tire

Abstract

To provide a tire having a small diameter that can make both wet performance and wear resistance performance compatible.SOLUTION: A tire 1 comprises a pair of bead cores 11 and 11, a carcass layer 13 stretched between the bead cores 11 and 11, a belt layer 14 arranged outside in a radial direction of the carcass layer 13 and a tread part. Outer diameters OD[mm] of the tire are in a range of 200≤OD≤660, and total widths SW[mm] of the tire are in a range of 100≤SW≤400. Groove area ratios Aa of the tread part are in a range of 0.008≤Aa / OD≤0.150, and a groove area ratio Ace of a center region of the tread part and a groove area ratio Ash of a shoulder region of the tread part satisfy a relational expression: Ace / Ash>1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tire, and more particularly to a small-diameter tire that can achieve both wet performance and wear resistance. [Background technology]

[0002] In recent years, small-diameter tires have been developed for use in vehicles with lower floors to expand interior space. These small-diameter tires have low rotational inertia and light weight, which is expected to reduce transportation costs. Meanwhile, small-diameter tires are required to have high load capacity. Patent Document 1 discloses a known technology for a conventional tire that addresses this issue. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 122169 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a small-diameter tire that is capable of achieving both wet performance and wear resistance. [Means for solving the problem]

[0005] In order to achieve the above object, the tire according to the present invention is a tire comprising a pair of bead cores, a carcass layer wrapped around the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, wherein the tire outer diameter OD [mm] is in the range of 200≦OD≦660, the tire total width SW [mm] is in the range of 100≦SW≦400, the groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, and the groove area ratio Ace [%] of a center region of the tread portion and the groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1. The relationship between the number of pitches Pce in the center region of the tread portion and the number of pitches Psh in the shoulder region of the tread portion is 0.4≦Pce / Psh≦1.2. It is characterized by: In order to achieve the above object, the tire of the present invention is a tire comprising a pair of bead cores, a carcass layer spanned between the bead cores, a belt layer arranged radially outward of the carcass layer, and a tread portion, wherein the tire outer diameter OD [mm] is in the range of 200≦OD≦660, the tire total width SW [mm] is in the range of 100≦SW≦400, the groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, the groove area ratio Ace [%] of a center region of the tread portion and the groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, and the relationship between the average lateral groove width WLce within the tire contact patch length in the center region of the tread portion and the average number of pitches PCce within the tire contact patch length in the center region of the tread portion is 1500≦(WLce×PCce×OD)≦33000. In order to achieve the above object, the tire of the present invention is a tire comprising a pair of bead cores, a carcass layer spanning the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, wherein the tire outer diameter OD [mm] is in the range of 200≦OD≦660, the tire total width SW [mm] is in the range of 100≦SW≦400, the groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, the groove area ratio Ace [%] of a center region of the tread portion and the groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, and the average number of pitches PCce within the tire contact length around the entire circumference of the tire in the center region of the tread portion satisfies the relationship of 0.005≦PCce / OD≦0.020. In order to achieve the above object, the tire according to the present invention is a tire comprising a pair of bead cores, a carcass layer spanned between the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, wherein the tire outer diameter OD [mm] is in the range of 200≦OD≦660, the tire total width SW [mm] is in the range of 100≦SW≦400, the groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, the groove area ratio Ace [%] of a center region of the tread portion and the groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, and the strength Tcs [N / 50mm] per 50 mm width [mm] of the carcass ply constituting the carcass layer is in the range of 17≦Tcs / OD≦120 with respect to the tire outer diameter OD [mm]. In order to achieve the above object, the tire according to the present invention is a tire comprising a pair of bead cores, a carcass layer stretched over the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, wherein the tire outer diameter OD [mm] is in the range of 200≦OD≦660, the tire total width SW [mm] is in the range of 100≦SW≦400, the groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, the groove area ratio Ace [%] of a center region of the tread portion and the groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, the belt layer comprises a pair of cross belts formed by steel belt cords covered with coating rubber, and the strength Tbt [N / 50mm] per 50mm width [mm] of each of the pair of cross belts is in the range of 25≦Tbt / OD≦250 with respect to the tire outer diameter OD [mm]. In order to achieve the above object, the tire of the present invention is a tire comprising a pair of bead cores, a carcass layer placed over the bead cores, a belt layer arranged radially outward of the carcass layer, and a tread portion, wherein the tire outer diameter OD [mm] is in the range of 200≦OD≦660, the tire total width SW [mm] is in the range of 100≦SW≦400, the groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, the groove area ratio Ace [%] of a center region of the tread portion and the groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, and the strength Tbd [N] of one of the bead cores is in the range of 45≦Tbd / OD≦120 with respect to the tire outer diameter OD [mm]. [Effects of the Invention]

[0006] In the tire according to the present invention, the load capacity of the carcass layer is appropriately ensured in a small-diameter tire, which has the advantage of achieving both wet performance and wear resistance of the tire. Specifically, the groove area ratio Ace in the center region of the tread portion [%] The above relationship between the groove area ratio Aa [%] in the tread and the groove area ratio Ash [%] in the shoulder region ensures wet performance of the tire. Also, the groove area ratio Aa [%] in the tread is in the range of 0.008≦Aa / OD≦0.150, and the groove area ratio Ace [%] and the groove area ratio Ash [%] have the relationship Ace / Ash>1, thereby maintaining wear resistance. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of the tire shown in FIG. [Figure 3] FIG. 3 is an explanatory diagram showing the layer structure of the belt layers of the tire shown in FIG. [Figure 4] FIG. 4 is an enlarged view showing the tread portion of the tire shown in FIG. [Figure 5] FIG. 5 is an enlarged view showing one side region of the tread portion shown in FIG. [Figure 6] FIG. 6 is an enlarged view showing a sidewall portion and a bead portion of the tire shown in FIG. [Figure 7] FIG. 7 is an enlarged view showing the sidewall portion shown in FIG. [Figure 8] FIG. 8 is a diagram showing an example of a tread surface of a tread portion. [Figure 9] FIG. 9 is a table showing the results of performance tests on the tire according to the embodiment of the present invention. [Figure 10] FIG. 10 is a table showing the results of performance tests on the tire according to the embodiment of the present invention. [Figure 11] FIG. 11 is a table showing the results of performance tests on the tire according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components of these embodiments include those that can be substituted and are obvious substitutes while maintaining the identity of the invention. Furthermore, the multiple modifications described in these embodiments can be arbitrarily combined within the scope obvious to those skilled in the art.

[0009] [tire] 1 is a cross-sectional view in the tire meridian direction showing a tire 1 according to an embodiment of the present invention. The figure shows a cross-sectional view of one side region in the tire radial direction of the tire 1 mounted on a rim 10. In this embodiment, a pneumatic radial tire for passenger cars will be described as an example of a tire.

[0010] In the figure, the tire meridian cross section is defined as a cross section of the tire cut by a plane including the tire rotation axis (not shown). The tire equatorial plane CL is defined as a plane that passes through the midpoint of the tire section width defined by JATMA and is perpendicular to the tire rotation axis. The tire width direction is defined as a direction parallel to the tire rotation axis, and the tire radial direction is defined as a direction perpendicular to the tire rotation axis. Point T is the tire ground contact edge, and point Ac is the tire's maximum width position.

[0011] The tire 1 has an annular structure centered on the tire rotation axis, and includes a pair of bead cores 11, 11, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, 16, a pair of rim cushion rubbers 17, 17, and an inner liner 18 (see Figure 1).

[0012] The pair of bead cores 11, 11 are formed by winding one or more steel bead wires in an annular and multiple pattern and are embedded in the bead portions to form the cores of the left and right bead portions. The pair of bead fillers 12, 12 are disposed on the outer periphery of the pair of bead cores 11, 11 in the tire radial direction, respectively, to reinforce the bead portions.

[0013] The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass plies stacked together, and is toroidally laid between the left and right bead cores 11, 11 to form the tire framework. Both ends of the carcass layer 13 are wrapped around and secured to the outside in the tire width direction so as to enclose the bead cores 11 and the bead fillers 12. The carcass ply of the carcass layer 13 is formed by covering multiple carcass cords made of steel or organic fiber material (e.g., aramid, nylon, polyester, rayon, etc.) with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction relative to the tire circumferential direction) of 80 degrees or more and 100 degrees or less.

[0014] The belt layer 14 is formed by laminating a plurality of belt plies 141 to 144, and is disposed by being wound around the outer periphery of the carcass layer 13. In the configuration of Fig. 1, the belt plies 141 to 144 are each composed of a pair of cross belts 141, 142, a belt cover 143, and a pair of belt edge covers 144, 144.

[0015] The pair of cross belts 141, 142 are formed by coating a plurality of belt cords made of steel or organic fiber material with coating rubber and rolling them, and have a cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 15 degrees or more and 55 degrees or less in absolute value. The pair of cross belts 141, 142 have cord angles of opposite signs to each other, and are layered with the longitudinal directions of the belt cords crossing each other (so-called cross-ply structure). The pair of cross belts 141, 142 are layered and arranged on the outer side of the carcass layer 13 in the tire radial direction.

[0016] The belt cover 143 and the pair of belt edge covers 144, 144 are configured by covering belt cover cords made of steel or organic fiber material with coating rubber, and have a cord angle of 0 degrees or more and 10 degrees or less in absolute value. The belt cover 143 and the belt edge cover 144 are, for example, strip materials made by covering one or more belt cover cords with coating rubber, and are configured by spirally winding this strip material multiple times around the outer circumferential surfaces of the cross belts 141, 142 in the tire circumferential direction. The belt cover 143 is disposed to cover the entire area of ​​the cross belts 141, 142, and the pair of belt edge covers 144, 144 are disposed to cover the left and right edge portions of the cross belts 141, 142 from the outside in the tire radial direction.

[0017] The tread rubber 15 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form a tread portion of the tire 1. The tread rubber 15 also includes a cap tread 151 and an undertread 152.

[0018] The cap tread 151 is made of a rubber material with excellent ground contact characteristics and weather resistance, and is exposed on the tread surface over the entire tire contact patch to form the outer surface of the tread portion. The cap tread 151 has a rubber hardness Hs_cap of 50 to 80, a modulus M_cap [MPa] at 100% elongation of 1.0 to 4.0, and a loss tangent tanδ_cap of 0.03 to 0.36, and preferably has a rubber hardness Hs_cap of 58 to 76, a modulus M_cap [MPa] at 100% elongation of 1.5 to 3.2, and a loss tangent tanδ_cap of 0.06 to 0.29.

[0019] Rubber hardness Hs is measured at a temperature of 20°C in accordance with JIS K6253.

[0020] The modulus (breaking strength) is measured by a tensile test using a dumbbell-shaped test piece at a temperature of 20°C in accordance with JIS K6251 (using a No. 3 dumbbell).

[0021] The loss tangent tanδ is measured using a viscoelasticity spectrometer manufactured by Toyo Seiki Seisakusho Co., Ltd. under the conditions of a temperature of 60°C, a shear strain of 10%, an amplitude of ±0.5%, and a frequency of 20Hz.

[0022] The undertread 152 is made of a rubber material having excellent heat resistance, and is sandwiched between the cap tread 151 and the belt layer 14 to form a base portion of the tread rubber 15. The undertread 152 has a rubber hardness Hs_ut of 47 to 80, a modulus M_ut [MPa] at 100% elongation of 1.4 to 5.5, and a loss tangent tanδ_ut of 0.02 to 0.23, and preferably has a rubber hardness Hs_ut of 50 to 65, a modulus M_ut [MPa] at 100% elongation of 1.7 to 3.5, and a loss tangent tanδ_ut of 0.03 to 0.10.

[0023] The difference in rubber hardness Hs_cap - Hs_ut is in the range of 3 to 20, preferably 5 to 15. The difference in modulus M_cap - M_ut [MPa] is in the range of 0 to 1.4, preferably 0.1 to 1.0. The difference in loss tangent tanδ_cap - tanδ_ut is in the range of 0 to 0.22, preferably 0.02 to 0.16.

[0024] A pair of sidewall rubbers 16, 16 are respectively arranged on the outer sides of the carcass layer 13 in the tire width direction to form left and right sidewall portions. In the configuration of FIG. 1 , the outer end of the sidewall rubber 16 in the tire radial direction is arranged in the lower layer of the tread rubber 15 and is sandwiched between the end of the belt layer 14 and the carcass layer 13. However, this is not limiting, and the outer end of the sidewall rubber 16 in the tire radial direction may also be arranged in the outer layer of the tread rubber 15 and exposed in the buttress portion of the tire (not shown). In this case, a belt cushion (not shown) is sandwiched between the end of the belt layer 14 and the carcass layer 13.

[0025] The sidewall rubber 16 has a rubber hardness Hs_sw of 48 to 65, a modulus M_sw [MPa] at 100% elongation of 1.0 to 2.4, and a loss tangent tanδ_sw of 0.02 to 0.22, and preferably has a rubber hardness Hs_sw of 50 to 59, a modulus M_sw [MPa] at 100% elongation of 1.2 to 2.2, and a loss tangent tanδ_sw of 0.04 to 0.20.

[0026] The pair of rim cushion rubbers 17, 17 extend from the radially inner side of the tire to the widthwise outer side of the tire of the left and right bead cores 11, 11 and the turned-up portions of the carcass layer 13, forming the rim fitting surface of the bead portion. In the configuration of Figure 1, the radially outer end of the rim cushion rubber 17 is inserted into the lower layer of the sidewall rubber 16, and is sandwiched between the sidewall rubber 16 and the carcass layer 13.

[0027] The inner liner 18 is an air permeation prevention layer disposed on the tire cavity surface and covering the carcass layer 13, suppressing oxidation due to exposure of the carcass layer 13 and preventing leakage of air filled in the tire. The inner liner 18 may be made of, for example, a rubber composition containing butyl rubber as a main component, or may be made of a thermoplastic resin or a thermoplastic elastomer composition in which an elastomer component is blended into a thermoplastic resin.

[0028] In FIG. 1 , the tire outer diameter OD [mm] is in the range of 200≦OD≦660, preferably in the range of 250 [mm]≦OD≦580 [mm]. By applying this type of small-diameter tire, the load performance improvement effect described below can be significantly achieved. Furthermore, the tire total width SW [mm] is in the range of 100≦SW≦400, preferably in the range of 105 [mm]≦SW≦340 [mm]. With this type of small-diameter tire 1, for example, the floor of a small vehicle can be lowered to expand the interior space. Furthermore, the small rotational inertia and light tire weight improve fuel efficiency and reduce transportation costs. In particular, when mounted on an in-wheel motor of a vehicle, the load on the motor is effectively reduced.

[0029] The tire outer diameter OD is measured with the tire mounted on a specified rim, pressurized to a specified internal pressure, and under no load.

[0030] The total tire width SW is measured as the straight-line distance between the sidewalls (including all parts such as patterns and lettering on the side of the tire) when the tire is mounted on a specified rim, pressurized to the specified internal pressure, and in an unloaded state.

[0031] The specified rim refers to the "applicable rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. The specified internal pressure refers to the "maximum air pressure" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "inflation pressure" specified by ETRTO. The specified load refers to the "maximum load capacity" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "load capacity" specified by ETRTO. However, in JATMA, for passenger car tires, the specified internal pressure is 180 kPa, and the specified load is 88% of the maximum load capacity.

[0032] The tire total width SW [mm] is in the range of 0.23≦SW / OD≦0.84 relative to the tire outer diameter OD [mm], and preferably in the range of 0.25≦SW / OD≦0.81.

[0033] It is also preferable that the tire outer diameter OD and the tire total width SW satisfy the following mathematical formula (1), where A1min=-0.0017, A2min=0.9, A3min=130, A1max=-0.0019, A2max=1.4, A3max=400, and preferably A1min=-0.0018, A2min=0.9, A3min=160, A1max=-0.0024, A2max=1.6, A3max=362.

[0034]

number

[0035] The tire 1 is assumed to use a rim 10 having a rim diameter of 5 inches to 16 inches (i.e., 125 mm to 407 mm). The rim diameter RD [mm] is in the range of 0.50≦RD / OD≦0.74 relative to the tire outer diameter OD [mm], and preferably in the range of 0.52≦RD / OD≦0.71. The lower limit ensures that the rim diameter RD is sufficient, and in particular, that space for installing an in-wheel motor is secured. The upper limit ensures that the tire's internal volume V, which will be described later, is secured, and the tire's load capacity is secured.

[0036] The tire inner diameter is equal to the rim diameter RD of the rim 10.

[0037] Furthermore, the tire 1 is expected to be used at an internal pressure higher than the specified level, specifically, an internal pressure of 350 kPa or more and 1200 kPa or less, preferably 500 kPa or more and 1000 kPa or less. The lower limit effectively reduces the rolling resistance of the tire, and the upper limit ensures safety during the internal pressure inflation operation.

[0038] The tire 1 is expected to be mounted on a vehicle that travels at a low speed, such as a small shuttle bus. The maximum speed of the vehicle is 100 km / h or less, preferably 80 km / h or less, and more preferably 60 km / h or less. The tire 1 is expected to be mounted on a vehicle with 6 to 12 wheels. This allows the tire to properly demonstrate its load capacity.

[0039] The tire aspect ratio, i.e., the ratio of the tire section height SH [mm] (see FIG. 2 described later) to the tire section width [mm] (dimension symbols omitted in the figure: in FIG. 1, it is the same as the tire total width SW), is in the range of 0.16 to 0.85, preferably in the range of 0.19 to 0.82.

[0040] The tire section height SH is half the distance between the tire outer diameter and the rim diameter, and is measured with the tire mounted on a specified rim, with the specified internal pressure applied, and with no load applied.

[0041] The tire section width is measured as the linear distance between the sidewalls (excluding any patterns or lettering on the side of the tire) when the tire is mounted on a specified rim, pressurized to the specified internal pressure, and in an unloaded state.

[0042] The tire contact width TW is in the range of 0.75≦TW / SW≦0.95 relative to the tire total width SW, and preferably in the range of 0.80≦TW / SW≦0.92.

[0043] The tire contact width TW is measured as the maximum linear distance in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0044] Furthermore, the tire internal volume V [m^3] is in the range of 4.0≦(V / OD)×10^6≦60, preferably 6.0≦(V / OD)×10^6≦50, relative to the tire outer diameter OD [mm]. This optimizes the tire internal volume V. Specifically, the above lower limit ensures the tire internal volume and the tire's load capacity. In particular, for small-diameter tires, it is expected that they will be used under high internal pressure and high load, so it is preferable that the tire internal volume V is sufficiently ensured. The above upper limit prevents the tire from becoming too large, which would otherwise result in an excessively large tire internal volume V.

[0045] The tire internal volume V [m^3] is in the range of 0.5≦V×RD≦17, preferably 1.0≦V×RD≦15, relative to the rim diameter RD [mm].

[0046] [Bead core] 1, as described above, a pair of bead cores 11, 11 are formed by winding one or more steel bead wires (not shown) in an annular and multiple manner. In addition, a pair of bead fillers 12, 12 are disposed on the outer peripheries of the pair of bead cores 11, 11 in the tire radial direction, respectively.

[0047] Furthermore, the strength Tbd [N] of one bead core 11 is in the range of 45≦Tbd / OD≦120, preferably 50≦Tbd / OD≦110, and more preferably 60≦Tbd / OD≦105, relative to the tire outer diameter OD [mm]. Furthermore, the strength Tbd [N] of the bead core is in the range of 90≦Tbd / SW≦400, preferably 110≦Tbd / SW≦350, relative to the tire total width SW [mm]. This ensures an appropriate load capacity of the bead core 11. Specifically, the above lower limit suppresses tire deformation during use under high loads, ensuring tire wear resistance. Furthermore, use at high internal pressures is possible, reducing tire rolling resistance. Small-diameter tires, in particular, are expected to be used under high internal pressures and high loads, and the above-described effects of tire wear resistance and reduced rolling resistance are significantly achieved. The above upper limit suppresses the deterioration of rolling resistance due to an increase in the mass of the bead core.

[0048] The strength Tbd [N] of the bead core 11 is calculated as the product of the strength per bead wire [N / wire] and the total number of bead wires [wires] in the radial cross section. The strength of the bead wire is measured by a tensile test at a temperature of 20°C in accordance with JIS K1017.

[0049] Furthermore, it is preferable that the strength Tbd [N] of the bead core 11 satisfies the following mathematical formula (2) with respect to the tire outer diameter OD [mm], distance SWD [mm], and rim diameter RD [mm]. Here, B1min = 0.26, B2min = 10.0, B1max = 2.5, B2max = 99.0, preferably B1min = 0.35, B2min = 14.0, B1max = 2.5, B2max = 99.0, more preferably B1min = 0.44, B2min = 17.6, B1max = 2.5, B2max = 99.0, and even more preferably B1min = 0.49, B2min = 17.9, B1max = 2.5, B2max = 99.0. Furthermore, using the specified tire internal pressure P [kPa], it is preferable that B1min = 0.0016 × P and B2min = 0.07 × P.

[0050]

number

[0051] The distance SWD is twice the radial distance from the tire rotation axis (not shown) to the tire's maximum width position Ac, i.e., the diameter of the tire's maximum width position Ac, and is measured with the tire mounted on a specified rim, pressurized to a specified internal pressure, and in an unloaded state.

[0052] The tire maximum width position Ac is defined as the maximum width position of the tire section width as specified by JATMA.

[0053] In addition, in a radial cross-section of one bead core 11, the total cross-sectional area σbd [mm^2] of the bead wires made of the above-mentioned steel is in the range of 0.025≦σbd / OD≦0.075, and preferably 0.030≦σbd / OD≦0.065, relative to the tire outer diameter OD [mm]. Also, the total cross-sectional area σbd [mm^2] of the bead wires is in the range of 11≦σbd≦36, and preferably 13≦σbd≦33. This allows the above-mentioned strength Tbd [N] of the bead core 11 to be achieved.

[0054] The total cross-sectional area σbd [mm^2] of the bead wires is calculated as the sum of the cross-sectional areas of the bead wires in a radial cross section of one bead core 11.

[0055] For example, in the configuration of Fig. 1, the bead core 11 has a quadrangle formed by arranging bead wires (not shown) with circular cross sections in a lattice pattern. However, the bead core 11 is not limited to this, and may have a hexagonal shape formed by arranging bead wires with circular cross sections in a close-packed structure (not shown). Any other bead wire arrangement structure may be adopted within the scope of what is obvious to a person skilled in the art.

[0056] It is also preferable that the total cross-sectional area σbd [mm^2] of the bead wires satisfies the following formula (3) with respect to the tire outer diameter OD [mm], the distance SWD [mm], and the rim diameter RD [mm], where Cmin=30, Cmax=8, and preferably Cmin=25, Cmax=10.

[0057]

number

[0058] Furthermore, the total cross-sectional area σbd [mm^2] of the bead wires is in the range of 0.50≦σbd / Nbd≦1.40, preferably 0.60≦σbd / Nbd≦1.20, where Nbd is the total number of bead wire cross sections (i.e., total number of turns) of one bead core 11 in a radial cross-section. That is, the cross-sectional area σbd' [mm^2] of a single bead wire is in the range of 0.50 [mm^2 / wire] to 1.40 [mm^2 / wire], preferably 0.60 [mm^2 / wire] to 1.20 [mm^2 / wire].

[0059] In addition, the maximum width Wbd [mm] of one bead core 11 in a radial cross-sectional view (see Figure 2 described later) is in the range of 0.16≦Wbd / σbd≦0.50 relative to the total cross-sectional area σbd [mm^2] of the bead wire, and preferably in the range of 0.20≦Wbd / σbd≦0.40.

[0060] 1, the distance Dbd [mm] between the centers of gravity of a pair of bead cores 11, 11 is in the range of 0.63≦Dbd / SW≦0.97, preferably 0.65≦Dbd / SW≦0.95, relative to the total tire width SW [mm]. The lower limit reduces the amount of tire deflection and reduces tire rolling resistance. The upper limit reduces stress acting on the tire sidewalls and suppresses tire failure.

[0061] [Carcass layer] Fig. 2 is an enlarged view of the tire 1 shown in Fig. 1. The drawing shows one side region bounded by the tire equatorial plane CL.

[0062] 1, as described above, the carcass layer 13 is made of a single carcass ply and is disposed to be toroidally bridged between the left and right bead cores 11, 11. In addition, both end portions of the carcass layer 13 are wrapped back and secured to the outside in the tire width direction so as to enclose the bead cores 11 and the bead fillers 12.

[0063] Furthermore, the strength Tcs [N / 50mm] per 50 mm of width of the carcass ply constituting the carcass layer 13 is in the range of 17≦Tcs / OD≦120, preferably 20≦Tcs / OD≦120, relative to the tire outer diameter OD [mm]. Furthermore, the strength Tcs [N / 50mm] of the carcass layer 13 is in the range of 30≦Tcs / SW≦260, preferably 35≦Tcs / SW≦220, relative to the tire total width SW [mm]. This ensures an appropriate load capacity of the carcass layer 13. Specifically, the above lower limit suppresses tire deformation during use under high loads, ensuring tire wear resistance. Furthermore, use at high internal pressures is possible, reducing tire rolling resistance. Small-diameter tires, in particular, are expected to be used under high internal pressures and high loads, and therefore the above-described effects of tire wear resistance and reduced rolling resistance are significantly achieved. The above upper limit suppresses deterioration of rolling resistance due to an increase in the mass of the carcass layer.

[0064] The strength of the carcass ply, Tcs [N / 50mm], is calculated as follows. That is, the carcass ply that spans the left and right bead cores 11 and extends across the entire inner circumference of the tire is defined as the effective carcass ply. The strength of the carcass ply, Tcs [N / 50mm], is calculated as the product of the strength of each carcass cord constituting the effective carcass ply [N / cord] and the number of carcass cords placed per 50 mm around the tire and on the tire equatorial plane CL [cords / 50mm]. The strength of the carcass cord is measured by a tensile test at a temperature of 20°C in accordance with JIS K1017. For example, if one carcass cord is configured by twisting together multiple wires, the strength of one twisted carcass cord is measured, and the strength of the carcass layer 13, Tcs, is calculated. In addition, in a configuration in which the carcass layer 13 has a multi-layer structure (not shown) formed by laminating a plurality of effective carcass plies, the above-mentioned strength Tcs is defined for each of the plurality of effective carcass plies.

[0065] 1, for example, the carcass layer 13 has a single-layer structure consisting of a single carcass ply (reference numeral omitted in the figure), and the carcass ply is configured by arranging carcass cords made of steel coated with a coating rubber at a cord angle of 80 degrees to 100 degrees relative to the tire circumferential direction (not shown). The carcass cords made of steel have a cord diameter φcs [mm] in the range of 0.3≦φcs≦1.1 and an end count Ecs [wires / 50mm] in the range of 25≦Ecs≦80, thereby achieving the strength Tcs [N / 50mm] of the carcass layer 13. The carcass cords are formed by twisting together a plurality of wires, and the wire diameter φcss [mm] is in the range of 0.12≦φcss≦0.24, preferably in the range of 0.14≦φcss≦0.22.

[0066] Furthermore, the carcass ply may be formed of carcass cords made of an organic fiber material (such as aramid, nylon, polyester, or rayon) coated with a coating rubber. In this case, the carcass cords made of the organic fiber material have a cord diameter φcs [mm] in the range of 0.6≦φcs≦0.9 and an end count Ecs [pieces / 50mm] in the range of 40≦Ecs≦70, thereby achieving the strength Tcs [N / 50mm] of the carcass layer 13. Other carcass cords made of organic fiber materials such as high-strength nylon, aramid, or hybrids can be adopted within the scope of those skilled in the art.

[0067] The carcass layer 13 may also have a multi-layer structure (not shown) formed by laminating a plurality of carcass plies, for example, two carcass plies, thereby effectively increasing the load carrying capacity of the tire.

[0068] Furthermore, the total strength TTcs [N / 50 mm] of the carcass layer 13, relative to the tire outer diameter OD [mm], is in the range of 300≦TTcs / OD≦3500, and preferably 400≦TTcs / OD≦3000. This ensures the overall load capacity of the carcass layer 13.

[0069] The total strength TTcs [N / 50mm] of the carcass layer 13 is calculated as the sum of the strengths Tcs [N / 50mm] of the above-mentioned effective carcass plies. Therefore, the total strength TTcs [N / 50mm] of the carcass layer 13 increases with an increase in the strength Tcs [N / 50mm] of each carcass ply, the number of carcass plies stacked, the circumferential length of the carcass ply, etc.

[0070] It is also preferable that the total strength TTcs [N / 50mm] of the carcass layer 13 satisfies the following formula (4) relative to the tire outer diameter OD [mm] and the distance SWD [mm]: Dmin = 2.2, Dmax = 40, preferably Dmin = 4.3, Dmax = 40, more preferably Dmin = 6.5, Dmax = 40, and even more preferably Dmin = 8.7, Dmax = 40. Furthermore, it is preferable that Dmin = 0.02 × P, where P [kPa] is the specified tire internal pressure.

[0071]

number

[0072] 1, the carcass layer 13 has a main body portion 131 extending along the tire inner surface and a turned-up portion 132 that is turned up outward in the tire width direction to wrap around the bead core 11 and extends in the tire radial direction. In FIG. 2, the radial height Hcs [mm] from the measurement point of the rim diameter RD to the end of the turned-up portion 132 of the carcass layer 13, relative to the tire cross-sectional height SH [mm], is in the range of 0.49≦Hcs / SH≦0.80, and preferably 0.55≦Hcs / SH≦0.75. This optimizes the radial height Hcs of the turned-up portion 132 of the carcass layer 13. Specifically, the lower limit ensures the load capacity of the tire sidewall, and the upper limit suppresses deterioration of rolling resistance due to an increase in the mass of the carcass layer.

[0073] The radial height Hcs [mm] of the turned-up portion 132 of the carcass layer 13 is measured with the tire mounted on a specified rim, a specified internal pressure applied, and no load applied.

[0074] For example, in the configuration of FIG. 2, the radially outer end (not shown in the figure) of the winding-up portion 132 of the carcass layer 13 is in the region between the tire maximum width position Ac and the end of the belt layer 14 (point Au described later), and more specifically, it is in the region up to the radial position Au' which is 70[%] of the distance Hu described later from the tire maximum width position Ac. At this time, the contact height Hcs' [mm] between the main body portion 131 and the winding-up portion 132 of the carcass layer 13 is in the range of 0.07 ≦ Hcs' / SH with respect to the tire section height SH [mm], and preferably in the range of 0.15 ≦ Hcs' / SH. Thereby, the load capacity of the tire side portion is effectively increased. The upper limit of the ratio Hcs' / SH is not particularly limited, but is restricted by the relationship Hcs' < Hcs with respect to the radial height Hcs of the winding-up portion 132 of the carcass layer 13.

[0075] The contact height Hcs' of the carcass layer 13 is the radial extension length of the region where the main body portion 131 and the winding-up portion 132 contact each other, and is measured with the tire mounted on a specified rim and applying a specified internal pressure and in a no-load state.

[0076] In addition, not limited to the above, due to the carcass layer 13 having a so-called rotor turn-up structure, the end of the winding-up portion 132 of the carcass layer 13 may be arranged in the region between the tire maximum width position Ac and the bead core (not shown).

[0077] [Belt layer] FIG. 3 is an explanatory view showing the laminated structure of the belt layer of the tire 1 described in FIG. 1. In the figure, the thin lines attached to each belt ply 141 to 144 schematically show the arrangement configuration of the belt cords.

[0078] In the configuration of FIG. 1, as described above, the belt layer 14 is formed by laminating a plurality of belt plies 141 to 144. Also, as shown in FIG. 3, these belt plies 141 to 144 are composed of a pair of crossed belts 141, 142, a belt cover 143, and a pair of belt edge covers 144, 144.

[0079] In this case, the strength Tbt [N / 50mm] per 50 mm of width of each of the pair of cross belts 141, 142 is in the range of 25≦Tbt / OD≦250, preferably 30≦Tbt / OD≦230, relative to the tire outer diameter OD [mm]. Furthermore, the strength Tbt [N / 50mm] of each of the cross belts 141, 142 is in the range of 45≦Tbt / SW≦500, preferably 50≦Tbt / SW≦450, relative to the tire total width SW [mm]. This ensures an appropriate load capacity for each of the pair of cross belts 141, 142. Specifically, the above lower limit suppresses tire deformation during use under high loads, ensuring the tire's wear resistance. Furthermore, use at high internal pressures is possible, reducing the tire's rolling resistance. In particular, in small-diameter tires, which are expected to be used under high internal pressure and high load, the above-mentioned effects of reducing tire wear resistance and rolling resistance are significantly achieved. The above upper limit prevents deterioration of rolling resistance due to an increase in the mass of the cross belt.

[0080] The belt ply strength Tbt [N / 50mm] is calculated as follows: That is, the belt ply extending across the entire area of ​​80% of the tire contact width TW (i.e., the center of the tire contact width) centered on the tire equatorial plane CL is defined as the effective belt ply. The belt ply strength Tbt [N / 50mm] is calculated as the product of the strength per belt cord constituting the effective belt ply [N / cord] and the belt cord count per 50 mm in the above-mentioned area of ​​80% of the tire contact width TW. The belt cord strength is measured by a tensile test at 20°C in accordance with JIS K1017. For example, if a single belt cord is configured by twisting together multiple wires, the strength of each twisted belt cord is measured to calculate the belt ply strength Tbt. In addition, in a configuration in which the belt layer 14 is formed by laminating a plurality of effective carcass plies (see FIG. 1), the above-mentioned strength Tbt is defined for each of the plurality of effective carcass plies. For example, in the configuration in FIG. 1, the pair of cross belts 141, 142 and the belt cover 143 correspond to the effective belt plies.

[0081] 3, for example, a pair of cross belts 141, 142 are configured by arranging steel belt cords covered with a coating rubber at a cord angle (dimension symbols omitted in the figure) of 15 degrees or more and 55 degrees or less with respect to the tire circumferential direction. The steel belt cords have a cord diameter φbt [mm] in the range of 0.50≦φbt≦1.80 and an end count Ebt [ends / 50mm] in the range of 15≦Ebt≦60, thereby achieving a strength Tbt [N / 50mm] of the cross belts 141, 142. The cord diameter φbt [mm] and end count Ebt [ends / 50mm] are preferably within the ranges of 0.55≦φbt≦1.60 and 17≦Ebt≦50, and more preferably within the ranges of 0.60≦φbt≦1.30 and 20≦Ebt≦40. The belt cord is formed by twisting together a plurality of wires, and the wire diameter φbts [mm] is in the range of 0.16≦φbts≦0.43, preferably in the range of 0.21≦φbts≦0.39.

[0082] Furthermore, the cross belts 141, 142 may be formed of belt cords made of an organic fiber material (such as aramid, nylon, polyester, or rayon) coated with a rubber coating. In this case, the belt cords made of the organic fiber material have a cord diameter φbt [mm] in the range of 0.50≦φbt≦0.90 and an end count Ebt [pieces / 50mm] in the range of 30≦Ebt≦65, thereby achieving the strength Tbt [N / 50mm] of the cross belts 141, 142. Furthermore, belt cords made of organic fiber materials such as high-strength nylon, aramid, and hybrids can be adopted within the scope of what is obvious to those skilled in the art.

[0083] The belt layer 14 may also include an additional belt (not shown). The additional belt may be, for example, (1) a third cross belt, which is formed by coating a plurality of belt cords made of steel or organic fiber material with a coating rubber and rolling the coated cords, and has a cord angle of 15 degrees or more and 55 degrees or less, or (2) a so-called high-angle belt, which is formed by coating a plurality of belt cords made of steel or organic fiber material with a coating rubber and rolling the coated cords, and has a cord angle of 45 degrees or more and 70 degrees or less, preferably 54 degrees or more and 68 degrees or less, in absolute value. The additional belt may be disposed (a) between the pair of cross belts 141, 142 and the carcass layer 13, (b) between the pair of cross belts 141, 142, or (c) radially outside the pair of cross belts 141, 142 (not shown). This improves the load capacity of the belt layer 14.

[0084] Furthermore, the total strength TTbt [N / 50 mm] of the belt layer 14 is in the range of 70≦TTbt / OD≦750, preferably 90≦TTbt / OD≦690, more preferably 110≦TTbt / OD≦690, and even more preferably 120≦TTbt / OD≦690, relative to the tire outer diameter OD [mm]. This ensures the overall load capacity of the belt layer 14. Furthermore, using the specified tire internal pressure P [kPa], it is preferable that 0.16×P≦TTbt / OD.

[0085] The total strength TTbt [N / 50mm] of the belt layer 14 is calculated as the sum of the strengths Tbt [N / 50mm] of the above-mentioned effective belt plies (the pair of cross belts 141, 142 and the belt cover 143 in FIG. 1). Therefore, the total strength TTbt [N / 50mm] of the belt layer 14 increases with an increase in the strength Tbt [N / 50mm] of each belt ply, the number of laminated belt plies, etc.

[0086] Furthermore, the width Wb1 [mm] of the widest cross belt (in FIG. 3, the inner diameter side cross belt 141) of the pair of cross belts 141, 142 (including the additional belt in the configuration with the above-described additional belt; not shown) is in the range of 1.00≦Wb1 / Wb2≦1.40, preferably 1.10≦Wb1 / Wb2≦1.35, relative to the width Wb2 [mm] of the narrowest cross belt (in FIG. 3, the outer diameter side cross belt 142). Furthermore, the width Wb2 [mm] of the narrowest cross belt is in the range of 0.61≦Wb2 / SW≦0.96, preferably 0.70≦Wb2 / SW≦0.94, relative to the total tire width SW [mm]. The above lower limits ensure the width of the belt plies, optimize the contact pressure distribution in the tire contact area, and ensure the tire's resistance to uneven wear. The upper limit reduces strain at the end of the belt ply when the tire rolls, and suppresses separation of the peripheral rubber at the end of the belt ply.

[0087] The width of the belt ply is the distance between the left and right ends of each belt ply in the direction of the tire rotation axis, and is measured with the tire mounted on a specified rim, with a specified internal pressure applied, and in an unloaded state.

[0088] Furthermore, the width Wb1 [mm] of the widest cross belt (in FIG. 3, the cross belt 141 on the inner diameter side) of the pair of cross belts 141, 142 (in the configuration having the above-mentioned additional belt, the additional belt is included; not shown) is in the range of 0.85≦Wb1 / TW≦1.23, and preferably 0.90≦Wb1 / TW≦1.20, relative to the tire contact width TW [mm].

[0089] 1 to 3, for example, a wide cross belt 141 is disposed in the innermost layer in the tire radial direction, and a narrow cross belt 142 is disposed radially outward of the wide cross belt 141. A belt cover 143 is disposed radially outward of the narrow cross belt 142 and covers the entire pair of cross belts 141, 142. A pair of belt edge covers 144, 144 are disposed radially outward of the belt cover 143 while being spaced apart from each other, and cover the left and right edge portions of the pair of cross belts 141, 142, respectively.

[0090] [Tread Profile and Tread Gauge] FIG. 4 is an enlarged view showing the tread portion of the tire 1 shown in FIG.

[0091] In Figure 4, the drop amount DA [mm] of the tread profile at the tire contact edge T, the tire contact width TW [mm], and the tire outer diameter OD [mm] satisfy the relationship 0.025 ≦ TW / (DA × OD) ≦ 0.400, preferably 0.030 ≦ TW / (DA × OD) ≦ 0.300. Furthermore, the drop amount DA [mm] of the tread profile at the tire contact edge T and the tire contact width TW [mm] satisfy the relationship 0.008 ≦ DA / TW ≦ 0.060, preferably 0.013 ≦ DA / TW ≦ 0.050. This optimizes the drop angle (defined as the ratio DA / (TW / 2)) of the tread shoulder region, ensuring the appropriate load capacity of the tread. Specifically, the above lower limit ensures the drop angle of the tread shoulder region, suppressing a decrease in wear life due to excessive contact pressure in the tread shoulder region. The upper limit above flattens the tire contact patch and equalizes the contact pressure, ensuring tire wear resistance. In particular, for small-diameter tires, which are expected to be used under high internal pressure and high loads, the above configuration effectively optimizes the contact pressure distribution in the tire contact patch.

[0092] The drop amount DA is the radial distance of the tire from the intersection C1 of the tire equatorial plane CL and the tread profile to the tire contact edge T in a cross-sectional view in the tire meridian direction, and is measured when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and in an unloaded state.

[0093] The tire profile is the outline of the tire in a cross section taken along the tire meridian, and is measured using a laser profiler, such as a tire profile measuring device (manufactured by Matsuo Corporation).

[0094] It is also preferable that the drop amount DA [mm] of the tread profile at the tire ground contact edge T satisfies the following formula (5) with respect to the tire outer diameter OD [mm] and the tire total width SW [mm]: where Emin=3.5, Emax=17, preferably Emin=3.8, Emax=13, and more preferably Emin=4.0, Emax=9.

[0095]

number

[0096] Also, in FIG. 4, a point C1 on the tread profile at the tire equatorial plane CL and a pair of points C2, C2 on the tread profile at a distance of 1 / 4 of the tire contact width TW from the tire equatorial plane CL are defined.

[0097] In this case, the radius of curvature TRc [mm] of the arc passing through point C1 and the pair of points C2 is in the range of 0.15≦TRc / OD≦15, preferably 0.18≦TRc / OD≦12, relative to the tire outer diameter OD [mm]. Furthermore, the radius of curvature TRc [mm] of the arc is in the range of 30≦TRc≦3000, preferably 50≦TRc≦2800, and more preferably 80≦TRc≦2500. This ensures an appropriate load capacity for the tread. Specifically, the lower limit flattens the tread center region, uniforming the contact pressure in the tire contact area and ensuring tire wear resistance. The upper limit prevents a reduction in wear life due to excessive contact pressure in the tread shoulder region. Small-diameter tires, in particular, are expected to be used under high internal pressure and high loads, and this effectively uniforms the contact pressure under such conditions.

[0098] The radius of curvature of the arc is measured with the tire mounted on a specified rim, with a specified internal pressure applied, and in an unloaded state.

[0099] In addition, in FIG. 4 , the radius of curvature TRw [mm] of the arc passing through point C1 on the tire equatorial plane CL and the left and right tire ground contact edges T, T is in the range of 0.30≦TRw / OD≦16, preferably 0.35≦TRw / OD≦11, relative to the tire outer diameter OD [mm]. Furthermore, the radius of curvature TRw [mm] of the arc is in the range of 150≦TRw≦2800, preferably 200≦TRw≦2500. This ensures an appropriate load capacity of the tread portion. Specifically, the above-mentioned lower limit flattens the entire tire ground contact area, uniforming the contact pressure and ensuring the tire's wear resistance. The above-mentioned upper limit prevents a decrease in wear life due to excessive contact pressure in the tread shoulder region. Small-diameter tires, in particular, are expected to be used under high internal pressure and high loads, so the above-mentioned configuration effectively optimizes the contact pressure distribution in the tire ground contact area.

[0100] Furthermore, the radius of curvature TRw [mm] of the first circular arc passing through the above-mentioned points C1 and C2 is in the range of 0.50≦TRw / TRc≦1.00, preferably 0.60≦TRw / TRc≦0.95, and more preferably 0.70≦TRw / TRc≦0.90, relative to the radius of curvature TRw [mm] of the second circular arc passing through point C1 and the tire ground contact edge T. This optimizes the tire ground contact shape. Specifically, the lower limit distributes the ground contact pressure in the tread center region, improving the tire's wear life. The upper limit suppresses a decrease in wear life caused by excessive ground contact pressure in the tread shoulder regions.

[0101] In FIG. 4, a point B1 on the carcass layer 13 at the tire equatorial plane CL and feet B2, B2 of perpendicular lines extending from the left and right tire ground contact edges T, T to the carcass layer 13 are defined.

[0102] In this case, the radius of curvature CRw of the arc passing through point B1 and the pair of points B2, B2 is in the range of 0.35≦CRw / TRw≦1.10, preferably 0.40≦CRw / TRw≦1.00, and more preferably 0.45≦CRw / TRw≦0.92, relative to the radius of curvature TRw of the arc passing through point C1 and the tire ground contact edges T, T. Furthermore, the radius of curvature CRw [mm] is in the range of 100≦CRw≦2500, preferably 120≦CRw≦2200. This further optimizes the tire ground contact shape. Specifically, the above lower limit suppresses a decrease in wear life due to an increase in the rubber gauge in the tread shoulder region. The above upper limit ensures the wear life of the tread center region.

[0103] FIG. 5 is an enlarged view showing one side region of the tread portion shown in FIG.

[0104] In the configuration of FIG. 1, the belt layer 14 has a pair of cross belts 141 and 142, and the tread rubber 15 has a cap tread 151 and an undertread 152, as described above.

[0105] 5, the distance Tce [mm] from the tread profile at the tire equatorial plane CL to the outer peripheral surface of the wide cross belt 141 satisfies the relationship 0.008≦Tce / OD≦0.13, preferably 0.012≦Tce / OD≦0.10, and more preferably 0.015≦Tce / OD≦0.07 relative to the tire outer diameter OD [mm]. Furthermore, the distance Tce [mm] is within the range of 5≦Tce≦25, preferably 7≦Tce≦20. This ensures an appropriate load capacity for the tread portion. Specifically, the lower limit suppresses tire deformation during use under high loads, ensuring tire wear resistance. Small-diameter tires, in particular, are expected to be used under high internal pressure and high loads, and therefore exhibit the aforementioned significant wear resistance. The upper limit suppresses deterioration of rolling resistance due to an increase in the mass of the tread rubber.

[0106] The distance Tce is measured with the tire mounted on a specified rim, with a specified internal pressure applied, and under no load.

[0107] The outer peripheral surface of the belt ply is defined as the radially outer peripheral surface of the entire belt ply made up of the belt cords and coating rubber.

[0108] Furthermore, it is preferable that the distance Tce [mm] from the tread profile at the tire equatorial plane CL to the outer peripheral surface of the wide cross belt 141 satisfies the following formula (6) relative to the tire outer diameter OD [mm], where Fmin=35, Fmax=207, and preferably Fmin=42, Fmax=202.

[0109]

number

[0110] Furthermore, the distance Tsh [mm] from the tread profile at the tire ground contact edge T to the outer peripheral surface of the wide cross belt 141, relative to the distance Tce [mm] at the tire equatorial plane CL, is in the range of 0.60≦Tsh / Tce≦1.70, preferably 1.01≦Tsh / Tce≦1.55, and more preferably 1.10≦Tsh / Tce≦1.50. The above lower limit ensures the tread gauge in the shoulder region, thereby suppressing repeated deformation of the tire during tire rotation and ensuring the tire's wear resistance. The above upper limit ensures the tread gauge in the center region, thereby suppressing tire deformation during use under high loads specific to small-diameter tires and ensuring the tire's wear resistance.

[0111] The distance Tsh is measured with the tire mounted on a specified rim, pressurized to a specified internal pressure, and under no load. If there is no wide cross belt directly under the tire contact edge T, the distance Tsh is measured as the distance from the tread profile to an imaginary line extending from the outer circumferential surface of the belt ply.

[0112] Furthermore, it is preferable that the distance Tsh [mm] from the tread profile at the tire ground contact edge T to the outer peripheral surface of the wide cross belt 141 satisfies the following formula (7) relative to the distance Tce [mm] at the tire equatorial plane CL, where Gmin=0.36, Gmax=0.72, preferably Gmin=0.37, Gmax=0.71, and more preferably Gmin=0.38, Gmax=0.70.

[0113]

number

[0114] 5, a section having a width ΔTW of 10% of the tire contact width TW is defined. In this case, the ratio of the maximum value Ta to the minimum value Tb of the rubber gauge of the tread rubber 15 in any section of the tire contact area is in the range of 0% to 40% and preferably in the range of 0% to 20%. In this configuration, the amount of change in the rubber gauge of the tread rubber 15 in any section of the tire contact area (particularly the section including the end of the belt plies 141 to 144) is set small, so the distribution of contact pressure in the tire width direction becomes smooth and the wear resistance of the tire is improved.

[0115] The rubber gauge of the tread rubber 15 is defined as the distance from the tread profile to the inner peripheral surface of the tread rubber 15 (in FIG. 5, the distance from the outer peripheral surface of the cap tread 151 to the inner peripheral surface of the undertread 152). Therefore, the rubber gauge of the tread rubber 15 is measured excluding grooves formed in the tread surface.

[0116] 5, the rubber gauge UTce of the undertread 152 at the tire equatorial plane CL is in the range of 0.04≦UTce / Tce≦0.60, and preferably in the range of 0.06≦UTce / Tce≦0.50, relative to the distance Tce at the tire equatorial plane CL. This optimizes the rubber gauge UTce of the undertread 152.

[0117] Furthermore, the distance Tsh at the tire ground contact edge T, where Tu [mm] is the rubber gauge from the end of the wide cross belt 141 to the outer circumferential surface of the carcass layer 13, is in the range of 1.50≦Tsh / Tu≦6.90, preferably 2.00≦Tsh / Tu≦6.50. This optimizes the profile of the carcass layer 13 and optimizes the tension of the carcass layer 13. Specifically, the lower limit ensures the tension of the carcass layer and the tread gauge of the shoulder region, thereby suppressing repeated deformation of the tire during tire rolling and ensuring the tire's wear resistance. The upper limit ensures the rubber gauge near the end of the belt ply, thereby suppressing separation of the peripheral rubber of the belt ply.

[0118] The rubber gauge Tu is measured substantially as the gauge of the rubber member (the sidewall rubber 16 in FIG. 5) inserted between the end of the wide cross belt 141 and the carcass layer 13.

[0119] The outer peripheral surface of the carcass layer 13 is defined as the outer peripheral surface in the radial direction of the entire carcass ply made up of carcass cords and coating rubber. When the carcass layer 13 has a multi-layer structure made up of a plurality of carcass plies (not shown), the outer peripheral surface of the outermost carcass ply forms the outer peripheral surface of the carcass layer 13. When a turned-up portion 132 (see FIG. 1) of the carcass layer 13 exists between the end of the wide cross belt 141 and the carcass layer 13 (not shown), the outer peripheral surface of the turned-up portion 132 forms the outer peripheral surface of the carcass layer 13.

[0120] For example, in the configuration of Fig. 5, the sidewall rubber 16 is inserted between the end of the wide cross belt 141 and the carcass layer 13 to form a rubber gauge Tu between the end of the wide cross belt 141 and the carcass layer 13. However, this is not limiting, and for example, a belt cushion may be inserted between the end of the wide cross belt 141 and the carcass layer 13 instead of the sidewall rubber 16 (not shown). In addition, the inserted rubber member has a rubber hardness Hs_sp of 46 to 67, a modulus M_sp [MPa] at 100[%] elongation of 1.0 to 3.5, and a loss tangent tanδ_sp of 0.02 to 0.22, and preferably has a rubber hardness Hs_sp of 48 to 63, a modulus M_sp [MPa] at 100[%] elongation of 1.2 to 3.2, and a loss tangent tanδ_sp of 0.04 to 0.20.

[0121] 1, tire 1 has, on its tread surface, a plurality of circumferential main grooves 21 a, 21 b, 22 a, and 22 b extending in the tire circumferential direction, and land portions (reference numerals omitted in the figure) defined by these circumferential main grooves 21 a, 21 b, 22 a, and 22 b. Main grooves are defined as grooves that are required to display a wear indicator as specified by JATMA.

[0122] In this case, the groove depth Gd1a [mm] of the circumferential main groove 21a, which is closest to the tire equatorial plane CL among the multiple circumferential main grooves 21a, 21b, 22a, and 22b, is in the range of 0.50≦Gd1a / Gce≦1.00, preferably 0.55≦Gd1a / Gce≦0.98, relative to the rubber gauge Gce [mm] of the tread rubber 15. This ensures the wear resistance of the tire. Specifically, the above lower limit distributes the ground contact pressure in the tread center region, improving the tire's wear life. The above upper limit ensures the rigidity of the land portions and also ensures the rubber gauge from the groove bottoms of the circumferential main grooves 21a, 21b, 22a, and 22b to the belt layer.

[0123] The circumferential main groove closest to the tire equatorial plane CL is defined as the circumferential main groove located on the tire equatorial plane CL (not shown), and if there is no circumferential main groove on the tire equatorial plane CL (see Figure 4), it is defined as the circumferential main groove 21a closest to the tire equatorial plane CL.

[0124] It is also preferable that the ratio Gd1a / Gce satisfies the following formula (8) relative to the tire outer diameter OD [mm]: where Hmin=0.10, Hmax=0.60, preferably Hmin=0.12, Hmax=0.50, and more preferably Hmin=0.14, Hmax=0.40.

[0125]

number

[0126] Furthermore, the groove depth Gd1a [mm] of the circumferential main groove 21a, which is closest to the tire equatorial plane CL among the multiple circumferential main grooves 21a, 21b, 22a and 22b, is greater than or equal to the groove depths Gd1b [mm], Gd2a [mm], Gd2b [mm] of the other circumferential main grooves 21b, 22a and 22b (Gd1b≦Gd1a, Gd2a≦Gd1a, Gd2b≦Gd1a). Specifically, when the region from the tire equatorial plane CL to the tire ground contact edge T is divided into two equal parts in the tire width direction, the groove depth Gd1a of the circumferential main groove 21a closest to the tire equatorial plane CL is in the range of 1.00 to 2.50 times, preferably 1.00 to 2.00 times, and more preferably 1.00 to 1.80 times, the maximum groove depths Gd1b, Gd2a, and Gd2b of the other circumferential main grooves 21b and the other circumferential main grooves 22a, 22b in the region closer to the tire ground contact edge T. The lower limit disperses the contact pressure in the tread center region, improving the tire's wear resistance. The upper limit suppresses uneven wear caused by an excessive difference in contact pressure between the tread center region and shoulder regions.

[0127] [Side Profile and Side Gauge] Fig. 6 is an enlarged view showing a sidewall portion and a bead portion of the tire 1 shown in Fig. 1. Fig. 7 is an enlarged view showing a sidewall portion shown in Fig. 6.

[0128] 6, a point Au on the side profile is defined as being at the same position in the tire radial direction as the end of the innermost layer of the belt layer 14 (inner diameter side cross belt 141 in FIG. 6), and a point Al on the side profile is defined as being at the same position in the tire radial direction as the radially outer end of the bead core 11. Also, a distance Hu in the tire radial direction from the tire maximum width position Ac to point Au, and a distance Hl in the tire radial direction from the tire maximum width position Ac to point Al are defined. Also, a point Au' on the side profile is defined as being at a radial position 70% of the distance Hu from the tire maximum width position Ac, and a point Al' on the side profile is defined as being at a radial position 70% of the distance Hl from the tire maximum width position Ac.

[0129] In this case, the sum of the distances Hu [mm] and Hl [mm] is in the range of 0.45≦(Hu+Hl) / SH≦0.90, preferably 0.50≦(Hu+Hl) / SH≦0.85, relative to the tire cross-sectional height SH [mm] (see FIG. 2). This optimizes the radial distance from the belt layer 14 to the bead core 11. Specifically, the lower limit ensures a deformable region in the tire side portion, thereby suppressing failures in the tire side portion (for example, separation of the rubber member at the radially outer end of the bead filler 12). The upper limit reduces the amount of deflection in the tire side portion when the tire is rolling, thereby reducing the rolling resistance of the tire.

[0130] The distances Hu and Hl are measured with the tire mounted on a specified rim, with a specified internal pressure applied, and under no load.

[0131] Furthermore, it is preferable that the sum of distance Hu [mm] and distance Hl [mm] satisfy the following formula (9) with respect to the tire outer diameter OD (FIG. 1), tire section height SH [mm] (see FIG. 2), and radius of curvature RSc [mm] of the arc passing through tire maximum width position Ac, point Au', and point Al': where I1min=0.06, I1max=0.20, and I2=0.70, and preferably I1min=0.09, I1max=0.20, and I2=0.65.

[0132]

number

[0133] The radius of curvature RSc of the circular arc is measured with the tire mounted on a specified rim, with a specified internal pressure applied, and under no load.

[0134] Furthermore, the distance Hu [mm] and the distance Hl [mm] have a relationship of 0.30≦Hu / (Hu+Hl)≦0.70, and preferably a relationship of 0.35≦Hu / (Hu+Hl)≦0.65. This optimizes the position of the tire maximum width position Ac in the deformable region of the tire side portion. Specifically, the above lower limit alleviates stress concentration near the end of the belt ply, which is caused by the tire maximum width position Ac being too close to the end of the belt layer 14, thereby suppressing separation of the surrounding rubber. The above upper limit alleviates stress concentration near the bead portion, which is caused by the tire maximum width position Ac being too close to the end of the bead core 11, thereby suppressing failure of the bead portion reinforcing member (bead filler 12 in FIG. 6 ).

[0135] Furthermore, the radius of curvature RSc [mm] of the arc passing through the tire maximum width position Ac, points Au', and Al' is in the range of 0.05≦RSc / OD≦1.70, preferably 0.10≦RSc / OD≦1.60, relative to the tire outer diameter OD [mm]. Furthermore, the radius of curvature RSc [mm] of the arc is in the range of 25≦RSc≦330, preferably 30≦RSc≦300. This optimizes the radius of curvature of the side profile, ensuring appropriate load capacity of the tire side portion. Specifically, the above lower limit reduces the amount of deflection of the tire side portion during tire rolling, thereby reducing tire rolling resistance. The above upper limit suppresses stress concentration due to flattening of the tire side portion, improving tire durability. Small-diameter tires, in particular, tend to experience large stresses acting on the tire side portion due to use under the above-mentioned high internal pressure and high load, making it necessary to ensure tire side cut resistance. In this regard, the lower limit ensures the radius of curvature of the side profile and optimizes the carcass tension, thereby suppressing tire collapse and side cuts in the tire, while the upper limit prevents side cuts in the tire caused by excessive tension in the carcass layer 13.

[0136] The radius of curvature RSc [mm] of the arc relative to the tire section height SH [mm] is in the range of 0.50≦RSc / SH≦0.95, preferably 0.55≦RSc / SH≦0.90.

[0137] It is also preferable that the radius of curvature RSc [mm] of the arc satisfies the following formula (10) with respect to the tire outer diameter OD [mm] and the rim diameter RD [mm]: where Jmin=15, Jmax=360, preferably Jmin=20, Jmax=330, and more preferably Jmin=25, Jmax=300.

[0138]

number

[0139] 6, a point Bc is defined on the main body portion 131 of the carcass layer 13, which is located at the same radial position as the tire maximum width position Ac. A point Bu' is defined on the main body portion 131 of the carcass layer 13, which is located at 70% of the distance Hu from the tire maximum width position Ac in the radial direction. A point Bl' is defined on the main body portion 131 of the carcass layer 13, which is located at 70% of the distance Hl in the radial direction from the tire maximum width position Ac.

[0140] In this case, the radius of curvature RSc [mm] of the arc passing through the tire maximum width position Ac, points Au', and Al' is in the range of 1.10≦RSc / RCc≦4.00, preferably 1.50≦RSc / RCc≦3.50, relative to the radius of curvature RCc [mm] of the arc passing through points Bc, Bu', and Bl'. The radius of curvature RCc [mm] of the arc passing through points Bc, Bu', and Bl' is in the range of 5≦RCc≦300, preferably 10≦RCc≦270. This optimizes the relationship between the radius of curvature RSc of the tire side profile and the radius of curvature RCc of the side profile of the carcass layer 13. Specifically, the lower limit ensures the radius of curvature RCc of the carcass profile, thereby ensuring the tire internal volume V (described later), and thus ensuring the load-bearing capacity of the tire. The upper limit ensures the total gauges Gu and Gl (described later) of the tire side portion, thereby ensuring the load-bearing capacity of the tire side portion.

[0141] It is also preferable that the radius of curvature RSc [mm] of the side profile satisfies the following formula (11) with respect to the radius of curvature RCc [mm] of the carcass profile and the tire outer diameter OD [mm]: where Kmin=1, Kmax=130, preferably Kmin=2, Kmax=100, and more preferably Kmin=3, Kmax=70.

[0142]

number

[0143] Also, in Figure 6, the total gauge Gu [mm] of the tire side portion at the above-mentioned point Au is in the range of 0.010 ≦ Gu / OD ≦ 0.080, preferably 0.017 ≦ Gu / OD ≦ 0.070, relative to the tire outer diameter OD [mm]. This optimizes the total gauge Gu of the radially outer region of the tire side portion. Specifically, the above-mentioned lower limit ensures the total gauge Gu of the radially outer region of the tire side portion, suppresses tire deformation during use under high load, and ensures tire wear resistance. In particular, small-diameter tires are expected to be used under high internal pressure and high load, so the above-mentioned effect of reducing tire rolling resistance is significantly achieved. The above-mentioned upper limit prevents deterioration of tire rolling resistance caused by an excessive total gauge Gu.

[0144] The total gauge of the tire side portion is measured as the distance from the side profile to the inner surface of the tire on a perpendicular line drawn from a predetermined point on the side profile to the main body portion 131 of the carcass layer 13.

[0145] 6, the total gauge Gu [mm] at the point Au is in the range of 1.30≦Gu / Gc≦5.00 relative to the total gauge Gc [mm] of the tire side portion at the tire maximum width position Ac, and preferably the ratio Gu / Gc is in the range of 1.90≦Gu / Gc≦3.00. This optimizes the gauge distribution of the tire side portion from the tire maximum width position Ac to the innermost layer of the belt layer 14. Specifically, the lower limit ensures the total gauge Gu in the radially outer region, suppresses tire deformation during use under high load, and ensures the tire's wear resistance. The upper limit prevents deterioration of the tire's rolling resistance due to an excessive total gauge Gu.

[0146] Furthermore, it is preferable that the total gauge Gu [mm] at the point Au described above, the total gauge Gc [mm] at the tire maximum width position Ac, and the tire outer diameter OD [mm] satisfy the following formula (12): where Lmin=0.10, Lmax=0.70, preferably Lmin=0.14, Lmax=0.70, and more preferably Lmin=0.19, Lmax=0.70.

[0147]

number

[0148] 6, the total gauge Gc [mm] of the tire side portion at the tire maximum width position Ac satisfies the relationship 0.003≦Gc / OD≦0.060 and preferably 0.004≦Gc / OD≦0.050 relative to the tire outer diameter OD [mm]. The lower limit ensures the total gauge Gc at the tire maximum width position Ac, thereby ensuring the tire's load capacity. The upper limit ensures the reduction in tire rolling resistance achieved by reducing the total gauge Gc at the tire maximum width position Ac.

[0149] It is also preferable that the total gauge Gc [mm] at the tire maximum width position Ac satisfies the following formula (13) relative to the tire outer diameter OD [mm], where Mmin=70, Mmax=450, and preferably Mmin=80, Mmax=400.

[0150]

number

[0151] It is also preferable that the total gauge Gc [mm] at the tire maximum width position Ac satisfies the following formula (14) with respect to the tire outer diameter OD [mm] and the tire total width SW [mm], where Nmin=0.20, Nmax=15, preferably Nmin=0.40, Nmax=15, and more preferably Nmin=0.60, Nmax=12.

[0152]

number

[0153] Furthermore, it is preferable that the total gauge Gc [mm] at the tire maximum width position Ac satisfies the following formula (15) with respect to the radius of curvature RSc [mm] of the arc passing through the tire maximum width position Ac, point Au', and point Al', where Omin=13, Omax=260, and preferably Omin=20, Omax=200.

[0154]

number

[0155] Also, in Figure 6, the total gauge Gl [mm] of the tire side portion at the above-mentioned point Al is in the range of 0.010 ≦ Gl / OD ≦ 0.150, preferably 0.015 ≦ Gl / OD ≦ 0.100, relative to the tire outer diameter OD. This optimizes the total gauge Gl of the radially inner region of the tire side portion. Specifically, the above-mentioned lower limit ensures the total gauge Gl of the radially inner region of the tire side portion, suppresses tire deformation during use under high load, and ensures tire wear resistance. In particular, small-diameter tires are expected to be used under high internal pressure and high load, so the above-mentioned effect of reducing tire rolling resistance is significantly achieved. The above-mentioned upper limit prevents deterioration of tire rolling resistance caused by an excessive total gauge Gl.

[0156] 6, the ratio Gl / Gc of the total gauge Gl [mm] of the tire side portion at point Al to the total gauge Gc [mm] of the tire side portion at tire maximum width position Ac is in the range of 1.00≦Gl / Gc≦7.00, and preferably the ratio Gu / Gc is in the range of 2.00≦Gl / Gc≦5.00. This optimizes the gauge distribution of the tire side portion from tire maximum width position Ac to the bead core 11. Specifically, the lower limit ensures the total gauge Gl of the radially inner region, suppresses tire deformation during high-load use, and ensures tire wear resistance. The upper limit prevents deterioration of the tire's rolling resistance due to an excessive total gauge Gl.

[0157] Furthermore, it is preferable that the total gauge Gl [mm] of the tire side portion at the above-mentioned point Al satisfies the following formula (16) with respect to the total gauge Gc [mm] at the tire maximum width position Ac and the tire outer diameter OD [mm]: where Pmin=0.12, Pmax=1.00, preferably Pmin=0.15, Pmax=1.00, and more preferably Pmin=0.18, Pmax=1.00.

[0158]

number

[0159] 6, the total gauge Gl [mm] at the point Al is in the range of 0.80≦Gl / Gu≦5.00, and preferably 1.00≦Gl / Gu≦4.00, relative to the total gauge Gu [mm] at the point Au, thereby optimizing the ratio between the total gauge Gl in the radially outer region of the tire side portion and the total gauge Gu in the radially inner region.

[0160] Furthermore, it is preferable that the total gauge Gl [mm] at the above-mentioned point Al satisfies the following mathematical formula (17) with respect to the total gauge Gu [mm] at the above-mentioned point Au and the tire outer diameter OD [mm]. Here, Qmin = 0.09, Qmax = 0.80, preferably Qmin = 0.10, Qmax = 0.70, and more preferably Qmin = 0.11, Qmax = 0.50.

[0161]

Number

[0162] Also, in FIG. 6, the average rubber hardness Hsc at the measurement position of the total gauge Gc, the average rubber hardness Hsu at the measurement position of the total gauge Gu, and the average rubber hardness Hsl at the measurement point position of the total gauge Gl have a relationship of Hsc ≦ Hsu < Hsl, preferably a relationship of 1 ≦ Hsu - Hsc ≦ 18 and 2 ≦ Hsl - Hsu ≦ 27, and more preferably a relationship of 2 ≦ Hsu - Hsc ≦ 15 and 5 ≦ Hsl - Hsu ≦ 23. Thereby, the relationship of the rubber hardness of the tire side portion is optimized.

[0163] The average rubber hardnesses Hsc, Hsu, and Hsl are calculated as the sum of the values obtained by dividing the product of the cross-sectional length and the rubber hardness of each rubber member at the respective measurement points of the total gauge Gc [mm] at the tire maximum width position Ac, the total gauge Gu at the point Au, and the total gauge Gl at the point Al by the total gauge.

[0164] 7, the distance ΔAu' [mm] in the tire width direction from the tire maximum width position Ac to point Au' is within the range of 0.03≦ΔAu' / (Hu×0.70)≦0.23, and preferably within the range of 0.07≦ΔAu' / (Hu×0.70)≦0.17, relative to 70% of the distance Hu [mm] from the tire maximum width position Ac. This optimizes the curvature of the side profile in the radially outer region. Specifically, the lower limit suppresses stress concentration due to flattening of the tire side portions, improving tire durability. The upper limit reduces the amount of deflection of the tire side portions during tire rolling, thereby reducing tire rolling resistance. In particular, small-diameter tires tend to be subject to large stresses on the tire side portions due to use under the high internal pressure and high load described above, and therefore, there is also the issue of ensuring tire side cut resistance. In this regard, the lower limit ensures the radius of curvature of the side profile and optimizes the carcass tension, thereby suppressing tire collapse and side cuts in the tire, while the upper limit prevents side cuts in the tire caused by excessive tension in the carcass layer 13.

[0165] Furthermore, the distance ΔAl' [mm] in the tire width direction from the tire maximum width position Ac to point Al' is in the range of 0.03≦ΔAl' / (Hl×0.70)≦0.28, and preferably in the range of 0.07≦ΔAl' / (Hl×0.70)≦0.20, relative to 70% of the distance Hl [mm] from the tire maximum width position Ac. This optimizes the curvature of the side profile in the radially inner region. Specifically, the above lower limit suppresses stress concentration due to flattening of the tire side portion, improving tire durability. In particular, in small-diameter tires, the bead core 11 is reinforced as described above, effectively suppressing stress concentration near the bead core 11. The above upper limit reduces the amount of deflection of the tire side portion during tire rotation, thereby reducing tire rolling resistance.

[0166] The distances ΔAu′ and ΔAl′ are measured with the tire mounted on a specified rim, with a specified internal pressure applied, and under no load.

[0167] Furthermore, it is preferable that the distance ΔAu' [mm] in the tire width direction from the tire maximum width position Ac to point Au' satisfies the following formula (18) with respect to the radius of curvature RSc [mm] of the arc passing through the tire maximum width position Ac, point Au', and point Al', where Rmin=0.05, Rmax=5.00, and preferably Rmin=0.10, Rmax=4.50.

[0168]

number

[0169] 7, the distance ΔBu' [mm] in the tire width direction from point Bc to point Bu' is in the range of 1.10≦ΔBu' / ΔAu'≦8.00, and preferably 1.60≦ΔBu' / ΔAu'≦7.50, relative to the distance ΔAu' [mm] in the tire width direction from the tire maximum width position to point Au'. This optimizes the relationship between the curvature of the side profile and the curvature of the carcass profile in the radially outer region. Specifically, the lower limit ensures cut resistance in the tire side portion. The upper limit ensures tension in the carcass layer 13 and rigidity in the tire side portion, thereby ensuring the load capacity and durability of the tire.

[0170] 7, the distance ΔBl' [mm] in the tire width direction from point Bc to point Bl' is in the range of 1.80≦ΔBl' / ΔAl'≦11.0, and preferably 2.30≦ΔBl' / ΔAl'≦9.50, relative to the distance ΔAl' [mm] in the tire width direction from tire maximum width position Ac to point Al'. This optimizes the relationship between the curvature of the side profile and the curvature of the carcass profile in the radially inner region. Specifically, the lower limit ensures the total gauge Gl of the tire side portion, thereby ensuring the load-bearing capacity of the tire side portion. The upper limit ensures the tension of the carcass layer 13 and the rigidity of the tire side portion, thereby ensuring the load-bearing capacity and durability of the tire.

[0171] The distances ΔBu' and ΔBl' are measured with the tire mounted on a specified rim, with a specified internal pressure applied, and under no load.

[0172] Furthermore, it is preferable that the distance ΔBu' [mm] in the tire width direction from point Bc to point Bu' satisfies the following formula (19) with respect to the radius of curvature RCc [mm] of the arc passing through points Bc, Bu', and Bl', where Smin=0.40 and Smax=7.0, and preferably Smin=0.50 and Smax=6.0.

[0173]

number

[0174] 7, the rubber gauge Gcr [mm] of the sidewall rubber 16 at the tire maximum width position Ac is in the range of 0.40≦Gcr / Gc≦0.90 relative to the total gauge Gc [mm] at the tire maximum width position Ac. The rubber gauge Gcr [mm] of the sidewall rubber 16 is in the range of 1.5≦Gcr, and preferably in the range of 2.5≦Gcr. The lower limit ensures the rubber gauge Gcr [mm] of the sidewall rubber 16, thereby ensuring the load capacity of the sidewall portion.

[0175] It is also preferable that the rubber gauge Gcr [mm] of the sidewall rubber 16 at the tire maximum width position Ac satisfies the following formula (20) with respect to the total gauge Gc [mm] at the tire maximum width position Ac and the tire outer diameter OD [mm]: where Tmin=80, Tmax=0.90, and preferably Tmin=120, Tmax=0.90.

[0176]

number

[0177] 7, the rubber gauge Gin [mm] (not shown) of the inner liner 18 at the tire maximum width position Ac is in the range of 0.03≦Gin / Gc≦0.50, and preferably 0.05≦Gin / Gc≦0.40, relative to the total gauge Gc [mm] at the tire maximum width position Ac. This ensures that the inner surface of the carcass layer 13 is properly protected.

[0178] As described above, the tire 1 includes a pair of bead cores 11, 11, a carcass layer 13 spanned between the bead cores 11, 11, and a belt layer 14 disposed radially outward of the carcass layer 13 (see FIG. 1). The tire outer diameter OD [mm] is in the range of 200≦OD≦660, and the tire total width SW [mm] is in the range of 100≦SW≦400. The strength Tcs [N / 50mm] per 50 mm of width [mm] of the carcass ply constituting the carcass layer 13 is in the range of 17≦Tcs / OD≦120 relative to the tire outer diameter OD [mm].

[0179] This configuration has the advantage that the load capacity of the carcass layer 13 is appropriately ensured in small-diameter tires, thereby achieving both tire wear resistance and low rolling resistance. Specifically, the above-mentioned lower limit of the ratio Tcs / OD suppresses tire deformation during use under high loads, ensuring tire wear resistance. It also enables use at high internal pressures, reducing tire rolling resistance. In particular, small-diameter tires are expected to be used under high internal pressures and high loads, so the above-mentioned tire wear resistance and reduced rolling resistance effects are significantly achieved. The above-mentioned upper limit of the ratio Tcs / OD suppresses deterioration of rolling resistance due to an increase in the mass of the carcass layer.

[0180] In the tire 1, the carcass ply of the carcass layer 13 is formed by covering steel carcass cords with coating rubber. The cord diameter φcs [mm] of the carcass cord is in the range of 0.3≦φcs≦1.1, and the end count Ecs [cords / 50 mm] of the carcass cord is in the range of 25≦Ecs≦80. This has the advantage of realizing the strength Tcs of the carcass layer 13 described above.

[0181] In the tire 1, the carcass ply of the carcass layer 13 is formed by covering carcass cords made of organic fibers with coating rubber. The cord diameter φcs [mm] of the carcass cord is in the range of 0.6≦φcs≦0.9, and the end count Ecs [cords / 50 mm] of the carcass cord is in the range of 40≦Ecs≦70. This has the advantage of realizing the strength Tcs of the carcass layer 13 described above.

[0182] In this tire 1, the carcass layer 13 has a main body portion 131 extending along the tire inner surface and a turned-up portion 132 that is turned up outward in the tire width direction to wrap around the bead core 11 and extends in the tire radial direction (see FIG. 1). The radial height Hcs [mm] from the measurement point of the rim diameter RD to the end of the turned-up portion 132 of the carcass layer 13, relative to the tire cross-sectional height SH [mm], is in the range of 0.49≦Hcs / SH≦0.80 (see FIG. 2). This has the advantage of optimizing the radial height Hcs of the turned-up portion 132 of the carcass layer 13. Specifically, the lower limit ensures the load capacity of the tire side portion, and the upper limit suppresses deterioration of rolling resistance due to an increase in the mass of the carcass layer.

[0183] In addition, in this tire 1, the contact height Hcs' [mm] between the main body 131 and the turned-up portion 132 of the carcass layer 13 is in the range of 0.07≦Hcs' / SH relative to the tire cross-sectional height SH [mm] (see FIG. 2 ), which has the advantage of effectively increasing the load capacity of the tire sidewalls.

[0184] In addition, in the tire 1, the distance Tsh at the tire ground contact edge T is in the range of 1.50≦Tsh / Tu≦6.90 where Tu [mm] is the rubber gauge from the end of the wide cross belt 141 to the outer circumferential surface of the carcass layer 13 (see FIG. 5 ). This has the advantage of optimizing the profile of the carcass layer 13 and optimizing the tension of the carcass layer 13.

[0185] Furthermore, in this tire 1, the distance ΔBu' [mm] in the tire width direction from point Bc to point Bu' is in the range of 1.10≦ΔBu' / ΔAu'≦8.00 relative to the distance ΔAu' [mm] in the tire width direction from tire maximum width position Ac to point Au' (see FIG. 7). This has the advantage of optimizing the relationship between the curvature of the side profile and the curvature of the carcass profile in the radially outer region. Specifically, the above lower limit ensures cut resistance in the tire side portion. The above upper limit ensures tension in the carcass layer 13 and rigidity in the tire side portion, thereby ensuring the load capacity and durability of the tire.

[0186] Furthermore, in this tire 1, the distance ΔBl' [mm] in the tire width direction from point Bc to point Bl' is in the range of 1.80≦ΔBl' / ΔAl'≦11.0 relative to the distance ΔAl' [mm] in the tire width direction from tire maximum width position Ac to point Al' (see FIG. 7). This has the advantage of optimizing the relationship between the curvature of the side profile and the curvature of the carcass profile in the radially inner region. Specifically, the lower limit ensures the total gauge Gl of the tire side portion, thereby ensuring the load-bearing capacity of the tire side portion. The upper limit ensures the radius of curvature RCc of the carcass profile, thereby ensuring the tire internal volume V, and therefore the tire load-bearing capacity.

[0187] Furthermore, in this tire 1, the drop amount DA [mm] of the tread profile at the tire contact edge T satisfies the relationship 0.008≦DA / TW≦0.060 relative to the tire contact width TW [mm] (see FIG. 4). This optimizes the drop angle (defined as the ratio DA / (TW / 2)) in the tread shoulder region, thereby ensuring the appropriate load capacity of the tread. Specifically, the lower limit ensures the drop angle in the tread shoulder region, suppressing a decrease in wear life due to excessive contact pressure in the tread shoulder region. The upper limit flattens the tire contact region and equalizes the contact pressure, ensuring the tire's wear resistance. In particular, small-diameter tires are expected to be used under high internal pressure and high loads, so the above configuration effectively optimizes the contact pressure distribution in the tire contact region.

[0188] In the tire 1, the belt layer 14 includes a pair of cross belts 141, 142 formed by coating steel belt cords with coating rubber (see FIG. 1). The strength Tbt [N / 50mm] per 50 mm of width of each of the pair of cross belts 141, 142 is in the range of 25≦Tbt / OD≦250 relative to the tire outer diameter OD [mm]. This has the advantage of ensuring the appropriate load capacity of the cross belts 141, 142. Specifically, the lower limit suppresses tire deformation during use under high loads, ensuring tire wear resistance. Furthermore, use under high internal pressure is possible, reducing tire rolling resistance. Small-diameter tires, in particular, are expected to be used under high internal pressures and high loads, and therefore the aforementioned effects of tire wear resistance and reduced rolling resistance are significantly achieved. The upper limit suppresses deterioration of rolling resistance due to an increase in the mass of the cross belts.

[0189] In addition, in this tire 1, the strength Tbd [N] of one bead core 11 is in the range of 45≦Tbd / OD≦120 relative to the tire outer diameter OD [mm]. This has the advantage of ensuring the appropriate load capacity of the bead core 11. Specifically, the above lower limit suppresses tire deformation during use under high load, ensuring the tire's wear resistance. It also enables use at high internal pressure, reducing the tire's rolling resistance. In particular, small-diameter tires are expected to be used under high internal pressure and high load, so the above-mentioned tire wear resistance and reduced rolling resistance are significantly achieved. The above upper limit suppresses deterioration of rolling resistance due to an increase in the mass of the bead core.

[0190] In the tire 1, the bead core 11 is made of a bead wire made of steel. The total cross-sectional area σbd [mm^2] of the bead wire is in the range of 0.025≦σbd / OD≦0.075 with respect to the tire outer diameter OD [mm]. This has the advantage of realizing the strength Tbd [N] of the bead core 11 described above.

[0191] [Tread surface] FIG. 8 is a diagram illustrating an example of a tread surface of a tread portion. As shown in FIG. 8, the tread portion has circumferential main grooves 21a, 21b, 22a, and 22b extending in the tire circumferential direction. These four circumferential main grooves 21a, 21b, 22a, and 22b define and define multiple land portions 30, 31a, 31b, 32a, and 32b. The tread portion also has lateral grooves 24a, 24b, 25a, and 25b. The lateral groove 24a extends in the tire circumferential direction and the tire width direction to connect the circumferential main grooves 21a and 22a. The lateral groove 24b extends in the tire circumferential direction and the tire width direction to connect the circumferential main grooves 21b and 22b. The lateral groove 25a extends from the circumferential main groove 22a outward in the tire width direction, reaching the outside of the ground contact edge T. The lateral grooves 25b extend outward in the tire width direction from the circumferential main groove 22b and reach the outside of the ground contact edge T. In Fig. 8, the symbol Tss indicates the tire ground contact region. In the ground contact region Tss, the tire ground contact width is indicated by the symbol TW, and the tire ground contact length is indicated by the symbol TL.

[0192] In Figure 8, the tread center region Rce is the region centered on the tire equatorial plane CL and is defined as the contact width TW × 40 × (OD / SW)^(1 / 4). The tread shoulder regions Rsh are the regions included in the contact width TW other than the tread center region Rce.

[0193] [Groove area ratio] In a tire 1 having a tread surface shown in FIG. 8, the tire outer diameter OD [mm] is in the range of 200≦OD≦660, the tire total width SW [mm] is in the range of 100≦SW≦400, and the groove area ratio Aa [%] is in the range of 0.008≦Aa / OD≦0.15, and further, the groove area ratio Ace of the center region Rce of the tread portion [%] and the groove area ratio Ash of the shoulder region Rsh of the tread [%] It is preferable that the relationship between Ace and Ash is Ace > Ash, i.e., Ace / Ash > 1. When the purpose is to compensate for drainage performance, the smaller the tire outer diameter OD, the larger the groove area ratio value must be. The center region Rce contributes more to drainage than the shoulder region Rsh. Therefore, wet performance can be effectively compensated for by making the groove area in the center region Rce larger than that in the shoulder region Rsh. Since a small total width SW also narrows the contact width, it is necessary to increase the center region Rce to improve wet performance. Similarly, a large outer diameter OD increases the tire contact length TL and narrows the contact width TW, so it is necessary to increase the center region Rce.

[0194] The groove area ratio is the ratio of the total area of ​​grooves arranged in a predetermined region of the tread portion to the area of ​​that region. [%] is the groove area / (groove area + contact area) ×100It is defined by. The groove area refers to the opening area of the groove on the ground contact surface. Also, the groove refers to the circumferential groove, fine groove, and transverse groove (lug groove) of the tread portion, excluding sipes and kerfs. Further, the ground contact area refers to the contact area between the tire and the ground contact surface. Also, the groove area and the ground contact area are measured at the contact surface between the tire and the flat plate when the tire is mounted on a specified rim, a specified internal pressure (230 kPa) is applied, and it is placed perpendicular to the flat plate in a stationary state and a load corresponding to a specified load (80% of the maximum load capacity) is applied.

[0195] This tire can be equipped with a sound-absorbing material as a noise countermeasure considering uses such as a moving conference room, or can be equipped with a sensor, a sealant, and a thermoplastic resin inner liner for the purpose of maintenance-free assuming the use of a dedicated transport vehicle. It is also highly effective to mount this tire on a vehicle equipped with a monitoring system. When used at a high internal pressure, since tread wear reaches its limit before the durability limits of the tire side portion and the belt portion, it is also suitable for retread use.

[0196] Also, the groove area ratio Ace [%] and the groove area ratio Ash [%] are more preferably in the relationship of 1 < Ace / Ash ≦ 2.0 + (100 / OD). By being in this relationship, wet performance and wear resistance can be improved. When the outer diameter OD is small, the tire ground contact length TL is short, and there is a possibility that the wet performance becomes insufficient. Therefore, it is good to increase the groove area ratio Ace.

[0197] The groove area ratio Ace [%] and the groove area ratio Ash [%] are more preferably in the relationship of 1.05 ≦ Ace / Ash ≦ 1.7 + (100 / OD). The groove area ratio Ace [%] and the groove area ratio Ash [%] are even more preferably in the relationship of 1.10 ≦ Ace / Ash ≦ 1.5 + (100 / OD).

[0198] [Groove depth] The maximum groove depth Gmax [mm] of the tread portion preferably satisfies the relationship 0.006≦Gmax / OD≦0.083. By satisfying this relationship, wet performance and wear resistance can be further improved. If the outer diameter OD is large, the tire contact length TL becomes long, which may lead to a deterioration in wear resistance, so it is advisable to make the groove depth deeper. The maximum groove depth Gmax [mm] more preferably satisfies the relationship 0.007≦Gmax / OD≦0.060. The maximum groove depth Gmax [mm] further preferably satisfies the relationship 0.008≦Gmax / OD≦0.050.

[0199] The relationship between the maximum groove depth Gce [mm] of the tread center region Rce and the maximum groove depth Gsh [mm] of the tread shoulder region Rsh is preferably 1≦Gce / Gsh≦2.5. For example, the groove depth of the circumferential main groove closest to the tire equatorial plane CL is the maximum groove depth Gce [mm]. Also, for example, the groove depth of the circumferential main groove closest to the contact edge T is the maximum groove depth Gsh [mm]. By satisfying this relationship, wet performance and wear resistance can be further improved. Groove depth has a large contribution to wet performance. For this reason, the groove area ratio Ace [%] and groove area ratio Ash [%] By making the maximum groove depth Gce larger than the maximum groove depth Gsh while satisfying the above relationship, wet performance and wear resistance can be further improved.

[0200] The relationship between the maximum groove depth Gce and the maximum groove depth Gsh is more preferably 1≦Gce / Gsh≦2.0. The relationship between the maximum groove depth Gce and the maximum groove depth Gsh is even more preferably 1≦Gce / Gsh≦1.8. Note that as the outer diameter OD increases, it is preferable to make the value of Gce / Gsh smaller (i.e., closer to the lower limit). When the outer diameter OD is large, wear performance is advantageous, so by deepening the grooves in the shoulder region, which has a small groove area ratio, it is possible to achieve both wet performance and good wet performance.

[0201] The relationship between the number of pitches Pce [pieces] in the tread center region Rce and the number of pitches Psh [pieces] in the shoulder regions Rsh is preferably 0.4≦Pce / Psh≦1.2. This relationship between the number of pitches Pce and the number of pitches Psh can improve wet performance and wear resistance. The relationship between the number of pitches Pce and the number of pitches Psh is more preferably 0.5≦Pce / Psh≦1.0. The number of pitches refers to the number of lateral grooves 24a or 24b formed at a predetermined pitch length around the circumference of the tire. When the outer diameter OD is small, it is preferable to reduce the number of pitches Pce.

[0202] In the tread center region Rce, the relationship between the average lateral groove width WLce [mm] within the tire contact length TL and the average number of pitches PCce [pieces] within the tire contact length TL is preferably 1500≦(WLce×PCce×OD)≦33000. Since the larger the outer diameter OD, the larger the contact area, it is preferable to reduce the lateral groove area within the contact area. The above relationship between the average lateral groove width WLce and the average number of pitches PCce can further improve wet performance and wear resistance. It is more preferable that the relationship between the average lateral groove width WLce and the average number of pitches PCce is 3000≦(WLce×PCce×OD)≦26000. If there are ribs with different average lateral groove widths and average number of pitches, the judgment is based on the average values ​​for each rib.

[0203] It is preferable that the average number of pitches PCce [pieces] within the tire contact patch length TL around the entire tire circumference in the tread center region Rce satisfies the relationship 0.005≦PCce / OD≦0.020. Within the range where this relationship is satisfied, the larger the outer diameter OD, the longer the tire circumference, so the number of pitches Pce can be increased to allow for the placement of more lateral grooves. By satisfying the above relationship, the same effect can be achieved at any contact patch, further improving wet performance and wear resistance. It is more preferable that the average number of pitches PCce [pieces] within the tire circumference satisfy the relationship 0.007≦PCce / OD≦0.017. The average number of pitches PCce is a natural number. [Example]

[0204] 9 to 11 are tables showing the results of performance tests of the tires according to the embodiments of the present invention.

[0205] In this performance test, several types of test tires were evaluated for (1) wet performance (wet steering stability) and (2) wear resistance. Two types of test tires were used as examples of small-diameter tires. Specifically, [A] a test tire with a tire size of 235 / 45R10 was mounted on a rim with a rim size of 10x8, and [B] a test tire with a tire size of 145 / 80R12 was mounted on a rim with a rim size of 12x4.00B.

[0206] (1) Evaluation of wet performance is performed by applying an internal pressure of 230 kPa and a load of 4.2 kN to the test tire [A] above, and applying an internal pressure of 80% of the JATMA-specified internal pressure and a load of 80% of the JATMA-specified load to the test tire [B] above. A four-wheel low-floor vehicle fitted with the test tires is then driven on a test course in the rain, and a test driver performs a sensory test on the handling stability performance. Evaluation is performed using an index with the comparative example as the standard (100), with the higher the index, the better the wet performance.

[0207] (2) In the evaluation of wear resistance, the test tire [A] above is pressurized to 230 kPa and subjected to a load of 4.2 kN, and the test tire [B] above is pressurized to 80% of the JATMA-specified internal pressure and subjected to a load of 80% of the JATMA-specified load. A four-wheel low-floor vehicle fitted with the test tires is driven 10,000 km on a dry test course. The amount of wear and uneven wear of each tire are then measured and evaluated. This evaluation is based on an index rating, with the comparative tire being assigned a standard of 100, with higher values ​​being more preferable.

[0208] The test tire of the example has the structure shown in Figure 1, and includes a pair of bead cores 11, 11, a carcass layer 13 consisting of a single-layer carcass ply, a belt layer 14 consisting of a pair of cross belts 141, 142, a belt cover 143 and a pair of belt edge covers 144, 144, a tread rubber 15, a sidewall rubber 16 and a rim cushion rubber 17.

[0209] The test tire of the comparative example is the test tire of Example 1, with a tire outer diameter OD of 531 mm, a tire total width SW of 143 mm, and a tire contact width TW of 123 mm, and is mounted on a rim of rim size 12.

[0210] As the test results show, the test tires of the examples have both good wet performance and good wear resistance. [Explanation of symbols]

[0211] 1 tire; 10 rim; 11 bead core; 12 bead filler; 13 carcass layer; 131 main body; 132 turn-up portion; 14 belt layer; 141, 142 cross belt; 143 belt cover; 144 belt edge cover; 15 tread rubber; 151 cap tread; 152 undertread; 16 sidewall rubber; 17 rim cushion rubber; 18 inner liner; 21a, 21b, 22a, 22b circumferential main groove; 24a, 24b, 25a, 25b lateral groove

Claims

1. A tire comprising a pair of bead cores, a carcass layer stretched across the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, The tire outer diameter OD [mm] is in the range of 200≦OD≦660, The total tire width SW [mm] is in the range of 100≦SW≦400, a groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, a groove area ratio Ace [%] of a center region of the tread portion and a groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, The tire is characterized in that the relationship between the number of pitches Pce in the center region of the tread portion and the number of pitches Psh in the shoulder regions of the tread portion satisfies 0.4≦Pce / Psh≦1.

2.

2. A tire comprising a pair of bead cores, a carcass layer stretched across the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, The tire outer diameter OD [mm] is in the range of 200≦OD≦660, The total tire width SW [mm] is in the range of 100≦SW≦400, a groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, a groove area ratio Ace [%] of a center region of the tread portion and a groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, A tire characterized in that the relationship between the average lateral groove width WLce within the tire ground contact length and the average pitch number PCce within the tire ground contact length in the center region of the tread portion is 1500≦(WLce×PCce×OD)≦33000.

3. A tire comprising a pair of bead cores, a carcass layer stretched across the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, The tire outer diameter OD [mm] is in the range of 200≦OD≦660, The total tire width SW [mm] is in the range of 100≦SW≦400, a groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, a groove area ratio Ace [%] of a center region of the tread portion and a groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, A tire characterized in that an average number of pitches PCce within a tire contact length over the entire circumference of the tire in a center region of the tread portion satisfies the relationship 0.005≦PCce / OD≦0.

020.

4. A tire comprising a pair of bead cores, a carcass layer stretched across the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, The tire outer diameter OD [mm] is in the range of 200≦OD≦660, The total tire width SW [mm] is in the range of 100≦SW≦400, a groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, a groove area ratio Ace [%] of a center region of the tread portion and a groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, A tire characterized in that the strength Tcs [N / 50mm] per 50 [mm] of the carcass ply constituting the carcass layer is in the range of 17≦Tcs / OD≦120 relative to the tire outer diameter OD [mm].

5. A tire comprising a pair of bead cores, a carcass layer stretched across the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, The tire outer diameter OD [mm] is in the range of 200≦OD≦660, The total tire width SW [mm] is in the range of 100≦SW≦400, a groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, a groove area ratio Ace [%] of a center region of the tread portion and a groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, The belt layer includes a pair of cross belts each formed by coating a steel belt cord with a coating rubber, and A tire characterized in that the strength Tbt [N / 50mm] per width 50 [mm] of each of the pair of cross belts is in the range of 25≦Tbt / OD≦250 relative to the tire outer diameter OD [mm].

6. A tire comprising a pair of bead cores, a carcass layer stretched across the bead cores, a belt layer disposed radially outward of the carcass layer, and a tread portion, The tire outer diameter OD [mm] is in the range of 200≦OD≦660, The total tire width SW [mm] is in the range of 100≦SW≦400, a groove area ratio Aa [%] of the tread portion is in the range of 0.008≦Aa / OD≦0.150, a groove area ratio Ace [%] of a center region of the tread portion and a groove area ratio Ash [%] of a shoulder region of the tread portion have a relationship of Ace / Ash>1, A tire characterized in that a strength Tbd [N] of one of the bead cores is in the range of 45≦Tbd / OD≦120 relative to the tire outer diameter OD [mm].

7. The bead core is made of a bead wire made of steel, and The tire according to claim 6, wherein the total cross-sectional area σbd [mm^2] of the bead wires is in a range of 0.025≦σbd / OD≦0.075 relative to the tire outer diameter OD [mm].

8. 8. The tire according to claim 1, wherein a groove area ratio Ace [%] in a center region of the tread portion and a groove area ratio Ash [%] in a shoulder region of the tread portion satisfy the relationship 1 < Ace / Ash ≦ 2.0 + (100 / OD).

9. The tire according to any one of claims 1 to 7, wherein the maximum groove depth Gmax of the tread portion satisfies the relationship: 0.006≦Gmax / OD≦0.

083.

10. 8. The tire according to claim 1, wherein a relationship between a maximum groove depth Gce in a center region of the tread portion and a maximum groove depth Gsh [mm] in shoulder regions of the tread portion satisfies 1≦Gce / Gsh≦2.5.

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