Pneumatic tire

Abstract

To provide a pneumatic tire improved in rolling resistance performance without impairing durability of a tread part.SOLUTION: A pneumatic tire according to the present invention includes a tread part 2, a first side wall part 3A, a first bead part 4A, a carcass 6 and an inner liner 20. The tread part 2 includes a belt layer 7, where an average thickness of one belt ply 7A is 0.66-0.98 mm. The inner liner 20 includes a butyl rubber layer 21 including butyl-system rubber with air impermeability. The butyl rubber layer 21 includes a first portion 26, a second portion 27 and a third portion 28. An average thickness t2 of the second portion 27 is 0.8-1.3 mm. An average thickness t1 of the first portion 26 and an average thickness t3 of the third portion are smaller than the thickness t2.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 listed below proposes a tire that is expected to improve rolling resistance when the vehicle starts moving by specifying the loss tangent of the cap rubber layer of the tread portion and the thickness of the tread portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7337333 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 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, it is known to reduce the thickness of the belt plies that constitute the belt layer, thereby reducing the weight of the tire.

[0005] However, the above method may cause the belt ply to easily separate, which may in turn impair the durability of the tread portion.

[0006] The present invention has been devised in view of the above circumstances, and has as its main object to provide a pneumatic tire having improved rolling resistance performance without impairing the durability of the tread portion. [Means for solving the problem]

[0007] The present invention provides a pneumatic tire including a tread portion, a first sidewall portion that is connected to a first end portion of the tread portion in the tire axial direction and extends radially inward in the tire direction, and that includes a tire maximum width position, a first bead portion that is connected to the first sidewall portion in the tire radial direction and is connected to the first bead portion on the tire radially inward, a carcass that extends from the tread portion to the first bead portion, and an inner liner that is disposed on the tire cavity side of the carcass, wherein the tread portion includes a belt layer that includes at least one belt ply in which a plurality of steel cords are covered with a topping rubber, and the average thickness of the one belt ply is 0.66 to 0.98 mm, and the inner liner is made of an air-impermeable buttock. a butyl rubber layer containing a butyl rubber-based rubber, the butyl rubber layer including a first portion extending from a position of the tire equator toward the first end portion to a first position in the tire axial direction that is 10 mm axially inward from an outer end of the belt layer in the tire axial direction, in a tire meridian cross section including the tire rotation axis; a second portion extending from the first portion to a tire maximum width position; and a third portion extending from the second portion to an inner end of the butyl rubber layer in the tire radial direction, the second portion having an average thickness t2 of 0.8 to 1.3 mm, and an average thickness t1 of the first portion and an average thickness t3 of the third portion each being smaller than the thickness t2. [Effects of the Invention]

[0008] By adopting the above-described configuration, the pneumatic tire of the present invention can improve rolling resistance performance without impairing the durability of the tread portion. [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 a development view showing the cord arrangement of the cord reinforcement layer of FIG. 1. [Figure 3] 2 is an enlarged view of the periphery of a first end portion of the tread portion, a first sidewall portion, and a first bead portion of FIG. 1. FIG. [Figure 4]FIG. 4 is an enlarged cross-sectional view showing the belt ply, the carcass ply, and the inner liner around the end of the belt layer of FIG. 3. [Figure 5] 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 1 (hereinafter, sometimes simply referred to as "tire 1") according to one embodiment of the present invention. FIG. 1 is a cross-sectional view of the tire 1 in a normal state, taken along a tire meridian including the tire rotation axis. As shown in FIG. 1, the 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 a pneumatic tire for heavy loads, for example.

[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 axial first end portion 2a (the right end portion in each drawing in this specification) of the tread portion 2 and extends radially inward. The second sidewall portion 3B is connected to an axial second end portion 2b (the left end portion in each drawing in this specification) of the tread portion 2 and extends radially inward. The first sidewall portion 3A and the second sidewall portion 3B each include a tire maximum width position 1M. 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 at least from the tread portion 2 to the first bead portion 4A. In this embodiment, the carcass 6 extends from the tread portion 2 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] The tread portion 2 of this embodiment includes a cord reinforcing layer 10. The cord reinforcing layer 10 is disposed on the outer side of the carcass 6 in the tire radial direction.

[0021] Fig. 2 shows a development view conceptually illustrating the cord arrangement of the cord reinforcement layer 10. As shown in Fig. 2, the cord reinforcement layer 10 of this embodiment includes at least one belt ply 7A in which a plurality of steel cords 12 are covered with a topping rubber 13. The cord reinforcement layer 10 of this embodiment is configured to include a belt layer 7 including the belt ply 7A, and a band layer 8.

[0022] The belt layer 7 of this embodiment includes two belt plies 7A laminated in the tire radial direction. In each of these belt plies 7A, 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. As shown in FIG. 1, in the present invention, the average thickness T2 of one belt ply 7A is 0.66 to 0.98 mm.

[0023] 2, the band layer 8 is composed of, for example, one band ply 8A. The band ply 8A includes, for example, band cords 8c arranged at an angle θ2 of 5° or less with respect to the tire circumferential direction, and a topping rubber 8g covering the band cords. The band layer 8 of this embodiment is arranged so as to cover the entire belt layer 7.

[0024] As shown in Fig. 1, the tire 1 of the present invention includes an inner liner 20 disposed on the tire cavity side of the carcass 6. This inner liner 20 is disposed on the tire cavity side of the carcass 6 in at least the tread portion 2, the first sidewall portion 3A, and the second sidewall portion 3B. In this embodiment, the inner liner 20 is continuous with the clinch rubber 18 that forms the outer surfaces of the first bead portion 4A and the second bead portion 4B. Note that although the inner liner 20 is hatched with one type of pattern in Fig. 1, the inner liner 20 includes multiple rubber layers, as described below.

[0025] Fig. 3 shows an enlarged view of the periphery of the first end 2a of the tread portion 2, the first sidewall portion 3A, and the first bead portion 4A. As shown in Fig. 3, the inner liner 20 includes a butyl rubber layer 21 containing air-impermeable butyl rubber. The inner liner 20 of this embodiment has a tie gum layer 22, which has high adhesiveness, between the butyl rubber layer 21 and the carcass 6.

[0026] The butyl rubber layer 21 includes a first portion 26, a second portion 27, and a third portion 28. The first portion 26 extends from the tire equator C (shown in FIG. 1) toward the first end 2a to a first position 17 (shown by a two-dot chain line in FIG. 3), which is a position in the tire axial direction that is a distance L1 of 10 mm axially inward from the axially outer end 7a of the belt layer 7. The second portion 27 extends from the first portion 26 to the tire maximum width position 1M. The third portion 28 extends from the second portion 27 to the radially inner end of the butyl rubber layer 21.

[0027] In the present invention, the average thickness t2 of the second portion 27 of the butyl rubber layer 21 is 0.8 to 1.3 mm. The average thickness t1 of the first portion 26 and the average thickness t3 of the third portion 28 are each smaller than the thickness t2. This allows the tire 1 of the present invention to improve rolling resistance performance without impairing the durability of the tread portion 2. The reasons for this are as follows.

[0028] In the tire 1 of the present invention, the average thickness T2 (shown in FIG. 1) of the belt ply 7A is set to 0.66 to 0.98 mm, which is smaller than conventional thicknesses, and therefore the weight of the tread portion 2 can be reduced, and rolling resistance performance can be improved.

[0029] The inventors investigated the cause of belt ply separation that occurs when the belt ply thickness is reduced in line with the above improvements, and found that one of the major causes of the separation is the permeation of air and moisture from the tire cavity side around the ends of the belt layer.

[0030] Based on the above findings, in the present invention, the average thickness t2 of the second portion 27 of the butyl rubber layer 21 is set to a large value of 0.8 to 1.3 mm. This makes it possible to suppress the permeation of air and moisture and to suppress separation of the belt ply 7A. This improves the durability of the tread portion 2. Furthermore, in the present invention, the average thickness t1 of the first portion 26 of the butyl rubber layer 21 and the average thickness t3 of the third portion 28 are each smaller than the thickness t2 of the second portion 27 of the butyl rubber layer 21. This allows the thickness of the inner liner 20 to be reduced, thereby reducing the weight of the tire and further improving rolling resistance performance.

[0031] 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.

[0032] The thickness t1 of the first portion 26 is preferably 0.3 to 0.9 mm. The thickness t3 of the third portion 28 is preferably 0.3 to 1.0 mm. This makes it possible to suppress the permeation of air and moisture throughout the entire tire 1 while improving rolling resistance performance.

[0033] In this embodiment, of the two belt plies 7A included in the belt layer 7, the belt ply 7A located radially inner in the tire direction is in contact with the carcass 6 at least in an end region 24 located axially outer than the first position 17. In a preferred embodiment, the entire belt ply 7A is in contact with the carcass 6 (as shown in FIG. 1).

[0034] Fig. 4 is an enlarged cross-sectional view showing the belt ply 7A, carcass ply 6A, and inner liner 20 around the end of the belt layer 7 (shown in Fig. 1). To facilitate understanding of the invention, Fig. 4 shows the actual curvature of each rubber layer and ply removed. Also, in Fig. 4, two types of hatching are used to distinguish between the steel cords 12 and the topping rubber 13 included in the belt ply 7A. Meanwhile, the carcass ply 6A is uniformly hatched, omitting the distinction between the carcass cords and the topping rubber.

[0035] As shown in FIG. 4, the belt end inner region 30 from the plurality of steel cords 12 of the belt ply 7A in the end region 24 to the outer surface 27s of the second portion 27 on the carcass 6 side has an average thickness t4 (mm).

[0036] As a result of various studies, it was found that in order to reliably suppress damage caused by air and moisture penetration at the ends of the belt layer 7 while preventing an excessive increase in rubber volume around the ends, it is desirable to comprehensively define the thickness t2 (shown in FIG. 3) of the second portion 27 of the butyl rubber layer 21 and the thickness t4 of the belt end inner region 30. From this perspective, in this embodiment, the product t4·t2 of the thickness t4 (mm) and the thickness t2 (mm) is set to 1.3 to 2.1. This improves the durability and rolling resistance performance of the tread portion 2 in a well-balanced manner.

[0037] 3, a known rubber component is appropriately used for the butyl rubber layer 21. In a desirable embodiment, the butyl rubber content in the butyl rubber layer 21 is 80% to 100%. Such a butyl rubber layer 21 can reliably prevent the permeation of moisture and air.

[0038] The loss tangent tanδ of the butyl rubber layer 21 at 70°C is, for example, 0.15 to 0.25. This optimizes the energy loss in the inner liner 20, improving the rolling resistance performance and ride comfort in a well-balanced manner. The loss tangent tanδ is measured under the following conditions using a viscoelasticity spectrometer in accordance with JIS-K6394. Initial distortion: 10% Amplitude: ±2% Frequency: 10Hz Deformation mode: tension Measurement temperature: 70℃

[0039] The air permeability coefficient of the butyl rubber layer 21 is, for example, 18.00×10 -14 cm 3 cm / (cm 2 It is desirable that the air permeability coefficient is 0.05 s Pa or less. This makes it possible to reliably prevent air permeation. However, the present invention is not limited to this embodiment. The air permeability coefficient can be determined by a known measurement method.

[0040] 1, in this embodiment, the thickness T2 of each of the two belt plies 7A is set to the above range. The belt layer 7 configured with such belt plies 7A can achieve a lightweight structure while exhibiting a reinforcing effect for the tread portion 2, and reliably improves rolling resistance performance.

[0041] From the same viewpoint, the weight per unit area of ​​one belt ply 7A is 1350 to 1980 g / m 2 The weight of the topping rubber contained per unit area of ​​one belt ply 7A is preferably 600 to 1300 g / m 2 It is desirable that:

[0042] As shown in FIG. 2, one belt ply preferably includes 40 to 60 steel cords 12 per 5 cm width (the width in the direction perpendicular to the longitudinal direction of the steel cords 12).

[0043] The steel cord 12 may be made of, for example, a so-called ST material (super tensile material) that can be expected to have a tensile strength of 3600 MPa or more, a so-called UT material (ultra tensile material) that can be expected to have a tensile strength of 4000 MPa or more, or a so-called MT material (mega tensile material) that can be expected to have a tensile strength of 4500 MPa or more. Therefore, 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 this embodiment. The tensile strength may be measured by a known method.

[0044] The strength of each steel cord 12 is preferably 350 to 540 N. The outer diameter of the steel cord 12 is 0.22 to 0.55 mm, and more preferably 0.36 to 0.55 mm. This ensures the reinforcing effect of the belt layer 7 on the tread portion 2, while reducing the tire weight and improving rolling resistance. The strength is measured by a well-known method, but if necessary, a measurement method in accordance with JIS G3510 may be adopted.

[0045] The steel cord 12 of this embodiment has, for example, a 1x1 structure made of monofilaments (not shown). The outer diameter of the monofilaments is, for example, 0.30 to 0.50 mm. However, the present invention is not limited to this embodiment.

[0046] Fig. 5 shows a cross-sectional view of a steel cord 12 in another embodiment. As shown in Fig. 5, the steel cord 12 may have a 1 x n structure made up of a plurality (n) of filaments 15. Fig. 5 shows a steel cord 12 with a 1 x 4 structure. The outer diameter D1 of each of the plurality of filaments 15 is, for example, 0.15 to 0.30 mm. This improves ride comfort and rolling resistance in a well-balanced manner.

[0047] 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]

[0048] Pneumatic tires of size 205 / 55R16 having the basic structure shown in Figure 1 were prototyped based on the specifications in Table 1. Tires were prototyped as Comparative Examples 1 and 2, in which the thickness of the belt ply and the thickness of the butyl rubber layer were outside the ranges of the present invention. The tires of Comparative Examples 1 and 2 were substantially the same as the tires of the Examples, except for the above-mentioned points. The rolling resistance performance and tread durability of each test tire were tested. The common specifications and test methods for each test tire are as follows: Mounted rim: 16 x 6.5 Tire pressure: 250kPa

[0049] <Rolling resistance performance> The rolling resistance of each test tire was measured using a rolling resistance tester. The results were expressed as an index of the measured rolling resistance, with a smaller value indicating a smaller rolling resistance.

[0050] <Tread durability> Each test tire was run on a drum testing machine under certain conditions, and the running distance until damage to the tread occurred was measured. The results were expressed as an index of the running distance, with a larger value indicating better durability of the tread.

[0051] The test results are shown in Table 1.

[0052] [Table 1]

[0053] As shown in Table 1, comparing Comparative Example 1 and Comparative Example 2, Comparative Example 2 has improved rolling resistance performance due to a small belt ply thickness T2, but the durability of the tread portion is significantly impaired. In contrast, Examples 1 to 5 solve the above-mentioned problem by specifying the thickness t2 of the second portion of the butyl rubber layer to 0.8 to 1.3 mm and making the thickness t1 of the first portion and the thickness t3 of the third portion of the butyl rubber layer smaller than the thickness t2. In other words, it was confirmed that the tire of the present invention has improved rolling resistance performance without impairing the durability of the tread portion.

[0054] [Note] The present invention includes the following aspects.

[0055] [Invention 1] A pneumatic tire, A tread portion; a first sidewall portion that is continuous with a first end portion of the tread portion in the tire axial direction, extends radially inward of the tire, and includes a maximum tire width position; a first bead portion connected to the first sidewall portion on the inner side in the tire radial direction; a carcass extending from the tread portion to the first bead portion; an inner liner disposed on the tire cavity side of the carcass, The tread portion includes a belt layer including at least one belt ply in which a plurality of steel cords are covered with a topping rubber, The average thickness of the one belt ply is 0.66 to 0.98 mm, the inner liner includes a butyl rubber layer containing an air-impermeable butyl-based rubber; The butyl rubber layer has, in a tire meridian cross section including the tire rotation axis, a first portion extending from a position of the tire equator toward the first end portion to a first position in the tire axial direction that is a position axially inwardly of an outer end of the belt layer by a distance of 10 mm in the tire axial direction; a second portion extending from the first portion to the tire maximum width position; a third portion extending from the second portion to an inner end of the butyl rubber layer in the tire radial direction, The average thickness t2 of the second portion is 0.8 to 1.3 mm, The average thickness t1 of the first portion and the average thickness t3 of the third portion are each smaller than the thickness t2. Pneumatic tires. [Invention 2] The pneumatic tire according to invention 1, wherein the thickness t1 is 0.3 to 0.9 mm. [Invention 3] The pneumatic tire according to invention 1 or 2, wherein the thickness t3 is 0.3 to 1.0 mm. [Invention 4] The belt ply is in contact with the carcass at least in an end region that is axially outward of the first position, a belt end inner region from the plurality of steel cords of the belt ply in the end region to an outer surface of the second portion on the carcass side has an average thickness t4 (mm), 4. The pneumatic tire according to any one of claims 1 to 3, wherein the product t4·t2 of the thickness t4 (mm) and the thickness t2 (mm) is 1.3 to 2.1. [Invention 5] 5. The pneumatic tire according to any one of claims 1 to 4, wherein the steel cord has an outer diameter of 0.22 to 0.55 mm. [Invention 6] The steel cord has a 1x1 structure made of monofilaments, 6. The pneumatic tire according to any one of Inventions 1 to 5, wherein the monofilament has an outer diameter of 0.30 to 0.50 mm. [Invention 7] The steel cord has a 1×n structure consisting of a plurality (n) of filaments, 7. The pneumatic tire according to any one of Inventions 1 to 6, wherein the outer diameter of each of the plurality of filaments is 0.15 to 0.22 mm. [Invention 8] 8. The pneumatic tire according to any one of claims 1 to 7, wherein the strength of one steel cord is 350 to 540N. [Invention 9] 9. The pneumatic tire according to any one of Inventions 1 to 8, wherein the carbon content of the steel cord is 0.79% to 1.00%. [Invention 10] 10. The pneumatic tire according to any one of claims 1 to 9, wherein one belt ply contains 40 to 60 of the steel cords per 5 cm width. [Explanation of symbols]

[0056] 2 Tread section 3A First sidewall 4A First bead section 6. Carcass 7 Belt Layer 7A Belt Ply 12 Steel Cord 13 Topping Rubber 20 Inner liner 21 Butyl rubber layer 26 Part 1 27 Part 2 28 Part 3

Claims

1. A pneumatic tire, A tread portion; a first sidewall portion that is continuous with a first end portion of the tread portion in the tire axial direction, extends radially inward of the tire, and includes a maximum tire width position; a first bead portion connected to the first sidewall portion on an inner side in the tire radial direction; a carcass extending from the tread portion to the first bead portion; an inner liner disposed on the tire cavity side of the carcass, The tread portion includes a belt layer including at least one belt ply in which a plurality of steel cords are covered with a topping rubber, The average thickness of the one belt ply is 0.66 to 0.98 mm, the inner liner includes a butyl rubber layer containing an air-impermeable butyl-based rubber; The butyl rubber layer has, in a tire meridian cross section including the tire rotation axis, a first portion extending from a position of the tire equator toward the first end portion to a first position in the tire axial direction that is a position axially inwardly of an outer end of the belt layer by a distance of 10 mm in the tire axial direction; a second portion extending from the first portion to the tire maximum width position; a third portion extending from the second portion to an inner end of the butyl rubber layer in the tire radial direction, The average thickness t2 of the second portion is 0.8 to 1.3 mm, The average thickness t1 of the first portion and the average thickness t3 of the third portion are each smaller than the thickness t2. Pneumatic tires.

2. 2. The pneumatic tire according to claim 1, wherein the thickness t1 is 0.3 to 0.9 mm.

3. The pneumatic tire according to claim 2, wherein the thickness t3 is 0.3 to 1.0 mm.

4. the belt ply is in contact with the carcass at least in an end region that is axially outward of the first position, a belt end inner region from the plurality of steel cords of the belt ply in the end region to an outer surface of the second portion on the carcass side has an average thickness t4 (mm), The pneumatic tire according to claim 3, wherein the product t4·t2 of the thickness t4 (mm) and the thickness t2 (mm) is 1.3 to 2.

1.

5. 5. The pneumatic tire according to claim 1, wherein the steel cord has an outer diameter of 0.22 to 0.55 mm.

6. The steel cord has a 1x1 structure made of monofilaments, 5. The pneumatic tire according to claim 1, wherein the monofilament has an outer diameter of 0.30 to 0.50 mm.

7. The steel cord has a 1×n structure consisting of a plurality (n) of filaments, 5. The pneumatic tire according to claim 1, wherein the outer diameter of each of the plurality of filaments is 0.15 to 0.22 mm.

8. 5. The pneumatic tire according to claim 1, wherein a strength of one of the steel cords is 350 to 540 N.

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

10. 5. The pneumatic tire according to claim 1, wherein one belt ply includes 40 to 60 steel cords per 5 cm width.

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