Pneumatic radial tires

Abstract

To provide a pneumatic radial tire which can improve durability.SOLUTION: A pneumatic radial tire is given in which a plurality of belt layers 7 and at least one circumferential reinforcement layer 8 are arranged at the outer peripheral side of a carcass layer 4 in a tread part 1. It satisfies the following expression: -5 GPa≤Em0-Em1<15 GPa in which Em0 is the maximum tangent elasticity modulus at the initial state of a steel cord constituting the circumferential reinforcement layer, and Em1 is the maximum tangent elasticity modulus at the state where the steel cord constituting the circumferential reinforcement layer is taken out from the tire. It satisfies the following expression: 0.5≤Wo / Wm≤0.9 in which Wo is width of the circumferential reinforcement layer 8 and Wm is maximum width of the belt layer. It satisfies the following expression: 0.8≤Ee / Ec≤1.2 in which Ee is elastic modulus when the steel cord arranged at the edge part of the circumferential reinforcement layer is elongated by 0.5% - 1.0%, and Ec is elastic modulus when the steel cord arranged at the center part of the circumferential reinforcement layer is elongated by 0.5% - 1.0%.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a pneumatic radial tire having a steel cord belt layer and a steel cord circumferential reinforcing layer in a tread portion, and more specifically, to a pneumatic radial tire that makes it possible to suppress the occurrence of failures caused by the belt layer and the circumferential reinforcing layer and to improve durability. [Background technology]

[0002] In recent years, in heavy-duty pneumatic radial tires used on trucks, buses, etc., dual wheels have been replaced with single wheels for the purpose of weight reduction and resource conservation. Tires with dual wheels replaced with single wheels tend to have a smaller aspect ratio because the tread width is wider without changing the outer diameter. In addition, the filling air pressure is set higher in order to cover the capacity of dual wheels with a single wheel.

[0003] In such a pneumatic radial tire for heavy loads with a wide tread width and a low aspect ratio, the load on the belt layer of the tread portion increases significantly during running, resulting in a problem of reduced durability of the belt layer. Conventionally, as a measure to reinforce the belt layer of such a pneumatic radial tire, a circumferential reinforcing layer including steel cords oriented in the tire circumferential direction has been proposed to be disposed on the outer periphery of the belt layer to increase the circumferential rigidity of the tread portion (for example, see Patent Documents 1 and 2).

[0004] However, since steel cords have a large elastic modulus and are weak against compression, if the steel cords are arranged in the circumferential direction of the tire as in the above-mentioned circumferential reinforcing layer, they are likely to break due to fatigue caused by repeated deformation during tire rolling. In particular, the steel cords arranged in the edge portions of the circumferential reinforcing layer break due to fatigue, which is a factor in reducing the durability of the tire.

[0005] Furthermore, if the circumferential reinforcing layer does not tighten sufficiently, it becomes difficult to prevent the belt layer from rising up due to centrifugal force during high-speed driving. Repeated rising up of the belt layer reduces the durability of the tire. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2001-522748 [Patent Document 2] Special Publication No. 2000-504655 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a pneumatic radial tire which makes it possible to suppress the occurrence of failures caused by the belt layer and the circumferential reinforcing layer and improve durability. [Means for solving the problem]

[0008] In order to achieve the above object, the pneumatic radial tire of the present invention is a pneumatic radial tire having a plurality of belt layers including steel cords inclined with respect to the circumferential direction of the tire and at least one circumferential reinforcing layer including steel cords oriented in the circumferential direction of the tire, disposed on the outer peripheral side of the carcass layer in the tread portion, The maximum tangent elastic modulus Em0 of the steel cord constituting the circumferential reinforcing layer in an initial state and the maximum tangent elastic modulus Em1 of the steel cord constituting the circumferential reinforcing layer in a state taken out of the tire -2GPa≦Em 0 -Em 1 ≦14GPa Satisfying the relationship, The width Wo of the circumferential reinforcing layer and the maximum width Wm of the belt layer satisfy the relationship of 0.5≦Wo / Wm≦0.9, The elastic modulus Ee of the steel cords arranged in the edge portions of the circumferential reinforcing layer at an elongation of 0.5% to 1.0% and the elastic modulus Ec of the steel cords arranged in the center portion of the circumferential reinforcing layer at an elongation of 0.5% to 1.0% satisfy the relationship 0.8≦Ee / Ec≦1.2. Effect of the Invention

[0009] In the present invention, in a pneumatic radial tire having a steel cord belt layer and a steel cord circumferential reinforcing layer in a tread portion, by defining as above the relationship between the maximum tangent elastic modulus Em0 of the steel cord constituting the circumferential reinforcing layer in its initial state and the maximum tangent elastic modulus Em1 of the steel cord constituting the circumferential reinforcing layer in its state after being removed from the tire, the relationship between the width Wo of the circumferential reinforcing layer and the maximum width Wm of the belt layer, and the relationship between the elastic modulus Ee of the steel cord arranged in the edge portions of the circumferential reinforcing layer at 0.5% to 1.0% elongation and the elastic modulus Ec of the steel cord arranged in the center portion of the circumferential reinforcing layer at 0.5% to 1.0% elongation, it is possible to suppress the occurrence of failures caused by the belt layer and the circumferential reinforcing layer and improve the durability of the pneumatic radial tire.

[0010] In the present invention, it is preferable that the rate of change Rc of the tread circumference at the tire equator and the rate of change Rs of the tread circumference at the shoulders, which change when the tire is inflated with an air pressure of 100 kPa to a specified air pressure corresponding to the maximum load capacity, satisfy the relationship 0.7≦Rc / Rs≦1.3. This makes it possible to suppress local deformation in the center and shoulders of the tread, and to suppress the occurrence of failures caused by the belt layer and the circumferential reinforcing layer.

[0011] The pneumatic radial tire of the present invention preferably has a maximum tire width of 350 mm or more when inflated to a specified air pressure corresponding to the maximum load capacity, and an aspect ratio of 60% or less. Remarkable effects can be obtained in such a wide-width and low-aspect ratio pneumatic radial tire.

[0012] In the present invention, the state of the steel cord taken out of the tire means the state in which the steel cord is taken out of the tire and the rubber covering the steel cord is removed. On the other hand, the initial state of the steel cord means the state of the steel cord in the raw material stage, and it is possible to substantially reproduce the initial state of the steel cord by immersing the steel cord taken out of the tire in toluene for at least 60 minutes and dissolving all the rubber attached to the steel cord. The maximum tangent modulus Em0 of the steel cord constituting the circumferential reinforcing layer in the initial state and the maximum tangent modulus Em1 of the steel cord constituting the circumferential reinforcing layer in the state taken out of the tire are maximum tangent moduli (GPa) obtained from the tensile stress-elongation curve obtained by performing a tensile test on the steel cord in a specified state under the conditions of a test length of 250 mm and a tensile speed of 5 mm / min according to the provisions of JIS-G3510. The maximum tangent moduli Em0 and Em1 are the average values ​​measured for each of the steel cords taken from the entire width direction of the circumferential reinforcing layer.

[0013] The elastic modulus Ee of the steel cord arranged in the edge portion of the circumferential reinforcing layer at 0.5% to 1.0% elongation and the elastic modulus Ec of the steel cord arranged in the center portion of the circumferential reinforcing layer at 0.5% to 1.0% elongation are calculated by the following formula (1) after a tensile test is performed on the steel cord removed from the tire in accordance with the JIS-G3510 regulations under conditions of a test length of 250 mm and a tensile speed of 5 mm / min. E = 0.2 × (L 1.0 -L 0.5 ) / S SC (1) Where E: Elastic modulus (GPa) L 0.5 : Tension at 0.5% elongation (N) L 1.0 : Tension at 1.0% elongation (N) S SC : Cross-sectional area of ​​steel cord [sum of cross-sectional areas of wires] (mm 2 )

[0014] The elastic modulus Ee of the steel cords arranged at the edge portions of the circumferential reinforcing layer is the average value of the elastic modulus measured for each of the steel cords included within an area from the edge end of the circumferential reinforcing layer that is 5% of the width of the circumferential reinforcing layer, while the elastic modulus Ec of the steel cords arranged at the center portion of the circumferential reinforcing layer is the average value of the elastic modulus measured for each of the steel cords included within an area that is 5% of the width of the circumferential reinforcing layer, centered on the tire equator. [Brief description of the drawings]

[0015] [Figure 1] 1 is a meridian cross-sectional view showing a heavy-duty pneumatic radial tire according to an embodiment of the present invention. [Diagram 2] 2 is a development view showing a belt layer and a circumferential reinforcing layer of the pneumatic radial tire of FIG. 1. FIG. [Diagram 3] 1 is a graph showing the relationship between tensile tension and elongation of a steel cord. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The configuration of the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 shows a heavy-duty pneumatic radial tire according to an embodiment of the present invention, and Fig. 2 shows the belt layer and the circumferential reinforcing layer. This embodiment depicts a pneumatic radial tire with a maximum tire width of 350 mm or more when inflated to a specified air pressure corresponding to the maximum load capacity, and an aspect ratio of 60% or less.

[0017] As shown in FIG. 1, the pneumatic radial tire of this embodiment includes a tread portion 1 extending circumferentially around the tire to form an annular shape, a pair of sidewall portions 2, 2 arranged on either side of the tread portion 1, and a pair of bead portions 3, 3 arranged radially inward of the sidewall portions 2.

[0018] A carcass layer 4 is mounted between a pair of bead portions 3, 3. This carcass layer 4 includes a plurality of steel cords extending in the tire radial direction, and has a structure in which it is wound from the inside to the outside of the tire around a bead core 5 disposed in each bead portion 3. A bead filler 6 made of a rubber composition having a triangular cross section is disposed on the outer periphery of the bead core 5.

[0019] Four belt layers 7 are embedded on the outer diameter side of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes a plurality of steel cords inclined with respect to the tire circumferential direction. These belt layers 7 include two central main belt layers 72, 73 in which the steel cords cross each other, and auxiliary belt layers 71, 74 arranged on the inner diameter side and outer diameter side of these main belt layers 72, 73. More specifically, the auxiliary belt layer 71 and the main belt layer 72 are inclined to one side (L-laying) with respect to the tire circumferential direction, and the main belt layer 73 and the auxiliary belt layer 74 are inclined to the other side (R-laying) with respect to the tire circumferential direction. The inclination angle of the steel cords constituting the main belt layers 72, 73 with respect to the tire circumferential direction is set in the range of, for example, 15° to 35°, and the inclination angle of the steel cords constituting the auxiliary belt layers 71, 74 with respect to the tire circumferential direction is set in the range of, for example, 15° to 75°.

[0020] Between the main belt layers 72 and 73, at least one circumferential reinforcing layer 8 including steel cords oriented in the tire circumferential direction is disposed. The circumferential reinforcing layer 8 has a jointless structure in which a strip material made of at least one steel cord aligned and rubber-coated is continuously wound at an angle of 5° or less, substantially 0°, with respect to the tire circumferential direction. The circumferential reinforcing layer 8 may be disposed between the auxiliary belt layer 71 and the main belt layer 72, or between the main belt layer 73 and the auxiliary belt layer 74, or may be disposed on the inner peripheral side of the auxiliary belt layer 71 or the outer peripheral side of the auxiliary belt layer 74.

[0021] Further, a plurality of circumferential main grooves 11 extending in the circumferential direction of the tire are formed in the tread portion 1, and a plurality of rows of land portions 12 are defined by these circumferential grooves 11.

[0022] In the above pneumatic radial tire, the maximum tangent modulus Em0 of the steel cord constituting the circumferential reinforcing layer 8 in its initial state and the maximum tangent modulus Em1 of the steel cord constituting the circumferential reinforcing layer 8 in its state after being removed from the tire satisfy the relationship -5GPa≦Em0-Em1<15GPa.

[0023] Fig. 3 is a graph showing the relationship between the tensile tension and the elongation of the steel cord. In Fig. 3, curve C0 shows the relationship between the tensile tension and the elongation of the steel cord constituting the circumferential reinforcing layer 8 in the initial state, and curve C1 shows the relationship between the tensile tension and the elongation of the steel cord constituting the circumferential reinforcing layer 8 in the state taken out of the tire. In the example of Fig. 3, the maximum tangent modulus Em1 of the steel cord constituting the circumferential reinforcing layer 8 in the state taken out of the tire is smaller than the maximum tangent modulus Em0 of the steel cord constituting the circumferential reinforcing layer 8 in the initial state due to the penetration of rubber into the steel cord. The steel cord constituting the circumferential reinforcing layer 8 has a cord structure in which the maximum tangent modulus Em0 in the initial state and the maximum tangent modulus Em1 in the state taken out of the tire satisfy the above relationship.

[0024] The twist structure of the steel cords used in the circumferential reinforcing layer 8 is not particularly limited, but it is preferable to adopt an N×M structure in which N (N=3-5) strands each made of M (M=5-10) wires are twisted together. An example of such an N×M structure is a 3×7 structure. The diameter of each wire should be in the range of 0.20 mm to 0.40 mm.

[0025] In this way, the maximum tangent elastic modulus Em0 of the steel cord constituting the circumferential reinforcing layer 8 in its initial state and the maximum tangent elastic modulus Em1 of the steel cord constituting the circumferential reinforcing layer 8 in its state after being removed from the tire satisfy a predetermined relationship, so that in a wide-width, low-aspect ratio pneumatic radial tire, the occurrence of failures caused by the belt layer 7 and the circumferential reinforcing layer 8 can be effectively suppressed and the durability can be improved.

[0026] Here, if the value of Em0-Em1 is greater than 15 GPa, the reinforcing effect on the belt layer 7 is reduced, making it difficult to suppress the phenomenon in which the edge portion of the belt layer 7 rises due to centrifugal force during high-speed running. Conversely, if the value of Em0-Em1 is less than -5 GPa, buckling in the compressive direction is likely to occur in the steel cords located at the edge portion of the circumferential reinforcing layer 8 due to in-plane bending of the belt layer 7 that occurs during cornering. In particular, it is desirable that the maximum tangent elastic modulus Em0 is in the range of 30 GPa to 40 GPa, and the maximum tangent elastic modulus Em1 is in the range of 20 GPa to 30 GPa.

[0027] 2, in the pneumatic radial tire, the width Wo of the circumferential reinforcing layer 8 and the maximum width Wm of the belt layer 7 satisfy the relationship 0.5≦Wo / Wm≦0.9. As a result, in a wide-width and low-aspect ratio pneumatic radial tire, the occurrence of failures caused by the belt layer 7 and the circumferential reinforcing layer 8 can be effectively suppressed, and the durability can be improved.

[0028] Here, if the value of Wo / Wm is less than 0.5, the reinforcing effect on the belt layer 7 is reduced, making it difficult to suppress the phenomenon in which the edge portions of the belt layer 7 rise due to centrifugal force during high-speed running. Conversely, if the value of Wo / Wm is greater than 0.9, buckling in the compressive direction is likely to occur in the steel cords located at the edge portions of the circumferential reinforcing layer 8 due to in-plane bending of the belt layer 7 that occurs during cornering.

[0029] Furthermore, the elastic modulus Ee of the steel cords arranged at the edge portions of the circumferential reinforcing layer 8 at 0.5% to 1.0% elongation and the elastic modulus Ec of the steel cords arranged at the center portion of the circumferential reinforcing layer 8 at 0.5% to 1.0% elongation satisfy the relationship 0.8≦Ee / Ec≦1.2. As a result, in a wide-width, low-aspect ratio pneumatic radial tire, the occurrence of failures caused by the belt layer 7 and the circumferential reinforcing layer 8 can be effectively suppressed, and the durability can be improved.

[0030] Here, if the value of Ee / Ec is less than 0.8, the reinforcing effect on the belt layer 7 is reduced, making it difficult to suppress the phenomenon in which the edge portion of the belt layer 7 rises due to centrifugal force during high-speed running. Conversely, if the value of Ee / Ec is greater than 1.2, buckling in the compressive direction is likely to occur in the steel cords located at the edge portion of the circumferential reinforcing layer 8 due to in-plane bending of the belt layer 7 that occurs during cornering. In particular, it is desirable that the elastic modulus Ee is in the range of 40 GPa to 65 GPa, and the elastic modulus Ec is in the range of 40 GPa to 65 GPa.

[0031] In the above pneumatic radial tire, the rate of change Rc of the circumferential length of the tread portion 1 at the tire equator, which changes between an inflated state of 100 kPa and an inflated state of a specified air pressure corresponding to the maximum load capacity, and the rate of change Rs of the circumferential length of the tread portion 1 at the shoulder portion preferably satisfy the relationship of 0.7≦Rc / Rs≦1.3. This makes it possible to suppress local deformation in the center portion and shoulder portion of the tread portion 1 and to suppress the occurrence of failures caused by the belt layer 7 and the circumferential reinforcing layer 8.

[0032] Here, if the value of Rc / Rs is smaller than 0.7, the deformation of the shoulder portion becomes large, and peeling of the edge portion of the belt layer 7 and fatigue fracture of the steel cord at the edge portion of the circumferential reinforcing layer 8 become likely to occur. Conversely, if the value of Rc / Rs is larger than 1.3, the deformation of the center portion becomes large, and peeling between the belt layer 7 and the circumferential reinforcing layer 8 becomes likely to occur.

[0033] In a pneumatic radial tire for heavy loads, the outer shape of the tread portion when inflated to an air pressure of 100 kPa corresponds to the outer shape of the tread molding surface of the molding die. Therefore, when the ratio Rc / Rs of the rate of change Rc of the tread portion's outer circumference at the tire equator to the rate of change Rs of the tread portion's outer circumference at the shoulders is in the above range, it means that the outer shape of the tread portion when inflated to the maximum specified air pressure allowed for the tire changes at a substantially uniform rate over the entire tread width from the tire equator to both shoulders with respect to the outer shape of the tread molding surface of the molding die. This contributes to improving durability, particularly in pneumatic radial tires with wide widths and low aspect ratios.

[0034] The tire equator where the peripheral change rate Rc is measured is the center position of the tread portion divided into two equal parts in the tire width direction. The shoulder portion where the peripheral change rate Rs is measured is a position 35% of the total tire width away from the tire equator. However, if the tire equator and shoulder portion each have a circumferential main groove 11, the position of the tire equator is a position on the land portion 12 closest to the circumferential main groove 11, and the position of the shoulder portion is a position on the land portion 12 closest to the circumferential main groove 11 and shifted outward in the tire width direction from the circumferential main groove 11.

[0035] The peripheral length change rates Rc and Rs are calculated by the following equations (2) and (3). Rc = (Cc2 - Cc1) / Cc1 (2) Rs = (Cs2 - Cs1) / Cs1 (3) However, Cc1: Circumference at the tire equator when inflated with an air pressure of 100 kPa Cc2: Circumference at the tyre equator when inflated to the specified air pressure corresponding to the maximum load capacity Cs1: Circumference at the shoulder when filled with air at 100 kPa Cs2: Circumference at the shoulder when inflated to the specified air pressure corresponding to the maximum load capacity The outer circumferential lengths Cs1 and Cs2 at the shoulder portions are the average values ​​of the values ​​measured at the left and right shoulder portions, respectively.

[0036] In the above embodiment, a pneumatic radial tire is described in which the maximum tire width is 350 mm or more when inflated to a specified air pressure corresponding to the maximum load capacity, and the aspect ratio is 60% or less, but the present invention is also applicable to pneumatic radial tires that do not satisfy the above requirements. However, the present invention is particularly effective in the wide pneumatic radial tires with low aspect ratios as described above. EXAMPLES

[0037] In a pneumatic radial tire having a tire size of 445 / 50R22.5, four belt layers including steel cords inclined with respect to the tire circumferential direction and one circumferential reinforcing layer including steel cords oriented in the tire circumferential direction are disposed on the outer peripheral side of the carcass layer in the tread portion. The maximum tangent elastic modulus Em0 of the steel cords constituting the circumferential reinforcing layer in the initial state, the maximum tangent elastic modulus Em1 of the steel cords constituting the circumferential reinforcing layer in the state when removed from the tire, the difference Em0-Em1, and the steel cord disposed in the center portion of the circumferential reinforcing layer are The elastic modulus Ec of the steel cord at 0.5% to 1.0% elongation, the elastic modulus Ee of the steel cord arranged at the edge portion of the circumferential reinforcing layer at 0.5% to 1.0% elongation, the ratio Ee / Ec, the ratio Wo / Wm of the width Wo of the circumferential reinforcing layer to the maximum width Wm of the belt layer, and the ratio Rc / Rs of the rate of change Rc of the outer circumferential length of the tread portion at the tire equator, which changes between an inflated state of 100 kPa and an inflated state of a specified air pressure corresponding to the maximum load capacity, to the rate of change Rs of the outer circumferential length of the tread portion at the tire equator and at the shoulder portion, were set as shown in Table 1. Tires of the conventional example, comparative examples 1 to 4, and examples 1 to 9 were manufactured.

[0038] The durability of these test tires was evaluated by the following test method, and the results are shown in Table 1.

[0039] Durability: Each test tire was mounted on a wheel with a rim size of 22.5 x 17.00 and inflated to 900 kPa. A drum test machine with a smooth steel drum with a diameter of 1707 mm was used to perform a preliminary run for 60 minutes under the conditions of controlling the ambient temperature at 38±3°C, running speed of 60 km / h, and load of 88% of the JATMA maximum load capacity. After completing the preliminary run, the main run was started at the same speed with a load of 120% of the JATMA maximum load capacity and a slip angle of ±4° with a sine wave of 0.05 Hz, and the running distance until the tire was destroyed was measured. The evaluation results were shown as an index with the conventional example being 100. The higher the index value, the better the durability.

[0040] [Table 1]

[0041] As can be seen from Table 1, the tires of Examples 1 to 9 had improved durability compared to the conventional tire. On the other hand, the tires of Comparative Examples 1, 3, and 4 had too small a value for the ratio Ee / Ec, so the rising of the belt layer could not be sufficiently suppressed, and the durability was worse than that of the conventional tire. The tire of Comparative Example 2 had too large a value for the ratio Ee / Ec, so the steel cords of the circumferential reinforcing layer buckled in the compression direction, and the durability was worse than that of the conventional tire. In addition, the tire of Comparative Example 3 had too small a value for the ratio Ee / Ec, so the rising of the belt layer could not be sufficiently suppressed, and the durability was worse than that of the conventional tire.

[0042] In addition, in comparing Examples 1 to 4, when the value of the ratio Rc / Rs is too large, the deformation of the center portion becomes large, making it easy for delamination to occur between the belt layer and the circumferential reinforcing layer, and when the value of the ratio Rc / Rs is too small, the deformation of the shoulder portion becomes large, making it easy for delamination of the edge portion of the belt layer and fatigue fracture of the steel cord of the circumferential reinforcing layer to occur. [Explanation of symbols]

[0043] 1 Tread section 2 Sidewall 3 Bead section 4 Carcass layer 5 Bead Core 6 Bead Filler 7 Belt layer 8 Circumferential reinforcement layer 11 Circumferential main groove 12 Land

Claims

1. A pneumatic radial tire having a tread portion, on the outer peripheral side of a carcass layer, a plurality of belt layers including steel cords inclined with respect to the circumferential direction of the tire, and at least one circumferential reinforcing layer including steel cords oriented in the circumferential direction of the tire, The maximum tangent elastic modulus Em of the steel cord constituting the circumferential reinforcing layer in the initial state 0 and the maximum tangent modulus of elasticity Em of the steel cord constituting the circumferential reinforcing layer when taken out of the tire 1 and satisfy the relationship -2 GPa≦Em 0 -Em 1 ≦14 GPa, a width Wo of the circumferential reinforcing layer and a maximum width Wm of the belt layer satisfy a relationship of 0.5≦Wo / Wm≦0.9, A pneumatic radial tire, characterized in that an elastic modulus Ee of a steel cord arranged in an edge portion of the circumferential reinforcing layer at an elongation of 0.5% to 1.0% and an elastic modulus Ec of a steel cord arranged in a center portion of the circumferential reinforcing layer at an elongation of 0.5% to 1.0% satisfy a relationship of 0.8≦Ee / Ec≦1.

2.

2. 2. The pneumatic radial tire according to claim 1, characterized in that a rate of change Rc of the outer circumferential length of the tread portion at the tire equator and a rate of change Rs of the outer circumferential length of the shoulder portion, which change between a state inflated with an air pressure of 100 kPa and a state inflated with a specified air pressure corresponding to the maximum load capacity, satisfy the relationship 0.7≦Rc / Rs≦1.

3.

3. 3. The pneumatic radial tire according to claim 1, wherein the maximum tire width when inflated to a specified air pressure corresponding to the maximum load capacity is 350 mm or more, and the aspect ratio is 60% or less.

Images