Heavy-duty tires

Abstract

This heavy-duty tire provides a balance between center rigidity and traction performance, while also offering excellent resistance to uneven wear. [Solution] The tread of the heavy-duty tire according to the present invention is provided with a center ridge and shoulder ridges. When not in use, the center ridge and shoulder ridges have a block pattern due to first circumferential grooves and second circumferential grooves extending in the circumferential direction of the tire, and first widthwise grooves and second widthwise grooves aligned in the circumferential direction of the tire. As the tread wears down, the center ridge and shoulder ridges change from a block pattern to a rib pattern.

Description

Technical Field

[0001] The present invention relates to a heavy-duty tire. Background Art

[0002] In heavy-duty tires used for heavy-duty vehicles and the like, the center land portion having high ground contact pressure is prone to wear, and during turning, a large lateral force is applied to the shoulder land portion, so uneven wear is likely to occur. This tendency is particularly remarkable when the tire is used in an electric vehicle (EV) that has a large vehicle body weight and applies a large torque to the tire. Patent Document 1 discloses a tire in which, in order to achieve both wear resistance and wet performance, a center land portion is constituted by center blocks, and the center block has center narrow grooves of a predetermined shape in which both ends communicate with a center lug groove extending in the tire width direction, and two or more bent portions are provided in the middle of the center narrow grooves. Prior Art Literature Patent Literature

[0003] Patent Document 1 Japanese Unexamined Patent Application Publication No. 2024-110220 Summary of the Invention Problem to be Solved by the Invention

[0004] Generally, when the rigidity of the center land portion is increased by reducing or shallowing grooves or sipes, the wear resistance is improved, but the traction performance is reduced. The technology described in Patent Document 1 still has room for improvement regarding the suppression of traction performance reduction.

[0005] An object of the present invention is to provide a heavy-duty tire that achieves both the rigidity of the center land portion and traction performance, and is excellent in the effect of suppressing uneven wear. Means for Solving the Problem

[0006] The heavy-duty tire according to the present invention has a tread comprising a center ridge and a shoulder ridge. When not in use, a first circumferential groove extending in the tire circumferential direction is formed between the center ridge and the shoulder ridge, and a second circumferential groove extending in the tire circumferential direction is formed approximately in the center of the center ridge in the tire width direction. The center ridge is divided into a center block by the second circumferential groove and a first width direction groove aligned in the tire circumferential direction, and the shoulder ridge is divided into a shoulder block by a second width direction groove aligned in the tire circumferential direction. The depth of the first width direction groove and the second width direction groove is the first circumferential groove. The groove depth is 10% to 30% of the groove depth, a first groove bottom sipe is formed at the bottom of the first widthwise groove, and a second groove bottom sipe is formed at the bottom of the second widthwise groove. The center block has a bent sipe that extends in the circumferential direction of the tire, with both ends opening into the first widthwise groove and having two bends, and a short sipe that extends in the circumferential direction of the tire, with one end opening into the first widthwise groove and the other end closed within the center block. As the tread wears down, the first and second widthwise grooves disappear, and the center and shoulder ridges change from a block pattern to a rib pattern.

[0007] In the above-mentioned heavy-duty tire, when unused, the width of the second circumferential groove is narrower than the width of the first circumferential groove, and the width of the first circumferential groove may decrease due to wear.

[0008] In the above heavy-duty tire, the curved sipe has the same shape as when unused when the first and second widthwise grooves disappear, and may be divided into three parts when the curved portion disappears due to further wear of the tread.

[0009] In the above-mentioned heavy-duty tire, the first groove bottom sipe and the second groove bottom sipe have the same shape as when unused when the first widthwise groove and the second widthwise groove disappear, and may be divided into two parts when the central part disappears due to further wear of the tread.

[0010] In the above-mentioned heavy-duty tire, the first groove bottom sipe may remain even when the second groove bottom sipe disappears due to further wear of the tread. [Effects of the Invention]

[0011] The heavy-duty tire according to the present invention achieves both rigidity of the center rim and traction performance while also being excellent in suppressing uneven wear. [Brief explanation of the drawing]

[0012] [Figure 1] This is a perspective view showing a part of a heavy-duty tire, which is an example of an embodiment. [Figure 2] This is an enlarged view of a portion of the tread in a heavy-duty tire, which is an example of an embodiment. [Figure 3] This figure shows a cross-section of line AA in Figure 2. [Figure 4] This figure shows a cross-section of line BB in Figure 2. [Figure 5] This figure shows a cross-section of the CC line in Figure 2. [Figure 6] This figure shows a cross-section of the DD line in Figure 2. [Figure 7] This is an enlarged view of the center block in a heavy-duty tire, which is one example of an embodiment. [Figure 8] This figure shows a cross-section of the EE line in Figure 7. [Figure 9] This figure shows the changes due to wear of the tread of a heavy-duty tire, which is an example of an embodiment. [Figure 10] This is an enlarged view of a portion of the sidewall of a heavy-duty tire, which is one example of an embodiment. [Modes for carrying out the invention]

[0013] Hereinafter, an example of an embodiment of the heavy-duty tire according to the present invention will be described in detail with reference to the drawings. The embodiments described below are merely examples, and the present invention is not limited to these embodiments. Furthermore, selectively combining the various components of the multiple embodiments and modifications described below is included in the present invention. Figures 1 to 8, except for Figure 9, all show the configuration of the tread 10 when not in use. Also, in the following, "depth" refers to the maximum depth.

[0014] Figure 1 is a perspective view showing a part of a heavy-duty tire 1, which is an example of an embodiment, and also illustrates the internal structure of the tire. As shown in Figure 1, the heavy-duty tire 1 comprises a tread 10, which is the part that contacts the road surface, a pair of sidewalls 11 extending radially inward from the tread 10, and a pair of beads 12 that contact the rim of the wheel. The tread 10, sidewalls 11, and beads 12 are formed in an annular shape along the circumferential direction of the tire. The sidewalls 11 and beads 12 form the left and right sides of the heavy-duty tire 1.

[0015] The heavy-duty tire 1 comprises a carcass 13, a belt 14, and an inner liner rubber 16. The carcass 13 is a rubber-coated cord layer that forms the skeleton of the heavy-duty tire 1, capable of withstanding loads, impacts, air pressure, etc. The carcass 13 is stretched between a pair of beads 12 on the radially inward side of the tread 10 and is folded back from the inside to the outside in the axial direction of the tire at the beads 12. The belt 14 is a reinforcing band positioned radially outward of the carcass 13, tightening the carcass 13 and increasing the rigidity of the heavy-duty tire 1. The belt 14 is made of, for example, rubber-coated steel cords. The inner liner rubber 16 is a rubber layer positioned radially inward of the carcass 13 and maintains the air pressure of the heavy-duty tire 1.

[0016] A heavy-duty tire 1 includes a bead core and a bead filler. The bead core and the bead filler are respectively provided in the beads 12 on both the left and right sides. The bead core is a ring-shaped member formed by coating bundled steel wires with rubber. The bead filler is formed of hard rubber and has a function of increasing the rigidity of the bead 12.

[0017] A side protector 18 protruding outward of the tire beyond a profile surface is formed on the sidewall 11. Here, the "profile surface" excludes protrusions such as the side protector 18, and means the contour of the outer surface of the sidewall main body. The side protector 18 is formed annularly along the tire circumferential direction. Since the sidewall 11 is thickened by the side protector 18, the impact resistance performance is improved.

[0018] It is preferable that the surface of the side protector 18 is flat. By flattening the surface of the side protector 18, the air flow around the tire is improved, and the air resistance can be reduced. Generally, convex side ribs formed by combining straight lines and curved lines, or concave depressions are formed on the surface of a conventional side protector, but the above effect can be obtained by making the surface of the side protector 18 flat without patterns, characters or the like.

[0019] The tread 10 comprises a center ridge 20 and shoulder ridges 22. A first circumferential groove 25 extending in the tire circumferential direction is formed between the center ridge 20 and the shoulder ridges 22, and a second circumferential groove 27 extending in the tire circumferential direction is formed approximately in the center of the center ridge 20 in the tire width direction. The center ridge 20 is divided in the tire width direction by the second circumferential groove 27, and the left and right treads divided by the second circumferential groove 27 in a plane perpendicular to the tread 10 have the same shape. In the example shown in Figure 1, the second circumferential groove 27 and the two first circumferential grooves 25 have approximately the same depth. Here, the depth of the first circumferential groove 25 and the second circumferential groove 27 refers to the distance in the tire radial direction from the top surface of the tread 10 to the bottom surface of the groove. The depths of the first circumferential groove 25 and the second circumferential groove 27 may be approximately the same around the entire circumference of the tire.

[0020] In the example shown in Figure 1, the center block 20 is divided into a center block 36 by a second circumferential groove 27 and a first widthwise groove 31 arranged in the circumferential direction of the tire. The shoulder block 22 is divided into a shoulder block 38 by a second widthwise groove 33 arranged alternately in the circumferential direction of the tire.

[0021] The tread 10, and in particular the center ridge 20, will be described in more detail below with reference to Figures 2 to 9. Figure 2 is an enlarged view of a part of the tread 10 in a heavy-duty tire 1, which is an example of an embodiment.

[0022] Preferably, the width W1 of the first circumferential groove 25 is 2.5% to 7% of the width E of the contact edge of the tread 10, the width W2 of the second circumferential groove 27 is 2% to 5% of the width of the contact edge of the tread, and the distance P between the first circumferential groove 25 and the second circumferential groove 27 is 20% to 28% of the width E of the contact edge of the tread 10. This allows for a larger center block 36 to improve rigidity and suppress excessive movement of the center block 36 during contact. The number of pitches of the center block 36 and shoulder blocks 38 in the circumferential direction of the tire is not particularly limited, but for example, both are 50 or less. By reducing the number of pitches, the center block 36 and shoulder blocks 38 can be made larger.

[0023] In this specification, the contact end refers to both ends of the axial region of the tire that contacts a flat road surface when an unused heavy-duty tire 1 is mounted on a regular rim, inflated to the regular internal pressure, and subjected to a load of 88% of the regular load (maximum load capacity) at the regular internal pressure.

[0024] Here, "standard rim" refers to the rim defined by the tire standard, which is "standard rim" for JATMA, "Design Rim" for TRA, and "Measuring Rim" for ETRTO. "Standard internal pressure" is "maximum air pressure" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "INFLATION PRESSURE" for ETRTO. "Standard load" is "maximum load capacity" for JATMA, the maximum value listed in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" for TRA, and "LOAD CAPACITY" for ETRTO.

[0025] The width W2 of the second circumferential groove 27 is preferably narrower than the width W1 of the first circumferential groove 25. This allows for a larger center block 36, improving rigidity and suppressing excessive movement of the center block 36 when it comes into contact with the ground.

[0026] The first circumferential groove 25 may extend in a zigzag pattern with respect to the tire circumferential direction, and similarly, the second circumferential groove 27 may also extend in a zigzag pattern with respect to the tire circumferential direction. In the example shown in Figure 2, the first circumferential groove 25 is composed of alternating connections of a first inclined section 25a that is inclined at 3° to 10° with respect to the tire circumferential direction and a second inclined section 25b that is inclined at 30° to 60° with respect to the tire circumferential direction. The first inclined section 25a is longer than the second inclined section 25b. The second circumferential groove 27 is composed of alternating connections of a third inclined section 27a that is inclined at 3° to 10° with respect to the tire circumferential direction and a fourth inclined section 27b that is inclined at 30° to 60° with respect to the tire circumferential direction. The third inclined section 27a is longer than the fourth inclined section 27b.

[0027] The first widthwise groove 31 is inclined at a certain angle with respect to the tire width direction. The angle of the first widthwise groove 31 with respect to the tire equator is, for example, in the range of 55° to 85°. A first groove bottom sipe 41, which is substantially parallel to the first widthwise groove 31, is formed on the bottom surface of the first widthwise groove 31. This ensures traction performance while maintaining the rigidity of the center block 36. Due to the first groove bottom sipe 41, adjacent center blocks 36 in the circumferential direction of the tire are substantially in contact with each other at the contact surface, so that the center block 20 can have a rigidity equivalent to that of a rib pattern, even if it is a block pattern. Here, a sipe is a thin, linear groove that is narrower in width than the circumferential groove and the widthwise groove. In this specification, a groove with a groove width of less than 1.5 mm is defined as a sipe.

[0028] Figure 3 shows a cross-section along line AA in Figure 2, illustrating the cross-sections of the first widthwise groove 31 and the first groove bottom sipe 41. The first widthwise groove 31 and the first groove bottom sipe 41 may have a substantially rectangular cross-section. The first groove bottom sipe 41 is formed, for example, approximately in the center of the widthwise direction of the bottom surface of the first widthwise groove 31.

[0029] The depth D1 of the first widthwise groove 31 is 10% to 30% of the depth of the first circumferential groove 25. If D1 is less than 10% of the depth of the first circumferential groove 25, traction performance decreases, and if D1 is greater than 30% of the depth of the first circumferential groove 25, the rigidity of the center block 36 decreases. Here, the depth D1 of the first widthwise groove 31 refers to the distance in the radial direction of the tire from the top surface of the center block 36 to the bottom surface of the groove. The depth of the first widthwise groove 31 is approximately the same from the end communicating with the first circumferential groove 25 to the end communicating with the second circumferential groove 27.

[0030] Figure 4 shows a cross-section of the BB line in Figure 2, illustrating the bottom surface of the first groove bottom sipe 41. Figure 4 also includes a dashed line 36i representing the surface of the center block 36 to indicate the depth of the first groove bottom sipe 41. The central portion 41A of the first groove bottom sipe 41 is shallower than the inner portion 41B, which is adjacent to the central portion 41A in the tire width direction, and the outer portion 41C, which is adjacent to the central portion 41A in the tire width direction. The depth D2 of the central portion 41A is, for example, 20% to 40% of the depth of the first circumferential groove 25, while the depths D3 of the inner portion 41B and the outer portion 41C are, for example, 80% to 100% of the depth of the first circumferential groove 25. This makes the effect of balancing the rigidity and traction performance of the center block 36 more pronounced. As shown in Figure 4, the central portion 41A may have a flat bottom surface with a depth D2, and the inner portion 41B and outer portion 41C may have flat bottom surfaces with a depth D3. The length L1 of the central portion 41A is, for example, 25% to 75% of the total length L2 of the first groove bottom sipe 41. The inner side of the inner portion 41B in the tire width direction and the outer side of the outer portion 41C in the tire width direction are in communication with the first widthwise groove 31 with a depth D1.

[0031] As shown in Figure 2, the second widthwise groove 33 may be curved. Furthermore, a second groove bottom sipe 43, substantially parallel to the second widthwise groove 33, may be formed at the bottom of the groove. This ensures traction performance while maintaining the rigidity of the shoulder block 38. The second groove bottom sipe 43 is formed substantially parallel to the second widthwise groove 33 and may be curved in the same way as the second widthwise groove 33. Also, as will be described later, the curved portion may be shallower than the other portions. Because the second groove bottom sipe 43 causes adjacent shoulder blocks 38 in the circumferential direction of the tire to substantially contact each other at the contact surface, the shoulder block 22 can have a rigidity equivalent to that of a rib pattern, even if it has a block pattern.

[0032] Figure 5 shows a cross-section along line CC in Figure 2, and illustrates the cross-sections of the second widthwise groove 33 and the second groove bottom sipe 43. The second widthwise groove 33 and the second groove bottom sipe 43 may have a substantially rectangular cross-section. The second groove bottom sipe 43 is formed, for example, approximately in the center of the widthwise direction of the bottom surface of the second widthwise groove 32.

[0033] The depth D4 of the second widthwise groove 33 is 10% to 30% of the depth of the first circumferential groove 25. If D1 is less than 10% of the depth of the first circumferential groove 25, traction performance decreases, and if D1 is greater than 30% of the depth of the first circumferential groove 25, the rigidity of the shoulder block 38 decreases. Here, the depth D4 of the second widthwise groove 33 refers to the distance in the radial direction of the tire from the top surface of the shoulder block 38 to the bottom surface of the groove. The depth of the second widthwise groove 33 is approximately the same from the end communicating with the first circumferential groove 25 to the contact end.

[0034] Figure 6 shows a cross-section along the DD line in Figure 2, illustrating the bottom surface of the second groove bottom sipe 43. Figure 6 also includes a dashed line 38i representing the surface of the shoulder block 38 to indicate the depth of the second groove bottom sipe 43. The central portion 43A of the second groove bottom sipe 43 is shallower than the inner portion 43B, which is adjacent to the central portion 43A in the tire width direction, and the outer portion 43C, which is adjacent to the central portion 43A in the tire width direction. The depth D5 of the central portion 43A is, for example, 20% to 40% of the depth of the first circumferential groove 25, while the depths D6 of the inner portion 43B and the outer portion 43C are, for example, 50% to 70% of the depth of the first circumferential groove 25. This makes the effect of balancing the rigidity and traction performance of the shoulder block 38 more pronounced. As shown in Figure 6, the central portion 43A may have a flat bottom surface with a depth of D5, and the inner portion 43B and outer portion 43C may have flat bottom surfaces with a depth of D6. The length L3 of the central portion 43A is, for example, 25% to 75% of the total length L4 of the second groove bottom sipe 43. The inner side of the inner portion 43B in the tire width direction and the outer side of the outer portion 43C in the tire width direction are in communication with the second widthwise groove 33 with a depth of D4.

[0035] Next, the center block 36 will be described in detail with reference to Figures 7 and 8. Figure 7 is an enlarged view of the center block 36 in a heavy-duty tire 1, which is an example of an embodiment. In Figure 7, a first circumferential groove 25 is provided on the right side of the center block 36, and a second circumferential groove 27 is provided on the left side of the center block 36. The center block 36 has a substantially parallelogram shape, with a pair of opposing vertices largely missing. This prevents uneven wear at the acute angles of the center block 36. The size of the missing portion of the vertices of the center block 36 may be 7% to 15% of the center block width and 7% to 15% of the center block circumferential width.

[0036] The center block 36 has a curved sipe 45 and a short sipe 47 formed thereon. The curved sipe 45 extends in the circumferential direction of the tire, with both ends opening into the first widthwise groove 31, and has two curved sections 45A and 45B. The curved sipe 45 also has a first straight section 45C between the curved sections 45A and 45B, and a second straight section 45D between the curved sections 45A and 45B and the open end 45E. The second straight section 45D extends approximately parallel to the widthwise end of the center block 36, i.e., the first widthwise groove 31. The first straight section 45C extends approximately parallel to the first widthwise groove 31 and extends near the circumferential center of the center block 36. The first straight section 45C and the second straight section 45D intersect at an obtuse angle at the intersection point, which is a curve. The short sipes 47 extend in the circumferential direction of the tire, with one end opening into the first widthwise groove 31 and the other end closed within the center block 36. By providing the bent sipes 45 within the center block 36, the two sections divided in the tire widthwise direction by the bent sipes 45 interlock with each other, suppressing the movement of the center block 36, thereby reducing slippage during rolling and turning and suppressing uneven wear. Furthermore, by providing the short sipes 47 within the center block 36, the movement of the center block 36 in the tire widthwise direction is reduced, suppressing uneven wear. The length of the short sipes 47 is 5% to 15% of the circumferential length of the center block 36. From the viewpoint of balancing the rigidity within the center block 36, it is preferable that the bent sections 45A and 45B be located approximately in the center of the tire circumferential length of the center block 36.

[0037] In the example shown in Figure 7, the distance L5 between the open end 45E and the center 36C, and the distance L6 between the open end 47E and the center 36C, are both 15% to 20% of the width W of the center block 36. In other words, the open end 45E of the bent sipe 45 and the open end 47E of the short sipe 47 are located, for example, within a range of 15% to 20% of the width of the center block 36 from the center 36C in the tire width direction of the center block 36. This allows for a better balance of rigidity within the center block 36.

[0038] Figure 8 shows a cross-section along the EE line in Figure 7, illustrating the configuration of the bottom surface of the bent sipe 45. Figure 8 also includes a dashed line 36i representing the surface of the center block 36 to indicate the depth of the bent sipe 45. The bent portions 45A and 45B of the bent sipe 45 are shallower than the first straight portion 45C and the second straight portion 45D. The depth D7 of the bent portions 45A and 45B is, for example, 5% to 30% of the depth of the first circumferential groove 25, while the depth D8 of the first straight portion 45C and the second straight portion 45D is, for example, 50% to 70% of the depth of the first circumferential groove 25. This makes the effect of balancing the rigidity and traction performance of the center block 36 more pronounced. As shown in Figure 8, the bent portions 45A and 45B may have a flat bottom surface with a depth D7, and the first straight portion 45C and the second straight portion 45D may have a flat bottom surface with a depth D8. The length L7 of the bent sections 45A and 45B is, for example, 10% to 30% of the total length L8 of the bent sipe 45. The end of the second straight section 45D is in communication with the first widthwise groove 31, which has a depth D1.

[0039] The depth of the short sipes 47 is not particularly limited, but for example, it is 10% to 30% of the depth of the first circumferential grooves 25. This makes the effect of balancing the rigidity and traction performance of the center block 36 more pronounced. The short sipes 47 may have a flat bottom surface of a certain depth.

[0040] The above describes the heavy-duty tire 1 when not in use using Figures 1 to 8. Next, we will explain the changes in the tread 10 due to wear, referring to Figure 9.

[0041] Figure 9 shows the changes due to wear of the tread 10 of a heavy-duty tire 1, which is an example of an embodiment. As shown in Figure 9, in the unused state (a), the center tread has a block pattern divided by grooves in the width direction.

[0042] As the tire is used, the tread wears down, and in (b), the first and second widthwise grooves disappear, and the center and shoulder ridges change from a block pattern to a rib pattern. Also, the short sipes disappear on the center ridge. Further use of the tire changes the tread to the shape shown in (c). When unused, widthwise grooves are provided to obtain excellent traction performance, but as the tire is used, the contact condition between the tire surface and the ground changes, and even if the widthwise grooves disappear, sufficient traction performance can be obtained by the sipes.

[0043] As shown in (b), the curved sipe has the same shape as when it was unused when the first widthwise groove disappears, and as further wear of the tread causes the curved portion to disappear and divide into three parts, as shown in (c).

[0044] As shown in (b), the first groove bottom sipe and the second groove bottom sipe have the same shape as when unused when the first widthwise groove and the second widthwise groove disappear, and as further wear of the tread may cause the central part to disappear and divide into two, as shown in (c).

[0045] The first groove bottom sipe may remain even after the second groove bottom sipe has disappeared due to further wear of the tread, as shown in (d). Because the contact pressure is higher on the center of the tread than on the sides, the traction performance of the tire can be ensured by retaining sipes on the center of the tread even after the sipes on the sides have disappeared. As wear progresses further, the tread will change to a state in which all sipes have disappeared. In this state, the treadwear indicator will appear on the tire surface, and it will be time to replace the tire.

[0046] When unused, the width of the second circumferential groove is narrower than the width of the first circumferential groove, and the width of the first circumferential groove may decrease due to wear. The tread can be changed as described above by making the inclination of the side surface of the first circumferential groove with respect to the tire diameter greater than the inclination of the side surface of the second circumferential groove with respect to the tire diameter. In the first circumferential groove, which is wider than the second circumferential groove, increasing the inclination of the side surface as described above can suppress foreign objects such as stones from becoming lodged in the first circumferential groove.

[0047] Next, with reference to Figure 10, we will describe the sidewall 11, particularly the area around the buttress. Figure 10 is an enlarged view of a part of the sidewall 11 of a heavy-duty tire 1, which is an example of an embodiment.

[0048] The second widthwise groove 33 communicates with the lug groove 51 formed in the sidewall 11, and the lug groove 51 may be deeper than the first circumferential groove in the radial direction of the tire. In large vehicles such as buses and trucks, the tread is hidden and cannot be visually inspected, so tire wear is usually checked on the sidewall 11. By making the lug groove 51 deeper in the radial direction of the tire, the degree of tire wear can be recognized more accurately.

[0049] Side sipes 53 may be formed between the lug grooves 51. Alternatively, counterbore windows 55 wider than the side sipes 53 may be created. By providing side sipes 53 or counterbore windows 55, the area near the contact end of the shoulder land 22 becomes more flexible, improving the driving stability of the road surface where ruts are formed. In the example shown in Figure 10, two side sipes 53 and one counterbore window are formed in the order of side sipe 53, counterbore window 55, side sipe 53, extending from one lug groove 51 to the adjacent lug groove 51.

[0050] In the radial direction of the tire, one end of the side sipe 53 may be in contact with the contact edge, or it may extend beyond the contact edge to the tread 10. The other end of the side sipe 53 may extend to a position deeper than the first circumferential groove. This reduces the lateral force acting on the shoulder ridge 22 and suppresses the occurrence of uneven wear. In the example shown in Figure 10, one end of the side sipe 53 extends beyond the contact edge to the tread 10.

[0051] As described above, the heavy-duty tire according to the present invention achieves both rigidity of the center tread and traction performance while also being excellent in suppressing uneven wear. Specifically, the above effect can be obtained by having a center tread and shoulder treads of a predetermined shape when unused, and by the center tread and shoulder treads changing from a block pattern to a rib pattern as the tread wears down. [Explanation of symbols]

[0052] 1 Heavy-duty tire, 10 Tread, 11 Sidewall, 12 Bead, 12a Bead core, 12b Bead filler, 13 Carcass, 14 Belt, 16 Inner liner rubber, 20 Center block, 22 Shoulder block, 25 First circumferential groove, 27 Second circumferential groove, 31 First widthwise groove, 33 Second widthwise groove, 36 Center block, 38 Shoulder block, 41 First groove bottom sipe, 43 Second groove bottom sipe, 45 Bent sipe, 47 Short sipe, 51 Lug groove, 53 Side sipe, 55 Counterbore window

Claims

1. A heavy-duty tire having a tread with a center tread and shoulder treads, When not in use, A first circumferential groove extending in the tire circumferential direction is formed between the center plate and the shoulder plate, and a second circumferential groove extending in the tire circumferential direction is formed approximately in the center of the center plate in the tire width direction. The aforementioned center land is divided into a center block by the second circumferential groove and the first widthwise grooves arranged in the circumferential direction of the tire. The aforementioned shoulder land is divided into shoulder blocks by second widthwise grooves arranged in the circumferential direction of the tire. The depths of the first widthwise groove and the second widthwise groove are 10% to 30% of the depth of the first circumferential groove. A first groove bottom sipe is formed at the bottom of the first widthwise groove, and a second groove bottom sipe is formed at the bottom of the second widthwise groove. The center block is formed with a bent sipe that extends in the circumferential direction of the tire, with both ends opening into the first widthwise groove and having two bent portions, and a short sipe that extends in the circumferential direction of the tire, with one end opening into the first widthwise groove and the other end being closed within the center block. A heavy-duty tire in which, due to wear of the tread, the first and second widthwise grooves disappear, and the center and shoulder ridges change from a block pattern to a rib pattern.

2. When not in use, the width of the second circumferential groove is narrower than the width of the first circumferential groove. The heavy-duty tire according to claim 1, wherein the width of the first circumferential groove decreases due to wear.

3. The heavy-duty tire according to claim 1, wherein the curved sipe has the same shape as when unused when the first widthwise groove and the second widthwise groove disappear, and the curved portion disappears and is divided into three parts due to further wear of the tread.

4. The heavy-duty tire according to claim 1, wherein the first groove bottom sipe and the second groove bottom sipe have the same shape as when unused when the first widthwise groove and the second widthwise groove disappear, and the central part disappears and the tire is divided into two due to further wear of the tread.

5. The heavy-duty tire according to claim 1, wherein the first groove bottom sipe remains even when the second groove bottom sipe disappears due to further wear of the tread.

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