A tire having an outer middle land portion demarcated between an outer shoulder circumferential groove and an outer crown circumferential groove and located at an outer side of a vehicle when the tire is mounted on the vehicle, and an inner middle land portion demarcated between an inner shoulder circumferential groove and an inner crown circumferential groove and located at an inner side of the vehicle when the tire is mounted on the vehicle formed in a tread portion. The outer middle land portion has first outer middle sipes extending from the outer crown circumferential groove toward the outer shoulder circumferential groove and terminating within the outer middle land portion. The inner middle land portion has first inner middle sipes extending from the inner shoulder circumferential groove toward the inner crown circumferential groove and terminating within the inner middle land portion. An angle θ1 of each first outer middle sipe with respect to a tire axial direction is smaller than an angle θ2 of each first inner middle sipe with respect to the tire axial direction.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a tire capable of achieving both steering stability and ride comfort.

Description of the Background Art

Hitherto, tires for which an attempt to achieve a plurality of performances required for tires is made, have been known. For example, Japanese Laid-Open Patent Publication No. 2017-128269 proposes a pneumatic tire for which an attempt to achieve both steering stability and ride comfort is made by specifying the lengths of shoulder lug grooves and the lengths of shoulder sipes.

However, when the pneumatic tire of Japanese Laid-Open Patent Publication No. 2017-128269 is mounted on a vehicle, there is no stiffness difference in the pneumatic tire between the outer side and the inner side of the vehicle, and thus self-aligning torque is not generated, so that a response delay may occur upon steering. Thus, further improvement is required for achievement of both steering stability and ride comfort.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a tire that basically has a tread portion with an asymmetric pattern and that is capable of achieving both steering stability and ride comfort.

The present invention is directed to a tire including a tread portion having a designated mounting direction to a vehicle, wherein: an outer middle land portion that is demarcated between an outer shoulder circumferential groove and an outer crown circumferential groove and that is located at an outer side of the vehicle when the tire is mounted on the vehicle, and an inner middle land portion that is demarcated between an inner shoulder circumferential groove and an inner crown circumferential groove and that is located at an inner side of the vehicle when the tire is mounted on the vehicle, are formed in the tread portion; the outer middle land portion has first outer middle sipes that extend from the outer crown circumferential groove toward the outer shoulder circumferential groove and that terminate within the outer middle land portion; the inner middle land portion has first inner middle sipes that extend from the inner shoulder circumferential groove toward the inner crown circumferential groove and that terminate within the inner middle land portion; and an angle of each of the first outer middle sipes with respect to a tire axial direction is smaller than an angle of each of the first inner middle sipes with respect to the tire axial direction.

In the tire according to the present invention, preferably, the angle of each of the first outer middle sipes is 5 to 15°, and the angle of each of the first inner middle sipes is 15 to 25°.

In the tire according to the present invention, a direction in which each of the first outer middle sipes is tilted relative to the tire axial direction, and a direction in which each of the first inner middle sipes is tilted relative to the tire axial direction, are preferably opposite to each other.

In the tire according to the present invention, the total number of the first outer middle sipes in a tire circumferential direction is preferably smaller than the total number of the first inner middle sipes in the tire circumferential direction.

In the tire according to the present invention, preferably, the total number of the first outer middle sipes is 60 to 70, and the total number of the first inner middle sipes is 70 to 80.

In the tire according to the present invention, the difference between the total number of the first outer middle sipes and the total number of the first inner middle sipes is preferably 5 to 15.

In the tire according to the present invention, preferably, an outer shoulder land portion demarcated between the outer shoulder circumferential groove and an outer tread edge and an inner shoulder land portion demarcated between the inner shoulder circumferential groove and an inner tread edge are formed in the tread portion, and the outer shoulder land portion has a width in the tire axial direction larger than that of the inner shoulder land portion.

In the tire according to the present invention, preferably, the width of the outer shoulder land portion is 15% to 25% of a tread width, and the width of the inner shoulder land portion is 10% to 20% of the tread width.

In the tire according to the present invention, preferably, the outer shoulder land portion has outer shoulder sipes that extend from the outer shoulder circumferential groove toward the outer tread edge and that terminate within the outer shoulder land portion, the inner shoulder land portion has inner shoulder sipes that extend from the inner shoulder circumferential groove toward the inner tread edge and that terminate within the inner shoulder land portion, and each of the outer shoulder sipes has a length in the tire axial direction smaller than that of each of the inner shoulder sipes.

In the tire according to the present invention, preferably, the length of each of the outer shoulder sipes is 20% to 40% of the width of the outer shoulder land portion, and the length of each of the inner shoulder sipes is 50% to 70% of the width of the inner shoulder land portion.

In the tire according to the present invention, each of the outer middle land portion, the inner middle land portion, the outer shoulder land portion, and the inner shoulder land portion is preferably continuous in a tire circumferential direction.

In the tire according to the present invention, preferably, a crown land portion demarcated between the outer crown circumferential groove and the inner crown circumferential groove is formed in the tread portion, the crown land portion has inner crown sipes that extend from the inner crown circumferential groove toward a tire equator and that terminate within the crown land portion, the inner middle land portion has second inner middle sipes that extend from the inner crown circumferential groove toward the inner shoulder circumferential groove and that terminate within the inner middle land portion, and each of the inner crown sipes and each of the second inner middle sipes are located so as to form a straight line across the inner crown circumferential groove.

In the tire according to the present invention, the outer middle land portion has first outer middle sipes that extend from the outer crown circumferential groove toward the outer shoulder circumferential groove and that terminate within the outer middle land portion, and the inner middle land portion has first inner middle sipes that extend from the inner shoulder circumferential groove toward the inner crown circumferential groove and that terminate within the inner middle land portion. Such first outer middle sipes and such first inner middle sipes can reduce the stiffness of the outer middle land portion and the stiffness of the inner middle land portion, respectively, to improve the ride comfort of the tire.

In the tire according to the present invention, the angle of each of the first outer middle sipes with respect to the tire axial direction is smaller than the angle of each of the first inner middle sipes with respect to the tire axial direction. With such an outer middle land portion and such an inner middle land portion, the stiffness of the outer middle land portion is higher than the stiffness of the inner middle land portion, and thus self-aligning torque can be generated in the tire. Therefore, the tire can improve responsiveness when the tire is steered, and the steering stability of the tire can be improved. Accordingly, the tire according to the present invention can achieve both steering stability and ride comfort at high levels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a development showing a tread portion2of a tire1according to the present embodiment. As shown inFIG. 1, the tire1according to the present embodiment has the tread portion2that has an asymmetric tread pattern and that has a designated mounting direction to a vehicle. The designated mounting direction to a vehicle is indicated, for example, on a sidewall portion (not shown) by characters or symbols.

The tire1is suitably used as, for example, a pneumatic tire for a passenger car. The tire1is not limited to a pneumatic tire for a passenger car, and can be used as, for example, various tires such as a heavy-duty pneumatic tire and a non-pneumatic tire the interior of which is not filled with pressurized air.

The tread portion2of the present embodiment has an outer tread edge Teo located at the outer side of the vehicle with respect to a tire equator C when the tire1is mounted on the vehicle, and an inner tread edge Tei located at the inner side of the vehicle with respect to the tire equator C when the tire1is mounted on the vehicle.

Here, the “outer tread edge Teo” and the “inner tread edge Tei” are each a ground contact position at the outermost side in the tire axial direction when a normal load is applied to the tire1in a normal state and the tire1is brought into contact with a flat surface at a camber angle of 0°. The center position in the tire axial direction between the outer tread edge Teo and the inner tread edge Tei corresponds to the tire equator C. In addition, the distance in the tire axial direction between the outer tread edge Teo and the inner tread edge Tei is a tread width TW.

In the case where the tire1is a pneumatic tire, the “normal state” is a state where: the tire1is mounted to a normal rim and adjusted to a normal internal pressure; and no load is applied to the tire1. In the present specifications, unless otherwise specified, dimensions and the like of components of the tire1are values measured in the normal state.

The “normal rim” is a rim that is defined, in a standard system including a standard on which the tire1is based, by the standard for each tire, and is, for example, the “standard rim” in the JATMA standard, the “Design Rim” in the TRA standard, or the “Measuring Rim” in the ETRTO standard.

The “normal internal pressure” is an air pressure that is defined, in a standard system including a standard on which the tire1is based, by the standard for each tire, and is the “maximum air pressure” in the JATMA standard, the maximum value indicated in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, or the “INFLATION PRESSURE” in the ETRTO standard.

The “normal load” is a load that is defined, in a standard system including a standard on which the tire1is based, by the standard for each tire, and is the “maximum load capacity” in the JATMA standard, the maximum value indicated in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, or the “LOAD CAPACITY” in the ETRTO standard.

The tread portion2preferably has a plurality of circumferential grooves3continuously extending in the tire circumferential direction, and a plurality of land portions4demarcated by the circumferential grooves3. Each of the plurality of land portions4of the present embodiment has no grooves and sipes continuously extending in the tire circumferential direction, and no grooves and sipes traversing the land portion4in the tire axial direction. Such land portions4have high stiffness and can improve the steering stability of the tire1. In the present specification, a sipe has opposing wall surfaces that come into contact with each other when coming into contact with the ground, and a groove has a gap between opposing wall surfaces that oppose each other even when coming into contact with the ground.

The circumferential grooves3of the present embodiment include an outer shoulder circumferential groove3A provided along the outer tread edge Teo at the outer tread edge Teo side with respect to the tire equator C, and an outer crown circumferential groove3B provided between the outer shoulder circumferential groove3A and the tire equator C. In addition, the circumferential grooves3of the present embodiment include an inner shoulder circumferential groove3C provided along the inner tread edge Tei at the inner tread edge Tei side with respect to the tire equator C, and an inner crown circumferential groove3D provided between the inner shoulder circumferential groove3C and the tire equator C.

The land portions4of the present embodiment include an outer middle land portion4A demarcated between the outer shoulder circumferential groove3A and the outer crown circumferential groove3B, and an inner middle land portion4B demarcated between the inner shoulder circumferential groove3C and the inner crown circumferential groove3D. Thus, the outer middle land portion4A located at the outer side of the vehicle when the tire1is mounted on the vehicle, and the inner middle land portion4B located at the inner side of the vehicle when the tire1is mounted on the vehicle, are formed in the tread portion2of the present embodiment.

The outer middle land portion4A preferably has first outer middle sipes5A that extend from the outer crown circumferential groove3B toward the outer shoulder circumferential groove3A and that terminate within the outer middle land portion4A. Such first outer middle sipes5A can reduce the stiffness of the outer middle land portion4A to improve the ride comfort of the tire1.

The inner middle land portion4B preferably has first inner middle sipes5B that extend from the inner shoulder circumferential groove3C toward the inner crown circumferential groove3D and that terminate within the inner middle land portion4B. Such first inner middle sipes5B can reduce the stiffness of the inner middle land portion4B to improve the ride comfort of the tire1.

The angle θ1of each first outer middle sipe5A of the present embodiment with respect to the tire axial direction is smaller than the angle θ2of each first inner middle sipe5B with respect to the tire axial direction. With such an outer middle land portion4A and such an inner middle land portion4B, the stiffness of the outer middle land portion4A is higher than the stiffness of the inner middle land portion4B, and thus self-aligning torque can be generated in the tire1. Therefore, the tire1according to the present embodiment can improve responsiveness when the tire1is steered, and thus the steering stability of the tire1can be improved. Accordingly, the tire1according to the present embodiment can achieve both steering stability and ride comfort at high levels.

As a more preferable mode, the circumferential grooves3each continuously extend in the tire circumferential direction in a straight manner. The groove width W1of the outer shoulder circumferential groove3A of the present embodiment is smaller than the groove width W2of the outer crown circumferential groove3B. The groove width W1of the outer shoulder circumferential groove3A is preferably the smallest among the circumferential grooves3. Such an outer shoulder circumferential groove3A can enhance the stiffness at the outer side of the vehicle when the tire1is mounted on the vehicle, to allow self-aligning torque to be generated in the tire1. Thus, the steering stability of the tire1can be improved.

The groove width W3of the inner shoulder circumferential groove3C is preferably substantially equal to or slightly smaller than the groove width W4of the inner crown circumferential groove3D. The groove width W4of the inner crown circumferential groove3D is preferably substantially equal to the groove width W2of the outer crown circumferential groove3B. Such a circumferential groove3can exhibit excellent drainage performance to improve the wet performance of the tire1.

The land portions4of the present embodiment include an outer shoulder land portion4C demarcated between the outer shoulder circumferential groove3A and the outer tread edge Teo, and an inner shoulder land portion4D demarcated between the inner shoulder circumferential groove3C and the inner tread edge Tei. The land portions4preferably further include a crown land portion4E demarcated between the outer crown circumferential groove3B and the inner crown circumferential groove3D.

Therefore, in the tread portion2of the present embodiment, the outer shoulder land portion4C, the outer middle land portion4A, the crown land portion4E, the inner middle land portion4B, and the inner shoulder land portion4D are formed in this order from the outer side of the vehicle when the tire1is mounted on the vehicle.

The width W5in the tire axial direction of the outer middle land portion4A is preferably larger than the width W6in the tire axial direction of the inner middle land portion4B. Such an outer middle land portion4A has higher stiffness than the inner middle land portion4B, and allows the self-aligning torque of the tire1to be generated more strongly. Thus, the steering stability of the tire1of the present embodiment can be further improved.

The width W5of the outer middle land portion4A is preferably 15% to 25% of the tread width TW. If the width W5is less than 15% of the tread width TW, the stiffness of the outer middle land portion4A is decreased, so that the effect of improving the steering stability of the tire1may be reduced. If the width W5is greater than 25% of the tread width TW, the stiffness of the outer middle land portion4A is excessively increased, so that the effect of improving the ride comfort of the tire1may be reduced.

The width W6of the inner middle land portion4B is preferably 10% to 20% of the tread width TW. If the width W6is less than 10% of the tread width TW, the stiffness of the inner middle land portion4B is decreased, so that the effect of improving the steering stability of the tire1may be reduced. If the width W6is greater than 20% of the tread width TW, the stiffness of the inner middle land portion4B is excessively increased, so that the effect of improving the ride comfort of the tire1may be reduced.

The width W7in the tire axial direction of the outer shoulder land portion4C is preferably larger than the width W8in the tire axial direction of the inner shoulder land portion4D. Such an outer shoulder land portion4C has higher stiffness than the inner shoulder land portion4D, and allows the self-aligning torque of the tire1to be generated more strongly. Thus, the steering stability of the tire1of the present embodiment can be further improved.

The width W7of the outer shoulder land portion4C is preferably 15% to 25% of the tread width TW. If the width W7is less than 15% of the tread width TW, the stiffness of the outer shoulder land portion4C is decreased, so that the effect of improving the steering stability of the tire1may be reduced. If the width W7is greater than 25% of the tread width TW, the stiffness of the outer shoulder land portion4C is excessively increased, so that the effect of improving the ride comfort of the tire1may be reduced.

The width W8of the inner shoulder land portion4D is preferably 10% to 20% of the tread width TW. If the width W8is less than 10% of the tread width TW, the stiffness of the inner shoulder land portion4D is decreased, so that the effect of improving the steering stability of the tire1may be reduced. If the width W8is greater than 20% of the tread width TW, the stiffness of the inner shoulder land portion4D is excessively increased, so that the effect of improving the ride comfort of the tire1may be reduced.

The width W9in the tire axial direction of the crown land portion4E is preferably the smallest among the land portions4. The width W9of the crown land portion4E is preferably 5% to 15% of the tread width TW. If the width W9is less than 5% of the tread width TW, the stiffness of the crown land portion4E is decreased, so that the effect of improving the steering stability of the tire1may be reduced. If the width W9is greater than 15% of the tread width TW, the stiffness of the crown land portion4E is excessively increased, so that the effect of improving the ride comfort of the tire1may be reduced.

FIG. 2is an enlarged view of the outer middle land portion4A and the outer shoulder land portion4C. As shown inFIG. 2, the outer middle land portion4A of the present embodiment has the above-described first outer middle sipes5A, and second outer middle sipes5C that extend from the outer shoulder circumferential groove3A toward the outer crown circumferential groove3B and that terminate within the outer middle land portion4A. Such an outer middle land portion4A continuously extends in the tire circumferential direction, and thus can maintain appropriate stiffness to achieve both the steering stability and the ride comfort of the tire1.

The angle θ1of each first outer middle sipe5A is preferably 5 to 15°. If the angle θ1is less than 5°, the stiffness of the outer middle land portion4A is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the angle θ1is greater than 15°, the stiffness of the outer middle land portion4A is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The angle θ3of each second outer middle sipe5C with respect to the tire axial direction is preferably 15 to 25°. If the angle θ3is less than 15°, the stiffness of the outer middle land portion4A is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the angle θ3is greater than 25°, the stiffness of the outer middle land portion4A is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The direction in which each first outer middle sipe5A of the present embodiment is tilted relative to the tire axial direction, and the direction in which each second outer middle sipe5C is tilted relative to the tire axial direction, are opposite to each other. Such first outer middle sipes5A and such second outer middle sipes5C serve to exhibit the same steering stability regardless of the rotation direction of the tire1.

The length L1in the tire axial direction of each first outer middle sipe5A is preferably 30% to 50% of the width W5of the outer middle land portion4A. If the length L1is less than 30% of the width W5, the stiffness of the outer middle land portion4A is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the length L1is greater than 50% of the width W5, the stiffness of the outer middle land portion4A is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The length L3in the tire axial direction of each second outer middle sipe5C is preferably 20% to 40% of the width W5of the outer middle land portion4A. If the length L3is less than 20% of the width W5, the stiffness of the outer middle land portion4A is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the length L3is greater than 40% of the width W5, the stiffness of the outer middle land portion4A is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The length L3of each second outer middle sipe5C is preferably smaller than the length L1of each first outer middle sipe5A. With such first outer middle sipes5A and such second outer middle sipes5C, when the tire1is mounted on the vehicle, the stiffness of the outer middle land portion4A is higher at the outer side of the vehicle than at the inner side of the vehicle, so that the self-aligning torque of the tire1can be generated more strongly. Thus, the steering stability of the tire1of the present embodiment can be further improved.

FIG. 3is a cross-sectional view taken along a line A-A inFIG. 2. As shown inFIGS. 2 and 3, the outer middle land portion4A preferably has a shallow groove portion6that has a large groove width W10and that is formed at the outer side in the tire radial direction of each first outer middle sipe5A. The groove width W10of the shallow groove portion6is preferably 2 to 4 mm. The depth d1of the shallow groove portion6is preferably 1 to 3 mm.

As shown inFIG. 2, the outer middle land portion4A of the present embodiment has a shallow groove portion6that is formed at the outer side in the tire radial direction of each second outer middle sipe5C and that is the same as that at each first outer middle sipe5A. Such shallow groove portions6can improve the drainage performance of the outer middle land portion4A to improve the wet performance of the tire1.

FIG. 4is a cross-sectional view taken along a line B-B inFIG. 1. As shown inFIG. 4, each first outer middle sipe5A of the present embodiment has a depth d2at the outer crown circumferential groove3B side smaller than the maximum depth d3of the first outer middle sipe5A. Each second outer middle sipe5C of the present embodiment has a depth d4at the outer shoulder circumferential groove3A side smaller than the maximum depth d5of the second outer middle sipe5C. Such first outer middle sipes5A and such second outer middle sipes5C do not excessively reduce the stiffness of the outer middle land portion4A and can achieve both the steering stability and the ride comfort of the tire1.

As shown inFIG. 2, each second outer middle sipe5C of the present embodiment has a first chamfered portion7A formed at an acute corner portion formed by the second outer middle sipe5C and the outer shoulder circumferential groove3A. Such a first chamfered portion7A can inhibit uneven wear or chipping of the acute corner portion to improve the durability of the tire1.

FIG. 5is an enlarged view of the inner middle land portion4B and the inner shoulder land portion4D. As shown inFIG. 5, the inner middle land portion4B of the present embodiment has the above-described first inner middle sipes5B, and second inner middle sipes5D that extend from the inner crown circumferential groove3D toward the inner shoulder circumferential groove3C and that terminate within the inner middle land portion4B. Such an inner middle land portion4B continuously extends in the tire circumferential direction, and thus can maintain appropriate stiffness to achieve both the steering stability and the ride comfort of the tire1.

The angle θ2of each first inner middle sipe5B is preferably 15 to 25°. If the angle θ2is less than 15°, the stiffness of the inner middle land portion4B is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the angle θ2is greater than 25°, the stiffness of the inner middle land portion4B is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The angle θ4of each second inner middle sipe5D with respect to the tire axial direction is preferably 15 to 25°. If the angle θ4is less than 15°, the stiffness of the inner middle land portion4B is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the angle θ4is greater than 25°, the stiffness of the inner middle land portion4B is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The direction in which each first inner middle sipe5B of the present embodiment is tilted relative to the tire axial direction, and the direction in which each second inner middle sipe5D is tilted relative to the tire axial direction, are opposite to each other. Such first inner middle sipes5B and such second inner middle sipes5D serve to exhibit the same steering stability regardless of the rotation direction of the tire1.

As shown inFIG. 1, the direction in which each first outer middle sipe5A of the present embodiment is tilted relative to the tire axial direction, and the direction in which each first inner middle sipe5B is tilted relative to the tire axial direction, are opposite to each other. Such first outer middle sipes5A and such first inner middle sipes5B serve to exhibit the same steering stability regardless of the rotation direction of the tire1.

As shown inFIG. 5, the length L2in the tire axial direction of each first inner middle sipe5B is preferably 30% to 50% of the width W6of the inner middle land portion4B. If the length L2is less than 30% of the width W6, the stiffness of the inner middle land portion4B is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the length L2is greater than 50% of the width W6, the stiffness of the inner middle land portion4B is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The length L4in the tire axial direction of each second inner middle sipe5D is preferably 20% to 40% of the width W6of the inner middle land portion4B. If the length L4is less than 20% of the width W6, the stiffness of the inner middle land portion4B is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the length L4is greater than 40% of the width W6, the stiffness of the inner middle land portion4B is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The length L4of each second inner middle sipe5D is preferably smaller than the length L2of each first inner middle sipe5B. With such first inner middle sipes5B and such second inner middle sipes5D, when the tire1is mounted on the vehicle, the stiffness of the inner middle land portion4B is higher at the outer side of the vehicle than at the inner side of the vehicle, so that the self-aligning torque of the tire1can be generated more strongly. Thus, the steering stability of the tire1of the present embodiment can be further improved.

The inner middle land portion4B of the present embodiment has a shallow groove portion6that is formed at the outer side in the tire radial direction of each of the first inner middle sipes5B and the second inner middle sipes5D and that is the same as that at each first outer middle sipe5A. Such shallow groove portions6can improve the drainage performance of the inner middle land portion4B to improve the wet performance of the tire1.

As shown inFIG. 4, each first inner middle sipe5B of the present embodiment has a depth d6at the inner shoulder circumferential groove3C side smaller than the maximum depth d7of the first inner middle sipe5B. Each second inner middle sipe5D of the present embodiment has a depth d8at the inner crown circumferential groove3D side smaller than the maximum depth d9of the second inner middle sipe5D. Such first inner middle sipes5B and such second inner middle sipes5D do not excessively reduce the stiffness of the inner middle land portion4B and can achieve both the steering stability and the ride comfort of the tire1.

The maximum depth d7of each first inner middle sipe5B of the present embodiment is larger than the maximum depth d3of each first outer middle sipe5A. The maximum depth d3of each first outer middle sipe5A is preferably smaller than each of the maximum depths of the first inner middle sipes5B, the second outer middle sipes5C, and the second inner middle sipes5D. Such first outer middle sipes5A and such first inner middle sipes5B can make the stiffness of the outer middle land portion4A higher than the stiffness of the inner middle land portion4B, and thus the self-aligning torque of the tire1can be generated more strongly. Therefore, the steering stability of the tire1of the present embodiment can be further improved.

As shown inFIG. 5, each first inner middle sipe5B of the present embodiment has a second chamfered portion7B formed at an acute corner portion formed by the first inner middle sipe5B and the inner shoulder circumferential groove3C. Each second inner middle sipe5D of the present embodiment has a first chamfered portion7A formed at an acute corner portion formed by the second inner middle sipe5D and the inner crown circumferential groove3D. The first chamfered portion7A is preferably larger than the second chamfered portion7B.

Such a first chamfered portion7A and such a second chamfered portion7B each can inhibit uneven wear or chipping of the acute corner portion to improve the durability of the tire1. In addition, since the first chamfered portion7A is larger than the second chamfered portion7B, even if great external force act during turning, uneven wear or chipping of the acute corner portion can be inhibited.

As shown inFIG. 1, the total number N1of the first outer middle sipes5A of the present embodiment in the tire circumferential direction is smaller than the total number N2of the first inner middle sipes5B in the tire circumferential direction. With such an outer middle land portion4A and such an inner middle land portion4B, the stiffness of the outer middle land portion4A is higher than the stiffness of the inner middle land portion4B, and thus the self-aligning torque of the tire1can be generated more strongly. Therefore, the steering stability of the tire1of the present embodiment can be further improved.

The total number N1of the first outer middle sipes5A is preferably 60 to 70. If the total number N1is less than 60, the stiffness of the outer middle land portion4A is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the total number N1is greater than 70, the stiffness of the outer middle land portion4A is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The total number N2of the first inner middle sipes5B is preferably 70 to 80. If the total number N2is less than 70, the stiffness of the inner middle land portion4B is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the total number N2is greater than 80, the stiffness of the inner middle land portion4B is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The difference between the total number N1of the first outer middle sipes5A and the total number N2of the first inner middle sipes5B is preferably 5 to 15. If the difference between the total number N1and the total number N2is less than 5, the stiffness difference between the outer middle land portion4A and the inner middle land portion4B is decreased, so that the effect of improving the steering stability of the tire1may be reduced. If the difference between the total number N1and the total number N2is greater than 15, the stiffness difference between the outer middle land portion4A and the inner middle land portion4B is excessively increased, and the stiffness balance is reduced, so that the effect of improving the steering stability of the tire1may be reduced.

As shown inFIG. 2, the outer shoulder land portion4C of the present embodiment has outer shoulder sipes8A that extend from the outer shoulder circumferential groove3A toward the outer tread edge Teo and that terminate within the outer shoulder land portion4C. In addition, the outer shoulder land portion4C preferably has outer shoulder lateral grooves9A that extend from the outer tread edge Teo toward the outer shoulder circumferential groove3A and that terminate within the outer shoulder land portion4C. Such an outer shoulder land portion4C continuously extends in the tire circumferential direction, and thus can maintain appropriate stiffness to achieve both the steering stability and the ride comfort of the tire1.

The angle θ5of each outer shoulder sipe8A with respect to the tire axial direction is preferably 15 to 25°. If the angle θ5is less than 15°, the stiffness of the outer shoulder land portion4C is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the angle θ5is greater than 25°, the stiffness of the outer shoulder land portion4C is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The direction in which each outer shoulder sipe8A is tilted relative to the tire axial direction, and the direction in which each second outer middle sipe5C is tilted relative to the tire axial direction, are preferably the same. Such outer shoulder sipes8A, in cooperation with the second outer middle sipes5C, can reduce the stiffness difference between the outer shoulder land portion4C and the outer middle land portion4A to improve the ride comfort of the tire1.

The length L5in the tire axial direction of each outer shoulder sipe8A is preferably 20% to 40% of the width W7of the outer shoulder land portion4C. If the length L5is less than 20% of the width W7, the stiffness of the outer shoulder land portion4C is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the length L5is greater than 40% of the width W7, the stiffness of the outer shoulder land portion4C is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The outer shoulder sipes8A and the outer shoulder lateral grooves9A are preferably separated from each other in the tire axial direction. Such an outer shoulder land portion4C can enhance the stiffness at the outer side of the vehicle when the tire1is mounted on the vehicle, to allow the self-aligning torque of the tire1to be generated more strongly. Thus, the steering stability of the tire1of the present embodiment can be further improved.

The outer shoulder land portion4C of the present embodiment has a shallow groove portion6that is formed at the outer side in the tire radial direction of each outer shoulder sipe8A and that is the same as that at each first outer middle sipe5A. Such shallow groove portions6can improve the drainage performance of the outer shoulder land portion4C to improve the wet performance of the tire1.

As shown inFIG. 4, each outer shoulder sipe8A of the present embodiment has a depth d10at the outer shoulder circumferential groove3A side smaller than the maximum depth d11of the outer shoulder sipe8A. Such outer shoulder sipes8A do not excessively reduce the stiffness of the outer shoulder land portion4C and can achieve both the steering stability and the ride comfort of the tire1.

As shown inFIG. 2, each outer shoulder sipe8A of the present embodiment has a second chamfered portion7B formed at an acute corner portion formed by the outer shoulder sipe8A and the outer shoulder circumferential groove3A. Such a second chamfered portion7B can inhibit uneven wear or chipping of the acute corner portion to improve the durability of the tire1.

As shown inFIG. 5, the inner shoulder land portion4D of the present embodiment has inner shoulder sipes8B that extend from the inner shoulder circumferential groove3C toward the inner tread edge Tei and that terminate within the inner shoulder land portion4D. In addition, the inner shoulder land portion4D preferably has inner shoulder lateral grooves9B that extend from the inner tread edge Tei toward the inner shoulder circumferential groove3C and that terminate within the inner shoulder land portion4D. Such an inner shoulder land portion4D continuously extends in the tire circumferential direction, and thus can maintain appropriate stiffness to achieve both the steering stability and the ride comfort of the tire1.

The angle θ6of each inner shoulder sipe8B with respect to the tire axial direction is preferably 15 to 25°. If the angle θ6is less than 15°, the stiffness of the inner shoulder land portion4D is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the angle θ6is greater than 25°, the stiffness of the inner shoulder land portion4D is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The direction in which each inner shoulder sipe8B is tilted relative to the tire axial direction is preferably the same as the direction in which each first inner middle sipe5B is tilted relative to the tire axial direction. Such inner shoulder sipes8B, in cooperation with the first inner middle sipes5B, can reduce the stiffness difference between the inner shoulder land portion4D and the inner middle land portion4B to improve the ride comfort of the tire1.

The length L6in the tire axial direction of each inner shoulder sipe8B is preferably 50% to 70% of the width W8of the inner shoulder land portion4D. If the length L6is less than 50% of the width W8, the stiffness of the inner shoulder land portion4D is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the length L6is greater than 70% of the width W8, the stiffness of the inner shoulder land portion4D is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The length L6of each inner shoulder sipe8B is preferably larger than the length L5of each outer shoulder sipe8A. That is, the length L5of each outer shoulder sipe8A of the present embodiment is smaller than the length L6of each inner shoulder sipe8B. Such outer shoulder sipes8A and such inner shoulder sipes8B can make the stiffness of the outer middle land portion4A higher than the stiffness of the inner middle land portion4B, and thus the self-aligning torque of the tire1can be generated more strongly. Therefore, the steering stability of the tire1of the present embodiment can be further improved.

The inner shoulder sipes8B and the inner shoulder lateral grooves9B preferably overlap each other in the tire axial direction. Such an inner shoulder land portion4D can cause a stiffness difference between the outer side of the vehicle and the inner side of the vehicle when the tire1is mounted on the vehicle, to allow the self-aligning torque of the tire1to be generated more strongly. Thus, the steering stability of the tire1of the present embodiment can be further improved.

The inner shoulder land portion4D of the present embodiment has a shallow groove portion6that is formed at the outer side in the tire radial direction of each inner shoulder sipe8B and that is the same as that at each first outer middle sipe5A. Such shallow groove portions6can improve the drainage performance of the inner shoulder land portion4D to improve the wet performance of the tire1.

As shown inFIG. 4, each inner shoulder sipe8B of the present embodiment has a depth d12at the inner shoulder circumferential groove3C side smaller than the maximum depth d13of the inner shoulder sipe8B. Such inner shoulder sipes8B do not excessively reduce the stiffness of the inner shoulder land portion4D and can achieve both the steering stability and the ride comfort of the tire1.

As shown inFIG. 5, each inner shoulder sipe8B of the present embodiment has a second chamfered portion7B formed at an acute corner portion formed by the inner shoulder sipe8B and the inner shoulder circumferential groove3C. Such a second chamfered portion7B can inhibit uneven wear or chipping of the acute corner portion to improve the durability of the tire1.

FIG. 6is an enlarged view of the crown land portion4E. As shown inFIG. 6, the crown land portion4E of the present embodiment has outer crown sipes10A located at the outer side of the vehicle with respect to the tire equator C when the tire1is mounted on the vehicle, and inner crown sipes10B located at the inner side of the vehicle with respect to the tire equator C when the tire1is mounted on the vehicle, and the outer crown sipes10A and the inner crown sipes10B are alternately provided in the tire circumferential direction.

Each outer crown sipe10A preferably extends from the outer crown circumferential groove3B toward the tire equator C and terminates within the crown land portion4E without crossing the tire equator C. Each inner crown sipe10B preferably extends from the inner crown circumferential groove3D toward the tire equator C and terminates within the crown land portion4E without crossing the tire equator C. Such a crown land portion4E continuously extends in the tire circumferential direction, and thus can maintain appropriate stiffness to achieve both the steering stability and the ride comfort of the tire1.

The angle θ7of each outer crown sipe10A with respect to the tire axial direction is preferably 15 to 25°. If the angle θ7is less than 15°, the stiffness of the crown land portion4E is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the angle θ7is greater than 25°, the stiffness of the crown land portion4E is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The direction in which each outer crown sipe10A is tilted relative to the tire axial direction is preferably the same as the direction in which each first outer middle sipe5A is tilted relative to the tire axial direction. Such outer crown sipes10A, in cooperation with the first outer middle sipes5A, can reduce the stiffness difference between the crown land portion4E and the outer middle land portion4A to improve the ride comfort of the tire1.

The angle θ8of each inner crown sipe10B with respect to the tire axial direction is preferably 15 to 25°. If the angle θ8is less than 15°, the stiffness of the crown land portion4E is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the angle θ8is greater than 25°, the stiffness of the crown land portion4E is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The direction in which each inner crown sipe10B is tilted relative to the tire axial direction is preferably the same as the direction in which each second inner middle sipe5D is tilted relative to the tire axial direction. Each inner crown sipe10B and each second inner middle sipe5D of the present embodiment are located so as to form a straight line across the inner crown circumferential groove3D. Such inner crown sipes10B, in cooperation with the second inner middle sipes5D, can reduce the stiffness difference between the crown land portion4E and the inner middle land portion4B to improve the ride comfort of the tire1.

The length L7in the tire axial direction of each outer crown sipe10A is preferably 20% to 40% of the width W9of the crown land portion4E. If the length L7is less than 20% of the width W9, the stiffness of the crown land portion4E is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the length L7is greater than 40% of the width W9, the stiffness of the crown land portion4E is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The length L8in the tire axial direction of each inner crown sipe10B is preferably 20% to 40% of the width W9of the crown land portion4E. If the length L8is less than 20% of the width W9, the stiffness of the crown land portion4E is not appropriately reduced, so that the effect of improving the ride comfort of the tire1may be reduced. If the length L8is greater than 40% of the width W9, the stiffness of the crown land portion4E is excessively reduced, so that the effect of improving the steering stability of the tire1may be reduced.

The crown land portion4E of the present embodiment has a shallow groove portion6that is formed at the outer side in the tire radial direction of each of the outer crown sipes10A and the inner crown sipes10B and that is the same as that at each first outer middle sipe5A. Such shallow groove portions6can improve the drainage performance of the crown land portion4E to improve the wet performance of the tire1.

As shown inFIG. 4, each outer crown sipe10A and each inner crown sipe10B of the present embodiment have substantially uniform maximum depths d14and d15, respectively. The maximum depth d14of each outer crown sipe10A is preferably substantially equal to the maximum depth d15of each inner crown sipe10B. Such outer crown sipes10A and such inner crown sipes10B can reduce the stiffness of the crown land portion4E in a well-balanced manner and can achieve both the steering stability and the ride comfort of the tire1.

As shown inFIG. 6, each outer crown sipe10A of the present embodiment has a first chamfered portion7A formed at an acute corner portion formed by the outer crown sipe10A and the outer crown circumferential groove3B. In addition, each inner crown sipe10B of the present embodiment has a second chamfered portion7B formed at an acute corner portion formed by the inner crown sipe10B and the inner crown circumferential groove3D. In such a crown land portion4E, uneven wear or chipping of the acute corner portion can be inhibited, thereby improving the durability of the tire1.

Although the particularly preferred embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and various modifications can be made to practice the present invention.

EXAMPLES

Tires having the basic pattern inFIG. 1were produced as test tires on the basis of specifications in Tables 1 and 2. Each test tire was tested for steering stability and ride comfort. The common specifications and the test methods for all the test tires are as follows.

Test vehicle: a front-wheel-drive car having an engine displacement of 2000 cc Tire mounted position: all wheels

One test driver got on the test vehicle, drove the test vehicle on a dry road surface, and made sensory evaluation for steering stability achieved when the test vehicle was driven. The results are represented by indexes with the result of a comparative example being regarded as 100. A higher numerical value indicates that the steering stability is better.

One test driver got on the test vehicle, drove the test vehicle on a dry road surface, and made sensory evaluation for ride comfort achieved when the test vehicle was driven. The results are represented by indexes with the result of the comparative example being regarded as 100. A higher numerical value indicates that the ride comfort is better.

The results of the tests are shown in Tables 1 and 2.

As a result of the tests, it was confirmed that the tires of the examples achieve both steering stability and ride comfort at high levels in a well-balanced manner as compared to the comparative example.