JP2728286B2 - Pneumatic radial tire - Google Patents

Description

The present invention is applied to a pneumatic radial tire, for example, a vehicle mounted on a vehicle that runs safely and at high speed on a road surface including a straight road and a curved road, and has wear resistance and heat resistance. The present invention relates to a pneumatic radial tire for motor sports, which has improved performance and high grip.

(Prior Art) In general, pneumatic radial tires, especially pneumatic radial tires for motor sports, are mounted on vehicles that travel at high speed on paved road surfaces including straight roads and curved roads, and perform rapid braking and rapid acceleration on straight roads. Make a sharp run, such as making a sharp turn on a curved road. For this reason, tires are mainly used pneumatic radial tires having a radial structure with a high cornering power and a high cornering force, and the tread has a good wear resistance when the running distance is long as a single rubber layer,
A rubber having high hardness at normal temperature and high temperature is used, and a rubber having low hardness at normal temperature and high temperature is used for traveling in which the grip property is emphasized, even if the abrasion resistance is relatively poor.

As a conventional pneumatic radial tire for racing, for example, there is a tire whose partial cross section is shown in FIG.
In FIG. 6, a conventional pneumatic radial tire 1 is:
The bead core 2 extends between the pair of bead cores 2.
Radial carcass 3 folded around
A reinforcing layer 4 of one steel cord for reinforcing the side portion along the carcass 3, a belt 5 extending circumferentially outside the crown 3 a of the carcass 3, and a tread 6 covering the outside of the belt 5. And the belt 5 so as to cover the end of the belt 5.
And two layer layers 7 interposed between the tread 6 and
A sidewall 8 that covers the outside of the side portion of the carcass 3, and has a symmetric structure with respect to the equatorial plane E of the tire.

When the pneumatic radial tire 1 for racing is mounted on a vehicle, in order to sufficiently exhibit the tire characteristics of the radial structure, as shown in FIGS. 7 and 8 (a) and (b),
Large camber angle in minus direction (so-called reverse camber) -3 ゜ to-
6 ° (the camber angle is larger than the actual camber angle for easy understanding. The inside and outside in the figure indicate the inside and outside when the tire is mounted on the vehicle, and the inside and outside of the tire are shown. Outer side; the same applies hereinafter). The reason is that the pneumatic radial tire has a high rigidity of the belt 5, so that when mounted on a vehicle at a camber angle α of zero degree,
During straight running, as shown in FIG. 9 (a), the tread 6 is in contact with the road surface 9 on the entire surface in the width direction. However, when cornering on a curved road at high speed, a large centrifugal force is applied to the center of gravity of the vehicle body. Therefore, the inside of the tire rises from the road surface 9 as schematically shown in FIG. 9 (b) due to the load movement (roll), and sufficient cornering performance cannot be obtained. Therefore, by mounting the tire on the vehicle so as to have a large camber angle in the minus direction in advance, the tread 6 can come into wide contact with the road surface 9 during cornering as shown in FIG. 8 (b), and good cornering performance can be obtained. It has been made to be.

(Problems to be Solved by the Invention) However, when the tire is mounted on the vehicle at such a large camber angle in the minus direction, the cornering performance of the tire is good, but when traveling straight ahead, FIG. 8 (a) and FIG. As shown in FIG. 3A, the contact pressure at the tread edge 6a inside the tire increases, promoting wear near the tread edge, causing early wear and increasing the temperature at the tread edge. There is a problem that too.

The pneumatic radial tire 1 has a radial structure, and as shown in FIG. 6, the tread end 6a, which is the ground end of the tread 6, and the end 5a of the belt 5 overlap at substantially the same position. There is also a problem that it causes a peeling failure or a rupture failure of the end 5a of the fifth member 5.

In order to solve these problems, a tread having good abrasion resistance and heat resistance is used. However, since racing tires run fast, high grip on the road surface is also required. There is a problem that it is difficult to further increase the rubber having both of these properties.

Therefore, the present invention provides a tire for tread wear resistance, heat resistance and high grip even when the tire is mounted on a car at a large camber angle in order to effectively exert the characteristics of a pneumatic radial tire for motor sports. It is an object of the present invention to provide a pneumatic radial tire that can sufficiently maintain the tire performance over a long period of time and can sufficiently exhibit cornering characteristics.

(Means for Solving the Problems) The present inventors mounted a pneumatic radial tire having no tread pattern for motor sports on a vehicle at a large camber angle in a minus direction, and traveled at high speed on straight roads and curved roads. The relationship between the stiffness of the side of the tire and the traction performance, braking performance, maneuvering performance, etc., as well as the stiffness of the side of the tire, the tire structure, tread thickness, tread pressure and the inside and outside of the tire Relationship between tread rubber properties and physical properties, especially tread high grip, abrasion resistance, heat resistance compatibility, hardness, internal loss (tan
Various tests and examinations were conducted on the relationship with δ).

As a result, focusing on the fact that it is necessary to increase the rigidity of the tire side part when cornering on a curved road, we found that increasing the rigidity of the tire's outer side part during this cornering is effective. Was.

Further, it has been found that the rigidity of the inner side portion of the tire does not increase the rigidity in order to make use of the characteristics of the radial tire, and does not impair the traction performance and the braking performance when traveling straight.

Also, the thickness of the tread has a suitable thickness, and in addition to reinforcing the side portions of the tire, the tread is further divided into the tire inside and outside the tire in the lateral direction of the tire, each having a different rubber material having different characteristics. It has been found that the overall performance of the tire can be further greatly improved by providing.

The present inventors have further studied diligently and have reached this conclusion.

A pneumatic radial tire according to the present invention includes a carcass having a folded portion extending between a pair of bead cores and folded around the bead core, and a non-extensible belt extending in a circumferential direction outside a crown portion of the carcass. And a substantially cylindrical tread covering the outside of the belt, and a sidewall covering the outside of the side portion of the carcass, wherein the pneumatic radial tire extends radially outward from the vicinity of at least one of the bead cores. At least one reinforcing layer for reinforcing the side portion of the tire is provided, and the folded portion of the carcass and the reinforcing layer are combined so that one side portion of the tire is reinforced more strongly than the other side portion, and the tread is Direction, and the hardness of the rubber of the first tread on the one side of the tire is the other side. Definitive second lower within 6 ° of rubber hardness of the tread, and the value obtained by dividing the tanδ of the rubber of the second tread tanδ of the rubber of the first tread 0.78
It is characterized by being in the range of 0.99.

Here, the fact that one side portion of the tire is more strongly reinforced than the other side portion by combining the folded portion of the tire and the reinforcing layer means that only the folded portion of the carcass or only the reinforcing layer is used for reinforcement. And may be reinforced by both. The reinforcement means that the side portion on one side of the tire is reinforced more strongly than the side portion on the other side of the tire.

Also, to reinforce the side parts of these tires,
The structure, material, material, or combination of each of the folded portion and the reinforcing layer may be used. As a specific method of these, the following may be performed.

(1) The number of reinforcing layers may be larger on one side than on the other side in order to make a difference in reinforcement depending on the structure of the carcass and the reinforcing layer on the side portion of the tire. The folded height of the folded portion of the carcass from the bead core to the tread side may be higher on one side than on the other side.

(2) A material having higher rigidity is used on one side than on the other side in order to make a difference in reinforcement depending on the material used and the material used for the reinforcing layer. For example, an organic fiber cord is used on the other side, and a steel cord is used on one side. Further, a material having high rigidity is used on one side than on the other side. For example, a cord having the same material and having a larger number of cords to be inserted or a cord having a larger diameter on one side than on the other side is used.

The reason why the tread is divided into two in the horizontal direction is that tread rubbers having different characteristics are used. In other words, a rubber material of the first tread (hereinafter, simply referred to as a first tread rubber) is provided with an emphasis on high grip properties, and a rubber of the second tread (hereinafter, simply referred to as a second tread rubber) is provided with wear resistance and resistance. This is for disposing a heat-generating device. Here, the most important and effective thing is to connect the first tread rubber to the stronger reinforced side portions. In consideration of the overall balance of the tire, the division ratio of the width of the tread in the lateral direction is 0.5, where TW ₁ and TW ₂ are the widths of the first and second tread rubbers, respectively, and the division ratio TW ₁ / TW ₂ is 0.5. To 1 are preferred.

The thickness of the tread central portion is preferably 7 mm or less. 7
If it exceeds mm, heat generation becomes large, and high-speed durability is reduced.

In addition, the reason why the hardness of the first tread rubber is lower than the hardness of the second tread rubber within 6 ° is that when the hardness difference exceeds 6 °, the hardness difference is excessive, and the performance during straight running and at the time of cornering, This is because any one of the performances is reduced. The hardness here refers to a value measured based on the JIS K6301 spring method.

The value of tan δ ₂ / tan δ ₁ obtained by dividing tan δ ₂ of the second tread rubber by tan δ ₁ of the first tread rubber was set to 0.78 to 0.99, because the effect of the present invention is sufficient even if it is less than 0.78 or exceeds 0.99. Because it cannot be used in Of this tread rubber
The tan δ (internal loss) is measured by a method of measuring dynamic tensile strain using a viscoelasticity measuring device under the conditions of a temperature of 70 ° C., a dynamic strain of 3%, and a frequency of 30 Hz.

When the pneumatic radial tire according to the present invention is mounted on a vehicle at a large camber angle in a minus direction, one side of the tire is located outside the vehicle and the other side of the tire is located inside. That is, the side portion of the tire is strongly reinforced on the outside of the vehicle, the rigidity is high, the rubber of the tread has low hardness, and the rubber having large internal loss comes. When mounted on a vehicle with a large camber angle in the opposite positive direction, the other side of the tire is located outside the vehicle and one side of the tire is located inside. That is, it is mounted in accordance with the camber of the vehicle.

(Operation) In the pneumatic radial tire of the present invention, one side portion of the tire is reinforced more strongly than the other side portion, and the one side portion has high side rigidity. Further, in addition to the reinforcement, the tread is divided into two in the lateral direction, each of which has a specific characteristic, the tread rubber on one side of the tire is soft, the grip on the road surface is good, and the other side has Tread rubber has low internal loss and generates less heat. Therefore, when such a pneumatic radial tire is mounted at a large camber angle in the minus direction with one side outside the vehicle and the other side inside the vehicle, the vehicle travels at a high speed.
As shown in the figure, when traveling on a straight road, the rigidity of the side portions of the tire is low inside the vehicle and the deflection of the tire is large. For this reason, the contact area becomes large, and the surface pressure is greatly reduced. Furthermore, the heat generation of the tread is small, and the durability is greatly increased.

Also, when the vehicle travels on a curved road, a load movement (roll) of the vehicle occurs. However, the rigidity of one side (outside) of the tire is sufficiently large, so that the tire is less bent and the tire has sufficient width. It has a ground contact width. Also, the tread rubber on one side (outside) of the tire is soft and has good grip on the road surface, so that the tire generates sufficient cornering power and cornering force, and can sufficiently exhibit traction performance and braking performance as a radial structure.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a first example of a pneumatic radial tire according to the present invention.
It is a partial sectional view showing an example. In this embodiment, the tire has a large camber angle in the minus direction to the vehicle,
This is a case where the tire is mounted so that one side of the tire is located outside the vehicle and the other side of the tire is located inside.

First, the configuration will be described. In FIG. 1, reference numeral 11 denotes a pneumatic radial tire having a tire size of 240/65.
5 R17. The pneumatic radial tire 11 extends substantially radially across a bead core 12A at the center of the pair of beads 12, and has a carcass 13 having a folded portion folded around the bead core 12A, and a crown portion 13 of the carcass 13.
a non-extensible belt 15 extending in the circumferential direction to the outside of a, and a substantially cylindrical tread 16 covering the radial outside of the belt 15,
Side wall 1 covering the outside of the side portion 13b of the carcass 13
7 and. The tread 16 is divided into two parts at the center in the lateral direction of the tire and extends in the circumferential direction.
And a second tread 16B. Carcass 13 is made of nylon cord of cord kind 1260d / 2,
It has a carcass ply 13A (the number of hits is 62.8 / 5cm) and a second carcass ply 13B on the outside. On one side (the right side of the figure, the same applies hereinafter) of the tire that comes to the outside of the vehicle when the pneumatic radial tire 11 is mounted on the vehicle, the folded portion 13Aao of the first carcass ply 13A is folded around the bead core 12A from inside to outside. It has reached the inside of the belt end 15a and is over. The second carcass ply 13B is the first
It is arranged outside the folded portion 13Aao of the carcass ply 13A,
The folded portion 13Bao is folded inward from the outside of the bead core 12A and ends near the bead 12. Therefore, the folded portion 13Aao of the first carcass ply 13A is fixed in the vicinity of the bead 12 by the bead core 12A, and the terminal portion 13c of the folded portion 13Aao is connected to the first and second carcass plies 13A, 13B and the belt 1A.
The side portion 13b is firmly reinforced by being fixed by the end portion 15a of the fifth portion and exerting a so-called anchor effect.

On the other side (the left side of the figure, the same applies hereinafter) of the tire that comes inside the vehicle when the pneumatic radial tire 11 is mounted on the vehicle, the folded portion 13Aai of the first carcass ply 13A is folded around the bead core 12A from inside to outside. Ends on the bead 12 side from the maximum width position S of the tire. The second carcass ply 13B is a folded portion 13Aa of the first carcass ply 13A.
i, which is located outside the bead core 12
It is folded from outside to inside of A and ends near bead 12. That is, the end position of the folded portion 13Aao of the first carcass ply 13A on one side is folded back from the bead 12 to a position higher (upper part in the figure) than the end position of the folded portion 13Aai on the other side (hereinafter, referred to as the upper end). , It is expensive).

Also, on one side of the tire, 21 is a first reinforcing layer, 22
Is a second reinforcing layer, both of which are made of rubber-coated steel cord (cord type 1 × 5). First
The reinforcement layer 21 extends radially outward from the vicinity of the bead core 12A along the inside of the folded portion 13Aao of the first carcass ply 13A.
And it extends beyond the maximum width position S of the tire. The second reinforcing layer 22 extends radially outward from near the bead core 12 and beyond the maximum width position S of the tire between the second carcass ply 13B and the folded portion 13Aao of the first carcass ply 13A. ing. The positions of these radially outer ends are shifted so that the second reinforcing layer 22 is closer to the tread 16 than the first reinforcing layer 21 is. On the other side of the tire, reference numeral 23 denotes a third reinforcing layer, and the third reinforcing layer 23 is made of rubber-coated Kevlar cord (cord type 1500d / 2), and is inside the folded portion 13Aai of the first carcass ply 13A. From the second carcass ply 13
Along the inside of B, it extends radially outward from near the bead core 12A and beyond the maximum width position S of the tire. The first and second reinforcement layers of steel cord layer have 38 shots.
/ 5cm and at an angle of about 20 ° to the tire circumferential direction. Hereinafter, the first, second, and third reinforcing layers 21, 22, and 23 are referred to as the reinforcing layer 20.

The reinforcement in which the folded portion of the carcass 13 and the reinforcing layer 20 are combined is such that the side portion on one side of the tire is formed of one high folded portion 13Aao and two steel cord layers in addition to the main portion of the two carcass 13. In contrast to the first and second reinforcing layers 21 and 22, the other side of the tire has only one reinforcing layer made of Kevlar cord in addition to the main part of the two carcass 13. Reinforced. Therefore, the reinforcement of the side portion of the tire is an asymmetric structure in which the one side portion is reinforced more strongly than the other side portion, and the one side portion has high rigidity.

Belt 15 is disposed between a pair of shoulders 2
It has a pair of two layer layers 15C covering the outside of the belt end 15a of the belt plies 15A and 15B. Belt ply 15A
And 15B are rubber-coated steel cords with a code type of 1 x 5 at an angle of 22 ° to the tire's circumferential direction.
/ 5cm) and inclined in opposite directions. The layer 15C is made of nylon cord of cord kind 1260d / 2, and suppresses the movement of the belt end 15a. Here, the entire width of the belt 15 may be covered with one cap ply made of a nylon cord, and the outside of the belt end 15a may be covered with a layer 15C.

The tread 16 has a first tread 16A on one side of the tire and a second tread 16
Tread 16B are arranged, when the width TW ₁ and TW ₂ of each tread, the division ratio TW ₁ / TW ₂ is 0.85. The thickness D ₁₆ of the tread 16 is 5 mm. The first and second tread rubbers of the first and second treads 16A and 16B have hardnesses H _A and H _B of 44 ° and 46 °, respectively, and a difference in hardness H of 2 °. The internal losses tan δ _A and tan δ _B of the first and second tread rubbers are 0.53 and 0.53 respectively.
0.47, which is a value obtained by dividing tan δ _B of the second tread rubber by tan δ _A of the first tread rubber, and a loss rate ratio tan δ _B / ta
nδ _A is 0.89. That is, the second tread rubber on the other side (in) has high hardness, excellent wear resistance, and generates little heat. The first tread rubber on one side has low hardness and excellent grip on the road surface.

In the pneumatic radial tire of the present invention, the side portion on one side of the tire is strongly reinforced, and the first tread rubber having low hardness and good grip properties is used for the tread on one side. Even if the movement occurs, the bending of the side portion 11b is small, the tread 16 has a wide horizontal contact width, and exhibits high grip performance.

Further, the second side tread rubber, which has a small reinforcement in the side portion on the other side and a high hardness, high abrasion resistance and little heat generation, is used for the tread on the other side. As shown in FIG. 10 (b), the contact area pressure at the tread end 16c on the other side is reduced, the abrasion resistance is good, and the durability is greatly improved.

FIGS. 2 (b) and 2 (a) show a case where a pneumatic radial tire is filled with a normal internal pressure and a normal load is applied at a camber angle of −6 ° (corresponding to FIG. 8 (a)).
FIG. 4 is a view showing the surface pressure distribution of the ground contact surface of a pneumatic radial tire having an asymmetric structure of a side portion and a conventional pneumatic radial tire having a side symmetric structure, corresponding to the present invention. The pneumatic radial tire of the present invention,
High portion F ₁ of the ground contact pressure of the inside of the tire than the conventional decreases in both the tire width direction and the circumferential direction, and portions F ₂ spreads low surface pressure, the inner surface pressure of the tire is significantly reduced I have.

Next, a second embodiment of the present invention will be described. FIG. 3 is a view showing a second embodiment of the pneumatic radial tire according to the present invention, and the same components as those in the first embodiment are denoted by the same reference numerals.

In the pneumatic radial tire 31 of the second embodiment,
The side portion 11b on one side (the right side in the figure) of the tire has the same or higher height in the folded portion of the carcass 13 as the side portion 11c on the other side (the left side in the figure) (high in this embodiment).
At the same time, the material of the reinforcement layer 20 is strengthened, the number is increased, the height is increased, and the reinforcement is strengthened.
The same two kinds of tread rubbers as in the example are used. That is, the height of the folded portion 13Aao of the first carcass ply 13A on one side is higher than the height of the folded portion 13Aai on the other side. Further, while the reinforcing layer 20 on the other side (in) is made of one steel cord, the reinforcing layer 20 on one side is made of two steel cords and is reinforced strongly by increasing the height. Further, similarly to the first embodiment, the first tread rubber which is soft and has a high grip is arranged on one side of the tread, and the second tread rubber which is hard and has good friction resistance and generates less heat is arranged on the other side.

 Next, a third embodiment of the present invention will be described.

FIG. 4 is a view showing a third embodiment of the present invention, and the same components as those in the first embodiment are denoted by the same reference numerals.

In the pneumatic radial tire 41 of the third embodiment,
The side portion 11b on one side (right side in the figure) of the tire is higher than the side portion 11c on the other side (left side in the figure) by increasing the height of the folded portion of the first carcass ply 13A to provide an anchor effect, The material and height of the reinforcing layer 20 are increased to provide strong reinforcement, and the tread is made of the same two types of specific tread rubber as in the first embodiment.

 Next, a fourth embodiment of the present invention will be described.

FIG. 5 is a view showing a fourth embodiment of the present invention, and the same components as those in the first embodiment are denoted by the same reference numerals.

In the pneumatic radial tire 51 of the fourth embodiment,
The height of the folded portion of the first carcass ply 13A is the same as that of the side portion 11b on one side (the right side in the figure) of the tire with respect to the side portion 11c on the other side (the left side in the figure), so that both have an anchor effect, The reinforcing layer 20 is provided with only the first reinforcing layer 21, which is a single steel cord, for strong reinforcement, and the tread uses the same two kinds of specific tread rubber as in the first embodiment.

Next, prepare test tires in two different tire sizes,
The control performance, the brake traction and the side rigidity, which are the difficulties in controlling the vehicle, were measured by a feeling test when the vehicle was running at high speed on a circuit course, and a comparison test was performed on the best lap time and whether or not a failure occurred.

The first test tire has a tire size of 240/655 R17. The tire of the present invention is the same as the first embodiment shown in FIG. 1 described above, and the conventional tire is the same as that shown in FIG. In the test, the test tires were mounted on the front and rear wheels of a Gr-A specification vehicle (FR vehicle) at camber angles of -6 ° and -4.5 °, respectively, and compared at a high speed on a circuit course. The failure course was checked every 10 laps on the lap course. The test results are shown in the following table as indices with the conventional tire set to 100. The larger the value, the better.

The test results show that, as shown in the preceding table, the tire of the present invention did not cause any failure, the controllability and the brake traction were greatly improved, and the best lap time was also greatly improved.

The second test tire has a front tire size of 180/58
0 R15 is the tire of the present invention. This is because, in the first embodiment shown in FIG. 1, the outer side of the vest ply 15A and 15B in the belt 15 covers the entire width of the belt 15 with one cap ply made of nylon cord, and furthermore, the belt end 15a Is covered with a single layer 15C. The tire size for the rear wheel is 155/580 R15, which is the conventional tire shown in FIG. The comparative example is a conventional tire having a belt structure corresponding to the tire of the present invention for both front wheels and rear wheels. The test was performed using a Gr-A specification vehicle (FF vehicle) in the same manner as the first test tire described above. The test results are shown in Table 2. The numbers indicate that a greater modulus is better.

The test results show that, as shown in the preceding table, the tire of the present invention did not cause any failure, the controllability and the brake traction were greatly improved, and the best lap time was also greatly improved.

(Effects) As described above, according to the present invention, in order to effectively exhibit the characteristics of a pneumatic radial tire for motor sports, even if the tire is mounted on a car at a large camber angle in a minus direction, the tire can be used. The abrasion resistance, heat resistance and high grip of the tread can be sufficiently maintained for a long time, and the cornering characteristics can be sufficiently exhibited.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a pneumatic radial tire according to the present invention. FIGS. 2 (a) and 2 (b) are diagrams showing the surface pressure on the contact surface when the camber angle is -6 °, and FIG. 2 (a) is a surface pressure distribution corresponding to a conventional tire, and FIG. 2 (b). FIG. 2 is a view showing a surface pressure distribution of the tire of the present invention. 3 to 5 are partial cross-sectional views showing second to fourth embodiments of the pneumatic radial tire according to the present invention. FIG. 6 is a partial sectional view of a conventional tire. FIG. 7 is a schematic diagram viewed from the front of the vehicle when the tire is mounted on the vehicle at a large camber angle in the minus direction. FIGS. 8 (a) and 8 (b) are schematic diagrams showing the grounding shape when the tire is mounted on the vehicle at a large camber angle in the minus direction when the vehicle is going straight and when cornering, respectively, and FIGS. 9 (a) and 9 (b). Are respectively shown in FIG. 8 (a),
FIG. 5B is a schematic diagram illustrating a ground contact shape at the time of straight traveling and cornering when the camber angle is zero degree in FIG. 10 (a) and 10 (b) are graphs showing the tread contact pressure at the tread end corresponding to FIG. 8 (a) of the conventional tire and the tire of the present invention, respectively. 11, 31, 41, 51 ... pneumatic radial tire, 12 ... bead, 13 ... carcass, 15 ... belt, 16 ... tread, 16A ... first tread, 16B ... second tread, 17 ... ... side wall, 20 ... reinforcement layer, 21 ... first reinforcement layer, 22 ... second reinforcement layer, 23 ... third reinforcement layer.

Claims (1)

(57) [Claims] 1. A carcass having a folded portion extending between a pair of bead cores and folded around the bead core; a non-extensible belt extending circumferentially outside a crown portion of the carcass; A pneumatic radial tire having a substantially cylindrical tread for covering the carcass and a sidewall for covering the outside of the side portion of the carcass, wherein the side portion of the tire extends radially outward from the vicinity of at least one of the bead cores. At least one reinforcing layer is provided to reinforce the tire, and the folded portion of the carcass and the reinforcing layer are combined so that one side portion of the tire is more strongly reinforced than the other side portion, and the tread is divided in the lateral direction. The first tread rubber on one side of the tire has a hardness of the second tread rubber on the other side. Low within 6 ° from the hardness, and, tan [delta of the rubber of the second tread in tan [delta rubber first tread
A pneumatic radial tire characterized in that the value obtained by dividing is in the range of 0.78 to 0.99.