Tire

Abstract

Provided is a tire with which a further improvement in rough road running performance can be achieved while ensuring excellent block durability. A plurality of shoulder blocks 12 are provided in a shoulder region of a tread portion 1, a plurality of side blocks 13 are provided in a side region adjacent to the shoulder region on the outer side in the width direction of the tire, two or more shoulder blocks 12 adjacent to one other in the circumferential direction of the tire and one side block 13 disposed on the outer side thereof in the width direction of the tire are defined as a block group B, a first narrow groove 21, a second narrow groove 22, and a third narrow groove 23 are provided in each block included in the block group B, and the narrow grooves constitute a series of narrow groove groups 20 that extend continuously from one shoulder block 12 included in the block group B through the side block 13 to the other shoulder block 12.

Description

tire

[0001] The present invention relates to a tire intended for running on unpaved roads and the like, and more particularly to a tire that enables further improvement in off-road performance while ensuring excellent block durability.

[0002] Tires (e.g., all-terrain tires, all-terrain tires, etc.) designed for running on unpaved roads (uneven terrain, muddy terrain, sandy terrain, rocky areas, etc.) in addition to paved roads are required to have excellent running performance on various road surfaces, and in particular, excellent off-road performance (rough road performance). Such tires have unevenness (e.g., side blocks) not only in the tread portion that contacts the road surface on paved roads, but also in the side region (region between the tread portion and the sidewall portion) that may come into contact with mud, snow, sand, stones, rocks, etc. (hereinafter, collectively referred to as "mud, etc.") on unpaved roads, thereby obtaining traction performance by gripping the mud, etc. (see, for example, Patent Documents 1 and 2). In recent years, tire performance requirements have become more stringent, and further improvements in rough road performance are required. Furthermore, since the side blocks tend to be easily damaged by stones, rocks, foreign objects, etc. on unpaved roads (rough roads), they are also required to have sufficient durability. Therefore, there is a demand for improving rough road performance while ensuring durability (particularly block durability), and achieving a high level of both performances.

[0003] Japanese Patent Publication No. 2017-124733 Japanese Patent Publication No. 2020-044882

[0004] An object of the present invention is to provide a tire that allows further improvement in off-road performance while ensuring excellent block durability.

[0005] The tire of the present invention for achieving the above object includes a tread portion extending in a circumferential direction of the tire and forming an annular shape, and a pair of sidewall portions disposed on both sides of the tread portion, the tire having a pair of main grooves on the surface of the tread portion extending along the tire circumferential direction on both sides of the tire equator, and a shoulder region located on the outer side of the main grooves in the tire width direction, the shoulder region being provided with a plurality of shoulder lug grooves extending from the main grooves toward the outer side in the tire width direction and spaced apart in the tire circumferential direction, and a plurality of shoulder blocks partitioned by the main grooves and the shoulder lug grooves and arranged along the tire circumferential direction, a plurality of side blocks protruding from the outer surface of the sidewall portion are provided in a side region adjacent to the outer side in the tire width direction of the shoulder region, one side block being disposed at a position in the tire width direction outer side of two or more shoulder blocks adjacent to each other in the tire circumferential direction, When a combination of the above shoulder block and one of the side blocks is considered to be a block group, one of the shoulder blocks included in the block group has a first narrow groove on a side surface thereof, one end of which opens into one of the shoulder lug grooves and the other end extending toward the side block, and another of the shoulder blocks included in the block group has a second narrow groove on a side surface thereof, one end of which opens into the other of the shoulder lug grooves and the other end extending toward the side block, and at least one third narrow groove is provided on a top surface of each of the side blocks included in the block group, extending to connect the other end of the first narrow groove and the other end of the second narrow groove, so that the first narrow groove, the second narrow groove, and the third narrow groove form a series of narrow groove groups extending continuously from one of the shoulder blocks, via the side block, to the other of the shoulder blocks included in the block group.

[0006] The tire of the present invention provides multiple side blocks in the side region, with one side block positioned on the tire widthwise outer side of a block group consisting of two or more circumferentially adjacent shoulder blocks. Therefore, the block group and the side blocks function as a substantially large block, thereby improving block durability. Furthermore, each block is provided primarily with first through third fine grooves, maintaining the rigidity of each block, further improving block durability. Meanwhile, the first through third fine grooves form a series of fine grooves extending continuously from one shoulder block to another shoulder block within the block group via the side block. This series of fine grooves (first through third fine grooves) functions as a single long groove, providing an excellent edge effect across the entire block group and improving traction performance. These features work together to achieve both high levels of block durability and rough-road performance.

[0007] In the present invention, it is preferable that the first narrow groove and the second narrow groove each have at least one bending point, and the third narrow groove has at least two bending points, which allows each groove to include portions extending in various directions, improving the edge effect and enhancing traction performance.

[0008] In the present invention, the groove widths of the first narrow groove, the second narrow groove, and the third narrow groove are preferably each 0.5 mm to 3 mm. The groove depths of the first narrow groove, the second narrow groove, and the third narrow groove are preferably each 0.5 mm to 2 mm. Having the groove width and groove depth of each groove within an appropriate range like this is advantageous for achieving both block durability and rough road performance.

[0009] In the present invention, the shoulder blocks may be provided with auxiliary grooves that branch off from the first or second narrow grooves and extend toward the tread side of the shoulder blocks. This configuration provides an edge effect from the auxiliary grooves, which is advantageous for improving traction performance.

[0010] In the present invention, it is preferable that the open ends of the first narrow groove and the second narrow groove are located on the same circumferential side of each shoulder block, so that the first narrow groove and the second narrow groove extend in the same direction, which is advantageous for improving the edge effect and enhancing traction performance.

[0011] In the present invention, the shoulder blocks may be provided with parallel auxiliary grooves extending parallel to the first narrow groove or the second narrow groove, which provides an edge effect and is advantageous in improving traction performance.

[0012] In the present invention, it is preferable that the third narrow groove includes a straight portion extending parallel to the contour line of the side block, which provides a good balance between the shape of the side block and the curved shape of the third narrow groove, and is advantageous for achieving both block durability and rough road performance.

[0013] In the present invention, it is preferable that the opening ends of the first narrow groove and the second narrow groove are located at different positions in the tire radial direction. By having the end positions of each groove differ in this way, these grooves can exert an edge effect at various positions in the tire radial direction, which is advantageous for improving traction performance.

[0014] The tire of the present invention is preferably a pneumatic tire, but may also be a non-pneumatic tire. In the case of a pneumatic tire, the interior thereof can be filled with air, an inert gas such as nitrogen, or other gases.

[0015] Fig. 1 is a meridian cross-section of a tire according to an embodiment of the present invention. Fig. 2 is a perspective view showing the shoulder and side regions of a tire according to an embodiment of the present invention. Fig. 3 is an explanatory diagram showing a schematic view of a shoulder block (side surface) and a side block (surface) according to the present invention. Fig. 4 is an explanatory diagram showing a schematic view of a shoulder block (side surface) and a side block (surface) according to another embodiment of the present invention.

[0016] The configuration of the present invention will be described in detail below with reference to the accompanying drawings.

[0017] When the tire of the present invention is a pneumatic tire as shown in Figure 1, it comprises a tread portion 1 that contacts the road surface, a pair of sidewall portions 2 arranged on both sides of the tread portion 1, and a pair of bead portions 3 arranged radially inward of the sidewall portions 2. In Figure 1, the symbol CL indicates the tire equator. Although not depicted in Figure 1 because it is a meridian cross-section, the tread portion 1, sidewall portions 2, and bead portions 3 each extend in the tire circumferential direction and form an annular shape, thereby constituting the basic toroidal structure of a pneumatic tire. The following explanation using Figure 1 will be basically based on the meridian cross-section shape shown, but each tire constituent member also extends in the tire circumferential direction and forms an annular shape.

[0018] A carcass layer 4 is installed between a pair of left and right bead portions 3. The carcass layer 4 includes multiple reinforcing cords extending in the tire radial direction and folded back from the inner side to the outer side in the tire width direction around bead cores 5 arranged in each bead portion 3. A bead filler 6 is arranged on the outer periphery of each bead core 5, and this bead filler 6 is wrapped by the main portion and folded back portion of the carcass layer 4. Meanwhile, multiple belt layers 7 (two layers in FIG. 1 ) are embedded on the outer periphery of the carcass layer 4 in the tread portion 1. Each belt layer 7 includes multiple reinforcing cords inclined with respect to the tire circumferential direction, and the reinforcing cords are arranged so as to cross each other between the layers. In these belt layers 7, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set, for example, in the range of 10° to 40°. Furthermore, at least one belt reinforcing layer 8 (two layers in FIG. 1 ) is provided on the outer periphery of the belt layer 7. The belt reinforcing layer 8 includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer 8, the organic fiber cords are set at an angle of, for example, 0° to 5° with respect to the tire circumferential direction.

[0019] Because the present invention relates to the shoulder and side regions of a tire as described below, the basic structure (cross-sectional structure) of the tire is not limited to the general structure described above. Furthermore, the detailed shape of the grooves and blocks formed on the surface of the tread portion 1 (tread pattern) is not particularly limited, except for the shoulder regions described below. The tread pattern in the portions excluding the shoulder regions described below is preferably a block-based pattern suitable for unpaved roads. The present invention can be applied to various types of tires, including non-pneumatic tires, as long as they have regions (regions corresponding to the shoulder and side regions) that may come into contact with mud or the like on the road surface when traveling on unpaved roads.

[0020] As shown in Figures 1 and 2, a pair of main grooves 10 are formed on the surface of the tread portion 1, extending circumferentially around the entire tire on both sides of the tire equator CL. The main grooves 10 preferably have a zigzag shape in which linear sections inclined in one direction relative to the tire circumferential direction and linear sections inclined in the other direction are alternately connected in the tire circumferential direction. The region between the pair of main grooves 10 is the center region (a region in which any tread pattern can be adopted without particular structural limitations in the present invention), and the regions on the outer sides of each main groove 10 in the tire width direction are shoulder regions. The main grooves 10 preferably have a groove width of 3 mm to 13 mm, more preferably 5 mm to 11 mm, and a groove depth of 8 mm to 16 mm, more preferably 10 mm to 15 mm.

[0021] A land portion (shoulder land portion) defined on the outer side of the main groove 10 in the tire width direction is provided with shoulder lug grooves 11 extending outward in the tire width direction from the main groove 10. A plurality of shoulder lug grooves 11 may be provided at intervals in the tire circumferential direction. These shoulder lug grooves 11 define the shoulder land portion into a plurality of blocks (shoulder blocks 12). When the main grooves 10 have a zigzag shape, the shoulder lug grooves 11 may be connected to the bending points of each main groove 10 on the outer side in the tire width direction. The groove width of the shoulder lug grooves 11 is not particularly limited, but is preferably 70% to 98%, more preferably 80% to 95%, of the groove width of the main groove 10. The groove depth of the shoulder lug grooves 11 is not particularly limited, but is preferably 75% to 100%, more preferably 80% to 98% of the groove depth of the main groove 10.

[0022] When the region adjacent to the shoulder region on the outer side in the tire width direction is defined as a side region, multiple side blocks 13 protruding from the outer surface of the sidewall portion 2 are provided in this side region. The protrusion height of each side block 13 from the outer surface of the sidewall 2 is not particularly limited, but can be set to, for example, 1 mm to 10 mm. As shown in Figures 2 and 3 , each side block 13 is positioned outward in the tire width direction at a position corresponding to two or more circumferentially adjacent shoulder blocks 12. For example, in the illustrated example, one side block 13 is positioned outward in the tire width direction from two shoulder blocks 12. In other words, side grooves 14 extending along the tire width direction (tire radial direction) are formed between circumferentially adjacent side blocks 13, and these side grooves 14 are connected to at least every other shoulder lug groove 11 spaced apart in the tire circumferential direction. Between these connected shoulder lug grooves 11 and side grooves 14, one side block 13 and two or more shoulder blocks 12 (and one or more shoulder lug grooves 11 not connected to a side groove 14) are positioned.

[0023] The side blocks 13 are preferably positioned within an appropriate radial range of the tire so that they can adequately contact the road surface when the tire becomes buried in mud or other debris while traveling on unpaved roads. Specifically, the radially innermost ends of the side blocks 13 are preferably located within a range of 20% to 50% of the tire cross-sectional height SH from the tire equator CL toward the tire's radially inward direction. In other words, the distance D from the tire equator CL to the radially innermost ends of the side blocks 13 is preferably 20% to 50% of the tire cross-sectional height SH. Positioning the side blocks 13 within an appropriate radial range of the sidewall portion 2 in this manner effectively improves driving performance on unpaved roads. Furthermore, the side blocks 13 can be appropriately sized, which is advantageous for ensuring block rigidity and improving durability. If the distance D is less than 20% of the tire cross-sectional height SH, the side blocks 13 become too small, making it difficult to maintain good block durability. If the distance D exceeds 50% of the tire cross-sectional height SH, the side blocks 13 become too large, which may affect normal running performance. With regard to the arrangement of the side blocks 13, it is preferable that the boundary between the shoulder region and the side region is located within a range of 20% to 25% of the tire cross-sectional height SH from the tire equator CL toward the tire radially inward, regardless of the presence or absence of the protrusions 17.

[0024] In the illustrated example, a protrusion 15 protruding from the sidewall surface and extending around the entire tire circumference is present at the boundary between the outer side of the shoulder block 12 in the tire width direction and the surface of the side block 13 (the boundary between the shoulder region and the side region). This protrusion 15 is an element formed due to the mold split position, etc., and is therefore not necessarily required. While this protrusion 15 is not an element that needs to be considered in the present invention, because it is an element formed during manufacturing, the shoulder region and side region may be distinguished based on the protrusion 15. In other words, the shoulder region can be considered to be the region adjacent to the protrusion 15 on the inner side in the tire width direction, and the side region can be considered to be the region adjacent to the protrusion 15 on the inner side in the tire radial direction.

[0025] When a combination of two or more shoulder blocks 12 and one side block 13 is defined as a block group B, one shoulder block 12 included in block group B has a first narrow groove 21 formed in its side surface, one end of which opens into one of the shoulder lug grooves 11 and the other end of which extends toward the side block 13. Similarly, another shoulder block 12 included in block group B has a second narrow groove 22 formed in its side surface, one end of which opens into another of the shoulder lug grooves 11 and the other end of which extends toward the side block 13. Furthermore, at least one third narrow groove 23 is formed in the top surface of each side block 13 included in block group B, extending to connect the other end of the first narrow groove 21 and the other end of the second narrow groove 22. The first narrow groove 21, second narrow groove 22, and third narrow groove 23 form a series of narrow groove groups 20 that extend continuously along the blocks from one shoulder block 12 included in block group B, through the side block 13, to the other shoulder block 12.

[0026] In the tire of the present invention, the shoulder blocks 12 and side blocks 13 function as a substantial large block (block group B), ensuring the rigidity of the large block. This improves block durability. Furthermore, because each block is primarily provided with only the first narrow groove 21, second narrow groove 22, and third narrow groove 23, the rigidity of each block is maintained, further improving block durability. Meanwhile, the first narrow groove 21, second narrow groove 22, and third narrow groove 23 form a series of narrow groove groups 20 that extend continuously along the blocks from one shoulder block 12 in block group B through the side blocks 13 to the other shoulder blocks 12. This is equivalent to providing a substantially long narrow groove (narrow groove group 20) in the substantially large block (block group B). This series of narrow groove groups 20 provides an excellent edge effect throughout block group B, effectively improving traction performance. These cooperations enable a high degree of both block durability and rough-road performance.

[0027] In the narrow groove group 20, the first narrow groove 21, the second narrow groove 22, and the third narrow groove 23 do not need to be completely continuous; even if they are intermittently connected, they can be considered to constitute a continuous narrow groove group 20. For example, in the illustrated example, a protrusion 15 is present between the first narrow groove 21 and the third narrow groove 23 and between the second narrow groove 22 and the third narrow groove 23, and these grooves are interrupted, but because the end of the third narrow groove 23 is located at the extension of the first narrow groove 21 or the second narrow groove 22, they can be considered to be substantially continuous. In addition, a notch is provided in the side block 13, which divides the third narrow groove 23, but because the third narrow grooves 23 on both sides of the division exist on extensions of each other, they can be considered to be substantially continuous. Specifically, if the sum of the lengths of the first narrow groove 21, the second narrow groove 22, and the third narrow groove 23 is 80% or more of the total length of an imaginary line (dashed line in the figure) drawn along the narrow groove group 20 from one end of the first narrow groove 21 (the opening end relative to the shoulder lug groove 11) to one end of the second narrow groove 22 (the opening end relative to the shoulder lug groove 11), then the narrow groove group 20 can be regarded as a substantially continuous series.

[0028] If any one of the first narrow groove 21, the second narrow groove 22, and the third narrow groove 23 is not formed and a series of narrow groove groups 20 extending continuously along each block included in block group B is not formed, a sufficient edge effect cannot be ensured and rough road driving performance cannot be improved. Even if the first narrow groove 21, the second narrow groove 22, and the third narrow groove 23 are all formed, if these grooves are not positioned so as to be continuous with each other and the narrow groove group 20 is not formed, the edge effect of each narrow groove can be ensured but the synergistic effect of the narrow groove group 20 cannot be ensured, and the effect of improving rough road driving performance will be limited.

[0029] The number of shoulder blocks 12 and side blocks 13 included in block group B is preferably two to three, and more preferably two, per side block 13. This provides a good balance between the number of side blocks 13 and the number of shoulder blocks 12, which is advantageous for achieving both block durability and rough-road performance. In a structure in which three shoulder blocks 12 are arranged per side block 13, as shown schematically in Figure 4, a first narrow groove 21 and a second narrow groove 22 are preferably provided in at least the two circumferentially outer shoulder blocks 12 of the three shoulder blocks 12, and a third narrow groove 23 is preferably provided in the side block 13 to connect these. In this structure, no fine grooves are formed in one of the three shoulder blocks 12, which is located at the circumferential center, but a series of fine groove groups 20 are formed that extend continuously across multiple blocks included in block group B. As a result, it is possible to achieve a high level of both block durability and rough-road performance, as in the above-mentioned configuration (a configuration in which two shoulder blocks 12 are arranged per side block 13).

[0030] The groove widths of the first narrow groove 21, the second narrow groove 22, and the third narrow groove 23 are preferably 0.5 mm to 3 mm, and more preferably 1.0 mm to 2.5 mm. Setting the groove width within this appropriate range is advantageous for achieving both block durability and rough road performance. If the groove width of each groove is less than 0.5 mm, the groove width is too small, making it difficult to ensure sufficient edge effect. If the groove width of each groove exceeds 3 mm, it becomes difficult to ensure sufficient block rigidity. Note that, in order to form a series of narrow groove groups 20, the groove widths of the first narrow groove 21, the second narrow groove 22, and the third narrow groove 23 should preferably be the same.

[0031] The groove depths of the first narrow groove 21, the second narrow groove 22, and the third narrow groove 23 are preferably 0.5 mm to 2 mm, and more preferably 0.7 mm to 1.5 mm. Setting the groove depth within this appropriate range is advantageous for achieving both block durability and rough road performance. If the groove depth of each groove is less than 0.5 mm, the groove depth is too small, making it difficult to ensure a sufficient edge effect. If the groove depth of each groove exceeds 2 mm, it becomes difficult to ensure sufficient block rigidity. Note that, in order to form a series of narrow groove groups 20, the groove depths of the first narrow groove 21, the second narrow groove 22, and the third narrow groove 23 are preferably the same.

[0032] Each of the first narrow groove 21 and the second narrow groove 22 preferably has at least one bending point as shown in the figure. By having such a bending point, each groove includes a component extending along the tire circumferential direction and a component extending along the tire radial direction, making it possible to exert an edge effect in each direction, which is advantageous for improving traction performance. The number of bending points is preferably one to two.

[0033] On the other hand, the third narrow groove 23 preferably has at least two bending points. More specifically, since the third narrow groove 23 connects the other end of the first narrow groove 21 and the other end of the second narrow groove 22 as described above, it is preferable that the third narrow groove 23 be composed of a portion extending along the tire radial direction from a position corresponding to the other end of the first narrow groove 21, a portion extending along the tire radial direction from a position corresponding to the other end of the second narrow groove 22, and a portion extending along the tire circumferential direction. Therefore, it is preferable that the number of bending points is at least two. By having such bending points, the third narrow groove 23 includes components extending in various directions, enabling it to exert an edge effect in each direction, which is advantageous for improving traction performance. The number of bending points in the third narrow groove 23 is preferably two to three.

[0034] As described above, the third narrow groove 23 preferably comprises a portion extending radially from a position corresponding to the other end of the first narrow groove 21, a portion extending radially from a position corresponding to the other end of the second narrow groove 22, and a portion extending circumferentially. In this case, at least the portion extending circumferentially should extend parallel to the contour line of the side block 13 (the radially inner edge of the tire). In addition to this portion, the third narrow groove 13 preferably includes a straight portion extending parallel to the contour line of the side block. This provides a good balance between the shape of the side block and the curved shape of the third narrow groove, which is advantageous for achieving both block durability and rough-road performance. Note that the angle difference between the contour line of the side block and the corresponding straight portion of the third narrow groove 23 is considered to be substantially parallel if it is between 0° and 30°.

[0035] Both the first narrow groove 21 and the second narrow groove 22 have ends (opening ends) that open into the shoulder lug groove 11, but the opening ends of these first narrow grooves 21 and second narrow grooves 22 are preferably located on the same circumferential side of the shoulder block 12 in which they are provided. For example, in the illustrated example, the first narrow groove 21 opens into the shoulder lug groove 11 adjacent to the shoulder block 12 in which the first narrow groove 21 is provided on one circumferential side of the tire (the right side in the figure), and the second narrow groove 22 opens into the shoulder lug groove 11 adjacent to the shoulder block 12 in which the second narrow groove 22 is provided on one circumferential side of the tire (the right side in the figure). With this arrangement of the opening ends, the portions of the first narrow groove 11 and the second narrow groove 12 that are continuous with their opening ends extend in the same direction. This improves the edge effect and is advantageous for enhancing traction performance.

[0036] On the other hand, it is preferable that the positions of the opening ends of the first narrow groove 11 and the second narrow groove 12 in the tire radial direction are different from each other. For example, in the illustrated example, the opening end of the first narrow groove 21 is located further outward in the tire radial direction (closer to the tread surface of the shoulder block 12) than the opening end of the second narrow groove 22. By having the end positions of each groove differ in this way, these grooves can exert an edge effect at various positions in the tire radial direction, which is advantageous for improving traction performance.

[0037] In the present invention, the rigidity of each block included in block group B is maintained by providing primarily the first narrow groove 21, second narrow groove 22, and third narrow groove 23 in block group B. However, auxiliary grooves can be added to the extent that the block rigidity is not significantly reduced. For example, as shown in the example, an auxiliary groove 24 branching from the first narrow groove 21 or second narrow groove 22 and extending toward the tread side of the shoulder block 12 can be provided on the side of the shoulder block 12. Also, a parallel auxiliary groove 25 extending parallel to the first narrow groove 21 or second narrow groove 22 can be provided on the side of the shoulder block 12. Adding such auxiliary grooves adds an edge effect to each groove, which is advantageous for improving traction performance. When providing these auxiliary grooves 24 and parallel auxiliary grooves 25, the groove width and groove depth of these grooves should preferably be set to be equivalent to the groove width and groove depth of the first narrow groove 21, second narrow groove 22, and third narrow groove 23 described above.

[0038] The side blocks 13 may also be provided with recesses 30 at positions that are on extensions of the shoulder lug grooves 11 located between the shoulder blocks 12 included in block group B and are surrounded by the third narrow grooves 23. Providing such recesses 30 complicates the unevenness formed by block group B, which is advantageous for improving traction performance. Note that the recesses 30 are positioned on extensions of the shoulder lug grooves 11, just like the side grooves 14, but unlike the side grooves 14, they terminate inside the side blocks 13, so the rigidity of the side blocks 13 can be sufficiently maintained even when the recesses 30 are provided.

[0039] The present invention will be further explained below with reference to examples, but the scope of the present invention is not limited to these examples.

[0040] Thirteen types of pneumatic tires were produced: Conventional Example 1, Comparative Examples 1-4, and Examples 1-8; the tire size was LT265 / 70R17 121 / 118S; the basic structure (cross-sectional structure) was as shown in FIG. 1; and the structures of the shoulder and side regions were based on those shown in FIG. 2. The number of shoulder blocks adjacent to one side block radially outward from the tire, the presence or absence of a first narrow groove, a second narrow groove, a third narrow groove, the presence or absence of a narrow groove group, the groove width of the narrow groove, the groove depth of the narrow groove, the presence or absence of an auxiliary groove, and the presence or absence of a parallel auxiliary groove were set as shown in Tables 1 and 2, respectively.

[0041] The tread pattern in the center region was common to all examples, with one row of blocks arranged between a pair of main grooves on each side of the tire equator.

[0042] The "Presence or Absence of Fine Groove Groups" columns in Tables 1 and 2 indicate whether a series of fine groove groups extending substantially continuously is formed by the first fine groove, the second fine groove, and the third fine groove. For example, Comparative Example 2 does not have a third fine groove, so a fine groove group is not formed, and the presence or absence of a series of fine groove groups is "absent." Similarly, Comparative Example 3 does not have a first fine groove or a second fine groove, so a series of fine groove groups is not formed, and the presence or absence of fine groove groups is "absent." Furthermore, Comparative Example 4 is an example in which the first to third fine grooves are present, but the end positions of these grooves are shifted and the structure does not extend substantially continuously, and the presence or absence of fine groove groups is "absent."

[0043] The groove width and groove depth of the first to third narrow grooves are common to the tires of each example. That is, the columns "Narrow Groove Width" and "Narrow Groove Depth" in Tables 1 and 2 indicate the common groove width and groove depth of all the first to third narrow grooves.

[0044] The auxiliary grooves in the "Auxiliary Groove Presence / Absence" columns of Tables 1 and 2 are auxiliary grooves that branch off from the first narrow groove or the second narrow groove and extend toward the tread side of the shoulder block, and the presence or absence of these auxiliary grooves is indicated in these columns. Furthermore, the parallel auxiliary grooves in the "Parallel Auxiliary Groove Presence / Absence" columns of Table 1 are parallel auxiliary grooves that extend parallel to the first narrow groove or the second narrow groove, and the presence or absence of these auxiliary grooves is indicated in these columns. The "absent" in these columns means that the auxiliary groove and / or parallel auxiliary groove has been removed from the structure based on FIG. 2.

[0045] These pneumatic tires were evaluated for rough road running performance and block durability by the following evaluation methods, and the results are shown in Tables 1 and 2.

[0046] Each test tire was mounted on a wheel with a rim size of 17x8J, and the front tire was inflated to an air pressure of 450 kPa and the rear tire was inflated to an air pressure of 550 kPa. The test vehicle (traction test vehicle) was then fitted with the tire, and a test driver performed a sensory evaluation of the traction (starting performance) on a test road consisting of an unpaved road (gravel road surface). The evaluation results were expressed as an index, with the value of Conventional Example 1 being 100. A higher index value indicates better off-road performance.

[0047] Block durability (cut resistance) Each test tire was mounted on a wheel with a rim size of 17x8J, and the air pressure was set to 350 kPa. The test vehicle (four-wheel drive SUV) was fitted with the tire, and the total length of cuts on the side was measured after driving 1000 km on an off-road endurance road. The evaluation results were expressed as an index, with the reciprocal of the measurement value for Conventional Example 1 being set to 100. The larger the index value, the smaller the total length of the cuts, which means better block durability (cut resistance).

[0048]

[0049]

[0050] As is clear from Tables 1 and 2, the pneumatic tires of Examples 1 to 8 improved rough-road performance and block durability compared to Conventional Example 1, achieving a good balance between these performance characteristics. On the other hand, Comparative Example 1 had a structure in which two shoulder blocks were adjacent to one side block, and thus improved block durability compared to Conventional Example 1. However, since Comparative Example 1 did not have first to third fine grooves and therefore did not form a continuous group of fine grooves, the effect of improving rough-road performance was not achieved. Comparative Example 2 did not have a third fine groove and therefore did not form a continuous group of fine grooves, and therefore did not sufficiently improve rough-road performance. Comparative Example 3 did not have a first fine groove or a second fine groove and therefore did not form a continuous group of fine grooves, and therefore did not sufficiently improve rough-road performance. Comparative Example 4 had first to third fine grooves, but their arrangement was inappropriate, and therefore did not form a continuous group of fine grooves, and therefore did not sufficiently improve rough-road performance.

[0051] REFERENCE SIGNS LIST 1 tread portion 2 sidewall portion 3 bead portion 4 carcass layer 5 bead core 6 bead filler 7 belt layer 8 belt reinforcing layer 10 main groove 11 shoulder lug groove 12 shoulder block 13 side block 14 side groove 15 protrusion 20 fine groove group 21 first fine groove 22 second fine groove 23 third fine groove 24 auxiliary groove 25 parallel auxiliary groove 30 recess CL tire equator B block group

Claims

1. A tire having a tread portion extending in a circumferential direction and forming an annular shape, and a pair of sidewall portions arranged on either side of the tread portion, the surface of the tread portion having a pair of main grooves extending circumferentially on either side of the tire equator, a shoulder region located on the outer side of the main groove in the tire width direction is provided with a plurality of shoulder lug grooves extending from the main groove toward the outer side in the tire width direction and spaced apart in the tire width direction, and a plurality of shoulder blocks partitioned by the main groove and the shoulder lug groove and arranged in the tire circumferential direction, a plurality of side blocks protruding from an outer surface of the sidewall portion are provided in a side region adjacent to the outer side in the tire width direction of the shoulder region, one side block is arranged at a position in the tire width direction outer side of two or more shoulder blocks adjacent in the tire circumferential direction, and when a combination of these two or more shoulder blocks and one side block is defined as a block group, a first narrow groove is provided on a side surface of one of the shoulder blocks included in the block group, the first narrow groove having one end opening into one of the shoulder lug grooves and the other end extending toward the side block, a second narrow groove having one end opening into another of the shoulder lug grooves and the other end extending toward the side block is provided on a side surface of another of the shoulder blocks included in the block group, and at least one third narrow groove extending to connect the other end of the first narrow groove and the other end of the second narrow groove is provided on a top surface of the side block included in the block group, the first narrow groove, the second narrow groove, and the third narrow groove form a series of narrow groove groups extending continuously from one of the shoulder blocks included in the block group through the side block to the other of the shoulder blocks.

2. The tire according to claim 1, wherein the first narrow groove and the second narrow groove each have at least one bending point, and the third narrow groove has at least two bending points.

3. The tire according to claim 1 or 2, wherein the first narrow groove, the second narrow groove, and the third narrow groove each have a groove width of 0.5 mm to 3 mm.

4. The tire according to any one of claims 1 to 3, characterized in that the first narrow groove, the second narrow groove, and the third narrow groove each have a groove depth of 0.5 mm to 2 mm.

5. A tire as described in any one of claims 1 to 4, characterized in that the shoulder block is provided with an auxiliary groove branching off from the first narrow groove or the second narrow groove and extending toward the tread side of the shoulder block.

6. A tire as described in any one of claims 1 to 5, characterized in that the open ends of the first narrow groove and the second narrow groove are present on the same side in the tire circumferential direction of each shoulder block.

7. A tire as described in any one of claims 1 to 6, characterized in that the shoulder block is provided with a parallel auxiliary groove extending parallel to the first narrow groove or the second narrow groove.

8. The tire according to any one of claims 1 to 7, characterized in that the third narrow groove includes a straight portion extending parallel to the contour line of the side block.

9. A tire according to any one of claims 1 to 8, characterized in that the opening ends of the first narrow groove and the second narrow groove are located at different positions in the tire radial direction.

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