Pneumatic tire

Abstract

To provide a pneumatic tire that is able to achieve both ride comfort performance and rolling resistance performance.SOLUTION: The present invention relates to a pneumatic tire having a tread portion 2. The tread portion 2 includes a tread rubber 2G and a belt layer 7. The belt layer 7 includes at least two belt plies 7A. A ground contact surface 2s includes a tread half-width TWh and a shoulder reference position 17. When the thickness of the tread rubber 2G at the position of a tire equator C is A (mm), the thickness of the tread rubber 2G at the position 17 of a shoulder reference is H (mm), the product of the strength (N) of one steel cord 12 and a cord count (cords) of steel cords 12 per widthwise 5 cm of one belt ply is X(N×cords / 5 cm), and the weight per 1 m2 of the one belt ply is G(g / m2), the following formula (1) is satisfied. (Equation 1) 9.8≤(H×X) / (A×G)≤11.2 (1)SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 below proposes a pneumatic tire having a belt layer in which reinforcing cords are coated with a rubber composition. This tire is expected to improve ride comfort and handling stability during high-speed driving by specifying the thickness of the tread portion, the complex modulus of the rubber composition, and the number of arranged reinforcing cords in relation to each other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-060432 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for improved fuel economy performance of vehicles, and a demand for further reduction in the rolling resistance of tires mounted on vehicles. As a method for reducing the rolling resistance of tires (hereinafter referred to as "improving rolling resistance performance"), for example, reducing the weight of the belt ply or increasing the rigidity of the belt ply can be considered.

[0005] However, the above method may result in unpleasant vibrations being easily transmitted to the driver, which may impair ride comfort.

[0006] The present invention has been devised in view of the above circumstances, and has as its main object to provide a pneumatic tire that can achieve both good ride comfort and good rolling resistance performance. [Means for solving the problem]

[0007] The present invention is a pneumatic tire having a tread portion, the tread portion including a first tread edge and a second tread edge, a contact patch between the first tread edge and the second tread edge, tread rubber constituting the contact patch, and a belt layer disposed radially inward of the tread rubber, the belt layer including at least two belt plies each including a plurality of steel cords arranged at an angle with respect to the tire equator and a topping rubber covering the steel cords, and the contact patch is a portion extending from the tire equator to the The tire width includes a tread half width, which is the distance in the tire axial direction to a first tread edge, and a shoulder reference position spaced from the tire equator toward the first tread edge by a distance of 75% of the tread half width, and the thickness of the tread rubber at the tire equator position is A (mm), the thickness of the tread rubber at the shoulder reference position is H (mm), the strength of one steel cord (N) is multiplied by the number of steel cords (number) per 5 cm width of one belt ply is X (N number / 5 cm), and the number of steel cords per 1 m width of one belt ply is X (N number / 5 cm). 2 The weight per unit is expressed as G (g / m 2 ) is a pneumatic tire that satisfies the following formula (1): (Number 1) 9.8≦(H·X) / (A·G)≦11.2…(1) [Effects of the Invention]

[0008] By adopting the above-described configuration, the pneumatic tire of the present invention can achieve both good ride comfort and good rolling resistance performance. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a tire according to one embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view of the tread portion of FIG. 1. [Figure 3] FIG. 2 is a development view showing the cord arrangement of the belt layer of FIG. 1. [Figure 4] FIG. 4 is a cross-sectional view of a steel cord according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described below with reference to the drawings. The drawings are intended to illustrate the features of the present invention, but may include exaggerated representations and representations that differ from the dimensional ratios of the actual structure to facilitate understanding of the present invention. Furthermore, identical or common elements are designated by the same reference numerals throughout the embodiments, and redundant explanations will be omitted. Furthermore, well-known configurations may be appropriately adopted for configurations not described in this specification.

[0011] FIG. 1 shows a cross-sectional view of a pneumatic tire (hereinafter, sometimes simply referred to as "tire 1") according to one embodiment of the present invention. FIG. 1 is a cross-sectional view of tire 1 in a normal state, taken along a tire meridian including the tire rotation axis. As shown in FIG. 1, tire 1 according to this embodiment is suitable for use as a pneumatic tire for passenger cars, for example. However, the present invention is not limited to this embodiment, and may also be applied to, for example, pneumatic tires for heavy loads.

[0012] "Normal condition" means, in the case of a pneumatic tire for which various standards are established, a state in which the tire is mounted on a normal rim, inflated to the normal internal pressure, and no load is applied. In the case of a tire for which various standards are not established, the normal condition means a standard use state according to the intended use of the tire, in which the tire is not mounted on a vehicle and no load is applied. In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured in the normal condition. In addition, the dimensions of components that cannot be measured in the normal condition (for example, the internal materials of the tire 1) are values ​​measured with the tire 1 in a state as close to the normal condition as possible.

[0013] A "genuine rim" is a rim that is defined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is called a "standard rim," in the case of TRA, it is called a "design rim," and in the case of ETRTO, it is called a "measuring rim."

[0014] "Normal internal pressure" is the air pressure specified for each tire by each standard in the standard system, including the standard on which the tire is based. For JATMA, it is the "maximum air pressure," for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, it is the "INFLATION PRESSURE."

[0015] The tire 1 includes a tread portion 2, a first sidewall portion 3A, a second sidewall portion 3B, and a first bead portion 4A and a second bead portion 4B. The first sidewall portion 3A is connected to an end portion of the tread portion 2 on one side in the tire axial direction (the left side in FIG. 1) and extends radially inward in the tire direction. The second sidewall portion 3B is connected to an end portion of the tread portion 2 on the other side in the tire axial direction (the right side in FIG. 1) and extends radially inward in the tire direction. The first bead portion 4A is connected to the radially inward side of the first sidewall portion 3A. The second bead portion 4B is connected to the radially inward side of the second sidewall portion 3B.

[0016] The tire 1 includes a carcass 6. The carcass 6 extends from the first bead portion 4A, through the first sidewall portion 3A, the tread portion 2 and the second sidewall portion 3B, to the second bead portion 4B.

[0017] The carcass 6 is composed of, for example, one carcass ply 6A. The carcass ply 6A includes, for example, a main body portion 6a and a turned-up portion 6b. The main body portion 6a extends, for example, between the first bead portion 4A and the second bead portion 4B. The turned-up portion 6b is continuous with the main body portion 6a and is turned up around the bead core 5 from the inside to the outside in the tire axial direction.

[0018] The carcass ply 6A includes a plurality of carcass cords and a topping rubber covering the cords (not shown). The carcass cords are made of organic fiber cords such as aramid or rayon. The carcass cords are preferably arranged at an angle of 70 to 90 degrees relative to the tire equator C. That is, the tire 1 of this embodiment has a radial structure carcass.

[0019] In this specification, when a numerical range for various parameters is described, unless otherwise specified, the numerical range refers to the numerical range for the average value of the parameter. Therefore, the numerical range for the carcass cord angle described above refers to the numerical range of the average value of angles measured at various positions for multiple carcass cords. The same applies to other parameters described below.

[0020] Fig. 2 shows an enlarged cross-sectional view of the tread portion 2. As shown in Fig. 2, the tread portion 2 includes a first tread edge Te1 and a second tread edge Te2, a contact patch 2s between the first tread edge Te1 and the second tread edge Te2, a tread rubber 2G that constitutes the contact patch 2s, and a belt layer 7 disposed radially inward of the tread rubber 2G.

[0021] The first tread edge Te1 and the second tread edge Te2 correspond to the edges of the contact patch 2s when the tire 1 in a normal state is loaded with 70% of the normal load and the tread portion 2 is brought into contact with a flat surface at a camber angle of 0°.

[0022] For pneumatic tires for which various standards are established, "normal load" refers to the load specified for each tire in the standard system including the standard on which the tire is based. For JATMA, this is "maximum load capacity," for TRA, this is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES," and for ETRTO, this is "LOAD CAPACITY." For tires for which various standards are not established, "normal load" refers to the maximum load that can be applied when using the tire in accordance with the above standards.

[0023] The tread rubber 2G constitutes at least the contact surface 2s, and in this embodiment, also constitutes part of the outer surface of the first sidewall portion 3A (shown in FIG. 1) and part of the outer surface of the second sidewall portion 3B (shown in FIG. 1). The tread rubber 2G shown in each drawing in this specification is described as being made of one type of rubber material, but the present invention is not limited to this embodiment. In other words, the tread rubber 2G may be made of multiple rubber layers.

[0024] Fig. 3 is a development view conceptually showing the cord arrangement of the belt layer 7. As shown in Fig. 3, the belt layer 7 includes at least two belt plies 7A, each of which includes a plurality of steel cords 12 arranged at an angle with respect to the tire equator C and a topping rubber 7g covering the steel cords 12.

[0025] In each of these belt plies 7A, the steel cords 12 are arranged at an angle θ1 of 15 to 45° with respect to the tire circumferential direction. The steel cords 12 included in one belt ply 7A and the steel cords 12 included in the other belt ply 7A are inclined in opposite directions with respect to the tire circumferential direction. This effectively reinforces the tread portion 2.

[0026] As shown in Figures 2 and 3, a band layer 8 is disposed on the radially outer side of the belt layer 7 of this embodiment. The band layer 8 is composed of, for example, one band ply 8A. The band ply 8A includes, for example, band cords 8c disposed at an angle θ2 of 5° or less with respect to the tire circumferential direction, and a topping rubber 8g covering the band cords 8c. The band layer 8 of this embodiment is disposed so as to cover the entire belt layer 7.

[0027] 2, the contact patch 2s of the tread portion 2 includes a tread half width TWh and a shoulder reference position 17. The tread half width TWh corresponds to the axial distance from the tire equator C to the first tread edge Te1. The shoulder reference position 17 corresponds to a position separated from the tire equator C toward the first tread edge Te1 by a distance L1 that is 75% of the tread half width TWh.

[0028] In the present invention, the thickness of the tread rubber 2G at the position of the tire equator C is A (mm), the thickness of the tread rubber 2G at the shoulder reference position 17 is H (mm), the product of the strength (N) of one steel cord 12 (shown in FIG. 3) and the number of steel cords 12 (number) per 5 cm width of one belt ply 7A is X (N number / 5 cm), and the number of steel cords 12 per 1 m width of one belt ply is X (N number / 5 cm). 2 The weight per unit is expressed as G (g / m 2 ), the following formula (1) is satisfied. (Number 1) 9.8≦(H·X) / (A·G)≦11.2…(1)

[0029] In another embodiment of the present invention, when grooves are provided at the position of the tire equator C or at the shoulder reference position 17, the thickness A and the thickness H are measured with the grooves filled. These thicknesses refer to the thickness of the tread rubber 2G in the normal direction perpendicular to the contact patch 2s. Furthermore, it is desirable to use the average of thicknesses measured at multiple positions around the tire.

[0030] The strength of the steel cord 12 (shown in FIG. 3, and the same applies hereinafter) is measured by a well-known method, but if necessary, a measurement method in accordance with JIS G3510 may be adopted. The end count refers to the number of steel cords 12 per 5 cm width of one belt ply in the direction perpendicular to the longitudinal direction of the steel cord 12.

[0031] Furthermore, in this embodiment, it is assumed that the distribution of the steel cords 12 in the two belt plies 7A is uniform. However, if there is a bias in the distribution or if the strength of the steel cords 12 differs depending on the measurement position, the values ​​of the strength and the number of strands are average values ​​sampled from the entire two belt plies 7A.

[0032] The tire 1 of the present invention can achieve both good ride comfort and good rolling resistance performance by satisfying the above-mentioned formula (1) for the following reasons.

[0033] The inventors have found that the product X (N·pieces / 5cm) of the strength (N) of one steel cord 12 and the number (pieces) of steel cords 12 placed per 5 cm width of one belt ply 7A can be used as a parameter for defining the rigidity of the belt ply 7A. 2 Weight per unit G (g / m 2 ) can be used.

[0034] The inventors also discovered that if the ratio X / G, which relates to the above parameters, is set within a specific range, the rigidity and weight of the belt ply 7A can be optimized, thereby improving rolling resistance performance while maintaining ride comfort performance.

[0035] As a result of further research, it was found that it is desirable not only to specify the ratio X / G that defines the characteristics of the belt ply 7A, but also to take into consideration the thickness distribution of the tread rubber 2G, i.e., the ratio H / A between the thickness A (mm) of the tread rubber 2G at the tire equator C and the thickness H (mm) of the tread rubber 2G at the shoulder reference position 17.

[0036] Specifically, it has been found that if the parameter "(H·X) / (A·G)" which is the product of the ratio H / A and the ratio X / G is set within a specific range, it is possible to take into consideration the stiffness and weight of the belt ply 7A as well as the thickness ratio of each portion of the tread rubber 2G, and it is possible to more reliably maintain ride comfort and improve rolling resistance. From this perspective, the tire of the present invention can achieve the above-mentioned effects by satisfying the above-mentioned formula (1).

[0037] The inventors also investigated whether the above-mentioned mechanism would be effective even when the above-mentioned various parameters were significantly changed. As a result, they found that, at least when the above-mentioned various parameters are within the numerical ranges that can be adopted in ordinary tires (hereinafter referred to as "adoptable ranges"), if the above-mentioned formula (1) is satisfied, it can be expected that ride comfort performance will be maintained and rolling resistance performance will be improved.

[0038] From the results of various experiments, the usable ranges of the thickness A and the thickness H are set to 5.0 to 15.0 mm. The usable range of the strength (N) of one steel cord 12 is set to 300 to 700 N. The usable range of the end count is set to 20 to 70. 2 The acceptable range of weight per unit is 1000 to 2500g.

[0039] The following describes the configuration of this embodiment in more detail. Note that each configuration described below represents a specific aspect of this embodiment. Therefore, it goes without saying that the present invention can achieve the above-described effects even if it does not include the configurations described below. Furthermore, even if any one of the configurations described below is applied alone to the tire 1 of the present invention having the above-described characteristics, an improvement in performance corresponding to each configuration can be expected. Furthermore, when several of the configurations described below are applied in combination, an improvement in combined performance corresponding to those configurations can be expected.

[0040] In this embodiment, the contact patch 2s of the tread portion 2 is provided with a plurality of circumferential grooves 9 extending continuously in the tire circumferential direction. However, the present invention is not limited to this aspect. In another embodiment of the present invention, a plurality of V-shaped grooves may be provided in the contact patch 2s in the tire circumferential direction. Although not shown in the drawings, the V-shaped groove includes, for example, a first inclined portion extending from the first tread edge Te1 at an inclination in a first direction with respect to the tire axial direction, and a second inclined portion extending from the second tread edge Te2 at an inclination in a second direction opposite to the first direction with respect to the tire axial direction.

[0041] The steel cord 12 of this embodiment has, for example, a 1×1 structure made up of a monofilament. Fig. 4 shows a cross-sectional view of a steel cord 12 in another embodiment. As shown in Fig. 4, the steel cord 12 may have a 1×n structure made up of multiple (n) filaments 15. Fig. 4 shows a steel cord 12 of a 1×4 structure made up of four filaments 15. In this case, the outer diameter D1 of each of the multiple filaments 15 is, for example, 0.15 to 0.30 mm. This improves ride comfort and rolling resistance in a well-balanced manner.

[0042] The steel cords 12 may be made of, for example, a so-called ST material (super tensile material) which can be expected to have a tensile strength of 3600 MPa or more, a so-called UT material (ultra tensile material) which can be expected to have a tensile strength of 4000 MPa or more, or a so-called MT material (mega tensile material) which can be expected to have a tensile strength of 4500 MPa or more. In particular, when the steel cords 12 have a 1x1 structure, it is desirable to use the ST material or MT material.

[0043] Furthermore, when the steel cord 12 has a 1x1 structure, the carbon content of the steel cord 12 is preferably 0.84% ​​to 1.00%. When the steel cord 12 has a 1x4 structure, the carbon content of the steel cord 12 is preferably 0.79% to 1.00%. However, the steel cord 12 of the present invention is not limited to such an embodiment. Note that a well-known measuring method is used to measure the tensile strength.

[0044] The outer diameter of the steel cord 12 is, for example, 0.36 to 0.55 mm. This numerical range is more suitable when the steel cord 12 has a 1x4 structure. When the steel cord 12 has a 1x1 structure, the outer diameter of the steel cord 12 is desirably 0.36 to 0.42 mm. Note that when the steel cord 12 has a 1x4 structure, the outer diameter corresponds to the diameter of a circle having the same area as the cross-sectional area of ​​the steel cord 12.

[0045] The strength of the steel cords 12 is, for example, 350 to 540 N. This range is more suitable when the steel cords 12 have a 1x4 structure. When the steel cords 12 have a 1x1 structure, the strength of the steel cords 12 is preferably 400 to 540 N. This improves ride comfort and rolling resistance in a well-balanced manner.

[0046] The end count of the steel cord 12 is, for example, 40 to 60. This range is more suitable when the steel cord 12 has a 1x4 structure. When the steel cord 12 has a 1x1 structure, the end count of the steel cord 12 is preferably, for example, 40 to 50.

[0047] The product X (N·pieces / 5 cm) of the strength (N) of the steel cord 12 and the end count (pieces) of the steel cord 12 is preferably 14,000 or more, more preferably 16,000 or more, and is preferably 24,000 or less, more preferably 22,000 or less.

[0048] As shown in Fig. 2, the thickness t1 of one belt ply 7A is, for example, 0.65 to 0.98 mm. When the steel cords 12 have a 1x4 structure, the thickness t1 is preferably 0.66 to 0.98 mm. When the steel cords 12 have a 1x1 structure, the thickness t1 is preferably 0.65 to 0.85 mm. This optimizes the thickness t1 of the belt ply 7A, further improving rolling resistance performance.

[0049] From the viewpoint of certainly reducing the weight of the tread portion 2, it is necessary to 2 The weight G per tire is preferably 2200 g or less, and more preferably 2100 g or less. From the viewpoint of ensuring the durability of the tread portion 2, the weight G is preferably 1500 g or more, and more preferably 1600 g or more.

[0050] The ratio H / A of the thickness H of the tread rubber 2G at the shoulder reference position 17 to the thickness A of the tread rubber 2G at the tire equator C is, for example, 0.80 to 0.95. This optimizes the thickness distribution of the tread rubber 2G, improving ride comfort and rolling resistance in a well-balanced manner.

[0051] Although a tire according to one embodiment of the present invention has been described in detail above, the present invention is not limited to the specific embodiment described above, and can be modified and practiced in various aspects. [Example]

[0052] Pneumatic tires of size 205 / 55R16 having the basic structure shown in Figure 1 were prototyped based on the specifications in Tables 1 and 2. Tires not satisfying the above-mentioned formula (1) of the present invention were prototyped as Comparative Examples 1 to 3. The tires of Comparative Examples 1 to 3 were substantially the same as the tires of the Examples, except for the above-mentioned points. The rolling resistance performance and ride comfort performance of each test tire were tested. The common specifications and test methods for each test tire are as follows: <Common specifications> Rim: 16x6.5 Tire pressure: 250kPa

[0053] <Rolling resistance performance> The rolling resistance of each test tire was measured using a rolling resistance tester. The results were expressed as an index by taking the reciprocal of the measured rolling resistance, with a larger index indicating a lower and more favorable rolling resistance.

[0054] <Ride comfort> The test tires were mounted on passenger cars and driven on public roads, and the ride comfort was evaluated by the driver. The results were expressed as a rating, with a higher number indicating better ride comfort.

[0055] The test results are shown in Tables 1-2. [Table 1]

[0056] [Table 2]

[0057] As shown in Tables 1 and 2, the tires of the examples have improved rolling resistance performance while maintaining ride comfort performance compared to the comparative examples, and are also excellent in overall performance, which is evaluated as the sum of rolling resistance performance and ride comfort performance, confirming that they achieve both ride comfort performance and rolling resistance performance.

[0058] [Note] The present invention includes the following aspects.

[0059] [Invention 1] A pneumatic tire having a tread portion, The tread portion is a first tread edge and a second tread edge; a contact patch between the first tread edge and the second tread edge; tread rubber that forms the ground contact surface; a belt layer disposed radially inward of the tread rubber, The belt layer includes at least two belt plies, each of which includes a plurality of steel cords arranged at an angle with respect to the tire equator and a topping rubber covering the steel cords, the contact patch includes a tread half width, which is a distance in the tire axial direction from the tire equator to the first tread edge, and a shoulder reference position, which is spaced from the tire equator toward the first tread edge by a distance of 75% of the tread half width, The thickness of the tread rubber at the tire equator is A (mm), The thickness of the tread rubber at the shoulder reference position is H (mm), The product of the strength of one steel cord (N) and the number of steel cords (pieces) per 5 cm width of one belt ply is X (N pieces / 5 cm), 1m of one of the belt plies 2 The weight per unit is expressed as G (g / m 2 ) satisfies the following formula (1): Pneumatic tires. (Number 1) 9.8≦(H·X) / (A·G)≦11.2…(1) [Invention 2] The pneumatic tire according to invention 1, wherein the ground contact surface is provided with a plurality of circumferential grooves extending continuously in the circumferential direction of the tire. [Invention 3] A plurality of V-shaped grooves are provided in the contact surface in the tire circumferential direction, A pneumatic tire as described in Invention 1, wherein the V-shaped groove includes a first inclined portion extending from the first tread edge at an incline in a first direction with respect to the tire axial direction, and a second inclined portion extending from the second tread edge at an incline in a second direction opposite to the first direction with respect to the tire axial direction. [Invention 4] 4. The pneumatic tire according to any one of claims 1 to 3, wherein the steel cord has a 1x1 structure made of monofilaments. [Invention 5] 5. The pneumatic tire according to any one of claims 1 to 4, wherein the steel cord has a 1x4 structure made up of four filaments. [Invention 6] 6. The pneumatic tire according to any one of Inventions 1 to 5, wherein the carbon content of the steel cord is 0.79% to 1.00%. [Invention 7] 7. The pneumatic tire according to any one of Inventions 1 to 6, wherein the steel cord has an outer diameter of 0.36 to 0.55 mm. [Invention 8] 8. The pneumatic tire according to any one of claims 1 to 7, wherein the strength of the steel cord is 350 to 540N. [Invention 9] 9. The pneumatic tire according to any one of aspects 1 to 8, wherein the end count of the steel cord is 40 to 60. [Invention 10] 10. The pneumatic tire according to any one of Inventions 1 to 9, wherein the thickness of one of the belt plies is 0.65 to 0.98 mm. [Explanation of symbols]

[0060] 2 Tread section 2G tread rubber 2s ground plane 7 Belt Layer 7g Topping Rubber 7A Belt Ply 12 Steel Cord 17 Shoulder reference position TWh Tread half width Te1 First tread edge Te2 Second tread edge A: Thickness of tread rubber at the tire equator H Thickness of tread rubber at shoulder reference position X is the product of the strength of one steel cord (N) and the number of steel cords (pieces) per 5cm width of one belt ply G Belt ply 1m 2 Per weight

Claims

1. A pneumatic tire having a tread portion, The tread portion is a first tread edge and a second tread edge; a contact patch between the first tread edge and the second tread edge; tread rubber that forms the ground contact surface; a belt layer disposed radially inward of the tread rubber, The belt layer includes at least two belt plies, each of which includes a plurality of steel cords arranged at an angle with respect to the tire equator and a topping rubber covering the steel cords, the contact patch includes a tread half width, which is a distance in the tire axial direction from the tire equator to the first tread edge, and a shoulder reference position, which is spaced from the tire equator toward the first tread edge by a distance of 75% of the tread half width, The thickness of the tread rubber at the tire equator is A (mm), The thickness of the tread rubber at the shoulder reference position is H (mm), The product of the strength (N) of one steel cord and the number (pieces) of the steel cords per 5 cm width of one belt ply is X (N pieces / 5 cm), 1 m of one of the belt plies 2 The weight per unit is expressed as G (g / m 2 ) satisfies the following formula (1): Pneumatic tires. (Equation 1) 9.8≦(H・X) / (A・G)≦11.2…(1)

2. The pneumatic tire according to claim 1 , wherein the ground contact surface is provided with a plurality of circumferential grooves extending continuously in the circumferential direction of the tire.

3. A plurality of V-shaped grooves are provided in the contact surface in the tire circumferential direction, 2. The pneumatic tire according to claim 1, wherein the V-shaped groove includes a first inclined portion extending from the first tread edge at an incline in a first direction with respect to the tire axial direction, and a second inclined portion extending from the second tread edge at an incline in a second direction opposite to the first direction with respect to the tire axial direction.

4. The pneumatic tire according to claim 1 , wherein the steel cord has a 1×1 structure made of monofilaments.

5. The pneumatic tire according to claim 1 , wherein the steel cord has a 1×4 structure made up of four filaments.

6. 4. The pneumatic tire according to claim 1, wherein the steel cord has a carbon content of 0.79% to 1.00%.

7. 4. The pneumatic tire according to claim 1, wherein the steel cord has an outer diameter of 0.36 to 0.55 mm.

8. 4. The pneumatic tire according to claim 1, wherein the strength of the steel cord is 350 to 540 N.

9. 4. The pneumatic tire according to claim 1, wherein the end count of the steel cord is 40 to 60.

10. 4. The pneumatic tire according to claim 1, wherein the thickness of one of the belt plies is 0.65 to 0.98 mm.

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