Two-wheeled vehicle tire for off-road travel

Abstract

To provide a two-wheeled vehicle tire for off-road travel that can exhibit excellent roll characteristics while maintaining shock absorbency.SOLUTION: The present invention relates to a two-wheeled vehicle tire for off-road travel having a tread part 2. The tread part 2 includes a first tread end T1, a second tread end T2, a tread development width TWe, a tire equator C, a crown area 6, and a side part area 7. The tread part 2 includes a plurality of crown blocks 10, and a plurality of outer blocks 20. Each tread of the plurality of outer blocks 20 has a narrow groove formed therein, or is a step surface 25 including a base surface 26, and a projection surface 27 which is locally projects to an outer side in a block height direction with respect to the base surface 26. Each tread of the plurality of crown blocks 10 has a narrow groove 15 formed therein, or is a step surface 28 with no projection surface 27.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a tire for a two-wheeled vehicle for traveling on rough ground.

Background Art

[0002] Patent Document 1 below proposes a tire for a two-wheeled motor vehicle for traveling on rough ground, in which a plurality of first blocks are provided in a tread portion. The first block includes a pair of sipes that divide the tread surface and extend without intersecting each other, a first portion formed between the pair of sipes, and a pair of second portions formed on both outer sides of the pair of sipes. Further, the block height of the first portion is different from the block height of the pair of second portions. In a specific embodiment shown in Patent Document 1, a middle block is configured as the above-described first block.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a fine groove or a stepped surface is formed on the tread surface of a block as in the above-described tire, the edge component of the block increases, and the traction performance and braking performance during straight travel and turning can be improved.

[0005] However, when the above-described fine grooves or stepped surfaces are adopted only for some blocks, the edge components are greatly different for each block, which may cause deterioration of the grip feeling and transient characteristics of the feedback (hereinafter referred to as "roll characteristics") perceived by the driver during rolling.

[0006] Also, when a stepped surface is formed on the blocks near the tire equator, since the tire outer diameter increases compared to the case where the stepped surface is not provided, it becomes necessary to adjust the tire outer diameter within the standard by members other than the blocks. Therefore, for example, there is a concern that the shock absorbency of the tire may be impaired by adjustments such as reducing the block height or reducing the gauge of the tread rubber inside the block.

[0007] The present invention has been devised in view of the above actual situation, and the main problem is to provide a two-wheeled vehicle tire for rough terrain travel that can exhibit excellent roll characteristics while maintaining shock absorbency.

Means for Solving the Problems

[0008] The present invention is a two-wheeled vehicle tire for rough terrain travel having a tread portion, wherein the tread portion includes a first tread end, a second tread end, a tread development width from the first tread end to the second tread end, a tire equator, a crown region having a width of 20% of the tread development width centered on the tire equator, and side regions on both outer sides of the crown region. The tread portion includes a plurality of crown blocks provided in the crown region and a plurality of outer blocks provided in the side regions. The tread surface of each of the plurality of outer blocks is a stepped surface including a fine groove or a base surface and a protruding surface that locally protrudes outward in the block height direction with respect to the base surface. The tread surface of each of the plurality of crown blocks is a non-stepped surface having a fine groove formed therein and not having the protruding surface, and is a two-wheeled vehicle tire for rough terrain travel.

Effects of the Invention

[0009] By adopting the above configuration, the two-wheeled vehicle tire for rough terrain travel of the present invention can exhibit excellent roll characteristics while maintaining shock absorbency.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Mode for Carrying Out the Invention

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Although the drawings include the features of the present invention, in order to assist in understanding the present invention, there may be exaggerated expressions or expressions different from the actual structural dimensional ratios. Also, throughout each embodiment, the same or common elements are denoted by the same reference numerals, and redundant explanations are omitted.

[0012] FIG. 1 shows a cross-sectional view of a tread portion 2 of a two-wheeled tire for rough terrain driving (hereinafter sometimes simply referred to as "tire") 1 according to the present embodiment in a normal state. FIG. 2 is a developed view of the tread portion 2 of the tire 1 developed on a plane. FIG. 1 corresponds to a cross-sectional view taken along line A-A of FIG. 2.

[0013] The "normal state" means that in the case of a tire with various specifications defined, the tire is rim-mounted on a normal rim and filled with a normal internal pressure, and moreover, it is in a no-load state. In the case of a tire without various specifications defined, the "normal state" means a standard use state corresponding to the purpose of use of the tire and is a no-load state. In this specification, unless otherwise specified, the dimensions and the like of each part are values measured in the above-mentioned normal state.

[0014] The "normal rim" is a rim defined for each tire in a standard system including the standard on which the tire is based. For example, in the case of JATMA, it is the "standard rim", in the case of TRA, it is the "Design Rim", and in the case of ETRTO, it is the "Measuring Rim".

[0015] The "normal internal pressure" is the air pressure defined for each tire in a standard system including the standard on which the tire is based. In the case of JATMA, it is the "maximum air pressure", in the case of TRA, it is the maximum value described in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES", and in the case of ETRTO, it is the "INFLATION PRESSURE".

[0016] As shown in FIG. 1, the tire 1 of the present embodiment is for a motorcycle and is suitably used, for example, as a tire for motocross racing. The tire 1 of the present embodiment is suitably used, for example, as a tire for the rear wheel of a motocross vehicle. However, the present invention is not limited to such an aspect. The tread portion 2 of the tire 1 of the present embodiment is curved in an arc shape convex outward in the tire radius direction in a cross section.

[0017] The tire 1 of the present embodiment includes, for example, a carcass and a tread reinforcement layer (not shown). Known configurations are appropriately adopted for these. Further, the tread portion 2 includes a plurality of blocks 5 that protrude from the tread bottom surface 4. When the tire 1 of the present embodiment travels on an uneven road surface, the blocks 5 pierce the road surface and exhibit a high reaction force. For this reason, the tread bottom surface 4 can also contact the road surface.

[0018] As shown in FIG. 2, the tread portion 2 of the tire 1 of the present invention has a directional pattern in which the rotational direction R is specified. The rotational direction R is indicated, for example, by characters or symbols on the sidewall portion 3 (shown in FIG. 1). However, the present invention is not limited to such a mode.

[0019] The tread portion 2 includes a first tread end T1, a second tread end T2, a tread development width TWe from the first tread end T1 to the second tread end T2, and a tire equator C. The first tread end T1 and the second tread end T2 each mean the outer edge in the tire axial direction of the tread surface of the block 5 included in the block row located most outside in the tire axial direction among the blocks 5 arranged in the tread portion 2.

[0020] The tread development width TWe corresponds to the distance in the tire axial direction from the first tread end T1 to the second tread end T2 when the tread portion 2 is developed in a plane. The tire equator C is an imaginary line extending parallel to the tire circumferential direction at the center position in the tire axial direction of the tread portion.

[0021] The tread portion 2 includes a crown region 6 and a side region 7. The crown region 6 has a width Wc of 20% of the tread development width TWe centered on the tire equator C. The side region 7 is a region arranged on both outer sides of the crown region 6. That is, the two side regions 7 are arranged so as to sandwich the crown region 6. In FIG. 2, the boundary 8 between the crown region 6 and the side region 7 is indicated by a two-dot chain line.

[0022] The tread portion 2 includes a plurality of crown blocks 10 provided in the crown region 6 and a plurality of outer blocks 20 provided in the side region 7. In the present embodiment, in the development view of the tread portion 2, those through which the boundary 8 between the crown region 6 and the side region 7 passes on the tread surface of the block 5 correspond to the crown blocks 10. In other words, for the outer blocks 20, the entire tread surface thereof is located outside the boundary 8 in the tire axial direction. Note that the tread surface of a block means a region that extends along a virtual tread bottom surface 4 passing through the base of the block among the outer surfaces of the block, and more specifically, means a region where the angle with respect to the tread bottom surface 4 is 30° or less.

[0023] The outer blocks 20 include a plurality of shoulder blocks 40 including the first tread end T1 or the second tread end T2, and a plurality of middle blocks 30 disposed between the plurality of shoulder blocks 40 and the crown region 6. FIG. 3 shows the end view taken along line B-B of FIG. 2 as a view showing the cross section of the shoulder block 40. FIG. 4 shows the end view taken along line C-C of FIG. 2 as a view showing the cross section of the middle block 30. Note that in the view showing the enlarged cross section of the block in this specification, for the purpose of facilitating understanding of the features, the curved components included in the tread surface of the actual block are appropriately excluded and shown.

[0024] As shown in FIGS. 3 and 4, the tread surface of each of the plurality of outer blocks 20 is a stepped surface 25 including a fine groove 15 or including a base surface 26 and a protruding surface 27 that protrudes locally outward in the block height direction with respect to the base surface 26. The fine groove 15 means a groove having a groove width of 3.0 mm or less and includes a fine notch called a sipe.

[0025] Each of the outer blocks 20 of the present embodiment has a fine groove 15 and has a stepped surface 25 in which one surface divided by the fine groove 15 is a base surface 26 and the other surface is a protruding surface 27. However, the present invention is not limited to such an aspect. FIGS. 5 and 6 show cross-sectional views of the outer block 20 of another embodiment. As shown in FIG. 5, the outer block 20 of the present invention may only have the fine groove 15 provided. Further, as shown in FIG. 6, the outer block 20 of the present invention may be configured with a stepped surface 25 including the base surface 26 and the protruding surface 27 without providing the fine groove.

[0026] FIG. 7 shows an end view taken along line D-D of FIG. 2 as a view showing a cross section of the crown block 10. As shown in FIG. 7, the tread surface of each of the plurality of crown blocks 10 is a non-stepped surface 28 in which the fine groove 15 is formed and which does not have the protruding surface 27 (shown in FIGS. 3 and 4). The non-stepped surface 28 means that no step is formed because the height of one surface divided by the fine groove 15 and the height of the other surface are substantially the same. However, from the viewpoint of allowing inevitable errors in a tire which is a rubber product, those including a step of 0.5 mm or less shall be treated as non-stepped surfaces.

[0027] By adopting the above configuration, the tire of the present invention can exhibit excellent roll characteristics while maintaining impact absorbability. The reason is as follows.

[0028] As shown in FIGS. 3 to 6, in the tire of the present invention, the tread surface of each of the plurality of outer blocks 20 is formed with the fine groove 15 or is formed as the stepped surface 25. Further, as shown in FIG. 7, the tread surface of each of the plurality of crown blocks 10 is a non-stepped surface 28 in which the fine groove 15 is formed and which does not have the protruding surface. Thereby, as shown in FIG. 2, since the edge component of each block 5 is increased by the fine groove 15 or the stepped surface 25, an improvement in roll characteristics can be expected.

[0029] On the one hand, conventionally, when a stepped surface is formed on a block near the tire equator, the outer diameter of the tire increases compared to the case where no stepped surface is provided. For this reason, it is necessary to adjust the outer diameter of the tire within the standard by reducing the block height or reducing the gauge of the tread rubber inside the block, etc., and these adjustments may impair the shock absorption of the tire. On the other hand, in the present invention, since the tread surface of the crown block 10 is a non-stepped surface 28, the outer diameter of the tire is not unnecessarily increased, and the shock absorption can be maintained.

[0030] Hereinafter, the more detailed configuration of the present embodiment will be described. It should be noted that the configuration described below shows a specific aspect of the present embodiment. Therefore, it goes without saying that the present invention can exhibit the above-described effects even if it does not have the configuration described below. In addition, even if any one of the following-described configurations is applied alone to the tire 1 of the present invention having the above-described features, an improvement in performance corresponding to each configuration can be expected. Further, when several of the following-described configurations are applied in combination, a combined improvement in performance corresponding to each configuration can be expected. Also, in the following, the outer block 20 disposed on the first tread end T1 side with respect to the tire equator C is shown as an example, but these configurations can also be applied to the outer block 20 disposed on the second tread end T2 side with respect to the tire equator C.

[0031] In the entire tread portion 2, the number N1 of outer blocks 20 having a protruding surface 27 (in the present embodiment, both the shoulder block 40 and the middle block 30) is desirably 75% or less of the total number Nt of the crown block 10 and the outer blocks 20. As a more desirable aspect, in the present embodiment, the number N1 is set to 60% to 70% of the total number Nt. By such an arrangement of the blocks, the roll characteristics can be further enhanced.

[0032] Throughout the entire tread portion 2, the number N2 of the blocks 5 having the narrow grooves 15 (in this embodiment, all the blocks 5 have the narrow grooves 15) is 40% to 200% of the number N1, and preferably 130% to 170%. Such an arrangement of the blocks 5 can enhance the roll characteristics while maintaining the wear resistance of the tread portion 2.

[0033] In the tread portion 2 of this embodiment, tie bars 35 for connecting adjacent blocks 5 are provided. FIG. 8 shows, as an example of the tie bar 35, an end face view taken along the line E-E in FIG. 2. As shown in FIGS. 2 and 8, this tie bar 35 locally protrudes from the tread bottom surface 4 and can enhance the rigidity of the root portion of the block. Further, as shown in FIG. 8, the protruding height h1 of the tie bar 35 is less than 20% of the height of the adjacent block, specifically, 1.0 to 2.5 mm. However, the tie bars 35 connecting the crown blocks 10 to each other are different from the above dimensions and will be described later.

[0034] As shown in FIG. 2, each of the plurality of crown blocks 10 is connected to an adjacent other crown block 10 and the outer block 20 by a tie bar 35. Each of the plurality of outer blocks 20 is connected to an adjacent other outer block 20 or crown block 10 by a tie bar 35. Thereby, the tilting of each block 5 is suppressed, and the traction performance and the braking performance are improved.

[0035] FIG. 9 shows an enlarged view of the plurality of shoulder blocks 40. As shown in FIG. 9, narrow grooves 15 extending in the tire circumferential direction are provided on the tread surface of the shoulder block 40 of this embodiment. This narrow groove 15 completely crosses the tread surface 40s of the shoulder block 40 in the tire circumferential direction, and divides this tread surface 40s into a base surface 26 arranged on the first tread end T1 side and a protruding surface 27 arranged on the tire equator C side.

[0036] The groove 15 preferably slopes toward the tire equator C toward the leading side in the rotational direction R. The angle θ1 of the groove 15 with respect to the tire circumferential direction is, for example, 45° or less, desirably 5 to 15°. When the groove 15 does not extend linearly, the angle θ1 means the average angle of the groove 15 with respect to the tire circumferential direction. The average angle corresponds to the sum of the angles of each minute region of the groove 15 with respect to the tire circumferential direction divided by the number of the minute regions. Hereinafter, the angles of each part shall be measured in the same manner.

[0037] In a more desirable embodiment, the groove 15 preferably has a continuously increasing groove width toward the leading side in the rotational direction R. As a result, the maximum groove width is formed at the leading side end of the groove 15, and the minimum groove width is formed at the trailing side end of the groove 15 in the rotational direction R. Further, the minimum groove width is, for example, 65% to 80% of the maximum groove width. Such a groove 15 can provide a large reaction force during braking and improve the braking performance.

[0038] As shown in FIG. 3, the shoulder block 40 of the present embodiment has a groove 15 formed therein, and the tread surface 40s is a stepped surface 25. Further, a base surface 26 is arranged on the first tread end T1 side of the stepped surface 25, and a protruding surface 27 is arranged on the tire equator C side. The step amount t1 between the base surface 26 and the protruding surface 27 is, for example, 1.0 to 2.0 mm. Such a shoulder block 40 helps to improve the cornering performance.

[0039] As shown in FIG. 9, the area of the base surface 26 of the shoulder block 40 is 55% to 65% of the total area of the tread surface 40s of the shoulder block 40 (the sum of the area of the base surface 26 and the area of the protruding surface 27, and the same shall apply hereinafter). Further, the area of the protruding surface 27 of the shoulder block 40 is 35% to 45% of the total area of the tread surface 40s. Thereby, while maintaining the durability of the shoulder block 40, the shoulder block 40 can be easily bitten into the road surface.

[0040] The shoulder block 40 includes a first shoulder block 41 and a second shoulder block 42 with different tread shapes. The tread of the first shoulder block 41 has two edges 41a extending in the tire axial direction that are inclined in the same direction with respect to the tire axial direction. Specifically, the two edges 41a of the first shoulder block 41 are inclined toward the rear side in the rotational direction R from the first tread end T1 toward the tire equator C side. Such a first shoulder block 41 can exhibit excellent traction performance during cornering.

[0041] The tread of the second shoulder block 42 has two edges 42a extending in the tire axial direction that are inclined in different directions with respect to the tire axial direction. In a preferred embodiment, these two edges 42a are inclined so as to approach each other toward the tire equator C side. As a result, the tread of the second shoulder block 42 has a continuously decreasing length in the tire circumferential direction toward the tire equator C side. Such a second shoulder block 42 has relatively high rigidity on the first tread end T1 side and helps to enhance the roll characteristics.

[0042] As shown in FIG. 2, it is desirable that the first shoulder block 41 and the second shoulder block 42 are connected to each other by a tie bar 35. In the present embodiment, these shoulder blocks 40 are also connected to a second middle block 32, which will be described later, by a tie bar 35. This makes it difficult for the shoulder block 40 to fall over and improves the traction performance and braking performance. Note that in FIG. 9, this tie bar 35 is omitted.

[0043] FIG. 10 shows an enlarged view of a plurality of middle blocks 30. As shown in FIG. 10, fine grooves 15 are provided on the tread 30s of the middle block 30 of the present embodiment. These fine grooves 15 bend and extend so as to communicate with an edge extending in the tire axial direction and an edge extending in the tire circumferential direction among the outer peripheral edges of the tread 30s. As a result, the fine grooves 15 divide the tread 30s of the middle block 30 into a base surface 26 and a protruding surface 27.

[0044] The land groove 15 extends, for example, from the trailing edge side edge 30a that extends in the tire axial direction on the trailing side of the circumferential direction R among the outer peripheral edges of the tread surface 30s to the tire equator side edge 30c that extends in the tire circumferential direction on the tire equator C side. Further, the land groove 15 includes a first groove portion 16, a second groove portion 17, and a third groove portion 18. The first groove portion 16 extends in the tire circumferential direction from the trailing edge side edge 30a. The second groove portion 17 is continuous with the first groove portion 16 and extends while being inclined with respect to the tire axial direction. The third groove portion 18 extends in the tire axial direction from the second groove portion 17 to the tire equator side edge 30c. The angle θ2 between the first groove portion 16 and the third groove portion 18 is, for example, 70 to 110°, preferably 80 to 90°. Such a land groove 15 can provide frictional force in multiple directions and can enhance the roll characteristics and traction performance in a well-balanced manner.

[0045] When the first groove portion 16 and the third groove portion 18 are non-linear, the angle θ2 corresponds to, for example, the sum of the average angle of the first groove portion 16 with respect to an arbitrary reference line (for example, a virtual straight line inclined at 45° with respect to the tire circumferential direction) and the average angle of the third groove portion 18 with respect to the reference line. The method for measuring the average angle is as described above. Also, the angle between the two members described below can be obtained by the same method.

[0046] In a preferred embodiment, in this land groove 15, the first groove portion 16 has a constant groove width in its length direction. Also, it is desirable that the groove width of the land groove 15 continuously increases from the end portion on the first groove portion 16 side of the second groove portion 17 to the end portion on the tire equator side edge 30c side of the third groove portion 18. Thereby, at the end portion of this land groove 15 that communicates with the tire equator side edge 30c, the maximum groove width is formed, and at the first groove portion 16 of this land groove 15, the minimum groove width is formed. Also, the minimum groove width is, for example, 20% to 40% of the maximum groove width. Such a land groove 15 can further improve the roll characteristics.

[0047] As shown in Fig. 4, in the middle block 30 of the present embodiment, the fine groove 15 is formed, and the tread surface 30s is a stepped surface 25. The step amount t2 between the base surface 26 and the protruding surface 27 is, for example, 1.0 to 2.0 mm.

[0048] Further, as shown in Fig. 10, the protruding surface 27 included in the stepped surface 25 is a surface surrounded by the fine groove 15, a part of the trailing side edge 30a, and a part of the tire equator side edge 30c. Also, the base surface 26 included in the stepped surface 25 is arranged so as to surround the protruding surface 27. Thereby, the base surface 26 is a surface surrounded by the fine groove 15, the remaining part of the trailing side edge 30a and the remaining part of the tire equator side edge 30c, the leading side edge 30b extending in the tire axial direction on the leading side in the rotational direction R, and the tread end side edge 30d extending in the tire circumferential direction on the first tread end T1 side. Thereby, the area of the protruding surface 27 on the tread surface 30s of the middle block 30 is smaller than the area of the base surface 26 of the tread surface 30s. Such a middle block 30 is likely to penetrate into an uneven road surface and can exert a large reaction force.

[0049] The area of the base surface 26 in the middle block 30 is 70% to 85% of the total area of the tread surface 30s of the middle block 30. Also, the area of the protruding surface 27 in the middle block 30 is 15% to 30% of the total area of the tread surface 30s. Thereby, while maintaining the durability of the middle block 30, the roll characteristics can be enhanced.

[0050] It is desirable that the leading edge 30b and the trailing edge 30a included in one middle block 30 are inclined in the same direction with respect to the tire axis direction. The angle θ3 of these edges with respect to the tire axis direction is, for example, 5 to 30°. Further, in the present embodiment, the directions of inclination of these edges with respect to the tire axis direction are different depending on the block. That is, the middle block 30 in which the leading edge 30b and the trailing edge 30a are inclined toward the trailing side in the rotational direction R toward the first tread end T1 side, and the middle block 30 in which these edges are inclined toward the leading side in the rotational direction R toward the first tread end T1 side are scattered in the tire circumferential direction. Such an arrangement of the middle blocks 30 can stably exert a reaction force under various road surface conditions and can further enhance the roll characteristics.

[0051] The middle block 30 includes, for example, a first middle block 31 and a second middle block 32 provided alternately in the tire circumferential direction. As shown in FIG. 2, the first middle block 31 is connected to the crown block 10 by a tie bar 35. The second middle block 32 is connected to the shoulder block 40 by a tie bar 35. The tie bar 35 connecting the first middle block 31 and the crown block 10 has the same bulge height h1 (shown in FIG. 9) as the above-described tie bar 35. Due to the arrangement of the tie bars 35, the first middle block 31 and the second middle block 32 have anisotropy with respect to the ease of falling of the blocks. Therefore, when driving on a muddy road surface, these blocks are likely to fall in different directions, and thus it becomes difficult to retain mud around these blocks. Due to such an action, high grip performance is continuously exhibited. In FIG. 10, these tie bars 35 are omitted.

[0052] In a desirable embodiment, one first middle block 31 is connected by two tie bars 35 to a crown block 10 adjacent to one side in the tire circumferential direction and a crown block 10 adjacent to the other side in the tire circumferential direction. Further, the tie bars 35 connecting the first middle block 31 and the crown block 10 include a mode in which the width thereof continuously increases from the crown block 10 to the first middle block 31, a mode in which the width continuously decreases from the crown block 10 to the first middle block 31, and a mode in which the width is constant. In this embodiment, these modes are scattered in the tire circumferential direction.

[0053] The second middle block 32 is connected to both the first shoulder block 41 and the second shoulder block 42. Specifically, the second middle block 32, the first shoulder block 41, and the second shoulder block 42 are connected by a tie bar 35 in which the region surrounded by these blocks is entirely raised. With such an arrangement of blocks and tie bars, excellent roll characteristics and cornering performance are exhibited.

[0054] FIG. 11 shows an enlarged view of a plurality of crown blocks 10. In FIG. 11, the tie bar 35 (shown in FIG. 2) connecting the first middle block 31 and the crown block 10 is omitted. As shown in FIG. 11, the grooves 15 provided on the tread surface of the crown block 10 have both ends communicating with the outer peripheral edge of the tread surface 10s.

[0055] The lug groove 15 extends, for example, from the trailing side edge 10a that extends in the tire axial direction on the trailing side of the circumferential edge of the tread surface, to the equatorial side edge 10c that extends in the tire circumferential direction on the tire equator C side. Further, the lug groove 15 includes a longitudinal portion 23 that extends in the tire circumferential direction and a lateral portion 24 that extends in the tire axial direction. The longitudinal portion 23 extends in the tire circumferential direction from the trailing side edge 10a. The lateral portion 24 extends from the longitudinal portion 23 to the equatorial side edge 10c. The angle θ4 between the longitudinal portion 23 and the lateral portion 24 is, for example, 70 to 90°. Such a lug groove 15 can provide frictional force in multiple directions and exhibit excellent roll characteristics and traction performance.

[0056] In a preferred embodiment, it is desirable that this lug groove 15 extends with a constant groove width from the end on the trailing side edge 10a side to the end on the equatorial side edge 10c side. In a more preferred embodiment, when the lug groove 15 is provided in the outer block 20 (shown in FIG. 2), the average groove width of the lug groove 15 provided in the crown block 10 is smaller than the average groove width of the lug groove 15 provided in the outer block 20. Thereby, the roll characteristics are further improved. The average groove width corresponds to the opening area of the lug groove 15 divided by the length of the lug groove 15 (the so-called peripheral length).

[0057] The tread surface 10s of the crown block 10 includes a first surface 36 and a second surface 37 separated by the lug groove 15. The first surface 36 is surrounded by the lug groove 15, a part of the trailing side edge 10a, and a part of the equatorial side edge 10c. The second surface 37 is arranged to surround the first surface 36. Thereby, the second surface 37 is surrounded by the lug groove 15, the remaining parts of the trailing side edge 10a and the equatorial side edge 10c, the leading side edge 10b that extends in the tire axial direction on the leading side of the rotational direction R, and the tread end side edge 10d that extends in the tire circumferential direction on the first tread end T1 side or the second tread end T2 (shown in FIG. 2) side. Thereby, the second surface 37 of the crown block 10 has a larger area than the first surface 36.

[0058] The area of the first surface 36 of the crown block 10 is 10% to 30% of the total area of the tread surfaces 10s of one crown block 10 (which is the sum of the area of the first surface 36 and the area of the second surface 37). Further, the area of the second surface 37 of the crown block 10 is 70% to 90% of the total area of the tread surfaces 10s. Thereby, while maintaining the durability of the crown block 10, the traction performance and the braking performance can be improved.

[0059] The distance L2 in the tire circumferential direction from the centroid 38c of the virtual tread 38 composed of the first surface 36, the fine grooves 15, and the second surface 37 to the centroid 36c of the first surface 36 is desirably 20% or more of the length L1 in the tire circumferential direction of the virtual tread 38 on the centroid 38c of the virtual tread 38, and more desirably 30% to 40%. Thereby, the amount of deformation of the region including the first surface 36 becomes large, and the traction performance and the braking performance can be further improved.

[0060] As shown in FIG. 2, in the entire tread portion 2, the sum of the area of the first surface 36 of the crown block 10 and the area of the protruding surface 27 of the outer block 20 is desirably 20% to 60% of the sum of the areas of the tread surfaces of the block 5. Thereby, while maintaining the durability of the tread portion 2, the roll characteristics can be enhanced.

[0061] As included in FIG. 11, it is desirable that the leading edge 10b and the trailing edge 10a included in one crown block 10 are inclined in the same direction with respect to the tire axial direction. The angle θ5 of these edges with respect to the tire axial direction is, for example, 10 to 20°. Further, in the present embodiment, the directions of inclination of these edges with respect to the tire axial direction differ depending on the block. That is, the crown block 10 in which the leading edge 10b and the trailing edge 10a are inclined toward the trailing side in the rotational direction R toward the tire equator C side and the crown block 10 in which these edges are inclined toward the leading side in the rotational direction R toward the tire equator C side are scattered. Thereby, the plurality of crown blocks 10 exhibit frictional forces in multiple directions, and the traction performance is further improved.

[0062] The angle θ6 between the leading edge 10b and the lateral portion 24 is, for example, 20° or less, desirably 5 to 15°. Thereby, these edges cooperate to provide a large frictional force, improving the traction performance and the braking performance.

[0063] As shown in FIG. 2, the crown block 10 includes a first middle block 31 disposed on the leading side in the rotational direction R and a first crown block 11 connected by a tie bar 35, and a first middle block 31 disposed on the trailing side in the rotational direction R and a second crown block 12 connected by a tie bar 35.

[0064] In the present embodiment, two first crown blocks 11 disposed so as to sandwich the tire equator C are connected by a tie bar 35, thereby constituting one first crown block pair 46. Also, two second crown blocks 12 disposed so as to sandwich the tire equator C are connected by a tie bar 35, thereby constituting one second crown block pair 47. Further, the first crown block pair 46 and the second crown block pair 47 are alternately arranged in the tire circumferential direction. Thereby, excellent traction performance and braking performance can be obtained even in various road surface conditions.

[0065] As a more desirable aspect, in the present embodiment, one first crown block pair 46 and one second crown block pair 47 are connected by a common first middle block 31 and a tie bar 35. Thereby, in the tread portion 2, a plurality of virtual annular bodies 45 that are annular in a tread plan view are arranged in the tire circumferential direction by the first crown block pair 46, the second crown block pair 47, the first middle block 31, and the tie bar 35 that connect them. Also, in one virtual annular body 45, the second crown block pair 47 is disposed on the leading side in the rotational direction R with respect to the first crown block pair 46.

[0066] As shown in Fig. 7, the tie bar 35 included in two adjacent crown blocks 10 in the tire axial direction has a raised height h2 that is larger than the tie bar 35 shown in Fig. 8. The raised height h2 of this tie bar 35 is, for example, 20% to 50% of the height h3 of the crown block 10.

[0067] As shown in Fig. 11, the maximum width W2 in the tire axial direction of the second crown block pair 47 (measured on the tread surface, and the same applies hereinafter) is larger than the maximum width W1 in the tire axial direction of the first crown block pair 46. Specifically, the maximum width W2 of the second crown block pair 47 is 130% to 160% of the maximum width W1 of the first crown block pair 46. Similarly, the width in the tire axial direction of the tie bar 35 included in the second crown block pair 47 is larger than the width in the tire axial direction of the tie bar 35 included in the first crown block pair 46. Thereby, when driving on a muddy road surface, the virtual annular body 45 can grab a lot of mud, and the traction performance and braking performance are further improved.

[0068] Fig. 12 is a developed view of the tread portion 2 of still another embodiment of the present invention. As shown in Fig. 12, in this embodiment, no fine grooves are provided on the tread surface 20s of the outer block 20. The tread surface 20s of the outer block 20 in this embodiment is configured as a stepped surface 25, and the boundary 34 between the base surface 26 and the protruding surface 27 is shown by a solid line. Even in such an embodiment, the protruding surface 27 can provide a sufficient edge component and can exhibit excellent roll characteristics.

[0069] As described above, the desirable aspects of the two-wheeled vehicle tire for rough terrain driving of the present invention have been described in detail. However, the present invention is not limited to the above specific embodiments and can be implemented in various aspects.

Example

[0070] A rear wheel tire for a two-wheeled vehicle for rough terrain travel having the basic pattern of FIG. 2 was prototyped. As Comparative Example 1, a tire having the pattern shown in FIG. 13 was prototyped. In the tire of Comparative Example 1, the tread surface of each block a is not a protruding surface but a flat surface, and moreover, no fine grooves are provided. Further, as Comparative Example 2, a tire having the pattern of FIG. 2 and having a crown block b with a stepped surface c as shown in FIG. 14 was prototyped. In Comparative Example 2, in order to adjust the tire outer diameter within the standard, the gauge of the tread rubber was slightly reduced on the inner side in the tire radial direction of the crown block b (not shown). The tires of Comparative Examples 1 and 2 are substantially the same as the tire of the Example except for the above matters. For these test tires, roll characteristics, shock absorption, traction performance, and braking performance were tested. The common specifications and test methods of each test tire are as follows. Vehicle used: Motocross racing vehicle with a displacement of 450 cc Tire size: 120 / 90-19 Rim size: 2.75WM Inner pressure: 80 kPa The test method is as follows.

[0071] <Roll characteristics, shock absorption, traction performance, and braking performance> When the test vehicle was run on a motocross course, the roll characteristics, shock absorption, traction performance, and braking performance were evaluated by the sensory evaluation of the test rider. The larger the numerical value, the better the various performances. The test results are shown in Table 1.

[0072]

Table 1

[0073] As shown in Table 1, it was confirmed that the tire of the Example exhibited excellent roll characteristics while maintaining shock absorption. Also, it was confirmed that the tire of the Example also had improved traction performance and braking performance.

[0074] [Supplementary Note] The present invention includes the following aspects.

[0075] [Invention 1] A two-wheeled tire for rough terrain travel having a tread portion, The tread portion includes a first tread end, a second tread end, a tread width from the first tread end to the second tread end, a tire equator, a crown region having a width of 20% of the tread width centered on the tire equator, and side regions on both outer sides of the crown region. The tread portion includes a plurality of crown blocks provided in the crown region and a plurality of outer blocks provided in the side regions. The tread surface of each of the plurality of outer blocks is a stepped surface in which fine grooves are formed or includes a base surface and a protruding surface that protrudes outward in the block height direction locally with respect to the base surface. The tread surface of each of the plurality of crown blocks is a non-stepped surface in which fine grooves are formed and does not have the protruding surface. A two-wheeled tire for rough terrain travel. [Invention 2] The rotation direction is specified, At least one of the tread surfaces of the plurality of crown blocks includes a leading edge that extends in the tire axial direction on the leading side in the rotation direction. The fine groove provided in the crown block having the leading edge includes a lateral portion that extends in the tire axial direction. The angle between the leading edge and the lateral portion is 20° or less. The two-wheeled tire for rough terrain travel according to Invention 1. [Invention 3] At least one of the tread surfaces of the plurality of crown blocks includes a first surface and a second surface having an area larger than that of the first surface, when both ends of the fine groove communicate with the outer peripheral edge of the tread surface. The distance in the tire circumferential direction from the centroid of the virtual tread surface composed of the first surface, the narrow groove, and the second surface to the centroid of the first surface is 20% or more of the length in the tire circumferential direction of the virtual tread surface at the centroid of the virtual tread surface. The two-wheeled vehicle tire for rough terrain travel according to Invention 1 or 2 of the present invention. [Invention 4] The tread portion includes a tread bottom surface and tie bars that locally protrude from the tread bottom surface and connect adjacent blocks. Each of the plurality of crown blocks is connected by the tie bars to another adjacent crown block, the outer block, and the like. Each of the plurality of outer blocks is connected by the tie bars to another adjacent outer block or the crown block. The two-wheeled vehicle tire for rough terrain travel according to any one of Claims 1 to 3 of the present invention. [Invention 5] The outer block includes a plurality of shoulder blocks including the first tread end, and a plurality of middle blocks arranged between the plurality of shoulder blocks and the crown region. The plurality of middle blocks alternately include, in the tire circumferential direction, a first middle block connected to the crown block by the tie bar and a second middle block connected to the shoulder block by the tie bar. The two-wheeled vehicle tire for rough terrain travel according to Invention 4 of the present invention. [Invention 6] The plurality of crown blocks include a first surface and a second surface having an area larger than that of the first surface when both ends of the narrow groove communicate with the outer peripheral edge of the tread surface. The tread surface of each of the plurality of outer blocks is the stepped surface including the protruding surface. In the entire tread portion, the sum of the area of the first surface and the area of the protruding surface is 20% to 60% of the sum of the areas of the tread surface. The two-wheeled vehicle tire for rough terrain travel according to any one of Claims 1 to 5 of the present invention. [Invention 7] In the entire tread portion, the number N1 of the outer blocks having the protruding surfaces is 75% or less of the total number Nt of the crown blocks and the outer blocks. The tire for a two-wheeled vehicle for rough terrain according to any one of Claims 1 to 6 of the present invention. [Invention 8] In the entire tread portion, the number N2 of the blocks having the narrow grooves is 40% to 200% of the number N1. The tire for a two-wheeled vehicle for rough terrain according to Claim 7 of the present invention.

Explanation of Signs

[0076] 2 Tread portion 6 Crown region 7 Side region 10 Crown block 15 Narrow groove 20 Outer block 25 Step surface 26 Base surface 27 Protruding surface 28 Non-step surface T1 First tread end T2 Second tread end TWe Tread width

Claims

1. A two-wheeled tire for rough terrain travel having a tread portion, wherein the tread portion includes a first tread edge, a second tread edge, a tread expansion width from the first tread edge to the second tread edge, a tire equator, a crown region having a width of 20% of the tread expansion width centered on the tire equator, and side regions on both outer sides of the crown region; the tread portion includes a plurality of crown blocks provided in the crown region and a plurality of outer blocks provided in the side regions; the tread surface of each of the plurality of outer blocks is a stepped surface including fine grooves or a base surface and a protruding surface that locally protrudes outward in the block height direction with respect to the base surface; the tread surface of each of the plurality of crown blocks is a non-stepped surface having fine grooves formed therein and not having the protruding surface; A two-wheeled tire for rough terrain travel.

2. The rotation direction is specified, at least one of the tread surfaces of the plurality of crown blocks includes a leading-edge side edge extending in the tire axial direction on the leading-edge side in the rotation direction; the fine grooves provided in the crown block having the leading-edge side edge include a lateral portion extending in the tire axial direction; The angle between the leading-edge side edge and the lateral portion is 20° or less. The two-wheeled tire for rough terrain travel according to Claim 1.

3. at least one of the tread surfaces of the plurality of crown blocks includes a first surface and a second surface having an area larger than that of the first surface, wherein both ends of the fine grooves communicate with the outer peripheral edge of the tread surface; The circumferential distance in the tire circumferential direction from the centroid of the virtual tread surface formed by the first surface, the fine grooves, and the second surface to the centroid of the first surface is 20% or more of the circumferential length of the virtual tread surface at the centroid of the virtual tread surface. The two-wheeled tire for rough terrain travel according to Claim 1 or 2.

4. the tread portion includes a tread bottom surface and tie bars that locally protrude from the tread bottom surface and connect adjacent blocks; each of the plurality of crown blocks is connected by the tie bars to other adjacent crown blocks and the outer blocks; each of the plurality of outer blocks is connected by the tie bars to other adjacent outer blocks or the crown blocks. The two-wheeled tire for rough terrain travel according to Claim 1 or 2.

5. The outer blocks include a plurality of shoulder blocks including the first tread end, and a plurality of middle blocks disposed between the plurality of shoulder blocks and the crown region. The plurality of middle blocks alternately include in the tire circumferential direction a first middle block connected to the crown block by the tie bar and a second middle block connected to the shoulder block by the tie bar, the two-wheeled vehicle tire for rough terrain travel according to claim 4.

6. The plurality of crown blocks include a first surface and a second surface having an area larger than the first surface, with both ends of the narrow grooves communicating with the outer peripheral edge of the tread surface. The tread surface of each of the plurality of outer blocks is the stepped surface including the protruding surface. In the entire tread portion, the sum of the area of the first surface and the area of the protruding surface is 20% to 60% of the sum of the areas of the tread surface, the two-wheeled vehicle tire for rough terrain travel according to claim 1 or 2.

7. In the entire tread portion, the number N1 of the outer blocks having the protruding surface is 75% or less of the total number Nt of the crown blocks and the outer blocks, the two-wheeled vehicle tire for rough terrain travel according to claim 1 or 2.

8. In the entire tread portion, the number N2 of the blocks having the narrow grooves is 40% to 200% of the number N1, the two-wheeled vehicle tire for rough terrain travel according to claim 7.

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