Tire

Abstract

Provided is a tire capable of reducing vehicle external noise and improving soil discharge performance from shoulder lug grooves. The tire includes an annular tread portion 1 that extends in the circumferential direction of the tire, wherein a main groove 10 extending in the circumferential direction of the tire and a plurality of shoulder lug grooves 25 extending in the width direction of the tire are formed in the tread portion 1, one end of each shoulder lug groove 25 communicating with the main groove 10, and the other end being located on the outer side, in the width direction of the tire, of a ground contact edge E of the tread portion 1, and wherein: each shoulder lug groove 25 has a bottom raised portion 51 in a part adjacent to the main groove 19, and has a slope portion 52 in which the groove depth of the shoulder lug groove 25 gradually increases from the bottom raised portion 51 toward the outer side in the width direction of the tire; groove depths Da and Db of the shoulder lug grooves 25 at a start point A and an end point B of the slope portion 52 satisfy the relationship 1.5 ≤ Db / Da ≤ 2.0; and a length Ls, in the width direction of the tire, of the slope portion 52 satisfies the relationship 0.5 ≤ Ls / L ≤ 0.8 with respect to a distance L in the width direction of the tire from the main groove 10 to the ground contact edge E.

Description

tire

[0001] The present invention relates to a tire having a plurality of shoulder lug grooves extending in the tire width direction in the tread portion, and more specifically to a tire that can reduce external noise and improve soil discharge performance from the shoulder lug grooves.

[0002] In recent years, regulations on external noise emitted from vehicles have been strengthened. Some of this external noise is generated when tires roll on the road. In particular, tires mounted on sports utility vehicles (SUVs) and the like tend to produce louder external noise because they employ a block-based tread pattern in the tread portion, which includes multiple main grooves extending in the tire circumferential direction and multiple lug grooves extending in the tire width direction.

[0003] Furthermore, tires mounted on sport utility vehicles and the like are required to have excellent off-road performance, but one drawback is that when soil gets stuck in the lug grooves during off-road driving, the off-road performance deteriorates. Therefore, there is a need to improve the soil discharge performance from the lug grooves.

[0004] Providing protrusions or raised bottom portions in the shoulder lug grooves of tires has been proposed (see, for example, Patent Documents 1 to 3). However, these protrusions and raised bottom portions do not improve soil discharge from the shoulder lug grooves.

[0005] Japanese Patent Publication No. 2007-1484 Japanese Patent Publication No. 2016-37277 Japanese Patent Publication No. 2016-55816

[0006] An object of the present invention is to provide a tire that can reduce external noise and improve soil discharge from shoulder lug grooves.

[0007] In order to achieve the above object, the tire of the present invention has a tread portion extending circumferentially and forming an annular shape, in which a main groove extending circumferentially and a plurality of shoulder lug grooves extending in the tire width direction are formed in the tread portion, one end of each shoulder lug groove communicates with the main groove and the other end is located outward in the tire width direction from the ground contact edge of the tread portion, wherein each shoulder lug groove has a raised bottom portion adjacent to the main groove and a slope portion whose groove depth gradually increases from the raised bottom portion toward the outer side in the tire width direction, wherein groove depths Da, Db of the shoulder lug groove at a start point A and an end point B of the slope portion satisfy the relationship 1.5≦Db / Da≦2.0, and wherein the length Ls of the slope portion in the tire width direction and the distance L in the tire width direction from the main groove to the ground contact edge satisfy the relationship 0.5≦Ls / L≦0.8.

[0008] In the present invention, the shoulder lug grooves that communicate with the main grooves have raised bottom portions formed adjacent to the main grooves, which prevents air column resonance generated in the main grooves from propagating to the outside of the tire through the shoulder lug grooves, thereby reducing exterior noise. Furthermore, each shoulder lug groove has a sloped portion in which the groove depth gradually increases from the raised bottom portion toward the outside in the tire width direction. This allows soil or mud that has entered the shoulder lug grooves to move outward in the tire width direction when compressed, making it easier for it to be discharged from the shoulder lug grooves. This reduces exterior noise while improving soil discharge from the shoulder lug grooves.

[0009] In the present invention, it is preferable that the distance La in the tire width direction from the main groove to the start point A of the slope portion and the distance L in the tire width direction from the main groove to the ground contact edge satisfy the relationship 0.05≦La / L≦0.2, and the distance Lb in the tire width direction from the main groove to the end point B of the slope portion and the distance L in the tire width direction from the main groove to the ground contact edge satisfy the relationship 0.55≦Lb / L≦1.0. By specifying the positions of the start point A and the end point B of the slope portion in this way and ensuring a sufficient bottom-up portion adjacent to the main groove, it is possible to enhance the effects of reducing external noise and improving soil discharge performance.

[0010] In the present invention, it is preferable that the groove width of each shoulder lug groove expands outward in the tire width direction in at least a portion of the longitudinal direction of the shoulder lug groove, the length Lx in the tire width direction from the main groove to the widening start position of each shoulder lug groove satisfies the relationship 0≦Lx / L≦0.2 with respect to the distance L in the tire width direction from the main groove to the tread edge, and the minimum width Wmin and maximum width Wmax of each shoulder lug groove satisfy the relationship 1.5≦Wmax / Wmin≦2.0. By expanding the groove width of each shoulder lug groove outward in the tire width direction in this way, soil discharge from the shoulder lug groove can be effectively improved.

[0011] It is preferable that the groove depth change rate X calculated from Db / Da and the groove width change rate Y calculated from Wmax / Wmin satisfy the relationship 1.0≦X / Y≦1.2, which can effectively improve soil discharge from the shoulder lug grooves.

[0012] In the present invention, the groove wall angle of the shoulder lug grooves relative to the normal to the tread surface of the tread portion gradually decreases toward the outer side in the tire width direction in the region corresponding to the slope portion, and the groove wall angle of the shoulder lug grooves is preferably in the range of 0° to 10°, thereby effectively improving soil discharge from the shoulder lug grooves.

[0013] In the present invention, it is preferable that circumferential auxiliary grooves extending in the tire circumferential direction and intersecting with the shoulder lug grooves are formed in the tread portion, and that the circumferential auxiliary grooves are located between the start point A and the end point B of the slope portion. This makes it possible to effectively improve soil discharge from the shoulder lug grooves.

[0014] The groove width of the circumferential auxiliary groove is preferably in the range of 30% to 60% of the groove width of the shoulder lug groove at the opening to the main groove, thereby effectively improving soil discharge from the shoulder lug groove without reducing the effect of reducing exterior noise.

[0015] The tire of the present invention is preferably a pneumatic tire, but may also be a non-pneumatic tire. In the case of a pneumatic tire, the interior thereof can be filled with air, an inert gas such as nitrogen, or other gases.

[0016] In the present invention, the "ground-contact edge" of the tread portion refers to the axially outermost edge of the contact area of ​​the tread portion formed when a tire mounted on a standard rim, inflated to a standard internal pressure (in the case of a pneumatic tire), placed vertically on a flat surface, and subjected to a standard load. The term "standard rim" refers to the rim specified for each tire in a standard system, including the standard on which the tire is based. For example, this is the standard rim in the case of JATMA, the "Design Rim" in the case of TRA, or the "Measuring Rim" in the case of ETRTO. The term "standard internal pressure" refers to the air pressure corresponding to the maximum load capacity specified for each tire in a standard system, including the standard on which the tire is based. The term "standard load" refers to a load equivalent to 88% of the maximum load capacity specified for each tire in a standard system, including the standard on which the tire is based.

[0017] Fig. 1 is a meridian cross-sectional view of a pneumatic tire according to an embodiment of the present invention. Fig. 2 is a development view showing the tread pattern of the pneumatic tire of Fig. 1. Fig. 3 is a cross-sectional view showing a shoulder land portion in which shoulder lug grooves are formed. Fig. 4 is a plan view showing a shoulder land portion in which shoulder lug grooves are formed. Fig. 5 is a cross-sectional view taken along the line V-V in Fig. 4.

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: Figures 1 to 5 show a pneumatic tire according to an embodiment of the present invention;

[0019] As shown in FIG. 1, the pneumatic tire of this embodiment includes a tread portion 1 extending circumferentially in a ring shape, a pair of sidewall portions 2, 2 disposed on both sides of the tread portion 1, and a pair of bead portions 3, 3 disposed radially inward of the sidewall portions 2.

[0020] A carcass layer 4 is mounted between the pair of bead portions 3, 3. This carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the inside to the outside of the tire around a bead core 5 disposed in each bead portion 3. A bead filler 6 made of a rubber composition and having a triangular cross section is disposed on the outer periphery of the bead core 5.

[0021] Meanwhile, multiple belt layers 7 are embedded on the outer peripheral side of the carcass layer 4 in the tread portion 1. These belt layers 7 include multiple reinforcing cords that are inclined with respect to the tire circumferential direction, and are arranged so that the reinforcing cords cross each other between layers. In the belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set to a range of 10° to 40°, for example. Steel cords are preferably used as the reinforcing cords of the belt layers 7. At least one belt cover layer 8 is arranged on the outer peripheral side of the belt layers 7, with the aim of improving high-speed durability, and the reinforcing cords are arranged at an angle of, for example, 5° or less with respect to the tire circumferential direction. Organic fiber cords such as nylon and aramid cords are preferably used as the reinforcing cords of the belt cover layer 8.

[0022] The above-described tire internal structure is a typical example of a pneumatic tire, but is not limited to this.

[0023] As shown in Figure 2, the tread 1 has four main grooves 10 extending in the tire circumferential direction. The main grooves 10 have a groove width ranging from 8 mm to 20 mm, a groove depth ranging from 6 mm to 10 mm, and are equipped with wear indicators. These main grooves 10 define five rows of land portions 11 to 15 in the tread 1. More specifically, the shoulder land portion 11 is located in a shoulder region on one side of the tread 1 in the width direction, the shoulder land portion 15 is located in a shoulder region on the other side of the tread 1 in the width direction, the center land portion 13 is located on the tire equator, the intermediate land portion 12 is located between the center land portion 13 and the shoulder land portion 11, and the intermediate land portion 14 is located between the center land portion 13 and the shoulder land portion 15.

[0024] The shoulder land portion 11 is formed with a plurality of shoulder lug grooves 21 extending in the tire width direction, a plurality of sipes 31 extending in the tire width direction, and circumferential auxiliary grooves 41 extending in the tire circumferential direction and intersecting the shoulder lug grooves 21. Each shoulder lug groove 21 is configured so that one end on the inner side in the tire width direction terminates within the shoulder land portion 11 without communicating with the main groove 10, while the other end is located outward in the tire width direction from the ground contact edge E of the tread portion 1. The circumferential auxiliary groove 41 has a groove width in the range of 1 mm to 3 mm and a groove depth of 1 mm to 5 mm.

[0025] A plurality of lug grooves 22 extending in the tire width direction and a plurality of sipes 32 extending in the tire width direction are formed in the intermediate land portion 12. These lug grooves 22 and sipes 32 cross the intermediate land portion 12 and are curved so as to be convex toward one side in the tire circumferential direction.

[0026] A plurality of lug grooves 23 extending in the tire width direction and a plurality of sipes 33 extending in the tire width direction are formed in the center land portion 13. The lug grooves 23 have closed ends that terminate within the center land portion 13 and open ends that open into the main grooves 10, and the open ends are alternately arranged on both sides of the center land portion 13 along the tire circumferential direction.

[0027] A plurality of lug grooves 24 extending in the tire width direction and a plurality of sipes 34 extending in the tire width direction are formed in the intermediate land portion 14. The lug grooves 24 have a closed end that terminates within the intermediate land portion 14 and an open end that opens into the main groove 10, and the open end is located on the outer side of the intermediate land portion 14 in the tire width direction.

[0028] The shoulder land portion 15 is formed with a plurality of shoulder lug grooves 25 extending in the tire width direction, a plurality of sipes 35 extending in the tire width direction, and a circumferential auxiliary groove 45 extending in the tire circumferential direction and intersecting the shoulder lug grooves 25. Each shoulder lug groove 25 is configured so that one end located on the inner side in the tire width direction communicates with the main groove 10, while the other end is located on the outer side in the tire width direction of the ground contact edge E of the tread portion 1. The circumferential auxiliary groove 45 has a groove width in the range of 1 mm to 3 mm and a groove depth of 1 mm to 5 mm.

[0029] 3 and 4 , in the above-described pneumatic tire, each shoulder lug groove 25 has a raised portion 51 adjacent to the main groove 10, and a slope portion 52 in which the groove depth of the shoulder lug groove 25 gradually increases from the raised portion 51 toward the outer side in the tire width direction. The groove depth of each shoulder lug groove 25 is minimum at the raised portion 51 and maximum at the ground contact edge. The groove depth of each shoulder lug groove 25 is constant along the raised portion 51. The groove depths Da and Db of the shoulder lug groove 25 at the start point A and end point B of the slope portion 52 satisfy the relationship 1.5≦Db / Da≦2.0, and the length Ls of the slope portion 52 in the tire width direction is set to satisfy the relationship 0.5≦Ls / L≦0.8 with respect to the distance L in the tire width direction from the main groove 10 to the ground contact edge E. When the slope portion 52 is smoothly connected to the raised bottom portions 51 and the groove bottoms of the shoulder lug grooves 25 located on both sides thereof, the start point A and end point B are defined as the intersections of an extension of the slope portion 52 with an extension of the raised bottom portion 51 and the groove bottoms of the shoulder lug grooves 25. When the intersections of a straight line passing through the start point A and end point B of the slope portion 52, perpendicular to the ground contact surface of the tread portion 1, and the ground contact surface are defined as points A' and B', respectively, the groove depths Da and Db of the shoulder lug grooves 25 are the distance between the start point A and point A' and the distance between the end point B and point B', respectively.

[0030] In the above-described pneumatic tire, the shoulder lug grooves 25 that communicate with the main grooves 10 have raised bottom portions 51 formed in the areas adjacent to the main grooves 10, which prevents air column resonance generated in the main grooves 10 from propagating to the outside of the tire through the shoulder lug grooves 25, thereby reducing exterior noise. Furthermore, each shoulder lug groove 25 has a slope portion 52 formed therein, in which the groove depth of the shoulder lug groove 25 gradually increases from the raised bottom portion 51 toward the outside in the tire width direction. Therefore, when soil or mud that has entered the shoulder lug grooves 25 is compressed, it moves toward the outside in the tire width direction, making it easier for it to be discharged from the shoulder lug grooves 25. This reduces exterior noise while improving soil discharge from the shoulder lug grooves 25.

[0031] If the ratio Db / Da of the groove depths Da and Db of the shoulder lug grooves 25 is less than 1.5, the effect of reducing external noise and the effect of improving soil dischargeability will be insufficient, while if it is greater than 2.0, the traction performance and drainage performance based on the shoulder lug grooves 25 may be impaired. Furthermore, if the ratio Ls / L of the length Ls of the slope portion 52 in the tire width direction is outside the above range, the effect of improving soil dischargeability will be insufficient.

[0032] The slope portion 52 is preferably flat, but may also be curved. The slope portion 52 may have slight undulations or irregularities along the longitudinal direction of the shoulder lug groove 25, but excessive undulations or irregularities can reduce the effect of improving soil discharge. Therefore, the height of the undulations or irregularities in the slope portion 52 is preferably 0.5 mm or less. Note that protrusions may be provided in the shoulder lug groove 25 as long as they are located outside the slope portion 52 in the tire width direction.

[0033] 4, in the pneumatic tire, it is preferable that the distance La in the tire width direction from the main groove 10 to the start point A of the slope portion 52 and the distance L in the tire width direction from the main groove 10 to the ground contact edge E satisfy the relationship 0.05≦La / L≦0.2, and the distance Lb in the tire width direction from the main groove 10 to the end point B of the slope portion 52 and the distance L in the tire width direction from the main groove 10 to the ground contact edge E satisfy the relationship 0.55≦Lb / L≦1.0. By specifying the positions of the start point A and the end point B of the slope portion 52 in this way and ensuring a sufficient bottom-raised portion 51 adjacent to the main groove 10, it is possible to enhance the effects of reducing external noise and improving soil discharge performance.

[0034] Here, if the ratio La / L, which is the distance La in the tire width direction from the main groove 10 to the start point A of the slope portion 52, is less than 0.05, the effect of reducing external noise decreases, and conversely, if it is greater than 0.2, the effect of improving soil discharge decreases. On the other hand, if the ratio Lb / L, which is the distance Lb in the tire width direction from the main groove 10 to the end point B of the slope portion 52, is outside the above range, the effect of improving soil discharge decreases. For example, a preferred combination is La / L = 0.1 and Lb / L = 0.7.

[0035] 4 , it is preferable that the groove width of each shoulder lug groove 25 expands outward in the tire width direction in at least a portion of the longitudinal direction of the shoulder lug groove 25, the length Lx in the tire width direction from the main groove 10 to the widening start position of each shoulder lug groove 25 satisfies the relationship 0≦Lx / L≦0.2 with respect to the distance L in the tire width direction from the main groove 10 to the tread edge E, and the minimum width Wmin and maximum width Wmax of each shoulder lug groove 25 satisfy the relationship 1.5≦Wmax / Wmin≦2.0. By expanding the groove width of each shoulder lug groove 25 outward in the tire width direction in this way, soil discharge from the shoulder lug grooves 25 can be effectively improved.

[0036] Here, if the ratio Lx / L, which is the length Lx in the tire width direction from the main groove 10 to the widening start position of each shoulder lug groove 25, is greater than 0.2, the effect of improving soil discharge is reduced. Also, if the ratio Wmax / Wmin, which is the ratio of the minimum width Wmin to the maximum width Wmax of each shoulder lug groove 25, is less than 1.5, the effect of improving soil discharge is reduced. Conversely, if it is greater than 2.0, the groove width change is too large, which may result in a decrease in drainage performance due to the shoulder lug grooves 25 and a decrease in rigidity of the shoulder land portion 15.

[0037] In the pneumatic tire, it is preferable that the groove depth change rate X calculated from Db / Da and the groove width change rate Y calculated from Wmax / Wmin satisfy the relationship 1.0≦X / Y≦1.2. This effectively improves soil discharge from the shoulder lug grooves 25. If the ratio X / Y of the groove depth change rate X to the groove width change rate Y falls outside the above range, the soil discharge improvement effect decreases. In particular, by satisfying the relationship 1.0<X / Y≦1.2, the soil discharge improvement effect can be enhanced.

[0038] In the above-described pneumatic tire, as shown in FIG. 5 , the groove wall angle θ of the shoulder lug groove 25 relative to the normal to the tread surface of the tread portion 1 gradually decreases toward the outer side in the tire width direction in the region corresponding to the slope portion 52 (i.e., the region between start point A and end point B), and it is preferable that the groove wall angle θ of the shoulder lug groove 25 be in the range of 0° to 10°. This effectively improves soil discharge from the shoulder lug groove 25. In other words, when the groove wall angle θ of the shoulder lug groove 25 gradually decreases toward the outer side in the tire width direction, the cross-sectional area of ​​the shoulder lug groove 25 gradually increases toward the outer side in the tire width direction, thereby improving soil discharge. For example, the groove wall angle θ of the shoulder lug groove 25 can be set to 5° at the start point A of the slope portion 52 and 0° at the end point B of the slope portion 52.

[0039] In the above-described pneumatic tire, circumferential auxiliary grooves 45 are formed in the tread portion 1, extending in the tire circumferential direction and intersecting the shoulder lug grooves 25, and the circumferential auxiliary grooves 45 are preferably located between the start point A and the end point B of the slope portion 52. This effectively improves soil discharge from the shoulder lug grooves 25. That is, soil and mud trapped in the shoulder lug grooves 25 move along the slope portion 52, and the presence of the circumferential auxiliary groove 45 between the start point A and the end point B of the slope portion 52 makes it easier for the soil and mud to be discharged. In particular, it is preferable that the circumferential auxiliary groove 45 is located closer to the end point B of the slope portion 52 than the start point A, thereby more effectively improving soil discharge.

[0040] The groove width of the circumferential auxiliary groove 45 is preferably in the range of 30% to 60% of the groove width of the shoulder lug groove 25 at the opening position to the main groove 10. This makes it possible to effectively improve soil discharge from the shoulder lug groove 25 without reducing the effect of improving external noise. If the groove width of the circumferential auxiliary groove 45 is less than 30% of the groove width of the shoulder lug groove 25 at the opening position to the main groove 10, the effect of improving soil discharge is reduced, and conversely, if it is more than 60%, it becomes a factor that worsens external noise.

[0041] In the above-described embodiment, a specific structure is applied to shoulder lug grooves formed in the shoulder land portion on one side of the tread portion in the tire width direction. However, in the present invention, the above structure can be applied to shoulder lug grooves on at least one side of the tread portion, and can also be applied to shoulder lug grooves on both sides of the tread portion.

[0042] In a pneumatic tire having a tire size of 265 / 65R17 112H, a tread portion, a pair of sidewall portions, and a pair of bead portions, and having the tread pattern shown in FIG. 2, tires of Comparative Examples 1 to 4 and Examples 1 to 6 were manufactured in which the shoulder lug groove structures communicating with the main grooves were variously varied.

[0043] In Comparative Examples 1 to 4 and Examples 1 to 6, the presence or absence of a bottom-up portion, the presence or absence of a slope portion, the groove depth change rate X of the shoulder lug groove (X = Db / Da), the ratio Ls / L relating to the length of the slope portion, the ratio La / L relating to the start point of the slope portion, the ratio Lb / L relating to the end point of the slope portion, the groove width change rate Y (Y = Wmax / Wmin), the ratio X / Y, the groove wall angle θ of the shoulder lug groove, the presence or absence of a circumferential auxiliary groove, the position of the circumferential auxiliary groove, and the groove width ratio of the circumferential auxiliary groove (the ratio to the groove width at the opening position of the shoulder lug groove to the main groove) were set as shown in Table 1. Regarding the groove wall angle θ of the shoulder lug groove, "5 → 0" means that the groove wall angle θ of the shoulder lug groove was 5° at the position of the start point A of the slope portion and 0° at the position of the end point B of the slope portion. Regarding the position of the circumferential auxiliary groove, "between A and B" means that the circumferential auxiliary groove is located between the start point A and the end point B of the slope portion.

[0044] These test tires were evaluated for soil discharge performance and vehicle exterior noise performance by the following test methods, and the results are shown in Table 1.

[0045] Dirt ejection performance: Each test tire was mounted on a wheel with a rim size of 17x8J and mounted on a test vehicle (SUV) with an engine displacement of 2700cc, and the tire pressure was set to 230kPa. A sensory evaluation was carried out by a test driver on an off-road test course. That is, off-road running performance was evaluated as an index of dirt ejection performance. The evaluation results were expressed as an index with Comparative Example 1 being 100. The higher the index value, the better the dirt ejection performance.

[0046] External noise performance: Each test tire was mounted on a wheel with a rim size of 17x8J and mounted on a test vehicle (SUV) with an engine displacement of 2700cc, and the tire was inflated to 230 kPa. The external noise [dB] was measured under the conditions of ECE R51.03. The evaluation results were expressed as an index using the reciprocal of the measured value, with Comparative Example 1 being set at 100. The higher the index value, the better the external noise performance.

[0047]

[0048] As can be seen from Table 1, the tires of Examples 1 to 6 were able to reduce external noise and improve soil dischargeability, thereby demonstrating excellent off-road driving performance, compared to Comparative Example 1. On the other hand, the tire of Comparative Example 2 had an excessively small groove depth change rate X (X = Db / Da) of the shoulder lug grooves, so the effect of improving soil dischargeability and the effect of reducing external noise were insufficient. The tire of Comparative Example 3 had an excessively small ratio Ls / L related to the length of the slope portion, so the effect of improving soil dischargeability was insufficient. The tire of Comparative Example 4 had an excessively large ratio Ls / L related to the length of the slope portion, so the effect of improving soil dischargeability was insufficient.

[0049] REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 10 main groove 11, 12, 13, 14, 15 land portion 21, 22, 23, 24, 25 lug groove 31, 32, 33, 34, 35 sipe 41, 45 circumferential auxiliary groove 51 bottom raised portion 52 slope portion E ground contact edge

Claims

1. A tire having a circumferentially extending annular tread portion, in which a circumferentially extending main groove and a plurality of shoulder lug grooves extending in the tire width direction are formed, one end of each shoulder lug groove is connected to the main groove and the other end is located outboard in the tire width direction of the ground contact edge of the tread portion, wherein each shoulder lug groove has a bottom-up portion adjacent to the main groove and a slope portion in which the groove depth of the shoulder lug groove gradually increases from the bottom-up portion toward the outside in the tire width direction, the groove depths Da, Db of the shoulder lug groove at a start point A and an end point B of the slope portion satisfy the relationship 1.5≦Db / Da≦2.0, and the length Ls of the slope portion in the tire width direction with respect to the distance L in the tire width direction from the main groove to the ground contact edge satisfies the relationship 0.5≦Ls / L≦0.

8.

2. The tire according to claim 1, wherein a distance La in the tire width direction from the main groove to a start point A of the slope portion and a distance L in the tire width direction from the main groove to the ground contact edge satisfy a relationship of 0.05≦La / L≦0.2, and a distance Lb in the tire width direction from the main groove to an end point B of the slope portion and a distance L in the tire width direction from the main groove to the ground contact edge satisfy a relationship of 0.55≦Lb / L≦1.

0.

3. A tire as described in claim 1 or 2, characterized in that the groove width of each shoulder lug groove expands outward in the tire width direction in at least a portion of the longitudinal direction of the shoulder lug groove, the length Lx in the tire width direction from the main groove to the widening start position of each shoulder lug groove satisfies the relationship 0≦Lx / L≦0.2 with respect to the distance L in the tire width direction from the main groove to the ground contact edge, and the minimum width Wmin and maximum width Wmax of each shoulder lug groove satisfy the relationship 1.5≦Wmax / Wmin≦2.

0.

4. The tire according to claim 3, wherein the groove depth change rate X calculated from Db / Da and the groove width change rate Y calculated from Wmax / Wmin satisfy the relationship 1.0≦X / Y≦1.

2.

5. A tire as described in any one of claims 1 to 4, characterized in that the groove wall angle of the shoulder lug groove with respect to the normal direction of the tread surface of the tread portion gradually decreases toward the outside in the tire width direction in the region corresponding to the slope portion, and the groove wall angle of the shoulder lug groove is in the range of 0° to 10°.

6. A tire as described in any one of claims 1 to 5, characterized in that a circumferential auxiliary groove is formed in the tread portion extending in the tire circumferential direction and intersecting with the shoulder lug grooves, and the circumferential auxiliary groove is located between a start point A and an end point B of the slope portion.

7. The tire according to claim 6, wherein the groove width of the circumferential auxiliary groove is in the range of 30% to 60% of the groove width of the shoulder lug groove at an opening position into the main groove.

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