WO2025069989A1 - Tire - Google Patents

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

The present invention relates to a tire intended for driving on unpaved roads, and more specifically, to a tire that allows for further improvement in rough road performance while maintaining excellent block durability.

Tires (e.g., all-terrain tires, all-terrain type tires, etc.) that are intended to run on unpaved roads (uneven ground, muddy ground, sandy ground, rocky areas, etc.) in addition to paved road surfaces are required to have excellent running performance on various road surfaces, and in particular, are required to have excellent off-road performance (bad road running performance). In such tires, not only the tread part that contacts the road surface on paved roads, but also the side area (area located between the tread part and the sidewall part) that may come into contact with mud, snow, sand, stones, rocks, etc. on the road surface on unpaved roads (hereinafter, these are collectively referred to as "mud, etc.") is provided with unevenness (side blocks, etc.), thereby biting into the mud, etc., and obtaining traction performance (for example, see Patent Documents 1 and 2). In recent years, the performance requirements for tires have become more sophisticated, and further improvement in bad road running performance is required. In addition, since the side blocks tend to be easily damaged by stones, rocks, foreign objects, etc. on the road surface on unpaved roads (bad roads), it is also required to ensure durability. Therefore, there is a need to improve rough-road performance while ensuring durability (particularly block durability), achieving a high level of both performance characteristics.

Japanese Patent Application Publication No. 2017-124733 Japanese Patent Application Publication No. 2020-044882

The objective of the present invention is to provide a tire that allows for further improvement in off-road performance while maintaining excellent block durability.

The tire of the present invention for achieving the above object is a tire having a tread portion extending in the tire circumferential direction and forming an annular shape, and a pair of sidewall portions arranged on both sides of the tread portion, the surface of the tread portion having a pair of main grooves extending along the tire circumferential direction on both sides of the tire equator, a shoulder region located on the tire widthwise outer side of the main grooves is provided with a plurality of shoulder lug grooves extending from the main grooves toward the tire widthwise outer side 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 tire widthwise outer side of the shoulder region, one of the side blocks is arranged at a position in the tire widthwise outer side of two or more of the shoulder blocks adjacent to each other in the tire circumferential direction, and these two or more When the combination of the above shoulder block and one of the side blocks is considered as a block group, one of the shoulder blocks included in the block group has a first narrow groove on the side surface thereof, one end of which opens into one of the shoulder lug grooves and the other end of which extends toward the side block, one of the other shoulder blocks included in the block group has a second narrow groove on the side surface thereof, one end of which opens into the other of the shoulder lug grooves and the other end of which extends toward the side block, and at least one third narrow groove is provided on the top surface of the side block 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, and the first narrow groove, the second narrow groove, and the third narrow groove constitute 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 shoulder block.

The tire of the present invention has a plurality of side blocks in the side region, and one side block is disposed at the tire widthwise outer side of a block group consisting of two or more shoulder blocks adjacent in the tire circumferential direction, so that the block group and the side blocks as a whole essentially function as a large block, thereby improving block durability. Also, since each block is provided mainly with only the first to third fine grooves, the rigidity of each block is maintained, and this also improves block durability. On the other hand, the first to third fine grooves constitute a series of fine groove groups that extend continuously from one shoulder block included in the block group through the side block to another shoulder block, so that this series of fine groove groups (first to third fine grooves) functions as one long groove, and the entire block group exhibits an excellent edge effect, improving traction performance. These cooperations make it possible to achieve a high level of both block durability and rough road driving performance.

In the present invention, it is preferable that the first fine groove and the second fine groove each have at least one bending point, and the third fine groove has at least two bending points. This allows each groove to include portions that extend in various directions, which is advantageous for improving the edge effect and enhancing traction performance.

In the present invention, it is preferable that the groove width of the first fine groove, the second fine groove, and the third fine groove is each 0.5 mm to 3 mm. It is also preferable that the groove depth of the first fine groove, the second fine groove, and the third fine groove is each 0.5 mm to 2 mm. Having the groove width and groove depth of each groove in such an appropriate range is advantageous in achieving both block durability and rough road driving performance.

In the present invention, the shoulder block can also be provided with an auxiliary groove that branches off from the first fine groove or the second fine groove and extends toward the tread side of the shoulder block. In this case, the auxiliary groove provides an edge effect, which is advantageous for improving traction performance.

In the present invention, it is preferable that the open ends of the first fine groove and the second fine groove are on the same circumferential side of each shoulder block. This allows the first fine groove and the second fine groove to extend in the same direction, which is advantageous for improving the edge effect and enhancing traction performance.

In the present invention, the shoulder block can also be provided with a parallel auxiliary groove that extends parallel to the first fine groove or the second fine groove. In this case, the parallel auxiliary grooves provide an edge effect, which is advantageous for improving traction performance.

In the present invention, it is preferable that the third fine groove includes a straight portion that extends 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 fine groove, which is advantageous in achieving both block durability and rough road performance.

In the present invention, it is preferable that the opening ends of the first fine groove and the second fine 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.

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

FIG. 1 is a meridian cross-sectional view of a tire according to an embodiment of the present invention. FIG. 2 is a perspective view showing a shoulder region and a side region of a tire according to an embodiment of the present invention. FIG. 3 is an explanatory diagram showing a schematic diagram of a shoulder block (side surface) and a side block (front surface) of the present invention. FIG. 4 is an explanatory diagram showing a schematic diagram of a shoulder block (side surface) and a side block (front surface) in another embodiment of the present invention.

The configuration of the present invention will be described in detail below with reference to the attached drawings.

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 on the tire radial inside 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 to form an annular shape, which constitutes the basic toroidal structure of a pneumatic tire. The following explanation using Figure 1 is basically based on the meridian cross section shape shown in the figure, but each tire component extends in the tire circumferential direction to form an annular shape.

A carcass layer 4 is mounted between a pair of left and right bead portions 3. The carcass layer 4 includes a plurality of reinforcing cords extending in the tire radial direction, and is folded back from the inner side to the outer side in the tire width direction around the bead cores 5 arranged in each bead portion 3. A bead filler 6 is arranged on the outer periphery of the bead cores 5, and this bead filler 6 is wrapped by the main body and folded back parts of the carcass layer 4. On the other hand, a plurality of 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 a plurality of reinforcing cords inclined with respect to the tire circumferential direction, and is arranged so that the reinforcing cords 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 to a range of, for example, 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.

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

As shown in Figures 1 and 2, a pair of main grooves 10 are formed on the surface of the tread portion 1, extending around the entire circumference of the tire along the tire circumferential direction on both sides of the tire equator CL. The main grooves 10 preferably have a zigzag shape in which linear portions inclined in one direction with respect to the tire circumferential direction and linear portions 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 any particular structure being limited 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.

The 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 from the main groove 10 toward the outer side in the tire width direction. It is preferable that multiple shoulder lug grooves 11 are provided at intervals in the tire circumferential direction. These shoulder lug grooves 11 define the shoulder land portion into multiple blocks (shoulder blocks 12). When the main groove 10 has a zigzag shape, it is preferable that the shoulder lug grooves 11 are connected to the bending points on the outer side of each main groove 10 in the tire width direction. The groove width of the shoulder lug groove 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 groove 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.

When the region adjacent to the shoulder region on the outside in the tire width direction is defined as the side region, multiple side blocks 13 protruding from the outer surface of the sidewall portion 2 are provided in this side region. The protruding 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 arranged on the outside in the tire width direction at a position corresponding to two or more shoulder blocks 12 adjacent in the tire circumferential direction. For example, in the illustrated example, one side block 13 is arranged at a position on the outside in the tire width direction of two shoulder blocks 12. In other words, side grooves 14 extending along the tire width direction (tire radial direction) are formed between the side blocks 13 adjacent in the tire circumferential direction, and these side grooves 14 are connected to at least every other one of the multiple shoulder lug grooves 11 arranged at intervals in the tire circumferential direction. Between the shoulder lug grooves 11 and side grooves 14 connected in this way, one side block 13 and two or more shoulder blocks 12 (and one or more shoulder lug grooves 11 that are not connected to the side groove 14) are arranged.

The side blocks 13 are preferably arranged in an appropriate range in the tire radial direction so that they can properly contact the road surface when the tire is buried in mud or the like while traveling on an unpaved road. Specifically, it is preferable that the tire radially innermost end of the side block 13 is located in a range of preferably 20% to 50% of the tire cross-sectional height SH from the tire equator CL position toward the tire radially inward. In other words, the distance D from the tire equator CL position to the tire radially innermost end of the side block 13 is preferably 20% to 50% of the tire cross-sectional height SH. By arranging the side blocks 13 in an appropriate range in the tire radial direction of the sidewall portion 2 in this way, it is possible to effectively improve the running performance on unpaved roads. In addition, since the size of the side blocks 13 can be appropriately secured, it is advantageous for securing 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 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 will become too large, which may affect normal driving performance. In relation to the arrangement of the side blocks 13, the boundary between the shoulder region and the side region should be located within a range of 20% to 25% of the tire cross-sectional height SH from the tire equator CL position toward the tire radially inward, regardless of the presence or absence of the protrusion 17.

In the illustrated example, 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), there is a protrusion 15 that protrudes from the sidewall surface and extends around the entire circumference of the tire. This protrusion 15 is an element formed due to the split position of the mold, and does not necessarily have to be provided. Although this protrusion 15 is an element that does not need to be taken into consideration in the present invention, since it is an element formed during manufacturing, the shoulder region and side region may be divided 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 inside in the tire width direction, and the side region can be considered to be the region adjacent to the protrusion 15 on the inside in the tire radial direction.

When the combination of two or more shoulder blocks 12 and one side block 13 is defined as block group B, one shoulder block 12 included in block group B has a first narrow groove 21 on the side thereof, 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, one second narrow groove 22 is provided on the side of another shoulder block 12 included in block group B, one end of which opens into the other one of the shoulder lug grooves 11 and the other end of which extends toward the side block 13. In addition, at least one third narrow groove 23 is provided on the top surface of the 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. These first narrow groove 21, second narrow groove 22, and third narrow groove 23 constitute 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.

In the tire of the present invention, the shoulder block 12 and the side block 13 function as a large block (block group B) and the rigidity of the large block can be secured, so that the block durability can be improved. In addition, since each block is provided with only the first fine groove 21, the second fine groove 22, and the third fine groove 23, the rigidity of each block is maintained, and the block durability can be improved from this point of view. On the other hand, the first fine groove 21, the second fine groove 22, and the third fine groove 23 constitute a series of fine 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, so that it is equivalent to a substantially large block (block group B) having a substantially long fine groove (fine groove group 20), and this series of fine groove groups 20 exerts an excellent edge effect in the entire block group B, and the traction performance can be effectively improved. These cooperations can achieve a high degree of both block durability and rough road running performance.

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, and even if they are intermittently connected, they can be considered to constitute a continuous narrow groove group 20. For example, in the illustrated example, there is a protrusion 15 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 since the end of the third narrow groove 23 exists at the extension position of the first narrow groove 21 and 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 since the third narrow groove 23 on both sides of the division exists on the extension line of each other, they can be considered to be substantially continuous. Specifically, if the sum of the lengths of the first thin groove 21, the second thin groove 22, and the third thin groove 23 is 80% or more of the total length of an imaginary line (dashed line in the figure) drawn along the thin groove group 20 from one end of the first thin groove 21 (the opening end relative to the shoulder lug groove 11) to one end of the second thin groove 22 (the opening end relative to the shoulder lug groove 11), then the thin groove group 20 can be regarded as a substantially continuous series.

If any of the first fine groove 21, second fine groove 22, and third fine groove 23 is not formed and a series of fine 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 fine groove 21, second fine groove 22, and third fine groove 23 are all formed, if these grooves are not positioned so that they are continuous with each other and fine groove group 20 is not formed, the edge effect of each fine groove can be ensured, but the synergistic effect of fine groove group 20 cannot be ensured, and the effect of improving rough road driving performance will be limited.

The number of shoulder blocks 12 and side blocks 13 included in block group B is preferably 2 to 3, and more preferably 2, shoulder blocks 12 per side block 13. This provides a good balance between the number of blocks in the combination of side blocks 13 and 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 diagrammatically in Figure 4, a first fine groove 21 and a second fine groove 22 are provided in at least the two circumferentially outermost shoulder blocks 12 of the three shoulder blocks 12, and a third fine groove 23 is provided in the side block 13 to connect these. In this structure, fine grooves are not formed in one of the three shoulder blocks 12 that 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, so it is possible to achieve a high level of both block durability and rough road performance, just like the above-mentioned embodiment (an embodiment in which two shoulder blocks 12 are arranged for one side block 13).

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 widths within an appropriate range in this way is advantageous for achieving both block durability and rough road performance. If the groove width of each groove is less than 0.5 mm, it will be difficult to ensure sufficient edge effect because the groove width is too small. If the groove width of each groove exceeds 3 mm, it will be difficult to ensure sufficient block rigidity. In order to form a series of narrow groove groups 20, it is preferable that the groove widths of the first narrow groove 21, the second narrow groove 22, and the third narrow groove 23 are the same.

The groove depth of the first fine groove 21, the second fine groove 22, and the third fine groove 23 is preferably 0.5 mm to 2 mm, and more preferably 0.7 mm to 1.5 mm. Setting the groove depth within an appropriate range in this way is advantageous for achieving both block durability and rough road performance. If the groove depth of each groove is less than 0.5 mm, it will be difficult to ensure a sufficient edge effect because the groove depth is too small. If the groove depth of each groove exceeds 2 mm, it will be difficult to ensure sufficient block rigidity. In order to form a series of fine groove groups 20, it is preferable that the groove depth of the first fine groove 21, the second fine groove 22, and the third fine groove 23 is the same.

The first narrow groove 21 and the second narrow groove 22 each preferably have at least one bending point as shown in the figure. By having a bending point in this way, 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 1 to 2.

On the other hand, it is preferable that the third narrow groove 23 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 is 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, and 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 that extend in various directions, making it possible 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.

As described above, the third narrow groove 23 is preferably 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. In this case, at least the portion extending along the tire circumferential direction should extend parallel to the contour line of the side block 13 (the edge portion on the inner side in the tire radial direction). In addition, it is preferable that the third narrow groove 13 includes a straight portion extending parallel to the contour line of the side block, not limited to this portion. 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 driving performance. It is to be noted that if the angle difference between the contour line of the side block and the corresponding straight portion of the third narrow groove 23 is 0° to 30°, they are considered to extend substantially parallel.

Both the first fine groove 21 and the second fine groove 22 have ends (opening ends) that open into the shoulder lug groove 11, but it is preferable that the opening ends of the first fine groove 21 and the second fine groove 22 are on the same side in the tire circumferential direction with respect to the shoulder block 12 in which each groove is provided. For example, in the illustrated example, the first fine groove 21 opens into the shoulder lug groove 11 adjacent to one side in the tire circumferential direction (the right side in the figure) of the shoulder block 12 in which the first fine groove 21 is provided, and the second fine groove 22 opens into the shoulder lug groove 11 adjacent to one side in the tire circumferential direction (the right side in the figure) of the shoulder block 12 in which the second fine groove 22 is provided. With such an arrangement of the opening ends, the parts connected to the opening ends of the first fine groove 11 and the second fine groove 12 extend in the same direction. As a result, it is advantageous for improving the edge effect and enhancing traction performance.

On the other hand, it is preferable that the opening ends of the first narrow groove 11 and the second narrow groove 12 are located at different positions in the tire radial direction. 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.

In the present invention, the rigidity of each block included in the block group B is maintained by providing the first fine groove 21, the second fine groove 22, and the third fine groove 23 in the block group B, but 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 that branches off from the first fine groove 21 or the second fine groove 22 and extends toward the tread side of the shoulder block 12 can be provided on the side of the shoulder block 12. In addition, a parallel auxiliary groove 25 that extends parallel to the first fine groove 21 or the second fine groove 22 can be provided on the side of the shoulder block 12. By adding auxiliary grooves in this way, the edge effect of each groove is added, 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 be set to be equal to the groove width and groove depth of the first fine groove 21, the second fine groove 22, and the third fine groove 23 described above.

The side block 13 can also be provided with a recess 30 at a position that is an extension of the shoulder lug groove 11 located between the multiple shoulder blocks 12 included in block group B and surrounded by the third narrow groove 23. Providing such a recess 30 complicates the unevenness formed by block group B, which is advantageous for improving traction performance. Note that the recess 30 is located on an extension of the shoulder lug groove 11 like the side groove 14, but unlike the side groove 14, it terminates inside the side block 13, so the rigidity of the side block 13 can be sufficiently maintained even if the recess 30 is provided.

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.

Thirteen types of pneumatic tires were produced: Conventional Example 1, Comparative Examples 1-4, and Examples 1-8, with tire sizes of LT265/70R17 121/118S, a basic structure (cross-sectional structure) as shown in Figure 1, and structures of the shoulder and side regions based on Figure 2. The number of shoulder blocks adjacent to the radially outer side of one side block, the presence or absence of a first fine groove, the presence or absence of a second fine groove, the presence or absence of a third fine groove, the presence or absence of a group of fine grooves, the groove width of the fine groove, the groove depth of the fine groove, the presence or absence of auxiliary grooves, and the presence or absence of parallel auxiliary grooves, were set as shown in Tables 1 and 2, respectively.

The tread pattern in the center area is the same for all examples, with a row of blocks arranged between a pair of main grooves, on each side of the tire equator.

The "Presence or Absence of Fine Groove Groups" columns in Tables 1 and 2 indicate whether or not a series of fine groove groups that extend substantially continuously is formed by the first fine groove, second fine groove, and third fine groove. For example, Comparative Example 2 does not have a third fine groove, so a series of fine groove groups is not formed, and the presence or absence of a series of fine groove groups is "none." 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 "none." Comparative Example 4 has the first to third fine grooves, but the end positions of these grooves are shifted and do not extend substantially continuously, and is an example in which the presence or absence of fine groove groups is "none."

The groove width and groove depth of the first to third narrow grooves are the same for each tire example. That is, the "Narrow Groove Width" and "Narrow Groove Depth" columns in Tables 1 and 2 are the common groove width and groove depth for all narrow grooves from the first to third narrow grooves.

The auxiliary grooves in the "Auxiliary Groove Presence" column of Tables 1 and 2 are auxiliary grooves that branch off from the first fine groove or the second fine groove and extend toward the tread side of the shoulder block, and the presence or absence of these auxiliary grooves is indicated in this column. Also, the parallel auxiliary grooves in the "Parallel Auxiliary Groove Presence" column of Table 1 are parallel auxiliary grooves that extend parallel to the first fine groove or the second fine groove, and the presence or absence of these auxiliary grooves is indicated in this column. "No" in these columns means that the structure is based on Figure 2, but the auxiliary groove and/or parallel auxiliary groove has been removed.

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

Rough road running performance Each test tire was mounted on a wheel with a rim size of 17x8J, and the front tire was set at an air pressure of 450 kPa and the rear tire at an air pressure of 550 kPa. The test tire was then mounted on a test vehicle (traction test vehicle), and a sensory evaluation was carried out by a test driver on the traction performance (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. The higher the index value, the better the rough road running performance.

Block durability (cut resistance)
Each test tire was mounted on a wheel with a rim size of 17×8J, and the air pressure was set to 350 kPa and mounted on a test vehicle (four-wheel drive SUV). After driving 1000 km on an off-road durability road, the total length of the cuts on the side was measured. The evaluation results were expressed as an index with the reciprocal of the measurement value of Conventional Example 1 set to 100. The larger the index value, the smaller the total length of the cuts and the better the block durability (cut resistance).

As is clear from Tables 1 and 2, the pneumatic tires of Examples 1 to 8 have improved rough-road performance and block durability compared to Conventional Example 1, and these performances are well balanced. On the other hand, Comparative Example 1 has a structure in which two shoulder blocks are adjacent to one side block, so although block durability is improved compared to Conventional Example 1, the first to third fine grooves are not provided and a series of fine grooves are not formed, so the effect of improving rough-road performance was not obtained. Comparative Example 2 does not have a third fine groove and a series of fine grooves are not formed, so the rough-road performance could not be sufficiently improved. Comparative Example 3 does not have the first and second fine grooves and a series of fine grooves are not formed, so the rough-road performance could not be sufficiently improved. Comparative Example 4 has the first to third fine grooves, but their arrangement is inappropriate and a series of fine grooves are not formed, so the rough-road performance could not be sufficiently improved.

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 (9)

A tire having a tread portion extending in a circumferential direction of the tire to form an annular shape, and a pair of sidewall portions disposed on both sides of the tread portion,
A pair of main grooves extending along a tire circumferential direction on both sides of a tire equator are provided on a surface of the tread portion,
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 circumferential direction, and a plurality of shoulder blocks partitioned by the main groove and the shoulder lug groove and arranged along 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 an outer side of the shoulder region in the tire width direction,
When one side block is disposed at a position on the outer side in the tire width direction of two or more shoulder blocks adjacent to each other in the tire circumferential direction, and a combination of the 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 is provided on a side surface of another shoulder block included in the block group, the second narrow groove having one end opening into another of the shoulder lug grooves and the other end extending toward the side block,
At least one third narrow groove is provided on a top surface of the side block included in the block group, the third narrow groove extending to connect the other end of the first narrow groove and the other end of the second narrow groove,
a tire characterized in 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 included in the block group through the side block to another of the shoulder blocks. The tire of claim 1, characterized in 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. The tire described in claim 1 or 2, characterized in that the groove widths of the first narrow groove, the second narrow groove, and the third narrow groove are each 0.5 mm to 3 mm. The tire according to any one of claims 1 to 3, characterized in that the groove depth of the first narrow groove, the second narrow groove, and the third narrow groove is 0.5 mm to 2 mm, respectively. A tire according to any one of claims 1 to 4, characterized in that the shoulder block is provided with an auxiliary groove that branches off from the first narrow groove or the second narrow groove and extends toward the tread side of the shoulder block. A tire according to any one of claims 1 to 5, characterized in that the opening ends of the first narrow groove and the second narrow groove are present on the same side of each shoulder block in the tire circumferential direction. The tire according to any one of claims 1 to 6, characterized in that the shoulder block is provided with a parallel auxiliary groove that extends parallel to the first narrow groove or the second narrow groove. 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. A tire as described in any one of claims 1 to 8, characterized in that the opening ends of the first narrow groove and the second narrow groove are positioned differently in the tire radial direction.

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