tire

Abstract

To make driving stability and ride comfort performance compatible with each other.SOLUTION: A tire is provided, having a specified mounting direction with respect a vehicle and comprising a tread in which three or more circumferential grooves are formed. A first circumferential groove positioned in a vehicle outermost side among the circumferential grooves has the shallowest depth and the narrowest width. A first sipe and a second sipe are formed in a mediation land portion adjacent to the first circumferential groove. The first sipe extends from a circumferential groove positioned in a tire equator side to a tire width direction and terminates in the mediation land portion, and the second sipe extends from a circumferential groove positioned in a tire ground-contact end side to the tire width direction and terminates in the mediation land portion. The first sipe and the second sipe are formed in such a length that the portions thereof having depth more than 2.0 mm do not overlap each other in the tire circumferential direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tire, and more particularly to a tire having a specified mounting direction on a vehicle. [Background technology]

[0002] Conventionally, tires having a tread pattern asymmetrical with respect to the tire equator and having a specified mounting direction on a vehicle have been widely known. Patent Document 1 discloses a tire having a specified mounting direction on a vehicle, in which the circumferential groove formed in the tread and positioned furthest outward from the vehicle has a shallower groove depth and a narrower groove width than the other circumferential grooves.

[0003] The tread of the tire in Patent Document 1 has land portions defined by a plurality of circumferential grooves, and in each land portion, a plurality of lateral grooves extending in the tire width direction are formed asymmetrically with respect to the tire equator. Patent Document 1 describes the effect that it is possible to improve steering stability on dry roads while suppressing a decrease in steering stability on wet roads. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-56479 Summary of the Invention [Problem to be solved by the invention]

[0005] In the tire of Patent Document 1, the circumferential grooves located on the outer side of the vehicle are formed shallower to improve steering stability on dry roads. However, in this case, the rigidity of the area located on the outer side of the vehicle becomes too high, resulting in a decrease in ride comfort. It is not easy to achieve both steering stability and ride comfort in a tire, and the tire of Patent Document 1 still has room for improvement in terms of achieving both of these performances. [Means for solving the problem]

[0006] The tire of the present invention has a tread with three or more circumferential grooves formed therein and has a specified mounting direction relative to a vehicle. A first circumferential groove located furthest from the vehicle's outermost circumferential grooves is shallowest and narrowest of all the circumferential grooves. The tread has shoulder land portions and intermediate land portions defined by the first circumferential groove. The intermediate land portions have first and second sipes formed therein that are alternately arranged along the tire circumferential direction. The first sipes extend in the tire width direction from the circumferential groove located on the tire equator side and terminate within the intermediate land portion. The second sipes extend in the tire width direction from the circumferential groove located on the ground contact edge side and terminate within the intermediate land portion. The first and second sipes are formed to such lengths that their respective portions with a depth exceeding 2.0 mm do not overlap in the tire circumferential direction. [Effects of the Invention]

[0007] The tire according to the present invention is excellent in handling stability and realizes a good ride comfort. That is, the tire according to the present invention can achieve both handling stability and ride comfort performance. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a perspective view of a tire according to an embodiment, showing the internal structure of the tire. [Figure 2] 1 is a diagram showing a portion of a widthwise cross section of a tire that is an example of an embodiment. [Figure 3] 1 is a plan view of a tire according to an embodiment, showing a portion of a tread. [Figure 4] 2 is a plan view showing a part of the tread, with an enlarged view of a first region R1 located on the outer side of the tire equator relative to the vehicle. FIG. [Figure 5] 3 is a plan view showing a part of the tread, with an enlarged view of a second region R2 located on the inner side of the tire equator toward the vehicle. FIG. [Figure 6]FIG. 3 is a perspective view of a portion of a first shoulder rib and a first intermediate rib located in a first region, as viewed from the tire equator side. [Figure 7] FIG. 4 is a perspective view of a part of a second shoulder rib and a second intermediate rib located in a second region, as viewed from the tire equator side. [Figure 8] FIG. 4 is an enlarged view of a lateral groove formed in a first shoulder rib. [Figure 9] FIG. 5 is a cross-sectional view taken along line AA in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an example of an embodiment of a tire according to the present invention will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present invention is not limited to the following embodiment. Furthermore, the present invention includes configurations obtained by selectively combining the respective components of the multiple embodiments and modified examples described below.

[0010] FIG. 1 is a perspective view of a tire 1 according to an embodiment, illustrating the internal structure of the tire 1. As shown in FIG. 1, the tire 1 includes a tread 10, which is the portion that comes into contact with the road surface. The tread 10 has a plurality of circumferential grooves that are formed in an annular shape along the tire circumferential direction. Four circumferential grooves 20, 21, 22, and 23 are formed in the tread 10 and extend parallel to one another along the tire circumferential direction. In this embodiment, the widths of the circumferential grooves are different from one another. Furthermore, the groove depths of all the circumferential grooves are not the same.

[0011] The tire 1 is a tire for which the mounting direction relative to the vehicle is specified. The tread 10 has a tread pattern that is asymmetrical with respect to the tire equator CL, and the tire 1 is mounted in opposite directions on the right and left sides of the vehicle. The tire equator CL refers to a line along the tire circumferential direction that passes through the center in the tire width direction. As will be described in detail later, the tire 1 is mounted on a vehicle so that the first circumferential groove 20, which is the shallowest and narrowest of the four circumferential grooves, is located on the outer side of the vehicle relative to the tire equator CL.

[0012] In this specification, the terms "left and right" are used to describe the tire 1 and its components for ease of explanation. The "right side" of the tire 1 means the right side when the tire 1 mounted on a vehicle is viewed in the direction of travel (forward movement) of the vehicle, and the "left side" means the left side when the tire 1 mounted on a vehicle is viewed in the direction of travel of the vehicle. The drawings show the main tire rotation direction and arrows indicating left and right. The "main tire rotation direction" means the direction of rotation of the tire 1 when the vehicle on which the tire 1 is mounted moves forward.

[0013] The tire 1 includes a pair of sidewalls 11 that bulge outward most in the tire width direction, and a pair of beads 12 that are fixed to the rim of a wheel. The sidewalls 11 and the beads 12 are formed in an annular shape along the tire circumferential direction and constitute the side surfaces of the tire 1. The sidewalls 11 extend in the tire radial direction from both ends of the tread 10 in the width direction. The side ribs 13 protrude outward in the tire width direction and are formed in an annular shape along the tire circumferential direction.

[0014] The tire 1 is a pneumatic tire that is filled with air at a predetermined pressure. The tread 10 and the sidewall 11 are made of, for example, different types of rubber. The portions of the tire 1 from the vicinity of the contact edges E1, E2 to the left and right side ribs 13 are generally called shoulders or buttress portions. The shoulders may be made of the same rubber as the contact surface of the tread 10, or may be made of a different rubber.

[0015] In this specification, the terms "ground contact edges E1 and E2" refer to both ends in the tire width direction of the area that comes into contact with a flat road surface when an unused tire 1 is mounted on a standard rim and inflated to the standard internal pressure, and a load of 70% of the standard load at the standard internal pressure is applied.

[0016] Here, a "regular rim" is a rim specified by the tire standard, and is a "standard rim" for JATMA, a "design rim" for TRA, and a "measuring rim" for ETRTO. "Regular internal pressure" is the "maximum air pressure" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "INFLATION PRESSURE" for ETRTO. "Regular load" is the "maximum load capacity" for JATMA, the maximum value listed in the "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" table for TRA, and "LOAD CAPACITY" for ETRTO.

[0017] The tire 1 includes a carcass 14, a belt 15, and an inner liner 16. The carcass 14 is a cord layer coated with rubber, and forms the framework of the tire 1 that can withstand loads, impacts, air pressure, etc. The belt 15 is a reinforcing band disposed between the carcass 14 and the rubber that constitutes the tread 10. The belt 15 tightly fastens the carcass 14, thereby increasing the rigidity of the tire 1. The inner liner 16 is a rubber layer provided on the inner surface of the carcass 14, and maintains the air pressure of the tire 1. The bead 12 also includes a bead core 17 and a bead filler 18.

[0018] The tire 1 is preferably provided with a marking to indicate the mounting direction relative to the vehicle. A symbol called a serial number is generally provided on the side of the tire 1. The serial number includes information such as a size code, manufacturing date (manufacturing year and week), and manufacturing location (manufacturing factory code). The mounting direction of the tire 1 relative to the vehicle can be specified by providing a serial number only on the side of the tire 1 facing the outside of the vehicle (sidewall 11), or by providing different serial numbers on the side facing the outside and the side facing the inside of the vehicle. A specific example is to provide a manufacturing factory code and a size code on both sides of the tire 1, and provide the manufacturing year and week only on the side facing the outside of the vehicle.

[0019] The rubber constituting the tread 10 may have a multi-layer structure. The tread rubber has, for example, a two-layer structure consisting of a base rubber and a cap rubber constituting the surface layer of the tread 10. An example of a suitable hardness of the cap rubber is 65 to 75. In this case, the rigidity of the tread 10 is likely to increase, which is effective in improving the limit performance. The hardness of the rubber is measured using a type A durometer at a temperature of 23°C in accordance with JIS K6253-3. The limit performance generally means the performance under limit conditions where stable running conditions can be maintained.

[0020] The 300% modulus of the cap rubber is, for example, 15 or less. In this case, the rigidity of the tread 10 is likely to increase, which is effective in improving marginal performance. There is no particular restriction on the lower limit of the 300% modulus of the cap rubber, but one example is 10. The 300% modulus of the rubber is measured in accordance with JIS K6301 under a temperature condition of 23°C. When the tread rubber has a single-layer structure, it is preferable that the physical properties of the entire tread rubber satisfy the above conditions.

[0021] The tread 10 has land portions defined by four circumferential grooves. The land portions are protrusions that protrude from a reference plane of the tread 10 toward the tire radially outward. The reference plane is an imaginary plane along the bottom surface of the deepest circumferential groove, and refers to the outer circumferential surface of the tread 10 when no land portions exist. The tread 10 has four circumferential grooves formed in this order from the outside of the vehicle: circumferential grooves 20, 21, 22, and 23. In other words, the tire 1 needs to be mounted on a vehicle so that the circumferential groove 20 is located on the outside of the vehicle and the circumferential groove 23 is located on the inside of the vehicle.

[0022] The tread 10 has the above-mentioned land portions, which are a center rib 30, shoulder ribs 40, 50, and intermediate ribs 60, 70. The tread 10 does not have grooves that cross each land portion in the width direction, and each land portion is formed in a rib shape that is continuous in the tire circumferential direction. Forming each land portion in a rib shape suppresses collapse of the land portion (especially lateral deformation) during high-speed cornering, contributing to improved limit performance.

[0023] The center rib 30 is disposed in the center of the tread 10 in the width direction. The shoulder ribs 40, 50 are disposed on both sides of the tread 10 in the width direction. The ground contact edge E1 is located at the first shoulder rib 40, and the ground contact edge E2 is located at the second shoulder rib 50. Parts of the shoulder ribs 40, 50 extend beyond the ground contact edges E1, E2 to the side ribs 13. The first intermediate rib 60 is disposed between the center rib 30 and the shoulder rib 40, and the second intermediate rib 70 is disposed between the center rib 30 and the shoulder rib 50.

[0024] The center rib 30 is a land portion sandwiched between circumferential grooves 21, 22 formed parallel to each other along the tire circumferential direction. The center rib 30 is separated from the intermediate rib 60 by the circumferential groove 21, and from the intermediate rib 70 by the circumferential groove 22. The center rib 30 is formed on the tire equator CL. Hereinafter, in the tread 10, the region from the tire equator CL to the ground contact edge E1 located on the outer side of the vehicle is referred to as a first region R1, and the region from the tire equator CL to the ground contact edge E2 located on the inner side of the vehicle is referred to as a second region R2.

[0025] The shoulder rib 40 is formed in a first region R1, which is a region on the ground contact edge E1 side of the tread 10, and is separated from the intermediate rib 60 by a circumferential groove 20. The shoulder rib 50 is formed in a second region R2, which is a region on the ground contact edge E2 side of the tread 10, and is separated from the intermediate rib 70 by a circumferential groove 23. The shoulder ribs 40, 50 have, for example, approximately the same width. Alternatively, the width of the shoulder rib 40 may be slightly wider than the width of the shoulder rib 50.

[0026] The intermediate rib 60 is disposed adjacent to the shoulder rib 40 across the circumferential groove 20 and adjacent to the center rib 30 across the circumferential groove 21 in the first region R1 of the tread 10. The intermediate rib 70 is disposed adjacent to the center rib 30 across the circumferential groove 22 and adjacent to the shoulder rib 50 across the circumferential groove 23 in the second region R2 of the tread 10. The intermediate ribs 60, 70 have, for example, approximately the same width. Alternatively, the width of the intermediate rib 60 may be slightly wider than the width of the intermediate rib 70.

[0027] Each of the ribs has a plurality of lateral grooves or sipes extending in the tire width direction. The shoulder rib 40 has a lateral groove 41, and the shoulder rib 50 has a lateral groove 51. The ends of the lateral grooves 41, 51 on the tire equator CL side are preferably located within the shoulder rib and are not connected to the circumferential grooves. The center rib 30 and the intermediate ribs 60, 70 have sipes connected to the circumferential grooves. The sipes are arranged in a staggered pattern in each rib along the tire circumferential direction.

[0028] Both lateral grooves and sipes are grooves that extend in the tire width direction, but lateral grooves are wide grooves and sipes are thin grooves. They are generally recognized as different. In this specification, a groove with a groove width of 1.0 mm or less, not including the tapered surface described below, is defined as a sipe, and a groove with a groove width of more than 1.0 mm is defined as a lateral groove. Groove width refers to the shortest distance between opposing groove walls at any position along the length of the lateral groove or sipe. Hereinafter, unless otherwise specified, the width of a lateral groove and a sipe refers to their maximum value (maximum width).

[0029] The ratio of the groove area to the contact area of ​​the tread 10 is not particularly limited, but a suitable example is 33 to 40%. Ensuring a large contact area is effective in improving braking performance. The groove area is the area of ​​the groove in the tread profile surface α along the contact surface of the tread 10, i.e., the area at the groove opening, and includes the areas of the circumferential grooves, lateral grooves, and sipes. The groove opening refers to the upper end opening of the groove facing outward in the tire radial direction.

[0030] Hereinafter, the four circumferential grooves formed in the tread 10 will be described in detail with reference to Fig. 2. Fig. 2 is a diagram showing a part of a widthwise cross section of the tire 1. In Fig. 2, the carcass 14 and the like are not shown.

[0031] As shown in Figure 2, the first circumferential groove 20, which is located furthest from the vehicle's outer side among the four circumferential grooves, has the shallowest depth and narrowest width of all the circumferential grooves. By forming the circumferential groove 20 shallow and narrow, the rigidity of the tread 10 can be increased in the first region R1 of the tread 10 located on the vehicle's outer side, improving the limit performance of steering stability on dry roads. The width W2 of the second circumferential groove 21 formed in the first region R1 of the tread 10 is wider than the width W1 of the circumferential groove 20, but is narrower than the widths W3 and W4 of the third and fourth circumferential grooves 22 and 23 formed in the second region R2 of the tread 10.

[0032] The tread 10 has two circumferential grooves each in the first region R1 and the second region R2, but the total area of ​​the circumferential grooves in a plan view of the tread 10 is smaller in the first region R1 than in the second region R2. The ground contact area of ​​the first region R1 is larger than the ground contact area of ​​the second region R2. The total volume of the circumferential grooves is also smaller in the first region R1 than in the second region R2. In this case, the limit performance of steering stability on dry roads is more effectively improved. The tire 1 is suitable for tires (UHP tires) for high-power, high-performance cars that require high limit performance.

[0033] If the rigidity of the first region R1 is increased, it becomes difficult for the tire to absorb impacts from the road surface, and it is expected that the ride quality will deteriorate, especially when driving on rough roads. As will be described in detail later, the tire 1 achieves both steering stability and ride quality by devising the sipe shape of the intermediate rib 60 adjacent to the circumferential groove 20.

[0034] In this embodiment, the three circumferential grooves 21, 22, and 23, excluding the circumferential groove 20, have approximately the same depth. In this specification, groove depth means the length from the tread profile surface α to the groove bottom along the contact patch of the tread 10. The groove bottoms of the circumferential grooves 21, 22, and 23 are formed to be approximately flat. The groove walls of the circumferential grooves 21, 22, and 23 are formed at an angle nearly perpendicular to the profile surface α, but are inclined so that the groove width slightly narrows toward the groove bottom. Each groove wall is slightly curved near the groove bottom.

[0035] The circumferential grooves 20 have bottoms that are curved so as to convexly extend radially inward. The groove bottoms of the circumferential grooves 20 have little or no flat regions. The groove walls 20a of the circumferential grooves 20 on the tire equator CL side have a smaller inclination angle with respect to the profile surface α than the groove walls of the other circumferential grooves. On the other hand, the groove walls of the circumferential grooves 20 on the ground contact edge E1 side have a larger angle with respect to the profile surface α than the groove walls 20a and the groove walls of the other circumferential grooves, and are formed substantially perpendicular to the profile surface α near the groove opening. That is, the depth of the circumferential groove 20 changes gradually from the upper end of the groove wall toward the groove bottom on the tire equator CL side and changes sharply on the ground contact edge E1 side.

[0036] The depth D1 of the circumferential groove 20 is preferably 50 to 80% of the depth of the deepest circumferential groove among the circumferential grooves. If the depth D1 is within this range, it is possible to effectively improve the steering stability on dry roads while ensuring good drainage performance and ride comfort, provided that other configurations are appropriately controlled. In this embodiment, the depths of the circumferential grooves 21, 22, and 23 other than the circumferential groove 20 are approximately the same, but the depths D2 and D3 of the circumferential grooves 21 and 22 may be substantially the same, and the depth D4 of the circumferential groove 23 may be slightly shallower than the depths D2 and D3.

[0037] The depth D1 of the circumferential groove 20 is preferably 50 to 80% of the depths D2 and D3 of the circumferential grooves 21 and 22. The depth D1 is more preferably 55 to 70% of the depths D2 and D3, and the relationship between the depths of the four circumferential grooves is, for example, <D4≦D2=D3である。

[0038] An example of the depth D1 of the circumferential groove 20 is 4.5 mm. An example of the depth D3 of the circumferential groove 22 is 7.6 mm. Unless otherwise specified, the depth of a circumferential groove refers to the depth of its deepest portion. Furthermore, unless otherwise specified, the width of a circumferential groove refers to the width at the groove opening, in other words, the length along the tire width direction on the profile surface α. In this embodiment, the width of each circumferential groove is approximately constant, and the width of each rib is also approximately constant.

[0039] The width W1 of the circumferential groove 20 is preferably 60% or less of the width W3 of the circumferential groove 22, which is the widest among the circumferential grooves. The width W1 of the circumferential groove 20 is more preferably 50% or less of the width W3 of the circumferential groove 22, and particularly preferably 30 to 50% of the width W3. If the widths W1 and W3 have such a relationship, it is possible to effectively improve steering stability on dry roads while ensuring good drainage performance and ride comfort, provided that other configurations are appropriately controlled. An example of the width W1 is 7.0 to 8.0 mm.

[0040] In this embodiment, on the upper ends of the groove walls 20a of the circumferential groove 20, the groove wall on the tire equator CL side of the circumferential groove 21, and the groove wall on the tire equator CL side of the circumferential groove 23, a region Rz inclined at an angle of 60° or less with respect to the profile surface α is formed. In other words, the region Rz is formed along the tire circumferential direction at the edges on the ground contact end E1 side of the center rib 30 and the intermediate rib 60, and at the edges on the ground contact end E2 side of the intermediate rib 70. The region Rz is formed, for example, within a depth range of 20% or less of the depth of the circumferential groove from the upper ends of the respective groove walls, at an inclination angle of 20 to 50° with respect to the profile surface α.

[0041] The width W2 of the circumferential groove 21 is larger than the width W1 of the circumferential groove 20 and smaller than the widths W3 and W4 of the circumferential grooves 22 and 23. The width W2 is preferably 1.3 to 2.5 times the width W1 of the circumferential groove 20, and more preferably 1.5 to 2.2 times. The width W2 is preferably 55 to 90% of the width W3 of the circumferential groove 22, and more preferably 65 to 80%. Also, the width W4 of the circumferential groove 23 is larger than the widths W1 and W2 of the circumferential grooves 20 and 21 and smaller than the width W3 of the circumferential groove 22. The width W4 of the circumferential groove 23 is, for example, 1.1 to 1.5 times the width W2 of the circumferential groove 21 and 75 to 95% of the width W3 of the circumferential groove 22.

[0042] That is, the relationship between the widths of the four circumferential grooves is W1 < W2 < W4 < W3. In this case, it becomes easy to achieve both good drainage performance and good handling stability and riding comfort performance. Note that no inclined surface like the region Rz is formed on the groove walls of the circumferential groove 22.

[0043] In the tread 10, as described above, the sum of the widths W1 and W2 of the circumferential grooves 20 and 21 formed in the first region R1 is smaller than the sum of the widths W3 and W4 of the circumferential grooves 22 and 23 formed in the second region R2. For this reason, the center in the width direction of the center rib 30 is located closer to the ground contact end E1 than the tire equator CL. Also, the distance from the intermediate rib 60 to the ground contact end E1 in the first region R1 is slightly shorter than the distance from the intermediate rib 70 to the ground contact end E2 in the second region R2.

[0044] The widths of the center rib 30 and the intermediate ribs 60, 70 may be the same or different. In this embodiment, the rib width refers to the length of the contact surface of the rib along the tire width direction. The width of the intermediate rib 60 is, for example, slightly larger than the widths of the center rib 30 and the intermediate rib 70. The center rib 30 and the intermediate rib 70 have approximately the same width.

[0045] The lateral grooves and sipes formed in each land portion will be described in detail below with reference to Figures 3 to 5. Figure 3 is a plan view showing a portion of the tread 10. Figure 4 is an enlarged plan view of the first region R1, and Figure 5 is an enlarged plan view of the second region R2. In Figure 3, dot hatching is applied to the upper surface of each land portion (the same applies to Figure 8).

[0046] As shown in FIGS. 3 to 5, sipes 31, 32 are formed in the center rib 30. The first sipe 31 extends in the tire width direction from the circumferential groove 21 located on the ground contact edge E1 side and terminates within the center rib 30. The second sipe 32 extends in the tire width direction from the circumferential groove 22 located on the ground contact edge E2 side and terminates within the center rib 30. That is, the first ends (hereinafter sometimes referred to as "starting ends") of the sipes 31, 32 in the length direction communicate with the circumferential groove, and the second ends (hereinafter sometimes referred to as "ending ends") are located within the center rib 30. The sipes 31, 32 are inclined with respect to the tire width direction so that the right ends (facing the vehicle's traveling direction) are located further forward in the tire's main rotational direction than the left ends.

[0047] The sipes 31 are formed with a length extending from the circumferential groove 21 beyond the tire equator CL, and the sipes 32 are formed with a length extending from the circumferential groove 22 beyond the tire equator CL. The sipes 31, 32 are alternately arranged along the tire circumferential direction and extend in substantially the same direction at substantially the same inclination angle with respect to the tire width direction. The sipes 31, 32 are formed at substantially equal intervals along the tire circumferential direction and in the same number. In this embodiment, the center rib 30 and the intermediate ribs 60, 70 each have the same number of sipes.

[0048] The length of the sipe 31 is longer than the length of the sipe 32, for example, 2 to 4 times or 2 to 3 times the length of the sipe 32. Unless otherwise specified, the length of a sipe refers to both the length along the sipe from the start to the end of the sipe in a plan view of the tread 10, and the length along the tire width direction (the same applies to the length of a lateral groove). The depth of the sipes 31, 32 is shallower near the end, for example, 2.0 mm or less. It is preferable that the portions of the sipes 31, 32 that are deeper than 2.0 mm do not overlap in the tire circumferential direction.

[0049] The depth of the sipe 31 is preferably shallower than the depth of the circumferential groove 21. Similarly, the depth of the sipe 32 is preferably shallower than the depth of the circumferential groove 22. In this embodiment, the depths of the sipes 31, 32 are, for example, substantially the same and constant over the entire length of the sipe. The depth of the sipes 31, 32 is preferably 70 to 95% of the depth of the circumferential grooves 21, 22, except for shallower portions near the terminal ends. An example of the depth of the sipes 31, 32 (depth at the deepest portion) is 5.8 mm.

[0050] The groove walls of the sipes 31 and 32 preferably have tapered surfaces, which are inclined regions so that the groove width increases toward the sipe opening, within a depth range of 2.0 mm from the opening of each sipe. In this embodiment, the sipe 31 has a first tapered surface 31A and a second tapered surface 31B, and the sipe 32 has a tapered surface 32A. That is, the tapered surfaces are formed on both sides of the sipe 31 in the width direction, and the tapered surfaces are formed on only one side of the sipe 32 in the width direction. Each tapered surface is formed, for example, over a depth range of 0.8 to 2.0 mm from the sipe opening.

[0051] The first tapered surface 31A is formed on a first groove wall along the length direction of the sipe 31, and the second tapered surface 31B is formed on a second groove wall along the length direction of the sipe 31. The first and second groove walls are disposed opposite each other in the tire circumferential direction. The first groove wall of the sipe 31 extends longer toward the circumferential groove 22 than the second groove wall, and the first tapered surface 31A is longer than the second tapered surface 31B. Each tapered surface is formed from a position tangent to the circumferential groove 21, but the second tapered surface 31B does not reach the tire equator CL. On the other hand, the first tapered surface 31A extends beyond the tire equator CL toward the circumferential groove 22.

[0052] The tapered surface 32A is formed on a first groove wall along the longitudinal direction of the sipe 32. The tapered surface 32A is arranged on the same side as a first tapered surface 51A of the lateral groove 51 and a tapered surface 72A of the sipe 72, which will be described later. A second groove wall of the sipe 32 facing the first groove wall is formed substantially perpendicular to the profile surface α. The tapered surface 32A extends from the circumferential groove 22 toward the circumferential groove 21, beyond the tire equator CL, and overlaps with the first tapered surface 31A of the sipe 31 in the tire circumferential direction.

[0053] The two tapered surfaces of the sipe 31 may have the same inclination angle relative to the profile surface α and may be formed with the same width. However, in this embodiment, the inclination angle of the first tapered surface 31A is slightly smaller than the inclination angle of the second tapered surface 31B. The maximum width of the first tapered surface 31A is slightly larger than the maximum width of the second tapered surface 31B. Each tapered surface has bent portions 33A and 33B in the middle of its length, and the orientation of the tapered surface changes slightly at the bent portions 33A and 33B. The width of each tapered surface also changes at the bent portions 33A and 33B. From the bent portions 33A and 33B toward the end of the sipe 31, the width of each tapered surface gradually decreases.

[0054] The maximum width of first tapered surface 31A is, for example, 1.05 to 1.30 times the maximum width of second tapered surface 31B. At the portion where the width of each tapered surface is greatest, the inclination angle of first tapered surface 31A with respect to profile surface α is preferably 15 to 60°, and the inclination angle of second tapered surface 31B with respect to profile surface α is preferably 15 to 60°. The inclination angle of each tapered surface with respect to profile surface α may be approximately constant over the entire length of the tapered surface.

[0055] The first tapered surface 31A has a maximum width in the range from the start of the sipe 31 to the bend 33A. On the other hand, the second tapered surface 31B has a maximum width at the bend 33B. The bend 33B is located closer to the tire equator CL than the bend 33A. The relationship between the inclination angle, width, etc. of the tapered surface of the sipe 31 and the tapered surface of the sipe 32 is not particularly limited. The maximum width of the tapered surface 32A of the sipe 32 is, for example, approximately the same as the maximum width of the second tapered surface 31B. Furthermore, the inclination angle of the tapered surface 32A with respect to the profile surface α may be the same as the inclination angle of the second tapered surface 31B with respect to the profile surface α.

[0056] Each tapered surface of the center rib 30, together with the tapered surfaces of the other land portions, contributes to the distribution of ground pressure. A configuration in which the sipe 31 has two tapered surfaces and the sipe 32 has one tapered surface, is effective in distributing and reducing ground pressure while ensuring a large contact area, thereby improving braking performance. The configuration of the center rib 30 has a significant impact on braking performance, particularly during straight-line driving, so the shape, size, positional relationship, etc. of each tapered surface of the center rib 30 described above contributes greatly to improving braking performance. In this embodiment, the configuration of the tapered surface of each land portion is designed to enable the tread 10 as a whole to function more effectively, from the perspective of improving braking performance.

[0057] The widths of the multiple sipes 31 may be slightly different from one another. For example, the widths of adjacent sipes 31 in the tire circumferential direction may be different, and sipes 31 having two to six different widths may be formed in the center rib 30. The two to six different sipes 31 may be arranged so that the widths gradually increase along the tire circumferential direction. The widths of the sipes 32, sipes in other ribs, and lateral grooves 41, 51 adjacent to one another in the tire circumferential direction may also be different.

[0058] The sipes formed on the intermediate ribs 60, 70 will be described in detail below with reference to Figures 3 to 5 as well as Figures 6 and 7 as appropriate. Figure 6 is a perspective view of a portion of the first intermediate rib 60 and the first shoulder rib 40 located in the first region R1, as viewed from the tire equator CL side. Figure 7 is a perspective view of a portion of the second intermediate rib 70 and the second shoulder rib 50 located in the second region R2, as viewed from the tire equator CL side.

[0059] As shown in Figures 3 and 4, sipes 61, 62 are formed in the intermediate rib 60 adjacent to the circumferential groove 20. The first sipe 61 extends in the tire width direction from the circumferential groove 21 located on the tire equator CL side and terminates within the intermediate rib 60. The second sipe 62 extends in the tire width direction from the circumferential groove 20 located on the ground contact edge E1 side and terminates within the intermediate rib 60. That is, the first ends of the sipes 61, 62 in the length direction communicate with the circumferential groove and the second ends are located within the intermediate rib 60. The sipe 61 extending from the tire equator CL side is longer than the sipe 62 extending from the ground contact edge E1 side.

[0060] The sipes 61, 62 are alternately arranged along the tire circumferential direction and extend in approximately the same direction at approximately the same inclination angle relative to the tire width direction. The same number of sipes 61, 62 are arranged at approximately equal intervals along the tire circumferential direction. As will be described in detail later, the sipes 61, 62 are formed to a length such that the portions of each sipe exceeding a depth of 2.0 mm do not overlap in the tire circumferential direction. By forming the sipes with such lengths on both sides of the intermediate rib 60 in the width direction, deformation of the intermediate rib 60 during high-speed cornering and braking can be suppressed, while good ride comfort can be ensured in the tire 1 having high rigidity in the first region R1. In other words, handling stability (limit performance) and ride comfort can be effectively achieved at the same time.

[0061] As shown in FIGS. 3 and 5, sipes 71 and 72 are formed in the intermediate rib 70 in the second region R2. The first sipe 71 extends in the tire width direction from the circumferential groove 22 located on the tire equator CL side and terminates within the intermediate rib 70. The second sipe 72 extends in the tire width direction from the circumferential groove 23 located on the ground contact edge E2 side and terminates within the intermediate rib 70. That is, the first ends of the sipes 71 and 72 in the length direction communicate with the circumferential groove, and the second ends are located within the intermediate rib 70. The sipe 71 extending from the tire equator CL side is longer than the sipe 72 extending from the ground contact edge E2 side. The sipe 71 has a bent portion 71C that is bent significantly.

[0062] The sipes 71, 72 are arranged alternately along the tire circumferential direction, similar to the sipes 61, 62. The same number of sipes 71, 72 are arranged at approximately equal intervals along the tire circumferential direction. In this embodiment, the sipe 72 has approximately the same inclination angle with respect to the tire width direction as the sipe 61 and the sipe 31 of the center rib 30, and is formed so as to be located on an extension of the sipes 31, 61. In other words, the sipes 31, 61, 72 are arranged on approximately the same straight line. The sipe 71 is bent, but a portion of the sipe 71 is formed so as to be located on an extension of the sipe 62 and the sipe 32 of the center rib 30.

[0063] The groove walls of each sipe in the intermediate ribs 60 and 70 have tapered surfaces that are inclined from the opening of each sipe to a depth of 2.0 mm so that the groove width increases toward the opening. The tapered surfaces are formed on both sides of the width of each sipe for sipes 61 and 71, and on only one side of the width of each sipe for sipes 62 and 72. Each tapered surface is formed, for example, over a depth range of 0.8 to 2.0 mm from the opening of the sipe.

[0064] The tapered surfaces of the sipes 62, 72 are formed on the intermediate rib 60 on a first side of the sipe 62 in the tire circumferential direction, and on the intermediate rib 70 on a second side of the sipe 72 in the tire circumferential direction. In a tire 1 mounted on the left side of a vehicle, the tapered surface 62A of the sipe 62 is formed on the groove wall of the sipe 62 that is on the rear side in the main tire rotation direction, and the tapered surface 72A of the sipe 72 is formed on the groove wall of the sipe 72 that is on the front side in the main tire rotation direction. In this case, the ground contact pressure can be distributed in a balanced manner throughout the tread 10, resulting in more significant improvements in braking performance and handling stability.

[0065] As shown in FIGS. 4 and 6, the sipe 61 formed in the intermediate rib 60 has a first tapered surface 61A and a second tapered surface 61B. As described above, the sipe 62 has a tapered surface 62A. The first tapered surface 61A is formed on a first groove wall along the longitudinal direction of the sipe 61, and the second tapered surface 61B is formed on a second groove wall facing the first groove wall along the longitudinal direction of the sipe 61. The first groove wall of the sipe 61 extends longer toward the circumferential groove 20 than the second groove wall, and the first tapered surface 61A is longer than the second tapered surface 61B. The tapered surfaces of both sipes 61, 62 narrow from the starting end to the terminal end of the sipe.

[0066] The two tapered surfaces of the sipe 61 may have different inclination angles relative to the profile surface α, but in this embodiment, they have approximately the same inclination angle. Furthermore, the maximum widths of the two tapered surfaces are approximately the same. At the portion where each tapered surface has its maximum width, the inclination angle of each tapered surface relative to the profile surface α is preferably 15 to 60°. The inclination angles of the first tapered surface 61A and the second tapered surface 61B relative to the profile surface α may be approximately constant over the entire length of the tapered surfaces.

[0067] The tapered surface 62A of the sipe 62 is formed on a first groove wall along the length direction of the sipe 62. The tapered surface 62A is arranged on the same side as a first tapered surface 41A of the lateral groove 41, which will be described later. A second groove wall of the sipe 62 facing the first groove wall is formed approximately perpendicular to the profile surface α. The relationship between the tapered surface 62A and the tapered surface of the sipe 61, such as the inclination angle and width, is not particularly limited. The maximum width of the tapered surface 62A is, for example, larger than the maximum width of the tapered surface of the sipe 61. In a tire 1 mounted on the left side of a vehicle, the first groove wall of the sipes 61, 62 is located on the rear side of the sipe 61 in the main rotation direction of the tire.

[0068] As described above, the sipe 61 is longer than the sipe 62. The length of the sipe 61 is preferably 1.1 to 2.5 times, and more preferably 1.2 to 2.0 times, the length of the sipe 62. The sipes 61, 62 are formed so that their respective portions having a depth exceeding 2.0 mm (hereinafter referred to as "first portions") do not overlap in the tire circumferential direction. In the tire width direction, a predetermined interval S1 exists between the end of the first portion of the sipe 61 and the end of the first portion of the sipe 62. The interval S1 is substantially equal to the distance between the groove bottom of the sipe 61 and the groove bottom of the sipe 62 in the tire width direction. The sipes 61, 62 are shallower near their ends, for example, to a depth of 2.0 mm or less (hereinafter referred to as "second portions").

[0069] The total length of the sipes 61, 62 along the tire width direction is preferably 60 to 90% of the width of the intermediate rib 60, and more preferably 70 to 80%. That is, the spacing S1 is preferably 10 to 40% of the width of the intermediate rib 60, and more preferably 20 to 30%. In this case, the limit performance of steering stability on dry roads can be more effectively improved while maintaining good ride comfort. For example, the length of the sipe 61 is 50 to 65% or more of the width of the intermediate rib 60, and the length of the sipe 62 is 30 to 45% or more of the width of the intermediate rib 60. The second portions of the sipes 61, 62 may overlap in the tire circumferential direction, but in this embodiment, the entire sipes, including the second portions, are formed to have lengths such that they do not overlap in the tire circumferential direction.

[0070] The depth of the sipe 61 is preferably shallower than the depth of the circumferential groove 21. The depth of the sipe 62 is preferably shallower than the depth of the circumferential groove 20. The sipes 61, 62 can have the same depth, but in this embodiment, the depth D1 of the circumferential groove 20 is < the depth D2 of the circumferential groove 21, so the depth of the sipe 61 is greater than the depth of the sipe 62. The depth of the sipe 61 (first portion) is, for example, 70 to 95% of the depth D2 of the circumferential groove 21. The depth of the sipe 62 (first portion) is, for example, 70 to 95% of the depth D1 of the circumferential groove 20.

[0071] As shown in FIGS. 5 and 7, the sipe 71 formed in the intermediate rib 70 has a first tapered surface 71A and a second tapered surface 71B, and the sipe 72 has a tapered surface 72A. The first tapered surface 71A is formed on a first groove wall along the longitudinal direction of the sipe 71, and the second tapered surface 71B is formed on a second groove wall along the longitudinal direction of the sipe 71 that faces the first groove wall. The sipe 71 has a large curve in the middle portion so as to be convex in the tire circumferential direction. The length of the sipe 71 along the tire width direction and the length along the sipe are both longer than those of the sipe 72.

[0072] The sipe 71 has a bent portion 71C, and for example, the first and second groove walls are bent at an angle of 90 to 120° at the bent portion 71C. The bent portion 71C is formed in the longitudinal center portion of the sipe 71 or in its vicinity. The sipe 71 is gently curved so that the portion from the bent portion 71C to the terminal end is convex toward the starting end of the sipe 71. The sipe 71 is formed so that it is convex in the tire circumferential direction in the same direction as the direction in which a recess 53 of a shoulder rib 50, which will be described later, contracts in width.

[0073] The two tapered surfaces of the sipe 71 may have the same inclination angle with respect to the profile surface α and may be formed with the same width, but in this embodiment, the inclination angles and widths are different from each other. The relationship between the inclination angles and widths of the two tapered surfaces changes between the range from the start of the sipe 71 to the bend 71C and the range from the bend 71C to the end of the sipe 71. In other words, the inclination angles and widths of the tapered surfaces change significantly at the bend 71C.

[0074] In the range from the start of the sipe 71 to the bend 71C, the inclination angle of the first tapered surface 71A with respect to the profile surface α is smaller than the inclination angle of the second tapered surface 71B with respect to the profile surface α, and the maximum width of the first tapered surface 71A is larger than the maximum width of the second tapered surface 71B. The width of each tapered surface gradually decreases from the start of the sipe 71 toward the bend 71C.

[0075] In the range from bend 71C to the terminal end of sipe 71, the inclination angle of first tapered surface 71A with respect to profile surface α is greater than the inclination angle of second tapered surface 71B with respect to profile surface α, and the maximum width of first tapered surface 71A is smaller than the maximum width of second tapered surface 71B. In a predetermined range from the terminal end of sipe 71, the depth of sipe 71 becomes shallower, and first tapered surface 71A and second tapered surface 71B are connected.

[0076] The tapered surface 72A of the sipe 72 is formed on a first groove wall that extends along the length of the sipe 72. The second groove wall of the sipe 72 that faces the first groove wall is formed substantially perpendicular to the profile surface α. The relationship between the inclination angle, width, etc. of the tapered surface 72A and the two tapered surfaces of the sipe 71 is not particularly limited, but in this embodiment, the maximum width of the tapered surface 72A is greater than the maximum width of the two tapered surfaces of the sipe 71. In a tire 1 mounted on the left side of a vehicle, the first groove walls of the sipes 71, 72 are located forward of the sipe 71 in the main rotational direction of the tire.

[0077] Like the sipes of the intermediate rib 60, the sipes 71, 72 have portions (first portions) that are greater than 2.0 mm in depth that do not overlap in the tire circumferential direction. A gap S2 exists between the end of the first portion of the sipe 71 and the end of the first portion of the sipe 72 in the tire width direction. The gap S2 is the distance in the tire width direction between the ends of the first portions (groove bottoms) of the sipes 71, 72. The sipes 71, 72 are shallower near the ends, for example, a depth of 2.0 mm or less.

[0078] The portions (second portions) of the sipes 71, 72 where the depth is shallower than 2.0 mm may overlap in the tire circumferential direction. The relationship between the intervals S1, S2 of the intermediate ribs 60, 70 is not particularly limited, but in this embodiment, the interval S1 is greater than the interval S2. The total length of each groove bottom of the sipes 71, 72 along the tire width direction is preferably 80 to 99% of the width of the intermediate rib 70. In other words, the interval S2 is preferably 1 to 20% of the width of the intermediate rib 70.

[0079] The depth of the sipe 71 is preferably shallower than the depth of the circumferential groove 22. Similarly, the depth of the sipe 72 is preferably shallower than the depth of the circumferential groove 23. In this embodiment, the depths of the sipes 71, 72 are, for example, substantially the same and constant over the entire length of the sipe. The depth of the sipes 71, 72 (first portion) is preferably 70 to 95% of the depths D2, D3 of the circumferential grooves 21, 22.

[0080] The configuration of each sipe formed on the intermediate ribs 60, 70, particularly the sipes 61, 62 of the intermediate rib 60, effectively improves ride comfort while suppressing large deformation of the rib, for example, during high-speed cornering and braking. The first region R1 of the tread 10 has a large contact area and high rigidity, and the tire 1 excels in marginal performance of handling stability, but such tires tend to have poor ride comfort. However, tire 1 achieves a high level of both handling stability and ride comfort. Furthermore, the tapered surface of each sipe ensures a large contact area while distributing ground pressure in a balanced manner, greatly contributing to improved braking performance and handling stability.

[0081] The lateral grooves formed in the shoulder ribs 40, 50 will be described in detail below with reference to Figures 3 to 7 as well as Figures 8 and 9 as appropriate. Figure 8 is an enlarged perspective view of one lateral groove 41 formed in the shoulder rib 40. Figure 9 is a cross-sectional view taken along line AA in Figure 4, and is a widthwise cross-sectional view of the lateral groove 41 at the portion where the width of each tapered surface of the lateral groove 41 is maximum.

[0082] As shown in Figures 3, 4, and 6, the shoulder rib 40 in the first region R1 has lateral grooves 41 extending in the tire width direction. The lateral grooves 41 are formed from a position away from the edge of the shoulder rib 40, past the contact edge E1, and across to the side rib 13. The lateral grooves 41 are not connected to the circumferential grooves 20, and their starting ends, which are the ends of the lateral grooves 41 on the tire equator CL side, are located within the shoulder rib 40. In this case, a reduction in the contact area due to deformation of the shoulder rib 40 is suppressed, resulting in good handling stability and braking performance.

[0083] The lateral grooves 41 are formed at approximately equal intervals along the tire circumferential direction, and in the same number as the sipes in the intermediate rib 60. The lateral grooves 41 are inclined in the same direction as the sipes in the intermediate rib 60 relative to the tire width direction, but the inclination angle is smaller than that of the sipes in the intermediate rib 60. The lateral grooves 41 also bend slightly near their starting ends, and their depth gradually decreases from the bend 41C toward the starting end. The depth of the lateral grooves 41 is deepest at the bend 41C. The depth of the lateral grooves 41 gradually decreases from the bend 41C toward the tread edge E1, and becomes even shallower as they pass the tread edge E1 and approach the side rib 13, which is their terminal position.

[0084] The groove wall of the lateral groove 41 has a tapered surface that is a region that slopes so that the groove width increases toward the opening, extending from the opening to a depth of 2.0 mm. The lateral groove 41 has a first tapered surface 41A and a second tapered surface 41B. The first tapered surface 41A (first region) is formed on the first groove wall along the length of the lateral groove 41, and the second tapered surface 41B (second region) is formed on the second groove wall that faces the first groove wall along the length of the lateral groove 41. The two tapered surfaces are formed on both sides of the lateral groove 41 in the width direction, over the entire length of the lateral groove 41. Each tapered surface is formed, for example, over a depth range of 0.8 to 2.0 mm from the opening of the lateral groove 41.

[0085] 3, 5, and 7, the shoulder rib 50 in the second region R2 has lateral grooves 51 extending in the tire width direction. Like the lateral grooves 41 in the shoulder rib 40, the lateral grooves 51 are formed from a position away from the edge of the shoulder rib 50, past the ground-contact edge E2, and across to the side rib 13. The lateral grooves 51 are not connected to the circumferential grooves 23, and the starting ends of the lateral grooves 51, which are the ends on the tire equator CL side, are located within the shoulder rib 50. The lateral grooves 41, 51 are not aligned in the tire width direction, and the lateral grooves 51 are arranged so as to be located on an extension of the lateral grooves 41 in the longitudinal direction.

[0086] The lateral grooves 51 are formed at approximately equal intervals along the tire circumferential direction, and the number of sipes is the same as the number of sipes in the intermediate rib 70. In this embodiment, the number of sipes in the lateral grooves 41, 51, the center rib 30, and the intermediate ribs 60, 70 is the same. Like the lateral grooves 41, the lateral grooves 51 bend slightly near their starting ends, and their depth gradually decreases from the bend 51C toward the starting end. The depth of the lateral grooves 51 gradually decreases from the bend 51C toward the tread edge E2, and becomes even shallower as they pass the tread edge E2 and approach the side rib 13, which is their terminal position.

[0087] The groove wall of the lateral groove 51 has a tapered surface that is a region that slopes so that the groove width increases toward the opening, extending from the opening to a depth of 2.0 mm. The lateral groove 51 has a first tapered surface 51A and a second tapered surface 51B. The first tapered surface 51A (first region) is formed on the first groove wall along the longitudinal direction of the lateral groove 51, and the second tapered surface 51B (second region) is formed on the second groove wall that faces the first groove wall along the longitudinal direction of the lateral groove 51. The two tapered surfaces are formed on both sides of the lateral groove 51 in the width direction, over the entire length of the lateral groove 51. Each tapered surface is formed, for example, over a depth range of 0.8 to 2.0 mm from the opening of the lateral groove 51.

[0088] As will be described in detail later, the first tapered surface 41A of the lateral groove 41 is wider than the second tapered surface 41B and has a smaller inclination angle with respect to the profile surface α. Similarly, the first tapered surface 51A of the lateral groove 51 is wider than the second tapered surface 51B and has a smaller inclination angle with respect to the profile surface α. In this embodiment, the first tapered surface is formed on the shoulder rib 40 on a first direction side of the lateral groove 41 in the tire circumferential direction, and is formed on the shoulder rib 50 on a second direction side of the lateral groove 51 in the tire circumferential direction.

[0089] In the tire 1 mounted on the left side of the vehicle, the first tapered surface 41A of the lateral groove 41 is formed on the groove wall of the lateral groove 41 that is on the rear side in the main rotational direction of the tire, similar to the tapered surface 62A of the intermediate rib 60. The first tapered surface 51A of the lateral groove 51 is formed on the groove wall of the lateral groove 51 that is on the front side in the main rotational direction of the tire, similar to the tapered surface 72A of the intermediate rib 70. In this case, the ground contact pressure can be distributed in a balanced manner throughout the tread 10, resulting in more significant improvements in braking performance and handling stability.

[0090] The shoulder rib 50 has recesses 53 formed on its edge along the circumferential groove 23, each recess having a substantially triangular shape in plan view. The second region R2 of the tread 10 has a smaller contact area than the first region R1, but the recesses 53 increase the grip on the road surface, contributing to improved handling and stability. The recesses 53 are formed, for example, to a depth that extends from the upper end opening of the circumferential groove 23 to a depth that exceeds the tapered surface of the lateral groove 51. The depth of the recesses 53 is preferably shallower than the depth of the lateral grooves 51. The number of recesses 53 is less than the number of lateral grooves 51 and is formed at substantially equal intervals in the circumferential direction of the tire. The number of recesses 53 is, for example, half the number of lateral grooves 51, and the recesses 53 are formed so as to be positioned between two lateral grooves 51 in the circumferential direction of the tire.

[0091] The recessed portion 53 is arranged to be aligned in the tire width direction with the sipes 71 of the intermediate rib 70. The recessed portion 53 is formed by recessing part of the groove wall of the circumferential groove 23 that forms the sidewall of the shoulder rib 50 inward of the rib, and has a width that varies along the tire circumferential direction so as to have a generally triangular shape in plan view. The width of the recessed portion 53 gradually decreases in the same direction as the direction in which the sipes 71 are convex. The depth of the recessed portion 53 is constant over the entire length in the tire circumferential direction.

[0092] The configuration of the tapered surfaces will be described in more detail below using the lateral groove 41 as an example. The configurations of the first tapered surfaces 41A and 51A are the same except that they face in opposite directions relative to the tire circumferential direction (the same applies to the second tapered surfaces 41B and 51B).

[0093] 8 and 9, the maximum width Wa of the first tapered surface 41A of the lateral groove 41 is larger than the maximum width Wb of the second tapered surface 41B. The two tapered surfaces each have a substantially constant maximum width between the bend 41C of the lateral groove 41 and the ground contact edge E1. The width of each tapered surface gradually decreases from the bend 41C toward the start of the lateral groove 41, and also decreases slightly from the ground contact edge E1 toward the side rib 13. The widths of the tapered surfaces may be approximately the same outside the ground contact edge E1 in the tire width direction, or the width of the second tapered surface 41B may be larger than the width of the first tapered surface 41A.

[0094] The maximum width Wa of the first tapered surface 41A is preferably 1.5 to 3.0 times, and more preferably 1.8 to 2.5 times, the maximum width Wb of the second tapered surface 41B. In this case, the ground pressure can be distributed more effectively and in a balanced manner while ensuring a large contact area of ​​the tread 10. If the maximum width Wa is less than 1.5 times the maximum width Wb, the effect tends to be reduced. On the other hand, if the maximum width Wa is more than 3.0 times the maximum width Wb, the effect of reducing ground pressure tends to be reduced.

[0095] The maximum width Wa of the first tapered surface 41A is preferably 30 to 50% of the maximum width W of the lateral groove 41, and more preferably 35 to 45%. The sum of the maximum widths of the first tapered surface 41a and the second tapered surface 41b is preferably 50% or more of the maximum width W of the lateral groove 41. In this case, it becomes easier to distribute the ground pressure in a balanced manner while ensuring a large contact area of ​​the tread 10, and the effects of improving steering stability and braking performance become more significant. The sum of the maximum widths of the two tapered surfaces is, for example, 50 to 80% or 55 to 70% of the maximum width W.

[0096] In the portions where the widths of the first tapered surface 41A and the second tapered surface 41B are greatest, the inclination angle θa of the first tapered surface 41A relative to the profile surface α is smaller than the inclination angle θb of the second tapered surface 41B relative to the profile surface α. Because the widths of the two tapered surfaces are greatest between the bend 41C of the lateral groove 41 and the tread edge E1, angle θa<angle θb at least in this range. Note that angle θa may be greater than angle θb on the outer side of the tread edge E1 in the tire width direction.

[0097] The difference between the inclination angle θa of the first tapered surface 41A and the inclination angle θb of the second tapered surface 41B is preferably 10° or more. In this case, the ground pressure can be distributed more effectively and in a balanced manner while ensuring a large contact area of ​​the tread 10. A suitable example of the inclination angle θa of the first tapered surface 41A with respect to the profile surface α is 20 to 40°, and more preferably 25 to 35°. A suitable example of the inclination angle θb of the second tapered surface 41B with respect to the profile surface α is 30 to 60°, and more preferably 40 to 50°.

[0098] If the inclination angles θa and θb of each tapered surface become too large beyond the above range, the effect of reducing ground contact pressure tends to be reduced. On the other hand, if the inclination angles θa and θb of each tapered surface become too small beyond the above range, it becomes difficult to ensure a large ground contact area. It is preferable that the inclination angles θa and θb of each tapered surface are within the above range, and that the difference between the angle θa and the angle θb (θb - θa) is 10° or more. An example of a suitable range for the difference between the angle θa and the angle θb is 10 to 25°, or 15 to 20°.

[0099] The tire 1 having the above-described configuration achieves excellent handling stability on dry roads. The tire 1 has high rigidity in the first region R1 located on the outer side of the vehicle in the tread 10. In particular, by forming the circumferential grooves 20 in the first region R1 shallower and narrower and separating the lateral grooves 41 of the shoulder rib 40 from the circumferential grooves 20, the rigidity of the shoulder rib 40 is increased, suppressing large deformation of the shoulder rib 40 during high-speed cornering and braking. This improves the limit performance of handling stability. In addition, the sipes 61, 62 with tapered surfaces formed on both sides of the intermediate rib 60 in the width direction ensure the rigidity of the first region R1 while achieving good ride comfort.

[0100] The tire 1 can also effectively distribute ground pressure while ensuring a large contact area, achieving excellent braking performance. When ground pressure concentrates in one part of the tread, the friction coefficient of the rubber decreases and the rubber deforms significantly, reducing the contact area, which is thought to significantly reduce braking performance and handling stability. The tire 1 effectively reduces ground pressure by suppressing the concentration of ground pressure, for example, through the synergistic effects of the tapered surfaces of the lateral grooves 41, 51 of the shoulder ribs 40, 50, the tapered surfaces of the sipes of the center rib 30, and the tapered surfaces of the sipes of the intermediate ribs 60, 70.

[0101] As described above, tire 1 has excellent handling stability and provides good ride comfort. That is, tire 1 can achieve both handling stability and ride comfort. Tire 1 also has excellent braking performance and high marginal performance of handling stability, making it suitable as a UHP tire. Tire 1 is an innovative, high-performance tire that has excellent handling stability, ride comfort, and braking performance.

[0102] The above-described embodiment can be appropriately modified in design as long as the object of the present invention is not impaired. For example, the land portions are preferably formed in a rib shape, but lateral grooves or sipes crossing the land portions may be formed as long as the desired rigidity of the tread 10 is ensured. In the above-described embodiment, four circumferential grooves with different widths are formed in the tread 10, but the number of circumferential grooves may be three. In three or more circumferential grooves, the width of the second circumferential groove adjacent to the first circumferential groove located furthest from the vehicle may be the largest.

[0103] In the above-described embodiment, the tapered surfaces of the shoulder ribs 40, 50, center rib 30, and intermediate ribs 60, 70 effectively distribute ground pressure. However, the configuration of the tapered surfaces may be changed as long as the desired effect of dispersing ground pressure is maintained. For example, sipes or lateral grooves without tapered surfaces may be formed in the center rib, intermediate rib, or shoulder rib. It is also possible to form the two tapered surfaces located on both sides of the lateral groove of the shoulder rib in the width direction with the same width or the same inclination angle.

[0104] In the above-described embodiment, the sipes 61, 62 of the intermediate rib 60 are formed to a length such that the portions of each sipe exceeding a depth of 2.0 mm do not overlap in the tire circumferential direction, but the entire sipes 60, 61, including the tapered surfaces, may be formed so that they do not overlap in the tire circumferential direction. [Explanation of symbols]

[0105] 1 tire, 10 tread, 11 sidewall, 12 bead, 13 side rib, 14 carcass, 15 belt, 16 inner liner, 17 bead core, 18 bead filler, 20, 21, 22, 23 circumferential groove, 30 center rib, 31, 32, 61, 62, 71, 72 sipe, 31A, 41A, 51A, 61A, 71A first tapered surface, 31B, 41B, 51B, 61B, 71B second tapered surface, 32A, 62A, 72A tapered surface, 40, 50 shoulder rib, 41, 51 lateral groove, 41C, 51C, 71C bend portion, 53 recess, 60, 70 intermediate rib, CL tire equator, E1, E2 ground contact edge, R1 first region, R2 second region

Claims

1. A tire having a tread with three or more circumferential grooves formed therein and a specified mounting direction on a vehicle, The other circumferential grooves, except for a first circumferential groove located furthest outward from the vehicle, have substantially the same depth, and the first circumferential groove has the shallowest depth and the narrowest width among the circumferential grooves, the tread has a shoulder land portion and a mediate land portion defined by the first circumferential groove, The intermediate land portion is formed with first sipes and second sipes that are alternately arranged along the tire circumferential direction, the first sipe extends in the tire width direction from the circumferential groove located on the tire equator side and terminates within the intermediate land portion, the second sipe extends in the tire width direction from the circumferential groove located on the ground contact edge side and terminates within the intermediate land portion, The first sipe and the second sipe are formed to have lengths such that portions of the first sipe and the second sipe whose depths exceed 2.0 mm do not overlap in the tire circumferential direction.

2. a depth of the first circumferential groove is 50 to 80% of a depth of the deepest groove among the circumferential grooves, The tire according to claim 1 , wherein the width of the first circumferential groove is 60% or less of the width of the widest groove among the circumferential grooves.

3. 3. The tire according to claim 1, wherein a total length of the first sipes and the second sipes along the tire width direction is 60 to 90% of a width of the intermediate land portion.

4. the shoulder land portion includes a lateral groove extending in the tire width direction, The tire according to any one of claims 1 to 3, wherein an end of the lateral groove on the tire equator side is located within the shoulder land portion.

5. The tire according to any one of claims 1 to 4, wherein the groove walls of the first sipe and the second sipe have an inclined region within a range of 2.0 mm deep from an opening of the sipe such that the sipe width increases toward the opening.

6. The first sipe is longer than the second sipe, The tire according to claim 5 , wherein the inclined region is formed on both sides in the width direction of the first sipe, and is formed on only one side in the width direction of the second sipe.

7. the circumferential grooves include the first circumferential groove, the second circumferential groove, the third circumferential groove, and the fourth circumferential groove, and the circumferential grooves are arranged in this order from an outer side of the vehicle; The tire according to any one of claims 1 to 6, wherein a width of the third circumferential groove is the widest among the circumferential grooves, and a width of the second circumferential groove is the second narrowest among the circumferential grooves.

8. The tire according to any one of claims 1 to 7, wherein the hardness of the rubber constituting the surface layer of the tread is 65 to 75.

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