JP7832438B2 - tire - Google Patents

Description

This invention relates to a tire, and more specifically, to a small-diameter tire that can achieve both excellent obstacle-climbing performance and fuel efficiency.

In recent years, small-diameter tires have been developed for vehicles with lowered floors to expand interior space. These small-diameter tires have low rotational inertia and low tire weight, which is expected to reduce transportation costs. However, small-diameter tires require high load capacity. Regarding conventional tires addressing these challenges, the technology described in Patent Document 1 is known.

International Publication No. 2020/122169

This invention aims to provide a small-diameter tire that achieves both excellent obstacle-climbing performance and fuel efficiency.

To achieve the above objective, the tire according to this invention comprises a pair of bead cores, a carcass layer spanning the bead cores, a belt layer arranged radially outside the carcass layer, and a tread portion, wherein the tire outer diameter OD [mm] is in the range of 250 ≤ OD ≤ 580 , the tire total width SW [mm] is in the range of 100 ≤ SW ≤ 400, the groove area ratio Aa [%] of the entire tread portion is in the range of 25 + 100 × (25.4/OD) ≤ Aa ≤ 50 + 100 × (25.4/OD), and the total gauge Gu [mm] of the tire side portion at point Au on the side profile, which is at the same position in the tire radial direction as the end of the innermost layer of the belt layer, is in the range of 0.010 ≤ Gu/OD ≤ 0.080 with respect to the tire outer diameter OD [mm].

The tire according to this invention has the advantage of achieving both excellent obstacle-climbing performance and fuel efficiency. Specifically, by having the groove area ratio Aa [%] of the tread section within the above range, the tire's obstacle-climbing performance and fuel efficiency are ensured.

Figure 1 is a cross-sectional view of a tire in the meridian direction, showing a tire according to an embodiment of this invention. Figure 2 is an enlarged view of the tire shown in Figure 1. Figure 3 is an explanatory diagram showing the laminated structure of the tire belt layer described in Figure 1. Figure 4 is an enlarged view showing the tire tread section described in Figure 1. Figure 5 is an enlarged view showing one side of the tread area described in Figure 4. Figure 6 is an enlarged view showing the sidewall and bead portions of the tire described in Figure 1. Figure 7 is an enlarged view showing the sidewall section described in Figure 6. Figure 8 shows an example of the tread surface of the tread section. Figure 9 is a diagram showing the results of a performance test of a tire according to an embodiment of this invention. Figure 10 is a diagram showing the results of a performance test of a tire according to an embodiment of this invention. Figure 11 is a chart showing the results of a performance test of a tire according to an embodiment of this invention. Figure 12 is a diagram showing the results of a performance test of a tire according to an embodiment of this invention.

The present invention will be described in detail below with reference to the drawings. However, this embodiment does not limit the present invention. Furthermore, the components of this embodiment include those that are substituted and obvious for substitution while maintaining the identity of the invention. Also, the various modifications described in this embodiment can be arbitrarily combined within the scope of what is obvious to those skilled in the art.

[tire]
Figure 1 is a cross-sectional view of a tire 1 according to an embodiment of the present invention, taken in the meridian direction of the tire. The figure shows a cross-sectional view of one side region in the 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.

In this figure, the tire meridian cross-section is defined as the cross-section obtained when the tire is cut by a plane containing the tire rotation axis (not shown). The tire equatorial plane CL is defined as a plane passing through the midpoint of the tire cross-sectional width as defined by JATMA and perpendicular to the tire rotation axis. The tire width direction is defined as the direction parallel to the tire rotation axis, and the tire radial direction is defined as the direction perpendicular to the tire rotation axis. Point T is the tire contact point, and point Ac is the tire's maximum width position.

The tire 1 has an annular structure centered on the tire rotation axis and comprises 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).

The pair of bead cores 11, 11 are made by winding one or more bead wires made of steel in a ring-like and multi-layered manner, and are embedded in the bead portion to form the core of the left and right bead portions. The pair of bead fillers 12, 12 are positioned on the outer circumference of the pair of bead cores 11, 11 in the radial direction of the tire, respectively, to reinforce the bead portion.

The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass ply layers stacked together, and is stretched in a toroidal manner between the left and right bead cores 11, 11 to form the tire's skeleton. Furthermore, both ends of the carcass layer 13 are wound back outward in the tire width direction and secured to enclose the bead cores 11 and bead filler 12. The carcass ply of the carcass layer 13 is constructed by covering multiple carcass cords made of steel or organic fiber material (e.g., aramid, nylon, polyester, rayon, etc.) with a coating rubber and then rolling it, and has a cord angle of 80 [deg] to 100 [deg] (defined as the longitudinal inclination angle of the carcass cords with respect to the tire's circumferential direction).

The belt layer 14 is formed by stacking multiple belt plies 141 to 144 and is arranged around the outer circumference of the carcass layer 13. In the configuration shown in Figure 1, the belt plies 141 to 144 consist of a pair of cross belts 141 and 142, a belt cover 143, and a pair of belt edge covers 144, 144.

The pair of cross belts 141 and 142 are constructed by coating multiple belt cords made of steel or organic fiber material with a rubber coating and then rolling them. They have a cord angle (defined as the angle of inclination of the belt cords in the longitudinal direction relative to the tire circumferential direction) of 15 degrees to 55 degrees in absolute value. Furthermore, the pair of cross belts 141 and 142 have cord angles of opposite signs, and are laminated with their longitudinal directions intersecting each other (a so-called cross-ply structure). The pair of cross belts 141 and 142 are also laminated and arranged on the radially outer side of the carcass layer 13.

The belt cover 143 and the pair of belt edge covers 144, 144 are constructed by covering a belt cover cord made of steel or organic fiber material with coated rubber, and have a cord angle of 0 [deg] or more and 10 [deg] or less in absolute value. Furthermore, the belt cover 143 and belt edge covers 144 are, for example, strip materials made by covering one or more belt cover cords with coated rubber, and these strip materials are wrapped spirally multiple times around the outer circumferential surface of the cross belts 141 and 142 in the tire circumferential direction. The belt cover 143 is positioned to cover the entire area of the cross belts 141 and 142, and the pair of belt edge covers 144, 144 are positioned to cover the left and right edges of the cross belts 141 and 142 from the outside in the tire radial direction.

The tread rubber 15 is arranged on the radial outer circumference of the carcass layer 13 and belt layer 14, forming the tread portion of the tire 1. The tread rubber 15 also includes a cap tread 151 and an under tread 152.

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

The rubber hardness Hs is measured under a temperature of 20°C in accordance with JIS K6253.

The modulus (breaking strength) is measured by a tensile test at 20°C using a dumbbell-shaped test specimen, in accordance with JIS K6251 (using a No. 3 dumbbell).

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

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

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

A pair of sidewall rubbers 16, 16 are positioned on the outer side of the carcass layer 13 in the tire width direction, forming the left and right sidewall sections. In the configuration shown in Figure 1, the outer ends of the sidewall rubbers 16 in the tire radial direction are positioned in the lower layer of the tread rubber 15 and sandwiched between the end of the belt layer 14 and the carcass layer 13. However, this is not limited to this configuration; the outer ends of the sidewall rubbers 16 in the tire radial direction may also be positioned in the outer layer of the tread rubber 15 and exposed in the buttress section 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.

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

The pair of rim cushion rubbers 17, 17 extend from the inner side in the tire radial direction to the outer side in the tire width direction of the bead cores 11, 11 and the winding portion of the carcass layer 13, forming the rim fitting surface of the bead portion. In the configuration shown in Figure 1, the outer end of the rim cushion rubber 17 in the tire radial direction is inserted into the lower layer of the sidewall rubber 16 and is sandwiched between the sidewall rubber 16 and the carcass layer 13.

The inner liner 18 is an air-permeability-preventing layer positioned on the inner surface of the tire and covering the carcass layer 13. It suppresses oxidation of the carcass layer 13 due to exposure and prevents air leakage from the tire. The inner liner 18 may be composed of, for example, a rubber composition primarily composed of butyl rubber, or a thermoplastic resin or a thermoplastic elastomer composition in which an elastomer component is blended into a thermoplastic resin.

Furthermore, in Figure 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 such small-diameter tires, the load performance improvement effect described later is significantly obtained. Also, 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 such small-diameter tires 1, for example, the floor of a small vehicle can be lowered to expand the interior space. Also, because the rotational inertia is low and the tire weight is small, fuel efficiency is improved and transportation costs are reduced. In particular, when mounted on an in-wheel motor of a vehicle, the load on the motor is effectively reduced.

The tire outer diameter (OD) is measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

The total tire width SW is measured as the straight-line distance between the sidewalls (including all parts of the tire's sidewall, such as patterns and lettering) when the tire is mounted on a specified rim, subjected to the specified internal pressure, and under no-load conditions.

The specified rim refers to the "Applicable Rim" as defined by JATMA, the "Design Rim" as defined by TRA, or the "Measuring Rim" as defined by ETRTO. The specified internal pressure refers to the "Maximum Air Pressure" as defined by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" as defined by TRA, or the "INFLATION PRESSURES" as defined by ETRTO. The specified load refers to the "Maximum Load Capacity" as defined by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" as defined by TRA, or the "LOAD CAPACITY" as defined 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.

Furthermore, the total tire width SW [mm] is within the range of 0.23 ≤ SW/OD ≤ 0.84 relative to the tire outer diameter OD [mm], and preferably within the range of 0.25 ≤ SW/OD ≤ 0.81.

Furthermore, it is preferable that the tire outer diameter OD and the tire total width SW satisfy the following formula (1). Here, 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.

The above tire 1 is assumed to use a rim 10 with a rim diameter of 5 inches to 16 inches (i.e., 125 mm to 407 mm). Furthermore, the rim diameter RD [mm] is within the range of 0.50 ≤ RD/OD ≤ 0.74 relative to the tire outer diameter OD [mm], preferably within the range of 0.52 ≤ RD/OD ≤ 0.71. The lower limit ensures the rim diameter RD, particularly securing space for the in-wheel motor. The upper limit ensures the tire's internal volume V, as described later, thus ensuring the tire's load capacity.

Note that the inner diameter of the tire is equal to the rim diameter RD of rim 10.

Furthermore, the above-mentioned tire 1 is intended for use at an internal pressure higher than the specified limit, specifically between 350 kPa and 1200 kPa, preferably between 500 kPa and 1000 kPa. The lower limit effectively reduces the tire's rolling resistance, while the upper limit ensures safety during the internal pressure filling process.

Furthermore, the above-mentioned tire 1 is envisioned to be mounted on vehicles that travel at low speeds, such as small shuttle buses. The vehicle's maximum speed is 100 km/h or less, preferably 80 km/h or less, and more preferably 60 km/h or less. The above-mentioned tire 1 is also envisioned to be mounted on vehicles with 6 to 12 wheels. This ensures that the tire's load capacity is properly utilized.

Furthermore, the tire aspect ratio, i.e., the ratio of the tire section height SH [mm] (see Figure 2 below) to the tire section width [mm] (dimension symbol omitted in the figure: same as the total tire width SW in Figure 1), is in the range of 0.16 to 0.85, preferably in the range of 0.19 to 0.82.

The tire section height SH is half the difference between the tire's outer diameter and its rim diameter. It is measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

The tire section width is measured as the straight-line distance between the sidewalls (excluding patterns, lettering, etc. on the tire sidewall) when the tire is mounted on a specified rim, subjected to the specified internal pressure, and under no load.

Furthermore, the tire contact patch width TW is within the range of 0.75 ≤ TW/SW ≤ 0.95 relative to the total tire width SW, and preferably within the range of 0.80 ≤ TW/SW ≤ 0.92.

The tire contact width TW is measured as the maximum straight-line distance in the axial direction of the tire at the contact surface between the tire and the flat plate when the tire is mounted on a specified rim, subjected to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state with a load corresponding to a specified load applied.

Furthermore, the tire internal volume V [m³] is within the range of 4.0 ≤ (V/OD) × 10⁶ ≤ 60 relative to the tire outer diameter OD [mm], preferably within the range of 6.0 ≤ (V/OD) × 10⁶ ≤ 50. This optimizes the tire internal volume V. Specifically, the lower limit ensures sufficient tire internal volume and thus the tire's load capacity. Especially for small-diameter tires, where high internal pressure and high loads are anticipated, it is preferable to ensure a sufficient tire internal volume V. The upper limit prevents the tire from becoming excessively large due to an oversized tire internal volume V.

Furthermore, the tire internal volume V [m³] is within the range of 0.5 ≤ V × RD ≤ 17 with respect to the rim diameter RD [mm], and preferably within the range of 1.0 ≤ V × RD ≤ 15.

[Bead Core]
In Figure 1, as described above, the pair of bead cores 11, 11 are formed by winding one or more bead wires (not shown) made of steel in a ring-like and multi-layered manner. In addition, the pair of bead fillers 12, 12 are arranged on the outer circumference of the pair of bead cores 11, 11 in the radial direction of the tire.

Furthermore, the strength Tbd [N] of one bead core 11 is in the range of 45 ≤ Tbd/OD ≤ 120 with respect to the tire outer diameter OD [mm], preferably in the range of 50 ≤ Tbd/OD ≤ 110, and more preferably in the range of 60 ≤ Tbd/OD ≤ 105. Also, the strength Tbd [N] of the bead core is in the range of 90 ≤ Tbd/SW ≤ 400 with respect to the total tire width SW [mm], preferably in the range of 110 ≤ Tbd/SW ≤ 350. This ensures that the load capacity of the bead core 11 is properly secured. Specifically, the above lower limits suppress tire deformation when used under high load, ensuring the wear resistance of the tire. In addition, it becomes possible to use the tire at high internal pressure, and the rolling resistance of the tire is reduced. In particular, for small diameter tires, where use under high internal pressure and high load is expected, the above-mentioned wear resistance and reduction of rolling resistance of the tire are significantly obtained. The above upper limit suppresses the deterioration of rolling resistance caused by the increase in bead core mass.

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-sectional view. The strength of the bead wire is measured by a tensile test at a temperature of 20 [°C] in accordance with JIS G3510 .

Furthermore, it is preferable that the strength Tbd [N] of the bead core 11 satisfies the following 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, it is preferable that B1min = 0.0016 × P and B2min = 0.07 × P, using the specified internal pressure P [kPa] of the tire.

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 at the tire's maximum width position Ac. It is measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

The tire's maximum width position Ac is defined as the position of the maximum width of the tire section as specified by JATMA.

Furthermore, in a radial cross-sectional view of a single bead core 11, the total cross-sectional area σbd [mm²] of the bead wire made of the steel described above is in the range of 0.025 ≤ σbd/OD ≤ 0.075 with respect to the tire outer diameter OD [mm], preferably in the range of 0.030 ≤ σbd/OD ≤ 0.065. Also, the total cross-sectional area σbd [mm²] of the bead wire is in the range of 11 ≤ σbd ≤ 36, preferably in the range of 13 ≤ σbd ≤ 33. This achieves the strong Tbd [N] of the bead core 11 described above.

The total cross-sectional area σbd [mm²] of the bead wire is calculated as the sum of the cross-sectional areas of the bead wire in the radial cross-sectional view of one bead core 11.

For example, in the configuration shown in Figure 1, the bead core 11 has a rectangular shape formed by arranging bead wires (not shown) with a circular cross-section in a grid pattern. However, it is not limited to this; the bead core 11 may also have a hexagonal shape formed by arranging bead wires with a circular cross-section in a close-packed structure (not shown). Furthermore, any bead wire arrangement structure can be adopted within the scope of what is obvious to those skilled in the art.

Furthermore, it is preferable that the total cross-sectional area σbd [mm²] of the bead wire satisfies the following formula (3) with respect to the tire outer diameter OD [mm], distance SWD [mm], and rim diameter RD [mm]. Here, Cmin = 30 and Cmax = 8, preferably Cmin = 25 and Cmax = 10.

Furthermore, the total cross-sectional area σbd [mm²] of the bead wire is in the range of 0.50 ≤ σbd/Nbd ≤ 1.40, and preferably in the range of 0.60 ≤ σbd/Nbd ≤ 1.20, with respect to the total number of cross-sections (i.e., total turns) Nbd [wires] of the bead wire in a radial cross-sectional view. That is, the cross-sectional area σbd' [mm²] of a single bead wire is in the range of 0.50 [mm²/wire] or more and 1.40 [mm²/wire] or less, and preferably in the range of 0.60 [mm²/wire] or more and 1.20 [mm²/wire] or less.

Furthermore, the maximum width Wbd [mm] of a single 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 with respect to the total cross-sectional area σbd [mm²] of the bead wire, preferably in the range of 0.20 ≤ Wbd/σbd ≤ 0.40.

Furthermore, in Figure 1, the distance Dbd [mm] between the centers of gravity of the pair of bead cores 11, 11 is in the range of 0.63 ≤ Dbd/SW ≤ 0.97 with respect to the total tire width SW [mm], preferably in the range of 0.65 ≤ Dbd/SW ≤ 0.95. The lower limit reduces the amount of tire deflection, thereby reducing tire rolling resistance. The upper limit reduces the stress acting on the tire sidewall, suppressing tire failure.

[Carcass layer]
Figure 2 is an enlarged view of tire 1 as shown in Figure 1. This figure shows one side of the tire, with the tire equatorial plane CL as the boundary.

In the configuration shown in Figure 1, as described above, the carcass layer 13 consists of a single carcass ply and is arranged in a toroidal manner between the left and right bead cores 11, 11. Furthermore, both ends of the carcass layer 13 are wrapped around the bead cores 11 and bead filler 12, and secured outwards in the tire width direction.

Furthermore, the strong Tcs [N/50mm] per 50 [mm] width of the carcass ply constituting the carcass layer 13 is in the range of 17 ≤ Tcs/OD ≤ 120 with respect to the tire outer diameter OD [mm], preferably in the range of 20 ≤ Tcs/OD ≤ 120. Also, the strong Tcs [N/50mm] of the carcass layer 13 is in the range of 30 ≤ Tcs/SW ≤ 260 with respect to the total tire width SW [mm], preferably in the range of 35 ≤ Tcs/SW ≤ 220. This ensures that the load capacity of the carcass layer 13 is properly secured. Specifically, the above lower limits suppress tire deformation when used under high load, ensuring the wear resistance of the tire. In addition, it becomes possible to use the tire at high internal pressure, reducing the rolling resistance of the tire. In particular, for small diameter tires, where use at high internal pressure and high load is expected, the above-mentioned wear resistance and reduction of rolling resistance of the tire are significantly obtained. The above upper limit suppresses the deterioration of rolling resistance caused by the increase in the mass of the carcass layer.

The strength Tcs [N/50mm] of the carcass ply is calculated as follows: The carcass ply that spans the left and right bead cores 11, 11 and extends across the entire inner circumference of the tire is defined as the effective carcass ply. The product of the strength per carcass cord [N/cord] constituting the effective carcass ply and the number of carcass cords driven in per 50 [mm] width [cords/50mm] on the tire's equatorial plane CL is calculated as the strength Tcs [N/50mm] of the carcass ply. The strength of the carcass cord is measured by a tensile test at a temperature of 20 [°C] in accordance with JIS L1017 . For example, in a configuration where one carcass cord is made up of multiple strands twisted together, the strength of the twisted single carcass cord is measured and the strength Tcs of the carcass layer 13 is calculated. Furthermore, in a configuration in which the carcass layer 13 has a multilayer structure (not shown) formed by stacking multiple effective carcass plies, the above-described strong Tcs is defined for each of the multiple effective carcass plies.

For example, in the configuration shown in Figure 1, the carcass layer 13 has a single-layer structure consisting of a single carcass ply (not shown in the figure), and the carcass ply is composed of carcass cords made of steel coated with coated rubber, arranged at a cord angle of 80 degrees to 100 degrees in the circumferential direction of the tire (not shown). Furthermore, the above-mentioned steel carcass cords have a cord diameter φcs [mm] in the range of 0.3 ≤ φcs ≤ 1.1 and a number of cords per 50 mm Ecs [cords/50 mm] in the range of 25 ≤ Ecs ≤ 80, thereby achieving the strong Tcs [N/50 mm] of the carcass layer 13. Also, the carcass cords are made by twisting together multiple strands, and the diameter of these strands φcss [mm] is in the range of 0.12 ≤ φcss ≤ 0.24, preferably in the range of 0.14 ≤ φcss ≤ 0.22.

Furthermore, the carcass ply may be composed of carcass cords made of organic fiber material (e.g., aramid, nylon, polyester, rayon, etc.) coated with a rubber coating. In this case, the strong Tcs [N/50mm] of the carcass layer 13 is achieved by having a cord diameter φcs [mm] in the range of 0.6 ≤ φcs ≤ 0.9 and a cord density Ecs [cords/50mm] in the range of 40 ≤ Ecs ≤ 70. Other carcass cords made of high-strength organic fiber material such as nylon, aramid, or hybrids can be used within the scope of what is obvious to those skilled in the art.

Furthermore, the carcass layer 13 may have a multilayer structure consisting of multiple, for example, two layers of carcass ply (not shown). This can effectively increase the load capacity of the tire.

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

The total strength TTcs [N/50mm] of the carcass layer 13 is calculated as the sum of the strength Tcs [N/50mm] of the effective carcass plies described above. Therefore, the total strength TTcs [N/50mm] of the carcass layer 13 increases with increasing strength Tcs [N/50mm] of each carcass ply, the number of layers of carcass plies, and the perimeter of the carcass plies.

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

Furthermore, in the configuration shown in Figure 1, the carcass layer 13 has a main body portion 131 that extends along the inner surface of the tire, and a winding portion 132 that is wound outward in the tire width direction to enclose the bead core 11 and extends in the tire radial direction. Also, in Figure 2, the radial height Hcs [mm] from the measurement point of the rim diameter RD to the end of the winding portion 132 of the carcass layer 13 is in the range of 0.49 ≤ Hcs/SH ≤ 0.80, preferably in the range of 0.55 ≤ Hcs/SH ≤ 0.75, relative to the tire cross-sectional height SH [mm]. This optimizes the radial height Hcs of the winding portion 132 of the carcass layer 13. Specifically, the lower limit ensures the load capacity of the tire sidewall, and the upper limit suppresses the deterioration of rolling resistance caused by an increase in the mass of the carcass layer.

The radial height Hcs [mm] of the winding portion 132 of the carcass layer 13 is measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

For example, in the configuration shown in Figure 2, the radially outer end (indicated by the symbol omitted in the figure) of the winding portion 132 of the carcass layer 13 lies in the region between the tire's maximum width position Ac and the end of the belt layer 14 (point Au, described later). More specifically, it lies within the region from the tire's maximum width position Ac to a radial position Au' at 70% of the distance Hu, described later. At this time, the contact height Hcs' [mm] between the main body portion 131 of the carcass layer 13 and the winding portion 132 is in the range of 0.07 ≤ Hcs'/SH with respect to the tire's cross-sectional height SH [mm], preferably in the range of 0.15 ≤ Hcs'/SH. This effectively increases the load capacity of the tire sidewall. While there is no particular upper limit to the ratio Hcs'/SH, it is constrained by the fact that the contact height Hcs' has the relationship Hcs' < Hcs with respect to the radial height Hcs of the winding portion 132 of the carcass layer 13.

The contact height Hcs' of the carcass layer 13 is the radial length of the area where the main body 131 and the winding portion 132 are in contact with each other. It is measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

Furthermore, the carcass layer 13 may have a so-called low-turn-up structure, so that the end of the winding portion 132 of the carcass layer 13 is positioned in the region between the tire's maximum width position Ac and the bead core (not shown).

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

In the configuration shown in Figure 1, as described above, the belt layer 14 is formed by laminating multiple belt plies 141 to 144. Furthermore, as shown in Figure 3, these belt plies 141 to 144 are composed of a pair of cross belts 141 and 142, a belt cover 143, and a pair of belt edge covers 144, 144.

At this time, the strength Tbt [N/50mm] per 50 [mm] width of each of the pair of cross belts 141 and 142 is in the range of 25 ≤ Tbt/OD ≤ 250 with respect to the tire outer diameter OD [mm], preferably in the range of 30 ≤ Tbt/OD ≤ 230. Furthermore, the strength Tbt [N/50mm] of the cross belts 141 and 142 is in the range of 45 ≤ Tbt/SW ≤ 500 with respect to the total tire width SW [mm], preferably in the range of 50 ≤ Tbt/SW ≤ 450. This ensures that the load capacity of each of the pair of cross belts 141 and 142 is appropriately secured. Specifically, the above lower limits suppress tire deformation during high-load use, ensuring the tire's wear resistance. It also enables use at high internal pressures, reducing the tire's rolling resistance. Especially with small-diameter tires, where high internal pressure and high loads are expected, the aforementioned wear resistance and reduction in rolling resistance of the tire are significantly improved. The above upper limit suppresses the deterioration of rolling resistance caused by the increase in mass of the cross belt.

The strength Tbt [N/50mm] of the belt ply is calculated as follows: The effective belt ply is defined as the belt ply that extends over the entire area of 80% of the tire contact width TW centered on the tire equatorial plane CL (i.e., the central part of the tire contact area). The strength Tbt [N/50mm] of the belt ply is calculated as the product of the strength per belt cord [N/cord] constituting the effective belt ply and the number of belt cords driven in per 50 mm width in the aforementioned 80% of the tire contact width TW area [cords]. The strength of the belt cord is measured by a tensile test at a temperature of 20°C in accordance with JIS L1017 . For example, in a configuration in which a single belt cord is made up of multiple strands twisted together, the strength of the twisted single belt cord is measured and the strength Tbt of the belt ply is calculated. Furthermore, in a configuration where the belt layer 14 is made up of multiple stacked effective carcass plies (see Figure 1), the above-described strong Tbit is defined for each of the multiple effective carcass plies. For example, in the configuration of Figure 1, the pair of cross belts 141 and 142 and the belt cover 143 correspond to effective belt plies.

For example, in the configuration shown in Figure 3, a pair of cross belts 141 and 142 are constructed by arranging steel belt cords covered with coated rubber at a cord angle (dimension symbols omitted in the figure) of 15 degrees to 55 degrees relative to the circumferential direction of the tire. Furthermore, the steel belt cords have a cord diameter φbt [mm] in the range of 0.50 ≤ φbt ≤ 1.80 and a number of cords Ebt [cords/50 mm] in the range of 15 ≤ Ebt ≤ 60, thereby achieving a strong Tbt [N/50 mm] for the cross belts 141 and 142. In addition, the cord diameter φbt [mm] and the number of cords Ebt [cords/50 mm] are preferably in the ranges of 0.55 ≤ φbt ≤ 1.60 and 17 ≤ Ebt ≤ 50, and more preferably in the ranges of 0.60 ≤ φbt ≤ 1.30 and 20 ≤ Ebt ≤ 40. Furthermore, the belt cord is made up of multiple strands twisted together, and the diameter of these strands, φbts [mm], is in the range of 0.16 ≤ φbts ≤ 0.43, preferably in the range of 0.21 ≤ φbts ≤ 0.39.

Furthermore, the cross belts 141 and 142 may also be constructed from belt cords made of organic fiber material (e.g., aramid, nylon, polyester, rayon, etc.) coated with coated rubber. In this case, the belt cord made of the organic fiber material has a cord diameter φbt [mm] in the range of 0.50 ≤ φbt ≤ 0.90 and a number of strands Ebt [strands/50 mm] in the range of 30 ≤ Ebt ≤ 65, thereby achieving the above-described strength Tbt [N/50 mm] of the cross belts 141 and 142. Additionally, belt cords made of high-strength organic fiber material such as nylon, aramid, or hybrids can be used within the scope of what is obvious to those skilled in the art.

Furthermore, the belt layer 14 may have an additional belt (not shown). Such an additional belt may be, for example, (1) a third crossing belt, constructed by covering multiple belt cords made of steel or organic fiber material with a rubber coating and rolling it, having a cord angle of 15 degrees to 55 degrees in absolute value, or (2) a so-called high-angle belt, constructed by covering multiple belt cords made of steel or organic fiber material with a rubber coating and rolling it, having a cord angle of 45 degrees to 70 degrees in absolute value, preferably 54 degrees to 68 degrees. The additional belt may also be positioned (a) between a pair of crossing belts 141, 142 and the carcass layer 13, (b) between the pair of crossing belts 141, 142, or (c) radially outside the pair of crossing belts 141, 142 (not shown). This improves the load capacity of the belt layer 14.

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

The total strength TTbt [N/50mm] of the belt layer 14 is calculated as the sum of the strength Tbt [N/50mm] of the effective belt plies (in Figure 1, the pair of cross belts 141, 142 and the belt cover 143). Therefore, the total strength TTbt [N/50mm] of the belt layer 14 increases with increasing strength Tbt [N/50mm] of each belt ply and the number of belt plies stacked.

Furthermore, the width Wb1 [mm] of the widest crossing belt (in Figure 3, the inner diameter crossing belt 141) of the pair of crossing belts 141 and 142 (including the additional belt in the configuration with the additional belt described above; not shown) is in the range of 1.00 ≤ Wb1/Wb2 ≤ 1.40 relative to the width Wb2 [mm] of the narrowest crossing belt (in Figure 3, the outer diameter crossing belt 142), preferably in the range of 1.10 ≤ Wb1/Wb2 ≤ 1.35. Also, the width Wb2 [mm] of the narrowest crossing belt is in the range of 0.61 ≤ Wb2/SW ≤ 0.96 relative to the total tire width SW [mm], preferably in the range of 0.70 ≤ Wb2/SW ≤ 0.94. The above lower limits ensure the width of the belt ply, optimize the contact pressure distribution in the tire contact area, and ensure the tire's resistance to uneven wear. The above upper limit reduces distortion at the ends of the belt ply during tire rolling, thereby suppressing separation of the surrounding rubber at the ends of the belt ply.

The width of the belt ply is the distance between the left and right ends of each belt ply along the tire's rotation axis. This measurement is taken with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

Furthermore, the width Wb1 [mm] of the widest of the pair of crossing belts 141 and 142 (including the additional belt in the configuration described above; not shown in the figure) is in the range of 0.85 ≤ Wb1/TW ≤ 1.23, and preferably in the range of 0.90 ≤ Wb1/TW ≤ 1.20, relative to the tire contact width TW [mm].

For example, in the configuration shown in Figures 1 to 3, a wide cross belt 141 is positioned in the innermost layer in the tire's radial direction, and a narrower cross belt 142 is positioned radially outside the wider cross belt 141. A belt cover 143 is positioned radially outside the narrower cross belt 142, covering the entirety of both the cross belts 141 and 142. Furthermore, a pair of belt edge covers 144, 144 are positioned radially outside the belt cover 143, spaced apart from each other, covering the left and right edges of the cross belts 141 and 142, respectively.

[Tread profile and tread gauge]
Figure 4 is an enlarged view showing the tread portion of tire 1 as described in Figure 1.

In Figure 4, the tread profile drop DA [mm] at the tire contact edge T, the tire contact width TW [mm], and the tire outer diameter OD [mm] have a relationship of 0.025 ≤ TW/(DA × OD) ≤ 0.400, preferably 0.030 ≤ TW/(DA × OD) ≤ 0.300. Furthermore, the tread profile drop DA [mm] at the tire contact edge T has a relationship of 0.008 ≤ DA/TW ≤ 0.060 with respect to the tire contact width TW [mm], preferably 0.013 ≤ DA/TW ≤ 0.050. This optimizes the drop angle of the tread shoulder region (defined as the ratio DA/(TW/2)), ensuring adequate load capacity for the tread. Specifically, the above lower limit ensures the drop angle of the tread shoulder region, suppressing a decrease in wear life caused by excessive contact pressure in the tread shoulder region. The above upper limit ensures a flat tire contact area and uniform contact pressure, thereby guaranteeing tire wear resistance. Especially for small-diameter tires, where high internal pressure and high loads are expected, the above configuration effectively optimizes the contact pressure distribution within the tire contact area.

The drop amount DA is the radial distance from the intersection point C1 of the tire's equatorial plane CL and tread profile in a cross-sectional view along the tire's meridian direction to the tire's contact edge T. It is measured under no-load conditions with the tire mounted on a specified rim and under specified internal pressure.

The tire profile is the contour line of the tire in a cross-sectional view along the tire meridian, and is measured using a laser profiler. For example, a tire profile measuring device (manufactured by Matsuo Co., Ltd.) is used as a laser profiler.

Furthermore, it is preferable that the tread profile drop DA [mm] at the tire contact edge T satisfies the following formula (5) with respect to the tire outer diameter OD [mm] and tire total width SW [mm]. Here, Emin = 3.5 and Emax = 17, preferably Emin = 3.8 and Emax = 13, and even more preferably Emin = 4.0 and Emax = 9.

Furthermore, in Figure 4, we define 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.

At this time, 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 with respect to the tire outer diameter OD [mm], preferably in the range of 0.18 ≤ TRc/OD ≤ 12. Furthermore, the radius of curvature TRc [mm] of the arc is in the range of 30 ≤ TRc ≤ 3000, preferably in the range of 50 ≤ TRc ≤ 2800, and even more preferably in the range of 80 ≤ TRc ≤ 2500. This ensures that the load capacity of the tread is properly secured. Specifically, the lower limit ensures that the center region of the tread is flat, the contact pressure in the tire contact area is uniform, and the tire's wear resistance is ensured. The upper limit suppresses the reduction in wear life caused by excessive contact pressure in the shoulder region of the tread. Especially in small-diameter tires, where high internal pressure and high load use are expected, the uniformity of contact pressure under such usage conditions is effectively achieved.

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

Furthermore, in Figure 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 contact edges T, T is in the range of 0.30 ≤ TRw/OD ≤ 16 with respect to the tire outer diameter OD [mm], preferably in the range of 0.35 ≤ TRw/OD ≤ 11. Also, the radius of curvature TRw [mm] of the arc is in the range of 150 ≤ TRw ≤ 2800, preferably in the range of 200 ≤ TRw ≤ 2500. This ensures that the load capacity of the tread is properly maintained. Specifically, the lower limit ensures that the entire tire contact area is flat, resulting in uniform contact pressure and ensuring the tire's wear resistance. The upper limit suppresses the reduction in wear life caused by excessive contact pressure in the tread shoulder area. Especially for small-diameter tires, where high internal pressure and high load use are anticipated, the above configuration effectively optimizes the contact pressure distribution in the tire contact area.

Furthermore, the radius of curvature TRw [mm] of the first arc passing through 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 arc passing through point C1 and the tire contact edge T. This optimizes the tire's contact shape. Specifically, the lower limit distributes the contact pressure in the center region of the tread, improving the tire's wear life. The upper limit suppresses the reduction in wear life caused by excessive contact pressure in the shoulder region of the tread.

Furthermore, in Figure 4, we define point B1 on the carcass layer 13 in the tire equatorial plane CL, the left and right tire contact points T, and the feet B2, B2 of the perpendiculars drawn from T to the carcass layer 13.

At this time, 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 in the range of 0.40 ≤ CRw/TRw ≤ 1.00, and more preferably in the range of 0.45 ≤ CRw/TRw ≤ 0.92, relative to the radius of curvature TRw of the arc passing through point C1 and the tire contact edges T, T. Furthermore, the radius of curvature CRw [mm] is in the range of 100 ≤ CRw ≤ 2500, preferably in the range of 120 ≤ CRw ≤ 2200. This further optimizes the tire contact shape. Specifically, the lower limit suppresses the decrease in wear life caused by the increase in rubber gauge in the tread shoulder area. The upper limit ensures the wear life in the tread center area.

Figure 5 is an enlarged view showing one side of the tread area described in Figure 4.

In the configuration shown in Figure 1, as described above, 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 under tread 152.

Furthermore, in Figure 5, the distance Tce [mm] from the tread profile on the tire equatorial plane CL to the outer surface of the wide cross belt 141 has a relationship of 0.008 ≤ Tce/OD ≤ 0.13 with respect to the tire outer diameter OD [mm], preferably 0.012 ≤ Tce/OD ≤ 0.10, and more preferably 0.015 ≤ Tce/OD ≤ 0.07. Also, the distance Tce [mm] is in the range of 5 ≤ Tce ≤ 25, preferably 7 ≤ Tce ≤ 20. This ensures that the load capacity of the tread portion is properly maintained. Specifically, the lower limit suppresses tire deformation during high-load use, ensuring the tire's wear resistance. Especially in small-diameter tires, where high internal pressure and high load use are expected, the above-mentioned wear resistance is significantly improved. The upper limit suppresses the deterioration of rolling resistance caused by an increase in the mass of the tread rubber.

The distance Tce is measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

The outer circumferential surface of the belt ply is defined as the radially outer surface of the entire belt ply, which consists of the belt cord and the coating rubber.

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

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

Distance Tsh is measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state. Furthermore, if there is no wide cross belt directly below the tire contact edge T, distance Tsh is measured as the distance from the tread profile to a virtual line extending the outer circumference of the belt ply.

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

Furthermore, in Figure 5, a section with 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%, preferably in the range of 0% to 20%. With 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 ends of the belt plies 141 to 144) is set to be small, resulting in a smoother contact pressure distribution in the tire width direction and improved tire wear resistance.

The rubber gauge of the tread rubber 15 is defined as the distance from the tread profile to the inner circumferential surface of the tread rubber 15 (in Figure 5, the distance from the outer circumferential surface of the cap tread 151 to the inner circumferential surface of the under tread 152). Therefore, the grooves formed on the tread surface are excluded when measuring the rubber gauge of the tread rubber 15.

Furthermore, in Figure 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 with respect to the distance Tce at the tire equatorial plane CL, and preferably in the range of 0.06 ≤ UTce/Tce ≤ 0.50. This optimizes the rubber gauge UTce of the undertread 152.

Furthermore, the distance Tsh at the tire contact end T is within the range of 1.50 ≤ Tsh/Tu ≤ 6.90, preferably within the range of 2.00 ≤ Tsh/Tu ≤ 6.50, relative to the rubber gauge Tu [mm] from the end of the wide cross belt 141 to the outer surface of the carcass layer 13. This optimizes the profile of the carcass layer 13 and optimizes its tension. Specifically, the lower limit ensures the tension of the carcass layer and the tread gauge in 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 surrounding rubber of the belt ply.

The rubber gauge Tu is essentially measured as a gauge of the rubber component (sidewall rubber 16 in Figure 5) inserted between the end of the wide cross belt 141 and the carcass layer 13.

The outer circumferential surface of the carcass layer 13 is defined as the radially outer circumferential surface of the entire carcass ply, which consists of carcass cords and coating rubber. Furthermore, if the carcass layer 13 has a multilayer structure consisting of multiple carcass plies (not shown), the outer circumferential surface of the outermost carcass ply constitutes the outer circumferential surface of the carcass layer 13. Also, if the winding portion 132 of the carcass layer 13 (see Figure 1) exists between the end of the wide cross belt 141 and the carcass layer 13 (not shown), the outer circumferential surface of this winding portion 132 constitutes the outer circumferential surface of the carcass layer 13.

For example, in the configuration shown in Figure 5, the sidewall rubber 16 is inserted between the end of the wide cross belt 141 and the carcass layer 13, forming a rubber gauge Tu between the end of the wide cross belt 141 and the carcass layer 13. However, this is not the only option; 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). Furthermore, the inserted rubber member has a rubber hardness Hs_sp between 46 and 67, a modulus M_sp [MPa] at 100% elongation between 1.0 and 3.5, and a loss tangent tanδ_sp between 0.02 and 0.22, preferably a rubber hardness Hs_sp between 48 and 63, a modulus M_sp [MPa] at 100% elongation between 1.2 and 3.2, and a loss tangent tanδ_sp between 0.04 and 0.20.

Furthermore, in the configuration shown in Figure 1, the tire 1 has a tread surface comprising multiple circumferential main grooves 21a, 21b, 22a, and 22b (see Figure 4) extending in the circumferential direction of the tire, and land areas (notation omitted in the figure) partitioned by these circumferential main grooves 21a, 21b, 22a, and 22b. The main grooves are defined as grooves that have a wear indicator display requirement as specified by JATMA.

At this time, 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 in the range of 0.55 ≤ Gd1a/Gce ≤ 0.98, relative to the rubber gauge Gce [mm] of the tread rubber 15. This ensures the tire's wear resistance. Specifically, the lower limit distributes the contact pressure in the center region of the tread, improving the tire's wear life. The upper limit ensures the rigidity of the ground portion, and also ensures the rubber gauge from the groove bottom of the circumferential main grooves 21a, 21b, 22a, and 22b to the belt layer.

The circumferential main groove closest to the tire's equatorial plane CL is defined as the circumferential main groove located on the tire's equatorial plane CL (not shown). If there is no circumferential main groove on the tire's equatorial plane CL (see Figure 4), it is defined as the circumferential main groove 21a closest to the tire's equatorial plane CL.

Furthermore, it is preferable that the above-mentioned ratio Gd1a/Gce satisfies the following formula (8) with respect to the tire outer diameter OD [mm]. Here, Hmin = 0.10 and Hmax = 0.60, preferably Hmin = 0.12 and Hmax = 0.50, and more preferably Hmin = 0.14 and Hmax = 0.40.

Furthermore, among the multiple circumferential main grooves 21a, 21b, 22a, and 22b, the groove depth Gd1a [mm] of the circumferential main groove 21a closest to the tire equatorial plane CL is greater than or equal to the groove depths Gd1b [mm], Gd2a [mm], and 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 contact edge T is divided equally 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 depth Gd1b, Gd2a, and Gd2b of the other circumferential main grooves 21b and the other circumferential main grooves 22a and 22b located in the region on the tire contact edge T side. The lower limit of this range distributes the contact pressure in the center region of the tread, improving the tire's wear resistance. The upper limit of this range suppresses uneven wear caused by an excessive difference in contact pressure between the center region and the shoulder region of the tread.

[Side Profile and Side Gauge]
Figure 6 is an enlarged view showing the sidefall portion and bead portion of tire 1 as described in Figure 1. Figure 7 is an enlarged view showing the sidewall portion as described in Figure 6.

In Figure 6, we define point Au on the side profile, which is at the same position in the tire radial direction as the end of the innermost layer of the belt layer 14 (in Figure 6, the inner diameter cross belt 141), and point Al on the side profile, which is at the same position in the tire radial direction as the radially outer end of the bead core 11. We also define the tire radial distance Hu from the tire maximum width position Ac to point Au, and the tire radial distance Hl from the tire maximum width position Ac to point Al. Furthermore, we define point Au' on the side profile, which is at a radial position 70% of the distance Hu from the tire maximum width position Ac, and point Al' on the side profile, which is at a radial position 70% of the distance Hl from the tire maximum width position Ac.

At this time, the sum of distances Hu [mm] and Hl [mm] is in the range of 0.45 ≤ (Hu + Hl) / SH ≤ 0.90 with respect to the tire cross-sectional height SH [mm] (see Figure 2), preferably in the range of 0.50 ≤ (Hu + Hl) / SH ≤ 0.85. This optimizes the radial distance from the belt layer 14 to the bead core 11. Specifically, the lower limit ensures a deformable area of the tire sidewall, suppressing failures of the tire sidewall (for example, separation of the rubber material at the radially outer end of the bead filler 12). The upper limit reduces the amount of deflection of the tire sidewall during tire rolling, thereby reducing the tire's rolling resistance.

Distances Hu and Hl are measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

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

The radius of curvature (RSc) of the arc is measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

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

Furthermore, the radius of curvature RSc [mm] of the arc passing through the tire's maximum width position Ac, point Au', and point Al' is in the range of 0.05 ≤ RSc/OD ≤ 1.70 with respect to the tire's outer diameter OD [mm], preferably in the range of 0.10 ≤ RSc/OD ≤ 1.60. Also, the radius of curvature RSc [mm] of the arc is in the range of 25 ≤ RSc ≤ 330, preferably in the range of 30 ≤ RSc ≤ 300. This optimizes the radius of curvature of the side profile and ensures the appropriate load capacity of the tire side. Specifically, the lower limit reduces the amount of deflection of the tire side during tire rolling, thereby reducing the tire's rolling resistance. The upper limit suppresses the occurrence of stress concentration caused by the flattening of the tire side, thereby improving the tire's durability. In particular, with small-diameter tires, the high internal pressure and high load conditions described above tend to cause significant stress on the tire sidewall, posing a challenge in ensuring the tire's resistance to sidewall cuts. In this regard, the lower limit ensures the radius of curvature of the side profile and optimizes the carcass tension, thereby suppressing tire deformation and preventing sidewall cuts. Furthermore, the upper limit suppresses sidewall cuts caused by excessive tension in the carcass layer 13.

Furthermore, the radius of curvature of the arc, RSc [mm], is in the range of 0.50 ≤ RSc/SH ≤ 0.95 with respect to the tire section height SH [mm], and preferably in the range of 0.55 ≤ RSc/SH ≤ 0.90.

Furthermore, it is 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 rim diameter RD [mm]. Here, Jmin = 15 and Jmax = 360, preferably Jmin = 20 and Jmax = 330, and more preferably Jmin = 25 and Jmax = 300.

Furthermore, in Figure 6, point Bc is defined on the main body portion 131 of the carcass layer 13 at the same position in the radial direction as the tire's maximum width position Ac. Also, point Bu' is defined on the main body portion 131 of the carcass layer 13 at a radial position 70% of the distance Hu from the tire's maximum width position Ac. Finally, point Bl' is defined on the main body portion 131 of the carcass layer 13 at a radial position 70% of the distance Hl from the tire's maximum width position Ac.

At this time, the radius of curvature RSc [mm] of the arc passing through the tire's maximum width position Ac, point Au', and point Al' is in the range of 1.10 ≤ RSc/RCc ≤ 4.00, preferably in the range of 1.50 ≤ RSc/RCc ≤ 3.50, with respect to the radius of curvature RCc [mm] of the arc passing through point Bc, point Bu', and point Bl'. Also, the radius of curvature RCc [mm] of the arc passing through point Bc, point Bu', and point Bl' is in the range of 5 ≤ RCc ≤ 300, preferably in the range of 10 ≤ RCc ≤ 270. This optimizes the relationship between the radius of curvature RSc of the tire's side profile and the radius of curvature RCc of the carcass layer 13's side profile. Specifically, the above lower limit ensures the radius of curvature RCc of the carcass profile, ensures the tire's internal volume V (described later), and ensures the tire's load capacity. The above upper limits ensure that the total gauges Gu and Glu of the tire sidewall, as described later, are maintained, thereby ensuring the load capacity of the tire sidewall.

Furthermore, it is preferable that the radius of curvature RSc [mm] of the side profile described above 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]. Here, Kmin = 1 and Kmax = 130, preferably Kmin = 2 and Kmax = 100, and more preferably Kmin = 3 and Kmax = 70.

Furthermore, in Figure 6, the total gauge Gu [mm] of the tire sidewall at point Au is in the range of 0.010 ≤ Gu/OD ≤ 0.080 with respect to the tire outer diameter OD [mm], preferably in the range of 0.017 ≤ Gu/OD ≤ 0.070. This optimizes the total gauge Gu in the radially outer region of the tire sidewall. Specifically, the lower limit ensures the total gauge Gu in the radially outer region of the tire sidewall, suppressing tire deformation during high-load use and ensuring the tire's wear resistance. Especially in small-diameter tires, where high internal pressure and high load use are anticipated, the reduction in tire rolling resistance described above is significantly achieved. The upper limit suppresses the deterioration of tire rolling resistance caused by an excessively large total gauge Gu.

The total gauge of the tire sidewall is measured as the distance from the sidewall to the inner surface of the tire, along a perpendicular line drawn from a predetermined point on the sidewall to the main body portion 131 of the carcass layer 13.

Furthermore, in Figure 6, the total gauge Gu [mm] at point Au is within the range of 1.30 ≤ Gu/Gc ≤ 5.00 relative to the total gauge Gc [mm] of the tire sidewall at the tire's maximum width position Ac, and preferably the ratio Gu/Gc is within the range of 1.90 ≤ Gu/Gc ≤ 3.00. This optimizes the gauge distribution of the tire sidewall from the tire's maximum width position Ac to the innermost layer of the belt layer 14. Specifically, the lower limit ensures a sufficient total gauge Gu in the radially outer region, suppressing tire deformation during high-load use and ensuring the tire's wear resistance. The upper limit prevents the deterioration of the tire's rolling resistance caused by an excessively large total gauge Gu.

Furthermore, it is preferable that the total gauge Gu [mm] at point Au satisfies the following formula (12) with respect to the total gauge Gc [mm] at the tire's maximum width position Ac and the tire's outer diameter OD [mm]. Here, Lmin = 0.10 and Lmax = 0.70, preferably Lmin = 0.14 and Lmax = 0.70, and more preferably Lmin = 0.19 and Lmax = 0.70.

Furthermore, in Figure 6, the total gauge Gc [mm] of the tire sidewall at the tire's maximum width position Ac has a relationship of 0.003 ≤ Gc/OD ≤ 0.060 with respect to the tire's outer diameter OD [mm], preferably 0.004 ≤ Gc/OD ≤ 0.050. The lower limit ensures the total gauge Gc at the tire's maximum width position Ac, thereby ensuring the tire's load capacity. The upper limit ensures the reduction in tire rolling resistance due to the thinning of the total gauge Gc at the tire's maximum width position Ac.

Furthermore, it is preferable that the total gauge Gc [mm] at the tire's maximum width position Ac satisfies the following formula (13) with respect to the tire's outer diameter OD [mm]. Here, Mmin = 70 and Mmax = 450, preferably Mmin = 80 and Mmax = 400.

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

Furthermore, it is preferable that the total gauge Gc [mm] at the tire's 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's maximum width position Ac, point Au', and point Al'. Here, Omin = 13 and Omax = 260, preferably Omin = 20 and Omax = 200.

Furthermore, in Figure 6, the total gauge Gl [mm] of the tire sidewall at point Al is in the range of 0.010 ≤ Gl/OD ≤ 0.150 with respect to the tire outer diameter OD, preferably in the range of 0.015 ≤ Gl/OD ≤ 0.100. This optimizes the total gauge Gl in the radially inner region of the tire sidewall. Specifically, the lower limit ensures the total gauge Gl in the radially inner region of the tire sidewall, suppressing tire deformation during high-load use and ensuring the tire's wear resistance. Especially in small-diameter tires, where high internal pressure and high load use are anticipated, the reduction in tire rolling resistance described above is significantly achieved. The upper limit suppresses the deterioration of tire rolling resistance caused by an excessively large total gauge Gl.

Furthermore, in Figure 6, the ratio Gl/Gc between the total gauge Gl [mm] of the tire sidewall at point Al and the total gauge Gc [mm] of the tire sidewall at the tire's 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 sidewall from the tire's maximum width position Ac to the bead core 11. Specifically, the lower limit ensures a sufficient total gauge Gl in the radially inner region, suppressing tire deformation during high-load use and ensuring the tire's wear resistance. The upper limit prevents the deterioration of the tire's rolling resistance caused by an excessively large total gauge Gl.

Furthermore, it is preferable that the total gauge Gl [mm] of the tire sidewall at point Al satisfies the following formula (16) with respect to the total gauge Gc [mm] at the tire's maximum width position Ac and the tire's outer diameter OD [mm]. Here, Pmin = 0.12 and Pmax = 1.00, preferably Pmin = 0.15 and Pmax = 1.00, and more preferably Pmin = 0.18 and Pmax = 1.00.

Furthermore, in Figure 6, the total gauge Gl [mm] at point Al is in the range of 0.80 ≤ Gl/Gu ≤ 5.00, and preferably in the range of 1.00 ≤ Gl/Gu ≤ 4.00, relative to the total gauge Gu [mm] at point Au. This optimizes the ratio of the total gauge Gl in the radially outer region of the tire sidewall to the total gauge Gu in the radially inner region.

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

Furthermore, in Figure 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 of the total gauge Glu have the relationship Hsc ≤ Hsu < Hsl, preferably 1 ≤ Hsu - Hsc ≤ 18 and 2 ≤ Hsl - Hsu ≤ 27, and more preferably 2 ≤ Hsu - Hsc ≤ 15 and 5 ≤ Hsl - Hsu ≤ 23. This optimizes the relationship of rubber hardness in the tire sidewall.

The average rubber hardness Hsc, Hsu, and Hsl are calculated as the sum of the values obtained by dividing the product of the cross-sectional length and rubber hardness of each rubber component by the total gauge at each measurement point: Total gauge Gc [mm] at the tire's maximum width position Ac, Total gauge Gu at point Au, and Total gauge Glu at point Al.

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

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

The distances ΔAu' and ΔAl' are measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

Furthermore, it is preferable that the distance ΔAu' [mm] in the tire width direction from the tire's 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's maximum width position Ac, point Au', and point Al'. Here, Rmin = 0.05 and Rmax = 5.00, preferably Rmin = 0.10 and Rmax = 4.50.

Furthermore, in Figure 7, the distance ΔBu' [mm] in the tire width direction from point Bc to point Bu' is within the range of 1.10 ≤ ΔBu'/ΔAu' ≤ 8.00, preferably within the range of 1.60 ≤ ΔBu'/ΔAu' ≤ 7.50, relative to the distance ΔAu' [mm] in the tire width direction from the tire's 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 the cut resistance of the tire sidewall. The upper limit ensures the tension of the carcass layer 13, ensuring the rigidity of the tire sidewall, and thus ensuring the tire's load capacity and durability.

Furthermore, in Figure 7, the distance ΔBl' [mm] in the tire width direction from point Bc to point Bl' is within the range of 1.80 ≤ ΔBl'/ΔAl' ≤ 11.0, and preferably within the range of 2.30 ≤ ΔBl'/ΔAl' ≤ 9.50, relative to the distance ΔAl' [mm] in the tire width direction from the tire's 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, thereby ensuring the load capacity of the tire side. The upper limit ensures the tension of the carcass layer 13, ensuring the rigidity of the tire side, and thus ensuring the tire's load capacity and durability.

The distances ΔBu' and ΔBl' are measured with the tire mounted on a specified rim, under specified internal pressure, and in an unloaded state.

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' as described above. Here, Smin = 0.40 and Smax = 7.0, preferably Smin = 0.50 and Smax = 6.0.

Furthermore, in Figure 7, the rubber gauge Gcr [mm] of the sidewall rubber 16 at the tire's maximum width position Ac is within the range of 0.40 ≤ Gcr/Gc ≤ 0.90 relative to the total gauge Gc [mm] at the tire's maximum width position Ac. Also, the rubber gauge Gcr [mm] of the sidewall rubber 16 is within the range of 1.5 ≤ Gcr, preferably within the range of 2.5 ≤ Gcr. This lower limit ensures that the rubber gauge Gcr [mm] of the sidewall rubber 16 is maintained, thereby ensuring the load capacity of the sidewall.

Furthermore, it is preferable that the rubber gauge Gcr [mm] of the sidewall rubber 16 at the tire's maximum width position Ac satisfies the following formula (20) with respect to the total gauge Gc [mm] and tire outer diameter OD [mm] at the tire's maximum width position Ac described above. Here, Tmin = 80 and Tmax = 0.90, preferably Tmin = 120 and Tmax = 0.90.

Furthermore, in Figure 7, the rubber gauge Gin [mm] (not shown) of the inner liner 18 at the tire's maximum width position Ac is in the range of 0.03 ≤ Gin/Gc ≤ 0.50, preferably in the range of 0.05 ≤ Gin/Gc ≤ 0.40, relative to the total gauge Gc [mm] at the tire's maximum width position Ac. This ensures proper protection of the inner surface of the carcass layer 13.

As described above, this tire 1 comprises a pair of bead cores 11, 11, a carcass layer 13 spanning the bead cores 11, 11, and a belt layer 14 positioned radially outside the carcass layer 13 (see Figure 1). Furthermore, 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. Also, the strength Tcs [N/50mm] per 50 [mm] width 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].

In this configuration, the load capacity of the carcass layer 13 is appropriately ensured in small-diameter tires, resulting in the advantage of achieving both wear resistance and low rolling resistance. Specifically, the lower limit of the relative Tcs/OD suppresses tire deformation during high-load use, ensuring tire wear resistance. Furthermore, it enables use at high internal pressures, reducing tire rolling resistance. Especially in small-diameter tires, where high internal pressure and high load use are anticipated, the above-mentioned effects of wear resistance and reduced rolling resistance are significantly achieved. The upper limit of the relative Tcs/OD suppresses the deterioration of rolling resistance caused by an increase in the mass of the carcass layer.

Furthermore, in this tire 1, the carcass ply of the carcass layer 13 is constructed by covering steel carcass cords with a coating rubber. The cord diameter φcs [mm] of the carcass cords is in the range of 0.3 ≤ φcs ≤ 1.1, and the number of carcass cords per 50 mm Ecs [cords/50 mm] is in the range of 25 ≤ Ecs ≤ 80. This provides the advantage of achieving the strong Tcs of the carcass layer 13 described above.

Furthermore, in this tire 1, the carcass ply of the carcass layer 13 is constructed by covering carcass cords made of organic fibers with a coating rubber. The cord diameter φcs [mm] of the carcass cords is in the range of 0.6 ≤ φcs ≤ 0.9, and the number of carcass cords per 50 mm Ecs [cords/50 mm] is in the range of 40 ≤ Ecs ≤ 70. This provides the advantage of achieving the strong Tcs of the carcass layer 13 described above.

Furthermore, in this tire 1, the carcass layer 13 has a main body portion 131 that extends along the inner surface of the tire, and a winding portion 132 that is wound outward in the tire width direction to enclose the bead core 11 and extends in the tire radial direction (see Figure 1). Also, the radial height Hcs [mm] from the measurement point of the rim diameter RD to the end of the winding portion 132 of the carcass layer 13 is within the range of 0.49 ≤ Hcs/SH ≤ 0.80 with respect to the tire cross-sectional height SH [mm] (see Figure 2). This has the advantage of optimizing the radial height Hcs of the winding portion 132 of the carcass layer 13. Specifically, the lower limit ensures the load capacity of the tire sidewall, and the upper limit suppresses the deterioration of rolling resistance caused by an increase in the mass of the carcass layer.

Furthermore, in this tire 1, the contact height Hcs' [mm] between the main body portion 131 and the winding portion 132 of the carcass layer 13 is within the range of 0.07 ≤ Hcs'/SH relative to the tire cross-sectional height SH [mm] (see Figure 2). This has the advantage of effectively increasing the load capacity of the tire sidewall.

Furthermore, in this tire 1, the distance Tsh at the tire contact edge T is within the range of 1.50 ≤ Tsh/Tu ≤ 6.90 relative to the rubber gauge Tu [mm] from the end of the wide cross belt 141 to the outer surface of the carcass layer 13 (see Figure 5). This has the advantage of optimizing the profile of the carcass layer 13 and thus optimizing the tension of the carcass layer 13.

Furthermore, in this tire 1, the distance ΔBu' [mm] in the tire width direction from point Bc to point Bu' is within the range of 1.10 ≤ ΔBu'/ΔAu' ≤ 8.00 relative to the distance ΔAu' [mm] in the tire width direction from the tire's maximum width position Ac to point Au' (see Figure 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 lower limit ensures the cut resistance of the tire sidewall. The upper limit ensures the tension of the carcass layer 13, ensuring the rigidity of the tire sidewall, and thus ensuring the tire's load capacity and durability.

Furthermore, in this tire 1, the distance ΔBl' [mm] in the tire width direction from point Bc to point Bl' is within the range of 1.80 ≤ ΔBl'/ΔAl' ≤ 11.0 relative to the distance ΔAl' [mm] in the tire width direction from the tire's maximum width position Ac to point Al' (see Figure 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, thereby ensuring the load capacity of the tire side. The upper limit ensures the radius of curvature RCc of the carcass profile, ensuring the tire's internal volume V, and thus ensuring the tire's load capacity.

Furthermore, in this tire 1, the amount of tread profile drop DA [mm] at the tire contact edge T has a relationship of 0.008 ≤ DA/TW ≤ 0.060 with respect to the tire contact width TW [mm] (see Figure 4). This optimizes the drop angle of the tread shoulder region (defined as the ratio DA/(TW/2)), ensuring adequate load capacity for the tread. Specifically, the lower limit ensures the drop angle of the tread shoulder region, suppressing a decrease in wear life caused by excessive contact pressure in the tread shoulder region. The upper limit makes the tire contact area flat and equalizes the contact pressure, ensuring the tire's wear resistance. Especially in small-diameter tires, where high internal pressure and high loads are expected, the above configuration effectively optimizes the contact pressure distribution in the tire contact area.

Furthermore, in this tire 1, the belt layer 14 comprises a pair of cross belts 141 and 142, each consisting of a steel belt cord covered with a coated rubber (see Figure 1). The strength Tbt [N/50mm] per 50mm width of each of the pair of cross belts 141 and 142 is within 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 and 142. Specifically, the lower limit suppresses tire deformation during high-load use, ensuring the tire's wear resistance. It also allows for use at high internal pressures, reducing the tire's rolling resistance. Especially in small-diameter tires, where high internal pressure and high load use are anticipated, the above-mentioned wear resistance and rolling resistance reduction effects are significantly achieved. The upper limit suppresses the deterioration of rolling resistance caused by an increase in the mass of the cross belts.

Furthermore, in this tire 1, the strength Tbd [N] of one bead core 11 is within 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 high-load use, ensuring the tire's wear resistance. It also allows for use at high internal pressures, reducing the tire's rolling resistance. Especially in small-diameter tires, where high internal pressure and high-load use are anticipated, the above-mentioned wear resistance and reduction in rolling resistance are significantly achieved. The above upper limit suppresses the deterioration of rolling resistance caused by an increase in the mass of the bead core.

Furthermore, in this tire 1, the bead core 11 is composed of bead wire made of steel. The total cross-sectional area σbd [mm²] of the bead wire is within the range of 0.025 ≤ σbd/OD ≤ 0.075 relative to the tire outer diameter OD [mm]. This has the advantage of achieving the strong Tbd [N] of the bead core 11 described above.

[Tread surface]
Figure 8 shows an example of the tread surface of the tread portion. As shown in Figure 8, the tread portion has circumferential main grooves 21a, 21b, 22a, and 22b that extend in the circumferential direction of the tire. These four circumferential main grooves 21a, 21b, 22a, and 22b divide and form 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 circumferential direction and the width direction of the tire and connects the circumferential main grooves 21a and 22a. The lateral groove 24b extends in the circumferential direction and the width direction of the tire and connects the circumferential main grooves 21b and 22b. The lateral groove 25a extends outward from the circumferential main groove 22a in the width direction of the tire and reaches the outside of the contact end T. The lateral groove 25b extends outward in the tire width direction from the circumferential main groove 22b and reaches the outside of the contact edge T. In Figure 8, the symbol Tss indicates the tire contact area. In the contact area Tss, the tire contact width is indicated by the symbol TW [mm] and the tire contact length is indicated by the symbol TL.

In Figure 8, the tread center region Rce is the region centered on the tire equatorial plane CL, and its dimensions are TW × 0.4 × (OD/SW)^(1/4) [mm]. The tread shoulder region Rsh is the region included in the contact width TW [mm], excluding the tread center region Rce.

[Groove area ratio]
In a tire 1 having the tread surface shown in Figure 8, it is preferable that 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 [%] of the entire tread portion is in the range of 25 + 100 × (25.4/OD) ≤ Aa ≤ 50 + 100 × (25.4/OD).

Reducing the outer diameter (OD) allows for a lower vehicle floor, increasing interior space. Furthermore, a smaller OD reduces rotational inertia and weight, significantly improving fuel efficiency.

To improve bump-climbing performance, the smaller the outer diameter (OD), the larger the groove area ratio needs to be. By changing the appropriate range of the groove area ratio according to the outer diameter (OD), the grooves can grip bumps more easily, making it easier to climb over them, thus achieving both bump-climbing performance and fuel efficiency. The groove area of the entire tread includes the groove area of the lateral grooves. Even tires that do not have circumferential main grooves in the tread and whose lateral groove area is within the above range can have their bump-climbing performance improved. Furthermore, it is more preferable that the groove area ratio Aa [%] of the entire tread is within the range of 25 + 100 × (25.4/OD) ≤ Aa ≤ 45 + 100 × (25.4/OD).

The groove area ratio is the ratio of the total groove area in a predetermined region of the tread to the area of that region. The groove area ratio [%] is defined as groove area / (groove area + contact area) × 100. Groove area refers to the opening area of the grooves on the contact surface. Grooves refer to the circumferential grooves, narrow grooves, and lateral grooves (lug grooves) of the tread, and do not include sipes or calves. Contact area refers to the contact area between the tire and the contact surface. The groove area and contact area are measured at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, subjected to a specified internal pressure (230 kPa), and placed perpendicular to a flat plate in a stationary state, with a load corresponding to a specified load (80% of the maximum load capacity) applied.

This tire can be fitted with sound-absorbing materials for noise reduction, such as for use in mobile conference rooms, or with sensors, sealants, and thermoplastic resin inner liners for maintenance-free applications, such as in transport vehicles. It is also highly effective when fitted to vehicles equipped with monitoring systems. When used at high internal pressure, the tread wear limit is reached before the durability limit of the tire sidewall and belt, making it suitable for retreading.

The maximum groove depth Gmax [mm] across the entire tread area preferably satisfies 0.006 ≤ Gmax/OD ≤ 0.083. As the outer diameter OD increases, the inertial force increases, and if the groove depth is not increased to reduce mass, fuel efficiency may deteriorate. If the tire groove depth is too large relative to the outer diameter OD, the groove walls may collapse under high load, preventing the groove effect from being fully realized. Furthermore, if the groove depth is appropriate for the outer diameter OD, the grooves will grip the bumps more easily when going over bumps, so the above range is desirable. The groove area across the entire tread area includes the groove area of the lateral grooves. Even if the tread area does not have circumferential main grooves but has lateral grooves, bump-going performance can be improved for tires where the maximum groove depth Gmax of the lateral grooves is within the above range. It is more preferable that the maximum groove depth Gmax across the entire tread area satisfies 0.009 ≤ Gmax/OD ≤ 0.060.

As shown in Figure 8, the tread portion of this example has circumferential main grooves 21a, 21b, 22a, and 22b that extend in the circumferential direction of the tire. The circumferential main grooves shall have a groove width of 3 mm or more. Furthermore, with respect to the product of the outer diameter OD and the total width SW, it is preferable that the projected area C [ ^mm² ] of the circumferential main grooves satisfies 0.03 ≤ C / (SW × OD) ≤ 1.01. By having the area of the circumferential main grooves within the above range relative to the outer diameter OD and the total width SW, the envelope characteristics are improved, making it easier to overcome bumps. The projected area C is the total area of the circumferential grooves around the circumference of the tire. As shown in Figure 8, if the tread portion has multiple circumferential main grooves, the projected area C is the sum of the areas of all circumferential main grooves. If the tread portion has only one circumferential main groove, the projected area C is the area of that single circumferential main groove. Furthermore, it is more preferable that the projected area C [ ^mm² ] of the circumferential main groove satisfies 0.15 ≤ C / (SW × OD) ≤ 0.94.

The average number of pitches P (where P is a natural number) within the tire contact length in the tread's contact area is preferably satisfied with OD/200 ≤ P ≤ OD/50 relative to the outer diameter OD. When the average number of pitches P is within this range, the number of lateral grooves is within an appropriate range according to the number of pitches, making it easier to grip bumps when going over them. Since bump-crossing performance is less favorable as the outer diameter OD decreases, it is desirable to reduce the pitch and increase block rigidity. The above average number of pitches P is preferably satisfied with OD/180 ≤ P ≤ OD/60 relative to the outer diameter OD. For example, when the outer diameter OD is 300 [mm], the number of pitches P is preferably a natural number between 2 and 6. Also, when the outer diameter OD is 650 [mm], the number of pitches P is preferably a natural number between 4 and 13.

Here, the average pitch count is the average value of the pitch counts within the ribs of the tire's contact patch, assuming that the number of pitches within the ribs within the contact patch varies with each tire rotation. Furthermore, if there are multiple ribs with different pitch counts, the average pitch count is calculated by averaging the values for each rib.

The tread section preferably has circumferential main grooves extending in the circumferential direction of the tire. Furthermore, the number of circumferential main grooves Nm (where Nm is a natural number) preferably satisfies SW/400 ≤ Nm ≤ SW/20. As the total width SW increases, the contact width TW increases. Therefore, when the number of circumferential main grooves falls within the above range, the envelope characteristics are further improved, and the ability to overcome obstacles is enhanced. For example, when the total width SW is 100 mm, the number of circumferential main grooves Nm is preferably between 1 and 3. Also, when the total width SW is 400 mm, the number of circumferential main grooves Nm is preferably between 1 and 13.

It is preferable that the groove area ratio Ace of the tread center region Rce and the groove area ratio Ash of the tread shoulder region Rsh (excluding the tread center region) satisfy the relationship Ace < Ash, i.e., Ace/Ash < 1. The tread center region Rce has a greater impact on noise performance than the tread shoulder region Rsh. Therefore, reducing the groove area ratio of the tread center region Rce effectively improves noise performance. When the overall width SW is small, the contact width TW is narrow and the tire contact length TL is long, worsening noise performance. Therefore, it is necessary to increase the tread center region Rce, which has fewer grooves. Similarly, increasing the outer diameter OD increases the tire contact length TL, thus requiring an increase in the tread center region Rce.

Furthermore, it is more preferable that the groove area ratio Ace and groove area ratio Ash satisfy the relationship 0.2 × (OD/300) ≤ Ace/Ash < 1. This relationship improves both noise performance and low rolling resistance performance. The larger the outer diameter OD, the larger the groove area ratio Ace in the tread center region Rce needs to be. It is more preferable that the relationship between groove area ratio Ace and groove area ratio Ash is 0.3 × (OD/300) ≤ Ace/Ash < 0.95. Even more preferable is that the relationship between groove area ratio Ace and groove area ratio Ash is 0.3 × (OD/300) ≤ Ace/Ash < 0.90.

The relationship between the number of pitches Pce [number of grooves] in the center region Rce of the tread and the number of pitches Psh [number of grooves] in the shoulder region Rsh is preferably 0.4 ≤ Pce/Psh ≤ 1.2. This relationship between the number of pitches Pce and Psh improves noise performance and low rolling resistance performance. More preferably, the relationship between the number of pitches Pce and Psh is 0.5 ≤ Pce/Psh ≤ 1.0. Note that the number of pitches refers to the number of lateral grooves 24a or lateral grooves 24b formed with 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.

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 a larger outer diameter OD results in a larger contact area, it is preferable to reduce the lateral groove area within the contact surface. The above relationship between the average lateral groove width WLce and the average number of pitches PCce allows for further improvement in noise performance and low rolling resistance performance. It is even 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 determination is made based on the average value for each rib.

In the tread center region Rce, it is preferable that the average number of pitches PCce [pitches] within the tire contact length TL around the entire circumference of the tire satisfies the relationship 0.005 ≤ PCce/OD ≤ 0.020. Within this range, as the outer diameter OD increases, the tire circumference increases, allowing for a larger number of lateral grooves to be arranged by increasing the number of pitches Pce. By satisfying the above relationship, similar effects can be obtained at any contact surface, further improving noise performance and low rolling resistance performance. It is even more preferable that the average number of pitches PCce [pitches] within the tire circumference satisfies the relationship 0.007 ≤ PCce/OD ≤ 0.017. Note that the average number of pitches PCce is a natural number.

Figures 9 to 12 are charts showing the results of performance tests on tires according to embodiments of this invention.

In this performance test, several types of test tires were evaluated for (1) bump-climbing performance and (2) fuel efficiency. As an example of small-diameter tires, two different tire sizes were used. Specifically, [A] a 235/45R10 test tire was mounted on a 10x8 rim, [B] a 145/80R12 test tire was mounted on a 12x4.00B rim, and [C] a 165/25R5 test tire was mounted on a 5x6.5 rim.

(1) In the evaluation of the step-climbing performance, the test tire [A] above was subjected to an internal pressure of 230 [kPa] and a load of 4.2 [kN], the test tire [B] above was subjected to an internal pressure of 80% of the JATMA specified internal pressure and a load of 80% of the JATMA specified load, and the test tire [C] above was subjected to an internal pressure of 230 [kPa] and a load of 1.1 [kN]. In addition, a four-wheeled low-floor vehicle equipped with the test tires on all wheels entered a step in a straight line at 10 km/h on the test course to perform step-climbing. The height of the step that could be overcome without the tires slipping was measured. The step height that could be overcome with the standard tire was set as the baseline (100), and a larger index is preferable, indicating that a higher step can be overcome and that the step-climbing performance is good. This evaluation is performed using an index-based rating system with the comparative example set as the baseline (100). A higher value indicates a more favorable outcome.

(2) In the evaluation of fuel efficiency, the test tire [A] above was subjected to an internal pressure of 230 [kPa] and a load of 4.2 [kN], the test tire [B] above was subjected to an internal pressure of 80% of the JATMA specified internal pressure and a load of 80% of the JATMA specified load, and the test tire [C] above was subjected to an internal pressure of 230 [kPa] and a load of 1.1 [kN]. Furthermore, a four-wheeled low-floor vehicle equipped with the test tires on all wheels was driven 50 laps of a 2 km test course at a speed of 100 km/h, and the fuel consumption rate (km/l) was measured. The evaluation was performed using an index with the comparative example as the baseline (100), and a higher value indicates better fuel efficiency.

The test tire of the embodiment has the structure shown in Figure 1, and comprises 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, and tread rubber 15, sidewall rubber 16, and rim cushion rubber 17.

The comparative example test tire has the same tire outer diameter (OD) as the test tire of Example 1 (531 mm), tire total width (SW) (143 mm), and tire contact width (TW) (123 mm), and is mounted on a rim of rim size 12.

As the test results show, the test tire in this example demonstrates a balance between tire performance in overcoming obstacles and fuel efficiency.

1. Tire; 10. Rim; 11. Bead core; 12. Bead filler; 13. Carcass layer; 131. Main body; 132. Wrap-around section; 14. Belt layer; 141, 142. Cross belt; 143. Belt cover; 144. Belt edge cover; 15. Tread rubber; 151. Cap tread; 152. Under tread; 16. Sidewall rubber; 17. Rim cushion rubber; 18. Inner liner; 21a, 21b, 22a, 22b. Circumferential main grooves; 24a, 24b, 25a, 25b. Lateral grooves.

Claims (5)

A tire comprising a pair of bead cores, a carcass layer spanning the bead cores, a belt layer positioned radially outward of the carcass layer, and a tread portion,
The tire outer diameter OD [mm] is in the range of 250 ≤ OD ≤ 580 .
The total tire width SW [mm] is in the range of 100 ≤ SW ≤ 400.
The groove area ratio Aa [%] across the entire tread portion is in the range of 25 + 100 × (25.4/OD) ≤ Aa ≤ 50 + 100 × (25.4/OD),
A tire characterized in that the total gauge Gu [mm] of the tire side portion at point Au on the side profile, which is at the same position in the tire radial direction with respect to the end of the innermost layer of the belt layer, is in the range of 0.010 ≤ Gu/OD ≤ 0.080 with respect to the tire outer diameter OD [mm]. The maximum groove depth Gmax [mm] across the entire tread area is,
The tire according to claim 1, satisfying 0.006 ≤ Gmax/OD ≤ 0.083. The tread portion has circumferential main grooves extending in the circumferential direction of the tire,
The aforementioned circumferential main groove has a groove width of 3 mm or more.
The projected area C [ ^mm² ] of the circumferential main groove is,
A tire according to claim 1 or claim 2, satisfying 0.03 ≤ C / (SW × OD) ≤ 1.01. The tire according to any one of claims 1 to 3, wherein the average number of pitches P (where P is a natural number) within the tire contact length in the contact area of the tread portion satisfies OD/200 ≤ P ≤ OD/50 with respect to the outer diameter OD [mm]. The tread portion is provided with circumferential main grooves extending in the circumferential direction of the tire,
The tire according to any one of claims 1 to 4, wherein the number of circumferential main grooves Nm [grooves] (where Nm is a natural number) satisfies SW/400 ≤ Nm ≤ SW/30.