JP5881438B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire that achieves both braking performance on a wet road surface and steering stability on a snowy road surface.

  Tires used when driving on snowy road surfaces are naturally required to have steering stability on snowy road surfaces, but generally, braking performance on wet road surfaces is not preferred, so steering stability on snowy road surfaces is not desirable. Therefore, a new tire is desired that achieves both high performance and braking performance on a wet road surface.

  As one of the approaches to meet this demand, the tread rubber that forms the contact surface is made into an asymmetrical composition with different composition on the inside and outside of the tire, or the tread pattern is made into an asymmetric structure with different on the inside and outside of the tire. Can be considered.

  As an example in which the tire is asymmetrically mixed and asymmetrical between the inner side and the outer side, for example, in Patent Document 1, a high-hardness rubber is disposed in the outer region of the cap rubber that forms the contact surface, and the inner region of the cap rubber is installed. In addition, a tire is disclosed in which a low-hardness rubber is disposed in an asymmetric composition and the groove area in the mounting outer region is smaller than the groove area in the mounting outer region.

JP 2003-326917 A

  The above-mentioned Patent Document 1 provides a hardness difference between the inside and outside of the mounting, and also makes the groove area different between the inside and outside of the mounting, thereby increasing the rigidity of the mounting outside, which requires a great load during turning, compared to the inside of the mounting. Only improving the steering stability on the road surface is disclosed, and no solution is disclosed for achieving both the steering stability on the snowy road surface and the braking performance on the wet road surface.

  As shown in Patent Document 1, the inventor of the present invention pays attention to a method of setting a hardness difference between the mounting inner region and the outer region, and for example, makes the inner hardness of the mounting lower than the outer hardness of the mounting or vice versa. However, just by setting a difference in hardness between the inside and outside of the vehicle, it is possible to obtain results that achieve both steering stability on snowy road surfaces and braking performance on wet road surfaces. There wasn't.

  The present invention has been made paying attention to such problems, and an object of the present invention is to provide a pneumatic tire that achieves both driving stability on a snowy road surface and braking performance on a wet road surface. .

  In order to achieve the above object, the present invention takes the following measures. That is, the pneumatic tire of the present invention is a pneumatic tire provided with a tread rubber that forms a contact surface, and the tread rubber has two contact surfaces on the inner side and the outer side on the tire equator. When divided, it has an inner cap rubber that forms an inner grounding surface and an outer cap rubber that forms an outer grounding surface, and the tread rubber has a groove area out1 from the tire equator to the outer grounding end of the mounting. And the groove area in1 from the tire equator to the grounding end on the inner side of the mounting has a tread pattern satisfying a relationship of 0.6 <(out1 / in1) <1.0, and the rebound resilience of the inner cap rubber The rate is 29% or more and 33% or less, and the rebound resilience of the outer cap rubber is set to 34% or more and 38% or less.

  The tire equator portion means within 15% of the maximum width W of the ground contact surface with the tire equator CL as the center.

  The groove area affects the stability of handling on snowy roads, but due to the camber, the effect on the inner side is large when driving straight, and the effect on the outer side is larger when turning, so the groove area on the inner side and outer side is larger. Even if there is too much difference, the balance is lost at the time of transition from either one of straight traveling or turning to the other, and the behavior of the vehicle becomes unstable. Therefore, in the present invention, as described above, by setting the groove area ratio (out1 / in1) inside and outside the mounting to be larger than 0.6 and less than 1.0, a balance between the inside and outside of the mounting can be taken and the snowy road surface It is possible to improve the steering stability of the vehicle.

  In addition, the impact resilience affects the braking on the wet road surface, but due to the camber, the impact on the inner side of the mounting is higher than that on the outer side of the mounting due to the camber. If the same setting is made, the balance between the inside and outside of the wearing will be lost, and the braking performance will deteriorate. Therefore, in the present invention, by setting the resilience elastic modulus of the inner cap rubber and the outer cap rubber as described above, it becomes possible to improve the braking performance on the wet road surface by balancing the inside and outside of the mounting.

  Therefore, the rubber composition of the cap part is made suitable for braking on wet road surfaces, and the tread pattern suitable for steering stability on snowy road surfaces is adopted, so steering stability on snowy road surfaces is achieved. And the braking performance on the wet road surface can both be achieved.

  In order to improve steering stability on a snowy road surface, the inner cap rubber and the outer cap rubber have a hardness at −5 ° C. set to 72 ° to 76 °, and the inner cap rubber is The outer cap rubber is blended so that the hardness difference between -5 ° C and 23 ° C is 1 ° or more and 9 ° or less. It is preferable that

  In order to improve the handling stability on the snowy road surface, the ground contact surface is disposed on the inner side and the outer side of the mounting with the three or four main grooves extending in the tire circumferential direction across the tire equator. And at least a pair of shoulder land portions arranged on the inner side and the outer side of the mounting on both sides of the tire equator on the shoulder side than the pair of mediate land portions, Of the pair of mediate land portions, the groove area out2 of the mediate land portion on the outside of the attachment and the groove area in2 of the mediate land portion on the inside of the attachment are 0.6 <(out2 / in2) <1. Among the paired shoulder land portions, the groove area out3 of the shoulder land portion on the outer side and the groove area in3 of the shoulder land portion on the inner side of the pair are 0.6 <(out3 / in3 <1 It is desirable to satisfy the relationship of. As for the above-mentioned steering stability performance, the inner side is dominant when going straight, and the outer side is dominant when turning, so the groove area ratio (out / in) in each land part is 0.6. If the value is below, the difference in snow performance between the inside and outside of the wearer becomes large, and this is to prevent an undesirable non-linear motion instead of a linear motion when moving from straight travel to turning. For example, the response is good for a small amount of steering when going straight, but the response becomes bad when the steering becomes large, and the initial steering is bent when turning, but the bending becomes worse when the steering becomes large after that. is there.

  In order to improve high-speed durability, it is effective that the boundary between the inner cap rubber and the outer cap rubber is offset from the tire equator to either the inside or outside of the tire.

The tire meridian cross-sectional view showing an example of the pneumatic tire according to the present invention. The figure which shows typically the tread pattern formed in the tread rubber. The figure which shows typically the tread pattern formed in the tread rubber. The figure which shows typically the tread pattern formed in the tread rubber which concerns on other embodiment of this invention.

  Hereinafter, a pneumatic tire according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the pneumatic tire T includes a pair of bead portions 1, sidewall portions 2 that extend outward from the respective bead portions 1 in the tire radial direction RD, and outer sides in the tire radial direction RD of both sidewall portions 2. And a tread portion 3 connected to the end. The bead portion 1 is provided with an annular bead core 1a formed by covering a converging body such as a steel wire with rubber and a bead filler 1b made of hard rubber.

  The tire T includes a toroidal carcass layer 4 that extends from the tread portion 3 through the sidewall portion 2 to the bead portion 1. The carcass layer 4 is provided between a pair of bead portions 1 and is constituted by at least one carcass ply, and its end is locked in a state of being wound up via a bead core 1a. The carcass ply is formed by covering a cord extending substantially perpendicular to the tire equator CL with a topping rubber. Inside the carcass layer 4 is disposed an inner liner rubber 4a for maintaining air pressure.

  Further, a sidewall rubber 6 is provided outside the carcass layer 4 in the sidewall portion 2. A rim strip rubber 7 is provided outside the carcass layer 4 in the bead portion 1 so as to come into contact with a rim (not shown) when the rim is mounted. In the present embodiment, the topping rubber, the rim strip rubber 7 and the side wall rubber 6 of the carcass layer 4 are made of conductive rubber.

  On the outer side of the carcass layer 4 in the tread portion 3, a belt 4b for reinforcing the carcass layer 4, a belt reinforcing material 4c, and a tread rubber 5 are provided in order from the inner side to the outer side. The belt 4b is composed of a plurality of belt plies. The belt reinforcing member 4c is configured by covering a cord extending in the tire circumferential direction with a topping rubber. The belt reinforcing material 4c may be omitted as necessary.

  The tread rubber 5 includes a cap portion 50 that constitutes a ground contact surface, and a base portion 51 that is provided on the inner side in the tire radial direction of the cap portion 50. In the above, the ground contact surface is a surface that is assembled to a regular rim and filled with a regular internal pressure, the tire is placed vertically on a flat road surface, and is grounded to the road surface when a regular load is applied. The outermost position is the ground contact E. The normal load and the normal internal pressure are the maximum load (design normal load in the case of passenger car tires) specified in JIS D4202 (the origin of automobile tires) and the air pressure corresponding to this, and the normal rim is As a rule, the standard rim specified in JIS D4202 etc. shall be used.

  As shown in FIG. 1, when the ground contact surface is divided into a mounting inner side WD1 and a mounting outer side WD2 at the tire equator portion, the cap portion 50 has an inner cap rubber 52 that forms the inner ground contact surface, and an outer contact surface. And an outer cap rubber 53 that forms the ground. In the present embodiment, the interface between the inner cap rubber 52 and the outer cap rubber 53 has a tapered shape inclined with respect to the tire radial direction RD and the tire width direction in the tire meridian cross section. Of course, the interface between the inner cap rubber 52 and the outer cap rubber 53 may be raised along the tire radial direction RD.

  Of the interface between the inner cap rubber 52 and the outer cap rubber 53, the boundary P1 exposed on the tire surface, that is, the boundary P1 that divides the ground contact surface into the mounting inner side WD1 and the mounting outer side WD2 is disposed in the tire equator. Here, the tire equator means within 15% of the maximum width W of the ground contact surface with the tire equator CL as the center. The boundary P1 only needs to be disposed at the tire equator, but the strongest centrifugal force acts on the tire equator CL, and therefore avoiding the boundary P1 from being disposed on the tire equator CL from the viewpoint of high-speed durability. Is preferred. That is, in order to improve high-speed durability, it is preferable that the boundary P1 is slightly offset from the tire equator CL to one of the tire width directions WD.

  In order to improve the braking performance on the wet road surface, the composition of the cap rubbers 52 and 53 is devised as follows. That is, the rebound resilience at 23 ° C. of the inner cap rubber 52 is set to 29% to 33%, and the rebound resilience at 23 ° C. of the outer cap rubber 53 is set to 34% to 38%. The rebound resilience means a rebound resilience measured in accordance with a rebound resilience test defined in JISK6255. The reason why the rebound resilience of the inner cap rubber 52 and the outer cap rubber 53 is set to the above value is that the smaller the rebound resilience, the greater the energy loss during braking on the wet road surface, and the contact force with the road surface. This is because it becomes larger, which is advantageous for braking. The difference in the resilience elastic modulus between the inner cap rubber 52 and the outer cap rubber 53 is that most recent tires are attached to the vehicle body with a camber, and the outer cap rubber is the outer mounting side. Since the inner cap rubber 52 on the inner side of the wearer has a higher contribution to braking than the inner wearer 53, if the resilience modulus of the outer side of the wearer and the inner side of the wearer are set in the same manner, the balance between the inner and outer sides of the wearer will collapse and This is because the pressure difference becomes uneven and the braking performance is deteriorated. In short, it is to balance the inside and outside of the wearing in consideration of camber.

  Moreover, in order to improve the handling stability on the snowy road surface, the tread pattern shape of the tread rubber 5 is devised as follows. That is, as shown in FIG. 2, the tread rubber 5 has a groove area out1 from the tire equator CL to the ground contact end E of the mounting outer side WD2, and a groove area in1 from the tire equator CL to the ground contact end E of the mounting inner side WD1. , 0.6 <(out1 / in1) <1.0. The larger the groove area, the higher the edge effect and the better the handling stability on the snowy road surface. In this way, the groove area affects the handling stability on the snowy road surface, but due to the camber, the effect on the inner side is large when going straight, and the effect on the outer side is larger when turning, so the inner side WD1 and the inner side are attached. Even if the groove area of the outer side WD2 is made the same, or conversely, there is too much difference, the balance is lost at the time of shifting from either one of straight traveling or turning, and the behavior of the vehicle becomes unstable. Therefore, by setting the groove area ratio between the inside and outside of the mounting as described above, the handling stability on the snowy road surface is improved by balancing the inside and outside of the mounting.

  In this embodiment, as shown in FIG. 3, the tread rubber 5 has four main grooves 5a extending in the tire circumferential direction. The ground contact surface is disposed by the main groove 5a on the center land portion 5b disposed on the tire equator CL, and on the mounting inner side WD1 and the mounting outer side WD2 across the tire equator CL on the shoulder side of the center land portion 5b. The pair of mediate land portions 5c and 5c and the shoulder land that forms a pair disposed on the inner side WD1 and the outer side WD2 across the tire equator CL on the shoulder side of the pair of the mediate land portions 5c and 5c. It is divided into parts 5d and 5d. The tread rubber 5 has a groove area out2 of the mediate land portion 5c in the mounting outer side WD2 and a groove area in2 of the mediate land portion 5c in the mounting inner side WD1 of the pair of mediate land portions 5c and 5c. 0.6 <(out2 / in2) <1.0 and satisfying the relationship of 0.6 <(out2 / in2) <1.0, of the shoulder land portions 5d and 5d forming a pair, the groove area out3 of the shoulder land portion 5d on the mounting outer side WD2 and the mounting inner side WD1 The groove area in3 of the shoulder land portion 5d has a tread pattern that satisfies a relationship of 0.6 <(out3 / in3) <1.0. As described above, it is possible to improve the handling stability on the snowy road surface by setting the groove area in units of land.

  Furthermore, in order to improve the handling stability on the snowy road surface, the composition of the cap rubbers 52 and 53 is devised as follows. That is, the inner cap rubber 52 and the outer cap rubber 53 have a hardness at −5 ° C. set to 72 ° to 76 °. The inner cap rubber 52 is blended so that the difference in hardness between −5 ° C. and 23 ° C. is 5 ° to 13 °. The outer cap rubber 53 is blended so that the difference in hardness between −5 ° C. and 23 ° C. is 1 ° to 9 °. Hardness means the hardness measured according to JISK6253 durometer hardness test (type A). The reason why the rubber hardness at −5 ° C. of both the cap rubbers 52 and 53 is set within the above range is to appropriately ensure the steering stability performance (snow performance) on the snowy road surface. Further, the smaller the difference in hardness between −5 ° C. and 23 ° C., the less the change in the hardness of the rubber, the better the contact with the road surface, and the more favorable the steering stability performance on the snowy road surface. This is because if the hardness difference between −5 ° C. and 23 ° C. is too large, the physical property change accompanying the temperature change is severe, the low temperature elastic modulus becomes remarkably high, and the steering stability performance on the snowy road surface deteriorates. . From this, it is considered that the difference in hardness between −5 ° C. and 23 ° C. may be set small for each of the inner cap rubber 52 and the outer cap rubber 53, but the groove area ratio is already different between the outer side and the inner side. Therefore, if both the inner cap rubber 52 and the outer cap rubber 53 are set in the same manner, the balance between the outer side and the inner side is lost, and the steering stability on the snowy road surface is impaired. Therefore, in consideration of the relationship with the groove area as described above, by setting the hardness difference between −5 ° C. and 23 ° C. for each of the inner cap rubber 52 and the outer cap rubber 53 as described above, This improves the handling stability on snowy road surfaces.

  As an example of blending the inner cap rubber 52 and the outer cap rubber 53, for example, the rebound resilience is 32%, the rubber hardness at −5 ° C. is 74 °, the rubber hardness at 23 ° C. is 65 ° C., and the hardness difference due to temperature is In order to mix 9 ° rubber, a mixture of raw rubber and raw rubber reinforcing agent in a high ratio is exemplified. For example, the silica is blended in an amount of 50 to 100 parts by weight with respect to 100 parts by weight of the raw rubber, and the average glass transition point (Tg) is -55 ° C to -35 ° C. Examples of the raw rubber include SBR (styrene butadiene rubber), natural rubber, butadiene rubber and the like, and these are used singly or in combination of two or more. A vulcanizing agent, a vulcanization accelerator, a plasticizer, an antiaging agent, and the like are appropriately blended with the raw rubber. In order to obtain a rubber having the same hardness as that of the rubber and having an increased impact resilience, the glass transition point (Tg) may be lowered or the amount of silica may be lowered. On the other hand, in order to obtain a rubber having the same hardness as that of the rubber and having a low impact resilience, the glass transition point (Tg) may be increased or the amount of silica may be increased.

  For example, in order to obtain a rubber having a rebound resilience of 32%, a rubber hardness at −5 ° C. of 76 °, a rubber hardness at 23 ° C. of 63 °, and a hardness difference of 13 ° depending on the temperature, The thing which mix | blended the silica with the high ratio as a reinforcing agent of rubber | gum and raw material rubber is illustrated. For example, the silica is blended in an amount of 50 to 100 parts by weight with respect to 100 parts by weight of the raw rubber, and the average glass transition point (Tg) is -75 ° C to -55 ° C. Examples of the raw rubber include SBR (styrene butadiene rubber), natural rubber, butadiene rubber and the like, and these are used singly or in combination of two or more. A vulcanizing agent, a vulcanization accelerator, a plasticizer, an antiaging agent, and the like are appropriately blended with the raw rubber. In order to obtain a rubber having the same rebound resilience as that of the rubber and a reduced hardness difference between −5 ° C. and 23 ° C., the glass transition point (Tg) of the raw rubber may be lowered and the amount of silica may be increased. On the other hand, in order to obtain a rubber having the same resilience modulus as that of the rubber and an increased hardness difference at −5 ° C. and 23 ° C., the glass transition point (Tg) of the raw rubber is increased and the amount of silica is decreased. .

  In the present embodiment, a tread-on-side structure in which both end portions of the tread rubber 5 are placed on the outer end in the tire radial direction RD of the sidewall rubber 6 is employed. However, the present invention is not limited to this structure. It is also possible to adopt a side-on-tread structure in which side wall rubber is placed on both ends of the.

[Other Embodiments]
(1) In the present embodiment, a pair of bead portions 1, a sidewall portion 2 extending outward from the respective bead portions 1 and 1 in the tire radial direction RD, and an outer side in the tire radial direction RD of the respective sidewall portions 2 and 2. A tread portion 3 connected to the end, a toroidal carcass layer 4 provided between the pair of bead portions 1, 1, and a tread provided outside the carcass layer 4 in the tread portion 3 and forming a ground contact surface The tread rubber 5 is provided with four main grooves 5a extending in the tire circumferential direction. As shown schematically in FIG. 4, the main groove 5a passing through the tire equator CL, and the tire The present invention can also be applied to a tire having three main grooves 5a including a pair of main grooves 5a and 5a arranged on the inner side WD1 and the outer side WD2 with the equator CL interposed therebetween. The relationship of the groove area in this case is the same as described above.

  In order to specifically show the configuration and effects of the present invention, the following evaluations were performed on the following examples.

(1) Braking performance on wet road surface Size: Use 225 / 55R19 99V tires, measure braking distance when running speed of actual vehicle (domestic vehicle) from 100 km / h to 0 km / h, and evaluate index Went. The braking distance on a wet road surface (wet road surface) was evaluated as braking performance. The larger the index, the higher the braking performance and the better.

(2) Steering stability on snowy road surface (snow performance)
Comparison was made by sensory evaluation by running on a snowy road surface using an actual vehicle equipped with a tire of the above size. The steering stability performance was evaluated by an index with the steering stability performance in Comparative Example 1 as 100. The larger the index, the higher the steering stability performance and the better.

Example 1
An asymmetric tread pattern with different groove areas on the inner and outer sides was adopted. In this tread pattern, the groove area ratios (out1 / in1), (out2 / in2), and (out3 / in3) were all set to 0.9. As shown in FIG. 1, the boundary P1 between the inner cap rubber 52 and the outer cap rubber 53 was offset by 5% of the ground contact surface maximum width W from the tire equator CL to the mounting outer WD2. The inner cap rubber 52 was blended so that the resilience elastic modulus was 32%, the rubber hardness at −5 ° C. was 74 °, and the rubber hardness at 23 ° C. was 65 °. The outer cap rubber 53 was blended so that the resilience modulus was 35%, the rubber hardness at −5 ° C. was 74 °, and the rubber hardness at 23 ° C. was 69 °.

Example 2
In contrast to Example 1, a symmetrical tread pattern having the same groove area on the inner side and the outer side was employed. In this tread pattern, the groove area ratios (out1 / in1), (out2 / in2), and (out3 / in3) were all set to 1.0. Otherwise, the tire was the same as the tire of Example 1.

Examples 3 and 4
In contrast to Example 1, the rebound elastic modulus of the inner cap rubber 52 and the outer cap rubber 53 was set to the upper limit of the range considered preferable, and Example 3 was set to the lower limit. . Otherwise, the tire was the same as the tire of Example 1.

Examples 5 and 6
In contrast to Example 1, for each of the inner cap rubber 52 and the outer cap rubber 53, the upper limit value of the range in which the hardness difference due to temperature is considered to be preferable is set as Example 5, and the lower limit value is set as Example It was set to 6. Otherwise, the tire was the same as the tire of Example 1.

Examples 7 and 8
In contrast to Example 1, the boundary P1 between the inner cap rubber 52 and the outer cap rubber 53 is offset by 15% of the ground contact surface maximum width W from the tire equator CL to the mounting inner side WD1, and is set to the mounting outer side WD2. % Offset was designated as Example 7. Otherwise, the tire was the same as the tire of Example 1.

Comparative Example 1
A symmetrical tread pattern having the same groove area on the inner side and the outer side is adopted, and the cap portion 50 has a rebound resilience of 38%, a rubber hardness at −5 ° C. of 71 °, and a rubber hardness at 23 ° C. of 64. A tire with a rubber composition that is symmetrical was produced.

Comparative Examples 2 and 3
Compared to Comparative Example 1, a tire in which the outer cap rubber 53 has a higher hardness than the inner cap rubber 52 is referred to as Comparative Example 1, and a tire in which the outer cap rubber 53 has a lower hardness is compared. Example 2 was adopted. Otherwise, the tire was the same as the tire of Comparative Example 1.

Comparative Examples 4 and 5
For Examples 3 and 4, the rebound elastic modulus of the inner cap rubber 52 and the outer cap rubber 53 is set to a value exceeding the upper limit value of the range considered to be preferable, and is set to a value lower than the lower limit value as Comparative Example 4. What was set was referred to as Comparative Example 5. Other than that, it was the same as the tires of Examples 3 and 4.

Comparative Examples 6 and 7
For Examples 5 and 6, for each of the inner cap rubber 52 and the outer cap rubber 53, a value that exceeds the upper limit value of the range in which the hardness difference due to temperature is considered to be preferable is referred to as Comparative Example 6, and the lower limit value is What was set to the lower value was set as Comparative Example 7. Other than that, it was the same as the tires of Examples 5 and 6.

Comparative Examples 8, 9, 10, 11
In comparison with Examples 7 and 8, the boundary P1 between the inner cap rubber 52 and the outer cap rubber 53 is offset by 16% of the ground contact surface maximum width W from the tire equator CL to the mounting inner WD1 as Comparative Example 8, and the mounting outer WD2 Comparative Example 9 was offset by 16%. Other than that, it was the same as the tires of Examples 7 and 8. Similarly, Examples 10 and 11 were obtained by offsetting the boundary P1 by 20% of the ground contact surface maximum width W from the tire equator CL to the mounting inner side WD1 and the mounting outer side WD2, respectively.

  From Tables 1 and 2, Examples 1 to 6 are improved in both braking performance on wet road surfaces and steering stability on snowy road surfaces as compared with Comparative Examples. While maintaining the performance of one, the performance of the other is improved. That is, it can be confirmed that both performances are compatible.

  Regarding the braking performance on the wet road surface, although Examples 3 and 4 are improved as compared with Comparative Example 1, they are worse than Example 1, and thus are considered to be the upper limit value and the lower limit value of the resilience elastic modulus. It is done. When it is higher than this upper limit value or lower than the lower limit value, it is considered that it is equivalent to or worse than Comparative Example 1. This is supported by the evaluation results of Comparative Examples 4 and 5.

  Regarding the handling stability on the snowy road surface, although Examples 5 and 6 are improved as compared with Comparative Example 1, they are worse than Example 1, and thus are the upper and lower limits of the hardness difference due to temperature. it is conceivable that. When it is higher than this upper limit value or lower than the lower limit value, it is considered that it is equivalent to or worse than Comparative Example 1. This is supported by the evaluation results of Comparative Examples 6 and 7. In addition, Example 2 in which the groove area is equal between the outer side and the inner side is improved as compared with Comparative Example 1, but is worse than Example 1, so that the groove area ratio is the steering stability on the snowy road surface. Can be confirmed.

  As for the boundary P1 between the inner cap rubber 52 and the outer cap rubber 53, in Examples 7 and 8, both performances are improved as compared with Comparative Example 1, but the boundary P1 is worse than that in Example 1. This is considered to be a threshold for deciding the position to place the. That is, when the boundary P1 is offset to the shoulder side from the seventh and eighth embodiments, the performance is considered to deteriorate. This is supported by the evaluation results of Comparative Examples 8 and 9.

  Further, when the boundary P1 is offset to the mounting inner side WD1 as in the seventh embodiment, the outer cap rubber 53 becomes larger than the inner cap rubber 52, and the steering stability on the snowy road surface is improved as compared with the first embodiment. On the other hand, it can be seen that the braking performance on the wet road surface is reduced.

  On the other hand, when the boundary P1 is offset to the mounting outer side WD2 as in the eighth embodiment, the inner cap rubber 52 becomes larger than the outer cap rubber 53, and the braking performance on the wet road surface is improved as compared with the first embodiment. On the other hand, it can be seen that the handling stability on the snowy road surface is reduced.

5 ... tread rubber 5a ... main groove 5c ... mediate land portion 5d ... shoulder land portion 52 ... inner cap rubber 53 ... outer cap rubber E ... grounding end WD1 ... mounting inner side WD2 ... mounting outer side

Claims (2)

A pneumatic tire having a tread rubber forming a contact surface,
The tread rubber includes an inner cap rubber that forms an inner ground surface and an outer cap rubber that forms an outer ground surface when the ground surface is divided into two parts, an inner side and an outer side, at the tire equator. Have
In the tread rubber, the groove area out1 from the tire equator to the grounding end on the outer side of the mounting and the groove area in1 from the tire equator to the grounding end on the inner side of the mounting are 0.6 <(out1 / in1) <1.0. It has a tread pattern that satisfies the relationship,
The rebound resilience of the inner cap rubber is 29% or more and 33% or less, and the rebound resilience of the outer cap rubber is set to 34% or more and 38% or less .
The inner cap rubber and the outer cap rubber have a hardness at −5 ° C. set to 72 ° to 76 °,
The inner cap rubber is blended so that the hardness difference between −5 ° C. and 23 ° C. is 5 ° to 13 °,
The outer cap rubber is a pneumatic tire in which a hardness difference between −5 ° C. and 23 ° C. is 1 ° to 9 ° . The ground contact surface is composed of three or four main grooves extending in the circumferential direction of the tire, and a pair of mediate land portions arranged on the inner side and the outer side of the mounting across the tire equator, and the pair of mediates It is at least partitioned into a pair of shoulder land portions arranged on the inner side and outer side of the mounting across the tire equator on the shoulder side from the land portion,
Of the pair of mediate land portions, the groove area out2 of the mediate land portion on the outside of the attachment and the groove area in2 of the mediate land portion on the inside of the attachment are 0.6 <(out2 / in2) <1. Among the paired shoulder land portions, the groove area out3 of the shoulder land portion on the outer side and the groove area in3 of the shoulder land portion on the inner side of the pair are 0.6 <(out3 / in3 2) The pneumatic tire according to claim 1 , which satisfies a relationship of <1.0.

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