tire

Abstract

To provide a tire capable of achieving both uneven wear resistance and on-snow performance.SOLUTION: A plurality of circumferential direction grooves 20 disposed on a tread surface 15A include: a pair of outermost circumferential direction grooves 21 disposed on the outermost side in a tire width direction respectively, and a circumferential direction narrow groove 22 whose groove width is 30% or less of the groove width of the outermost circumferential direction groove 21. The width CW in the tire width direction of a center part 31 is 45% or more of a tread width TW. A lug groove 40 includes a closed lug groove 40a whose groove bottom 40ab side is closed at least from the position half a groove depth Dc at the time of touching the ground, and an open lug groove 40b whose groove bottom 40ab side is not closed when touching the ground. A block 30 includes a center block 31Ba zoned by the circumferential direction grooves 20 disposed inside in the tire width direction of the outermost circumferential direction groove 21. The closed lug groove 40a and the open lug groove 40b are disposed alternately in the tire circumferential direction in a center block row 31B where the center blocks 31Ba are aligned in the tire circumferential direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Tires mounted on vehicles have grooves formed in the tread portion to ensure various performance characteristics according to the manner in which the tire is used, and performance is improved by devising the shape of the grooves. For example, a pneumatic tire described in Patent Document 1 has circumferential narrow grooves extending along the tire circumferential direction in the tread portion to define and form central rib-like land portions, and when the tire comes into contact with the ground, the openings of the circumferential narrow grooves close, so that adjacent central rib-like land portions positioned across the circumferential narrow grooves come into contact with and support each other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-020714 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, in order to reduce rolling resistance in tires for drive shafts, many tires have adopted narrow circumferential grooves with block rows concentrated in the tire widthwise center. By concentrating block rows closer to the center, block deformation during contact with the ground can be reduced, which is expected to suppress uneven wear. However, concentrating block rows with narrow circumferential grooves also reduces groove volume. A reduced groove volume in the tread portion can reduce snow column shear force during driving on snowy roads, potentially reducing traction performance on snowy roads. This has made it extremely difficult to simultaneously suppress uneven wear and improve driving performance on snowy roads.

[0005] The present invention has been made in view of the above, and has an object to provide a tire that can achieve both uneven wear resistance and performance on snow. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, a tire according to the present invention includes at least four or more circumferential grooves arranged on a tread surface and extending in a tire circumferential direction, a plurality of lug grooves arranged at least between the circumferential grooves on the tread surface and extending in a tire width direction, and blocks defined by the circumferential grooves and the lug grooves, wherein the plurality of circumferential grooves each include a pair of outermost grooves arranged on the outermost sides in the tire width direction among the plurality of circumferential grooves, and a circumferential narrow groove having a groove width of 30% or less of the groove width of the outermost groove, The center portion, which is the portion between the circumferential grooves, has a width in the tire width direction of 45% or more of the developed width of the tread surface, and the lug grooves have closed lug grooves that close at the bottom side from at least half the groove depth when the block is in contact with the ground, and open lug grooves that do not close when the block is in contact with the ground, and the blocks have center blocks separated by the circumferential grooves that are arranged on the tire widthwise inner side of the outermost grooves, and in the center block row in which the center blocks are lined up in the tire circumferential direction, the closed lug grooves and the open lug grooves are arranged alternately in the tire circumferential direction. [Effects of the Invention]

[0007] The tire according to the present invention has an effect of achieving both uneven wear resistance and performance on snow. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 shows a meridian section of a pneumatic tire according to an embodiment, which is a cross section of a region on one side of a tire rotation axis in the tire radial direction. [Figure 2] FIG. 2 is a plan view of a tread surface of a pneumatic tire according to the embodiment. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line BB in FIG. [Figure 5] 5 is a cross-sectional view taken along the line CC in FIG. 2, showing the open lug groove as viewed along the extending direction of the open lug groove. [Figure 6] 6 is an E-E cross-sectional view of FIG. 2, and is a cross-sectional view of the close lug groove when the close lug groove is viewed along the extending direction of the close lug groove. [Figure 7] FIG. 7 is a cross-sectional view of the open lug groove when a block adjacent to the open lug groove is in contact with the ground. [Figure 8] FIG. 8 is a cross-sectional view of the close lug groove when a block adjacent to the close lug groove is in contact with the ground. [Figure 9] FIG. 9 is a cross-sectional view taken along the line FF in FIG. [Figure 10] FIG. 10 is a cross-sectional view taken along line GG in FIG. [Figure 11A] FIG. 11A is a chart showing the results of a performance evaluation test of a pneumatic tire. [Figure 11B] FIG. 11B is a chart showing the results of a performance evaluation test of a pneumatic tire. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to these embodiments. Furthermore, the components of these embodiments include those that can be substituted and are obvious substitutes while maintaining the identity of the invention. Furthermore, the multiple modifications described in these embodiments can be arbitrarily combined within the scope obvious to those skilled in the art.

[0010] [Embodiment] In the following description, the tire radial direction refers to the direction perpendicular to the tire rotational axis (not shown), which is the rotational axis of the pneumatic tire 1 of this embodiment. The tire radial inner side refers to the side toward the tire rotational axis in the tire radial direction, and the tire radial outer side refers to the side away from the tire rotational axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotational axis as the central axis. The tire width direction refers to the direction parallel to the tire rotational axis. The tire width inner side refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the tire width outer side refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane that is perpendicular to the tire rotational axis and passes through the center of the tire width of the pneumatic tire 1. The tire equatorial plane CL coincides in position in the tire width direction with the tire width centerline, which is the center position of the pneumatic tire 1 in the tire width direction. The tire equator line refers to a line that is on the tire equatorial plane CL and runs along the tire circumferential direction of the pneumatic tire 1. Also, a cross section in the tire meridian direction (meridian cross section) refers to a cross section of the tire cut by a plane including the tire rotation axis.

[0011] FIG. 1 is a meridian cross section of a pneumatic tire 1 according to an embodiment, showing a cross section of one side of the tire rotation axis in the tire radial direction. In this embodiment, as an example, a heavy-duty pneumatic radial tire mounted on heavy-duty vehicles such as trucks and buses will be described. The pneumatic tire 1 according to this embodiment is particularly suitable as a tire mounted on the drive axle of a heavy-duty vehicle. Furthermore, the pneumatic tire 1 according to this embodiment is a pneumatic tire 1 in which the rotation direction when mounted on a vehicle is specified. For this reason, the pneumatic tire 1 according to this embodiment has a rotation direction indicator (not shown) that specifies the rotation direction. The rotation direction indicator is configured, for example, by a mark or irregularities attached to the sidewall portion.

[0012] The pneumatic tire 1 according to the embodiment has an annular structure centered on the tire rotation axis, and as shown in FIG. 1, includes a pair of bead cores 11, a pair of bead fillers 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, and a pair of rim cushion rubbers 17.

[0013] The pair of bead cores 11 are formed by winding one or more bead wires made of steel in an annular and multiply fashion, and are embedded in the bead portions to form the cores of the bead portions on both sides in the tire width direction.

[0014] The pair of bead fillers 12 are made up of a lower filler 121 and an upper filler 122, and are respectively arranged on the outer periphery of the pair of bead cores 11 in the tire radial direction to reinforce the bead portion.

[0015] The carcass layer 13 has a single-layer structure consisting of one carcass ply or a multi-layer structure consisting of multiple carcass plies stacked together. The carcass layer 13 is toroidally laid between the bead cores 11 to form the tire framework. Both ends of the carcass layer 13 are wound back and secured to the outside in the tire width direction so as to enclose the bead cores 11 and the bead fillers 12. The carcass ply of the carcass layer 13 is formed by covering multiple carcass cords made of steel with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction of the tire) of 80 degrees or more and 90 degrees or less in absolute value for a radial tire, or 30 degrees or more and 45 degrees or less in absolute value for a bias tire.

[0016] The belt layer 14 is formed by laminating multiple belt plies 141 to 144 and is disposed around the outer periphery of the carcass layer 13. These belt plies 141 to 144 include a high-angle belt 141, a pair of cross belts 142 and 143, and a belt cover 144. The high-angle belt 141 is formed by covering multiple steel belt cords with coating rubber and rolling them, and has a cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 45 degrees or more and 70 degrees or less in absolute value. The pair of cross belts 142 and 143 are formed by covering multiple steel belt cords with coating rubber and rolling them, and have a cord angle (defined as the inclination angle of the belt cords in the longitudinal direction with respect to the tire circumferential direction) of 10 degrees or more and 55 degrees or less in absolute value. The pair of cross belts 142 and 143 have cord angles of opposite signs to each other and are laminated with the belt cords' longitudinal directions crossing each other (having a so-called cross-ply structure). The belt cover 144 is made by covering a plurality of belt cover cords made of steel or organic fiber material with coating rubber and rolling them, and has a cord angle of 10 degrees or more and 55 degrees or less in absolute value.

[0017] The tread rubber 15 is disposed on the outer periphery of the carcass layer 13 and the belt layer 14 in the tire radial direction to form a tread portion of the pneumatic tire 1. In the tread portion, the tread rubber 15 forms a tread surface (tread contact surface) 15A on the outer circumferential surface that comes into contact with the road surface during running.

[0018] The pair of sidewall rubbers 16 are disposed on the outer sides of the carcass layer 13 in the tire width direction, and form sidewall portions on both sides in the tire width direction.

[0019] The pair of rim cushion rubbers 17 extend from the inner side in the tire radial direction to the outer side in the tire width direction of each bead core 11 and the turned-up portion of the carcass layer 13, and form the rim fitting surface of the bead portion.

[0020] Fig. 2 is a plan view of a tread surface 15A of a pneumatic tire 1 according to the embodiment. As shown in Fig. 2, the pneumatic tire 1 according to the embodiment has a tread pattern on the tread surface 15A. Here, each dimension of the tread pattern is measured in an unloaded state with the tire mounted on a specified rim and inflated to a specified internal pressure.

[0021] Specified rim refers to the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. Specified internal pressure refers to the "maximum air pressure" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "inflation pressures" specified by ETRTO. Specified load refers to the "maximum load capacity" specified by JATMA, the maximum value of the "tire load limits at various cold inflation pressures" specified by TRA, or the "load capacity" specified by ETRTO.

[0022] The pneumatic tire 1 has at least four circumferential grooves 20 arranged on the tread surface 15A. In this embodiment, the four circumferential grooves 20 extend in the tire circumferential direction and have an annular structure that is continuously provided around the entire tire circumference. The four circumferential grooves 20 include a pair of outermost grooves 21 and at least one circumferential narrow groove 22.

[0023] The pair of outermost circumferential grooves 21 are respectively arranged at the outermost positions in the tire width direction among the four circumferential grooves 20, and are the circumferential grooves 20 with the widest groove width. In other words, the two outermost circumferential grooves 21 are provided at the outermost positions in the tire width direction among the four circumferential grooves 20, with the tire equatorial plane CL sandwiched between them. In this embodiment, the pair of outermost circumferential grooves 21 are each formed in a zigzag shape that extends along the tire circumferential direction and bends repeatedly in the tire width direction.

[0024] In this embodiment, the outermost circumferential groove 21 is configured as a so-called main groove. The main groove here is defined as a groove that is required to display a treadwear indicator defined by JATMA at the groove bottom 21b.

[0025] In the pneumatic tire 1, three rows of land portions are formed in the tire circumferential direction and in the tire width direction on the tread surface 15A by the pair of outermost grooves 21. Specifically, the pneumatic tire 1 has a center portion 31 defined between the two outermost grooves 21 in the tire width direction, and shoulder portions 32 defined on the outer sides of each outermost groove 21 in the tire width direction.

[0026] The center portion 31 is disposed at a position including the tire equatorial plane CL. Specifically, the width CW of the center portion 31 in the tire width direction is within a range of 45% to 60% of the developed width TW of the tread surface 15A, and the center portion 31 is disposed near the center in the tire width direction. The shoulder portions 32 defined on the outer sides of the outermost grooves 21 in the tire width direction are disposed on both outermost sides of the tread surface 15A in the tire width direction.

[0027] Here, the developed width TW is the dimension obtained by developing the tread surface 15A between the ground contact edges T on both sides in the tire width direction. The ground contact edges T are defined as the maximum width position in the tire width direction of the contact surface between the pneumatic tire 1 and a flat plate when the pneumatic tire 1 is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate and subjected to a load corresponding to a specified load. The width CW of the center portion 31 in the tire width direction is the dimension obtained by developing the center portion 31 between the inner ends in the tire width direction of the openings 21a (see FIG. 9) of the outermost circumferential grooves 21 in the tire width direction.

[0028] Of the four circumferential grooves 20, the circumferential narrow grooves 22 are arranged in the center portion 31. In this embodiment, two circumferential narrow grooves 22 are provided adjacent to each other in the tire width direction with the tire equatorial plane CL sandwiched therebetween. The circumferential narrow grooves 22 are formed in a linear shape along the tire circumferential direction.

[0029] The groove width Wh of the circumferential narrow groove 22 is smaller than the groove width W1 at the opening 21a of the outermost peripheral groove 21. Specifically, the groove width Wh of the circumferential narrow groove 22 is 30% or less of the groove width W1 of the outermost peripheral groove 21.

[0030] Fig. 3 is a cross-sectional view taken along the line AA in Fig. 2. The groove width Wh of the circumferential narrow groove 22 here is the groove width Wh at a position that is 50% of the groove depth Dn, which is the distance in the tire radial direction from the position of the opening 22a of the circumferential narrow groove 22 to the groove bottom 22b. In other words, the groove width Wh of the circumferential narrow groove 22 at a position that is 50% of the groove depth Dn of the circumferential narrow groove 22 radially outward from the position of the groove bottom 22b of the circumferential narrow groove 22 is 30% or less of the groove width W1 of the outermost peripheral groove 21.

[0031] Fig. 4 is a cross-sectional view taken along the line BB in Fig. 2. In this embodiment, some of the blocks 30 defined on the tread surface 15A by the circumferential narrow grooves 22 have chamfered portions 61 and cutout portions 60 (described later) formed in positions adjacent to the circumferential narrow grooves 22, but these chamfered portions 61 and cutout portions 60 are located radially outward in the tire than a position that is 50% of the groove depth Dn from the groove bottom 22b of the circumferential narrow groove 22. Therefore, even when the chamfered portions 61 and cutout portions 60 are formed in positions adjacent to the circumferential narrow grooves 22 in the blocks 30, the groove width Wh of the circumferential narrow grooves 22 at a position that is 50% of the groove depth Dn radially outward in the tire is 30% or less of the groove width W1 of the outermost groove 21.

[0032] The circumferential narrow groove 22 thus formed has a groove width Wh of 1 mm or more and 3 mm or less at a position 50% of the groove depth Dn radially outward from the groove bottom 22b, and a groove depth Dn of 10 mm or more and 23.5 mm or less.

[0033] It is sufficient that one or more circumferential narrow grooves 22 are provided in the center portion 31. That is, the pneumatic tire 1 may have, among the at least four circumferential grooves 20, a circumferential groove 20 different from the circumferential narrow grooves 22 in addition to the circumferential narrow grooves 22 in the center portion 31 located between the pair of outermost circumferential grooves 21 arranged on the outermost sides in the tire width direction. When a circumferential groove 20 different from the circumferential narrow grooves 22 is provided in the center portion 31, the circumferential groove 20, although not explicitly shown in the drawings, is preferably formed in a linear shape along the tire circumferential direction, has a groove width in the range of 5 mm to 20 mm, and has a groove depth in the range of 13.5 mm to 23.5 mm.

[0034] Furthermore, a plurality of lug grooves 40 extending in the tire width direction are arranged on the tread surface 15A. The lug grooves 40 here are grooves that extend in the tire width direction and have a groove width of greater than 1 mm. The plurality of lug grooves 40 are arranged at least between the circumferential grooves 20 on the tread surface 15A. A plurality of blocks 30 defined by the circumferential grooves 20 and the lug grooves 40 are arranged on the tread surface 15A on which the plurality of circumferential grooves 20 and the plurality of lug grooves 40 are arranged in this manner.

[0035] The lug grooves 40 include a middle lug groove 41 arranged between the outermost groove 21 and the circumferential narrow groove 22 adjacent in the tire width direction, a center lug groove 42 arranged between the two circumferential narrow grooves 22, and a shoulder lug groove 45 arranged on the outer side of the outermost groove 21 in the tire width direction.

[0036] The middle lug groove 41 has an outer end in the tire width direction that communicates with the outermost circumferential groove 21, and an inner end in the tire width direction that communicates with the circumferential narrow groove 22. A plurality of middle lug grooves 41 formed in this manner are arranged in the tire circumferential direction. Therefore, a middle block 31Aa, which is a block 30 defined by the outermost circumferential groove 21, the circumferential narrow groove 22, and the middle lug groove 41, is formed between the outermost circumferential groove 21 and the circumferential narrow groove 22 in the tire width direction. The middle block 31Aa has an outer portion in the tire width direction that is defined by the outermost circumferential groove 21, an inner portion in the tire width direction that is defined by the circumferential narrow groove 22, and both portions in the tire circumferential direction that are defined by the middle lug grooves 41.

[0037] Since multiple middle lug grooves 41 are arranged side by side in the tire circumferential direction, multiple middle blocks 31Aa are arranged side by side in the tire circumferential direction between the outermost peripheral groove 21 and the circumferential narrow groove 22 that are adjacent in the tire width direction. The multiple middle blocks 31Aa lined up in the tire circumferential direction between the outermost peripheral groove 21 and the circumferential narrow groove 22 form a middle block row 31A. In other words, the middle block row 31A in which multiple middle blocks 31Aa lined up in the tire circumferential direction is formed between the outermost peripheral groove 21 and the circumferential narrow groove 22 that are adjacent in the tire width direction.

[0038] The middle lug grooves 41 are formed so as to be gently curved in an S-shape in the direction in which the middle lug grooves 41 extend and to be inclined in the tire circumferential direction with respect to the tire width direction. The portion of the middle lug grooves 41 that communicates with the outermost circumferential grooves 21 communicates with the zigzag-shaped portion of the outermost circumferential grooves 21 that is bent inward in the tire width direction.

[0039] Furthermore, the pneumatic tire 1 according to this embodiment has a specified rotation direction, and the specified rotation direction is the direction of arrow R shown in Fig. 2. The middle lug grooves 41 are inclined relative to the tire width direction so that the inner end in the tire width direction touches the ground first during tire rotation, and the outer end in the tire width direction touches the ground last during tire rotation.

[0040] Both ends of the center lug groove 42 are connected to two circumferential narrow grooves 22 adjacent to each other in the tire width direction. A plurality of center lug grooves 42 formed in this manner are arranged in the tire circumferential direction. Therefore, a center block 31Ba, which is a block 30 defined by the two circumferential narrow grooves 22 and the center lug groove 42, is formed between two circumferential narrow grooves 22 adjacent to each other in the tire width direction. In other words, the center block 31Ba is a block 30 defined by the circumferential narrow grooves 22 arranged on the inner side of the outermost circumferential groove 21 in the tire width direction. The center block 31Ba is defined on both sides in the tire width direction by the circumferential narrow grooves 22, and on both sides in the tire circumferential direction by the center lug grooves 42.

[0041] Since multiple center lug grooves 42 are arranged side by side in the tire circumferential direction, multiple center blocks 31Ba are arranged side by side in the tire circumferential direction between two circumferential narrow grooves 22 adjacent in the tire width direction. Furthermore, the multiple center blocks 31Ba arranged side by side in the tire circumferential direction between the two circumferential narrow grooves 22 constitute a center block row 31B. In other words, a center block row 31B in which multiple center blocks 31Ba are arranged side by side in the tire circumferential direction is formed between two circumferential narrow grooves 22 adjacent in the tire width direction. Since the two circumferential narrow grooves 22 are arranged on both sides of the tire equatorial plane CL in the tire width direction, the center block row 31B is arranged across the tire equatorial plane CL in the tire width direction.

[0042] The center lug grooves 42 are formed to curve in a gentle arc shape in the direction in which the center lug grooves 42 extend. The center lug grooves 42 are curved in a direction in which a position near the center in the tire width direction faces forward in the tire rotation direction. Both the center lug grooves 42 and the middle lug grooves 41 communicate with the circumferential narrow grooves 22, but the position in the tire circumferential direction of the portion where the center lug groove 42 communicates with the circumferential narrow groove 22 is different from the position in the tire circumferential direction of the portion where the middle lug groove 41 communicates with the circumferential narrow groove 22.

[0043] The shoulder lug grooves 45 have their inner ends in the tire width direction connected to the outermost circumferential grooves 21, and extend from the position of the outermost circumferential grooves 21 outward in the tire width direction to intersect with the ground contact edge T. A plurality of shoulder lug grooves 45 formed in this manner are arranged in the tire circumferential direction. Therefore, shoulder blocks 32a, which are blocks 30 defined by the outermost circumferential grooves 21 and the shoulder lug grooves 45, are formed in the outer portions of the outermost circumferential grooves 21 in the tire width direction. The shoulder blocks 32a have their inner portions in the tire width direction defined by the outermost circumferential grooves 21, their portions on both sides in the tire circumferential direction defined by the shoulder lug grooves 45, and their outer portions in the tire width direction located at the ground contact edges T.

[0044] Since multiple shoulder lug grooves 45 are arranged side by side in the tire circumferential direction, multiple shoulder blocks 32a are arranged side by side in the tire circumferential direction in the outer portion in the tire width direction of the outermost circumferential groove 21. The shoulder portion 32 defined on the outer side in the tire width direction of the outermost circumferential groove 21 has multiple shoulder blocks 32a arranged side by side in the tire circumferential direction in this way.

[0045] The shoulder lug grooves 45 are formed so as to curve in a gentle arc shape in the direction in which the shoulder lug grooves 45 extend and to be inclined in the tire circumferential direction with respect to the tire width direction. Specifically, like the middle lug grooves 41, the shoulder lug grooves 45 are inclined so that their inner ends in the tire width direction contact the ground first during tire rotation and their outer ends in the tire width direction contact the ground last during tire rotation. Both the shoulder lug grooves 45 and the middle lug grooves 41 communicate with the outermost peripheral grooves 21, but the position in the tire circumferential direction of the portion where the shoulder lug groove 45 communicates with the outermost peripheral grooves 21 is different from the position in the tire circumferential direction of the portion where the middle lug groove 41 communicates with the outermost peripheral grooves 21.

[0046] The shoulder lug grooves 45 thus formed are arranged at equal intervals in the tire circumferential direction, and the pitch in the tire circumferential direction is preferably within a range of 65 mm to 75 mm.

[0047] Additionally, center sub-lug grooves 43 are arranged in the center block row 31B. The center sub-lug grooves 43 extend in the tire width direction, with one end communicating with the circumferential narrow groove 22 and the other end forming a lug groove 40 that terminates within the center block 31Ba. A plurality of center sub-lug grooves 43 are arranged in the tire circumferential direction, with one for each center block 31Ba. In other words, the center sub-lug grooves 43 are arranged between center lug grooves 42 that are adjacent in the tire circumferential direction. Therefore, the center lug grooves 42 and center sub-lug grooves 43, of which a plurality are arranged in each center block row 31B, are arranged alternately in the tire circumferential direction.

[0048] Furthermore, adjacent center sublug grooves 43 sandwiching a center lug groove 42 in the tire circumferential direction communicate with different circumferential narrow grooves 22. That is, the center sublug grooves 43 disposed in adjacent center blocks 31Ba in the tire circumferential direction communicate with different circumferential narrow grooves 22. Furthermore, the ends of these center sublug grooves 43 that terminate within the center block 31Ba are all located near the tire equatorial plane CL. In other words, the center sublug groove 43 that terminates within the center block 31Ba terminates near the center of the center block 31Ba in the tire width direction. Therefore, the center sublug groove 43 is disposed in a range from near the center of the center block 31Ba in the tire width direction to one side of the center block 31Ba in the tire width direction.

[0049] The center sublug groove 43 communicates with the circumferential narrow groove 22 as described above, but the position in the tire circumferential direction where the center sublug groove 43 communicates with the circumferential narrow groove 22 is the same position in the tire circumferential direction where any one of the multiple middle lug grooves 41 that communicate with the circumferential narrow groove 22 communicates with the circumferential narrow groove 22. Therefore, the portion where the center sublug groove 43 communicates with the circumferential narrow groove 22 faces the portion where any one of the multiple middle lug grooves 41 communicates with the circumferential narrow groove 22. As a result, the center sublug groove 43 communicates with the middle lug groove 41 via the circumferential narrow groove 22.

[0050] A plurality of sipes 50 are further arranged on the tread surface 15A. The sipes 50 referred to here are formed in the shape of narrow grooves on the tread surface 15A. When the pneumatic tire 1 is mounted on a specified rim and under a specified internal pressure condition, the wall surfaces of the narrow grooves do not contact each other under no load. However, when a load is applied vertically on a flat plate and the narrow grooves are positioned in the contact patch formed on the flat plate, or when the blocks 30 on which the narrow grooves are formed collapse, the wall surfaces of the narrow grooves come into contact with each other due to deformation of the blocks 30. In this embodiment, the sipes 50 have a groove width of 1 mm or less and a maximum depth from the tread surface 15A within a range of 10 mm to 18 mm.

[0051] The sipes 50 arranged on the tread surface 15A include middle sipes 51 arranged on the middle blocks 31Aa and center sipes 52 arranged on the center blocks 31Ba.

[0052] The middle sipes 51 arranged in the middle blocks 31Aa extend in the tire width direction, with their outer ends in the tire width direction communicating with the outermost circumferential grooves 21 and their inner ends in the tire width direction communicating with the circumferential narrow grooves 22. The portions of the middle sipes 51 that communicate with the outermost circumferential grooves 21 communicate with portions of the outermost circumferential grooves 21 that extend circumferentially while repeatedly bending in a zigzag shape, bending outward in the tire width direction. A plurality of middle sipes 51 are arranged in the middle block row 31A, and are arranged alternately with the middle lug grooves 41 in the tire circumferential direction in the middle block row 31A. Therefore, the middle sipes 51 are arranged so as to bisect the middle blocks 31Aa, both ends of which in the tire circumferential direction are partitioned by the middle lug grooves 41, in the tire circumferential direction. In this way, the middle sipes 51 arranged so as to bisect the middle blocks 31Aa are arranged approximately parallel to the direction in which the middle lug grooves 41 extend.

[0053] The center sipes 52 arranged in the center block 31Ba extend in the tire width direction, with their outer ends in the tire width direction communicating with the circumferential narrow grooves 22 and their inner ends in the tire width direction terminating within the center block 31Ba. The ends of the center sipes 52 that terminate within the center block 31Ba communicate with the ends of the center sublug grooves 43 that terminate within the center block 31Ba.

[0054] Specifically, the center sipes 52 are disposed on extensions of the center sublug grooves 43, and the circumferential narrow grooves 22 to which the center sipes 52 communicate communicate with a circumferential narrow groove 22 different from the circumferential narrow groove 22 to which the center sublug groove 43 communicates. That is, the center sipes 52 are disposed in an area on the opposite side of the side to which the center sublug groove 43 is disposed, within an area on both sides near the center in the tire width direction of the center block 31Ba in which the center sipes 52 are disposed. In this case, the center sublug grooves 43 disposed in center blocks 31Ba adjacent in the tire circumferential direction communicate with different circumferential narrow grooves 22, and therefore the center sipes 52 disposed in center blocks 31Ba adjacent in the tire circumferential direction also communicate with different circumferential narrow grooves 22.

[0055] Furthermore, the position in the tire circumferential direction of the portion where the central sipe 52 communicates with the circumferential narrow groove 22 is the same as the position in the tire circumferential direction of the portion where any of the middle sipes 51 arranged in the middle block row 31A communicates with the circumferential narrow groove 22. Therefore, the portion where the central sipe 52 communicates with the circumferential narrow groove 22 faces the portion where any of the multiple middle sipes 51 communicates with the circumferential narrow groove 22. As a result, the central sipe 52 communicates with the middle sipe 51 via the circumferential narrow groove 22.

[0056] A plurality of center sipes 52 are arranged in the center block row 31B together with the center sub-lug grooves 43, and are arranged alternately with the center lug grooves 42 in the tire circumferential direction in the center block row 31B. Therefore, the center sub-lug grooves 43 and center sipes 52, which are arranged in communication with each other, are arranged so as to divide the center block 31Ba, whose both ends in the tire circumferential direction are divided by the center lug grooves 42, into two in the tire circumferential direction by the center sub-lug grooves 43 and the center sipes 52. In this way, the center sub-lug grooves 43 and center sipes 52, which are arranged so as to divide the center block 31Ba into two, are arranged approximately parallel to the direction in which the center sub-lug grooves 43 extend.

[0057] In the blocks 30 defined on the tread surface 15A by the circumferential grooves 20 and the lug grooves 40, cutouts 60 are formed at the openings of the lug grooves 40 relative to the circumferential grooves 20.

[0058] Specifically, the middle block 31Aa has a notch 60 formed at an opening of the middle lug groove 41 relative to the circumferential narrow groove 22 and at an opening of the middle lug groove 41 relative to the outermost peripheral groove 21. The notch 60 on the circumferential narrow groove 22 side of the middle block 31Aa and the notch 60 on the outermost peripheral groove 21 side are formed at acute angles at diagonal positions of the middle block 31Aa.

[0059] In other words, because the middle lug grooves 41 that define the middle blocks 31Aa are inclined in the tire circumferential direction with respect to the tire width direction, the middle blocks 31Aa are formed in a parallelogram shape in a plan view. The two cutouts 60 formed in the middle blocks 31Aa are formed at acute angles diagonally across the parallelogram shape of the middle blocks 31Aa thus formed. Therefore, the two cutouts 60 formed in the middle blocks 31Aa are formed at the corner portion of the middle block 31Aa that is first stepped on and the corner portion of the middle block 31Aa that is last kicked off as the pneumatic tire 1 rotates.

[0060] Furthermore, the center block 31Ba has a cutout 60 formed at the opening of the center lug groove 42 relative to the circumferential narrow groove 22. The cutout 60 of the center block 31Ba is formed at a corner of the center block 31Ba on either side of the center lug groove 42 in the tire circumferential direction, where the angle formed by the curved groove wall of the center lug groove 42 and the groove wall of the circumferential narrow groove 22 is an acute angle. In this way, the cutout 60 formed in the center block 31Ba at the opening of the center lug groove 42 relative to the circumferential narrow groove 22 is formed at both corners in the tire width direction of the center block 31Ba that are kicked out last when the pneumatic tire 1 rotates.

[0061] A cutout 60 is formed in each shoulder block 32a at the opening of the shoulder lug groove 45 relative to the outermost circumferential groove 21. The cutout 60 in each shoulder block 32a is formed at a corner of the shoulder block 32a on either side of the shoulder lug groove 45 in the tire circumferential direction, where the angle formed by the curved groove wall of the shoulder lug groove 45 and the groove wall of the outermost circumferential groove 21 is acute. In this way, the cutout 60 formed in the shoulder block 32a at the opening of the shoulder lug groove 45 relative to the outermost circumferential groove 21 is formed in the corner of the shoulder block 32a that is first stepped on when the pneumatic tire 1 rotates.

[0062] Furthermore, the center block 31Ba has a chamfered portion 61 formed at one of its two end portions in the tire width direction. That is, the center block 31Ba has a chamfered portion 61 formed at one edge in the tire width direction. The chamfered portion 61 is smallest near the center of the center block 31Ba in the tire circumferential direction, and the chamfered portion becomes larger toward both ends of the center block 31Ba in the tire circumferential direction.

[0063] The chamfered portions 61 formed on the center blocks 31Ba in this manner are formed on the edges on both sides of the center blocks 31Ba in the tire width direction, on the edge formed by the circumferential narrow grooves 22 that communicate with the center sipes 52. Therefore, similar to the center sipes 52, the chamfered portions 61 formed on the center blocks 31Ba adjacent to each other across the center lug grooves 42 in the tire circumferential direction are formed on edges of the center blocks 31Ba on different sides in the tire width direction.

[0064] The tread surface 15A has a tread pattern formed by a plurality of circumferential grooves 20 and a plurality of lug grooves 40, of which the lug grooves 40 include closed lug grooves 40a and open lug grooves 40b. The closed lug grooves 40a are lug grooves 40 that close at least from a position halfway through the groove depth when the block 30 adjacent to the closed lug groove 40a comes into contact with the ground. The open lug grooves 40b are lug grooves 40 that do not close when the block 30 adjacent to the open lug groove 40b comes into contact with the ground.

[0065] Of the lug grooves 40 arranged in the center block row 31B, the center lug grooves 42 are closed lug grooves 40a, and the center sub-lug grooves 43 are open lug grooves 40b. Therefore, in the center block row 31B in which the center blocks 31Ba are lined up in the tire circumferential direction, the closed lug grooves 40a and the open lug grooves 40b are arranged alternately in the tire circumferential direction. In this embodiment, the closed lug grooves 40a arranged in the center block row 31B are center lug grooves 42, and therefore both ends thereof communicate with the circumferential narrow grooves 22. In addition, the open lug grooves 40b arranged in the center block row 31B are center sub-lug grooves 43, and therefore one end thereof communicates with the circumferential narrow groove 22, and the other end thereof terminates within the center block 31Ba.

[0066] Furthermore, the middle lug grooves 41, which are the lug grooves 40 arranged in the middle block row 31A, are all closed lug grooves 40a. Therefore, the lug grooves 40 that define the plurality of middle blocks 31Aa arranged in the middle block row 31A are all closed lug grooves 40a. In this embodiment, the closed lug grooves 40a arranged in the middle block row 31A are middle lug grooves 41, so that their outer ends in the tire width direction communicate with the outermost circumferential groove 21 and their inner ends in the tire width direction communicate with the circumferential narrow groove 22.

[0067] Fig. 5 is a CC cross-sectional view of Fig. 2, which is a cross-sectional view of the open lug groove 40b when the open lug groove 40b is viewed along the extension direction of the open lug groove 40b. Fig. 6 is an EE cross-sectional view of Fig. 2, which is a cross-sectional view of the closed lug groove 40a when the closed lug groove 40a is viewed along the extension direction of the closed lug groove 40a. The relationship between the groove width Wo and the groove depth Do of the open lug groove 40b is within the range of 3.5≦Do / Wo≦15. In this case, the groove width Wo of the open lug groove 40b is the groove width at the position of the opening 40ba, and the groove depth Do is the distance in the tire radial direction from the position of the opening 40ba to the position of the groove bottom 40bb.

[0068] The relationship between the groove width Wc and the groove depth Dc of the close lug groove 40a is within the range of 5.0≦Dc / Wc≦15. In this case, the groove width Wc of the close lug groove 40a is the groove width at the position of the opening 40aa, and the groove depth Dc is the distance in the tire radial direction from the position of the opening 40aa to the position of the groove bottom 40ab.

[0069] 7 is a cross-sectional view of the open lug groove 40b when the block 30 adjacent to the open lug groove 40b touches the ground. When the block 30 adjacent to the open lug groove 40b touches the ground, the block 30 deforms due to the load at the time of contact, and the groove width of the open lug groove 40b becomes smaller. In this way, the width Wog of the opening 40ba of the open lug groove 40b when the block 30 adjacent to the open lug groove 40b touches the ground is within the range of 1.5 mm≦Wog≦7 mm.

[0070] FIG. 8 is a cross-sectional view of the close lug groove 40a when the block 30 adjacent to the close lug groove 40a touches the ground. Similarly, when the block 30 adjacent to the close lug groove 40a touches the ground, the block 30 deforms due to the load at the time of contact, causing the groove width of the close lug groove 40a to decrease. As a result, when the block 30 adjacent to the close lug groove 40a touches the ground, the close lug groove 40a closes from the groove bottom 40ab position at least halfway through the groove depth Dc. In this embodiment, the relationship between the height Hc from the groove bottom 40ab at the closed position when the block 30 adjacent to the close lug groove 40a touches the ground and the groove depth Dc of the close lug groove 40a is within the range of 0.5≦Hc / Dc≦0.8.

[0071] Therefore, even when the portion of the close lug groove 40a on the groove bottom 40ab side is closed due to the block 30 adjacent to the close lug groove 40a coming into contact with the ground, the portion of the close lug groove 40a near the opening 40aa remains open. In this way, the close lug groove 40a that maintains the opening 40aa side open when the block 30 adjacent to the close lug groove 40a comes into contact with the ground has a width Wcg of the opening 40aa within the range of 1.5 mm≦Wcg≦5 mm.

[0072] The groove width of these closed lug grooves 40a and open lug grooves 40b when in contact with the ground is measured, for example, using CT scan images or the like while a load of 70% to 100% of the specified load is applied to the pneumatic tire 1.

[0073] 9 is an FF cross-sectional view of FIG. 2. Of the four circumferential grooves 20, a pair of outermost circumferential grooves 21 arranged outermost in the tire width direction have a pair of first groove walls 21c, a pair of terraced portions 21d, and a pair of second groove walls 21e between the opening 21a and the groove bottom 21b. The pair of first groove walls 21c extend from the tread surface 15A toward the groove bottom 21b on both sides of the opening 21a in the tire width direction. The pair of terraced portions 21d are connected to the groove bottom 21b sides of the respective first groove walls 21c and form terraces higher than the groove bottom 21b on the tire radial direction outer side so as to extend along the tread surface 15A. The pair of second groove walls 21e are located closer to the center of the outermost circumferential groove 21 in the groove width direction than the respective first groove walls 21c, and extend from the respective terraced portions 21d to the groove bottom 21b.

[0074] The outermost grooves 21 thus formed have a groove width W1 of the openings 21a in the range of 10.0 mm to 20.0 mm, a groove width W2 between the second groove walls 21e or a spacing W2 between the platform portions 21d in the range of 3.0 mm to 4.5 mm, and a groove depth D1 from the tread surface 15A to the groove bottom 21b in the range of 13.5 mm to 23.5 mm, and a groove depth D2 from the tread surface 15A to the platform portion 21d in the range of 7.5 mm to 17.5 mm.

[0075] Furthermore, the outermost grooves 21 are formed such that the angle θ1 of each first groove wall 21c widens from the groove bottom 21b toward the opening 21a toward the tread surface 15A. The angle θ1 of the first groove wall 21c of each outermost groove 21 is within a range of 10 degrees to 14 degrees with respect to a normal to the profile of the tread surface 15A at the tire width direction end of the opening 21a.

[0076] Fig. 10 is a cross-sectional view taken along the line G-G in Fig. 2. Shoulder lug grooves 45, which communicate with outermost circumferential grooves 21 from the outer side in the tire width direction, have upper bottom portions 45b that protrude from the groove bottom toward the outer side in the tire radial direction. An apex 45ba of each upper bottom portion 45b, which protrudes most from the groove bottom, is provided along the profile of the tread surface 15A where the shoulder lug groove 45 opens.

[0077] The groove depth D3 of the shoulder lug grooves 45 from the tread surface 15A to the apex 45ba of the bottom upper portion 45b is shallower than the groove depth D1 (see FIG. 9) of the outermost peripheral grooves 21 from the tread surface 15A to the groove bottom 21b and the groove depth D2 (see FIG. 9) of the outermost peripheral grooves 21. The groove depth D3 of the shoulder lug grooves 45 from the apex 45ba of the bottom upper portion 45b is within a range of 2.0 mm to 8.0 mm.

[0078] The groove depths D1, D2, and D3 of the outermost peripheral grooves 21 and the shoulder lug grooves 45 satisfy the relationships 0.50≦D2 / D1≦0.90 and 0.10≦D3 / D1≦0.40. It is preferable that the groove depths D1, D2, and D3 of the outermost peripheral grooves 21 and the shoulder lug grooves 45 satisfy the relationships 0.60≦D2 / D1≦0.70 and 0.25≦D3 / D1≦0.35.

[0079] The bottom upper portion 45b has an inclined surface 45bb that slopes radially inward from the apex 45ba toward the platform portion 21d of the outermost circumferential groove 21 on the inner side in the tire width direction. The angle θ2 of the inclined surface 45bb with respect to the normal to the profile of the tread surface 15A where the shoulder lug grooves 45 open is within a range of 20 degrees to 60 degrees. The angle θ2 of the inclined surface 45bb is preferably within a range of 40 degrees to 50 degrees. The inclined surface 45bb is smoothly connected to the apex 45ba of the bottom upper portion 45b by a circular arc 45bc in the tire meridian cross section. The inclined surface 45bb is smoothly connected to the platform portion 21d of the outermost circumferential groove 21 on the outermost side in the tire width direction by a circular arc 45bd in the tire meridian cross section. It is preferable that the radius r of arc 45bd connecting inclined surface 45bb of bottom upper portion 45b and platform portion 21d of outermost peripheral groove 21 is within the range of 2 mm≦r≦15 mm.

[0080] The bottom upper portion 45b has an inclined surface 45be on the outer side in the tire width direction, which slopes radially inward from the apex 45ba toward the outer end 45a of the shoulder lug groove 45 in the tire width direction. The angle θ3 of the inclined surface 45be with respect to the normal to the profile of the tread surface 15A where the shoulder lug groove 45 opens is within a range of 10 degrees to 30 degrees. The angle θ3 of the inclined surface 45be is preferably within a range of 15 degrees to 25 degrees. The inclined surface 45be is smoothly connected to the apex 45ba of the bottom upper portion 45b by a circular arc 45bf in the tire meridian cross section.

[0081] The bottom upper portion 45b of the shoulder lug groove 45 has a tire width direction dimension WS1 of the shoulder lug groove 45 and a tire width direction dimension WS2 of an apex 45ba of the bottom upper portion 45b that satisfy the relationship 0.50≦WS2 / WS1≦0.90. In this case, the tire width direction dimension WS2 of the apex 45ba is the tire width direction distance between a normal to the profile of the tread surface 15A passing through the intersection of an extension of the inclined surface 45bb of the bottom upper portion 45b and an extension of the apex 45ba, and a normal to the profile of the tread surface 15A passing through the intersection of an extension of the inclined surface 45be and an extension of the apex 45ba. In addition, the tire width direction dimension WS1 of the shoulder lug groove 45 is the tire width direction distance between the normal to the profile of the tread surface 15A at the tire width direction outer end of the opening 21a of the outermost circumferential groove 21 and the normal to the profile of the tread surface 15A at the position of the ground contact edge T.

[0082] The dimension WS1 of the shoulder lug groove 45 in the tire width direction defined as above and the dimension WS2 of the apex 45ba in the tire width direction preferably satisfy the relationship 0.60≦WS2 / WS1≦0.80.

[0083] When mounting the pneumatic tire 1 according to this embodiment on a vehicle, the pneumatic tire 1 is mounted on a rim wheel, filled with air, and mounted on the vehicle in an inflated state. At this time, the pneumatic tire 1 according to this embodiment has a specified rotation direction, so the pneumatic tire 1 is mounted on the vehicle in an orientation that causes the pneumatic tire 1 to rotate in the specified direction when the vehicle moves forward. In other words, the pneumatic tire 1 is mounted on the vehicle in an orientation that causes the pneumatic tire 1 to rotate in the rotation direction specified by the rotation direction indicator attached to the sidewall.

[0084] When a vehicle equipped with pneumatic tire 1 travels, the lower part of tread surface 15A of the tread contacts the road surface while rotating pneumatic tire 1. When a vehicle equipped with pneumatic tire 1 travels on a dry road surface, the vehicle travels by transmitting driving force and braking force to the road surface and generating turning force mainly due to friction between tread surface 15A and the road surface.

[0085] Furthermore, when traveling on a wet road surface, water between the tread surface 15A and the road surface enters grooves such as the circumferential grooves 20 and lug grooves 40, and the sipes 50, and these grooves drain the water between the tread surface 15A and the road surface while traveling. This makes it easier for the tread surface 15A to make contact with the road surface, and the frictional force between the tread surface 15A and the road surface enables the vehicle to travel.

[0086] Furthermore, when traveling on snowy roads, the pneumatic tire 1 compacts snow on the road surface with the tread surface 15A. Furthermore, the snow on the road surface also compacts within the circumferential grooves 20 and lug grooves 40. In this state, when a driving force or braking force acts on the pneumatic tire 1, or when a force acts in the tire width direction due to turning, a shear force acting on the snow in the grooves, known as a snow column shear force, is generated between the pneumatic tire 1 and the snow. When traveling on snowy roads, this snow column shear force generates resistance between the pneumatic tire 1 and the road surface, allowing the driving force and braking force to be transmitted to the road surface, ensuring snow traction. This allows the vehicle to travel on snowy roads.

[0087] Furthermore, when traveling on snowy or icy road surfaces, the tire also utilizes the edge effects of the circumferential grooves 20, lug grooves 40, and sipes 50. In other words, when traveling on snowy or icy road surfaces, the tire also utilizes the resistance caused by the edges of the circumferential grooves 20, the edges of the lug grooves 40, and the edges of the sipes 50 catching on the snowy or icy surface.

[0088] Furthermore, when traveling on an icy road surface, the sipes 50 absorb water on the surface of the icy road surface, removing the water film between the icy road surface and the tread surface 15A, making it easier for the icy road surface and the tread surface 15A to come into contact. This increases the resistance between the tread surface 15A and the icy road surface due to frictional force and edge effect, ensuring the driving performance of a vehicle equipped with the pneumatic tire 1.

[0089] When a vehicle equipped with pneumatic tire 1 travels, tread surface 15A comes into contact with the road surface, generating friction between tread surface 15A and the road surface, causing tread surface 15A to gradually wear as the travel distance increases. Furthermore, when tread surface 15A comes into contact with the road surface, slippage may occur between tread surface 15A and the road surface, which also gradually wears tread surface 15A.

[0090] On the other hand, when the tread surface 15A comes into contact with the road surface while the vehicle is traveling, the blocks 30 having the contacting tread surface 15A are deformed by the load acting on the blocks 30. When the vehicle travels, the blocks 30 deform as described above, and the tread surface 15A is prone to have different levels of friction with the road surface and different levels of slippage between the tread surface 15A and the road surface due to the deformation of the blocks 30. When the level of friction with the road surface and the level of slippage between the tread surface 15A and the road surface differs depending on the location of the tread surface 15A, uneven wear may occur on the tread surface 15A.

[0091] In contrast, in this embodiment, among the multiple circumferential grooves 20 extending in the tire circumferential direction, the groove width of a pair of outermost circumferential grooves 21 arranged outermost in the tire width direction is wider than the groove width of the circumferential narrow grooves 22 arranged inward in the tire width direction of the outermost circumferential grooves 21. This allows the blocks 30 to be concentrated in a portion closer to the center in the tire width direction, where ground contact pressure is likely to be high when the tread surface 15A comes into contact with the tire. This makes it possible to suppress deformation of the blocks 30 in the center portion 31, where ground contact pressure is likely to be high, when the tire comes into contact with the tire, and to suppress uneven wear caused by deformation of the blocks 30.

[0092] On the other hand, if the blocks 30 are concentrated near the center in the tire width direction, the groove area of ​​the circumferential grooves 20 near the center in the tire width direction will be reduced, which may make it difficult to ensure performance on snow. In contrast, in this embodiment, by arranging multiple lug grooves 40 between the circumferential grooves 20, it is possible to ensure snow column shear force by the lug grooves 40, and it is possible to maintain driving performance on snowy roads.

[0093] Furthermore, since the closed lug grooves 40a and the open lug grooves 40b are alternately arranged in the tire circumferential direction in the center block row 31B, even if multiple lug grooves 40 are arranged in the center portion 31 where ground contact pressure is likely to be high, the closed lug grooves 40a close during contact with the ground, thereby suppressing deformation of the blocks 30. This suppresses uneven wear that would otherwise occur if many lug grooves 40 were arranged near the center in the tire width direction, where ground contact pressure is likely to be high. As a result, uneven wear resistance and on-snow performance can be achieved at the same time.

[0094] Furthermore, because all of the lug grooves 40 that define the middle blocks 31Aa are closed lug grooves 40a, deformation of the middle blocks 31Aa when they come into contact with the ground can be suppressed. This suppresses uneven wear in the middle block row 31A where the middle blocks 31Aa are lined up in the tire circumferential direction. As a result, uneven wear resistance can be more reliably improved.

[0095] Furthermore, the relationship between the groove width Wc and the groove depth Dc of the close lug groove 40a is within the range of 5.0≦Dc / Wc≦15, which can suppress uneven wear while ensuring driving performance on snowy roads. In other words, if the relationship between the groove width Wc and the groove depth Dc of the close lug groove 40a is Dc / Wc<5.0, the groove depth Dc of the close lug groove 40a is too shallow, which may make it difficult for the close lug groove 40a to close when the block 30 adjacent to the close lug groove 40a comes into contact with the ground. In this case, it may be difficult for the close lug groove 40a to suppress deformation of the block 30 when it comes into contact with the ground, which may make it difficult to suppress uneven wear. Furthermore, if the relationship between the groove width Wc and the groove depth Dc of the close lug groove 40a is Dc / Wc>15, the groove width Wc of the close lug groove 40a is too narrow, which may make it difficult for the close lug groove 40a to secure snow column shear force. In this case, even if the closed lug grooves 40a are provided, it may be difficult to effectively ensure driving performance on snowy road surfaces.

[0096] In contrast, when the relationship between the groove width Wc and groove depth Dc of the close lug groove 40a is within the range of 5.0≦Dc / Wc≦15, the groove depth Dc of the close lug groove 40a is prevented from becoming too shallow, and the groove width Wc of the close lug groove 40a is prevented from becoming too narrow. This ensures snow column shear force in the close lug groove 40a and ensures driving performance on snowy roads, while closing the close lug groove 40a when the block 30 adjacent to the close lug groove 40a comes into contact with the ground, thereby preventing uneven wear. As a result, uneven wear resistance and on-snow performance can be more reliably achieved.

[0097] Furthermore, the relationship between the groove width Wo and groove depth Do of the open lug grooves 40b is within the range of 3.5≦Do / Wo≦15, which more reliably ensures snow column shear force at the open lug grooves 40b and ensures driving performance on snowy roads. In other words, if the relationship between the groove width Wo and groove depth Do of the open lug grooves 40b is Do / Wo<3.5, the groove depth Do of the open lug grooves 40b is too shallow, which may make it difficult to ensure snow column shear force at the open lug grooves 40b. In this case, even if the open lug grooves 40b are provided, it may be difficult to effectively ensure driving performance on snowy roads. Furthermore, if the relationship between the groove width Wo and groove depth Do of the open lug grooves 40b is Do / Wo>15, the groove depth Do of the open lug grooves 40b is too deep, which may make it difficult to maintain the open state of the open lug grooves 40b when the blocks 30 adjacent to the open lug grooves 40b make contact with the ground. In this case, it may be difficult to ensure snow column shear force in the open lug grooves 40b, and therefore even if the open lug grooves 40b are provided, it may be difficult to effectively ensure driving performance on snowy roads.

[0098] In contrast, when the relationship between the groove width Wo and groove depth Do of the open lug grooves 40b is within the range of 3.5≦Do / Wo≦15, the groove depth Do of the open lug grooves 40b can be set to an appropriate depth relative to the groove width Wo. This ensures more reliable snow column shear force in the open lug grooves 40b and ensures driving performance on snowy roads. As a result, snow performance can be more reliably improved.

[0099] Furthermore, the width Wcg of the opening 40aa of the close lug groove 40a when the block 30 adjacent to the close lug groove 40a is in the range of 1.5 mm≦Wcg≦5 mm, so the close lug groove 40a can suppress deformation of the block 30 when it is in contact with the ground while ensuring snow column shear force at the close lug groove 40a. In other words, if the width Wcg of the opening 40aa of the close lug groove 40a when the block 30 is in contact with the ground is Wcg<1.5 mm, the width Wcg of the opening 40aa of the close lug groove 40a when it is in contact with the ground is too narrow, which may make it difficult to ensure snow column shear force at the close lug groove 40a. Furthermore, if the width Wcg of the opening 40aa of the close lug groove 40a when the block 30 is in contact with the ground is Wcg > 5 [mm], the width Wcg of the opening 40aa of the close lug groove 40a when the block 30 is in contact with the ground will be too wide, making it difficult for the close lug groove 40a to suppress deformation of the block 30 when the block 30 is in contact with the ground, and there is a risk that it will be difficult to suppress the occurrence of uneven wear.

[0100] In contrast, if the width Wcg of the opening 40aa of the block 30 adjacent to the close lug groove 40a when the block 30 is in contact with the ground is within the range of 1.5 mm≦Wcg≦5 mm, the width Wcg of the opening 40aa when the block 30 is in contact with the ground can be made appropriate. This allows the close lug groove 40a to suppress deformation of the block 30 when the block 30 is in contact with the ground, thereby suppressing uneven wear, while ensuring snow column shear force in the close lug groove 40a and ensuring driving performance on snowy roads. As a result, uneven wear resistance and on-snow performance can be more reliably achieved at the same time.

[0101] Furthermore, the relationship between the height Hc of the close lug groove 40a from the groove bottom 40ab at the closed position when the block 30 contacts the ground and the groove depth Dc of the close lug groove 40a is within the range of 0.5≦Hc / Dc≦0.8, so the close lug groove 40a can suppress deformation of the block 30 when it contacts the ground while ensuring snow column shear force in the close lug groove 40a. In other words, if the relationship between the height Hc of the closed position of the block 30 adjacent to the close lug groove 40a when it contacts the ground and the groove depth Dc is Hc / Dc<0.5, the height Hc of the closed position is too low, making it difficult to suppress deformation of the block 30 when it contacts the ground by the close lug groove 40a, and there is a risk that uneven wear will be difficult to suppress. Furthermore, if the relationship between the height Hc of the closing position when the block 30 adjacent to the close lug groove 40a comes into contact with the ground and the groove depth Dc is Hc / Dc>0.8, the height Hc of the closing position will be too high, which may make it difficult to ensure snow column shear force in the close lug groove 40a.

[0102] In contrast, when the relationship between the height Hc of the block 30 adjacent to the close lug groove 40a when in contact with the ground and the groove depth Dc is within the range of 0.5≦Hc / Dc≦0.8, the height Hc of the block 30 when in contact with the ground can be set to an appropriate height. This allows the close lug groove 40a to suppress deformation of the block 30 when in contact with the ground, thereby suppressing uneven wear, while ensuring snow column shear force in the close lug groove 40a and ensuring driving performance on snowy roads. As a result, uneven wear resistance and on-snow performance can be more reliably achieved at the same time.

[0103] Furthermore, the width Wog of the opening 40ba of the block 30 adjacent to the open lug groove 40b when the block 30 is in contact with the ground is within the range of 1.5 mm≦Wog≦7 mm, so the snow column shear force at the open lug groove 40b can be secured while ensuring the rigidity of the block 30 adjacent to the open lug groove 40b. In other words, if the width Wog of the opening 40ba of the open lug groove 40b when the block 30 is in contact with the ground is Wog<1.5 mm, the width Wog of the opening 40ba of the open lug groove 40b when the block 30 is in contact with the ground is too narrow, which may make it difficult to ensure the snow column shear force at the open lug groove 40b. Furthermore, if the width Wog of the opening 40ba of the open lug groove 40b when the block 30 is in contact with the ground is Wog>7 mm, the width Wog of the opening 40ba of the open lug groove 40b when the block 30 is in contact with the ground is too wide, which may easily reduce the rigidity of the block 30 adjacent to the open lug groove 40b. In this case, the blocks 30 adjacent to the open lug grooves 40b are likely to deform when they come into contact with the ground, which may make it difficult to prevent uneven wear.

[0104] In contrast, if the width Wog of the opening 40ba of the block 30 adjacent to the open lug groove 40b when the block 30 is in contact with the ground is within the range of 1.5 mm≦Wog≦7 mm, the width Wog of the opening 40ba when the block 30 is in contact with the ground can be made appropriate. This ensures the rigidity of the block 30 adjacent to the open lug groove 40b and suppresses deformation of the block 30 when the block 30 is in contact with the ground, while ensuring snow column shear force in the open lug groove 40b and ensuring driving performance on snowy roads. As a result, it is possible to more reliably achieve both uneven wear resistance and on-snow performance.

[0105] Furthermore, the blocks 30 are formed with cutouts 60 at the openings of the lug grooves 40 relative to the circumferential grooves 20, which increases the groove volume. This ensures more reliable snow column shear force and driving performance on snowy roads. As a result, on-snow performance can be improved more reliably.

[0106] Furthermore, since the groove width Wh of the circumferential narrow groove 22 at a position that is 50% of the groove depth Dn is 3 mm or less, the distance between the blocks 30 arranged in the center portion 31 can be reduced. As a result, when the blocks 30 arranged in the center portion 31 come into contact with each other and support each other, deformation of the blocks 30 can be suppressed, and uneven wear can be suppressed. As a result, uneven wear resistance can be more reliably improved.

[0107] Furthermore, because bottom upper portions 45b are formed in shoulder lug grooves 45, bottom upper portions 45b can suppress sound from outermost circumferential grooves 21 from passing through shoulder lug grooves 45 to the outside in the tire width direction when pneumatic tire 1 rolls. This makes it possible to suppress pass-by sound, which is noise generated when pneumatic tire 1 rolls, and improve pass-by sound performance.

[0108] Furthermore, because the outermost circumferential grooves 21 are formed in a stepped shape with a pair of steps 21d, the groove width W1 at the openings 21a can be ensured while ensuring the rigidity of the blocks 30 defined by the outermost circumferential grooves 21. Furthermore, the bottom upper portions 45b of the shoulder lug grooves 45 and the steps 21d of the outermost circumferential grooves 21 are smoothly connected by the arcs 45bd, which more reliably ensures the rigidity of the blocks 30. This ensures drainage performance in the outermost circumferential grooves 21 while suppressing deformation of the blocks 30, thereby reducing rolling resistance while ensuring wet performance, which is the driving performance on wet roads. As a result, rolling resistance can be reduced while improving pass-by noise performance and wet performance.

[0109] Furthermore, outermost circumferential groove 21 is formed in a stepped shape, shoulder lug groove 45 is formed with bottom upper portions 45b, and bottom upper portions 45b of shoulder lug groove 45 and step portions 21d of outermost circumferential groove 21 are smoothly connected by arcs 45bd, thereby preventing stones that may enter the connection between outermost circumferential groove 21 and shoulder lug groove 45 from reaching groove bottom 21b of outermost circumferential groove 21. This improves stone trapping resistance.

[0110] Furthermore, since the groove depth D1 of the outermost circumferential groove 21 and the groove depth D2 up to the platform portion 21d satisfy the relationship 0.50≦D2 / D1≦0.90, the groove depth D2 of the platform portion 21d can be set within an appropriate range, preventing trapped stones from reaching the groove bottom 21b of the outermost circumferential groove 21 and making it easier for the stones to escape. Furthermore, since the groove depth D1 of the outermost circumferential groove 21 and the groove depth D3 up to the bottom upper portion 45b of the shoulder lug groove 45 satisfy the relationship 0.10≦D3 / D1≦0.40, the groove depth D3 up to the bottom upper portion 45b can be set within an appropriate range, suppressing sound leakage outward in the tire width direction and improving pass-by sound performance.

[0111] Furthermore, the pair of first groove walls 21c of the outermost circumferential grooves 21 are formed to widen toward the tread surface 15A, which creates a difference in groove width between the tread surface 15A side and the platform portion 21d side, improving the ability to remove trapped stones. Furthermore, the groove volume of the outermost circumferential grooves 21 decreases toward the groove bottom 21b, which does not affect the effect of reducing passing noise.

[0112] Furthermore, because the tire width direction dimension WS1 of the shoulder lug groove 45 and the tire width direction dimension WS2 of the apex 45ba of the bottom upper portion 45b satisfy the relationship 0.50≦WS2 / WS1≦0.90, the tire width direction dimension WS2 of the bottom upper portion 45b can be set within an appropriate range. This improves the stone trapping resistance of the shoulder lug groove 45. Furthermore, by locating the bottom upper portion 45b in the shoulder lug groove 45 in the shoulder portion 32, where sound tends to escape to the outer side in the tire width direction, sound escape is reduced and the smaller groove volume reduces pass-by noise.

[0113] Furthermore, the angle θ2 of the inclined surface 45bb of the bottom upper portion 45b of the shoulder lug groove 45 is between 20 and 60 degrees, and the angle θ3 of the inclined surface 45be is between 10 and 30 degrees. This allows the angles θ2 and θ3 of the inclined surface 45bb and 45be to be set within appropriate ranges. This allows stones trapped in the shoulder lug groove 45 to be smoothly removed, improving stone trapping resistance. Furthermore, keeping the angles θ2 and θ3 of the bottom upper portion 45b within the specified ranges does not affect the effectiveness of reducing passing noise.

[0114] Furthermore, when multiple shoulder lug grooves 45 are arranged at equal intervals around the tire circumference, the groove area of ​​the shoulder portion 32 can be made uniform, maintaining the effect of reducing passing noise. Furthermore, because the shoulder lug grooves 45 extend in an arc shape, trapped stones can be smoothly removed.

[0115] Additionally, shoulder block 32a has chamfered notch 60 formed at the acute angle where shoulder lug groove 45 communicates with outermost circumferential groove 21, sloping radially inward in the tire direction to reach platform 21d of outermost circumferential groove 21. This can suppress the generation of hitting noise during running.

[0116] [Variations] In the above-described embodiment, two of the four circumferential grooves 20 are circumferential narrow grooves 22, but the number of circumferential narrow grooves 22 may be other than two, for example, it may be one. In this case, the circumferential groove 20 that is located more inward in the tire width direction than the outermost circumferential groove 21 and different from the circumferential narrow groove 22 is formed with a groove width wider than the circumferential narrow groove 22.

[0117] In addition, in the above-described embodiment, four circumferential grooves 20 are arranged, but the number of circumferential grooves 20 may be other than four. For example, the number of circumferential grooves 20 may be five or six, as long as it is four or more.

[0118] In addition, in the above-described embodiment, the open lug grooves 40b arranged in the center block row 31B terminate within the center block 31Ba, but the open lug grooves 40b may not terminate within the center block 31Ba, and both ends may be connected to the circumferential groove 20.

[0119] In the above-described embodiment, all of the lug grooves 40 arranged in the middle block row 31A are closed lug grooves 40a, but open lug grooves 40b may also be arranged in the middle block row 31A. In the middle block row 31A, the closed lug grooves 40a and the open lug grooves 40b may be arranged alternately in the tire circumferential direction, similar to, for example, the center block row 31B.

[0120] In the present embodiment, as described above, a pneumatic tire 1 has been described as an example of a tire. The pneumatic tire 1 can be filled with air, an inert gas such as nitrogen, or other gases. However, the tread pattern configuration of the pneumatic tire 1 described in the present embodiment can be applied to other tires as desired within the scope of what is obvious to those skilled in the art. Examples of other tires include airless tires and solid tires.

[0121] [Example] 11A and 11B are tables showing the results of performance evaluation tests of the pneumatic tire 1. Below, we will explain performance evaluation tests conducted on the conventional pneumatic tire 1 and the pneumatic tire 1 according to the present invention regarding the above-mentioned pneumatic tire 1. The performance evaluation tests were conducted on uneven wear resistance and acceleration performance on snow.

[0122] The performance evaluation test was carried out under the condition that a pneumatic tire 1 having a tire nominal size of 315 / 80R22.5 724D was mounted on a rim wheel having a rim size of 22.5 x 9.00, and the air pressure was adjusted to the specified air pressure.

[0123] As for the evaluation method for each test item, for uneven wear resistance, a road test was conducted by mounting the test tire on a heavy-duty vehicle and running until the wear rate of the outermost circumferential grooves 21, which are the main grooves, reached 30%, after which the degree of so-called heel-and-toe wear was confirmed. Specifically, the difference in the amount of wear between both edges in the tire circumferential direction for each block 30 was measured, and the reciprocal of the difference in the measured amount of wear was expressed as an index, with the conventional example described below being set at 100. The larger this index value, the less uneven wear there was in the block 30, indicating better uneven wear resistance.

[0124] Additionally, snow acceleration performance was measured in accordance with UN R117-04 (UN Regulation No. 117 Revision 4), measuring the distance required for a heavy-duty vehicle fitted with the test tires to accelerate from a specified initial speed to a terminal speed on a snowy road surface, and calculating the acceleration. Snow acceleration performance was evaluated by expressing the calculated acceleration as an index, with the conventional example (described below) set at 100, with a higher index indicating better acceleration performance on snowy roads.

[0125] The performance evaluation test was conducted on 16 types of pneumatic tires, including conventional pneumatic tires and Examples 1 to 15, which are pneumatic tires 1 according to the present invention. Of these, the conventional pneumatic tires have circumferential narrow grooves but do not have closed lug grooves, and closed lug grooves and open lug grooves are not arranged alternately in the circumferential direction of the tire.

[0126] In contrast, Examples 1 to 15, which are examples of the pneumatic tire 1 according to the present invention, all have closed lug grooves 40a and open lug grooves 40b, and the closed lug grooves 40a and the open lug grooves 40b are alternately arranged in the tire circumferential direction in the center block row 31B. Furthermore, the pneumatic tires 1 according to Examples 1 to 15 differ from one another in the width Wcg of the opening of the closed lug groove 40a when in contact with the ground, the ratio Hc / Dc of the height Hc of the closed position of the closed lug groove 40a to the groove depth Dc, the width Wog of the opening of the open lug groove 40b when in contact with the ground, the presence or absence of a notch 60 formed at the opening of the lug groove 40 relative to the circumferential groove 20 in the block 30, and whether the groove width Wh of the circumferential narrow groove 22 is 3 mm or less.

[0127] 11A and 11B, performance evaluation tests were conducted using these pneumatic tires 1. As a result, it was found that the pneumatic tires 1 according to Examples 1 to 15 were able to improve both uneven wear resistance and acceleration performance on snow compared to the conventional tire. In other words, the pneumatic tires 1 according to Examples 1 to 15 were able to achieve both uneven wear resistance and performance on snow.

[0128] The present disclosure encompasses the following inventions. Invention[1] At least four circumferential grooves disposed on the tread surface and extending in the tire circumferential direction; a plurality of lug grooves disposed at least between the circumferential grooves on the tread surface and extending in the tire width direction; a block defined by the circumferential groove and the lug groove; Equipped with The plurality of circumferential grooves each include a pair of outermost peripheral grooves disposed outermost in the tire width direction among the plurality of circumferential grooves, and a circumferential narrow groove having a groove width of 30% or less of the groove width of the outermost peripheral grooves, a center portion between the pair of outermost grooves on the tread surface has a width in the tire width direction of 45% or more of the developed width of the tread surface, The lug grooves have closed lug grooves that close at the bottom side from at least half the groove depth when the block is in contact with the ground, and open lug grooves that do not close when the block is in contact with the ground, the blocks have center blocks partitioned by the circumferential grooves arranged on the inner side of the outermost circumferential groove in the tire width direction, The tire is characterized in that the closed lug grooves and the open lug grooves are arranged alternately in the tire circumferential direction in a center block row in which the center blocks are arranged in the tire circumferential direction. Invention[2] the blocks include middle blocks partitioned by the circumferential groove and the outermost circumferential groove, the middle blocks being disposed on the inner side of the outermost circumferential groove in the tire width direction, The tire according to the invention [1], wherein the lug grooves that define the middle block are all closed lug grooves. Invention[3] The tire according to the invention [1] or [2], wherein the relationship between the groove width Wc and the groove depth Dc of the closed lug groove is within the range of 5.0≦Dc / Wc≦15. Invention[4] The tire according to any one of the inventions [1] to [3], wherein the relationship between the groove width Wo and the groove depth Do of the open lug groove is within the range of 3.5≦Do / Wo≦15. Invention[5] The tire according to any one of the inventions [1] to [4], wherein the width Wcg of the opening of the closed lug groove when the block is in contact with the ground is within the range of 1.5 [mm] ≦ Wcg ≦ 5 [mm]. Invention[6] The tire according to any one of the inventions [1] to [5], wherein the relationship between the height Hc from the groove bottom at the position where the closed lug groove is closed when the block is in contact with the ground and the groove depth Dc of the closed lug groove is within the range of 0.5≦Hc / Dc≦0.8. Invention[7] The tire according to any one of the inventions [1] to [6], wherein the width Wog of the opening of the open lug groove when the block is in contact with the ground is within the range of 1.5 [mm]≦Wog≦7 [mm]. Invention[8] The tire according to any one of inventions [1] to [7], wherein the block has a notch formed at an opening portion of the lug groove relative to the circumferential groove. Invention[9] The tire according to any one of the inventions [1] to [8], wherein the circumferential narrow groove has a groove width Wh of 3 mm or less at a position of 50% of the groove depth. Invention

[10] The outermost circumferential groove is A pair of first groove walls extending from the tread surface toward the groove bottom side; a pair of platform portions connected to the groove bottom sides of the first groove walls and forming platforms along the tread surface; a pair of second groove walls located closer to the center in the groove width direction than the first groove walls and extending from the platform portions toward the groove bottom; and the lug grooves include shoulder lug grooves that are arranged on the outer side of the outermost peripheral grooves in the tire width direction, communicate with the outermost peripheral grooves, and have bottom upper portions formed at the groove bottoms, The tire according to any one of inventions [1] to [9], wherein the bottom upper portion of the shoulder lug groove and the platform portion of the outermost circumferential groove are smoothly connected by an arc in the tire meridian section. [Explanation of symbols]

[0129] 1 pneumatic tire 11 Bead core 12 Bead filler 13 Carcass layer 14 Belt Layer 15 Tread rubber 15A tread surface 16 Sidewall rubber 17 Rim cushion rubber 20 Circumferential groove 21 Outermost circumferential groove 22 Circumferential thin groove 30 blocks 31 Center Section 31A Middle Block Row 31Aa Middle Block 31B Center Block Row 31Ba Center Block 32 Shoulder section 32a Shoulder Block 40 lug groove 40a closed lug groove 40b open lug groove 41 Middle lug groove 42 Center lug groove 43 Center sub-lug groove 45 Shoulder lug groove 45b Bottom top 50 sipes 60 Notch 61 Chamfered part

Claims

1. At least four circumferential grooves disposed on the tread surface and extending in the tire circumferential direction; a plurality of lug grooves disposed at least between the circumferential grooves on the tread surface and extending in the tire width direction; a block defined by the circumferential groove and the lug groove; Equipped with The plurality of circumferential grooves include a pair of outermost peripheral grooves disposed outermost in the tire width direction among the plurality of circumferential grooves, and a circumferential narrow groove having a groove width of 30% or less of the groove width of the outermost peripheral grooves, a center portion between the pair of outermost grooves on the tread surface has a width in the tire width direction of 45% or more of a developed width of the tread surface, The lug grooves have closed lug grooves that close at the bottom side from at least half the groove depth when the block is in contact with the ground, and open lug grooves that do not close when the block is in contact with the ground, the blocks have center blocks partitioned by the circumferential grooves arranged on the inner side of the outermost circumferential groove in the tire width direction, The tire is characterized in that the closed lug grooves and the open lug grooves are arranged alternately in the tire circumferential direction in a center block row in which the center blocks are arranged in the tire circumferential direction.

2. the blocks include middle blocks partitioned by the circumferential groove and the outermost circumferential groove, the middle blocks being disposed on the inner side of the outermost circumferential groove in the tire width direction, The tire according to claim 1 , wherein all of the lug grooves that define the middle block are closed lug grooves.

3. The tire according to claim 1, wherein the relationship between the groove width Wc and the groove depth Dc of the closed lug groove is within a range of 5.0≦Dc / Wc≦15.

4. The tire according to claim 1, wherein the relationship between the groove width Wo and the groove depth Do of the open lug groove is within a range of 3.5≦Do / Wo≦15.

5. The tire according to claim 1, wherein the width Wcg of the opening of the closed lug groove when the block is in contact with the ground is within a range of 1.5 mm≦Wcg≦5 mm.

6. 2. The tire according to claim 1, wherein the relationship between the height Hc of the closed lug groove from the groove bottom at the position where the block is closed when in contact with the ground and the groove depth Dc of the closed lug groove is within a range of 0.5≦Hc / Dc≦0.

8.

7. 2. The tire according to claim 1, wherein the open lug groove has an opening width Wog when the block is in contact with the ground, which is within a range of 1.5 mm≦Wog≦7 mm.

8. The tire according to claim 1 , wherein the blocks are formed with notches at openings of the lug grooves relative to the circumferential grooves.

9. The tire according to claim 1, wherein the circumferential narrow groove has a groove width Wh of 3 mm or less at a position that is 50% of the groove depth.

10. The outermost circumferential groove is a pair of first groove walls extending from the tread surface toward the groove bottom; a pair of platform portions connected to groove bottom sides of the first groove walls and forming platforms along the tread surface; a pair of second groove walls located closer to the center in the groove width direction than the first groove walls and extending from the platform portions toward the groove bottom; and the lug grooves include shoulder lug grooves that are arranged on the outer side of the outermost peripheral grooves in the tire width direction, communicate with the outermost peripheral grooves, and have bottom upper portions formed at the groove bottoms, The tire according to claim 1 , wherein a bottom upper portion of the shoulder lug groove and the platform portion of the outermost circumferential groove are smoothly connected by a circular arc in a tire meridian section.

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