tire

Abstract

To provide a tire capable of compatibly achieving the noise performance, the snow traction performance and the side slip resistant performance of the tire.SOLUTION: A tire includes a shoulder shallow groove 311 having a groove depth shallower than that of a shoulder main groove 21 and continuously extending over the whole periphery of the tire, a plurality of first shoulder lug grooves 312A opening to a tire grounding end T at one end part and connected to the shoulder shallow groove 311 at the other end part, a plurality of first shoulder blocks 313A formed by being partitioned by the shoulder shallow groove 311 and the first shoulder lug grooves 312A, a plurality of second shoulder lug grooves 312B connected to the shoulder main groove 21 at one end part and connected to the shoulder shallow groove 311 at the other end part, a plurality of second shoulder blocks 313B formed by being partitioned by the shoulder shallow groove 311 and the second shoulder lug grooves 312B, and a thin lib 314 formed at a groove bottom of the shoulder shallow groove 311 and continuously extending over the whole periphery of the tire.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tire, and more particularly to a tire that can achieve a balance between tire noise performance, snow traction performance, and sideslip resistance performance. [Background technology]

[0002] In heavy-duty winter tires, there is a need to improve the snow traction and skid resistance of the tires. A technology described in Patent Document 1 is known as a conventional tire that addresses such a problem. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-144653 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, in recent heavy duty tires, there is a need to improve the noise performance of the tires.

[0005] Therefore, the present invention has been made in consideration of the above, and has an object to provide a tire that can achieve a balance between tire noise performance, snow traction performance, and skid resistance performance. [Means for solving the problem]

[0006] In order to achieve the above object, the tire according to the present invention is a tire having a plurality of circumferential main grooves and a plurality of land portions defined by the circumferential main grooves, and defines a pair of shoulder main grooves located at the outermost positions in the tire width direction among the plurality of circumferential main grooves, and a pair of shoulder land portions located at the outermost positions in the tire width direction among the plurality of land portions, and is characterized in that at least one of the shoulder land portions comprises a shoulder shallow groove having a groove depth shallower than the shoulder main groove and extending continuously around the entire circumference of the tire, a plurality of first shoulder lug grooves opening at one end at the tire ground contact edge and connected to the shoulder shallow groove at the other end, a plurality of first shoulder blocks defined by the shoulder shallow groove and the first shoulder lug groove, a plurality of second shoulder lug grooves connected to the shoulder main groove at one end and connected to the shoulder shallow groove at the other end, a plurality of second shoulder blocks defined by the shoulder shallow groove and the second shoulder lug groove, and a thin rib formed at a groove bottom of the shoulder shallow groove and extending continuously around the entire circumference of the tire. Effect of the Invention

[0007] In the tire according to the present invention, (1) the shoulder land portion has first and second shoulder lug grooves connected to the shoulder shallow groove, and a fine rib formed at the groove bottom of the shoulder shallow groove and extending continuously around the entire circumference of the tire, so that compared to a configuration without a fine rib, the snow column shear force at the connection point between the shoulder shallow groove and the shoulder lug groove is increased, improving the snow traction performance of the tire, and (2) because the fine rib extends continuously around the entire circumference of the tire, the edge components of the fine rib improve the skid performance of the tire when traveling on snowy roads, and the sound insulation effect of the fine rib improves the noise performance of the tire. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view in the tire meridian direction showing a tire according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view showing a tread surface of the tire shown in FIG. [Diagram 3] FIG. 3 is an enlarged view showing the shoulder land portion shown in FIG. [Figure 4] FIG. 4 is an enlarged view showing a main part of the shoulder land portion shown in FIG. [Diagram 5] FIG. 5 is a cross-sectional view showing the shoulder land portion shown in FIG. [Figure 6] FIG. 6 is an enlarged cross-sectional view showing a fine rib of the shoulder land portion shown in FIG. [Figure 7] FIG. 7 is an enlarged view showing the middle land portion and the center land portion shown in FIG. [Figure 8] FIG. 8 is a cross-sectional view showing the middle land portion shown in FIG. [Figure 9] FIG. 9 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. [Figure 10] FIG. 10 is a table showing the results of performance tests of the tire according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The present invention will be described in detail below with reference to the drawings. Note that the present invention is not limited to the embodiments. The components of the embodiments include those that can be substituted and are obvious substitutes while maintaining the identity of the invention. The multiple modified examples described in the embodiments can be arbitrarily combined within the scope of what is obvious to those skilled in the art.

[0010] [tire] Fig. 1 is a cross-sectional view in the tire meridian direction showing a tire 1 according to an embodiment of the present invention. The figure shows a cross-sectional view of one side region in the tire radial direction. In this embodiment, as an example of a tire, a heavy-duty pneumatic radial tire that is mounted on the driving wheels, steering wheels, or all wheels of a vehicle for long-distance transportation such as a truck or bus will be described.

[0011] In the figure, the tire meridian cross section is defined as a cross section of the tire cut by a plane including the tire rotation axis (not shown). The tire equatorial plane CL is defined as a plane that passes through the midpoint of the tire section width defined by JATMA and is perpendicular to the tire rotation axis. The tire width direction is defined as a direction parallel to the tire rotation axis, and the tire radial direction is defined as a direction perpendicular to the tire rotation axis.

[0012] The tire 1 has an annular structure centered on the tire rotation axis, and includes a pair of bead cores 11, 11, a pair of bead fillers 12, 12, a carcass layer 13, a belt layer 14, a tread rubber 15, a pair of sidewall rubbers 16, 16, and a pair of rim cushion rubbers 17, 17 (see Figure 1).

[0013] The pair of bead cores 11, 11 are formed by winding one or more steel bead wires in an annular manner in multiple layers, and are embedded in the bead portions to form the cores of the left and right bead portions. The pair of bead fillers 12, 12 are made up of a lower filler 121 and an upper filler 122, and are disposed on the outer periphery of the pair of bead cores 11, 11 in the tire radial direction, respectively, to reinforce the bead portions.

[0014] 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, and is toroidally stretched between the left and right bead cores 11, 11 to form the tire framework. In addition, both ends of the carcass layer 13 are wrapped back and secured to the outside in the tire width direction so as to envelop the bead cores 11 and the bead fillers 12. In addition, 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 an absolute cord angle (defined as the inclination angle of the carcass cords in the longitudinal direction with respect to the tire circumferential direction) of 80 degrees or more and 90 degrees or less.

[0015] The belt layer 14 is formed by laminating a plurality of 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 a plurality of belt cords made of steel with a coating rubber and rolling it, and has a cord angle (defined as the inclination angle of the longitudinal direction of the belt cord 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 a plurality of belt cords made of steel with a coating rubber and rolling it, and have a cord angle of 10 degrees or more and 55 degrees or less in absolute value. In addition, the pair of cross belts 142 and 143 have cord angles of opposite signs to each other, and are laminated with the longitudinal directions of the belt cords crossing each other (so-called cross-ply structure). The belt cover 144 is formed by covering a plurality of belt cover cords made of steel or organic fiber material with coating rubber and rolling the covered cords, and has a cord angle of 10 degrees or more and 55 degrees or less in absolute value.

[0016] The tread rubber 15 is disposed on the outer periphery in the tire radial direction of the carcass layer 13 and the belt layer 14 to form a tread portion of the tire 1. A pair of sidewall rubbers 16, 16 are disposed on the outer sides in the tire width direction of the carcass layer 13, respectively, to form left and right sidewall portions. A pair of rim cushion rubbers 17, 17 extend from the inner side in the tire radial direction of the left and right bead cores 11, 11 and the turned-up portions of the carcass layer 13 to the outer side in the tire width direction, to form a rim fitting surface of the bead portion.

[0017] [Tread surface] FIG. 2 is a plan view showing the tread surface of the tire 1 shown in FIG. 1. The figure shows the tread surface of a winter tire. In the figure, the tire circumferential direction refers to the direction around the tire rotation axis. Also, the symbol T is the tire ground contact edge, and the dimension symbol TW is the tire ground contact width. In the figure, since the tire 1 has a tread surface that is approximately point symmetric, some of the symbols of the components in the right area of ​​the figure are omitted.

[0018] As shown in FIG. 2, the tire 1 has a plurality of circumferential main grooves 21, 22 and a plurality of land portions 31 to 33 defined by these circumferential main grooves 21, 22 on the tread surface.

[0019] The circumferential main grooves 21, 22 are grooves that extend in the circumferential direction of the tire and have a continuous annular structure around the entire circumference of the tire. Each of the circumferential main grooves 21, 22 is a main groove that is required to display a wear indicator as specified by JATMA, and has a maximum width of 6.0 mm or more and a maximum depth of 10 mm or more.

[0020] The groove width is measured as the distance between the opposing groove walls at the groove opening when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. In a configuration in which the groove opening has a notch or chamfer, the groove width is measured at the intersection of an extension of the tread surface and an extension of the groove wall in a cross-sectional view parallel to the groove width direction and the groove depth direction.

[0021] The groove depth is measured as the distance from the tread surface to the bottom of the groove when the tire is mounted on a specified rim, inflated to a specified internal pressure, and under no load. In the case of a tire having partial unevenness or sipes at the bottom of the groove, the groove depth is measured excluding these.

[0022] The specified rim refers to the "standard rim" specified by JATMA, the "design rim" specified by TRA, or the "measuring rim" specified by ETRTO. The 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. The 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. However, in JATMA, for passenger car tires, the specified internal pressure is 180 kPa, and the specified load is 88% of the maximum load capacity at the specified internal pressure.

[0023] 2, among the multiple circumferential main grooves 21, 22, a pair of circumferential main grooves 21, 21 located at the outermost sides in the tire width direction are defined as shoulder main grooves. The shoulder main grooves 21 are defined in left and right regions bounded by the tire equatorial plane CL. The circumferential main groove 22 located closer to the tire equatorial plane CL than the pair of shoulder main grooves 21, 21 is defined as a center main groove.

[0024] 2, each of the left and right regions defined by the tire equatorial plane CL has two circumferential main grooves 21, 22. Moreover, these circumferential main grooves 21, 22 are arranged symmetrically with respect to the tire equatorial plane CL.

[0025] However, the present invention is not limited to this, and three or five or more circumferential main grooves may be arranged, the circumferential main grooves may be arranged asymmetrically about the tire equatorial plane CL (not shown), or one circumferential main groove may be arranged on the tire equatorial plane CL (not shown).

[0026] The land portions 31-33 are defined by the circumferential main grooves 21, 22 and form an annular tread extending around the entire circumference of the tire. In the configuration of FIG. 2, five rows of the land portions 31-33 are defined by the four circumferential main grooves 21, 22. One land portion 33 is disposed on the tire equatorial plane CL. However, this is not limiting, and the land portion may be disposed at a position deviated from the tire equatorial plane CL by disposing one circumferential main groove on the tire equatorial plane CL (not shown).

[0027] 2, among the multiple land portions 31-33, the land portions 31, 31 on the outer side in the tire width direction defined by the shoulder main grooves 21, 21 are defined as shoulder land portions, and the land portions 32, 32 on the inner side in the tire width direction are defined as middle land portions. Also, the land portion 33 located closer to the tire equatorial plane CL than the middle land portions 32, 32 is defined as a center land portion.

[0028] In a configuration having four circumferential main grooves 21, 22 as shown in Fig. 2, a pair of shoulder land portions 31, 31, a pair of middle land portions 32, 32, and a single center land portion 33 are defined. In a configuration having five or more circumferential main grooves, for example, two or more rows of center land portions are defined (not shown), and in a configuration having three circumferential main grooves, the center land portion is omitted (not shown). In addition, the center land portion 33 may be disposed on the tire equatorial plane CL (see Fig. 2) or may be disposed at a position deviated from the tire equatorial plane CL (not shown).

[0029] 2, the maximum ground contact width Wb1 of the shoulder land portion 31 is in the range of 0.15≦Wb1 / TW≦0.25 relative to the tire ground contact width TW. The maximum ground contact width Wb2 of the middle land portion 32 is in the range of 0.10≦Wb2 / TW≦0.15 relative to the tire ground contact width TW. The maximum ground contact width Wb3 of the center land portion 33 is in the range of 0.10≦Wb3 / TW≦0.15 relative to the tire ground contact width TW. The maximum ground contact width Wb1 of the shoulder land portion 31 is in the range of 1.00≦Wb1 / Wb2≦2.50 relative to the tire ground contact width Wb2 of the middle land portion 32, and preferably in the range of 1.50≦Wb1 / Wb2≦2.00.

[0030] The contact width of the land portion is measured as the straight-line distance in the axial direction of the tire at the contact surface between the land portion and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0031] The tire contact width TW is measured as the straight-line distance in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0032] The tire ground contact edge T is defined as the widest position in the axial direction of the tire at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, pressurized to a specified internal pressure, and placed perpendicular to a flat plate in a stationary state and subjected to a load corresponding to a specified load.

[0033] The groove area ratio in the entire tire contact patch is 0.35 to 0.40. The lower limit ensures the tire's anti-skid performance, and the upper limit ensures the tire's snow traction performance.

[0034] The groove area ratio is defined as the ratio of the total area of ​​grooves arranged in a given region to the area of ​​the said region. The groove area is the opening area of ​​the grooves on the tread surface, and is measured at the contact surface between the tire and a flat plate when the tire is mounted on a specified rim, a specified internal pressure is applied, and the tire is placed perpendicular to a flat plate in a stationary state and a load corresponding to a specified load is applied. The groove refers to a groove that is open when the tire is in contact with the ground and contributes to drainage, and does not include sipes, kerfs, etc. that are closed when the tire is in contact with the ground.

[0035] 2, the tire 1 has a point-symmetric tread pattern with a center point on the tire equatorial plane CL. However, the tire 1 is not limited to this, and may have a tread pattern that is line-symmetric about the tire equatorial plane CL, a tread pattern that has directionality in the tire rotation direction, or an asymmetric tread pattern (not shown).

[0036] [Shoulder land area] Fig. 3 is an enlarged view showing the shoulder land portion 31 shown in Fig. 2. Fig. 4 is an enlarged view showing a main part of the shoulder land portion 31 shown in Fig. 3. Fig. 5 is a cross-sectional view showing the shoulder land portion 31 shown in Fig. 3. Fig. 6 is an enlarged cross-sectional view showing a thin rib 314 of the shoulder land portion 31 shown in Fig. 3.

[0037] In FIG. 3, the shoulder land portion 31 includes a single shoulder shallow groove 311, a plurality of first and second shoulder lug grooves 312A, 312B, a plurality of first and second shoulder blocks 313A, 313B, a single narrow rib 314, a plurality of through sipes 315A, 315B and a plurality of closed sipes 316A, 316B.

[0038] The shoulder shallow groove 311 is a shallow groove that extends continuously around the entire circumference of the tire, and is disposed in the center in the tire width direction of the shoulder land portion 31. Specifically, as shown in Fig. 3, the groove center line (not shown) of the shoulder shallow groove 311 is in the range of 30% to 70% of the maximum ground contact width Wb1 of the shoulder land portion 31. In addition, a single shoulder shallow groove 311 is formed in the shoulder land portion 31, and divides the shoulder land portion 31 into two in the tire width direction.

[0039] 3, the maximum width W11 of the shoulder shallow groove 311 is in the range of 0.15≦W11 / Wb1≦0.25 with respect to the maximum ground contact width Wb1 of the shoulder land portion 31, and preferably in the range of 0.17≦W11 / Wb1≦0.19. The maximum width W11 of the shoulder shallow groove 311 is in the range of 4.5 [mm]≦W11. The lower limit ensures the groove volume of the shoulder shallow groove 311 and ensures the snow column shearing action at the connection position between the shoulder shallow groove 311 and the shoulder lug grooves 312A, 312B, and the upper limit ensures the ground contact width of the first and second shoulder blocks 313A, 313B.

[0040] In addition, in FIG. 5, the maximum depth H11 of the shoulder shallow groove 311 is shallower than the maximum depth Hg1 of the shoulder main groove 21. Specifically, the maximum depth H11 of the shoulder shallow groove 311 is in the range of 0.50≦H11 / Hg1<1.00 with respect to the maximum depth Hg1 of the shoulder main groove 21, and preferably in the range of 0.60≦H11 / Hg1≦0.80. In addition, the maximum depth H11 of the shoulder shallow groove 311 is in the range of 10 [mm]≦H11. The above lower limit ensures the maximum depth H11 of the shoulder shallow groove 311, and ensures the improvement of the snow column shear force at the connection position between the shoulder shallow groove 311 and the shoulder lug grooves 312A and 312B, and the above upper limit ensures the rigidity of the shoulder land portion 31. In the configuration of FIG. 5, the shoulder shallow groove 311 is divided into two in the tire width direction by a thin rib 314 described later, forming a pair of groove portions (reference numbers omitted in the figure). The maximum widths of these grooves are approximately equal, specifically, the maximum width of one groove is within ±10% of the maximum width of the other groove. The maximum depths of these grooves are approximately equal, specifically, the maximum depth of one groove is within ±10% of the maximum depth of the other groove. The groove wall angle of shoulder shallow groove 311 (dimension symbols omitted in the drawing) is within the range of 0 degrees to 5 degrees.

[0041] 5, the maximum depth H11 of the shoulder shallow groove 311 is in the range of 1.00≦H11 / H12≦2.00 with respect to the maximum depth H12 of the first and second shoulder lug grooves (H12A, H12B), and preferably in the range of 1.30≦H11 / H12≦1.70. Therefore, the maximum depth H11 of the shoulder shallow groove 311 is approximately equal to the maximum depth H12 of the first and second shoulder lug grooves (H12A, H12B). The above lower limit ensures the maximum depth H11 of the shoulder shallow groove 311, and the above upper limit ensures the rigidity of the shoulder land portion 31.

[0042] The maximum width W11 of the shoulder shallow groove 311 is measured as the distance between opposing groove walls at the groove opening, excluding the narrow rib 314.

[0043] As described above, shoulder shallow groove 311 is divided into two in the tire width direction by thin rib 314, and therefore maximum depth H11 of shoulder shallow groove 311 is defined for each of the two divided groove portions.

[0044] As shown in Fig. 3, one end of the first shoulder lug groove 312A opens to the tire ground contact edge T and the other end connects to the shoulder shallow groove 311. A plurality of first shoulder lug grooves 312A are arranged at predetermined intervals in the tire circumferential direction. One end of the second shoulder lug groove 312B connects to the shoulder main groove 21 and the other end connects to the shoulder shallow groove 311. A plurality of second shoulder lug grooves 312B are arranged at predetermined intervals in the tire circumferential direction.

[0045] 3, the first and second shoulder lug grooves 312A, 312B are disposed opposite each other with the shoulder shallow groove 311 in between. Specifically, as shown in FIG. 4, the distance Dc between the extension of the groove centerline of the first and second shoulder lug grooves 312A, 312B and the groove centerline of the shoulder shallow groove 311 is in the range of 0≦Dc / W12A≦0.80 with respect to the maximum width W12A of the first shoulder lug groove 312A, and preferably in the range of 0≦Dc / W12A≦0.40. This ensures an overlap amount of the first and second shoulder lug grooves 312A, 312B in the tire circumferential direction, improving the snow traction of the tire.

[0046] In addition, the inclination angles θ12A, θ12B of the first and second shoulder lug grooves 312A, 312B with respect to the tire circumferential direction are in the range of 70 degrees or more and 110 degrees or less. In the configuration of Fig. 3, the first and second shoulder lug grooves 312A, 312B are inclined in the same direction with respect to the tire circumferential direction. In addition, the inclination angle θ12A of the first shoulder lug groove 312A with respect to the inclination angle θ12B of the second shoulder lug groove 312B is in the range of 0 degrees ≦ θ12A - θ12B ≦ 10 degrees.

[0047] The inclination angles θ12A, θ12B of the shoulder lug grooves 312A, 312B are measured as an angle between a virtual line passing through the intersection of the left and right openings of the shoulder lug grooves 312A, 312B and the groove center line in a plan view of the tread and the tire circumferential direction. In a configuration in which a notch or chamfer is formed at the end of the lug groove, the virtual line is drawn on the main body of the lug groove excluding these.

[0048] The first and second shoulder lug grooves 312A, 312B have maximum widths W12A, W12B (see FIG. 3) of 6.0 mm or more and maximum depths H12A, H12B (see FIG. 5) of 10 mm or more. In the configuration of FIG. 3, the maximum width W12A of the first shoulder lug groove 312A and the maximum width W12B of the second shoulder lug groove 312B have a relationship of 1.00≦W12A / W12B≦2.00. As shown in FIG. 5, the maximum depth H12A of the first shoulder lug groove 312A and the maximum depth H12B of the second shoulder lug groove 312B are in the range of 1.00≦H12A / H12B≦1.50, preferably 1.00≦H12A / H12B≦1.20. The maximum depth H12B of the second shoulder lug groove 312B is in the range of 0.50≦H12B / Hg1≦0.90 relative to the maximum depth Hg1 of the shoulder main groove 21. The groove wall angle of the shoulder lug grooves 312A, 312B is in the range of 0 degrees or more and 5 degrees or less (not shown).

[0049] The maximum widths W12A and W12B of the shoulder lug grooves 312A and 312B are measured as the distance between the opposing groove walls at the groove opening when the tire is mounted on a specified rim and inflated to a specified internal pressure and in an unloaded state. In configurations in which the groove width is partially widened by forming a notch or chamfer at the end of the lug groove, the groove width is measured at the main body of the lug groove excluding these.

[0050] The maximum depths H12A and H12B of the shoulder lug grooves 312A and 312B are measured as the distance from the tread surface to the bottom of the groove. In configurations in which the groove depth is partially expanded by forming a notch or chamfer at the end of the lug groove, the groove depth is measured in the main body of the lug groove excluding these.

[0051] 3 and 5, for example, the first shoulder lug groove 312A has a notch 3121 at an end on the tire ground contact edge T side, and the second shoulder lug groove 312B has a notch 3121 at an end on the shoulder main groove 21 side. The groove width and groove depth at the ends of the first and second shoulder lug grooves 312A, 312B are enlarged by these notches 3121. In FIG. 3, the extension distance D12' of the notch 3121 of the second shoulder lug groove 312B in the tire width direction is in the range of 0.05≦D12' / Wb1≦0.15 with respect to the maximum ground contact width Wb1 of the shoulder land portion 31.

[0052] The first shoulder block 313A is defined by the shoulder shallow groove 311 and the first shoulder lug groove 312A. The first shoulder blocks 313A are arranged at a predetermined interval in the tire circumferential direction. The second shoulder block 313B is defined by the shoulder shallow groove 311 and the second shoulder lug groove 312B. The second shoulder blocks 313B are arranged at a predetermined interval in the tire circumferential direction. Therefore, the shoulder land portion 31 has two block rows.

[0053] The thin rib 314 is a narrow rib formed at the bottom of the shoulder shallow groove 311, and extends continuously around the entire circumference of the tire together with the shoulder shallow groove 311. In addition, in Fig. 3, the distance D11 from the tire ground contact edge T to the center line of the thin rib 314 is in the range of 0.30 ≦ D11 / Wb1 ≦ 0.70 with respect to the maximum ground contact width Wb1 of the shoulder land portion 31. Therefore, the thin rib 314 is disposed at approximately the center of the shoulder land portion 31.

[0054] In the above configuration, (1) shoulder land portion 31 includes first and second shoulder lug grooves 312A, 312B connected to shoulder shallow groove 311, and narrow rib 314 formed at the groove bottom of shoulder shallow groove 311 and extending continuously around the entire circumference of the tire, so that the snow column shear force at the connection point between shoulder shallow groove 311 and shoulder lug grooves 312A, 312B is increased and the snow traction performance of the tire is improved compared to a configuration without narrow ribs (not shown). Also, (2) narrow rib 314 extends continuously around the entire circumference of the tire, so that the edge component of narrow rib 314 improves the skid performance of the tire when traveling on snowy roads, and the sound insulation effect of narrow rib 314 improves the noise performance of the tire.

[0055] 3, the maximum width W14 of the thin rib 314 is in the range of 0.20≦W14 / W11≦0.60 relative to the maximum width W11 of the shoulder shallow groove 311, and preferably in the range of 0.30≦W14 / W11≦0.45. The above lower limit ensures the rigidity of the thin rib 314 and ensures the improvement of skid performance on snowy roads. The above upper limit ensures the groove volume of the shoulder shallow groove 311 and ensures the snow column shearing action at the connection position between the shoulder shallow groove 311 and the shoulder lug grooves 312A, 312B.

[0056] The maximum width W14 of the narrow rib 314 is measured as the maximum width in a region from the tread surface to 50[%] of the maximum depth H11 of the shoulder shallow groove 311 in a cross section in the groove width direction of the shoulder shallow groove 311 (see FIG. 5).

[0057] 6, the maximum distance H14 from the tread surface of the shoulder land portion 31 to the top of the thin rib 314 is in the range of 0≦H14 / H11≦0.30, and preferably in the range of 0≦H14 / H11≦0.10, relative to the maximum depth H11 of the shoulder shallow groove 311. It is also preferable that the maximum distance H14 is in the range of H14≦0.5 [mm]. The above upper limit ensures the edge action and sound insulation action of the thin rib 314 on snowy road surfaces.

[0058] 6, the top of the thin rib 314 has a top surface (reference numeral omitted in the figure) parallel to the tread surface of the shoulder land portion 31. The width W14' of this top surface is in the range of 0.05≦W14' / W14≦0.20 with respect to the maximum width W14 of the thin rib 314, and preferably in the range of 0.12≦W14' / W14≦0.14. The maximum width W14' of the top surface is in the range of 0.5 [mm]≦W14'≦1.0 [mm]. The above lower limit ensures the edge action and sound insulation action of the thin rib 314 on snowy road surfaces, and the above upper limit ensures the groove volume of the shoulder shallow groove 311.

[0059] For example, in the configuration of FIG. 3, as shown in FIG. 6, the thin rib 314 has a chamfered portion 3141 at its top that extends around the entire circumference of the thin rib 314. The chamfered portion 3141 is formed only at the edge of the thin rib 314 on the tire ground contact end T side. The inclination angle α of the chamfered portion 3141 with respect to the tread surface of the shoulder land portion 31 is in the range of 10[deg]≦α≦60[deg], and preferably in the range of 30[deg]≦α≦50[deg]. The thin rib 314 has a top surface parallel to the tread surface of the shoulder land portion 31 at the edge on the tire equatorial plane CL side. However, this is not limited to this, and the thin rib 314 may have the chamfered portion 3141 at the left and right edge portions and have the parallel top surface at the center portion. In FIG. 6, the sidewall angle of the thin rib 314 (dimension symbols omitted in the figure) is in the range of 0[deg] to 5[deg].

[0060] The through sipes 315A, 315B and the closed sipes 316A, 316B are cuts formed on the tread surface, and have a maximum width of less than 1.5 [mm] and a maximum depth of 2.0 [mm] or more, so that they are closed when the tire comes into contact with the ground. In the configuration of FIG. 3, the first and second shoulder blocks 313A, 313B each have a single through sipe 315A, 315B and a pair of closed sipes 316A, 316A; 316B, 316B, respectively. In addition, the through sipes 315A; 315B are disposed in the center of the shoulder blocks 313A; 313B in the tire circumferential direction, dividing the shoulder blocks 313A; 313B into a pair of small block portions (reference numbers omitted in the figure), and each of these small blocks has a single closed sipe 316A; 316B. In addition, the through sipes 315A, 315B and the closed sipe 316A of the first shoulder block 313A have a straight shape, and the closed sipe 316B of the second shoulder block 313B has a step shape.

[0061] The sipe width is measured as the opening width of the sipe on the tread surface when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state.

[0062] The sipe depth is measured as the distance from the tread surface to the bottom of the sipe when the tire is mounted on a specified rim, inflated to a specified internal pressure, and in an unloaded state. In addition, if the sipe has a partial bottom top or a concave / convex part at the bottom of the sipe, the sipe depth is measured excluding these.

[0063] [Middle and Center Land Sections] Fig. 7 is an enlarged view showing the middle land portion 32 and the center land portion 33 shown in Fig. 2. Fig. 8 is a cross-sectional view showing the middle land portion 32 shown in Fig. 7.

[0064] As shown in FIG. 7, the middle land portion 32 includes a plurality of middle lug grooves 321, a plurality of middle blocks 322, a fine groove 323, a fine rib 324, a plurality of through sipes 325, and a plurality of closed sipes 326.

[0065] The middle lug groove 321 penetrates the middle land portion 32 in the tire width direction and connects to the shoulder main groove 21 and the center main groove 22. A plurality of middle lug grooves 321 are arranged at a predetermined interval in the tire circumferential direction. The inclination angle θ21 of the middle lug groove 321 with respect to the tire circumferential direction is in the range of 70 degrees or more and 80 degrees or less. As shown in FIG. 2, the middle lug groove 321 is inclined in the opposite direction in the tire circumferential direction to the second shoulder lug groove 312B of the shoulder land portion 31. The middle lug groove 321 of the middle land portion 32 and the second shoulder lug groove 312B of the shoulder land portion 31 are arranged in a staggered pattern in the tire circumferential direction along the shoulder main groove 21. This enhances the snow traction effect.

[0066] The middle lug groove 321 has a maximum width W21 (see FIG. 7) of 6.0 mm or more and a maximum depth H21 (see FIG. 8) of 10 mm or more. In FIG. 8, the maximum depth H21 of the middle lug groove 321 is in the range of 0.50≦H21 / Hg1≦0.90 with respect to the maximum depth Hg1 of the shoulder main groove 21. The groove wall angle of the middle lug groove 321 is in the range of 0 degrees or more and 5 degrees or less (not shown). In the configuration of FIG. 7, the middle lug groove 321 has cutouts 3211 at both ends as shown in FIG. 8. The groove width and groove depth of the middle lug groove 321 at both ends are enlarged by these cutouts 3211. The middle lug groove 321 has a sipe (not shown) at the groove bottom.

[0067] The middle blocks 322 are defined by middle lug grooves 321. A plurality of middle blocks 322 are arranged in a line in the tire circumferential direction.

[0068] 7, the narrow grooves 323 and narrow ribs 324 are formed on the edge portion of the middle block 322 on the tire equatorial plane CL side. Specifically, the narrow grooves 323 extend along the edge portion of the middle block 322 on the tire equatorial plane CL side, i.e., on the center main groove 22 side, and penetrate the middle block 322 in the tire circumferential direction. In addition, the narrow ribs 324 are defined by the narrow grooves 323 and extend along the edge portion of the middle block 322 on the tire equatorial plane CL side. In addition, a set of narrow grooves 323 and narrow ribs 324 is formed in each of the multiple middle blocks 322.

[0069] The fine groove 323 has a maximum width W23 of 1.0 mm or more and 3.0 mm or less (see FIG. 7) and a maximum depth H23 of 10 mm or more and 20 mm or less (see FIG. 8). In FIG. 8, the maximum depth H23 of the fine groove 323 is in the range of 0.80≦H23 / H21≦1.20 with respect to the maximum depth H21 of the middle lug groove 321, and is in the range of 0.50≦H23 / Hg2≦0.90 with respect to the maximum depth Hg2 of the center main groove 22.

[0070] 7, the maximum width W24 of the thin rib 324 is in the range of 0.10≦W24 / Wg2≦0.20 with respect to the maximum width Wg2 of the center main groove 22. The above lower limit ensures the rigidity of the thin rib 324, and the above upper limit ensures the groove volume of the center main groove 22. Also, in FIG. 8, the maximum distance (dimension symbol omitted in the figure) from the tread surface of the middle land portion 32 to the top of the thin rib 324 is in the range of 0[%] to 10[%] with respect to the maximum depth H23 of the thin groove 323. Also, the thin rib 324 has a chamfered portion (symbol omitted in the figure) at the top that extends around the entire circumference of the thin rib 324. Also, the chamfered portion is formed only on the edge portion of the thin rib 324 on the center main groove 22 side. Moreover, the inclination angle (dimension symbols are omitted in the drawing) of the chamfered portion of the middle land portion 32 with respect to the tread surface is in the range of 0 degrees or more and 60 degrees or less.

[0071] In the above-mentioned configuration, the middle block 322 has the thin rib 324 on the edge portion on the tire equatorial plane CL side, which increases the snow column shear force in the center main groove 22. This improves the snow traction performance of the tire.

[0072] The through sipes 325 and the closed sipes 326 are cuts formed on the tread surface, and have a maximum width of less than 1.5 mm and a maximum depth of 2.0 mm or more, so that they are closed when the tire comes into contact with the ground. In the configuration of FIG. 7, each of the middle blocks 322 has a single through sipe 325 and a pair of closed sipes 326, 326. The through sipe 325 is disposed in the center of the middle block 322 in the tire circumferential direction, and divides the middle block 322 into a pair of small block portions (reference numbers omitted in the figure), and each of these small blocks has a single closed sipe 326. The through sipe 325 has a straight shape, and the closed sipe 326 has a step shape.

[0073] As shown in FIG. 2, the center land portion 33 includes a plurality of center lug grooves 331 and a plurality of center blocks 332.

[0074] The center lug groove 331 penetrates the center land portion 33 in the tire width direction and connects to the left and right center main grooves 22, 22. In addition, a plurality of center lug grooves 331 are arranged at a predetermined interval in the tire circumferential direction. In addition, the inclination angle of the center lug groove 331 with respect to the tire circumferential direction (dimension symbols omitted in the figure) is in the range of 70 [deg] or more and 80 [deg] or less. In addition, as shown in FIG. 2, the center lug groove 331 is inclined in the opposite direction in the tire circumferential direction to the middle lug groove 321 of the middle land portion 32. In addition, the center lug groove 331 of the center land portion 33 and the middle lug groove 321 of the middle land portion 32 are arranged in a staggered manner in the tire circumferential direction along the center main groove 22. This enhances the snow traction effect. In addition, a plurality of center lug grooves 331 are arranged at a predetermined interval in the tire circumferential direction. The center lug groove 331 has a maximum width of 6.0 [mm] or more and a maximum depth of 10 [mm] or more (dimension symbols omitted in the figure).

[0075] The center block 332 is defined by a center lug groove 331. A plurality of center blocks 332 are arranged in a line in the tire circumferential direction.

[0076] [effect] As described above, the tire 1 includes a plurality of circumferential main grooves 21, 22, and a plurality of land portions 31 to 33 defined by the circumferential main grooves 21, 22 (see FIG. 2). In addition, at least one of the shoulder land portions 31 is provided with a shoulder shallow groove 311 having a groove depth shallower than the shoulder main groove 21 and extending continuously around the entire circumference of the tire, a plurality of first shoulder lug grooves 312A opening at one end to the tire ground contact edge T and connecting to the shoulder shallow groove 311 at the other end, a plurality of first shoulder blocks 313A defined by the shoulder shallow groove 311 and the first shoulder lug groove 312A, a plurality of second shoulder lug grooves 312B connecting to the shoulder main groove 21 at one end and connecting to the shoulder shallow groove 311 at the other end, a plurality of second shoulder blocks 313B defined by the shoulder shallow groove 311 and the second shoulder lug groove 312B, and a thin rib 314 formed at the groove bottom of the shoulder shallow groove 311 and extending continuously around the entire circumference of the tire (see FIG. 3).

[0077] In this configuration, (1) shoulder land portion 31 includes first and second shoulder lug grooves 312A, 312B connected to shoulder shallow groove 311, and thin rib 314 formed at the groove bottom of shoulder shallow groove 311 and extending continuously around the entire circumference of the tire, so that compared to a configuration without thin ribs (not shown), snow column shear force at the connection point between shoulder shallow groove 311 and shoulder lug grooves 312A, 312B is increased, improving the snow traction performance of the tire. Also, (2) thin rib 314 extends continuously around the entire circumference of the tire, so that the edge component of thin rib 314 improves the skid performance of the tire when traveling on snowy roads, and the sound insulation effect of thin rib 314 improves the noise performance of the tire.

[0078] In addition, in this tire 1, the maximum depth H11 of the shoulder shallow groove 311 is in the range of 0.50≦H11 / Hg1<1.00 relative to the maximum depth Hg1 of the shoulder main groove 21 (see FIG. 5). The above lower limit ensures the maximum depth H11 of the shoulder shallow groove 311, thereby ensuring the improvement of the snow column shear force at the connection position between the shoulder shallow groove 311 and the shoulder lug grooves 312A, 312B, while the above upper limit has the advantage of ensuring the rigidity of the shoulder land portion 31.

[0079] In addition, in this tire 1, the maximum distance H14 from the tread surface of the shoulder land portion 31 to the top of the fine rib 314 is in the range of 0≦H14 / H11≦0.10 with respect to the maximum depth H11 of the shoulder shallow groove 311 (see FIG. 6). The above upper limit has the advantage of ensuring the edge action and sound insulation action of the fine rib 314 on snowy road surfaces.

[0080] In the tire 1, the distance D11 from the tire ground contact edge T to the center line of the narrow rib 314 is in the range of 0.30≦D11 / Wb1≦0.70 with respect to the maximum ground contact width Wb1 of the shoulder land portion 31. This has the advantage of ensuring the ground contact width of the first and second shoulder blocks 313A, 313B.

[0081] In addition, in this tire 1, the distance Dc (see FIG. 4) between the extension of the groove centerline of the first and second shoulder lug grooves 312A, 312B and the intersection point of the groove centerline of the shoulder shallow groove 311 is in the range of 0≦Dc / W12A≦0.80 with respect to the maximum width W12A of the first shoulder lug groove 312A. This ensures an overlap amount of the first and second shoulder lug grooves 312A, 312B in the tire circumferential direction, which has the advantage of improving the snow traction of the tire.

[0082] Also, in tire 1, maximum width W14 of thin rib 314 is in the range of 0.20≦W14 / W11≦0.60 relative to maximum width W11 of shoulder shallow groove 311 (see FIG. 3). The above lower limit ensures the rigidity of thin rib 314 and ensures the improvement of skid performance on snowy roads, while the above upper limit has the advantage of ensuring the groove volume of shoulder shallow groove 311 and ensuring the snow column shearing effect at the connection points between shoulder shallow groove 311 and shoulder lug grooves 312A, 312B.

[0083] Also, in this tire 1, the maximum width W11 of the shoulder shallow groove 311 is in the range of 0.17≦W11 / Wb1≦0.19 relative to the maximum ground contact width Wb1 of the shoulder land portion 31. The above lower limit has the advantage that the groove volume of the shoulder shallow groove 311 is ensured and the snow column shearing action is ensured at the connection position between the shoulder shallow groove 311 and the shoulder lug grooves 312A, 312B, and the above upper limit ensures the ground contact width of the first and second shoulder blocks 313A, 313B.

[0084] Also, in this tire 1, the top of the fine rib 314 has a top surface parallel to the tread surface of the shoulder land portion 31, and the maximum width W14' of the top surface is in the range of 0.05≦W14' / W14≦0.20 relative to the maximum width W14 of the fine rib 314 (see FIG. 6). The above lower limit ensures the maximum width W14' of the top surface of the fine rib 314, ensuring the edge action and sound insulation action of the fine rib 314 on snowy road surfaces, while the above upper limit ensures the groove volume of the shoulder shallow groove 311, ensuring the snow column shearing action at the connection position between the shoulder shallow groove 311 and the shoulder lug grooves 312A, 312B.

[0085] In addition, in the tire 1, the fine ribs 314 have the above-mentioned parallel top surfaces at the edge portions on the tire equatorial plane CL side (see FIGS. 2 and 6). This has the advantage that the fine ribs 314 improve the edge effect and sound insulation effect on snowy road surfaces.

[0086] In the tire 1, the maximum depth H11 of the shoulder shallow groove 311 is in the range of 1.00≦H11 / H12≦2.00 with respect to the maximum depth H12 (H12A, H12B) of the first and second shoulder lug grooves 312A, 312B (see FIG. 5). The above lower limit ensures the maximum depth H11 of the shoulder shallow groove 311, and the above upper limit has the advantage of ensuring the rigidity of the shoulder land portion 31.

[0087] In addition, in the tire 1, the fine rib 314 has a chamfered portion 3141 (see FIG. 6) at its apex that extends around the entire circumference of the fine rib 314, and the inclination angle α of the chamfered portion with respect to the tread surface of the shoulder land portion 31 is in the range of 10 degrees≦α≦60 degrees. This configuration has the advantage that the chamfered portion 3141 of the fine rib 314 ensures the groove volume of the shoulder shallow groove 311.

[0088] In the tire 1, the middle land portion 32 includes a plurality of middle lug grooves 321 penetrating the middle land portion 32 and a plurality of middle blocks 322 defined by the middle lug grooves 321 (see FIG. 2). The middle block 322 also includes a narrow groove 323 extending along the edge portion of the middle block 322 on the tire equatorial plane CL side, and a narrow rib 324 defined by the narrow groove 323 (see FIG. 7). In this configuration, the middle block 322 has the narrow rib 324 on the edge portion on the tire equatorial plane CL side, thereby increasing the snow column shear force in the center main groove 22. This has the advantage of improving the snow traction performance of the tire.

[0089] Applies to In this embodiment, as described above, a heavy-duty pneumatic tire has been described as an example of a tire. However, the present invention is not limited to this, and the configuration described in this 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. EXAMPLES

[0090] 9 and 10 are tables showing the results of performance tests of the tire according to the embodiment of the present invention.

[0091] In this performance test, several types of test tires were evaluated for (1) noise performance, (2) snow traction performance, and (3) skid resistance. A test tire with a tire size of 315 / 70R22.5 was mounted on a rim with a rim size of 22.5 x 9.00, and an internal pressure of 900 kPa and the specified load of JATMA were applied to the test tire. The test tires were also mounted on all wheels of a 2-D4 tractor, which was the test vehicle.

[0092] (1) In the evaluation of noise performance, the vehicle pass-by noise (external noise) is measured under test conditions that comply with ECE (Economic Commission for Europe) R117-2 (Regulation No. 117 Revision 2). Based on the measurement results, an index evaluation is performed with the comparative example set as the standard (100). The higher the evaluation value, the more preferable it is.

[0093] (2) The evaluation of snow traction performance is carried out by calculating the snow traction index STI in the tire circumferential direction over the entire circumference of the tire. Based on the measurement results, an index evaluation is carried out with the comparative example set as the standard (100). The higher the value, the better the evaluation.

[0094] The Snow Traction Index STI is an empirical formula proposed by Uniroyal at the SAE (Society of Automotive Engineers), and is defined by the following formula (1). In this formula, Pg is the groove density [1 / mm], and is calculated as the ratio of the groove length [mm] of all grooves (all grooves excluding sipes) projected in the tire circumferential direction on the tire contact surface to the tire contact area (the product of the tire contact width and tire circumference) [mm^2]. Also, ρs is the sipe density [1 / mm], and is calculated as the ratio of the sipe length [mm] of all sipes projected in the tire circumferential direction on the tire contact surface to the tire contact area [mm^2]. Also, Dg is the average groove depth [mm] of all grooves projected in the tire circumferential direction on the tire contact surface.

[0095] STI=-6.8+2202×Pg+672×ρs+7.6×Dg (1)

[0096] (3) The evaluation of skid resistance is carried out by running the test vehicle on a specified snow test road, and a professional driver performs a sensory evaluation of braking, driving, and skid. Based on the measurement results, an index evaluation is performed with the comparative example set as the standard (100). The higher the value, the better.

[0097] In the test tire of Example 1, in the configuration of FIG. 1 and FIG. 2, the shoulder land portion 31 has a narrow rib 314 in the shoulder shallow groove 311, while the middle land portion 32 does not have a narrow groove 323 or a narrow rib 324. The tire ground contact width TW is 268 [mm], the maximum ground contact width Wb1 of the shoulder land portion 31 is 57.6 [mm], the maximum ground contact width Wb2 of the middle land portion 32 is 30.4 [mm], and the maximum ground contact width Wb3 of the center land portion 33 is 37.8 [mm]. The maximum depths Hg1 and Hg2 of the shoulder main groove 21 and the center main groove 22 are 20.6 [mm]. The maximum width W11 of the shoulder shallow groove 311 is 9.1 [mm], and the maximum depth H11 is 12.6 [mm]. The shoulder lug grooves 312A and 312B have maximum widths W12A and W12B of 6.9 mm and maximum depths H12A and H12B of 12.6 mm. The distance D11 is 27.5 mm.

[0098] The test tire of the comparative example is the test tire of Example 1, in which the shoulder land portion 31 does not have the thin rib 314 in the shoulder shallow groove 311.

[0099] As the test results show, the test tires of the examples achieve a balance between tire noise performance, snow traction performance, and anti-skid performance. [Explanation of symbols]

[0100] 1 tire;11 bead core;12 bead filler;121 lower filler;122 upper filler;13 carcass layer;14 belt layer;141 high angle belt;142, 143 cross belt;144 belt cover;15 tread rubber;16 sidewall rubber;17 rim cushion rubber;21 shoulder main groove;22 center main groove;31 shoulder land portion;311 shoulder shallow groove;312A, 312B shoulder lug groove;3121 cutout portion;313A, 313B shoulder block;314 fine rib;3141 chamfer portion;315A through sipe;316A, 316B closed sipe;32 middle land portion;321 middle lug groove;3211 cutout portion;322 middle block;323 fine groove;324 fine rib;325 Through sipes; 326 Closed sipes; 33 Center land area; 331 Center lug groove; 332 Center block

Claims

1. A tire having a plurality of circumferential main grooves and a plurality of land portions defined by the circumferential main grooves, A pair of shoulder main grooves arranged at the outermost positions in the tire width direction among the plurality of circumferential main grooves, and a pair of shoulder land portions arranged at the outermost positions in the tire width direction among the plurality of land portions are defined, a shoulder shallow groove having a groove depth shallower than that of the shoulder main groove and extending continuously around the entire circumference of the tire; a plurality of first shoulder lug grooves having one end opening toward the tire ground contact edge and connected to the shoulder shallow groove at the other end; a plurality of first shoulder blocks defined by the shoulder shallow groove and the first shoulder lug groove; a plurality of second shoulder lug grooves connected to the shoulder main groove at one end and connected to the shoulder shallow groove at the other end; a plurality of second shoulder blocks defined by the shoulder shallow groove and the second shoulder lug groove; and a thin rib formed in a groove bottom of the shoulder shallow groove and extending continuously around the entire circumference of the tire.

2. 2. The tire according to claim 1, wherein a maximum depth H11 of the shoulder shallow groove and a maximum depth Hg1 of the shoulder main groove are in a range of 0.50≦H11 / Hg1<1.

00.

3. 3. The tire according to claim 1, wherein a maximum distance H14 from the tread surface of the shoulder land portion to the top of the narrow rib is in a range of 0≦H14 / H11≦0.10 with respect to a maximum depth H11 of the shoulder shallow groove.

4. 4. The tire according to claim 1, wherein a distance D11 from a tire ground contact edge to a center line of the narrow rib is in a range of 0.30≦D11 / Wb1≦0.70 with respect to a maximum ground contact width Wb1 of the shoulder land portion.

5. The tire according to any one of claims 1 to 4, wherein a distance Dc between an extension of the groove center lines of the first and second shoulder lug grooves and a groove center line of the shoulder shallow groove is in a range of 0≦Dc / W12A≦0.80 with respect to a maximum width W12A of the first shoulder lug groove.

6. The tire according to any one of claims 1 to 5, wherein a maximum width W14 of the narrow rib and a maximum width W11 of the shoulder shallow groove are in a range of 0.20≦W14 / W11≦0.

60.

7. The tire according to any one of claims 1 to 6, wherein a maximum width W11 of the shoulder shallow groove is in a range of 0.17≦W11 / Wb1≦0.19 with respect to a maximum ground contact width Wb1 of the shoulder land portion.

8. The top of the narrow rib has a top surface parallel to the tread surface of the shoulder land portion, and 8. The tire according to claim 6, wherein a maximum width W14' of the top face is in a range of 0.05≦W14' / W14≦0.20 relative to a maximum width W14 of the narrow rib.

9. 9. The tire according to claim 8, wherein the narrow rib has the parallel top surfaces at edges on the tire equatorial plane side.

10. The tire according to any one of claims 1 to 9, wherein a maximum depth H11 of the shoulder shallow groove and a maximum depth H12 of the first and second shoulder lug grooves are in a range of 1.00≦H11 / H12≦2.

00.

11. The tire according to any one of claims 1 to 10, wherein the fine rib has a chamfered portion at a top portion thereof extending around the entire circumference of the fine rib, and an inclination angle α of the chamfered portion with respect to the tread surface of the shoulder land portion is in a range of 1 deg≦α≦60 deg.

12. A middle land portion is defined adjacent to the shoulder land portion among the plurality of land portions, The middle land portion includes a plurality of middle lug grooves penetrating the middle land portion and a plurality of middle blocks defined by the middle lug grooves, and 12. The tire according to claim 1, wherein the middle block has a narrow groove extending along an edge portion of the middle block on the tire equatorial plane side, and a narrow rib defined by the narrow groove.

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