JPH10297215A - Pneumatic radial tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remarkably improve the F/S resistance without lowering the riding comfortableness performance, by mounting the extremely low heating rubber layers having specific tan δof the rubber obtained under a specific measurement condition, on the both edges of a central area in the tread rubber, and mounting at least one code reinforcement layer within a specific range of the sectional height. SOLUTION: The extremely low heating rubber layers 7 are buried in the tread rubber 3t on the outer peripheral areas of the cap layers 6c at least on the both edges of a central area of a tread part 3. The rubber of this layer should be the extremely low loss rubber having tan δ within a range of 0.02-0.11 measured under a measurement conditions of 25 deg.C ambient temperature, 1% dynamic distortion, and 52 Hz of vibration frequency. Further at least one code reinforcement layer 8 of which the outermost side edge in a radius direction is located within a range of 0.5-0.6 times of the sectional height SH, is mounted on an area between a bead part 1 and a side wall part 2. Whereby the F/S resistance (flat spot), the operation stability and the riding comfortableness can be simultaneously improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic radial tire, and more particularly to a radial tire mainly mounted on a passenger car traveling on a pavement road surface. The present invention relates to a pneumatic radial tire that can advantageously prevent a flat spot from occurring on the ground.

[0002]

2. Description of the Related Art A flat spot (hereinafter abbreviated as F / S) phenomenon, which tends to occur in a bias ply tire using an organic fiber code such as a nylon cord, hardly occurs in a radial tire. , F / S was not taken up as much of a problem.

[0003] However, under the current situation in which so-called high performance radial tires tend to be widely used as tires for passenger cars, the F / S resistance is becoming a problem that cannot be ignored for the following reasons. The first point is the belt structure, that is, high performance radial tires need to be highly flattened, especially high-speed durability and high-speed steering stability, as compared with general-purpose radial tires, so that the belt is a normal type. In addition to the cord cross layer, an organic fiber code, for example, a nylon cord or a vinylon cord is arranged on the outer periphery of the cross layer in a direction substantially along the circumference of the tread surface of the tread (hereinafter referred to as a circumferential direction). This is because the structure has a structure in which a reinforcing layer called a cap layer is arranged.

[0004] The second reason is that a tire running at a high speed on a highway or the like cannot prevent a tread portion from having a considerably high temperature mainly in a radial tire having a cap layer. (Nylon cord or vinylon cord) is much more deformed by heat than steel cord, etc., and if this high temperature tire is left for a long time under a corresponding load load, the tire temperature will drop, especially This is because the action force of the large creep deformation of the directionally arranged organic fiber cord acts greatly, and residual deformation occurs in the tread portion in the tire contact area.

[0005] However, although this residual deformation is a reversible deformation, it does not immediately return to its original shape even when it starts running again. Since the temperature of the tire needs to be increased, a considerable running time is required.

Until the restoration of the original shape, the fluctuation input from the deformed tread portion is transmitted as vibration to the vehicle via the tire when the tire rolls, and the so-called F / S phenomenon occurs even in a radial tire. This is no exception. This F /
The S phenomenon causes the vehicle to vibrate in accordance with the degree of the residual deformation. Even if the vibration is not as large as that of the bias tire, it naturally causes the deterioration of the ride comfort due to the vibration. Stability is also significantly impaired.

[0007]

Accordingly, in order to keep the temperature of the tread portion as low as possible during high-speed running and to lower the temperature of the cap layer, the tread rubber has a two-layer structure and low-loss rubber is applied to the base rubber. It is possible to reduce the F / S degree by lowering the temperature, but it is possible to reduce the F / S degree. However, the reduction in the loss of the base rubber required to realize the desired F / S resistance is accompanied by a remarkably low rigidity of the rubber. However, with this, the steering stability is greatly reduced, and cannot be used as a high-performance radial tire. Even a general-purpose radial tire cannot achieve the required steering stability.

As another means for improving the F / S resistance, it is effective to increase the longitudinal spring constant of the tire and reduce the amount of deformation under load, but on the other hand, a longitudinal spring that sufficiently improves the F / S resistance. Tires having a constant are not practical because the riding comfort is significantly impaired.

Accordingly, the inventions described in claims 1 to 5 of the present invention ensure excellent handling stability of the conventional tire, and at the same time, maintain the ride comfort at least at the same level as the conventional tire without deteriorating the riding comfort, and provide an F / F / An object of the present invention is to provide a pneumatic radial tire with significantly improved S-performance.

[0010]

In order to achieve the above object, the present invention according to claim 1 of the present invention comprises a pair of bead portions, a pair of sidewall portions, and a tread portion. A carcass which is a rubber coating of at least one ply of radially arranged cords for reinforcing between the bead cores embedded in the carcass, and a belt for reinforcing the tread portion at the outer periphery of the carcass; In a pneumatic radial tire having a folded portion to be rolled up and having two layers of cord cross layers and a cap layer of one or more circumferentially arranged organic fiber codes covering the outer periphery thereof, an ambient temperature of 25% was obtained.
C., a dynamic strain of 1%, and an extremely low heat generation rubber layer having a tan .delta. Of 0.02 to 0.11 obtained under the measurement conditions of an excitation frequency of 52 Hz is embedded in the tread rubber to form the cap layer. At least one cord reinforcing layer having a tire radially outermost end within a range of 0.5 to 0.6 times the tire cross-section height and arranged at least in the outer peripheral regions on both sides of the tread central region. In a region extending from the to the sidewall portion.

Here, the tire section height is defined as JATMA.
According to the definition described in the general information section of YEAR BOOK (1997 version), the difference between the outer diameter of the tire (the outer diameter of the tire mounted on the applicable rim, the specified air pressure and the unloaded state) and the rim diameter is 1 / 2, and the outermost end position of the cord reinforcing layer in the tire radial direction also follows this definition, and details will be described later.

[0012] Further, the circumferentially arranged organic fiber
The term “do” includes a cord arrangement in which one or a plurality of cords are spirally wound in the width direction of the tread surface in addition to the cord arrangement parallel to the circumferential line of the tread portion tread surface (parallel to the tire equatorial plane). Also, the cap layer covers the entire width of the maximum width code layer of the code crossing layer, and it is preferable that the cap layer has at least one layer having a width larger than the maximum width code layer width. This includes the case where two relatively narrow layers (also referred to as layers) covering both side edges of the cross layer are distributed on both sides of the belt. In addition, the tread portion center region referred to here refers to a region defined in claim 2 below.

In carrying out the invention described in claim 1, there is an appropriate application area of the extremely low heat generation rubber layer in accordance with the above-mentioned object, and accordingly, as in the invention described in claim 2, The distance of the extremely low heat generation rubber layer from the equatorial plane to the inner edge is 0.1 mm of the maximum width of the belt cord layer.
It is suitable to be less than twice. Therefore, the above-described tread central region refers to a region where 0.2 times the maximum width of the belt cord layer is distributed to both sides of the tire equatorial plane. Of course, the above 0.2 times or less includes zero, and then the extremely low heat generation rubber layer is continuous over the entire width in the width direction.

Further, regarding the outer edge position of the appropriate application area of the extremely low heat generation rubber layer, the distance from the tire equatorial plane to the outer edge of the low heat generation rubber layer is determined as in the invention described in claim 3. Is the maximum width of the cord crossing layer of the belt.
It is effective to be within the range of 5-0.55 times. Further, there is a thickness range that is practically appropriate. Therefore, as in the invention described in claim 4, the thickness of the extremely low heat generation rubber is 1.
Suitably within the range of 5 to 3 mm.

[0015] Further, in order to keep the tire rigidity in the extremely low heat generation rubber layer within an appropriate range, the innermost end of the cord reinforcing layer in the tire radial direction is located near the bead core, and It is advantageous to arrange the cord reinforcement layer along the turn of the ply. As described above, a pneumatic radial tire for a passenger car, particularly a high-performance tire having an aspect ratio of 60 or less, exhibits excellent effects.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 and 2
FIG. 2 is a right half cross-sectional view schematically illustrating a main part of a pneumatic radial tire (hereinafter simply referred to as a tire). In FIGS. 1 and 2, reference numeral E denotes a tire equatorial plane, and a pair of beads 1 (only one side is shown), a pair of sidewalls 2 (only one side is shown), and a tread portion 3 are provided with respective parts 1 to 3. The bead cores 4 embedded in the part 1 are reinforced by a carcass 5 which becomes a rubber coating of a radial arrangement cord of one ply or more (one ply in the illustrated example) between the bead cores 4. Have. The radial arrangement code of the carcass 5 is an organic fiber code, for example, a polyester code.

The belt 6 serves to reinforce the tread portion 3 at the outer periphery of the carcass 5, and the belt 6 has two cord crossing layers 6-6 where cords intersect each other across the tire equatorial plane E.
1, 6-2, and one or more wide layers (one layer in the illustrated example) covering the outer periphery of the cord crossing layer. In the illustrated example of the code cross layer, the code layer 6-1 near the carcass 5 has a width Bw wider than the outer code layer 6-2, and the cap layer 6c has a width wider than the width Bw. A spiral wound layer of cord, for example, nylon cord or vinylon cord. Steel cords are suitable for the cords of the cross cord layers 6-1 and 6-2.

It is assumed that an extremely low heat generation rubber layer 7 is buried in the tread rubber 3t at least in the outer peripheral area of the cap layer 6c on both sides of the central area of the tread portion 3. The rubber of the rubber layer having an extremely low heat generation has a tan δ of 0. 0 measured under the conditions of an ambient temperature of 25 ° C, a dynamic strain of 1% and an excitation frequency of 52 Hz.
It is necessary that the rubber has an extremely low loss in the range of 02 to 0.11.

Referring to FIG. 1 and FIG.
Is the central area of 0.2 times the maximum width Bw of the belt 6.
The width a of 2 × Bw is defined to indicate both side regions sandwiching the tire equatorial plane E (total width region of 0.4 × Bw = 2a),
The distance a corresponding to the width 0.2 × Bw from the distance b from the tire equatorial plane E to the outer edge of the extremely low heat generation rubber layer 7 is defined as the distance a to the outer peripheral area of the cap layer 6 c on both sides of the central area of the tread portion 3. Is the area (ba) from which the extremely low heat generation rubber layer 7 is disposed at least in this area (ba). It is assumed that the distance a is equal to or less than 0.2 × Bw and includes zero.

T accompanying the arrangement of the extremely low heat generation rubber layer 7 described above.
FIG. 3 is a diagram showing the relationship between an δ and the degree of F / S. As is clear from FIG. 3, if tan δ exceeds 0.1 (correctly 0.11) and exceeds this, the degree of F / S increases and then increases sharply, so that the tan δ of the extremely low heat generation rubber layer 7 increases. The value must be less than or equal to 0.11. Considering practicalities such as durability and steering stability, ta
The lower limit of nδ needs to be 0.02.

Further, the tire section height SH is set to 0.5 to 0.5.
Tire radial direction within the range of 6 times (hereinafter referred to as radial direction)
One or more cord reinforcing layers 8 having the outermost end
To the side wall portion. FIG. 1 shows an example in which one cord reinforcing layer 8 is arranged, and FIG. 2 shows an example in which two cord reinforcing layers 8 are arranged. Reference numeral 9 denotes a bead filler rubber or a stiffener rubber.

Here, the tire section height SH is defined as JATM
As specified by A, the tire is mounted on an applicable rim (not shown), and a specified air pressure (air pressure corresponding to the maximum load capacity of the tire) is applied (load). In FIGS. 1 and 2, the rim diameter position is shown as a rim diameter line RL. Therefore, the height Hmax of the outermost end in the radial direction of the cord reinforcing layer 8 measured from the rim diameter line RL is Hmax = (0.5 to 0.6) ×
SH must be set. It is desirable that the height h of the innermost end in the radial direction be a position near the bead core 4.

The single cord reinforcing layer 8 shown in FIG. 1 is disposed along the tire outer surface of the folded portion 5u of the carcass 5,
The two-layer cord reinforcing layer 8 shown in FIG. 2 is an example in which the folded portion 5u of the carcass 5 is interposed therebetween. As another modified example,
Although not shown, the two-layer cord reinforcing layer 8 is
u along the inner and outer surfaces of the tire,
One or two layers of the cord reinforcing layer 8 can be arranged along the tire inner surface of the folded portion 5u.

The cord of the cord reinforcing layer 8 is made of organic fiber
For example, polyester cords and Kevlar cords are suitable, and the average inclination angle of these cords with respect to the circumferential line in the bead portion 1 is preferably in the range of 45 to 60 °.

The effect of the extremely low heat generation rubber layer 7 on the organic fiber code used for the cap layer 6c, particularly on the nylon cord, is described below. By arranging the heating rubber layer 7, the temperature of the rubber closest to the outer periphery of the belt 6 of the tire 6 running at a high speed is significantly lower than that of the conventional tire,
In particular, a temperature drop near the end of the belt 6, which tends to become high in temperature, is brought about. Due to this temperature drop, the amount of residual deformation (creep strain) due to shrinkage of the organic fiber cords which are arranged in the circumferential direction on the ground contact surface of the tread portion 3 for a long time under load is significantly reduced.

FIG. 4 is a diagram showing the relationship between the temperature (° C.) of the nylon cord and the creep strain. As is clear from this, the creep strain of the nylon cord increases as the temperature increases. FIG. 5 shows the temperature (° C.) and the F of the nylon cord.
The relationship with the degree of / S is shown as a diagram, and the degree of F / S increases as the temperature of the nylon cord increases, as in FIG. Therefore, lowering the temperature by disposing the extremely low heat generation rubber layer 7 exhibits the effect of simultaneously reducing both the creep strain and the F / S degree. The temperature of the end of the belt 6 when the tire for a passenger car runs on a highway is about 60 ° C. when the outside air temperature is 25 ° C.

However, the extremely low heat generation rubber layer 7 is inevitably disadvantageous in terms of low rigidity. As a result, the rigidity of the entire tread portion 3 is reduced, so that the cornering force characteristics, especially the cornering power characteristics, are reduced, and the steering is performed. The disadvantage that the stability is deteriorated is compensated for by arranging one or more cord reinforcing layers 8 in the region between the bead portion 1 and the height Hmax to appropriately improve the rigidity of the entire tire. In addition, it is possible to secure the steering stability equal to or higher than that of the conventional tire and to maintain the riding comfort equal to or higher than that of the conventional tire. FIG. 6 shows the relationship between the steering stability and the riding comfort using the height Hmax of the cord reinforcing layer 8 as a parameter.

From FIG. 6, it can be seen that the higher the value of the height Hmax of the cord reinforcing layer 8 is, the higher the steering stability is, but the lower the value of the height Hmax is, while the lower the value of the height Hmax is. It has been found that the ride comfort is improved, but the steering stability is reduced, and as a result, it has been confirmed that the preferred balance between the two performances is that the height Hmax is in the range of 0.5 SH to 0.6 SH.

The reason why the cord reinforcing layer 8 is applied instead of the rubber reinforcing layer is that the relationship between the F / S degree and the steering stability is shown in FIG. ), The F / S degree of the cord reinforcing layer 8 is lower than that of the rubber reinforcing layer at the same high lateral rigidity (good steering stability). is there.

What has been described above is, at least, that the outer peripheral regions on both sides of the belt 6 at which the temperature is most likely to be the highest become tan.
By sufficiently covering the extremely low heat generation rubber layer 7 with δ of 0.02 to 0.11, the F / S resistance is greatly improved, and the rigidity of the tread portion 3 is reduced by disposing the extremely low heat generation rubber layer 7. The outermost end height Hmax in the radial direction is 0.5 to 0.5 mm of the tire section height SH.
By compensating by the arrangement of one or more cord reinforcing layers 8 within the range of 6 times, the rigidity of the entire tire is appropriately improved, and excellent steering stability and riding comfort equal to or higher than conventional tires are secured. This means that F / S resistance, steering stability, and riding comfort are simultaneously realized.

FIG. 8 shows an experimental result of the distance b from the tire equatorial plane E to the outer edge of the extremely low heat generation rubber layer 7, and FIG.
1, the maximum width Bw of 6-2 (in the illustrated example, the code layer 6-
2 times the distance b as an index value with 100 as the width of 1), 2 ×
4 is a graph in which the vertical axis indicates the F / S degree when the index of b is changed. As can be seen, the distance b is in the range of 0.5 to 0.55 times the maximum width Bw with respect to the F / S degree. Preferably within. If it exceeds 0.55 times, a problem such as a thick gauge of the buttress portion occurs, which is not desirable.

Also, there is an appropriate range for the thickness of the extremely low heat generation rubber layer 7, and in this case also, the experimental results in which the thickness of the rubber layer 7 is set every 0.5 mm are shown in FIG. As shown in FIG. 9, the thickness of the rubber layer 7 is 1.5 to 3.
It is suitable to be within the range of 0 mm. 1.5mm thickness
If it is less than 3.0 mm or more than 3.0 mm, the F / S degree increases and the F / S resistance decreases, which is not suitable.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radial ply tire for a passenger car having a size of 235 / 60ZR16, and a first embodiment according to FIG.
In the configuration in which the distance a is set to 18% of the maximum width Bw of the cord crossing layer of the belt 6, the cap layer 6c covers only the both sides of the cord crossing layers 6-1 and 6-2 of the belt 6 with two layers. Other than that, according to FIG. 2, the distance a is set to 18% of the maximum width Bw of the cord crossing layer of the belt 6, and in the third embodiment, the extremely low heat generation rubber layer 7 is a continuous layer extending between both end edges (distance a is smaller). 2) except that the cap layer 6c has two layers, and the two cord reinforcing layers 8 are laminated and arranged along the tire inner surface of the folded portion 5u of the carcass 5, respectively. Have.

The carcass 5 of each of Examples 1 to 3 is a rubber coating of a one-ply radially-arranged polyester cord, and has a folded portion 5u around which the bead core 4 is wound. Example 1
3, the cord crossing layers 6-1 and 6-2 of the belt 6
Becomes the rubber coating layer of the steel cord, and the cap layer 6c
Becomes a rubber coating layer of a nylon cord, and the cord reinforcing layer 8 becomes a rubber coating layer of a Kevlar cord having a number of hits of 41.3 per 5 cm. The average inclination angle of the reinforcing layer 8 with respect to the circumferential line in the bead portion 1 of the cord is about 60 °.

In common with Examples 1 to 3, the tan δ is 0.09, the distance b is 55% of the maximum width Bw of the cord crossing layer, and the thickness is 2.5 mm for the extremely low heat generation rubber layer 7. And Further, the maximum height Hmax of the cord reinforcing layer 8 from the rim diameter line RL is 70 mm, which corresponds to 53% of the tire section height SH.

In contrast to the above Examples 1 to 3, the conventional tire according to Example 3 is provided except that the extremely low heat generation rubber layer and the cord reinforcing layer are not provided. Comparative tires according to Example 3 were prepared, and comparative evaluation tests described below were performed on the tires of Examples 1 to 3 and the comparative tire using the conventional tire as a control tire.

(1) F / S characteristics: Each test tire was assembled on a standard rim 7JJ-16 among applicable rims, and the internal pressure was 2.2 kg.
Filled with f / cm ² , pressed against the drum under a load of 600 kg, allowed to run at a surface speed of the drum of 150 km / h for 24 minutes, and immediately attached to the uniformity tester after the end of the run, under the condition of a load of 600 kg. The first RFV (radial force variation) was measured, immediately after the RFV measurement was completed, removed from the uniformity tester, pressed on a flat plate under a load of 600 kg for 1 hour, and then immediately mounted again on the uniformity tester. The second RFV was measured under load. A value obtained by subtracting the first RFV value from the second RFV value was defined as an F / S amount (degree), and expressed as an index with the F / S amount of the conventional example being 100. The smaller the value, the better.

(2) Steering stability and riding comfort; mounted on an actual vehicle with the above rim and internal pressure, traveled on a test course by a skilled driver, and evaluated based on control tires based on feeling. ○ Conventional example
Mark (excellent), and based on this mark,
⁺ Mark is better, ○ ^- mark is a little negative if anything is excellent, △, △ ⁺ mark is not so much as slightly inferior but practical problems, was × mark lacks in practicality . Table 1 shows the test results of the above performances (1) and (2).

[0039]

[Table 1]

As is clear from Table 1, the F / S amount (degree) and the riding comfort are improved in the comparative example as compared with the conventional example, but the steering stability is remarkably reduced. On the other hand, in Examples 1 to 3, the F / S amount is greatly reduced as compared with the conventional example and the F / S resistance is sufficient, which means that the steering stability and the riding comfort are low. It can be seen that this is supported by an excellent level almost equivalent to that of the conventional example. It should be noted that the fact that all the examples are further improved in the F / S amount compared with the comparative example means that the longitudinal spring constant of each example is further improved as compared with the comparative example due to the effect of the cord reinforcing layer 8. In this regard, the effect of cooperation between the extremely low heat generation rubber layer 7 and the cord reinforcing layer 8 is also exhibited.

[0041]

According to the first to fifth aspects of the present invention, the degree of F / S generation is maintained while maintaining both superior handling stability and ride comfort, which are almost the same as those of conventional tires. And a pneumatic radial tire capable of greatly reducing the pressure.

[Brief description of the drawings]

FIG. 1 is a right half sectional view of a tire showing an example of an embodiment of the present invention.

FIG. 2 is a right half sectional view of a tire showing another example of the embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between an F / S degree and a tan δ of an extremely low heat generation rubber layer.

FIG. 4 is a diagram showing a relationship between a nylon cord temperature and a creep strain.

FIG. 5 is a diagram showing the relationship between nylon cord temperature and F / S degree.

FIG. 6 is a diagram showing a relationship between ride comfort and steering stability using a cord reinforcement layer height as a parameter.

FIG. 7 is a diagram showing an influence of a change in tire rigidity due to a cord reinforcing layer and a rubber reinforcing layer on an F / S degree and steering stability.

FIG. 8 is a diagram showing a relationship between a distance index between both ends of an extremely low heat generation rubber layer and an F / S degree.

FIG. 9 is a graph showing the relationship between the extremely low heat generation rubber layer thickness and the F / S degree.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tread part 3t Tread rubber 4 Bead core 5 Carcass 5u Carcass turning back part 6 Belt 6-1 and 6-2 Cord cross layer of belt 6c Belt cap layer 7 Extremely low heat generation rubber layer 8 Cord reinforcement layer 9 Bead filler rubber E Tire equatorial plane a Inner edge of extremely low heat generation rubber layer b Outer edge of extremely low heat generation rubber layer Bw Maximum width of code cross layer RL Rim diameter line SH Tire section height Hmax Cord reinforcement layer outermost end height H Height of innermost end of cord reinforcement layer

Claims (5)

[Claims] A carcass comprising a pair of beads, a pair of sidewalls, and a tread portion, and a rubber coating of one or more plies of a radially arranged cord which reinforces these portions between bead cores embedded in the beads. And a belt for reinforcing the tread portion at the outer periphery of the carcass. At least one ply of the carcass has a folded portion wound around the bead core, and the belt covers two cord cross layers and the outer periphery. In a pneumatic radial tire having at least one layer of a circumferentially arranged organic fiber cord cap layer, the tan δ of rubber obtained under the measurement conditions of an ambient temperature of 25 ° C., a dynamic strain of 1%, and an excitation frequency of 52 Hz is 0. .02-0.11
Embedded in the tread rubber and disposed at least in the outer peripheral regions on both sides of the center region of the cap layer, and within a range of 0.5 to 0.6 times the tire sectional height. A pneumatic radial tire, wherein at least one cord reinforcing layer having an outermost end in the tire radial direction is disposed in a region extending from a bead portion to a sidewall portion. 2. The tire according to claim 1, wherein the distance of the extremely low heat generation rubber layer from the equatorial plane of the tire to the inner edge is 0.2 times or less the maximum width of the cord layer of the belt. 3. The distance from the equatorial plane of the tire to the outer edge of the extremely low heat generation rubber layer is within a range of 0.5 to 0.55 times the maximum width of the cord crossing layer of the belt. Or the tire described in 2. 4. The thickness of the extremely low heat generation rubber is 1.5-3.
The tire according to any one of claims 1 to 3, which is within a range of mm. 5. The tire according to claim 1, wherein the innermost end of the cord reinforcing layer in the tire radial direction is located near the bead core, and the cord reinforcing layer is arranged along the turn-back portion of the carcass ply.