Tire

Abstract

To improve steering stability on a dry road surface while maintaining wet performance in a tire of four rib structure.SOLUTION: A tire has a tread part 2. The tread part 2 comprises four rib structure configured from three circumferential grooves 3 and four land parts 4. At least one of shoulder land parts 7 is provided with a plurality of shoulder lateral grooves 20, and a plurality of first shoulder sipes 21. Each of a pair of crown land parts 8 is provided with a plurality of full-open type first crown sipes 11. Each first crown sipe 11 provided on one crown land part 8 is provided at a position where the same is continuous with a first shoulder sipe 21. Each first crown sipe 11 provided on the other crown land part 8 is provided at a position where the same is not continuous with the first crown sipe 11 provided on one crown land part 8.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a tire. [Background technology]

[0002] The following Patent Document 1 proposes a pneumatic tire whose tread portion is composed of four land portions in the tire axial direction. This pneumatic tire is provided with lateral grooves and sipes that extend at an angle with respect to the tire equator and sipes that extend in the tire circumferential direction in the center land portion on the central side of the tread portion. This pneumatic tire improves wet braking performance while maintaining steering stability performance by using these lateral grooves and sipes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-139194 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, with the advancement of vehicle performance, tires with excellent steering stability on dry roads are required. In order to improve the steering stability, it is effective to reduce the volume of each groove arranged in the tread portion and increase the rigidity of each land portion. However, such a method tends to impair wet performance. In particular, a tire with a four-rib structure has fewer circumferential grooves than a tire with a five-rib structure, and it tends to be difficult to maintain wet performance.

[0005] The present invention was devised in consideration of the above-mentioned circumstances, and its main objective is to improve steering stability on dry roads while maintaining wet performance, assuming a tire with a four-rib structure. [Means for solving the problem]

[0006] The present invention relates to a tire having a tread portion, the tread portion having a four-rib structure constituted by three circumferential grooves extending continuously in the tire circumferential direction between a pair of tread ends and four land portions divided by the three circumferential grooves, the three circumferential grooves being a pair of shoulder circumferential grooves and one crown circumferential groove extending between the pair of shoulder circumferential grooves, the four land portions including a pair of shoulder land portions divided on the tire axially outer side of the pair of shoulder circumferential grooves and a pair of crown land portions divided by the crown circumferential groove and the pair of shoulder circumferential grooves, at least one of the shoulder land portions being provided with a plurality of shoulder lateral grooves and a plurality of first shoulder sipes, each of the shoulder lateral grooves being , extending at least from the tread edge toward the axially inner side of the tire and having an interrupted end within the shoulder land portion, each of the first shoulder sipes extending from the interrupted end of the shoulder lateral groove to the shoulder circumferential groove, and each of the pair of crown land portions is provided with a plurality of fully open type first crown sipes, each of the first crown sipes provided in one of the crown land portions is provided in a position continuous with the first shoulder sipe via the shoulder circumferential groove, and each of the first crown sipes provided in the other crown land portion is provided in a position not continuous with the first crown sipe provided in the one of the crown land portions via the crown circumferential groove.

[0007] In the tire of the present invention, it is desirable that, in a plan view of the tread, each of the shoulder lateral grooves is curved in an arc shape so as to be convex toward one side in the circumferential direction of the tire, and each of the first shoulder sipes is curved in an arc shape so as to be convex in the same direction as the shoulder lateral grooves.

[0008] In a plan view of the tread of the tire of the present invention, it is desirable that each of the shoulder lateral grooves has a first groove edge curved in an arc shape, and that the first shoulder sipe has the same or approximately the same radius of curvature as the first groove edge.

[0009] In a plan view of the tread of the tire of the present invention, it is preferable that each of the first shoulder sipes extends along an imaginary extension line of the first groove edge of each of the shoulder lateral grooves.

[0010] In a plan view of the tread of the tire of the present invention, it is preferable that each of the first crown sipes is curved in an arc shape with a smaller radius of curvature than the first groove edge of the shoulder lateral groove.

[0011] In the tire of the present invention, it is preferable that the shoulder lateral groove crosses the center position in the tire axial direction of the contact surface of the shoulder land portion.

[0012] In the tire of the present invention, it is desirable that the first shoulder sipe includes an inner portion on the shoulder circumferential groove side and an outer portion on the shoulder lateral groove side, and the depth of the inner portion is smaller than the depth of the outer portion.

[0013] In the tire of the present invention, it is desirable that the maximum depth of the first shoulder sipes is the same as the maximum depth of the first crown sipes. Effect of the Invention

[0014] By adopting the above-mentioned configuration, the tire of the present invention can improve the driving stability on dry road surfaces while maintaining the wet performance. [Brief description of the drawings]

[0015] [Figure 1] 1 is a development view of a tread portion of a tire according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged view of a pair of crown land portions in FIG. [Diagram 3] FIG. 2 is an enlarged view of a crown land portion and a shoulder land portion of FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line AA in FIG. [Diagram 5] FIG. 2 is an enlarged view of a tread portion of a tire of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a development view of a tread portion 2 of a tire 1 showing one embodiment of the present invention. As shown in Fig. 1, the tire 1 of this embodiment is suitably used as a pneumatic tire for passenger cars, for example. However, the present invention is not limited to such an embodiment.

[0017] As shown in Fig. 1, a tire 1 of the present invention has a tread portion 2 with a four-rib structure. That is, the tread portion 2 has three circumferential grooves 3 extending continuously in the tire circumferential direction between a pair of tread ends Te, and four land portions 4 divided by the three circumferential grooves 3.

[0018] The tread end Te corresponds to the axially outermost contact position when the tire 1 in a normal state is loaded with a normal load and contacts a flat surface with a camber angle of 0°.

[0019] "Normal condition" means, in the case of a pneumatic tire for which various standards are established, that the tire is mounted on a normal rim, inflated to the normal internal pressure, and unloaded. In the case of a tire for which various standards are not established or a non-pneumatic tire, the normal condition means a standard use condition according to the intended use of the tire, in which the tire is not mounted on a vehicle and is unloaded. In this specification, unless otherwise specified, the dimensions of each part of the tire are values ​​measured in the normal condition.

[0020] A "genuine rim" is a rim that is defined for each tire by the standard system that includes the standard on which the tire is based. For example, in the case of JATMA, it is called a "standard rim," in the case of TRA, it is called a "Design Rim," and in the case of ETRTO, it is called a "Measuring Rim."

[0021] "Normal internal pressure" is the air pressure set for each tire by each standard in the standard system on which the tire is based. In the case of JATMA, it is the "maximum air pressure." In the case of TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES." In the case of ETRTO, it is the "INFLATION PRESSURE."

[0022] In the case of a pneumatic tire for which various standards are established, the "normal load" is the load that each standard specifies for each tire in the standard system including the standard on which the tire is based. For JATMA, it is the "maximum load capacity", for TRA, it is the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and for ETRTO, it is the "LOAD CAPACITY". In addition, in the case of a tire for which various standards are not established or a non-pneumatic tire, the "normal load" refers to the load acting on one tire in the standard mounting state of the tire. The "standard mounting state" refers to a state in which the tire is mounted on a standard vehicle according to the intended use of the tire, and the vehicle is stationary on a flat road surface in a drivable state.

[0023] The three circumferential grooves 3 are composed of a pair of shoulder circumferential grooves 5 and one crown circumferential groove 6 extending between the pair of shoulder circumferential grooves 5. The pair of shoulder circumferential grooves 5 are provided to sandwich the tire equator C. The one crown circumferential groove 6 is provided, for example, on the tire equator C. The circumferential grooves 3 of this embodiment extend, for example, linearly. Each circumferential groove 3 may extend in a wavy or zigzag manner.

[0024] The distance L1 in the tire axial direction from the tire equator C to the groove center line of the shoulder circumferential groove 5 is preferably, for example, 15% to 30% of the tread width TW. The tread width TW is the distance in the tire axial direction between the two tread ends Te in the normal state.

[0025] The groove width W1 of the circumferential groove 3 is desirably, for example, 4.0% to 8.0% of the tread width TW. The depth of the circumferential groove 3 is, for example, 5 to 12 mm in the case of a pneumatic tire for a passenger car.

[0026] The four land portions 4 are composed of a pair of shoulder land portions 7 and a pair of crown land portions 8. The shoulder land portions 7 are located axially outward of the shoulder circumferential grooves 5 and include the tread edge Te. The crown land portion 8 is located between the crown circumferential groove 6 and the shoulder circumferential groove 5.

[0027] FIG. 2 shows an enlarged view of a pair of crown land portions 8. As shown in FIG. 2, each of the pair of crown land portions 8 is provided with a plurality of fully open first crown sipes 11. The fully open sipes refer to sipes that completely cross the land portion in the tire axial direction. As a preferred embodiment, each of the pair of crown land portions 8 of this embodiment is provided with a plurality of crown lateral grooves 10 and a plurality of semi-open second crown sipes 12. The semi-open sipes refer to sipes that do not completely cross the land portion and have discontinuous ends within the land portion.

[0028] In this specification, the term "sipe" refers to a cut element having a small width, and the width between two inner walls facing each other is 1.5 mm or less. The width of the sipe is preferably 0.5 to 1.5 mm. Each sipe in this embodiment extends with a constant width from the opening to the bottom. However, this is not limited to such an embodiment, and the opening of the sipe may be connected to a chamfered portion having a width exceeding 1.5 mm. Also, the bottom of the sipe may be connected to a flask bottom having a width exceeding 1.5 mm.

[0029] Fig. 3 shows an enlarged view of the crown land portion 8 and the shoulder land portion 7. As shown in Fig. 3, at least one of the shoulder land portions 7 is provided with a plurality of shoulder lateral grooves 20 and a plurality of first shoulder sipes 21.

[0030] Each of the shoulder lateral grooves 20 extends at least from the tread edge Te toward the axially inner side of the tire, and has an interrupted end 20a within the shoulder land portion 7. Each of the first shoulder sipes 21 extends from the interrupted end 20a of the shoulder lateral groove 20 to the shoulder circumferential groove 5.

[0031] In the present invention, each of the first crown sipes 11 provided in one crown land portion 8 is provided at a position continuous with the first shoulder sipe 21 via the shoulder circumferential groove 5. Note that "a sipe (first sipe) provided in one land portion and a sipe (second sipe) provided in the other land portion are continuous via a circumferential groove" includes a mode in which a first virtual sipe obtained by extending the first sipe into the circumferential groove while maintaining its curvature, and a second virtual sipe obtained by extending the second sipe into the circumferential groove while maintaining its curvature, overlap in the circumferential groove, and also includes a mode in which the minimum distance between the first virtual sipe and the second virtual sipe in the circumferential groove parallel to the tire circumferential direction is 3.0 mm or less. In addition, "a sipe (first sipe) provided in one land portion and a sipe (second sipe) provided in the other land portion are continuous via a circumferential groove" also includes a configuration in which the end (first end) of the first sipe on the circumferential groove side and the end (second end) of the second sipe on the circumferential groove side are arranged on the same tire axial line, and a configuration in which the tire circumferential distance between the first end and the second end is 3.0 mm or less.

[0032] In other words, the minimum distance parallel to the tire circumferential direction between the imaginary sipe 31 (shown by a dot in FIG. 3) obtained by extending the first shoulder sipe 21 into the shoulder circumferential groove 5 while maintaining its curvature, and the imaginary sipe 32 (shown by a dot in FIG. 3) obtained by extending the first crown sipe 11 into the shoulder circumferential groove 5 while maintaining its curvature, is 3.0 mm or less. In a more desirable embodiment, the imaginary sipe 31 and the imaginary sipe 32 extend substantially parallel to each other, and the minimum distance between them parallel to the tire circumferential direction is 2.0 mm or less.

[0033] As shown in FIG. 2, each of the first crown sipes 11 provided in the other crown land portion 8 (the right crown land portion 8 in FIG. 2) is provided in a position that is not continuous with the first crown sipes 11 provided in one crown land portion 8 (the left crown land portion 8 in FIG. 2) via the crown circumferential groove 6.

[0034] In other words, the minimum distance parallel to the tire circumferential direction within the crown circumferential groove 6 between a virtual sipe 36 (shown by a dot in Figure 2) formed by extending the first crown sipe 11 provided in one crown land portion 8 into the crown circumferential groove 6 while maintaining its curvature, and a virtual sipe 37 (shown by a dot in Figure 2) formed by extending the first crown sipe 11 provided in the other crown land portion 8 into the crown circumferential groove 6 while maintaining its curvature, is greater than 3.0 mm.

[0035] In the present invention, by adopting the above-mentioned configuration, it is possible to improve the driving stability on dry road surfaces (hereinafter, sometimes simply referred to as "driving stability") while maintaining the wet performance. The following mechanism is presumed to be the reason for this.

[0036] The shoulder lateral grooves 20 and the first shoulder sipes 21 provide friction on wet road surfaces while maintaining the rigidity of the shoulder land portion 7 to improve steering stability. Similarly, the first crown sipes 11 provide friction on wet road surfaces while maintaining the rigidity of the crown land portion 8. This improves wet performance and steering stability in a well-balanced manner.

[0037] In addition, the first shoulder sipes 21 and the first crown sipes 11 are continuous with each other via the shoulder circumferential groove 5, so that they cooperate to provide friction and maintain wet performance. In addition, due to the arrangement of these sipes, the shoulder land portion 7 and the crown land portion 8 cooperate to provide a large cornering force, improving cornering performance.

[0038] In addition, by arranging the first crown sipes 11 in the pair of crown land portions 8 as described above, deformation of the crown land portions 8 near the tire equator C where a large ground contact pressure acts is suppressed. This improves initial response during steering and improves handling stability. It is believed that the tire of the present invention can improve handling stability on dry roads while maintaining wet performance due to the above mechanism.

[0039] A more detailed configuration of this embodiment will be described below. Each configuration described below shows a specific aspect of this embodiment. Therefore, it goes without saying that the present invention can achieve the above-mentioned effects even if it does not have the configuration described below. In addition, even if any one of the configurations described below is applied alone to the tire of the present invention having the above-mentioned characteristics, an improvement in performance according to each configuration can be expected. Furthermore, when some of the configurations described below are applied in combination, a composite improvement in performance according to each configuration can be expected.

[0040] 1, the tread portion 2 of this embodiment is point symmetrical with the center on the tire equator C, except that the arrangement pitches of the respective portions are shifted in the tire circumferential direction for the pattern between the tire equator C and one tread end Te and the pattern between the tire equator C and the other tread end Te. However, the tire 1 of the present invention is not limited to this embodiment.

[0041] It is desirable that the maximum groove width W3 of the shoulder circumferential groove 5 is smaller than the maximum groove width W2 of the crown circumferential groove 6. Specifically, the groove width W3 of the shoulder circumferential groove 5 is 60% to 80% of the groove width W2 of the crown circumferential groove 6. This provides excellent driving stability.

[0042] The total groove width of the three circumferential grooves 3 is preferably 15% to 25% of the tread width TW, which improves the driving stability and wet performance in a well-balanced manner.

[0043] 2, the crown lateral groove 10 extends from the shoulder circumferential groove 5 and has a discontinued end 10a within the crown land portion 8. The second crown sipe 12 extends from the discontinued end 10a of the crown lateral groove 10 toward the crown circumferential groove 6 and is discontinued within the crown land portion 8. Such crown lateral grooves 10 and second crown sipes 12 improve driving stability and wet performance in a well-balanced manner.

[0044] The groove width W4 of the crown lateral groove 10 is, for example, 50% to 90% of the maximum groove width W3 (shown in FIG. 1) of the shoulder circumferential groove 5, and preferably 55% to 75%.

[0045] The crown lateral grooves 10 do not cross, for example, the axial center position of the crown land portion 8. In other words, the axial length L2 of the crown lateral grooves 10 is 50% or less, and preferably 35% to 45%, of the axial width W5 of the crown land portion 8. Such crown lateral grooves 10 can exhibit excellent drainage performance while maintaining the rigidity of the crown land portion 8.

[0046] The second crown sipes 12 are connected to the discontinuous ends 10a so as to be offset in the tire circumferential direction with respect to the groove center line 10c of the crown lateral groove 10 at the discontinuous ends 10a. In this embodiment, the second crown sipes 12 arranged in the crown land portion 8 on one side in the tire axial direction (left side in FIG. 2) are offset in the tire circumferential direction with respect to the groove center line 10c to one side (upper side in FIG. 2). In addition, the second crown sipes 12 arranged in the crown land portion 8 on the other side in the tire axial direction (right side in FIG. 2) are offset in the tire circumferential direction to the other side (lower side in FIG. 2) with respect to the groove center line 10c. Such an arrangement of the second crown sipes 12 is useful for turning the impact sound of each crown land portion 8 at the time of contact with the ground into white noise and improving noise performance.

[0047] The axial length L3 of the second crown sipes 12 is smaller than the axial length L2 of the crown lateral grooves 10. Specifically, the length L3 of the second crown sipes 12 is 15% to 30% of the axial width W5 of the crown land portion 8. In a preferred embodiment, the second crown sipes 12 cross the axial center position of the crown land portion 8. Such second crown sipes 12 provide large frictional force during wet driving while maintaining the rigidity of the crown land portion 8.

[0048] The distance L4 in the tire axial direction from the discontinuous end 12a of the second crown sipe 12 to the crown circumferential groove 6 is, for example, 25% to 40% of the width W5 in the tire axial direction of the crown land portion 8. The length L3 in the tire axial direction of the second crown sipe 12 is smaller than the distance L4. It is also preferable that no other grooves or sipes are provided in the region between the discontinuous end 12a and the crown circumferential groove 6. This reliably maintains the rigidity of the crown land portion 8, and provides excellent driving stability.

[0049] In order to further enhance the above-mentioned effects, it is desirable that the maximum depth of the second crown sipes 12 is smaller than the maximum depth of the crown lateral grooves 10 and smaller than the maximum depth of the first crown sipes 11. The maximum depth of the second crown sipes 12 is 85% to 95% of the maximum depth of the crown lateral grooves 10.

[0050] A distance L5 in the tire circumferential direction between an end of the first crown sipe 11 provided in one crown land portion 8 on the crown circumferential groove 6 side and an end of the first crown sipe 11 provided in the other crown land portion 8 on the crown circumferential groove 6 side is, for example, 25% to 50% of one pitch length P1 of the first crown sipe 11 in the tire circumferential direction.

[0051] In a plan view of the tread, the crown lateral grooves 10, the first crown sipes 11, and the second crown sipes 12 are preferably curved in an arc shape so as to be convex in the same circumferential direction of the tire. The radius of curvature of these sipes is, for example, 50 to 100 mm. This allows the crown land portion 8 to deform smoothly as a whole, and the cornering force to increase linearly in response to the steering amount, improving the cornering performance.

[0052] As shown in FIG. 3, in the shoulder land portion 7, in addition to the above-mentioned shoulder lateral grooves 20 and first shoulder sipes 21, a plurality of second shoulder sipes 22 are provided.

[0053] Although omitted in the drawings of this specification, the shoulder lateral grooves 20 extend in the axial direction of the tire in the shoulder land portion 7 also in an area axially outboard of the tread edge Te.

[0054] It is desirable that the shoulder lateral groove 20 crosses the center position in the tire axial direction of the contact surface of the shoulder land portion 7. Specifically, the length L6 of the shoulder lateral groove 20 in the tire axial direction at the contact surface of the shoulder land portion 7 is 55% to 70% of the width W6 in the tire axial direction of the contact surface of the shoulder land portion 7. Such a shoulder lateral groove 20 improves the driving stability and wet performance in a well-balanced manner.

[0055] It is preferable that the groove width of the shoulder lateral grooves 20 increases toward the axially outer side of the tire. It is preferable that the groove width W7 of the shoulder lateral grooves 20 on the tread end Te is larger than the groove width of the shoulder circumferential grooves 5 of the crown lateral grooves 10. Such shoulder lateral grooves 20 can exhibit excellent drainage properties.

[0056] The shoulder lateral groove 20 has a first groove edge 20e that is curved in an arc shape in a plan view of the tread. The angle of the first groove edge 20e with respect to the tire axial direction at the tread end Te is 5° or less. The radius of curvature of the first groove edge 20e is, for example, 150 to 250 mm. In this embodiment, the shoulder lateral groove 20 and the first crown sipe 11 are curved in an arc shape so as to be convex in the same direction in the tire circumferential direction. In a preferred embodiment, each of the first crown sipes 11 is curved in an arc shape with a smaller radius of curvature than the first groove edge of the shoulder lateral groove 20. As a result, the shoulder land portion 7 and the crown land portion 8 cooperate to provide a large cornering force, improving cornering performance.

[0057] The length L7 of the first shoulder sipe 21 in the tire axial direction at the contact surface of the shoulder land portion 7 is, for example, 25% to 40% of the width W6 of the contact surface of the shoulder land portion 7 in the tire axial direction.

[0058] In a plan view of the tread, the first shoulder sipes 21 are curved in an arc shape so as to protrude in the same direction as the shoulder lateral grooves 20. The first shoulder sipes 21 extend along an imaginary extension line of the first groove edge 20e of the shoulder lateral groove 20. It is desirable that the first shoulder sipes 21 have the same or approximately the same radius of curvature as the first groove edge 20e of the shoulder lateral groove 20. Specifically, the radius of curvature of the first shoulder sipes is 90% to 110% of the radius of curvature of the first groove edge of the shoulder lateral groove 20.

[0059] Fig. 4 shows a cross-sectional view taken along line AA in Fig. 3. As shown in Fig. 4, the first shoulder sipe 21 includes an inner portion 26 on the shoulder circumferential groove 5 side and an outer portion 27 on the shoulder lateral groove 20 side. The depth d1 of the inner portion 26 is preferably smaller than the depth d2 of the outer portion 27. The depth d1 of the inner portion 26 is 70% to 80% of the depth d2 of the outer portion 27. Such a first shoulder sipe 21 improves driving stability and wet performance in a well-balanced manner.

[0060] From the same viewpoint, the length L8 of the inner portion 26 in the axial direction of the tire is, for example, 50% to 70% of the length L7 (shown in FIG. 3) in the axial direction of the first shoulder sipe 21. When the length of the inner portion 26 in the axial direction of the tire varies in the radial direction of the tire, the length in the axial direction of the tire is measured at the center position of the inner portion 26 in the radial direction of the tire.

[0061] The maximum depth of the first shoulder sipes 21 (corresponding to the depth d2 of the outer portion 27 in this embodiment) is 90% to 110% of the maximum depth of the first crown sipes 11, and in a desirable embodiment, these depths are the same.

[0062] 3, in a more desirable embodiment, the length of the second crown sipes 12 is shorter than the axial length L7 of the first shoulder sipes 21. This relatively increases the rigidity of the crown land portion 8, improving the initial response during cornering.

[0063] The second shoulder sipes 22 extend axially inward from at least the tread edge Te, and have a discontinued end 22a within the shoulder land portion 7. Although omitted in the drawings of this specification, the second shoulder sipes 22 also extend axially through the shoulder land portion 7 in an area axially outward of the tread edge Te.

[0064] From the standpoint of achieving a good balance between steering stability and wet performance, the axial length L9 of each second shoulder sipe 22 on the contact surface of the shoulder land portion 7 is 30% to 70% of the axial width W6 of the contact surface of the shoulder land portion 7, and preferably 40% to 60%.

[0065] The distance L10 in the tire axial direction between each end 22a of the second shoulder sipes 22 and each end 20a of the shoulder lateral grooves 20 is preferably 30% or less, and more preferably 20% or less, of the width W6 in the tire axial direction of the contact surface of the shoulder land portion 7. As a result, the shoulder lateral grooves 20 and the second shoulder sipes 22 work together to improve wet performance.

[0066] The second shoulder sipes 22 are curved in an arc shape so as to protrude in the same direction as the shoulder lateral grooves 20. In a preferred embodiment, the second shoulder sipes 22 extend along the first groove edge 20e of the shoulder lateral grooves 20, and in a more preferred embodiment, they are parallel to each other. This allows the shoulder land portion 7 to deform smoothly, so that the entire land portion can generate a large cornering force.

[0067] The maximum depth of the second shoulder sipes 22 is desirably smaller than the maximum depth of the first shoulder sipes 21, for example. Also, the maximum depth of the second shoulder sipes 22 is desirably larger than the depth d1 (shown in FIG. 4) of the inner portion 26 of the first shoulder sipe 21. Such second shoulder sipes 22 are useful for improving wet performance.

[0068] Although the tire according to one embodiment of the present invention has been described in detail above, the present invention is not limited to the above specific embodiment and can be modified and carried out in various aspects. EXAMPLES

[0069] A pneumatic tire of size 195 / 65R15 having the basic pattern of FIG. 1 was prototyped based on the specifications of Table 1. As a comparative example, a tire having a tread portion shown in FIG. 5 was prototyped. As shown in FIG. 5, in the comparative tire, the first shoulder sipe a and the first crown sipe b are provided at positions where they are not continuous, and the first crown sipe b provided in one crown land portion and the first crown sipe b provided in the other crown land portion are provided at positions where they are continuous via a crown circumferential groove. The comparative tire is substantially the same as that shown in FIG. 1, except for the above-mentioned points. The steering stability on dry road surfaces and wet performance of each test tire were tested. The common specifications and test methods of each test tire are as follows. Rim: 15×6.0J Tire pressure: front wheel 230kPa, rear wheel 220kPa Test vehicle: 1800cc, front-wheel drive

[0070] <Steering stability on dry roads> The driving stability of the test vehicle was evaluated by the driver when the vehicle was driven at 20 to 120 km / h on a test course with a dry asphalt road surface. The results are given as a score based on the comparative example being 100, with a higher score indicating better driving stability on a dry road surface.

[0071] <Wet performance> The wet performance of the test vehicle when it was driven on a wet road surface was evaluated by the driver. The results are given as a score based on the comparative example being 100, with a higher score indicating better wet performance. The test results are shown in Table 1.

[0072] [Table 1]

[0073] As a result of the test, it was confirmed that the tire of the example maintained wet performance of 101 to 105 points, and the steering stability on dry roads was improved to 102 to 109 points. In other words, it was confirmed that the tire of the example maintained wet performance while improving the steering stability on dry roads. [Explanation of symbols]

[0074] 2 Tread section 3 Circumferential groove 4 Land 5 Shoulder circumferential groove 6 Shoulder Land Section 7 Shoulder Land Section 8 Crown Land Division 11 First crown sipe 20 Shoulder groove 20a End 21 First shoulder sipe Te tread edge

Claims

1. A tire having a tread portion, wherein the tread portion has a four-rib structure composed of three circumferential grooves continuously extending in the tire circumferential direction between a pair of tread ends and four land portions divided by the three circumferential grooves, the three circumferential grooves are a pair of shoulder circumferential grooves and one crown circumferential groove extending between the pair of shoulder circumferential grooves, the four land portions include a pair of shoulder land portions divided outside the tire axial direction of the pair of shoulder circumferential grooves and a pair of crown land portions divided by the crown circumferential groove and the pair of shoulder circumferential grooves, at least one of the shoulder land portions is provided with a plurality of shoulder lateral grooves and a plurality of first shoulder sipes, each of the shoulder lateral grooves extends at least inward in the tire axial direction from the tread end and has a break end within the shoulder land portion, each of the first shoulder sipes extends from the break end of the shoulder lateral groove to the shoulder circumferential groove, each of the pair of crown land portions is provided with a plurality of first crown sipes of a full-open type, each of the first crown sipes provided in one of the crown land portions is provided at a position continuous with the first shoulder sipes via the shoulder circumferential groove, each of the first crown sipes provided in the other crown land portion is provided at a position not continuous with the first crown sipes provided in the one crown land portion via the crown circumferential groove, in a tread plan view, each of the shoulder lateral grooves has a first groove edge curved in an arc shape, the radius of curvature of the first shoulder sipes is 90% to 110% of the radius of curvature of the first groove edge of the shoulder lateral groove, in a tread plan view, each of the first shoulder sipes extends along a virtual extension line of the first groove edge of each of the shoulder lateral grooves, the radius of curvature of the first groove edge is 150 to 250 mm, a tire.

2. The tire according to claim 1, wherein in a tread plan view, each of the shoulder lateral grooves is curved in an arc shape so as to be convex on one side in the tire circumferential direction, and each of the first shoulder sipes is curved in an arc shape so as to be convex in the same direction as the shoulder lateral groove. **Claim 3**: The tire according to claim 1 or 2, wherein in a plan view of the tread, each of the first crown sides is curved in an arc shape with a radius of curvature smaller than that of the first groove edge of the shoulder lateral groove. **Claim 4**: The tire according to any one of claims 1 to 3, wherein the shoulder lateral groove crosses the center position in the tire axial direction of the ground contact surface of the shoulder land portion. **Claim 5**: The first shoulder side includes an inner portion on the side of the shoulder circumferential groove and an outer portion on the side of the shoulder lateral groove. The tire according to any one of claims 1 to 4, wherein the depth of the inner portion is smaller than the depth of the outer portion. **Claim 6**: The tire according to any one of claims 1 to 5, wherein the maximum depth of the first shoulder side is the same as the maximum depth of the first crown side.

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