of the tire is adjusted to 230 kPa, and no load is applied to the tire, the contour of the tread surface is represented by a plurality of curved contour lines consisting of circular arcs and parallel to each other in the axial direction, A curved contour line located at a center among the plurality of curved contour lines is a center curved contour line, The radius of the center curved contour is 500 mm or more and 1000 mm or less. A tire according to any one of claims 1 to 3.

5. A ratio of a loss tangent at 30° C. of the cap layer to a loss tangent at 30° C. of the intermediate layer is 125% or more and 200% or less. A tire according to any one of claims 1 to 4.

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