tire

Abstract

To achieve both low rolling resistance and snow traction performance. [Solution] The pneumatic tire 1 has a center area CC that is located in the center of the tread area and has a range of 45% or more of the unfolded width TDW of the tread area, and the groove width W of each circumferential groove 20 (shoulder circumferential groove 22) on the outermost side in the tire width direction and the groove width W1 of each other circumferential groove 20 (center circumferential groove 21) are W1

Description

【Technical Field】 【0001】 This invention relates to a tire. 【Background Art】 【0002】 Conventionally, for example, Patent Document 1 discloses a technique for solving the problem of achieving both noise performance, snow traction performance, and anti-skid performance of a heavy-duty winter tire. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2022-066922 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 In heavy-duty winter tires, in order to ensure snow performance, the groove area ratio is increased and a block-based structure that moves smoothly is often adopted. However, compared with summer tires, the rolling resistance becomes larger. 【0005】 An object of this invention is to provide a tire capable of achieving both low rolling resistance performance and snow traction performance. 【Means for Solving the Problems】 【0006】 In order to achieve the above object, a tire according to one aspect of the present invention includes a center land portion at the center in the tire width direction, which is defined by circumferential grooves extending along the tire circumferential direction in the tread portion and arranged at least four in the tire width direction; middle land portions on both outer sides in the tire width direction of the center land portion; and shoulder land portions on the outer sides in the tire width direction of each of the middle land portions. In the center land portion, there is a center block defined by center lug grooves extending along the tire width direction and having both ends opening into the circumferential grooves and arranged a plurality in the tire circumferential direction. In the middle land portion, there is a middle block defined by middle lug grooves extending along the tire width direction and having both ends opening into the circumferential grooves and arranged a plurality in the tire circumferential direction. At least one of the tire width direction ends of the center block and the middle block includes a rib defined by fine grooves extending along the tire circumferential direction. Taking the area between the inner ends in the tire width direction of each of the circumferential grooves on the outermost side in the tire width direction as a center region, the center region has a range of 45% or more with respect to the developed width of the tread portion and is arranged at the center of the tread portion. The groove width W of each of the circumferential grooves on the outermost side in the tire width direction and the groove width W1 of each of the other circumferential grooves satisfy the relationship W1 < W. The groove width W1 of the circumferential grooves is 2% or less with respect to the developed width. The groove width of the fine grooves is 0.9% or less with respect to the developed width. The groove width W1 of the circumferential grooves and the rib width Wr of the rib satisfy the relationship 1.0 ≦ Wr / W1 ≦ 2.0. The groove width W1 of the circumferential grooves and the tire width direction dimension Wc of the center block satisfy the relationship W1 ≦ Wc × 0.2. The groove area ratio in the center region is 33% or less. 【Advantages of the Invention】 【0007】 According to this invention, it is possible to achieve both low rolling resistance performance and snow traction performance. 【Brief Description of the Drawings】 【0008】 [Figure 1] FIG. 1 is an enlarged partial meridional cross-sectional view of a pneumatic tire according to an embodiment. [Figure 2]Figure 2 is a plan view of the tread portion of a pneumatic tire according to an embodiment. [Figure 3] Figure 3 is a partially enlarged cross-sectional view of the tread portion of a pneumatic tire according to an embodiment. [Figure 4] Figure 4 is a partially enlarged plan view of the tread portion of a pneumatic tire according to an embodiment. [Figure 5] Figure 5 is a partially enlarged plan view of the tread portion of a pneumatic tire according to an embodiment. [Figure 6] Figure 6 is a partially enlarged cross-sectional view of the tread portion of a pneumatic tire according to an embodiment. [Figure 7] Figure 7 is a partially enlarged plan view of the tread portion of a pneumatic tire according to an embodiment. [Figure 8] Figure 8 is a partially enlarged cross-sectional view of the tread portion of a pneumatic tire according to an embodiment. [Figure 9] Figure 9 is a partially enlarged cross-sectional view of the tread portion of a pneumatic tire according to an embodiment. [Figure 10] Figure 10 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 11] Figure 11 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 12] Figure 12 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 13] Figure 13 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 14] Figure 14 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Figure 15] Figure 15 is a chart showing the results of a performance test of a pneumatic tire according to the embodiment. [Modes for carrying out the invention] 【0009】 Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited by these embodiments. Furthermore, the components of these embodiments include those that are substituted and obvious for substitution while maintaining the identity of the invention. In addition, the multiple modifications described in these embodiments can be arbitrarily combined within the scope of what is obvious to those skilled in the art. 【0010】 In the following description, the tire radial direction refers to the direction perpendicular to the tire rotation axis (not shown), which is the rotation axis of the pneumatic tire 1 of the embodiment. The inner side of the tire radial direction refers to the side toward the tire rotation axis in the tire radial direction, and the outer side of the tire radial direction refers to the side away from the tire rotation axis in the tire radial direction. The tire circumferential direction refers to the direction around the tire rotation axis as the central axis. The tire width direction refers to the direction parallel to the tire rotation axis. The inner side of the tire width direction refers to the side toward the tire equatorial plane (tire equator line) CL in the tire width direction, and the outer side of the tire width direction refers to the side away from the tire equatorial plane CL in the tire width direction. The tire equatorial plane CL is a plane perpendicular to the tire rotation axis and passing through the center of the tire width of the pneumatic tire 1. The position of the tire equatorial plane CL in the tire width direction coincides with the tire width direction center line, which is the center position of the pneumatic tire 1 in the tire width direction. The tire equator line refers to a line on the tire equatorial plane CL that runs along the tire circumferential direction of the pneumatic tire 1. Furthermore, a meridional cross-section of a tire (meridian section) refers to the cross-section obtained when the tire is cut along a plane containing the tire's axis of rotation. 【0011】 Figure 1 is a meridional cross-section of the pneumatic tire 1 of the embodiment. This embodiment describes a radial tire for heavy-duty vehicles that is mounted on a heavy-duty vehicle and is applied as a winter tire. 【0012】 The pneumatic tire 1 of this embodiment has an annular structure centered on the tire rotation axis and comprises a pair of bead cores 11, a pair of bead fillers 12, a carcass layer 13, a belt layer 14, tread rubber 15, a pair of sidewall rubbers 16, and a pair of rim cushion rubbers 17. 【0013】 A pair of bead cores 11 are formed by annularly and multiply winding one or more bead wires made of steel, and are respectively embedded in bead portions on both sides in the tire width direction to constitute the cores of the bead portions. 【0014】 A pair of bead fillers 12 are respectively disposed on the outer circumferences in the tire radial direction of the pair of bead cores 11 to reinforce the bead portions. In the embodiment, the bead filler 12 is configured to have a lower filler 121 on the inner side in the tire radial direction and an upper filler 122 on the outer side in the tire radial direction. 【0015】 The carcass layer 13 has a single-layer structure composed of one carcass ply or a multi-layer structure formed by laminating a plurality of carcass plies. In the pneumatic tire 1 of the embodiment, the carcass layer 13 is composed of one carcass ply. The carcass layer 13 is bridged in a toroidal shape between both bead cores to constitute the skeleton of the tire. Further, both end portions of the carcass layer 13 are wound back to the outside in the tire width direction so as to wrap the bead core 11 and the bead filler 12 and are locked. Further, the carcass ply of the carcass layer 13 is formed by covering a plurality of carcass cords made of steel with a coat rubber and performing rolling processing, and in the case of a radial tire, it has a cord angle (defined as the inclination angle of the longitudinal direction of the carcass cord with respect to the tire circumferential direction) of 80° or more and 90° or less in absolute value. 【0016】 The belt layer 14 is made up of multiple belt plies 141 to 144 stacked together and arranged around the outer circumference of the carcass layer 13. These belt plies 141 to 144 are a combination of belts of various configurations, such as zero-degree belts, high-angle belts, and a pair of crossing belts. The belt plies are made by coating multiple belt cords (also called wires) made of steel with rubber and rolling them. A zero-degree belt is defined as a belt ply in which the belt cords extend along the circumferential direction of the tire. A high-angle belt is defined as a belt ply in which the angle of inclination of the belt cords extending with respect to the circumferential direction of the tire is, for example, 45° to 70°. A pair of crossing belts has a so-called cross-ply structure in which each belt cord has a cord angle with a different sign from the others, and the extension directions of the belt cords are stacked together so as to intersect each other. 【0017】 The tread rubber 15 is arranged on the outer circumference in the radial direction of the carcass layer 13 and belt layer 14 to form the tread portion of the pneumatic tire 1. In the tread portion, the tread rubber 15 forms a tread surface (also called a tread) 15A on the outer surface that comes into contact with the road surface during driving. The outer end of the tread surface 15A in the tire width direction becomes the contact end T (see Figure 2). The straight-line distance in the tire width direction when the tread surface 15A is unfolded between each contact end T is defined as the unfolded width TDW. 【0018】 A pair of sidewall rubbers 16 are positioned on the outer side of the carcass layer 13 in the tire width direction, forming the sidewall portions on both sides of the pneumatic tire 1 in the tire width direction. 【0019】 A pair of rim cushion rubbers 17 extend from the inside in the tire radial direction to the outside in the tire width direction of the folded-over portion of each bead core 11 and carcass layer 13, forming the rim fitting surface of the bead portion. 【0020】 As shown in Figure 2, the pneumatic tire 1 of the embodiment has a tread pattern on the tread surface 15A of the tread portion. Here, each dimension of the tread pattern is measured in an unloaded state with the pneumatic tire 1 mounted on a specified rim and filled with a specified internal pressure. The above-mentioned contact end T is defined as the position of the maximum width in the tire width direction at the contact surface between the tread surface 15A and the flat plate when the tire is mounted on a specified rim, filled with a specified internal pressure, the tire equatorial plane CL is placed perpendicular to the flat plate, and a load corresponding to a specified load is applied. 【0021】 A specified rim refers to a "standard rim" as defined by JATMA, a "design rim" as defined by TRA, or a "measuring rim" as defined by ETRTO. Furthermore, specified internal pressure refers to the "maximum air pressure" as defined by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" as defined by TRA, or "INFLATION PRESSURES" as defined by ETRTO. Finally, specified load refers to the "maximum load capacity" as defined by JATMA, the maximum value of "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" as defined by TRA, or "LOAD CAPACITY" as defined by ETRTO. 【0022】 The groove width is measured as the maximum distance between opposing groove walls at the groove opening on the surface of the tread surface 15A when the tire is mounted on a specified rim and filled to the specified internal pressure in an unloaded state. In configurations where the groove opening has a notch or chamfer, the groove width is measured using the intersection of the extension line (profile) of the tread surface 15A and the extension line of the groove wall as the endpoint in a cross section parallel to the tire width direction and tire diameter direction. 【0023】 The groove depth is measured as the maximum distance from the surface of the tread surface 15A to the bottom of the groove when the tire is mounted on a specified rim and filled to the specified internal pressure in an unloaded state. In addition, if the groove depth has a configuration with partial irregularities or sipes at the bottom of the groove, these are excluded from the measurement. 【0024】 As shown in Figures 1 and 2, the pneumatic tire 1 of the embodiment mainly has circumferential grooves 20 and lug grooves 40 on the tread surface 15A of the tread portion. 【0025】 The circumferential grooves 20 are provided extending along the circumferential direction of the tire. In the embodiment, at least four circumferential grooves 20 are provided side by side in the tire width direction. In the embodiment, the circumferential grooves 20 include two center circumferential grooves 21 provided on both sides of the tire equatorial plane CL in the tire width direction, and two shoulder circumferential grooves 22 provided on the outside of each center circumferential groove 21 in the tire width direction. 【0026】 The center circumferential groove 21 has a groove width W1 of 3.0 mm to 6.0 mm (see Figures 2 and 3). The center circumferential groove 21 also has a groove depth D of 15.0 mm to 25.0 mm (see Figure 3). 【0027】 The shoulder circumferential groove 22 has a groove width W of 7.0 mm to 15.0 mm (see Figure 2). The shoulder circumferential groove 22 also has a groove depth D0 of 15.0 mm to 25.0 mm (see Figure 3). The shoulder circumferential groove 22 is applied as a main groove subject to the wear indicator marking requirements specified by JATMA. 【0028】 Each circumferential groove 20 defines a land area 30 in the tire width direction. In this embodiment, the land area 30 includes a single center land area 31 located on the tire equatorial plane CL, which is the center in the tire width direction and is located between the two center circumferential grooves 21; two middle land areas 32 located between each center circumferential groove 21 and each shoulder circumferential groove 22; and two shoulder land areas 33 located between each shoulder circumferential groove 22 and each contact end T. As shown in Figure 2, the area between the inner ends in the tire width direction of the outermost shoulder circumferential grooves 22 is defined as the center region (inner region) CC, and the area outside the outermost end in the tire width direction of the outermost shoulder circumferential grooves 22 is defined as the shoulder region (outer region) SC. That is, the center region CC is the central region in the tire width direction of the tread surface 15A, including the center land area 31, each middle land area 32, and the tire equatorial plane CL. Furthermore, the shoulder region SC is the region on both outer sides in the tire width direction of the tread surface 15A, including the shoulder land portion 33. 【0029】 Although not explicitly shown in the diagram, in configurations with five or more circumferential grooves 20, six or more land sections 30 are partitioned, with each of the outermost land sections 30 in the tire width direction being designated as a shoulder land section 33, each land section 30 adjacent to the inner side of each shoulder land section 33 in the tire width direction being designated as a middle land section 32, and multiple land sections 30 on the inner side of each middle land section 32 in the tire width direction being designated as a center land section 31. 【0030】 As shown in Figure 2, the lug grooves 40 are provided extending along the tire width direction and divide each land portion 30 into multiple sections in the tire circumferential direction. The lug grooves 40 include a center lug groove 41 that divides the center land portion 31, a middle lug groove 42 that divides the middle land portion 32, and a shoulder lug groove 43 that divides the shoulder land portion 33. 【0031】 As shown in Figure 2, the center lug grooves 41 are provided with their ends open in each center circumferential groove 21 so as to penetrate the center land portion 31 in the tire width direction. Multiple center lug grooves 41 are provided side by side at intervals in the tire circumferential direction. As a result, the center lug grooves 41 divide the center land portion 31 into multiple center blocks 311 in the tire circumferential direction. The center lug grooves 41 have a groove width W3c of 2.0 [mm] to 13.5 [mm] (see Figures 4, 5, and 7). The center lug grooves 41 also have a groove depth D5 of 15.0 [mm] to 25.0 [mm] (see Figures 6 and 8). 【0032】 As shown in Figures 5 and 7, the center lug groove 41 is formed with a wider groove width at each end that opens towards the center circumferential groove 21. Specifically, the center lug groove 41 is formed with a wider end by providing a notch 41a at the corner of the center block 311. The center lug groove 41 is formed uniformly with a groove width W3c between both ends excluding the notch 41a. The center lug groove 41 is formed by bending with a bent portion 41b within the range of the groove width W3c between both ends. Figure 5 shows an example where two bent portions 41b are provided, and Figure 7 shows an example where one bent portion is provided on the tire equatorial plane CL. As shown in Figure 4, the center lug groove 41 is formed inclined at an angle θc of 10° to 20° with respect to the tire width direction. The angle θc is based on a straight line connecting the centers of both ends of the center lug groove 41. As shown in Figures 5 to 8, the center lug groove 41 has a raised section 81 positioned at the bottom 41c of the groove. The raised section 81 is provided within the range of the groove width W3c between the two ends of the center lug groove 41, excluding the notches 41a. The raised section 81 is formed in a stepped shape having two stepped sections 81a with different depths D3 and D4 from the tread surface 15A. In Figures 5 and 6, the stepped shape shows an example where there are two stepped sections 81a at the positions of two bends 41b, resulting in a convex center in the tire width direction, while in Figures 7 and 8, it shows an example where there is one stepped section 81a at the position of one bend 41b, resulting in a convex end in the tire width direction. This raised section 81 has a raised sipe 91 that penetrates along the extending direction (inclination direction) of the center lug groove 41. The raised sipe 91 is formed with a width of 1.0 [mm] or less. The raised sipe 91 is formed by bending, having two bent portions 91a in the central part (on the tire equatorial plane CL). 【0033】 As shown in Figure 2, the middle lug grooves 42 are provided with their ends opening into the center circumferential groove 21 and the shoulder circumferential groove 22, respectively, so as to penetrate the middle land portion 32 in the tire width direction. Multiple middle lug grooves 42 are provided side by side at intervals in the tire circumferential direction. As a result, the middle lug grooves 42 divide the middle land portion 32 into multiple middle blocks 321 in the tire circumferential direction. The middle lug grooves 42 have a groove width W3m of 2.0 [mm] to 13.5 [mm] (see Figure 4). The middle lug grooves 42 also have a groove depth D6 of 15.0 [mm] to 25.0 [mm] (see Figure 3). 【0034】 As shown in Figure 4, the middle lug groove 42 is formed with a wider groove width at each end that opens to the center circumferential groove 21 side and the shoulder circumferential groove 22 side. Specifically, the middle lug groove 42 is formed with a wider end by providing a notch 42a at the corner of the middle block 321. The middle lug groove 42 is formed uniformly with a groove width W3m between both ends excluding the notch 42a. Within the range of the groove width W3m between both ends, the middle lug groove 42 is formed with a bend, similar to the center lug groove 41. The bend in the middle lug groove 42 is provided in two places (see Figure 5) or one place (see Figure 7). As shown in Figure 4, the middle lug groove 42 is formed inclined at an angle θm of 10[°] to 20[°] with respect to the tire width direction. The angle θm is based on the straight line connecting the centers of both ends of the middle lug groove 42. As shown in Figure 3, the middle lug groove 42 has a raised section 82 positioned at the groove bottom 42c. The raised section 82 is provided in the area between the two ends of the middle lug groove 42. The raised section 82 has a raised sipe 92 that penetrates along the extending direction (inclination direction) of the middle lug groove 42. The raised sipe 92 is formed with a width of 1.0 [mm] or less. The raised sipe 92 is formed by bending, having two bent sections in the center, similar to the raised sipe 91. 【0035】 As shown in Figure 2, the shoulder lug grooves 43 are provided with their ends opening at the shoulder circumferential groove 22 and the contact end T, respectively, so as to penetrate the shoulder land portion 33 in the tire width direction. Multiple shoulder lug grooves 43 are provided side by side at intervals in the tire circumferential direction. As a result, the shoulder lug grooves 43 divide the shoulder land portion 33 into multiple shoulder blocks 331 in the tire circumferential direction. The shoulder lug grooves 43 have a groove width (not shown) of 2.0 [mm] to 13.5 [mm]. The shoulder lug grooves 43 also have a groove depth D7 (see Figure 9) of 15.0 [mm] to 25.0 [mm]. 【0036】 The shoulder lug groove 43 is formed with a wider groove width at each end that opens to the shoulder circumferential groove 22 side and the ground end T side. Specifically, the shoulder lug groove 43 is formed with a wider end by providing a notch at the corner of the shoulder block 331. A raised base portion 83 is placed at the bottom of the shoulder lug groove 43. The raised base portion 83 is provided in the area between both ends of the shoulder lug groove 43. 【0037】 As shown in Figures 2 to 4, the middle block 321 has a rib 62 positioned at its end in the tire width direction. The rib 62 is demarcated by a narrow groove 52 extending along the tire circumferential direction at the inner end of the middle block 321 in the tire width direction. The narrow groove 52 has a groove width W2 (see Figure 3) of 2.0 [mm] or less (preferably 1.5 [mm]). The narrow groove 52 also has a groove depth D1 (see Figure 3) of 4.5 [mm] or more and 24.0 [mm] or less. The groove depth D1 of the narrow groove 52 is equivalent to the depth from the tread surface 15A of the raised bottom portion 82. The rib 62 has a rib width Wr (see Figure 3) of 1.0 [mm] or more and 4.0 [mm] or less. As shown in Figure 3, the rib 62 is positioned to form the groove wall of the center circumferential groove 21 that demarcates the middle block 321 on which it is positioned. Furthermore, the rib 62 has an inclined surface 62a that slopes from the tread surface 15A to a depth D2 toward the center circumferential groove 21, which itself forms the groove wall. 【0038】 Although not explicitly shown in the figure, the rib 62 may be demarcated by a narrow groove 52 extending along the tire circumferential direction at the outer end of the middle block 321 in the tire width direction. In this case, the rib 62 is positioned to form the groove wall of the shoulder circumferential groove 22 that demarcates the middle block 321 on which it is located. In this case, the rib 62 also has an inclined surface 62a that slopes from the tread surface 15A to a depth D2 toward the shoulder circumferential groove 22 on which it forms the groove wall. 【0039】 Although not explicitly shown in the figures, the ribs may also be demarcated by narrow grooves extending along the tire circumferential direction at at least one end of the center block 311 in the tire width direction. In this case, the narrow grooves have a groove width W2 of 2.0 [mm] or less (preferably 1.5 [mm]) (see Figure 3). The narrow grooves also have a groove depth D1 of 4.5 [mm] or more and 24.0 [mm] or less (see Figure 3). The groove depth D1 of the narrow grooves is equivalent to the depth D4 of the raised portion 81 from the tread surface 15A (see Figures 6 and 8). The ribs have a rib width Wr of 1.0 [mm] or more and 4.0 [mm] or less (see Figure 3). In this case, the ribs are arranged to form the groove walls of the center circumferential grooves 21 that demarcate the center block 311 on which they are located. In this case, the ribs also have inclined surfaces that slope from the tread surface 15A to a depth D2 toward the center circumferential grooves 21 on which they form the groove walls. 【0040】 As shown in Figures 2 and 9, the shoulder block 331 has a rib 63 positioned at its end in the tire width direction. The rib 63 is partitioned between two narrow grooves 53 that extend along the tire circumferential direction, so as to partition the shoulder block 331 in the tire width direction. Thus, the shoulder block 331 includes two inner shoulder small blocks 331A and 331B in the tire width direction, with the two narrow grooves 53 and the rib 63 in between. The narrow grooves 53 have a groove width W4 (see Figure 9) of 2.0 [mm] or less (preferably 1.5 [mm]). The narrow grooves 53 also have a groove depth D8 (see Figure 9) of 4.5 [mm] or more and 24.0 [mm] or less. The groove depth D8 of the narrow grooves 53 is equivalent to the depth from the tread surface 15A of the raised section 83. The rib 63 has a rib width W5 (see Figure 9) of 1.0 [mm] or more and 4.0 [mm] or less. The rib 63 has an inclined surface 63a that slopes outward in the tire width direction from the tread surface 15A to a depth of D9. 【0041】 Furthermore, as shown in Figure 4, the center block 311 has an open sipe 71A that extends along the tire width direction and has open ends, and a closed sipe 71B that has closed ends in each of the two regions divided by the open sipe 71A. The open sipe 71A has a width of 1.0 [mm] or less and is positioned at an angle to the center lug groove 41 within a range of ±5°. The closed sipe 71B has a width of 1.0 [mm] or less and is positioned at an angle to the center lug groove 41 within a range of ±5°, and has two bends in the middle. 【0042】 Furthermore, as shown in Figure 4, the middle block 321 has an open sipe 72A that extends along the tire width direction and has open ends, and a closed sipe 72B that has closed ends in each of the two regions divided by the open sipe 72A. The open sipe 72A has a width of 1.0 [mm] or less and is positioned at an angle to the middle lug groove 42 within a range of ±5°. The closed sipe 72B has a width of 1.0 [mm] or less and is positioned at an angle to the middle lug groove 42 within a range of ±5°, and has two bends in the middle. 【0043】 Furthermore, the small shoulder block 331A has an open sipe 73A that extends along the tire width direction and has open ends, and a closed sipe 73B that has closed ends in each of the two regions divided by the open sipe 73A. The open sipe 73A has a width of 1.0 [mm] or less and is positioned to extend in the same direction as the shoulder lug groove 43 within a range of ±5°. The closed sipe 73B has a width of 1.0 [mm] or less and is positioned to extend in the same direction as the shoulder lug groove 43 within a range of ±5°, and has two bends in the middle. 【0044】 Furthermore, the small shoulder block 331B has an open sipe 74A that extends along the tire width direction and has open ends, and a closed sipe 74B that has closed ends in each of the two regions divided by the open sipe 74A. The open sipe 74A has a width of 1.0 [mm] or less and is positioned to extend in the same direction as the shoulder lug groove 43 within a range of ±5°. The closed sipe 74B has a width of 1.0 [mm] or less and is positioned to extend in the same direction as the shoulder lug groove 43 within a range of ±5°. 【0045】 The pneumatic tire 1 of the embodiment is characterized in that, in the tread portion, a center land portion 31 at the center in the tire width direction, middle land portions 32 on both outer sides in the tire width direction of the center land portion 31, and shoulder land portions 33 on the outer sides in the tire width direction of each middle land portion 32, which are defined by circumferential grooves 20 extending along the tire circumferential direction and arranged in at least four rows in the tire width direction; in the center land portion 31, a center block 311 defined by center lug grooves 41 extending along the tire width direction with both ends opening into the circumferential grooves 20 and arranged in a plurality in the tire circumferential direction; in the middle land portion 32, a middle block 321 defined by middle lug grooves 42 extending along the tire width direction with both ends opening into the circumferential grooves 20 and arranged in a plurality in the tire circumferential direction; and ribs 62 defined by narrow grooves 52 extending along the tire circumferential direction at at least one end in the tire width direction of the center block 311 and the middle block 321. And, in the pneumatic tire 1 of the embodiment, a center region CC is defined between the inner ends in the tire width direction of each circumferential groove 20 on the outermost side in the tire width direction, and the center region CC has a range of 45[%] or more with respect to the developed width TDW of the tread portion and is arranged at the center of the tread portion. Further, in the pneumatic tire 1 of the embodiment, the groove width W of each circumferential groove 20 (shoulder circumferential groove 22) on the outermost side in the tire width direction and the groove width W1 of each other circumferential groove 20 (center circumferential groove 21) satisfy the relationship of W1 < W. Further, in the pneumatic tire 1 of the embodiment, the groove width W1 of the center circumferential groove 21 is 2[%] or less with respect to the developed width TDW. Further, in the pneumatic tire 1 of the embodiment, the groove width W2 of the narrow groove 52 is 0.9[%] or less with respect to the developed width TDW. Further, in the pneumatic tire 1 of the embodiment, the groove width W1 of the center circumferential groove 21 and the rib width Wr of the rib 62 satisfy the relationship of 1.0 ≦ Wr / W1 ≦ 2.0. Further, in the pneumatic tire 1 of the embodiment, the groove width W1 of the center circumferential groove 21 and the tire width direction dimension Wc of the center block 311 satisfy the relationship of W1 ≦ Wc × 0.2. Further, in the pneumatic tire 1 of the embodiment, the groove area ratio in the center region CC is 33[%] or less. 【0046】 Here, the groove area ratio is defined as the percentage of groove area / (groove area + contact area). The groove area is the sum of the groove opening areas on the tread surface 15A. The contact area is measured between the contact edge T, relative to the plane where the tread surface 15A contacts the flat plate, when the pneumatic tire 1 is mounted on a regular rim, filled to the regular internal pressure, and placed perpendicular to a flat plate with the tire's equatorial plane CL perpendicular to the plate in a stationary state, and a load corresponding to the regular load is applied. The groove area does not include sipes. 【0047】 Furthermore, the center region CC is measured by the shortest distance between the inner ends in the tire width direction of each circumferential groove 22 under an unloaded condition with the pneumatic tire 1 mounted on a specified rim and filled to a specified internal pressure. 【0048】 With this pneumatic tire 1, the placement of the rib 62 provides a lateral edge effect, enhancing resistance to skidding on ice, resulting in improved acceleration and contributing to snow traction performance. Furthermore, with this pneumatic tire 1, the center area CC is positioned closer to the center of the tread, ensuring rigidity of the center area CC and contributing to low rolling resistance. In addition, with this pneumatic tire 1, the groove width W2 of the narrow groove 52 is narrowed relative to the unfolded width TDW, and the groove width W1 of the center circumferential groove 21 is narrowed to approach the rib width Wr of the rib 62, increasing the rigidity of the center area CC and contributing to low rolling resistance, while also improving resistance to skidding by the rib 62 and contributing to snow traction performance. Furthermore, with this pneumatic tire 1, the relationship between the groove width W1 of the center circumferential groove 21 and the tire width dimension Wc of the center block 311 is defined, increasing the rigidity of the center area CC and contributing to low rolling resistance. Furthermore, with this pneumatic tire 1, the relatively low groove area ratio in the center region CC increases the rigidity of the center region CC, contributing to low rolling resistance performance. As a result, this pneumatic tire 1 can achieve both low rolling resistance performance and snow traction performance. 【0049】 Furthermore, for this pneumatic tire 1, it is preferable to set the groove width W1 of the center circumferential groove 21 to 1.5% of the unfolded width TDW in order to improve low rolling resistance performance. Also, for this pneumatic tire 1, it is preferable to set the groove width W2 of the narrow groove 52 to 0.5% of the unfolded width TDW in order to improve snow traction performance. Furthermore, for this pneumatic tire 1, it is preferable to set the groove width W1 of the center circumferential groove 21 and the tire width dimension Wc of the center block 311 to W1 ≤ Wc × 0.15 in order to improve low rolling resistance performance. Also, for this pneumatic tire 1, it is preferable to set the groove area ratio in the center region CC to 30% in order to improve low rolling resistance performance. 【0050】 Furthermore, in the pneumatic tire 1 of the embodiment, the center block 311 satisfies the relationship 0.7 ≤ Lc / Wc ≤ 1.5 between the tire circumferential dimension Lc and the tire widthwise dimension Wc, and the middle block 321 satisfies the relationship 0.7 ≤ Lm / Wm ≤ 1.5 between the tire circumferential dimension Lm and the tire widthwise dimension Wm. 【0051】 With this pneumatic tire 1, by setting the aspect ratio of each block 311,321 within an appropriate range, sufficient block rigidity can be ensured, suppressing block deformation during tire rolling and improving low rolling resistance performance. Furthermore, it is preferable for this pneumatic tire 1 to satisfy the relationships 0.8 ≤ Lc / Wc ≤ 1.3 and 0.8 ≤ Lm / Wm ≤ 1.3 in order to improve low rolling resistance performance. 【0052】 Furthermore, in the pneumatic tire 1 of the embodiment, the center block 311 has an open sipe 71A that extends along the tire width direction and has open ends, and a closed sipe 71B that has closed ends in each of the two regions divided by the open sipe 71A, so that the area Ac of the tread surface 15A of the center block and the respective areas Ac1 and Ac2 of the tread surface 15A divided by the open sipe 71A satisfy the relationships 0.3 ≤ Ac1 / Ac ≤ 0.7 and 0.3 ≤ Ac2 / Ac ≤ 0.7. Furthermore, the middle block 321 has an open sipe 72A that extends along the tire width direction and has open ends, and a closed sipe 72B that has closed ends in each of the two regions divided by the open sipe 72A, so that the area Am of the tread surface 15A of the middle block 321 and the respective areas Am1 and Am2 of the tread surface 15A divided by the open sipe 72A satisfy the relationships 0.3 ≤ Am1 / Am ≤ 0.7 and 0.3 ≤ Am2 / Am ≤ 0.7. 【0053】 With this pneumatic tire 1, by providing open sipes 71A, 72A and closed sipes 71B, 72B in relation to the above area, edge components can be secured and snow traction performance can be improved. Furthermore, it is preferable for this pneumatic tire 1 to satisfy the relationships 0.4≦Ac1 / Ac≦0.6, 0.4≦Ac2 / Ac≦0.6, 0.4≦Am1 / Am≦0.6, and 0.4≦Am2 / Am≦0.6 in order to improve snow traction performance. 【0054】 Furthermore, in the pneumatic tire 1 of the embodiment, the groove width W3c of the center lug groove 41 and the groove width W of each shoulder circumferential groove 22 on the outermost side in the tire width direction satisfy the relationship 0.3 ≤ W3c / W ≤ 0.9, and the groove width W3m of the middle lug groove 42 and the groove width W of each shoulder circumferential groove 22 on the outermost side in the tire width direction satisfy the relationship 0.3 ≤ W3m / W ≤ 0.9. 【0055】 With this pneumatic tire 1, by appropriately setting the groove widths W3c and W3m of the lug grooves 41 and 42 relative to the groove width W of the circumferential shoulder groove 22 on the outer side in the tire width direction, the groove volume of the center region CC can be secured, thereby improving snow traction performance. Furthermore, it is preferable for this pneumatic tire 1 to satisfy the relationships 0.4 ≤ W3c / W ≤ 0.8 and 0.4 ≤ W3m / W ≤ 0.8 in order to improve snow traction performance. 【0056】 Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 4, the angle θc of the center lug groove 41 with respect to the tire width direction is in the range of 10[°]≦θc≦20[°] in absolute value, and the angle θm of the middle lug groove 42 with respect to the tire width direction is in the range of 10[°]≦θm≦20[°] in absolute value, and the inclination directions of the center lug groove 41 and the middle lug groove 42 with respect to the tire width direction are different. 【0057】 With this pneumatic tire 1, by defining the angle θc of the center lug groove 41 with respect to the tire width direction and the angle θm of the middle lug groove 42 with respect to the tire width direction, and by making the inclination directions of the lug grooves 41 and 42 of the land portions 31 and 32, which are aligned in the tire width direction, the edge effect can be increased and snow traction performance can be improved. 【0058】 Furthermore, in the pneumatic tire 1 of the embodiment, as shown in Figure 4, the tire circumferential dimension L1 of the rib 62 and the tire circumferential dimension L of the end in the tire width direction of the block adjacent to the rib 62 via the narrow groove 52 (in this embodiment, the middle block 321) satisfy the relationship 0.8 ≤ L1 / L ≤ 1.2. 【0059】 In this pneumatic tire 1, by making the tire circumferential dimension L1 of the rib 62 equal to the tire circumferential dimension L of the tire width direction end of the block (middle block 321) adjacent to the rib 62, mutual support occurs when the rib 62 collapses, thus ensuring rigidity and improving low rolling resistance performance. Furthermore, it is preferable for this pneumatic tire 1 to satisfy the relationship 0.9 ≤ L1 / L ≤ 1.1 in order to improve low rolling resistance performance. 【0060】 Further, in the pneumatic tire 1 of the embodiment, as shown in FIGS. 6 and 8, the center lug groove 41 has a bottom raising portion 81 disposed therein, and the bottom raising portion 81 is formed in a stepped shape having two different depths D3 and D4 from the tread surface 15A, and satisfies the relationship of D3 < D4 < D with respect to the groove depth D of the center circumferential groove 21 through which the center lug groove 41 opens. 【0061】 According to this pneumatic tire 1, by providing the bottom raising portion 81 in the center lug groove 41 disposed in the center land portion 31 with high ground pressure, the rigidity of the base of the center block 311 is improved, and the low rolling resistance performance can be improved. Moreover, according to this pneumatic tire 1, by forming the bottom raising portion 81 in a stepped shape, the groove volume can be secured and the snow traction performance can be maintained. In the case where the stepped shape is biased in the tire width direction as shown in FIG. 8, it is preferable to alternately arrange the biased forms in the tire circumferential direction in order to balance the snow traction performance. 【0062】 Further, in the pneumatic tire 1 of the embodiment, the center lug groove 41 has a bottom raising portion 81 disposed therein, and the bottom raising portion 81 has a bottom raising sipe 91 penetrating along the extending direction of the center lug groove 41. 【0063】 According to this pneumatic tire 1, by disposing the bottom raising sipe 91 in the bottom raising portion 81, an edge effect is generated after wear of the center land portion 31, and the snow traction performance can be secured. The bottom raising sipe 91 having a bent portion 91a can secure rigidity by meshing and secure the uneven wear resistance performance. 【0064】 Further, in the pneumatic tire 1 of the embodiment, as shown in FIG. 3, the groove depth D1 of the fine groove 52 and the groove depth D of the center circumferential groove 21 with the rib 62 partitioned by the fine groove 52 satisfy the relationship of 0.3 ≦ D1 / D ≦ 1.0. 【0065】 With this pneumatic tire 1, by optimizing the relationship between the groove depth D of the center circumferential groove 21 separated by the rib 62 and the groove depth D1 of the narrow groove 52, it is possible to maintain the balance of rigidity of the rib 62 while securing groove volume, thereby improving the effect of achieving both snow traction performance and low rolling resistance performance. Furthermore, it is preferable for this pneumatic tire 1 to satisfy the relationship 0.5 ≤ D1 / D ≤ 0.7 in order to improve the effect of achieving both snow traction performance and low rolling resistance performance. 【0066】 Furthermore, in the pneumatic tire 1 of the embodiment, the rib 62 has an inclined surface 62a that slopes from the tread surface 15A to a depth D2 toward the center circumferential groove 21 with respect to the rib 62, and satisfies the relationship 0.1 ≤ D2 / D1 ≤ 0.5 with respect to the groove depth D1 of the narrow groove 52. 【0067】 With this pneumatic tire 1, by providing an appropriate depth at the end of the rib 62 on the tread surface 15A side on the center circumferential groove 21 side, the groove volume is secured while maintaining the balance of rigidity of the rib 62, thereby improving the effect of achieving both snow traction performance and low rolling resistance performance. Moreover, with this pneumatic tire 1, by providing an inclined surface 62a at the end of the rib 62 on the tread surface 15A side, it is possible to make clean contact with the ground when lateral force is applied. Furthermore, it is preferable for this pneumatic tire 1 to satisfy the relationship 0.1 ≤ D2 / D1 ≤ 0.3 in order to improve the effect of achieving both snow traction performance and low rolling resistance performance. 【0068】 By the way, in this embodiment, as described above, a pneumatic tire 1 was described as an example of a tire. This 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 this embodiment can be arbitrarily applied to other tires within the scope of what is obvious to those skilled in the art. Other tires include, for example, airless tires and solid tires. [Examples] 【0069】 Figures 10 to 15 are charts showing the results of performance tests of the pneumatic tire according to the embodiment. Below, we will describe the performance evaluation tests conducted on the conventional and comparative examples of pneumatic tires and the pneumatic tire according to the embodiment. The performance evaluation tests included tests for low rolling resistance performance and snow performance (snow traction performance). The test tires were 315 / 80R22.5 in size, mounted on a specified rim, and filled to the specified internal pressure. 【0070】 The low rolling resistance performance evaluation test uses a drum testing machine with a drum diameter of 1707 mm. In accordance with ISO 28580, the reciprocal of the rolling resistance coefficient of the test tire is calculated and evaluated at a speed of 80 km / h. This evaluation is performed using an index evaluation with the conventional example as the baseline (100), and a higher value is preferable. 【0071】 Snow performance evaluation tests are conducted by measuring the distance required to accelerate from a specified initial speed to a specified terminal speed on a snow-covered test course using a heavy-duty vehicle equipped with test tires, and calculating the acceleration. This evaluation is performed using an index evaluation with conventional examples as the baseline (100), and a higher value is preferable. 【0072】 Conventional pneumatic tires, as shown in Figures 1 and 2, have a configuration in which the center, middle, and shoulder areas are formed by four circumferential grooves, and the center block and middle block are formed by lug grooves. However, they do not have narrow grooves or ribs, and the ratio of the center area to the unfolded width, the relationship with the width of the circumferential grooves, the relationship between the circumferential groove width W1 and the center block width dimension Wc, and the groove area ratio of the center area are outside the specified range. 【0073】 In the comparative example pneumatic tire, as shown in Figures 1 and 2, the center land area, middle land area, and shoulder land area are formed by four circumferential grooves, the center block and middle block are formed by lug grooves, and it is equipped with narrow grooves and ribs. The relationship between the circumferential groove width W1 and the unfolded width, the relationship between the narrow groove width and the unfolded width, and the relationship between the circumferential groove width W1 and the rib width Wr are within the specified range. However, the ratio of the center area to the unfolded width, the relationship between the circumferential groove width W1 and the center block width dimension Wc, and the groove area ratio of the center area are outside the specified range. In Comparative Example 2, the configurations in Figures 1 and 2 show that the center land area, middle land area, and shoulder land area are formed by four circumferential grooves, the center block and middle block are formed by lug grooves, and the structure is equipped with narrow grooves and ribs. The ratio of the center area to the developed width, the relationship with the width of the circumferential grooves, and the relationship of the circumferential groove width W1 to the developed width are within the specified range. However, the relationship of the narrow groove width to the developed width, the relationship with the rib width Wr to the circumferential groove width W1, the relationship between the circumferential groove width W1 and the center block width dimension Wc, and the groove area ratio of the center area are outside the specified range. 【0074】 The pneumatic tire of the embodiment has the configuration shown in Figures 1 and 2, in which the center land area, middle land area, and shoulder land area are formed by four circumferential grooves, the center block and middle block are formed by lug grooves, and it is equipped with narrow grooves and ribs, and the ratio of the center area to the unfolded width, the relationship of the circumferential groove width W1 to the unfolded width, the relationship of the narrow groove width to the unfolded width, the relationship of the rib width Wr to the circumferential groove width W1, the relationship between the circumferential groove width W1 and the center block width dimension Wc, and the groove area ratio of the center area are all within the specified range. 【0075】 As the test results show, the pneumatic tire of the example maintains wet performance while improving low rolling resistance and resistance to uneven wear compared to the conventional example and each comparative example. 【0076】 The present disclosure includes the following inventions. [Invention 1] A center land portion at the center in the tire width direction, which is partitioned by circumferential grooves extending along the tire circumferential direction in the tread portion and arranged in at least four rows in the tire width direction, middle land portions on both outer sides in the tire width direction of the center land portion, and shoulder land portions on the outer sides in the tire width direction of each of the middle land portions, In the center land portion, a center block partitioned by center lug grooves extending along the tire width direction with both ends opening into the circumferential grooves and arranged in a plurality in the tire circumferential direction, In the middle land portion, a middle block partitioned by middle lug grooves extending along the tire width direction with both ends opening into the circumferential grooves and arranged in a plurality in the tire circumferential direction, A rib partitioned by a narrow groove extending along the tire circumferential direction at at least one end in the tire width direction of the center block and the middle block, including Taking the space between the inner ends in the tire width direction of the outermost circumferential grooves in the tire width direction as a center region, the center region has a range of 45% or more with respect to the developed width of the tread portion and is arranged at the center of the tread portion, The groove width W of the outermost circumferential groove in the tire width direction and the groove width W1 of each of the other circumferential grooves satisfy the relationship W1 < W, The groove width W1 of the circumferential groove is 2% or less with respect to the developed width, The groove width of the narrow groove is 0.9% or less with respect to the developed width, The groove width W1 of the circumferential groove and the rib width Wr of the rib satisfy the relationship 1.0 ≦ Wr / W1 ≦ 2.0, The groove width W1 of the circumferential groove and the tire width direction dimension Wc of the center block satisfy the relationship W1 ≦ Wc × 0.2, The groove area ratio in the center region is 33% or less, a tire. [Invention 2] In the center block, the tire circumferential direction dimension Lc and the tire width direction dimension Wc satisfy the relationship 0.7 ≦ Lc / Wc ≦ 1.5, In the aforementioned middle block, the tire circumferential dimension Lm and the tire widthwise dimension Wm satisfy the relationship 0.7 ≤ Lm / Wm ≤ 1.5. The tire described in Invention 1. [Invention 3] The center block has an open sipe extending along the tire width direction with open ends, and closed sipes with closed ends in each of the two regions divided by the open sipe, The area Ac of the center block and the areas Ac1 and Ac2 separated by the open sipes satisfy the relationships 0.3 ≤ Ac1 / Ac ≤ 0.7 and 0.3 ≤ Ac2 / Ac ≤ 0.7. The middle block has an open sipe that extends along the tire width direction and has open ends, and closed sipes that have closed ends in each of the two regions divided by the open sipe, The area Am of the middle block and the areas Am1 and Am2 separated by the open sipes satisfy the relationships 0.3 ≤ Am1 / Am ≤ 0.7 and 0.3 ≤ Am2 / Am ≤ 0.7. A tire according to invention 1 or 2. [Invention 4] The groove width W3c of the center lug groove and the groove width W of each of the circumferential grooves on the outermost side in the tire width direction satisfy the relationship 0.3 ≤ W3c / W ≤ 0.9. The groove width W3m of the middle lug groove and the groove width W of each of the circumferential grooves on the outermost side in the tire width direction satisfy the relationship 0.3 ≤ W3m / W ≤ 0.9. A tire according to any one of inventions 1 to 3. [Invention 5] The angle θc of the center lug groove with respect to the tire width direction is in the range of 10[°]≦θc≦20[°] in absolute value. The angle θm of the middle lug groove with respect to the tire width direction is in the range of 10[°]≦θm≦20[°] in absolute value, The inclination direction of the center lug groove and the middle lug groove is different with respect to the tire width direction. A tire according to any one of inventions 1 to 4. [Invention 6] The tire circumferential dimension L1 of the rib and the tire circumferential dimension L of the edge in the tire width direction of the block adjacent to the rib through the narrow groove satisfy the relationship of 0.8 ≦ L1 / L ≦ 1.2. The tire according to any one of Inventions 1 to 5. [Invention 7] The center lug groove has a bottom raising portion disposed therein. The bottom raising portion is formed in a stepped shape having two different depths D3 and D4 from the tread surface, and satisfies the relationship of D3 < D4 < D with respect to the groove depth D of the circumferential groove at which the center lug groove opens. The tire according to any one of Inventions 1 to 6. [Invention 8] The center lug groove has a bottom raising portion disposed therein. The bottom raising portion has a bottom raising sipe penetrating along the extending direction of the center lug groove. The tire according to any one of Inventions 1 to 7. [Invention 9] The groove depth D1 of the narrow groove and the groove depth D of the circumferential groove bounded by the rib partitioned by the narrow groove satisfy the relationship of 0.3 ≦ D1 / D ≦ 1.0. The tire according to any one of Inventions 1 to 8. [Invention 10] The rib has an inclined surface inclined at a depth D2 from the tread surface toward the circumferential groove bounded by the rib, and satisfies the relationship of 0.1 ≦ D2 / D1 ≦ 0.5 with respect to the groove depth D1 of the narrow groove. The tire according to any one of Inventions 1 to 9. 【Explanation of Reference Numerals】 【0077】 1 Pneumatic tire 15A Tread surface 20 Circumferential groove 31 Center land portion 32 Middle land portion 33 Shoulder land portion 41 Center lug groove 42 Middle lug groove 52 Narrow groove 62 Rib 62a Slope 71A, 72A Open Sipe 71B, 72B Closed Sipe 81 Raised base 81a Stepped section 91 Bottom-raising sipes 311 Center Block 321 Middle Block

Claims

[Claim 1] The tread portion is divided by circumferential grooves that extend along the tire's circumferential direction and are arranged in the tire's width direction, comprising a center land portion in the tire's width direction, middle land portions on both outer sides of the center land portion in the tire's width direction, and shoulder land portions on the outer sides of each of the middle land portions in the tire's width direction, In the aforementioned center land portion, a center block is provided, which extends along the tire width direction, has both ends opening into the circumferential grooves, and is partitioned by a plurality of center lug grooves arranged in the circumferential direction of the tire; In the aforementioned middle land portion, a middle block is provided, which extends along the tire width direction, has both ends opening into the circumferential grooves, and is partitioned by a plurality of middle lug grooves arranged in the circumferential direction of the tire; A rib is provided at at least one end of the center block and the middle block in the tire width direction, which is demarcated by a narrow groove extending along the tire circumferential direction. Includes, The area between the inner ends in the tire width direction of each of the outermost circumferential grooves in the tire width direction is defined as the center region, and this center region is positioned in the center of the tread portion with an area of ​​45% or more of the unfolded width of the tread portion. The groove width W of each of the circumferential grooves on the outermost side in the tire width direction and the groove width W1 of each of the other circumferential grooves satisfy the relationship W1 < W. The groove width W1 of the circumferential groove is 2% or less of the unfolded width. The groove width of the aforementioned narrow groove is 0.9% or less of the expanded width. The groove width W1 of the circumferential groove and the rib width Wr of the rib satisfy the relationship 1.0 ≤ Wr / W1 ≤ 2.

0. The groove width W1 of the circumferential groove and the tire width dimension Wc of the center block satisfy the relationship W1 ≤ Wc × 0.

2. The groove area ratio in the aforementioned center region is 33% or less. tire. [Claim 2] In the aforementioned center block, the tire circumferential dimension Lc and the tire widthwise dimension Wc satisfy the relationship 0.7 ≤ Lc / Wc ≤ 1.

5. In the aforementioned middle block, the tire circumferential dimension Lm and the tire widthwise dimension Wm satisfy the relationship 0.7 ≤ Lm / Wm ≤ 1.

5. The tire according to claim 1. [Claim 3] The center block has an open sipe extending along the tire width direction with open ends, and closed sipes with closed ends in each of the two regions divided by the open sipe, The area Ac of the center block and the areas Ac1 and Ac2 separated by the open sipes satisfy the relationships 0.3 ≤ Ac1 / Ac ≤ 0.7 and 0.3 ≤ Ac2 / Ac ≤ 0.

7. The middle block has an open sipe that extends along the tire width direction and has open ends, and closed sipes that have closed ends in each of the two regions divided by the open sipe, The area Am of the middle block and the areas Am1 and Am2 separated by the open sipes satisfy the following relationships: 0.3 ≤ Am1 / Am ≤ 0.7 and 0.3 ≤ Am2 / Am ≤ 0.

7. The tire according to claim 1. [Claim 4] The groove width W3c of the center lug groove and the groove width W of each of the circumferential grooves on the outermost side in the tire width direction satisfy the relationship 0.3 ≤ W3c / W ≤ 0.

9. The groove width W3m of the middle lug groove and the groove width W of each of the circumferential grooves on the outermost side in the tire width direction satisfy the relationship 0.3 ≤ W3m / W ≤ 0.

9. The tire according to claim 1. [Claim 5] The angle θc of the center lug groove with respect to the tire width direction is in the range of 10 [°] ≤ θc ≤ 20 [°] in absolute value. The angle θm of the middle lug groove with respect to the tire width direction is in the range of 10 [°] ≤ θm ≤ 20 [°] in absolute value. The inclination direction of the center lug groove and the middle lug groove is different with respect to the tire width direction. The tire according to claim 1. [Claim 6] The tire circumferential dimension L1 of the rib and the tire circumferential dimension L of the tire width direction end of the block adjacent to the rib via the narrow groove satisfy the relationship 0.8 ≤ L1 / L ≤ 1.

2. The tire according to claim 1. [Claim 7] The aforementioned center lug groove has a raised bottom portion, The raised portion is formed in a stepped shape having two different depths D3 and D4 from the tread surface, and satisfies the relationship D3 < D4 < D with respect to the groove depth D of the circumferential groove through which the center lug groove opens. The tire according to claim 1. [Claim 8] The aforementioned center lug groove has a raised bottom portion, The raised portion has a raised sipe that penetrates along the extending direction of the center lug groove. The tire according to claim 1. [Claim 9] The groove depth D1 of the aforementioned narrow groove and the groove depth D of the circumferential groove separated by the rib partitioned by the aforementioned narrow groove satisfy the relationship 0.3 ≤ D1 / D ≤ 1.

0. The tire according to claim 1. [Claim 10] The rib has an inclined surface that slopes from the tread surface to a depth D2 toward the circumferential groove with respect to the rib, and satisfies the relationship 0.1 ≤ D2 / D1 ≤ 0.5 with respect to the groove depth D1 of the narrow groove. The tire according to claim 1.

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