JP3733055B2 - Pneumatic radial tire - Google Patents

Description

【００４８】
【発明の効果】
叙上の如く本発明は、タイヤ周方向に短繊維を配向させた短繊維補強ゴム層を、ビードエーペックスゴムの外側面に沿って配しているため、耐久性及び乗り心地性を悪化させることなく、操縦安定性を向上させることができる。
【図面の簡単な説明】
【図１】本発明の一実施例のタイヤの断面図である。
【図２】ビード部を短繊維補強ゴム層とともに拡大して示す断面図である。
【図３】短繊維の配合量に基づく、周方向及び半径方向の複素弾性率Ｅａ＊、Ｅｂ＊の変化の一例を示す線図である。
【図４】表１の比較例１を説明する線図である。
【符号の説明】
２ トレッド部
３ サイドウォール部
４ ビード部
５ ビードコア
６ カーカス
８ ビードエーペックスゴム
１０ 短繊維補強ゴム層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic radial tire in which steering stability is improved without deteriorating durability and riding comfort by providing a short fiber reinforced rubber layer adjacent to an outer surface of a bead apex rubber.
[0002]
[Background Art and Problems to be Solved by the Invention]
In recent years, with higher output and higher performance of automobiles, improvement of steering stability as well as high ride comfort is strongly desired for tires.
[0003]
On the other hand, in pneumatic radial tires, it is known that the steering stability performance can be improved by increasing the lateral stiffness of the tire. Therefore, conventionally, a cord reinforcement layer using a steel cord or an organic fiber cord is used as a bead portion. It is provided from the side wall to the side wall portion to increase the bending rigidity of the side wall.
[0004]
However, the use of such a cord reinforcing layer is accompanied by an increase in tire longitudinal rigidity, which leads to a deterioration in riding comfort. Also, the cord reinforcement layer tends to concentrate stress at its end, especially when it is used in high performance tires that reduce the tire flatness to 55% or less and increase the contact width and contact area. Since the flexible region is narrow and stress concentration becomes remarkable, the durability tends to be impaired.
[0005]
Therefore, the present inventor noticed that not only the lateral stiffness of the tire but also the torsional stiffness in the rotational direction, that is, the circumferential stiffness is greatly involved in the steering stability, and by orienting the short fibers in the tire circumferential direction, Proposed to arrange a short fiber reinforced rubber layer with a significantly increased circumferential elastic modulus while maintaining a low elastic modulus in the tire radial direction without protruding from the bead apex rubber and along its outer surface. did. As a result, it has been found that the torsional rigidity of the tire is effectively increased and the steering stability is improved, while the longitudinal rigidity of the tire can be kept low.
[0006]
That is, the present invention is based on the arrangement of the short fiber reinforced rubber layer in which the short fibers are oriented in the tire circumferential direction along the outer surface of the bead apex rubber, without deteriorating durability and riding comfort. The objective is to provide a pneumatic radial tire with improved handling stability.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 of the present application is characterized by a taper extending from the tread portion to the bead core of the bead portion through the sidewall portion and the radially outer surface of the bead core toward the outer side in the tire radial direction. A pneumatic radial tire having a bead apex rubber extending in a shape,
A short fiber reinforced rubber layer extending along the tire shaft outer surface of the bead apex rubber and extending radially from the bead core to an inner height position from the radially outer end of the bead apex rubber, and
The short fiber reinforced rubber layer is formed by blending 10 to 30 parts by weight of short fibers with respect to 100 parts by weight of rubber, and orienting the short fibers in the tire circumferential direction ,
Moreover, the short fiber reinforced rubber layer has a ratio TLi / TLo of 1.0 mm between the thickness TLi that is the shortest distance from the radially inner end to the tire inner surface and the thickness TLo that is the shortest distance to the tire outer surface. -7.0, and the ratio TUi / TUo between the thickness TUi from the radially outer end to the tire inner surface and the thickness TUo from the tire outer surface is 0.3 to 1.0 . .
[0008]
The invention of claim 2 is characterized in that the short fiber reinforced rubber layer has a thickness of 0.3 to 2.0 mm.
[0009]
In the invention of claim 3, the short fibers have an average fiber length L of 20 μm to 5000 μm, and an aspect ratio L / D between the average fiber length L and the fiber diameter D of 10 to 500. It is said.
[0010]
According to a fourth aspect of the present invention, the short fiber reinforced rubber layer bead has a complex elastic modulus Ea * in the tire circumferential direction larger than a complex elastic modulus E * of the bead apex rubber and a complex elastic modulus Eb * in the radial direction. The elastic modulus is smaller than the complex elastic modulus E * of the apex rubber, and the ratio Ea * / Eb * between the complex elastic modulus Ea * and Eb * is 10 to 30.
[0011]
In the invention of claim 5, the short fiber reinforced rubber layer is characterized in that the radial complex elastic modulus Eb * is 10 Mpa or less.
[0012]
In the invention of claim 6, the short fiber reinforced rubber layer has a radial distance between its radially outer end and the radially outer end of the bead apex rubber of 5 mm or more, and the short fiber reinforced rubber layer. The height Ha from the bead core at the outer end in the radial direction is 0.1 to 0.25 times the tire cross-section height HT.
[0013]
According to a seventh aspect of the present invention, the sidewall portion includes a reinforcing rib for preventing rim detachment on an outer surface thereof, and the reinforcing rib protrudes most outward in the axial direction of the tire and has a maximum thickness. 11M and a thickness that gradually decreases from the central portion inward and outward in the radial direction, and has a substantially trapezoidal shape including outer inclined portions 11U and 11L, and a thickness that is lowered from the maximum thickness point Q to the tire inner surface. With respect to the direction line J, the outer end e1 of the short fiber reinforced rubber layer is separated radially inward by a distance U of 3 mm or more , and the outer end of the bead apex rubber is more radial than the thickness direction line J. It is characterized by being outside .
[0014]
In the invention of claim 8, the short fiber reinforced rubber layer has the carcass folded portion disposed on the outer side in the tire axial direction, and the outer surface in the tire axial direction of the bead apex rubber is at least the short fiber. It is characterized in that it is linear in the range along which the reinforcing rubber layer extends, and the tire flatness is in the range of 30 to 55%.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a meridional sectional view illustrating a case where the pneumatic radial tire of the present invention is a high-performance passenger car tire having a tire flatness ratio of 55% or less. FIG. 2 is an enlarged cross-sectional view of the bead portion.
[0016]
As shown in FIG. 1, the pneumatic radial tire 1 includes a carcass 6 extending from the tread portion 2 through the sidewall portion 3 to the bead core 5 of the bead portion 4, inside the tread portion 2 and outside the carcass 6. The bead portion 4 is provided with a bead apex rubber 8 that rises outward in the tire radial direction from the radial outer surface of the bead core 5.
[0017]
The belt layer 7 is composed of two or more belt plies 7A and 7B in this example, in which high elasticity belt cords are arranged at an angle of, for example, 10 to 35 ° with respect to the tire circumferential direction. The belt plies 7A and 7B are stacked with different inclination directions so that the belt cords cross each other between the plies, thereby increasing the belt rigidity, and having a substantially full width of the tread portion 2 with a tagging effect. Strongly reinforced. As the belt cord, a steel cord or a high modulus organic fiber cord such as an aromatic polyamide fiber comparable to this is preferably used.
[0018]
Further, in this example, the case where the band layer 9 is disposed outside the belt layer 7 is illustrated for the purpose of increasing the restraining force on the belt layer 7 and improving the high speed durability performance. The band layer 9 has a band cord spirally wound at an angle of, for example, 5 ° or less with respect to the tire circumferential direction, and extends at least covering the outer end portion of the belt layer 7 in the tire axial direction.
[0019]
The carcass 6 is formed of one or more carcass plies 6A in this example in which carcass cords are arranged at an angle of 75 to 90 ° with respect to the tire circumferential direction. The carcass ply 6 </ b> A is integrally provided with folded portions 6 b that are folded back from the inside around the bead core 5 at both ends of the main body portion 6 a that extends between the bead cores 5 and 5. As the carcass cord, in addition to organic fiber cords such as nylon, rayon, polyester, and aromatic polyamide, steel cords can be used as appropriate, but organic fiber cords are preferable from the viewpoint of weight reduction.
[0020]
Next, the bead apex rubber 8 has a triangular cross section that extends between the main body portion 6a and the folded portion 6b of the carcass ply 6A and extends outward in the tire radial direction. In this example, in order to ensure the tire rigidity necessary as a high-performance tire, the height h1 of the radially outer end 8e from the bead base line BL is 0.25 to 0.5 times the tire cross-section height HT. The range is as follows. The bead apex rubber 8 is made of rubber having a complex elastic modulus E * of 35 to 60 Mpa and higher elasticity than the side wall rubber (usually having a complex elastic modulus of 2.5 to 6 Mpa).
[0021]
In the present embodiment, in such a tire 1, the short fiber reinforced rubber layer 10 is provided in the bead portion 4 in order to improve steering stability without deteriorating durability and riding comfort.
[0022]
As shown in FIG. 2, the short fiber reinforced rubber layer 10 is a thin rubber layer having a substantially constant rubber thickness t along the outer surface of the bead apex rubber 8 and the bead core. 5 extends in the radial direction from the outer end 8e of the bead apex rubber 8 to an inner height position.
[0023]
The short fiber reinforced rubber layer 10 is made of a short fiber blended rubber in which 10 to 30 parts by weight of short fibers are blended with 100 parts by weight of rubber, and the short fibers are oriented in the tire circumferential direction. Note that “orienting in the tire circumferential direction” means that 90% or more of the short fibers are oriented in an angular range of ± 20 degrees or less with the tire circumferential direction as the center.
[0024]
Due to the orientation of the short fibers, as shown in FIG. 3, the short fiber reinforced rubber layer 10 greatly increases the complex elastic modulus Ea * in the tire circumferential direction while suppressing the increase in the complex elastic modulus Eb * in the radial direction. The ratio Ea * / Eb * can be increased to 10 or more, for example. In addition, FIG. 3 shows an example of the change of the complex elastic modulus Ea * and Eb * of the circumferential direction and radial direction based on the compounding quantity of a short fiber.
[0025]
Thus, since the short fiber reinforced rubber layer 10 significantly increases the complex elastic modulus Ea * in the tire circumferential direction, it is possible to effectively increase the circumferential rigidity of the tire, that is, the torsional rigidity during tire rotation. It is possible to improve steering stability. On the other hand, as shown in FIG. 3, the longitudinal rigidity of the tire can be kept low, for example, almost no influence on the complex elastic modulus Eb * in the radial direction can be avoided, and a decrease in riding comfort can be suppressed. For this purpose, the complex elastic modulus Ea * in the tire circumferential direction is larger than the complex elastic modulus E * of the bead apex rubber (Ea *> E *), and the complex elastic modulus Eb * in the radial direction is a bead. It is necessary to be smaller (Eb * <E *) than the complex elastic modulus E * of the apex rubber.
[0026]
In order to exhibit the effects of improving the steering stability and suppressing the decrease in ride comfort more preferably, the ratio Ea * / Eb * is preferably set to 10 to 30, and the ratio Ea * / Eb * When the value is less than 10, the steering stability improvement effect becomes insufficient, and the steering response tends to decrease. Moreover, it is technically difficult for the ratio Ea * / Eb * to exceed 30, which causes a disadvantage in productivity and production cost, and tends to lower the rubber strength. Therefore, the ratio Ea * / Eb * is more preferably 15-25.
[0027]
At this time, the complex elastic modulus Eb * in the tire radial direction is preferably 10 MPa or less, and further preferably 5 MPa or less for ride comfort.
[0028]
The complex elastic modulus is a value measured by using a viscoelastic spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. at a temperature of 70 ° C., a frequency of 10 Hz, an initial strain of 10%, and a dynamic strain of ± 1%.
[0029]
Here, the short fibers tend to be oriented in the extrusion direction when the short fiber compounded rubber is extruded into a sheet shape by an extruder or a calender roll, and using this, the short fibers of the short fiber reinforced rubber layer 10 are converted into the above-described short fibers. It can be oriented in the circumferential direction. However, when the thickness t of the short fiber reinforced rubber layer 10 exceeds 2.0 mm, it becomes difficult to ensure the ratio Ea * / Eb * to 10 or more, for example, the orientation of the short fibers deteriorates. As a result, the effect of improving the steering stability is reduced, and the tire weight is also increased to increase the rolling resistance. On the other hand, if the thickness t is smaller than 0.3 mm, the material is too thin to exhibit the reinforcing effect, and it is difficult to handle and disadvantageous in productivity. Thus, the thickness t is preferably 0.3 to 2.0 mm, and more preferably 0.3 to 1.5 mm.
[0030]
Next, as the rubber base material of the short fiber compounded rubber, for example, a kind of diene rubber such as natural rubber (NR), styrene-butadiene rubber (SBR), butadiene rubber (BR), or isoprene rubber (IR), or What combined multiple types can use it conveniently.
[0031]
Examples of the short fibers include organic fibers such as nylon, polyester, aramid, rayon, vinylon, cotton, cellulose resin, crystalline polybutadiene, and inorganic fibers such as metal fibers, whiskers, boron, and glass fibers. These can be used alone or in combination of two or more. More preferably, the short fiber may be subjected to an appropriate surface treatment in order to improve the adhesion to the rubber substrate.
[0032]
The average fiber length L of the short fibers is preferably 20 μm or more, particularly preferably 50 to 5000 μm. The aspect ratio L / D between the average fiber length L and the fiber diameter D is preferably 10 or more, particularly preferably 20 to 500. When the average fiber length L is less than 20 μm and the aspect ratio L / D is less than 10, a sufficient difference can be secured between the complex elastic modulus Ea * and Eb * even when the short fibers are oriented with high accuracy. It becomes difficult to achieve both improvement in handling stability and suppression of reduction in ride comfort, such as disappearance. On the other hand, when the average fiber length L is greater than 5000 μm and the aspect ratio L / D is greater than 500, the orientation of the short fibers itself is lowered, and the above-mentioned compatibility is similarly difficult.
[0033]
Further, the blending amount of the short fiber needs to be 10 to 30 parts by weight, and if it is less than 10 parts by weight, the reinforcing effect is inferior, and the necessary complex elastic modulus Ea * in the tire circumferential direction cannot be secured. The effect of improving sex is not demonstrated. On the other hand, if the amount exceeds 30 parts by weight, the complex elastic modulus Ea * in the tire radial direction tends to increase even when the short fibers are oriented with high precision, and the riding comfort is reduced. In addition, the viscosity of the unvulcanized rubber increases and the processability also decreases.
[0034]
In the short fiber blended rubber, carbon black can be further blended with the rubber base material, and the carbon black having an iodine adsorption of 30 to 90 mg / g can be suitably used. Carbon black having an iodine adsorption of less than 30 mg / g has low rubber reinforcing properties and is inferior in both strength and cut resistance. On the other hand, if it exceeds 90 mg / g, exothermicity increases and rolling resistance is deteriorated.
[0035]
The compounding amount of the carbon black is 40 parts by weight or less, preferably 20 to 30 parts by weight with respect to 100 parts by weight of the rubber base material. When the amount exceeds 40 parts by weight, the heat generation property of the rubber increases and the rolling resistance also increases. Getting worse. In addition to the above short fibers and carbon black, conventional additives for tire rubber such as oil, anti-aging agent, wax, vulcanization accelerator and the like can be appropriately blended with the short fiber blended rubber.
[0036]
In addition, the short fiber reinforced rubber layer 10 of the present embodiment has a radially outer end e1 which is held radially inward from the outer end 8e of the bead apex rubber 8, so that stress concentration is reduced. Deterioration of durability can be prevented. In particular, the radial distance L between the outer end e1 and the outer end 8e is preferably 5 mm or more from the viewpoint of durability.
[0037]
The height Ha of the outer end e1 from the bead core 5, that is, the radial width of the short fiber reinforced rubber layer 10, is preferably 0.1 to 0.25 times the tire cross-section height HT. If it is less than 1 time, the effect of improving the steering stability is not sufficiently exhibited. Conversely, if it exceeds 0.25 times, there is a disadvantage that the riding comfort is deteriorated.
[0038]
Further, since the short fiber reinforced rubber layer 10 is disposed between the bead apex rubber 8 and the folded portion 6b of the carcass 6, the rubber thickness t is reduced such that the rubber flow during vulcanization molding is suppressed. Uniformity can be secured. That is, when it is provided in another part, the rubber thickness t is partially changed, and there is no inconvenience such as damage due to weakness of strength, and durability can be maintained.
[0039]
The short fiber reinforced rubber layer 10 preferably extends substantially linearly from the inner end e2 to the outer end e1 as in this example, whereby the torsional rigidity can be increased more effectively. The “substantially linear” means that the diameter of a three-point arc passing through the inner end e2, the outer end e1, and the middle point of the short fiber reinforced rubber layer 10 is 100 mm or more.
[0040]
The short fiber reinforced rubber layer 10 has a ratio TLi / TLo between the thickness TLi, which is the shortest distance from the inner end e2 to the tire inner surface, and the thickness TLo, which is the shortest distance to the tire outer surface, of 1.0 to 1.0. 7.0, and the ratio TUi / TUo between the thickness TUi from the outer end e1 to the tire inner surface and the thickness TUo from the tire outer surface is preferably 0.3 to 1.0. This is because when the ratio TLi / TLo is set to 1.0 or more, the inner end e2 is arranged outside the tire from the thickness center line, that is, in the compression region when the tire is deformed, and the ratio TUi / TUo is set to 1.0 or less. This is because the outer end e1 is arranged on the tire inner side from the thickness center line, that is, in the compression region when the tire is deformed. As described above, the inner end e2 and the outer end e1 are arranged in the compression region when the tire is deformed, respectively, and compression / tensile stress is not applied alternately, which is preferable for durability.
[0041]
In this example, in order to prevent rim detachment during run-flat travel, the case where a reinforcing rib 11 for preventing rim detachment is provided on the outer surface of the sidewall portion 3 is illustrated. As shown in FIG. 2, the reinforcing rib 11 has a central portion 11M that protrudes most outward in the tire axial direction and has the maximum thickness, and an inner and outer portion that gradually decreases in thickness radially inward and outward from the central portion. The inclined portions 11U and 11L are substantially trapezoidal and are formed at positions radially outward from the flange separation point P0 that is separated from the rim flange.
[0042]
In such a tire provided with the reinforcing ribs 11, the bending deformation stress is likely to be concentrated on the inner side in the radial direction from the maximum thickness point Q of the central portion 11M, which is likely to cause a failure. Therefore, from the viewpoint of durability, the outer end e1 of the short fiber reinforced rubber layer 10 is radially inward with respect to the thickness direction line J extending from the maximum thickness point Q to the tire inner surface. It is preferable to separate in the direction. Similarly, from the viewpoint of durability, the outer end 8e of the bead apex rubber 8 is positioned radially outward from the thickness direction line J and further radially outward from the central portion 11M as in this example. Is preferred.
[0043]
In addition, although the said effect by the said short fiber reinforced rubber layer 10 can function effectively by a high performance tire with a tire flatness ratio of 30 to 55% as in this example, the present invention is limited to the illustrated embodiment. Without modification, the present invention can be carried out with various modifications.
[0044]
【Example】
A tire having a tire size of 215 / 45ZR17 and having the structure shown in FIG. 1 was prototyped based on the specifications shown in Table 1, and the handling stability and riding comfort of each sample tire were tested. In Comparative Example 1, as schematically shown in FIG. 4, a cord reinforcing layer of a steel cord is provided so as to protrude from the outer end of the bead apex rubber.
The test method is as follows.
[0045]
(1) Steering stability;
-Tires are mounted on all wheels of a passenger vehicle (domestic FR passenger car, displacement of 2500 cc) under conditions of rim (17 x 7 JJ) and internal pressure (200 kPa), and run at high speed on a dry asphalt road surface at a speed of 120 km / H. In addition, the straight running stability and the lane change stability are indicated by an index with a conventional example of 100 by sensory evaluation of the driver. A larger index is better.
・ Using the same test vehicle, run at a speed of 80 km / H on a wet asphalt road. The driving stability performance including the straight running stability and the lane change stability at that time is 100 as the conventional example based on the driver's sensory evaluation. The index is displayed. A larger index is better.
[0046]
(2) Ride comfort;
-The ride comfort when driving on the asphalt road surface (good road) using the test vehicle is displayed as an index with a conventional example of 100 by sensory evaluation of the driver. A larger index is better.
-The ride comfort when driving on the Belgian road surface (bad road) using the test vehicle is displayed as an index with the conventional example being 100 based on the sensory evaluation of the driver. A larger index is better.
[0047]
[Table 1]

[0048]
【The invention's effect】
As described above, according to the present invention, the short fiber reinforced rubber layer in which short fibers are oriented in the tire circumferential direction is disposed along the outer surface of the bead apex rubber, so that durability and ride comfort are deteriorated. In addition, the steering stability can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a tire according to an embodiment of the present invention.
FIG. 2 is an enlarged cross-sectional view of a bead portion together with a short fiber reinforced rubber layer.
FIG. 3 is a diagram showing an example of changes in complex elastic moduli Ea * and Eb * in the circumferential direction and radial direction based on the blending amount of short fibers.
4 is a diagram for explaining Comparative Example 1 in Table 1. FIG.
[Explanation of symbols]
2 Tread part 3 Side wall part 4 Bead part 5 Bead core 6 Carcass 8 Bead apex rubber 10 Short fiber reinforced rubber layer

Claims (8)

A pneumatic radial tire comprising a carcass extending from a tread portion through a sidewall portion to a bead core of a bead portion, and a bead apex rubber extending in a tapered shape from a radially outer surface of the bead core toward a radially outer side of the tire. And
A short fiber reinforced rubber layer extending along the tire shaft outer surface of the bead apex rubber and extending radially from the bead core to an inner height position from the radially outer end of the bead apex rubber, and
The short fiber reinforced rubber layer is formed by blending 10 to 30 parts by weight of short fibers with respect to 100 parts by weight of rubber, and orienting the short fibers in the tire circumferential direction .
Moreover, the short fiber reinforced rubber layer has a ratio TLi / TLo of 1.0 mm between the thickness TLi that is the shortest distance from the radially inner end to the tire inner surface and the thickness TLo that is the shortest distance to the tire outer surface. -7.0, and the ratio TUi / TUo between the thickness TUi from the radially outer end to the tire inner surface and the thickness TUo from the tire outer surface is 0.3 to 1.0. Radial tire.   The pneumatic radial tire according to claim 1, wherein the short fiber reinforced rubber layer has a thickness of 0.3 to 2.0 mm.   3. The short fiber has an average fiber length L of 20 μm to 5000 μm, and an aspect ratio L / D between the average fiber length L and the fiber diameter D of 10 to 500. 4. Pneumatic radial tires.   The short fiber reinforced rubber layer has a complex elastic modulus Ea * in the tire circumferential direction that is greater than a complex elastic modulus E * of the bead apex rubber, and a complex elastic modulus Eb * in the radial direction of the complex elastic modulus E * of the bead apex rubber. The pneumatic radial tire according to any one of claims 1 to 3, wherein the pneumatic radial tire is smaller and has a ratio Ea * / Eb * between the complex elastic modulus Ea * and Eb * of 10 to 30. The pneumatic radial tire according to claim 4, wherein the short fiber reinforced rubber layer has a complex elastic modulus Eb * in the radial direction of 10 Mpa or less.   The short fiber reinforced rubber layer has a radial distance between its radially outer end and the radially outer end of the bead apex rubber of 5 mm or more, and the bead core at the radially outer end of the short fiber reinforced rubber layer. The pneumatic radial tire according to any one of claims 1 to 5, wherein a height Ha from the tire is 0.1 to 0.25 times a tire cross-sectional height HT. The sidewall portion includes a reinforcing rib for preventing rim detachment on the outer surface, and the reinforcing rib protrudes most outward in the tire axial direction and has a maximum thickness, and a radius from the central portion. The thickness gradually decreases inward and outward in the direction, and has a substantially trapezoidal shape composed of outer inclined portions 11U and 11L. The thickness direction line J extends from the maximum thickness point Q to the tire inner surface, and the short direction The outer end e1 of the fiber-reinforced rubber layer is spaced radially inward by a distance U of 3 mm or more , and the outer end of the bead apex rubber is radially outward from the thickness direction line J. The pneumatic radial tire according to any one of claims 1 to 6.   The short fiber reinforced rubber layer has the carcass folded portion disposed on the outer side in the tire axial direction, and the outer side surface in the tire axial direction of the bead apex rubber is at least within a range along the short fiber reinforced rubber layer. The pneumatic radial tire according to any one of claims 1 to 7, characterized in that the tire flatness is in the range of 30 to 55%.

Images