Tire

Abstract

The invention provides a tire capable of suppressing increase of rolling resistance and suppressing generation of tread peeling. A tire (2) has a tread (4) and a belt (20). The end (BE) of the base layer (34) of the tread (4) is positioned axially inward of the end (20e) of the belt (20). The tread (4) includes a plurality of circumferential grooves (30), thereby constituting a plurality of land sections (32). The land sections (32) include crown land sections (32c), shoulder land sections (32s), and middle land sections (32m). The top layer ratio (ARc) of the crown land portion (32c) is 1.5 or more and 3.5 or less. The top layer ratio (ARm) of the middle land sections (32m) is equal to or greater than the top layer ratio (ARc) of the crown land sections (32c). The top layer ratio (ARs) of the shoulder land sections (32s) is greater than the top layer ratio (ARm) of the middle land sections (32m), and is 5.0-9.5 inclusive.

Description

Technical Field

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

[0002] For environmental considerations, in tires mounted on vehicles, it is required to reduce the rolling resistance. Therefore, studies have been made on reducing the number of elements constituting the tire, reducing the thickness of the elements, and using rubber having a low loss tangent value in the materials of the constituent elements (for example, Patent Document 1 below).

[0003] The tread of the tire contacts the road surface. The top layer wears out, and soon the base layer is exposed. In extreme driving (for example, when the vehicle turns at high speed), the shoulder portion of the tire (specifically, the tread portion) also contacts the road surface.

[0004] In extreme driving, a large load acts on the shoulder portion. The base layer is more brittle than the top layer. When the top layer wears out and the base layer is exposed, the tread may peel off. Therefore, various countermeasures have been taken for the tire so as not to cause the tread to peel off.

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-120242 Summary of the Invention

[0006] An object of the present invention is to provide a tire capable of suppressing an increase in rolling resistance and suppressing the occurrence of tread peeling.

[0007] A tire according to one embodiment of the present invention has a pair of bead portions, a carcass disposed between the pair of bead portions, a tread located radially outside the carcass, and a belt located between the tread and the carcass. The tread has a base layer and a top layer covering the entire base layer. The top layer is harder than the base layer. The loss tangent value of the base layer at 70°C is lower than the loss tangent value of the top layer at 30°C. The end portion of the base layer is located axially inside the end portion of the belt. The belt has an inner belt ply and an outer belt ply located radially outside the inner belt ply. The end portion of the outer belt ply is located axially inside the end portion of the inner belt ply. The tread has a tread pattern including a plurality of circumferential grooves, whereby a plurality of land portions arranged axially are formed on the tread. The plurality of land portions in a portion between the equatorial plane of the tire and the end portion of the tread include a crown land portion on the equatorial plane side, a shoulder land portion on the tread end side, and an intermediate land portion between the crown land portion and the shoulder land portion. The proportion ARc of the top layer in the crown land portion is represented by the average value of the ratio of the top layer thickness to the base layer thickness in the crown land portion, the proportion ARm of the top layer in the intermediate land portion is represented by the average value of the ratio of the top layer thickness to the base layer thickness in the intermediate land portion, and the proportion ARs of the top layer in the shoulder land portion is represented by the average value of the ratio of the top layer thickness to the base layer thickness in the shoulder land portion. The top layer proportion ARc of the crown land portion is 1.5 or more and 3.5 or less. The top layer proportion Arm of the intermediate land portion is equal to or greater than the top layer proportion ARc of the crown land portion. The top layer proportion ARs of the shoulder land portion is larger than the top layer proportion ARm of the intermediate land portion and is 5.0 or more and 9.5 or less.

[0008] According to the present invention, a tire can be obtained that can suppress an increase in rolling resistance and the occurrence of tread peeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a cross-sectional view showing a part of a tire according to one embodiment of the present invention.

[0010] Figure 2 is a developed view showing the tread pattern.

[0011] Figure 3 is a schematic view showing the ground contact shape of the tire.

[0012] Figure 4 is an enlarged cross-sectional view showing a part of the tire.

[0013] Figure 5 is an enlarged cross-sectional view showing a part of the tire.

[0014] Figure 6 is an enlarged cross-sectional view showing a part of a tire.

[0015] Figure 7 is a developed view showing a modified example of a tread pattern.

[0016] Figure 8 is an enlarged cross-sectional view showing a shoulder portion of an existing tire.

[0017] Figure 9 is an enlarged cross-sectional view showing a shoulder portion of another existing tire.

[0018] Reference Numeral Explanation

[0019] 2: Tire; 4: Tread; 12: Bead; 14: Carcass; 20: Belt; 24: Tread Surface; 30, 30s, 30m: Circumferential Groove; 32, 32s, 32m, 32c: Land; 32c1: First Portion of the Crown Land 32c; 32c2: Second Portion of the Crown Land 32c; 34: Base Layer; 36: Top Layer; 48, 50, 52: Belt Ply. Detailed Description of the Invention

[0020] The tire of the present invention is assembled to a rim. Air is filled inside the tire, and the internal pressure of the tire is adjusted. The tire assembled to the rim is also referred to as a tire-rim assembly. The tire-rim assembly has a rim and a tire assembled to the rim.

[0021] In the present invention, a state in which a tire is assembled to a regular rim, the internal pressure of the tire is adjusted to a regular internal pressure, and no load is applied to the tire is referred to as a regular state.

[0022] A state in which a tire is assembled to a regular rim, the internal pressure of the tire is adjusted to 250 kPa, and no load is applied to the tire is referred to as a standard state.

[0023] In the present invention, unless otherwise specified, the dimensions and angles of each part of the tire are measured in the regular state.

[0024] The dimensions and angles of each part in the meridian cross-section of the tire that cannot be measured in the state where the tire is assembled to the regular rim are measured in the cut surface of the tire obtained by cutting the tire along a plane including the rotation axis. In this measurement, the tire is set such that the distance between the left and right beads is the same as the distance between the beads in the tire assembled to the regular rim. In addition, the structure of the tire that cannot be confirmed in the state where the tire is assembled to the regular rim is confirmed in the aforementioned cut surface.

[0025] A regular rim refers to the rim specified in the tire specifications. The "standard rim" in the JATMA specifications, the "Design Rim" in the TRA specifications, and the "Measuring Rim" in the ETRTO specifications are regular rims.

[0026] The regular internal pressure refers to the internal pressure specified in the tire specifications. The "maximum air pressure" in the JATMA specifications, the "maximum value" described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA specifications, and the "INFLATION PRESSURE" in the ETRTO specifications are regular internal pressures.

[0027] The regular load refers to the load determined in the tire specifications. The "maximum load capacity" in the JATMA specifications, the "maximum value" described in "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA specifications, and the "LOAD CAPACITY" in the ETRTO specifications are regular loads.

[0028] In the present invention, the "nominal section width" is the "nominal section width" included in the "tire nominal" specified in JIS D4202 "Automobile Tires - Nominal Methods and Specifications".

[0029] In the present invention, the load index (LI) is, for example, an index that represents the maximum mass, i.e., the maximum load capacity, that allows a load to be applied to the tire under specified conditions as specified in the JATMA specifications.

[0030] In the present invention, among the elements constituting the tire, the hardness of the elements made of crosslinked rubber is measured using a Type A durometer under the temperature condition of 23°C in accordance with the provisions of JIS K6253.

[0031] In the present invention, among the elements constituting the tire, the loss tangent value (tanδ) of the elements made of crosslinked rubber is measured using a viscoelastic spectrometer in accordance with the provisions of JIS K6394. The measurement conditions are as follows.

[0032] Initial strain = 10%

[0033] Dynamic strain = ±1%

[0034] Frequency = 10 Hz

[0035] Mode = elongation mode

[0036] Temperature = 30°C or 70°C

[0037] In this measurement, the test piece (length 40 mm × width 4 mm × thickness 1 mm) is sampled from a tire. The length direction of the test piece is the same as the circumferential direction of the tire. In the case where it is impossible to sample a test piece from the tire, a test piece is sampled from a sheet-like crosslinked rubber (hereinafter also referred to as a rubber sheet) obtained by pressing and heating a rubber composition for forming an element to be measured at a temperature of 170 °C for 12 minutes.

[0038] In the present invention, the tread portion of a tire refers to the portion of the tire that contacts the road surface. The bead portion refers to the portion of the tire that is fitted to the rim. The sidewall portion refers to the portion of the tire that bridges between the tread portion and the bead portion. A tire has a tread portion, a pair of bead portions, and a pair of sidewall portions as parts.

[0039] The portion at the end of the tread portion is also referred to as the shoulder portion. The portion of the equatorial plane of the tread portion, that is, the central portion, is also referred to as the crown portion.

[0040] [Insight underlying the present invention]

[0041] Figure 8 A part of an existing tire 2a is shown. The tread 4a of this tire 2a has a top layer 36a and a base layer 34a. As Figure 8 shown, the end BEa of the base layer 34a coincides with the end CEa of the top layer 36a.

[0042] Figure 9 The shoulder portion of another existing tire 2b is shown. In this tire 2b, the end BEb of the base layer 34b is located axially inside the end CEb of the top layer 36b. In this tire 2b, compared with the tire 2a Figure 8 shown, the top layer 36b covering the portion of the end BEb of the base layer 34b is thicker. In the shoulder portion, the base layer 34b of this tire 2b is Figure 8 less likely to be exposed compared to the base layer 34a of the tire 2a shown. The tread 4b of this tire 2b is less likely to peel off compared to the tread 4a of the tire 2a.

[0043] In consideration of the environmental impact, electric vehicles are becoming popular. Electric vehicles are equipped with batteries. A battery capable of traveling a distance of about 500 km is heavy. Therefore, electric vehicles tend to be heavier than conventional gasoline vehicles. A higher load acts on the tires installed on electric vehicles than on the tires installed on gasoline vehicles.

[0044] As described above, Figure 9 the tread 4b of the tire 2b shown is less likely to peel off compared to the tread 4a of the tire 2a Figure 8 shown. However, since electric vehicles are heavier than conventional gasoline vehicles, the tread 4b may also peel off in the tire 2b in which a tread peeling countermeasure has been implemented.

[0045] Therefore, the present inventors considered the installation on an electric vehicle and studied a technique capable of minimizing the influence on other performances (such as rolling resistance) and suppressing the peeling of the tread, thereby completing the invention described below.

[0046] [Summary of Embodiment of the Present Invention]

[0047] The present invention relates to a tire having a pair of bead portions, a carcass stretched between the pair of bead portions, a tread located radially outside the carcass, and a belt located between the tread and the carcass. The tread has a base layer and a top layer covering the entire base layer. The top layer is harder than the base layer. The loss tangent value of the base layer at 70 °C is lower than the loss tangent value of the top layer at 30 °C. The end portion of the base layer is located axially inside the end portion of the belt. The belt has an inner belt ply and an outer belt ply located radially outside the inner belt ply. The end portion of the outer belt ply is located axially inside the end portion of the inner belt ply. The tread has a tread pattern including a plurality of circumferential grooves, whereby a plurality of land portions arranged axially are formed on the tread. The plurality of land portions in a portion between the equatorial plane of the tire and the end portion of the tread include a crown land portion on the equatorial plane side, a shoulder land portion on the tread end side, and an intermediate land portion between the crown land portion and the shoulder land portion. The proportion ARc of the top layer in the crown land portion is represented by the average value of the ratio of the top layer thickness to the base layer thickness in the crown land portion. The proportion ARm of the top layer in the intermediate land portion is represented by the average value of the ratio of the top layer thickness to the base layer thickness in the intermediate land portion. The proportion ARs of the top layer in the shoulder land portion is represented by the average value of the ratio of the top layer thickness to the base layer thickness in the shoulder land portion. The top layer proportion ARc of the crown land portion is 1.5 or more and 3.5 or less. The top layer proportion Arm of the intermediate land portion is equal to or greater than the top layer proportion ARc of the crown land portion. The top layer proportion ARs of the shoulder land portion is larger than the top layer proportion ARm of the intermediate land portion and is 5.0 or more and 9.5 or less.

[0048] The tire of the present invention can suppress an increase in rolling resistance and can suppress the occurrence of tread peeling. The mechanism for exerting such an effect is not yet clear, but it is speculated as follows.

[0049] In this tire, the end portion of the base layer is located axially inside the end portion of the belt. In this tire, compared with existing tires, the top layer covering the end portion of the base layer is thicker. In the shoulder portion, the base layer is not easily exposed. In extreme driving where a large load acts on the shoulder portion, the tread is not easily peeled.

[0050] In this tire, the proportion of the base layer in the shoulder land portion is low. The top layer is harder than the base layer. Therefore, it is possible that the rolling resistance increases, the riding comfort decreases, the road surface noise increases, and the quietness decreases.

[0051] However, in this tire, the top layer ratio ARc of the crown land portion is 1.5 or more and 3.5 or less, the top layer ratio Arm of the intermediate land portion is equal to or greater than the top layer ratio ARc of the crown land portion, and the top layer ratio ARs of the shoulder land portion is greater than the top layer ratio ARm of the intermediate land portion and is 5.0 or more and 9.5 or less. In other words, the proportion of the base layer in the land portion is low in the shoulder land portion and high in the crown land portion and the intermediate land portion. The base layer is softer than the top layer and is not easily heated. The crown land portion and the intermediate land portion with a high proportion of the base layer can help suppress the increase in rolling resistance, the decrease in riding comfort, and the decrease in quietness.

[0052] This tire can suppress the increase in rolling resistance, the decrease in riding comfort, and the decrease in quietness, and can suppress the occurrence of tread peeling.

[0053] Preferably, the position of the end of the top layer coincides axially with the position of the end of the belt, or the end of the top layer is located axially outside the end of the belt.

[0054] In this case, the end of the base layer is covered by the top layer with sufficient thickness. In the shoulder portion, the base layer is not easily exposed. In extreme driving where a large load acts on the shoulder portion, the tread is not easily peeled off. This tire can effectively suppress the occurrence of tread peeling.

[0055] Preferably, the tire is assembled on a regular rim, the internal pressure of the tire is adjusted to 250 kPa, the camber angle of the tire is set to 0 degrees, a longitudinal load is applied to the tire, and the contact surface obtained when the tire contacts a road surface composed of a plane is a standard contact surface. The longitudinal load applied to the tire is 60% or more and 80% or less of the load indicated by the load index of the tire. The grounding width of the standard contact surface is 70% or more and 80% or less of the nominal cross-sectional width of the tire. The ratio of the total width of the plurality of circumferential grooves included in the standard contact surface to the grounding width of the standard contact surface is 20% or more and 30% or less.

[0056] In this case, the responsiveness, riding comfort, and quietness can be adjusted evenly. This tire can suppress the increase in rolling resistance, the decrease in responsiveness, the decrease in riding comfort, and the decrease in quietness, and can suppress the occurrence of tread peeling.

[0057] Preferably, the tread pattern includes four circumferential grooves, thereby forming five land portions on the tread. The five land portions are the crown land portion located on the equatorial plane, a pair of intermediate land portions located axially outside the crown land portion, and a pair of shoulder land portions located axially outside each intermediate land portion. The ratio of the width of the crown land portion to the grounding width of the standard contact surface is 14% or more and 16% or less.

[0058] In this case, a crown land portion with an appropriate width is formed. In a four-wheel vehicle (such as a passenger car) equipped with this tire, a higher lateral force resistance is generated in the front-wheel tires than in existing tires. This tire can suppress a decrease in responsiveness and effectively suppress an increase in rolling resistance and the occurrence of tread peeling.

[0059] Preferably, among the two ends of the tread, one end configured on the inner side in the vehicle width direction when the tire is mounted on the vehicle is the first reference end, and the other end is the second reference end. The width of the shoulder land portion on the first reference end side is 90% or more and 100% or less of the width of the crown land portion. The width of the intermediate land portion on the first reference end side is 90% or more and 100% or less of the width of the crown land portion. The width of the intermediate land portion on the second reference end side is 97% or more and 107% or less of the width of the crown land portion. The width of the shoulder land portion on the second reference end side is 114% or more and 124% or less of the width of the crown land portion.

[0060] In this case, compared with existing tires, the ratio of the lateral force resistance of the rear-wheel tires to the lateral force resistance of the front-wheel tires can be effectively increased. This tire can achieve an improvement in linearity and effectively suppress an increase in rolling resistance and the occurrence of tread peeling.

[0061] Preferably, the first reference end side across the equatorial plane in the crown land portion is the first part, and the second reference end side is the second part. The ratio of the width of the second part to the width of the crown land portion is 51% or more and 55% or less.

[0062] In this case, compared with existing tires, this tire can effectively increase the lateral force resistance generated in the front-wheel tires and can effectively increase the ratio of the lateral force resistance of the rear-wheel tires to the lateral force resistance of the front-wheel tires. This tire can achieve an improvement in responsiveness and linearity and can effectively suppress an increase in rolling resistance and the occurrence of tread peeling.

[0063] [Details of the Embodiments of the Present Invention]

[0064] Hereinafter, with appropriate reference to the drawings, the present invention will be described in detail based on preferred embodiments.

[0065] Figure 1 Shows a part of a tire 2 according to an embodiment of the present invention. The tire 2 is a pneumatic tire for a passenger car. Figure 1 The tire 2 is new. The tread 4 has not been worn.

[0066] Figure 1 Shows a part of a cross-section of the tire 2 along a plane including the rotation axis (not shown) of the tire 2. Figure 1 The cross-section shown is also referred to as 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 refers to the 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 Figure 1 the paper surface of is the circumferential direction of the tire 2.

[0067] In Figure 1 , the single-dot chain line EL extending in the radial direction represents the equatorial plane of the tire 2.

[0068] In Figure 1 , the tire 2 is assembled to a rim R. For example, air is filled between the tire 2 and the rim R, and the internal pressure of the tire 2 is adjusted. The rim R is a standard rim.

[0069] In Figure 1 , the solid line BBL extending in the axial direction is the bead base line. The bead base line BBL is a line that defines the rim diameter of the rim R (refer to JATMA, etc.).

[0070] In Figure 1 , the position indicated by the reference numeral Eq is the intersection of the outer surface 2G of the tire 2 (specifically, the tread surface described later) and the equatorial plane EL. The intersection Eq is the equator of the tire 2.

[0071] When the groove is located on the equatorial plane EL, the equator Eq is determined based on the imaginary outer surface obtained by assuming that there are no grooves or other irregularities. The equator Eq is the radially outer end of the tire 2.

[0072] In Figure 1 , the position indicated by the reference numeral PW is the axially outer end of the tire 2 (hereinafter referred to as the outer end PW). When there are patterns, letters, etc. on the outer surface 2G, the outer end PW is determined based on the imaginary outer surface obtained by assuming that there are no decorations. The axial distance from one outer end PW to the other outer end PW determined in the normal state of the tire 2 is the cross-sectional width of the tire 2 (refer to JATMA, etc.).

[0073] In the present invention, the "nominal section width" is the "nominal section width" included in the "tire nominal" specified in JIS D4202 "Automobile Tires - Nominal Methods and Dimensions". For example, when the tire size shown in the "tire nominal" of tire 2 is 245 / 50R19, the nominal section width of tire 2 is 245 mm.

[0074] The nominal section width of the tire (i.e., tire 2) which is the object of the present invention is 215 mm or more and 325 mm or less. The load index (LI) of the tire 2 is 90 or more.

[0075] The tire 2 has a tread 4, a pair of sidewalls 6, a pair of wings 8, a pair of bead edges 10, a pair of beads 12, a carcass 14, an inner liner 16, a pair of chafer plies 18, a belt 20, and a cap ply 22.

[0076] The tread 4 is located radially outside the carcass 14. The tread 4 is made of crosslinked rubber. In Figure 1 the position indicated by the reference numeral Te is the end of the tread 4.

[0077] In the present invention, among the two ends Te of the tread 4, the end Te disposed on the inner side in the vehicle width direction by mounting the tire 2 on a vehicle (not shown) is the first reference end Te1, and the other end Te is the second reference end Te2. In Figure 1 the end Te of the tread 4 on the side of arrow AD1 is the first reference end Te1, which is disposed on the inner side in the vehicle width direction by mounting the tire 2 on a vehicle. Although not shown, the end Te of the tread 4 on the side of arrow AD2 is the second reference end Te2, which is disposed on the outer side in the vehicle width direction by mounting the tire 2 on a vehicle.

[0078] The tread 4 contacts the road surface on the tread surface 24. The tread 4 has a tread surface 24.

[0079] The side surface 26 is connected 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 the equator Eq, and each side surface 26 includes the maximum width position PW.

[0080] Although not described in detail, in the meridian cross-section, the profile of the tread surface 24 is represented by the profile of a hypothetical tread surface obtained by assuming no irregularities such as grooves. The profile of the tread surface 24, i.e., the profile of the hypothetical tread surface, includes a plurality of circular arcs, which are combined in such a way that adjacent circular arcs are tangent to each other.

[0081] Among the plurality of circular arcs constituting the profile of the tread surface 24, the circular arc located outermost axially has the smallest radius. The side surface 26 is connected to the circular arc having the smallest radius.

[0082] Grooves 28 are engraved on the tread 4. Thus, a tread pattern is formed.

[0083] The tread pattern has a plurality of circumferential grooves 30 extending continuously in the circumferential direction. Thus, a plurality of land portions 32 arranged axially are formed on the tread 4. The land surfaces of the land portions 32 are included in the tread surface 24.

[0084] Figure 2 It is a developed view showing a part of the tread surface 24. The direction indicated by the double arrow AD is the axial direction of the tire 2. The direction indicated by the double arrow CD is the circumferential direction of the tire 2. In Figure 2 it, the direction indicated by the arrow AD1 is the first reference end Te1 side, and the direction indicated by the arrow AD2 is the second reference end Te2 side.

[0085] In this Figure 2 it, for the sake of convenience of explanation, the grooves other than the circumferential grooves 30 are not shown. The tread 4 of this tire 2 is not limited to the tread 4 having only the circumferential grooves 30. Transverse grooves and sipes extending substantially in the axial direction may also be engraved on this tread 4.

[0086] The tread pattern of this tire 2 has 4 circumferential grooves 30 arranged axially. The groove depth of each circumferential groove 30 is 5.0 mm or more and 7.5 mm or less. The groove width of the circumferential groove 30 is 5.0 mm or more and 20.0 mm or less.

[0087] Among the 4 circumferential grooves 30, the two circumferential grooves 30 located outermost axially are the shoulder circumferential grooves 30s. The two circumferential grooves 30 located axially inside the shoulder circumferential grooves 30s are the intermediate circumferential grooves 30m. The tread pattern of this tire 2 includes a pair of shoulder circumferential grooves 30s and a pair of intermediate circumferential grooves 30m located between the pair of shoulder circumferential grooves 30s. In this tire 2, at least one circumferential groove may also be provided between the pair of intermediate circumferential grooves 30m.

[0088] In this tire 2, among the two intermediate circumferential grooves 30m, the intermediate circumferential groove 30m located on the first reference end Te1 side is the first intermediate circumferential groove 30m1, and the intermediate circumferential groove 30m located on the second reference end Te2 side is the second intermediate circumferential groove 30m2.

[0089] Among the two shoulder circumferential grooves 30s, the shoulder circumferential groove 30s located on the first reference end Te1 side is the first shoulder circumferential groove 30s1, and the shoulder circumferential groove 30s located on the second reference end Te2 side is the second shoulder circumferential groove 30s2.

[0090] As described above, the tread pattern of this tire 2 has 4 circumferential grooves 30 arranged axially. Thus, 5 land portions 32 extending in the circumferential direction are formed. The edges of the circumferential grooves 30 are also the edges of the land portions 32.

[0091] Of the five land portions 32 arranged axially, the two outermost land portions 32 are the shoulder land portions 32s. The shoulder land portions 32s include the grounding ends SEs of the standard ground contact surface described later. The two land portions 32 axially inside the shoulder land portions 32s are the intermediate land portions 32m. The land portion 32 between the two intermediate land portions 32m is the crown land portion 32c. The crown land portion 32c of the tire 2 includes the equator Eq.

[0092] In this tread pattern, the four circumferential grooves 30 are symmetrically arranged with respect to the equatorial plane EL. Therefore, the five land portions 32 are also symmetrically arranged with respect to the equatorial plane EL.

[0093] The five land portions 32 constituting the tread 4 are the crown land portion 32c located on the equatorial plane EL, a pair of intermediate land portions 32m axially outside the crown land portion 32c, and a pair of shoulder land portions 32s axially outside each intermediate land portion 32m.

[0094] As Figure 1 shown, in the tire 2, the portions of the multiple land portions 32 between the equatorial plane EL and the end Te of the tread 4 include the crown land portion 32c on the equatorial plane EL side, the shoulder land portion 32s on the end Te side of the tread 4, and the intermediate land portion 32m between the crown land portion 32c and the shoulder land portion 32s.

[0095] Although not shown, for example, a circumferential groove 30 may also be provided between a pair of intermediate circumferential grooves 30m to form two crown land portions 32c. In this case, the circumferential groove 30 between the two crown land portions 32c is also referred to as the crown circumferential groove. In this case, the multiple land portions 32 constituting the tread 4 also include, in the portion between the equatorial plane EL and the end Te of the tread 4, the crown land portion 32c on the equatorial plane EL side, the shoulder land portion 32s on the end Te side of the tread 4, and the intermediate land portion 32m between the crown land portion 32c and the shoulder land portion 32s. The crown land portion 32c does not include the equator Eq, but the crown circumferential groove is located on the equatorial plane EL.

[0096] In the tire 2, of the two intermediate land portions 32m, the intermediate land portion 32m on the first reference end Te1 side is the first intermediate land portion 32m1, and the intermediate land portion 32m on the second reference end Te2 side is the second intermediate land portion 32m2.

[0097] Of the two shoulder land portions 32s, the shoulder land portion 32s on the first reference end Te1 side is the first shoulder land portion 32s1, and the shoulder land portion 32s on the second reference end Te2 side is the second shoulder land portion 32s2.

[0098] The width of the tread portion 32 of the tread 4, excluding the shoulder tread portion 32s, is represented by the axial distance from one edge of the tread portion 32 to the other edge. The width of the shoulder tread portion 32s is represented by the axial distance from the edge on the equatorial plane EL side of the shoulder tread portion 32s to the grounding end SEs of the standard grounding surface.

[0099] In the case where the edges of the tread portion 32 are formed with chamfers such as circles, the intersection of the extension line of the tread surface of the tread portion 32 and the extension line of the wall surface of the tread portion 32 is taken as the edge of the tread portion 32 to represent the width of the tread portion 32. The extension line of the tread surface is the contour of the tread surface 24. The extension line of the wall surface is represented by the tangent line of the wall surface with the boundary between the wall surface and the chamfered portion as the tangent point.

[0100] In Figure 2 the length indicated by the double arrow WC is the width of the crown tread portion 32c. In this tire 2, the equatorial plane EL intersects the crown tread portion 32c at the center of the width WC of the crown tread portion 32c.

[0101] In Figure 2 the length indicated by the double arrow WM1 is the width of the first intermediate tread portion 32m1. The length indicated by the double arrow WM2 is the width of the second intermediate tread portion 32m2. In this tire 2, the width WM1 of the first intermediate tread portion 32m1 is the same as the width WM2 of the second intermediate tread portion 32m2.

[0102] In Figure 2 the length indicated by the double arrow WS1 is the width of the first shoulder tread portion 32s1. The length indicated by the double arrow WS2 is the width of the second shoulder tread portion 32s2. In this tire 2, the width WS1 of the first shoulder tread portion 32s1 is the same as the width WS2 of the second shoulder tread portion 32s2.

[0103] Figure 3 Schematically shows the shape of the grounding surface of the tire 2. In Figure 3 the direction indicated by the double arrow ADe corresponds to the axial direction of the tire 2. The direction indicated by the double arrow CDe corresponds to the circumferential direction of the tire 2. In Figure 3 the direction indicated by the arrow ADe1 is the side of the first reference end Te1, and the direction indicated by the arrow ADe2 is the side of the second reference end Te2.

[0104] The grounding surface is obtained, for example, using a grounding surface shape measuring device (not shown). The grounding surface is obtained by assembling the tire 2 on the rim R in this device, adjusting the internal pressure of the tire 2, and applying a longitudinal load to the tire 2 so that the tire 2 contacts the road surface composed of a plane. When obtaining the grounding surface, the tire 2 is arranged with its rotation axis parallel to the road surface. In this tire 2, the above longitudinal load is applied in the direction perpendicular to the road surface. In other words, in a state where the camber angle of the tire 2 is set to 0°, a longitudinal load is applied to the tire 2.

[0105] Although not described in detail, an image of the contact surface formed by bringing the tire 2 into contact with a flat surface is obtained by a known method. Based on the obtained image, the contour of the contact surface is determined.

[0106] The contour of the contact surface, that is, the contact surface shape of the contact surface, is obtained by tracing the periphery of the contact surface in the image of the contact surface.

[0107] In the present invention, the tire 2 is assembled on a regular rim, the internal pressure of the tire 2 is adjusted to 250 kPa, the camber angle of the tire 2 is set to 0 degrees, and a longitudinal load is applied to the tire 2 and the tire 2 is brought into contact with a road surface composed of a flat surface to obtain a standard contact surface. When obtaining the standard contact surface, the longitudinal load applied to the tire 2 is 60% or more and 80% or less of the load indicated by the load index of the tire 2.

[0108] In Figure 3 the positions indicated by the reference numeral SEs are the grounding ends of the standard contact surface. Among the two grounding ends SEs, the grounding end SEs on the arrow ADe1 side is the first grounding end SEs1, and the grounding end SEs on the arrow ADe2 side is the second grounding end SEs2. The first grounding end SEs1 side corresponds to the first reference end Te1 side described above, and the second grounding end SEs2 side corresponds to the second reference end Te2 side described above.

[0109] As Figure 3 shown, the standard contact surface includes the contact surface corresponding to the land portion 32, specifically, the contact surfaces of the crown land portion 32c, the two intermediate land portions 32m, and the two shoulder land portions 32s. The contact surfaces corresponding to the land portion 32 between two adjacent ones correspond to the circumferential grooves 30. Therefore, the standard contact surface includes a plurality of circumferential grooves 30, specifically, two intermediate circumferential grooves 30m and two shoulder circumferential grooves 30s.

[0110] The tread 4 has a base layer 34 and a top layer 36. The tread 4 of the tire 2 is composed of the base layer 34 and the top layer 36 arranged radially.

[0111] As Figure 1 shown, the base layer 34 is laminated on the belt 22. The whole of the base layer 34 is covered by the top layer 36. The base layer 34 is made of a crosslinked rubber with low heat generation.

[0112] The top layer 36 is located radially outside the base layer 34. The top layer 36 includes the above-mentioned tread surface 24. The top layer 36 is in contact with the road surface. The top layer 36 is made of a crosslinked rubber considering wear resistance and grip performance.

[0113] In Figure 1The position indicated by reference numeral BE is the end of the base layer 34. The length indicated by the double arrow WTB is the width of the base layer 34. The width WTB of the base layer 34 is the axial distance from one end BE of the base layer 34 to the other end BE. The position indicated by reference numeral CE is the end of the top layer 36. The length indicated by the double arrow WTC is the width of the top layer 36. The width WTC of the top layer 36 is the axial distance from one end CE of the top layer 36 to the other end CE.

[0114] In this tire 2, the end CE of the top layer 36 is located axially outside the end BE of the base layer 34. The width WTC of the top layer 36 is wider than the width WTB of the base layer 34.

[0115] The end CE of the top layer 36 is the end Te of the tread 4. The width of the tread 4 is represented by the width WTC of the top layer 36.

[0116] In this tire 2, the top layer 36 is harder than the base layer 34. Specifically, the hardness of the top layer 36 is 60 or more and 70 or less, and the hardness of the base layer 34 is 50 or more and 65 or less. The difference in hardness between the top layer 36 and the base layer 34 is 10 or more and 20 or less.

[0117] The measurement temperature of the loss tangent value of the base layer 34 is 70 °C. The loss tangent value of the base layer 34 at 70 °C is 0.02 or more and 0.10 or less.

[0118] The measurement temperature of the loss tangent value of the top layer 36 is 30 °C. The loss tangent value of the top layer 36 at 30 °C is 0.12 or more and 0.40 or less.

[0119] The loss tangent value of the base layer 34 at 70 °C is lower than the loss tangent value of the top layer 36 at 30 °C. The ratio of the loss tangent value of the base layer 34 at 30 °C to the loss tangent value of the top layer 36 at 70 °C is 0.10 or more and 0.38 or less.

[0120] Each sidewall 6 is located radially inside the tread 4. The sidewall 6 is located axially outside the carcass 14. The sidewall 6 includes the aforementioned maximum width position PW. The sidewall 6 is made of crosslinked rubber considering cut resistance.

[0121] Each wing 8 is located between the tread 4 and the sidewall 6. The tread 4 and the sidewall 6 are joined via the wing 8. The wing 8 is made of crosslinked rubber considering adhesiveness.

[0122] Each bead heel 10 is located radially inside the sidewall 6. The bead heel 10 contacts the rim R. The bead heel 10 is made of crosslinked rubber considering wear resistance.

[0123] Each bead 12 is located radially inside the sidewall 6. The bead 12 is located axially inside the bead heel 10.

[0124] The bead 12 has a core 38 and a chafer 40. The core 38 extends circumferentially. Although not shown, the core 38 includes steel wire. The chafer 40 is located radially outside the core 38. The chafer 40 tapers outwardly. The chafer 40 is made of crosslinked rubber having high rigidity.

[0125] The carcass 14 is located inside the tread 4, a pair of sidewalls 6, and a pair of bead heels 10. The carcass 14 is stretched between a pair of beads 12.

[0126] The carcass 14 includes at least one carcass ply 42. The carcass 14 of the tire 2 is composed of two carcass plies 42. Inside the tread 4 in the radial direction, the carcass ply 42 located on the inner surface 2N side of the tire 2 is the first carcass ply 44, and the carcass ply 42 located outside the first carcass ply 44 is the second carcass ply 46.

[0127] As Figure 1 shown, the two carcass plies 42 are each folded back from the axially inner side to the outer side at their respective beads 12. The end 44e of the first carcass ply 44 is located radially outside the maximum width position PW. The end 46e of the second carcass ply 46 is located between the chafer 40 and the folded-back first carcass ply 44.

[0128] Although not shown, the carcass ply 42 includes a plurality of carcass cords arranged side by side. These carcass cords cross the equatorial plane EL. The carcass 14 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.

[0129] The innerliner 16 is located inside the carcass 14. The innerliner 16 forms the inner surface 2N of the tire 2. The innerliner 16 is made of crosslinked rubber having excellent air barrier properties. The innerliner 16 maintains the internal pressure of the tire 2.

[0130] Each bead filler 18 is located radially inside the bead 12. The bead filler 18 contacts the rim R. The bead filler 18 of the tire 2 is composed of cloth and rubber impregnated in the cloth.

[0131] As Figure 1 shown, the inner end of the bead filler 18 forms a part of the inner surface 2N of the tire. The outer end of the bead filler 18 is located radially outside its inner end. The outer end of the bead filler 18 is located between the folded-back first carcass ply 44 and the bead heel 10.

[0132] The belt 20 is located radially between the tread 4 and the carcass 14. The belt 20 is laminated on the carcass 14.

[0133] The above-mentioned equatorial plane EL intersects the belt 20 at the center of the width of the belt 20. Both ends 20e of the belt 20 are arranged so as to face each other across the equatorial plane EL.

[0134] The belt 20 has a plurality of belt plies 48 arranged radially. The innermost belt ply 48 among the plurality of belt plies 48 is the inner belt ply 50, and the outermost belt ply 48 is the outer belt ply 52. The belt 20 has an inner belt ply 50 and an outer belt ply 52. The outer belt ply 52 is located radially outside the inner belt ply 50.

[0135] The belt 20 of the tire 2 is composed of two belt plies 48. Specifically, the belt 20 is composed of an inner belt ply 50 and an outer belt ply 52.

[0136] The inner belt ply 50 is laminated on the carcass 14 radially inside the tread 4. The outer belt ply 52 is laminated on the inner belt ply 50.

[0137] In Figure 1 the double arrow WBU is the width of the inner belt ply 50. The width WBU of the inner belt ply 50 is the axial distance from one end 50e to the other end 50e of the inner belt ply 50. The double arrow WBS is the width of the outer belt ply 52. The width WBS of the outer belt ply 52 is the axial distance from one end 52e to the other end 52e of the outer belt ply 52.

[0138] Although not shown, each of the plurality of belt plies 48 constituting the belt 20 contains a plurality of belt cords arranged side by side. The belt cords are steel cords.

[0139] Each belt cord is inclined with respect to the equatorial plane EL. The inclination direction of the belt cords contained in the outer belt ply 52 is opposite to the inclination direction of the belt cords contained in the inner belt ply 50.

[0140] As Figure 1 shown, the end 52e of the outer belt ply 52 is located axially inside the end 50e of the inner belt ply 50. The length from the end 52e of the outer belt ply 52 to the end 50e of the inner belt ply 50 is 3 mm or more and 10 mm or less.

[0141] The width WBS of the outer belt ply 52 is narrower than the width WBU of the inner belt ply 50. In other words, the inner belt ply 50 is the belt ply 48 with the widest width among the belt plies 48 constituting the belt 20. The width of the belt 20 is represented by the width WBU of the wide inner belt ply 50. The end 50e of the inner belt ply 50 is the end 20e of the belt 20.

[0142] In the tire 2, the width WBU of the inner belt ply 50, which is also the width WBU of the belt 20, is 40% or more and 65% or less of the sectional width of the tire 2.

[0143] The crown belt 22 is located radially between the tread 4 and the belt 20. The end 22e of the crown belt 22 is located axially inside the end Te of the tread 4. The entire crown belt 22 is covered by the tread 4.

[0144] The crown belt 22 is laminated on the belt 20. The end 22e of the crown belt 22 is located axially outside the end 20e of the belt 20. The length from the end 20e of the belt 20 to the end 22e of the crown belt 22 is 3 mm or more and 7 mm or less.

[0145] The above-mentioned equatorial plane EL intersects the crown belt 22 at the center of the width of the crown belt 22. The two ends 22e of the crown belt 22 are respectively arranged in a manner of being opposite to each other across the equatorial plane EL. The crown belt 22 is a full crown belt. The crown belt 22 may also be a pair of edge crown belts that are axially separated across the equatorial plane EL and configured to cover the end 20e of the belt 20. The crown belt 22 may also be composed of a full crown belt and a pair of edge crown belts.

[0146] Although not shown, the crown belt 22 includes crown belt cords wound in a spiral shape. In the crown belt 22, the crown belt cords extend substantially in the circumferential direction. Specifically, the angle formed by the crown belt cords with respect to the circumferential direction is 5° or less. The crown belt 22 has a seamless structure. Cords made of organic fibers are used as the crown belt cords. Examples of the organic fibers include nylon fibers, rayon fibers, polyester fibers, and aramid fibers.

[0147] As Figure 1 shown, in the meridian cross-section, the base layer 34 and the top layer 36 constituting the tread 4 extend in layers along the tread surface 24.

[0148] In the tire 2, the thickness of each layer constituting the tread 4 is represented by the length along the normal line of the outer surface 2G (specifically, the tread surface 24) of the tire 2 in the meridian cross-section of the tire 2. The normal line is determined based on the contour of the tread surface 24 and is also called the thickness reference line.

[0149] Figure 4 Shows Figure 1 a part of the tire 2 shown in Figure 4 Shows the cross-section of the crown land 32c. The position indicated by the reference numeral PCe is the edge of the crown land 32c. The edge PCe is the intersection point of the extension line of the land surface, that is, the contour OL of the tread surface 24 and the extension line LCe of the wall surface. The straight line ECL is the line segment connecting the edge PCe on the first reference end Te1 side and the edge PCe on the second reference end Te2 side of the crown land 32c.

[0150] In Figure 4 it, the straight lines LC1, LC2, and LC3 are the thickness reference lines of the crown land portion 32c. The reference numerals PC1, PC2, and PC3 are the positions that divide the line segment ECL connecting the edge PCe on the first reference end Te1 side and the edge PCe on the second reference end Te2 side of the crown land portion 32c into four equal parts. The thickness reference line LC1 passes through the position PC1, the thickness reference line LC2 passes through the position PC2, and the thickness reference line LC3 passes through the position PC3. The thickness reference line LC2 of the tire 2 coincides with the equatorial plane EL.

[0151] The length indicated by the double arrow CC1 along the thickness reference line LC1 is the thickness of the top layer 36 at the position PC1. The length indicated by the double arrow BC1 is the thickness of the base layer 34 at the position PC1. The ratio CC1 / BC1 of the thickness CC1 of the top layer 36 to the thickness BC1 of the base layer 34 is the top layer thickness ratio ARc1 at the position PC1.

[0152] The length indicated by the double arrow CC2 along the thickness reference line LC2 is the thickness of the top layer 36 at the position PC2. The length indicated by the double arrow BC2 is the thickness of the base layer 34 at the position PC2. The ratio CC2 / BC2 of the thickness CC2 of the top layer 36 to the thickness BC2 of the base layer 34 is the top layer thickness ratio ARc2 at the position PC2.

[0153] The length indicated by the double arrow CC3 along the thickness reference line LC3 is the thickness of the top layer 36 at the position PC3. The length indicated by the double arrow BC3 is the thickness of the base layer 34 at the position PC3. The ratio CC3 / BC3 of the thickness CC3 of the top layer 36 to the thickness BC3 of the base layer 34 is the top layer thickness ratio ARc3 at the position PC3.

[0154] In the tire 2, the proportion ARc of the top layer 36 in the crown land portion 32c is represented by the average value of the ratio CC / BC of the thickness CC of the top layer to the thickness BC of the base layer in the crown land portion 32c. Specifically, the top layer proportion ARc is represented by the average value of the top layer thickness ratio CC1 / BC1 at the position PC1, the top layer thickness ratio CC2 / BC2 at the position PC2, and the top layer thickness ratio CC3 / BC3 at the position PC3.

[0155] Figure 5 It shows Figure 1 a part of the tire 2 shown. Figure 5The cross-section of the intermediate land portion 32m is shown. The position indicated by the label PMe is the edge of the intermediate land portion 32m. The edge PMe is the intersection point of the extension line of the land surface, that is, the contour OL of the tread surface 24 and the extension line LMe of the wall surface. The straight line EML is the line segment connecting the edge PMe on the equatorial plane EL side of the intermediate land portion 32m and the edge PMe on the end Te side of the tread 4.

[0156] In Figure 5 the straight lines LM1, LM2, and LM3 are the thickness reference lines of the intermediate land portion 32m. The labels PM1, PM2, and PM3 are the positions that divide the line segment EML connecting the edge PMe on the equatorial plane EL side of the intermediate land portion 32m and the edge PMe on the end Te side of the tread 4 into four equal parts. The thickness reference line LM1 passes through the position PM1, the thickness reference line LM2 passes through the position PM2, and the thickness reference line LM3 passes through the position PM3.

[0157] The length indicated by the double arrow CM1 along the thickness reference line LM1 is the thickness of the top layer 36 at the position PM1. The length indicated by the double arrow BM1 is the thickness of the base layer 34 at the position PM1. The ratio CM1 / BM1 of the thickness CM1 of the top layer 36 to the thickness BM1 of the base layer 34 is the top layer thickness ratio ARm1 at the position PM1.

[0158] The length indicated by the double arrow CM2 along the thickness reference line LM2 is the thickness of the top layer 36 at the position PM2. The length indicated by the double arrow BM2 is the thickness of the base layer 34 at the position PM2. The ratio CM2 / BM2 of the thickness CM2 of the top layer 36 to the thickness BM2 of the base layer 34 is the top layer thickness ratio ARm2 at the position PM2.

[0159] The length indicated by the double arrow CM3 along the thickness reference line LM3 is the thickness of the top layer 36 at the position PM3. The length indicated by the double arrow BM3 is the thickness of the base layer 34 at the position PM3. The ratio CM3 / BM3 of the thickness CM3 of the top layer 36 to the thickness BM3 of the base layer 34 is the top layer thickness ratio ARm3 at the position PM3.

[0160] In this tire 2, the proportion ARm of the top layer 36 in the intermediate land portion 32m is represented by the average value of the ratio CM / BM of the thickness CM of the top layer to the thickness BM of the base layer in the intermediate land portion 32m. Specifically, the top layer proportion ARm is represented by the average value of the top layer thickness ratio CM1 / BM1 at the position PM1, the top layer thickness ratio CM2 / BM2 at the position PM2, and the top layer thickness ratio CM3 / BM3 at the position PM3.

[0161] Figure 6 Shows Figure 1 a part of the tire 2 shown. Figure 6Shows a cross-section of the shoulder land portions 32s. The position indicated by the label PSe is the edge of the shoulder land portion 32s. The edge PSe is the intersection point of the extension line of the land surface, that is, the contour OL of the tread surface 24 and the extension line LSe of the wall surface. The straight line LB is the normal line of the tread surface 24 passing through the end portion 52e of the outer belt ply 52. The position indicated by the label PB is the intersection point of the normal line LB and the tread surface 24. The intersection point PB is the reference position for defining the thicknesses of the top layer 36 and the base layer 34 in the shoulder land portion 32s. The straight line SML is the line segment connecting the edge PSe of the shoulder land portion 32s and the reference position PB.

[0162] In Figure 6 , the straight lines LS1, LS2, and LS3 are the thickness reference lines of the shoulder land portion 32s. The labels PS1, PS2, and PS3 are the positions that divide the line segment SML connecting the edge PSe of the shoulder land portion 32s and the reference position PB into four equal parts. 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.

[0163] The length indicated by the double arrow CS1 along the thickness reference line LS1 is the thickness of the top layer 36 at the position PS1. The length indicated by the double arrow BS1 is the thickness of the base layer 34 at the position PS1. The ratio CS1 / BS1 of the thickness CS1 of the top layer 36 to the thickness BS1 of the base layer 34 is the top layer thickness ratio ARs1 at the position PS1.

[0164] The length indicated by the double arrow CS2 along the thickness reference line LS2 is the thickness of the top layer 36 at the position PS2. The length indicated by the double arrow BS2 is the thickness of the base layer 34 at the position PS2. The ratio CS2 / BS2 of the thickness CS2 of the top layer 36 to the thickness BS2 of the base layer 34 is the top layer thickness ratio ARs2 at the position PS2.

[0165] The length indicated by the double arrow CS3 along the thickness reference line LS3 is the thickness of the top layer 36 at the position PS3. The length indicated by the double arrow BS3 is the thickness of the base layer 34 at the position PS3. The ratio CS3 / BS3 of the thickness CS3 of the top layer 36 to the thickness BS3 of the base layer 34 is the top layer thickness ratio ARs3 at the position PS3.

[0166] In this tire 2, the proportion ARs of the top layer 36 in the shoulder land portion 32s is represented by the average value of the ratio CS / BS of the thickness CS of the top layer to the thickness BS of the base layer in the shoulder land portion 32s. Specifically, the top layer proportion ARs is represented by the average value of the top layer thickness ratio CS1 / BS1 at the position PS1, the top layer thickness ratio CS2 / BS2 at the position PS2, and the top layer thickness ratio CS3 / BS3 at the position PS3.

[0167] In the tire 2, the end BE of the base layer 34 is located axially inward of the end 20e of the belt 20. In the tire 2, compared with the conventional tire, the top layer 36 covering the part of the end BE of the base layer 34 is thicker. In the shoulder part, the base layer 34 is not easily exposed. During extreme driving with a large load acting on the shoulder part, the tread 4 is not easily peeled off.

[0168] In the tire 2, the ratio ARs of the top layer 36 in the shoulder land 32s is higher than that of the conventional tire. In other words, the ratio of the base layer 34 in the shoulder land 32s is lower. The top layer 36 is harder and more likely to generate heat compared with the base layer 34. Therefore, it is possible that the rolling resistance increases, the riding comfort decreases, the road noise increases, and the quietness decreases.

[0169] However, in the tire 2, the top layer ratio ARc of the crown land 32c is 1.5 or more and 3.5 or less, the top layer ratio ARm of the intermediate land 32m is equal to or greater than the top layer ratio ARc of the crown land 32c, and the top layer ratio ARs of the shoulder land 32s is larger than the top layer ratio ARm of the intermediate land 32m, being 5.0 or more and 9.5 or less. In other words, the ratio of the base layer 34 in the land 32 is lower in the shoulder land 32s and higher in the crown land 32c and the intermediate land 32m. The base layer 34 is softer and less likely to generate heat compared with the top layer 36. The crown land 32c and the intermediate land 32m with a high base layer ratio can help suppress the increase in rolling resistance, the decrease in riding comfort, and the decrease in quietness.

[0170] The tire 2 can suppress the increase in rolling resistance, the decrease in riding comfort, and the decrease in quietness, and can suppress the occurrence of tread peeling.

[0171] From the viewpoint that the tire 2 can suppress the increase in rolling resistance, the decrease in riding comfort, and the decrease in quietness, and can effectively suppress the occurrence of tread peeling, the top layer ratio ARc of the crown land 32c is preferably 2.0 or more and 3.0 or less. From the same viewpoint, it is preferable that the top layer ratio ARm of the intermediate land 32m is the same as the top layer ratio ARc of the crown land 32c. From the same viewpoint, it is preferable that the top layer ratio ARs of the shoulder land 32s is 7.0 or more and 9.0 or less. More preferably, the top layer ratio ARc of the crown land 32c is 2.0 or more and 3.0 or less, the top layer ratio ARm of the intermediate land 32m is the same as the top layer ratio ARc of the crown land 32c, and the top layer ratio ARs of the shoulder land 32s is 7.0 or more and 9.0 or less.

[0172] For example, such as Figure 1As shown, the end CE of the top layer 36 is located axially outside the end 50e of the inner belt ply 50, i.e., the end 20e of the belt 20. The position of the end CE of the top layer 36 may also be axially aligned with the position of the end 20e of the belt 20. As described above, the end BE of the base layer 34 is located axially inside the end 20e of the belt 20. The end BE of the base layer 34 is covered by the top layer 36 having a sufficient thickness. In the shoulder portion, the base layer 34 is not easily exposed. During extreme driving with a large load acting on the shoulder portion, the tread 4 is not easily peeled off. The tire 2 can effectively suppress the occurrence of tread peeling. From this viewpoint, it is preferable that the position of the end CE of the top layer 36 is axially aligned with the position of the end 20e of the belt 20, or the end CE of the top layer 36 is located axially outside the end 20e of the belt 20, and more preferably the end CE of the top layer 36 is located axially outside the end 20e of the belt 20.

[0173] From the same viewpoint, the ratio WTC / WBU of the width WTC of the top layer 36 to the width WBU of the belt 20 is preferably 100% or more, and more preferably 103% or more. From the viewpoint of appropriately maintaining the volume of the top layer 36 included in the shoulder land 32s and effectively suppressing the influence of the top layer 36 included in the shoulder land 32s on ride comfort and quietness, the ratio WTC / WBU is preferably 110% or less, and more preferably 107% or less.

[0174] As described above, the end BE of the base layer 34 is located axially inside the end 20e of the belt 20. In the tire 2, it is preferable that the end BE of the base layer 34 is located near the end 52e of the outer belt ply 52. Specifically, the ratio WTB / WBS of the width WTB of the base layer 34 to the width WBS of the outer belt ply 52 is preferably 90% or more and 110% or less.

[0175] By setting the ratio WTB / WBS to 90% or more, the base layer 34 can effectively contribute to reducing the rolling resistance. In addition, in the shoulder land 32s, the base layer 34 can contribute to suppressing the deterioration of responsiveness, ride comfort, and quietness. From these viewpoints, the ratio WTB / WBS is more preferably 95% or more, and further preferably 98% or more.

[0176] By setting the ratio WTB / WBS to 110% or less, the end BE of the base layer 34 is covered by the top layer 36 having a sufficient thickness. The tire 2 can effectively suppress the occurrence of tread peeling. From this viewpoint, the ratio WTB / WBS is more preferably 105% or less, and further preferably 102% or less.

[0177] For example, as Figure 6As shown, in the shoulder land portion 32s, the base layer 34 tapers gradually toward the axially outer side. The end BE of the base layer 34 is covered by the top layer 36 having a sufficient thickness. In the shoulder portion, the base layer 34 is not easily exposed. In extreme driving where a large load acts on the shoulder portion, the tread 4 is not easily peeled off. The tire 2 can effectively suppress the occurrence of tread peeling. From this viewpoint, it is preferable that the base layer 34 tapers gradually toward the axially outer side in the shoulder land portion 32s.

[0178] From the same viewpoint, the top layer thickness ratio ARs3 at the position PS3 is preferably 0.4 times or less, more preferably 0.3 times or less, of the top layer thickness ratio ARs1 at the position PS1. From the viewpoint that the base layer 34 can contribute to the reduction of rolling resistance, the top layer thickness ratio ARs3 at the position PS3 is preferably 0.1 times or more, more preferably 0.2 times or more, of the top layer thickness ratio ARs1 at the position PS1.

[0179] In Figure 3 The length indicated by the double arrow CW in the figure is the contact width of the standard contact surface with the road surface. The contact width CW is represented by the axial distance from the first contact end SEs1 to the second contact end SEs2. The single dotted line LPs is the center line of the contact width of the standard contact surface with the road surface. The length indicated by the double arrow CG, which is the length of the intersection line of the standard contact surface and the contact width center line LPs, is the contact length at the center of the contact width of the standard contact surface with the road surface.

[0180] In this tire 2, the contact width CW of the standard contact surface with the road surface is preferably 70% or more and 80% or less of the nominal cross-sectional width of the tire 2. Thereby, the tire 2 can contact the road surface with a sufficient width. The tire 2 can effectively suppress the reduction in responsiveness caused by increasing the proportion of the base layer in the crown land portion 32c and the intermediate land portion 32m. The tire 2 can maintain good handling stability.

[0181] In Figure 3 The double arrow WGM in the figure is the groove width of the intermediate circumferential groove 30m at the standard contact surface with the road surface. The double arrow WGS is the groove width of the shoulder circumferential groove 30s at the standard contact surface with the road surface.

[0182] The solid line LA is a straight line passing through the center of the contact length CG and extending axially. The groove width WGM and the groove width WGS are measured along this straight line LA.

[0183] In the tire 2, the total width of a plurality of circumferential grooves 30 included in the standard contact surface, that is, the total WGT of the groove width WGM of two intermediate circumferential grooves 30m and the groove width WGS of two shoulder circumferential grooves 30s included in the standard contact surface, is adjusted. Specifically, the ratio (WGT / CW) of the total WGT of the groove widths of the plurality of circumferential grooves 30 included in the standard contact surface to the contact width CW of the standard contact surface is preferably 20% or more and 30% or less. Thereby, in the tire 2, responsiveness, riding comfort, and quietness can be adjusted in a well-balanced manner. From this viewpoint, the ratio (WGT / CW) is more preferably 22% or more and 28% or less, and still more preferably 24% or more and 26% or less.

[0184] From the viewpoint that the tire 2 can suppress an increase in rolling resistance, a decrease in responsiveness, a decrease in riding comfort, and a decrease in quietness and can suppress the occurrence of tread peeling, it is more preferable that the contact width CW of the standard contact surface is 70% or more and 80% or less of the nominal cross-sectional width of the tire 2, and the ratio (WGT / CW) of the total WGT of the groove widths of the plurality of circumferential grooves 30 included in the standard contact surface to the contact width CW of the standard contact surface is 20% or more and 30% or less.

[0185] Figure 7 A modified example of the tread pattern is shown. In this Figure 7 as well, for the sake of convenience of explanation, only 4 circumferential grooves 30 are shown as the grooves 28 constituting the tread pattern. In Figure 2 the direction indicated by the arrow AD1 is the first reference end Te1 side, and the direction indicated by the arrow AD2 is the second reference end Te2 side. Figure 7 In this

[0186] In this tread pattern, the 4 circumferential grooves 30 are arranged asymmetrically with respect to the equatorial plane EL. Therefore, the 5 land portions 32 are also arranged asymmetrically with respect to the equatorial plane EL.

[0187] In Figure 7 the tread pattern shown, the width WC of the crown land portion 32c is considered. Specifically, the crown land portion 32c is configured to have a width WC wider than the width WC of the crown land portion 32c shown in Figure 2 thereby, in a vehicle equipped with this tire 2, a higher lateral resistance is generated in the front-wheel tire. This tire 2 can help suppress the response delay of the front-wheel tire. This tire 2 can suppress a decrease in responsiveness and effectively suppress an increase in rolling resistance and the occurrence of tread peeling. From this viewpoint, the ratio WC / CW of the width WC of the crown land portion 32c to the contact width CW of the standard contact surface is preferably 14% or more.

[0188] The ratio WC / CW is preferably 16% or less. Thereby, in a vehicle equipped with this tire 2, a relatively high lateral resistance force is generated evenly between the front and rear tires. This tire 2 can contribute to the improvement of linearity.

[0189] In this tire 2, the intermediate land portion 32m on the first reference end Te1 side (hereinafter referred to as the first intermediate land portion 32m1) has a width WM1 approximately equal to the width WS1 of the shoulder land portion 32s on the first reference end Te1 side (hereinafter referred to as the first shoulder land portion 32s1). The crown land portion 32c has a width WC approximately equal to the width WM1 of the first intermediate land portion 32m1, or has a width WC wider than the width WM1. The intermediate land portion 32m on the second reference end Te2 side (hereinafter referred to as the second intermediate land portion 32m2) has a width WM2 approximately equal to the width WC of the crown land portion 32c, or has a width WM2 wider than the width WC. The shoulder land portion 32s on the second reference end Te2 side (hereinafter referred to as the second shoulder land portion 32s2) has a width WS2 wider than the width WM2 of the second intermediate land portion 32m2. By adopting this Figure 7 tread pattern, compared with existing tires, the ratio of the lateral resistance force of the rear tire to the lateral resistance force of the front tire can be effectively increased. When this tire 2 is mounted on a vehicle, the linearity is improved. This tire 2 can achieve an improvement in linearity. In other words, it can improve the handling stability of the vehicle and effectively suppress an increase in rolling resistance and the occurrence of tread peeling.

[0190] The width WS1 of the first shoulder land portion 32s1 is preferably 90% or more and 100% or less of the width WC of the crown land portion 32c.

[0191] By setting the width WS1 to 90% or more of the width WC, this tire 2 can form the crown land portion 32c, the first intermediate land portion 32m1, and the second intermediate land portion 32m2 with appropriate widths. When this tire 2 is mounted on a vehicle, a relatively high lateral resistance force is generated evenly between the front and rear tires, so the linearity is improved.

[0192] By setting the width WS1 to 100% or less of the width WC, this tire 2 can form the crown land portion 32c, the first intermediate land portion 32m1, and the second intermediate land portion 32m2 with appropriate widths. When this tire 2 is mounted on a vehicle, a relatively high lateral resistance force is generated in the front tire, so the response delay of the front tire is suppressed.

[0193] The width WM1 of the first intermediate land portion 32m1 is preferably 90% or more and 100% or less of the width WC of the crown land portion 32c.

[0194] By setting the width WM1 to be more than 90% of the width WC, when this tire 2 is mounted on a vehicle, a higher lateral resistance force is generated in the front-wheel tire. This tire 2 can help suppress the response delay of the front-wheel tire.

[0195] By setting the width WM1 to be 100% or less of the width WC, when this tire 2 is mounted on a vehicle, a higher lateral resistance force is generated evenly in the front-wheel tire and the rear-wheel tire. This tire 2 can help improve the linearity.

[0196] The width WM2 of the second intermediate land portion 32m2 is preferably 97% or more and 107% or less of the width WC of the crown land portion 32c.

[0197] By setting the width WM2 to be 97% or more of the width WC, when this tire 2 is mounted on a vehicle, a higher lateral resistance force is generated in the front-wheel tire. This tire 2 can help suppress the response delay of the front-wheel tire.

[0198] By setting the width WM2 to be 107% or less of the width WC, when this tire 2 is mounted on a vehicle, a higher lateral resistance force is generated evenly in the front-wheel tire and the rear-wheel tire. This tire 2 can help improve the linearity.

[0199] The width WS2 of the second shoulder land portion 32s2 is preferably 114% or more and 124% or less of the width WC of the crown land portion 32c.

[0200] By setting the width WS2 to be 114% or more of the width WC, this tire 2 can form the crown land portion 32c, the first intermediate land portion 32m1, and the second intermediate land portion 32m2 with appropriate widths. When this tire 2 is mounted on a vehicle, a higher lateral resistance force is generated evenly in the front-wheel tire and the rear-wheel tire, so the linearity is improved.

[0201] By setting the width WS2 to be 124% or less of the width WC, this tire 2 can form the crown land portion 32c, the first intermediate land portion 32m1, and the second intermediate land portion 32m2 with appropriate widths. When this tire 2 is mounted on a vehicle, a higher lateral resistance force is generated in the front-wheel tire, so the response delay of the front-wheel tire is suppressed.

[0202] In Figure 7In the crown land portion 32c shown, its width center is disposed on the second reference end Te2 side with respect to the equatorial plane EL. That is, when the crown land portion 32c is divided into a first portion 32c1 on the first reference end Te1 side and a second portion 32c2 on the second reference end Te2 side by the equatorial plane EL, the width of the second portion 32c2 is wider than the width of the first portion 32c1. Thus, the tire 2 can effectively increase the lateral resistance generated in the front tire and can effectively increase the ratio of the lateral resistance of the rear tire to the lateral resistance of the front tire. The tire 2 can achieve an improvement in responsiveness and linearity and can effectively suppress an increase in rolling resistance and the occurrence of tread peeling.

[0203] In Figure 7 the double arrow W2 is the width of the second portion 32c2. This width W2 is represented by the axial distance from the equatorial plane EL to the edge on the second reference end Te2 side of the crown land portion 32c.

[0204] From the viewpoint that the tire 2 can achieve an improvement in responsiveness and linearity and can effectively suppress an increase in rolling resistance and the occurrence of tread peeling, the ratio (W2 / WC) of the width W2 of the second portion 32c to the width WC of the crown land portion 32c is preferably 51% or more and 55% or less.

[0205] From the viewpoint that the tire 2 can achieve an improvement in responsiveness and linearity and can effectively suppress an increase in rolling resistance and the occurrence of tread peeling, when the tread pattern of the tire 2 includes 4 circumferential grooves 30 and 5 land portions 32 are formed in the tread 4, the ratio WC / CW of the width WC of the crown land portion 32c to the grounding width CW of the standard contact surface is preferably 14% or more and 16% or less. In this case, it is more preferable that the width WS1 of the shoulder land portion 32s1 on the first reference end Te1 side is 90% or more and 100% or less of the width WC of the crown land portion 32c, the width WM1 of the intermediate land portion 32m1 on the first reference end Te1 side is 90% or more and 100% or less of the width WC of the crown land portion 32c, the width WM2 of the intermediate land portion 32m2 on the second reference end Te2 side is 97% or more and 107% or less of the width WC of the crown land portion 32c, the width WS2 of the shoulder land portion 32s2 on the second reference end Te2 side is 114% or more and 124% or less of the width WC of the crown land portion 32c, and the ratio (W2 / WC) of the width W2 of the second portion 32c2 of the crown land portion 32c to the width WC of the crown land portion 32c is 51% or more and 55% or less. In particular, when the grounding width CW of the standard contact surface is 70% or more and 80% or less of the nominal cross-sectional width of the tire 2 and the ratio (WGT / CW) of the total WGT of the groove widths of the plurality of circumferential grooves 30 included in the standard contact surface to the grounding width CW of the standard contact surface is 20% or more and 30% or less, theFigure 7 The tread pattern shown can more effectively contribute to the improvement of responsiveness and linearity. The tire 2 can achieve the improvement of responsiveness and linearity, and can effectively suppress the increase in rolling resistance and the occurrence of tread peeling.

[0206] From the above description, according to the present invention, a tire capable of suppressing the increase in rolling resistance and the occurrence of tread peeling can be obtained. The present invention particularly has a remarkable effect in tires with a nominal cross-sectional width of 215 mm or more and 325 mm or less and a load index (LI) of 90 or more.

[0207]

Embodiment

[0208] Hereinafter, the present invention will be described in more detail by way of examples and the like, but the present invention is not limited to these examples.

[0209] [Embodiment 1]

[0210] A tire (tire size = 245 / 50R19) having the Figure 1 shown basic structure and the specifications shown in Table 1 below was obtained.

[0211] As Figure 6 shown, the end of the base layer is disposed near the end of the outer belt ply. This is indicated by " Figure 6 " in the "Top layer / base layer structure" column of Table 1 below.

[0212] The ratio WTB / WBS of the width WTB of the base layer to the width WBS of the outer belt ply is 100%.

[0213] The top layer ratio ARc of the crown land portion, the top layer ratio ARm of the intermediate land portion, and the top layer ratio ARs of the shoulder land portion are as shown in Table 1 below.

[0214] The four circumferential grooves provided in the tread are arranged as Figure 2 shown. This is indicated by " Figure 2 " in the "Tread pattern" column of Table 1 below.

[0215] The ratio WGT / CW of the total width WGT of the circumferential grooves included in the standard ground contact surface to the ground contact width CW of the standard ground contact surface, the ratio WS2 / WC of the width WS2 of the second shoulder land portion to the width WC of the crown land portion, the ratio WM2 / WC of the width WM2 of the second intermediate land portion to the width WC of the crown land portion, the ratio WM1 / WC of the width WM1 of the first intermediate land portion to the width WC of the crown land portion, the ratio WS1 / WC of the width WS1 of the first shoulder land portion to the width WC of the crown land portion, the ratio W2 / WC of the width W2 of the second part of the crown land portion to the width WC of the crown land portion, and the ratio WC / CW of the width WC of the crown land portion to the ground contact width CW of the standard ground contact surface are as shown in Table 1 below.

[0216] [Comparative Example 1 and Comparative Example 2]

[0217] The tires of Comparative Example 1 and Comparative Example 2 are existing tires (tire size = 245 / 50R19). The specifications of the tires of Comparative Example 1 and Comparative Example 2 are as shown in Table 1 below.

[0218] [Example 2]

[0219] As Figure 7 shown, the circumferential groove configuration is changed so that the ratio WGT / CW, the ratio WS2 / WC, the ratio WM2 / WC, the ratio WM1 / WC, the ratio WS1 / WC, the ratio W2 / WC, and the ratio WC / CW are as shown in Table 1 below. Except for this, it is the same as Example 1, thereby obtaining the tire of Example 2.

[0220] [Example 3]

[0221] The ratio WTB / WBS is set as shown in Table 1 below. Except for this, it is the same as Example 2, thereby obtaining the tire of Example 3.

[0222] [Comparative Examples 3 - Comparative Examples 4]

[0223] The top layer ratio ARc of the crown land portion is set as shown in Table 1 below. Except for this, it is the same as Example 2, thereby obtaining the tires of Comparative Examples 3 - Comparative Examples 4.

[0224] [Example 4 and Comparative Example 5]

[0225] The top layer ratio ARm of the intermediate land portion is made as shown in Table 2 below. Except for this, it is the same as Example 2, thereby obtaining the tires of Example 4 and Comparative Example 5.

[0226] [Comparative Examples 6 - Comparative Examples 7]

[0227] Make the top layer ratio ARs of the shoulder land part as shown in Table 2 below, and the rest is the same as in Example 2, thereby obtaining the tires of Comparative Examples 6 - 7.

[0228] [Examples 5 - 12]

[0229] Set the ratios WS2 / WC, WM2 / WC, WM1 / WC, WS1 / WC, and WC / CW as shown in Tables 2 and 3 below, and the rest is the same as in Example 1, thereby obtaining the tires of Examples 5 - 12.

[0230] [Rolling Resistance (RRC)]

[0231] Using a rolling resistance testing machine, measure the rolling resistance coefficient (RRC) of the trial - manufactured tire when it travels on a drum at a speed of 80 km / h under the following conditions. The results are shown in the "RRC" column of Tables 1 - 3 below with the index of Comparative Example 1 being 100. The larger the value, the lower the rolling resistance of the tire.

[0232] Rim: 7.5 inches

[0233] Internal pressure: 250 kPa

[0234] Longitudinal load: 7.26 kN

[0235] [Running Test]

[0236] Assemble the trial - manufactured tire on a rim (size = 7.5 inches), fill it with air, and adjust the internal pressure of the tire to 250 kPa. Install the tire on a test vehicle (passenger car). Make the test vehicle travel on a test route on a dry road surface to conduct a sensory evaluation related to responsiveness and riding comfort. The results are shown in the "Responsiveness" and "Riding Comfort" columns of Tables 1 - 3 below with the index of Comparative Example 1 being 100. The larger the value, the more the reduction in responsiveness or riding comfort is suppressed, and the better.

[0237] [Durability]

[0238] For the tire that has undergone the above - mentioned running test, observe the appearance, confirm the occurrence status of tread peeling, and obtain the size (area) of the peeled part. The results are shown in the "Durability" column of Tables 1 - 3 below with the index of Comparative Example 1 being 100. The larger the value, the more the tread peeling is suppressed.

[0239] [Sound Insulation (Road Noise: R / N)]

[0240] The trial - produced tire was assembled on a rim (size = 7.5 inches), air was filled, and the internal pressure of the tire was adjusted to 250 kPa. The tire was installed on a test vehicle (a front - wheel - drive passenger car with a displacement of 2000 cc). The sound pressure level of the cavity resonance sound (road noise) when driving at a speed of 30 km / h on a test route on a dry road surface was collected using a microphone set at the position near the driver's window side ear. The results are shown in the "R / N" column of Table 1 - 3 below with the index of Comparative Example 1 being 100. The larger the value, the better. Additionally, the cavity resonance sound has a peak near 240 Hz.

[0241] [Sound insulation performance (pattern noise: P / N)]

[0242] The trial - produced tire was assembled on a rim (size = 7.5 inches), air was filled, and the internal pressure of the tire was adjusted to 250 kPa. The tire was installed on a test vehicle (a front - wheel - drive passenger car with a displacement of 2000 cc). A sensory evaluation related to shear sound was conducted when driving at a speed of 100 km / h on a test route on a dry road surface. The results are shown in the "P / N" column of Table 1 - 3 below with the index of Comparative Example 1 being 100. The larger the value, the better.

[0243] [Comprehensive performance]

[0244] The sum of the index values obtained in each evaluation was calculated. The results are shown in the "Comprehensive" column of Table 1 - 3 below. The larger the value, the more preferable.

[0245]

Table 1

[0246]

[0247]

Table 2

[0248]

[0249]

Table 3

[0250]

[0251] As shown in Tables 1 - 3, in the examples, it was confirmed that an increase in rolling resistance could be suppressed and the occurrence of tread peeling could be suppressed. The superiority of the present invention is obvious from this evaluation result.

[0252] [Industrial applicability]

[0253] The technology described above that can suppress an increase in rolling resistance and the occurrence of tread peeling can be applied to various tires.

[0254] [Supplementary note]

[0255] The present invention includes the following embodiments.

[0256] [1] A tire having a pair of bead portions, a carcass stretched between the pair of bead portions, a tread located radially outside the carcass, and a belt located between the tread and the carcass, wherein,

[0257] The tread has a base layer and a top layer covering the entire base layer,

[0258] The top layer is harder than the base layer,

[0259] The loss tangent value of the base layer at 70 °C is lower than the loss tangent value of the top layer at 30 °C,

[0260] The end of the base layer is located axially inside the end of the belt,

[0261] The belt has an inner belt ply and an outer belt ply located radially outside the inner belt ply,

[0262] The end of the outer belt ply is located axially inside the end of the inner belt ply,

[0263] The tread has a tread pattern including a plurality of circumferential grooves, whereby a plurality of land portions arranged axially are formed on the tread,

[0264] The plurality of land portions in a portion between the equatorial plane of the tire and the end of the tread include a crown land portion on the equatorial plane side, a shoulder land portion on the tread end side, and an intermediate land portion between the crown land portion and the shoulder land portion,

[0265] The proportion ARc of the top layer in the crown land portion is represented by the average value of the ratio of the top layer thickness to the base layer thickness in the crown land portion,

[0266] The proportion Arm of the top layer in the intermediate land portion is represented by the average value of the ratio of the top layer thickness to the base layer thickness in the intermediate land portion,

[0267] The proportion ARs of the top layer in the shoulder land portion is represented by the average value of the ratio of the top layer thickness to the base layer thickness in the shoulder land portion,

[0268] The top layer proportion ARc of the crown land portion is 1.5 or more and 3.5 or less,

[0269] The top layer proportion Arm of the intermediate land portion is equal to or greater than the top layer proportion ARc of the crown land portion,

[0270] The top layer proportion ARs of the shoulder land portion is larger than the top layer proportion ARm of the intermediate land portion and is 5.0 or more and 9.5 or less.

[0271] [2] The tire according to [1] described above, wherein,

[0272] The position of the end of the top layer coincides axially with the position of the end of the belt, or the end of the top layer is located axially outside the end of the belt.

[0273] [3] The tire according to [1] or [2] described above, wherein,

[0274] When the tire is assembled on a regular rim, the internal pressure of the tire is adjusted to 250 kPa, the camber angle of the tire is set to 0 degrees, a longitudinal load is applied to the tire, and the tire is brought into contact with a road surface composed of a plane, and the resulting contact surface is the standard contact surface.

[0275] The longitudinal load applied to the tire is 60% or more and 80% or less of the load indicated by the load index of the tire.

[0276] The contact width of the standard contact surface is 70% or more and 80% or less of the nominal cross-sectional width of the tire.

[0277] The ratio of the total width of the plurality of circumferential grooves included in the standard contact surface to the contact width of the standard contact surface is 20% or more and 30% or less.

[0278] [4] The tire according to [3] described above, wherein,

[0279] The tread pattern includes 4 of the circumferential grooves, thereby forming 5 land portions on the tread.

[0280] The 5 land portions are the crown land portion located on the equatorial plane, a pair of intermediate land portions located axially outside the crown land portion, and a pair of shoulder land portions located axially outside each of the intermediate land portions.

[0281] The ratio of the width of the crown land portion to the contact width of the standard contact surface is 14% or more and 16% or less.

[0282] [5] The tire according to [4] described above, wherein,

[0283] Among the two ends of the tread, one end configured on the inner side in the vehicle width direction by mounting the tire on a vehicle is the first reference end, and the other end is the second reference end.

[0284] The width of the shoulder land portion on the first reference end side is 90% or more and 100% or less of the width of the crown land portion.

[0285] The width of the intermediate land portion on the first reference end side is 90% or more and 100% or less of the width of the crown land portion.

[0286] The width of the intermediate land portion on the second reference end side is 97% or more and 107% or less of the width of the crown land portion.

[0287] The width of the shoulder land portion on the second reference end side is 114% or more and 124% or less of the width of the crown land portion.

[0288] [6] The tire according to [4] or [5] above, wherein

[0289] The first reference end side across the equatorial plane in the crown land portion is the first part, and the second reference end side is the second part.

[0290] The ratio of the width of the second part to the width of the crown land portion is 51% or more and 55% or less.

Claims

1. A tire comprising a pair of beads, a carcass mounted between the pair of beads, a tread located radially outside the carcass, and a belt located between the tread and the carcass, wherein: The tread comprises a base layer and a top layer covering the entire base layer. The top layer is harder than the base layer, The loss tangent value of the base layer at 70°C is lower than the loss tangent value of the top layer at 30°C, The end of the base layer is located axially inside the end of the belt, The belt has an inner belt ply and an outer belt ply located radially outward of the inner belt ply, The end of the outer belt ply is located axially inward of the end of the inner belt ply, The tread has a tread pattern including a plurality of circumferential grooves, thereby constituting a plurality of land portions arranged in the axial direction on the tread, The plurality of land portions include a crown land portion located on the equatorial plane side, a shoulder land portion located on the tread end side, and an intermediate land portion located between the crown land portion and the shoulder land portion, The ratio ARc of the top layer in the crown land portion is represented by the average value of the ratio of the thickness of the top layer to the thickness of the base layer in the crown land portion. The ratio ARm of the top layer in the middle land portion is represented by the average value of the ratio of the thickness of the top layer to the thickness of the base layer in the middle land portion. The ratio ARs of the top layer in the shoulder land portion is represented by the average value of the ratio of the thickness of the top layer to the thickness of the base layer in the shoulder land portion. The top layer ratio ARc of the crown land portion is 1.5 or more and 3.5 or less, The top layer ratio Arm of the middle land portion is equal to or greater than the top layer ratio ARc of the crown land portion, The top layer ratio ARs of the shoulder land portion is greater than the top layer ratio ARm of the middle land portion, and is 5.0 or more and 9.5 or less.

2. The tire according to claim 1, wherein: The position of the end of the top layer is consistent with the position of the end of the belt in the axial direction, or the end of the top layer is located axially outside the end of the belt.

3. The tire according to claim 1, wherein: The tire is assembled on a regular rim, the internal pressure of the tire is adjusted to 250 kPa, the camber angle of the tire is set to 0 degrees, a longitudinal load is applied to the tire, and the tire is brought into contact with a flat road surface to obtain a contact surface as a standard contact surface, The longitudinal load applied to the tire is 60% or more and 80% or less of the load indicated by the load index of the tire, The contact width of the standard contact patch is not less than 70% and not more than 80% of the nominal cross-sectional width of the tire, A ratio of a total groove width of the plurality of circumferential grooves included in the standard ground contact surface to a ground contact width of the standard ground contact surface is greater than or equal to 20% and less than or equal to 30%.

4. The tire according to claim 3, wherein: The tread pattern includes four circumferential grooves, thereby forming five land portions on the tread. The five land portions are the crown land portion located on the equatorial plane, a pair of the middle land portions located axially outside the crown land portion, and a pair of the shoulder land portions located axially outside each of the middle land portions, A ratio of the width of the crown land portion to a ground contact width of the standard ground contact surface is 14% or more and 16% or less.

5. The tire according to claim 4, wherein: Of the two end portions of the tread, one end disposed on the inner side in the width direction of the vehicle when the tire is mounted on the vehicle is a first reference end, and the other end is a second reference end. The width of the shoulder land portion on the first reference end side is 90% or more and 100% or less of the width of the crown land portion, The width of the intermediate land portion on the first reference end side is 90% or more and 100% or less of the width of the crown land portion, The width of the middle land portion on the second reference end side is 97% or more and 107% or less of the width of the crown land portion, The width of the shoulder land portion on the second reference end side is not less than 114% and not more than 124% of the width of the crown land portion.

6. The tire according to claim 5, wherein: The first reference end side of the crown land portion across the equatorial plane is a first portion, and the second reference end side is a second portion. A ratio of a width of the second portion to a width of the crown land portion is 51% or more and 55% or less.

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