Patent Description:
Patent document <NUM> below discloses a motorcycle tire for running on rough terrain with a tread having a block pattern. The block pattern of the tire includes a plurality of connected block pairs. Each connected block pair includes two blocks and a tie-bar connecting these blocks. In each connected block pair, the tie-bar has the trailing edge having a height equal to or smaller than the height of the blocks, and the leading edge having a height smaller than the height of the trailing edge.

The tire described above had room for improvement in terms of grip and steering characteristics on soft road surfaces.

The present invention has been made in view of the above circumstances and has a major object to provide a two-wheeled vehicle tire for running on rough terrain capable of exhibiting excellent grip and steering characteristics on soft road surfaces while maintaining running performance on hard road surfaces.

In one aspect of the present invention, a two-wheeled vehicle tire for running on rough terrain, the tire includes a tread portion having a designated rotation direction, the tread portion including at least one first block, wherein the at least one first block includes a pair of block pieces adjacent to each other in a tire axial direction, and a tie-bar connecting the pair of block pieces, the tie-bar has an outer surface in a tire radial direction, the outer surface of the tie-bar having a height increasing toward a trailing side in the rotation direction, the pair of block pieces each has an outer surface in the tire radial direction, the outer surface of each block piece having an axially extending leading edge located on a leading side in the rotation direction, and the leading edge of each of the pair of block pieces is inclined toward the trailing side in the rotation direction from an end on a tie-bar side thereof outwardly in a block-width direction.

<FIG> illustrates a cross-sectional view of a tread portion <NUM> of a two-wheeled vehicle tire for running on rough terrain (hereinafter may simply be referred to as "tire") <NUM> of the present embodiment of the invention under the normal state. <FIG> is a development view of the tread portion <NUM> of the tire <NUM>. <FIG> corresponds to the cross-sectional view taken along the line A-A in <FIG>.

As used herein, when the tire <NUM> is a tire based on a standard, the "normal state" is such that the tire <NUM> is mounted onto a standard wheel rim with a standard pressure but loaded with no tire load. If the tire is not based on the standards, the normal state is a standard state of use according to the purpose of use of the tire and means a state of no load. As used herein, unless otherwise noted, dimensions of portions of the tire are values measured under the normal state.

As used herein, the "standard wheel rim" is a wheel rim officially approved for each tire by standards organizations on which the tire is based, wherein the standard wheel rim is the "standard rim" specified in JATMA, the "Design Rim" in TRA, and the "Measuring Rim" in ETRTO, for example.

As used herein, the "standard pressure" is a standard pressure officially approved for each tire by standards organizations on which the tire is based, wherein the standard pressure is the "maximum air pressure" in JATMA, the maximum pressure given in the "Tire Load Limits at Various Cold Inflation Pressures" table in TRA, and the "Inflation Pressure" in ETRTO, for example.

As shown in <FIG>, the tire <NUM> suitable for use, for example, as a tire for motocross competitions. In particular, the tire <NUM> according to the present embodiment is suitable for use, for example, as a front tire of a motocross bike. The tread portion <NUM> of the tire <NUM> according to the present embodiment of the invention is curved in a cross-sectional view in the form of an arc whose outer surface is convex outwardly in the tire radial direction.

The tire <NUM> includes a carcass and a tread reinforcing layer (not illustrated). These are made up of known components as appropriate.

As shown in <FIG>, the tread portion <NUM> of the tire <NUM> according to the present invention has a directional pattern in which the rotation direction R is designated. The rotation direction R is indicated, for example, by letters or symbols on at least one of sidewall portions <NUM> (shown in <FIG>). In some of the figures herein, the rotation direction R is indicated by arrows.

The tread portion <NUM>, for example, includes a crown region Cr, a pair of middle regions Mi, and a pair of shoulder regions Sh.

The crown region Cr is the region having the width of <NUM>/<NUM> of the tread development width TWe, centered at the tire equator C. The shoulder regions Sh are the regions having the width of <NUM>/<NUM> of the tread development width TWe from the respective tread edges Te toward the tire equator C. The middle regions Mi are the regions between the crown region Cr and each of the shoulder regions Sh.

The tread development width TWe is the distance in the tire axial direction between the tread edges Te and Te when the tread portion <NUM> is developed on a plane. The tread edges Te mean the axially outer edges of the respective blocks positioned outermost in the tire axial direction among the blocks arranged in the tread portion <NUM>.

The tread portion <NUM> includes a base surface <NUM> and a plurality of blocks <NUM> protruding outwardly in the tire radial direction from the base surface <NUM>. Outer surfaces in the tire radial direction of the blocks <NUM> extend in parallel with the outer surface of the base surface <NUM>. In the present embodiment of the invention, the blocks <NUM> include a plurality of crown blocks <NUM> on the tire equator C side, a plurality of shoulder blocks <NUM> on the respective tread edge Te sides, and a plurality of middle blocks <NUM> arranged therebetween. The crown blocks <NUM> include outer surfaces in the tire radial direction (meaning the surfaces that come into contact with the ground when the tire is running on a plane, the same shall apply hereinafter) whose centroids are located in the crown region Cr. The middle blocks <NUM> include radially outer surfaces whose centroids are located in the middle regions Mi. The shoulder blocks <NUM> include radially outer surfaces whose centroids are located in the shoulder regions Sh.

In the present invention, the tread portion <NUM> includes at least one first block <NUM>. In the present embodiment of the invention, the tread portion <NUM> includes a plurality of first blocks <NUM> and a plurality of second blocks <NUM> which are arranged alternately in the tire circumferential direction. In the present embodiment of the invention, the first blocks <NUM> and the second blocks <NUM> are configured as the crown blocks <NUM> located in the crown region Cr. Hereinafter, the first blocks <NUM> may be referred to as first crown blocks <NUM>, and the second blocks <NUM> may be referred to as second crown blocks <NUM>.

<FIG> illustrates an enlarged perspective view of one of the first blocks <NUM>, and <FIG> illustrates an enlarged plan view of the first block <NUM>. In this specification, an enlarged plan view showing the outer surface of a block as shown in <FIG> mainly clearly shows the outline of the outer surface of the block, and the structure of the side surfaces and the base of the block may be omitted even if it can be observed in the plan view of the block. As shown in <FIG> and <FIG>, each first block <NUM> includes a pair of block pieces <NUM> adjacent to each other in the tire axial direction, and a tie-bar <NUM> connecting the pair of block pieces <NUM>.

<FIG> illustrates a cross-sectional view taken along the line B-B in <FIG>. As shown in <FIG>, the outer surface <NUM> of the tie-bar <NUM> has a height increasing toward the trailing side in the rotation direction (hereinafter, simply referred to as "trailing side"). In addition, as shown in <FIG>, the outer surface <NUM> of each block piece <NUM> has an axially extending leading edge 16a located on the leading side in the rotation direction R (hereinafter, simply referred to as "leading side") which comes into contact with the ground prior to the trailing edge 16b when the tire rotates in the rotation direction R. The leading edge 16a of each of the pair of block pieces <NUM> is inclined toward the trailing side in the rotation direction R from the end on the tie-bar side thereof outwardly in the block-width direction. By adopting the above configuration, the tire <NUM> according to the present invention can exhibit excellent grip and steering characteristics on soft road surfaces while maintaining running performance on hard road surfaces. The reasons for this are as follows. Note that in this specification, "hard road surfaces" refer to uneven road surfaces which are relatively strongly compacted, and "soft road surfaces" refer to uneven road surfaces which are relatively soft, such as muddy and sandy roads.

In the tire <NUM> according to the present invention, the first blocks <NUM> can have a high rigidity by the tie-bars <NUM>, maintaining running performance on hard road surfaces. In addition, in the present invention, since the tie-bars <NUM> and the leading edges 16a of the block pieces have the above configuration, the leading edges 16a of the first blocks <NUM> and the tie-bars <NUM> can bite the ground more easily when driving on soft road surfaces, providing excellent grip and steering characteristics. For the above reasons, the tire <NUM> according to the present invention can exhibit excellent grip and steering characteristics on soft road surfaces while maintaining running performance on hard road surfaces.

Hereinafter, a more detailed configuration of the present embodiment of the invention will be described. Note that each configuration described below shows a specific aspect of the present embodiment of the invention. Hence, the present invention can exert the above-mentioned effects even if the tire does not include the configuration described below. In addition, if any one of the configurations described below is applied independently to the tire of the present invention having the above-mentioned characteristics, the performance improvement according to each additional configuration can be expected. Further, when some of the configurations described below are applied in combination, it is expected that the performance of the additional configurations will be improved.

As shown in <FIG>, the first blocks <NUM>, for example, are located on the tire equator C. In some more preferred embodiments of the invention, the tie-bars <NUM> of the first blocks <NUM> are located on the tire equator C. In addition, each first block <NUM> is arranged such that the pair of the block pieces <NUM> is lineally symmetric with respect to the tire equator C in a plan view of its outer surface. Thus, the configuration of one of the block pieces <NUM> described below can be applied to each of the pair of block pieces <NUM>.

Preferably, the maximum length L1 in the tire axial direction of the outer surface of each first block <NUM> is in the range from <NUM>% to <NUM>% of the tread development width TWe. In addition, the maximum length L2 in the tire circumferential direction of the outer surface of each first block <NUM> is, for example, in the range from <NUM>% to <NUM>% of the length L1.

As shown in <FIG> and <FIG>, it is preferable that the outer surface <NUM> of each tie-bar <NUM> has a smooth and flat shape. In another embodiment of the invention, the outer surface <NUM> of each or at least one tie-bar <NUM> may include an uneven surface. In some preferred embodiments of the invention, the outer surface <NUM> of each tie-bar <NUM>, in a plan view, has a rectangular shape bounded by two lateral edges parallel to the tire axial direction and two longitudinal edges parallel to the tire circumferential direction.

As shown in <FIG>, the maximum length L4 in the tire circumferential direction of the outer surface <NUM> of each tie-bar <NUM> is preferably in the range from <NUM>% to <NUM>%, more preferably <NUM>% to <NUM>%, of the maximum length L3 in the tire circumferential direction of the outer surface <NUM> of the block pieces <NUM>. When the length L4 of each tie-bar <NUM> is smaller than the length L3 of the block pieces <NUM>, a recess <NUM> can preferably be formed by the tie-bar <NUM> at least on the sidewall of each first block <NUM> on the leading-edge side in the rotation direction R. In other words, the sidewall of the tie-bar <NUM> may be smoothly continuous with the sidewall of the block pieces <NUM> on the trailing edge side in the rotation direction R of the first block <NUM>. In the present embodiment of the invention, as a preferred aspect, the recesses <NUM> are formed by the tie-bar <NUM> on both sidewalls of each first block <NUM> on the leading and trailing sides in the rotation direction R. This allows each first block <NUM> to provide a large grip in each direction of the tire circumferential direction.

As shown in <FIG>, the maximum angle θ1 of the outer surface <NUM> of each tie-bar <NUM> with respect to the tire circumferential direction is, for example, in the range from <NUM> to <NUM> degrees. The angle θ1 is preferably equal to or more than <NUM> degrees, more preferably equal to or more than <NUM> degrees, but preferably equal to or less than <NUM> degrees, more preferably equal to or less than <NUM> degrees. Such a tie-bar <NUM> can improve grip on both soft road surfaces and hard road surfaces in a well-balanced manner. In the present embodiment of the invention, the outer surface <NUM> of each tie-bar <NUM> is configured such that the substantially entire surface is at the angle θ1 described above with respect to the tire circumferential direction. In addition, in the present embodiment of the invention, the contour line formed by the outer surface <NUM> of the tie-bar <NUM> of each first block <NUM> is parallel to the contour line formed by the outer surface <NUM> of the block pieces <NUM> in a cross-sectional view that is orthogonal to the outer surface <NUM> of the block pieces <NUM> and is parallel to the tire axial direction (not shown).

In each first block <NUM>, the height h2 at the end 17a on the leading side of the outer surface <NUM> of the tie-bar <NUM> is, for example, in the range from <NUM>% to <NUM>% of the maximum height h1 of the outer surface <NUM> of the block pieces <NUM>. The height h2 of the tie-bar <NUM> is preferably equal to or less than <NUM>% of the height h1 of the block pieces <NUM>, more preferably equal to or less than <NUM>%. In addition, in each first block <NUM>, the height h3 at the end 17b on the trailing side of the outer surface <NUM> of the tie-bar <NUM> is, for example, in the range from <NUM>% to <NUM>%, more preferably from <NUM>% to <NUM>%, of the maximum height h1 of the outer surface <NUM> of the block pieces <NUM>.

In another embodiment of the invention, the height h3 at the end 17b on the trailing side of the outer surface <NUM> of the tie-bar <NUM> may be the same as the height h1 of the outer surface <NUM> of the block pieces <NUM>, as indicated by the two-dotted chain line in <FIG>. Such a tie-bar <NUM> can increase the rigidity of each first block <NUM>, and can improve grip performance and steering characteristics on hard road surfaces.

As shown in <FIG>, in each first block <NUM>, the maximum length L3 in the tire circumferential direction of the outer surface <NUM> of the block pieces <NUM> is the same as the maximum length L2 (shown in <FIG>) in the tire circumferential direction of the outer surface of the first block <NUM>. In addition, a length L5 in the tire axial direction of the outer surface <NUM> of each block piece <NUM> is, for example, in the range from <NUM>% to <NUM>% of the maximum length L1 in the tire axial direction of the outer surface of the first block <NUM>.

The outer surface <NUM> of each block piece <NUM> is surrounded by the leading edge 16a, the trailing edge 16b, a circumferentially extending inner longitudinal edge 16c on the tie-bar <NUM> side, and a circumferentially extending outer edge 16d on the tread edge Te side. As a result, the outer surface <NUM> of each block piece <NUM> has a pentagonal shape.

In the present embodiment of the invention, the leading edge 16a, for example, extends straight. In another embodiment of the invention, the leading edge 16a may extend in an arc-shape that is concave toward the center of the outer surface <NUM> of each block piece <NUM>, as indicated by the two-dot chain line in <FIG>. In such an embodiment of the invention, the corners of the block pieces <NUM> can easily bite road surfaces, improving grip performance further on soft road surfaces.

An angle θ2 of the leading edge 16a of each block piece <NUM> is, for example, equal to or more than <NUM> degrees with respect to the tire circumferential direction, preferably equal to or more than <NUM> degrees, more preferably equal to or more than <NUM> degrees. In addition, the angle θ2 is preferably equal to or less than <NUM> degrees. Such a leading edge 16a can improve grip performance on soft road surfaces while suppressing uneven wear of the block piece <NUM>.

In the present embodiment of the invention, the trailing edge 16b of each of the block pieces <NUM> is inclined toward the leading side in the rotation direction R from an end on the tie-bar side thereof outwardly in the block-width direction. The block pieces <NUM> with these trailing edges 16b can bite the ground more easily and help to further improve the steering characteristics on soft and hard road surfaces.

The trailing edge 16b of each of the block pieces <NUM>, for example, extends straight. In another embodiment of the invention, the trailing edge 16b may extend in an arc-shape that is concave toward the center of the outer surface <NUM> of each block piece <NUM>, as indicated by the two-dot chain line in <FIG>. Such an embodiment of the invention can further improve the grip performance and steering characteristics on soft road surfaces.

The maximum angle θ3 with respect to the tire circumferential direction of the trailing edge 16b of each block piece <NUM>, for example, is equal to or more than <NUM> degrees, preferably equal to or more than <NUM> degrees, more preferably equal to or more than <NUM> degrees. In some preferred embodiments of the invention, the angle θ3 of the trailing edge 16b is preferably greater than the angle θ2 of the leading edges 16a with respect to the tire circumferential direction. The difference between the angles θ2 and θ3 is, for example, equal to or less than <NUM> degrees, preferably equal to or less than <NUM> degrees. This can improve the steering and gripping performance on soft and hard road surfaces while suppressing uneven wear of the block pieces <NUM>.

The inner longitudinal edge 16c of each block piece <NUM>, for example, extends straight in parallel with the tire circumferential direction. On the other hand, the outer longitudinal edge 16d of each block piece <NUM> is preferably bent to protrude toward the tread edge Te. For example, the outer longitudinal edge 16d includes two edges inclined in opposite directions with respect to the tire circumferential direction and these edges extend at an angle of equal to or less than <NUM> degrees with respect to the tire circumferential direction. Such an outer longitudinal edge 16d can help to enhance steering performance.

<FIG> illustrates an enlarged perspective view of one of the second blocks <NUM>, and <FIG> illustrates an enlarged plan view the second block <NUM>. As shown in <FIG> and <FIG>, the outer surface <NUM> of each second block <NUM> has a hexagonal shape. The area of the outer surface <NUM> of each second block <NUM> is preferably smaller than the sum of the areas of the outer surfaces <NUM> of the block pieces <NUM> of each first block <NUM>. Such a second block <NUM> can bite the ground easily even on hard road surfaces, and can enhance the grip and steering characteristics on hard road surfaces.

Each second block <NUM> is configured as a plain block with no recessed elements such as grooves or sipes on its outer surface <NUM>. In this specification, the term "sipe" refers to a cut having a narrow width, and the width between two inner walls facing each other is equal to or less than <NUM>.

As shown in <FIG>, the outer surface <NUM> of each second block <NUM> includes a leading end 12e on the leading side in the rotation direction R, a first edge 12a extending to one side in the tire axial direction from the leading end 12e, and a second edge 12b extending to the other side in the tire axial direction from the leading end 12e. In addition, each of the first edge 12a and the second edge 12b are inclined from the leading end 12e outwardly in the block-width direction toward the trailing side in the rotational direction R. An angle θ4 of the first edge 12a with respect to the tire circumferential direction and an angle θ5 of the second edge 12b with respect to the tire circumferential direction, for example, are in the range from <NUM> to <NUM> degrees, preferably from <NUM> to <NUM> degrees. Thus, the second blocks <NUM> can provide a well-balanced grip force in the tire circumferential direction and tire axial direction.

Similarly, the outer surface <NUM> of each second block <NUM> includes a trailing end 12f on the trailing side in the rotation direction R, a third edge 12c extending to one side in the tire axial direction from the trailing end 12f, and a fourth edge 12d extending to the other side in the tire axial direction from the trailing end 12f. In addition, each of the third edge 12c and the fourth edge 12d are inclined from the trailing end 12f outwardly in the block-width direction toward the leading side in the rotational direction R. An angle θ6 of the third edge 12c with respect to the tire circumferential direction and an angle θ7 of the fourth edge 12d with respect to the tire circumferential direction, for example, are in the range from <NUM> to <NUM> degrees, preferably from <NUM> to <NUM> degrees.

In the present embodiment of the invention, the first edge 12a and the second edge 12b extend straight. In addition, the third edge 12c and the fourth edge 12d extend straight. In another embodiment of the invention, each of the first edge 12a and the second edge 12b may extend in an arc-shape that is concave toward the center of the outer surface <NUM> of the second block <NUM>. Similarly, each of the third edge 12c and the fourth edge 12d may extend in an arc-shape that is concave toward the center of the outer surface <NUM> of the second block <NUM>. In such an embodiment of the invention, each second block <NUM> can bite the ground more easily on soft road surfaces, and grip performance and steering characteristics on soft road surfaces can be improved further.

As shown in <FIG>, in the present embodiment of the invention, the first blocks <NUM> described above are configured as the first crown blocks <NUM> provided in the crown region Cr, and the second blocks <NUM> described above are configured as the second crown blocks <NUM> provided in the crown region Cr. In such an embodiment of the invention, these blocks can provide a large grip force in the tire circumferential direction when driving straight and when turning at relatively small camber angles, and can exhibit excellent braking performance.

In the present invention, the plurality of middle blocks <NUM> provided in the tread portion <NUM> include at least one first middle block <NUM> and at least one second middle block <NUM>, and the area of the outer surface of the second middle block <NUM> is larger than the area of the outer surface of the first middle block <NUM>. Note that the area of the outer surface means the area in a state in which all recessed elements such as sipes and grooves provided on the outer surface are filled. In the present embodiment of the invention, a plurality of first middle blocks <NUM> and a plurality of second middle blocks <NUM> are alternately arranged in the tire circumferential direction.

<FIG> illustrates an enlarged perspective view of one of the first middle blocks <NUM> in <FIG>. <FIG> illustrates an enlarged perspective view of one of the second middle blocks <NUM> in <FIG>. <FIG> is an enlarged plan view of one of the first middle blocks <NUM> and one of the second middle blocks <NUM> in <FIG>. Note that a part of the area between the first middle block <NUM> and the second middle block <NUM> is omitted in <FIG>. As shown in <FIG>, as a preferred aspect, in the present embodiment of the invention, the outer surface <NUM> of each first middle block <NUM> is not provided with any sipe, and the outer surface <NUM> of each second middle block <NUM> is provided with at least one sipe <NUM>.

As a result, the rigidity of each first middle block <NUM> can be maintained to improve slide controllability on hard road surfaces, while the rigidity of each second middle block <NUM> can be relaxed by the sipes <NUM>, improving slide controllability on soft road surfaces. Hence, the tire <NUM> according to the present embodiment of the invention can exhibit stable slide controllability on both soft and hard road surfaces. Note that in this specification, "exhibit stable slide controllability" means that sudden sliding is difficult to occur and that the amount of sliding is easy to control, and that the above characteristics can be demonstrated without much influence from the road surfaces.

As shown in <FIG>, preferably, the first middle block <NUM> is configured as a plain block without any grooves, sipes or other recessed elements on its outer surface <NUM>. Preferably, the area of the outer surface <NUM> of each first middle block <NUM> is equal to or more than <NUM>% of the area of the outer surface <NUM> of each second middle block <NUM> (whose sipes <NUM> are filled). Thus, the grip performance on hard road surfaces can be improved.

As shown in <FIG>, an outer surface <NUM> of each first middle block <NUM> includes a leading edge 21a, a trailing edge 21b, an inner longitudinal edge 21c, and an outer longitudinal edge 21d. The leading edge 21a extends in the tire axial direction on the leading side in the rotation direction R. The trailing edge 21b extends in the tire axial direction on the trailing side. The inner longitudinal edge 21c extends in the tire circumferential direction from the end of the tire equator C side of the leading edge 21a to the trailing edge 21b. The outer longitudinal edge 21d extends from the end of the tread edge Te side of the leading edge 21a to the trailing edge 21b.

The leading edge 21a of each first middle block <NUM>, for example, is inclined with respect to the tire axial direction. As a preferred embodiment of the invention, the leading edge 21a of each first middle block <NUM> is inclined toward the trailing side in the rotation direction R from the tread edge Te side (right side in <FIG>) to the tire equator C side (left side in <FIG>). Each first middle block <NUM> having such a leading edge 21a can guides mud, soil and the like to the crown region Cr (shown in <FIG>) when running on soft road surfaces, thereby further improving braking performance.

As angle θ8 between the leading edge 21a and the inner longitudinal edge 21c is, for example, equal to or more than <NUM> degrees, preferably in the range from <NUM> to <NUM> degrees. Thus, the corner between the leading edge 21a and the inner longitudinal edge 21c can have high rigidity, improving slide controllability on hard road surfaces. On the other hand, an angle θ9 between the leading edge 21a and the outer longitudinal edge 21d is smaller than the angle θ8. For example, the angle θ9 is in the range from <NUM> to <NUM> degrees. This makes it easier for the corner between the leading edge 21a and the outer longitudinal edge 21d to be moderately deformed, so that the first middle blocks <NUM> can easily remove the mud and soil attached thereto when driving on soft road surfaces.

For example, in each first block <NUM>, an angle of the trailing edge 21b with respect to the tire axial direction is smaller than an angle of the leading edge 21a with respect to the tire axial direction. Specifically, the angle of the trailing edge 21b with respect to the tire axial direction is equal to or less than <NUM> degrees. This allows the trailing edge 21b to provide a large friction force in the tire circumferential direction on soft road surfaces, improving braking performance.

In each first block <NUM>, the inner longitudinal edge 21c is recessed toward the centroid of the outer surface <NUM> by connecting two straight edges. Similarly, the outer longitudinal edge 21d is recessed toward the centroid of the outer surface <NUM> by connecting two straight edges. As a result, the block sidewalls connected to the inner longitudinal edge 21c and the outer longitudinal edge 21d are recessed, so that these block sidewalls can push away dirt and mud on soft road surfaces and provide a large reaction force, improving cornering performance.

An angle θ10 between the two edges of the inner longitudinal edge 21c, for example, is in the range of from <NUM> to <NUM> degrees. An angle θ11 between the two edges of the outer longitudinal edge 21d, for example, is smaller than the angle θ10, and the angle θ11 is in the range from <NUM> to <NUM> degrees, for example. This makes it possible to demonstrate stable slide controllability in various road surface conditions.

As shown in <FIG>, each first middle block <NUM> is preferably adjacent to one of the second crown blocks <NUM>. Specifically, in a plan view of the tread portion <NUM>, the respective virtual areas <NUM> in which the respective first middle blocks <NUM> are expanded parallel to the tire axial direction preferably overlaps the respective second crown blocks <NUM> at least partially. By arranging the blocks in this way, the effects described above can be reliably obtained.

As shown in <FIG> and <FIG>, the outer surface <NUM> of each second middle block <NUM> is provided with a plurality of sipes <NUM> (e.g., two sipes). The sipes <NUM> traverse completely the outer surface <NUM> of the second middle block <NUM> in the tire axial direction.

As shown in <FIG>, the sipes <NUM> extend straight. Additionally, the sipes <NUM> are arranged non-parallel to each other. In some preferred embodiment of the invention, a circumferential length of a part of block between the sipes <NUM> increases toward the tread edge Te side (right side in <FIG>). An angle θ12 between the sipes <NUM>, for example, is in the range from <NUM> to <NUM> degrees. Thus, in each second middle block <NUM>, while the rigidity on the tread edge Te side can be improved, the rigidity on the tire equator C side (left side in <FIG>) can be moderately deformable. This can prevent dirt and mud from clogging between the crown blocks <NUM> and the middle blocks <NUM>.

Each sipe <NUM> includes a pair of sipe walls, and a width between the sipe walls is preferably in the range from <NUM> to <NUM>. In the present embodiment of the invention, the width of the sipes <NUM> is substantially constant in the depth direction of the sipe <NUM>. However, a chamfer portion having a width of equal to or more than <NUM> may be provided on the opening of one or more sipes <NUM>, and/or a flask bottom having a width of equal to or more than <NUM> may be provided with the bottom of one or more sipes <NUM>.

As shown in <FIG>, each second middle block <NUM> includes a first portion <NUM> sectioned between the sipes <NUM>, and two second portions <NUM> located on both outer sides of the first portion <NUM>. In addition, the first portion <NUM> and the second portions <NUM> have different heights. In this specification, the height of each part of a block means the distance in the normal direction from the imaginary bottom at the base of the block to the outer surface of each part passing through said imaginary bottom. The imaginary bottom is the bottom extending along the base surface <NUM> bounded by the ridge formed by the side walls of the block and the base surface <NUM> of the tread portion <NUM>. If the outer surface of the block is non-parallel to the imaginary base, the height of the block means its maximum height.

In the present embodiment of the invention, the maximum height of the first portion <NUM> is greater than the maximum height of the second portions <NUM>. In some preferred embodiments of the invention, the entire outer surface of the first portion <NUM> protrudes beyond the outer surfaces of the second portions <NUM>. The difference between the maximum height of the first portion <NUM> and the maximum height of the second portions <NUM>, for example, is equal to or less than <NUM>, preferably equal to or less than <NUM>. Thus, the first portion <NUM> can provide a large frictional force while suppressing uneven wear of the first portion <NUM>. The maximum height of the second portions <NUM> may be greater than the maximum height of the first portion <NUM>.

As shown in <FIG>, the outer surface <NUM> of each first portion <NUM> includes an outer longitudinal edge 31d extending in the tire circumferential direction on the tread edge Te side and an inner longitudinal edge 31c extending in the tire circumferential direction on the tire equator C side. In each first portion <NUM>, the actual length of the inner longitudinal edge 31c of each first portion <NUM> (the actual length is the length along the edge, hereafter the same) is smaller than the actual length of the outer longitudinal edge 31d. However, the actual length of the inner longitudinal edge 31c is preferably equal to or more than <NUM>. Specifically, the actual length of the inner longitudinal edge 31c is in the range from <NUM>% to <NUM>% of that of the outer longitudinal edge 31d. As a result, excellent grip performance can be exhibited on soft and hard road surfaces. Note that the inner longitudinal edge 31c does not include the edge extending along the sipes <NUM>.

In a plan view of the outer surface <NUM> of each second middle block <NUM>, it is preferable that the outer surface <NUM> of the first portion <NUM> includes a projection <NUM> (dotted in <FIG>) that projects outwardly in the block-width direction from the virtual extensions 32v of the longitudinal edge 32c of the outer surface <NUM> of the second portions <NUM>. Such a protrusion <NUM> can provide multi-directional friction force on soft road surfaces and can remove mud and soil from between blocks of the tread portion <NUM>. Note that the protrusion <NUM> means the area protruding outward in the block-width direction from the virtual extension lines 32v of both of two second portions <NUM>.

The protrusion <NUM> is preferably arranged on the tire equator C side. In addition, an area of the protrusion <NUM>, for example, is equal to or less than <NUM>% of the entire area of the outer surface <NUM> of the first portion <NUM>, preferably equal to or less than <NUM>%. This can suppress uneven wear of the protrusion <NUM> while achieving the above-mentioned effect.

Preferably, each of the second portions <NUM> has a length in the tire circumferential direction decreasing toward the tread edge Te side. This can improve the slide controllability further.

The outer surface <NUM> of each second middle block <NUM> includes a leading edge 22a, a trailing edge 22b, an inner longitudinal edge 22c, and an outer longitudinal edge 22d. The leading edge 22a extends in the tire axial direction on the leading side in the rotation direction R. The trailing edge 22b extends in the tire axial direction on the trailing side. The inner longitudinal edge 22c extends in the tire circumferential direction from the end on the tire equator C side of the leading edge 22a to the trailing edge 22b. The outer longitudinal edge 22d extends in the tire circumferential direction from end on the tread edge Te side of the leading edge 22a to the trailing edge 22b.

In each second middle block <NUM>, the leading edge 22a, for example, is inclined with respect to the tire axial direction. In some preferred embodiments of the invention, the leading edge 22a of the second middle block <NUM> is inclined toward the trailing side in the rotation direction R from the tire equator C side to the tread edge Te side (right side in <FIG>). In other words, the leading edge 22a of each second middle block <NUM> is inclined in the opposite direction with respect to the tire axial direction to the leading edge 21a of each first middle block <NUM>. As a result, the middle blocks can provide frictional force in multiple directions, demonstrating excellent braking performance.

In each second middle block <NUM>, an angle θ13 between the leading edge 22a and the inner longitudinal edge 22c is, for example, in the range from <NUM> to <NUM> degrees. In some preferred embodiments of the invention, the angle θ8 between the leading edge 21a and the inner longitudinal edge 21c of each first middle block <NUM> is greater than the angle θ13 between the leading edge 22a and the inner longitudinal edge 22c of each second middle block <NUM>. This can improve slide controllability on various road surfaces further.

An angle θ14 between the leading edge 22a and the outer longitudinal edge 22d of each second middle block <NUM> is, for example, in the range from <NUM> to <NUM> degrees. Thus, the corner between the leading edge 22a and the outer longitudinal edge 22d has high rigidity, improving slide controllability on hard road surfaces.

The trailing edge 22b of each second middle block <NUM>, for example, is inclined in the opposite direction with respect to the tire axial direction to the leading edge 22a of each second middle block <NUM>. In some preferred embodiments of the invention, an angle of the trailing edge 22b of each second middle block <NUM> with respect to the tire axial direction is greater than an angle of the trailing edge 21b of the first middle block <NUM> with respect to the tire axial direction. As a result, the first middle blocks <NUM> and the second middle blocks <NUM> have different rigidity in the tire circumferential direction, improving slide control performance on various road surfaces.

The inner longitudinal edge 22c of each second middle block <NUM> extends in a zigzag manner due to longitudinal edges of the first portion <NUM> and the second portions <NUM>. In addition, the outer longitudinal edge 22d of each second middle block <NUM> is recessed toward the centroid of the outer surface <NUM> by connecting two straight edges. This can provide excellent cornering performance.

As shown in <FIG>, it is preferable that the second middle blocks <NUM> are adjacent to the respective first crown blocks <NUM>. Specifically, in a plan view of the tread portion <NUM>, the respective virtual areas <NUM> in which the second middle blocks <NUM> are expanded parallel to the tire axial direction preferably overlap the respective first crown blocks <NUM> at least partially. Such an arrangement of the blocks can ensure the above-mentioned effect.

As shown in <FIG> and <FIG>, the tread portion <NUM> includes at least one shoulder block <NUM> that is located on the tread edge Te side with respect to the middle blocks <NUM>, and a shoulder tie-bar <NUM> that connects the shoulder block <NUM> with one of the middle blocks <NUM>. In some preferred embodiments of the invention, a plurality of shoulder blocks <NUM> are arranged in the tire circumferential direction, and the shoulder blocks <NUM> are connected with the respective middle blocks <NUM> by the shoulder tie-bars <NUM>. These shoulder blocks <NUM> and shoulder tie-bars <NUM> can further improve grip performance in the tire circumferential direction.

As shown in an enlarged perspective view of a block (for example, <FIG>), the block sidewalls of each block extend in a block height direction such that their generating lines have the same characteristics as the edges of the outer surface of the block.

Claim 1:
A two-wheeled vehicle tire (<NUM>) for running on rough terrain, the tire (<NUM>) comprising:
a tread portion (<NUM>) having a designated rotation direction (R), the tread portion (<NUM>) comprising at least one first block (<NUM>), wherein
the at least one first block (<NUM>) comprises a pair of block pieces (<NUM>) adjacent to each other in a tire axial direction, and a tie-bar (<NUM>) connecting the pair of block pieces (<NUM>),
the tie-bar (<NUM>) has an outer surface (<NUM>) in a tire radial direction, and
the pair of block pieces (<NUM>) each has an outer surface (<NUM>) in the tire radial direction, the outer surface (<NUM>) of each block piece (<NUM>) having an axially extending leading edge (16a) located on a leading side in the rotation direction (R),
characterized in that
the outer surface (<NUM>) of the tie-bar (<NUM>) has a height increasing toward a trailing side in the rotation direction (R), and
the leading edge (16a) of each of the pair of block pieces (<NUM>) is inclined toward the trailing side in the rotation direction (R) from an end on a tie-bar (<NUM>) side thereof outwardly in a block-width direction.