Patent Description:
The following Patent Document <NUM> discloses a pneumatic tire in which the tread portion is provided with blocks.

The block has a ground contacting top surface having a heel-side edge, and a heel-side side wall surface extending radially inwardly from the heel-side edge while inclining toward the toe side in the tire rotation direction.

Such block is explained as being capable of exerting a large shearing force and deeply digging into mud or soft ground. Patent Document <NUM>: <CIT>.

A tire in accordance with the preamble of claim <NUM> is known from <CIT>. Related tires are described in <CIT>, <CIT> (document according to Article <NUM>(<NUM>) EPC), <CIT>, <CIT> (document according to Article <NUM>(<NUM>) EPC) and <CIT>.

In recent years, it is desired that tires for traveling on rough terrain have further improved traction performance on rough terrain.

The present invention was made in view of the above circumstances, and
a primary object of the present invention is to provide a tire for running on rough terrain in which the traction performance on rough terrain can be further improved.

The object is solved by a tire having the features of claim <NUM>. Sub-claims are directed to preferable embodiments of the invention.

According to the present invention, a tire for running on rough terrain for which an intended tire rotational direction is specified, comprises a tread portion provided with blocks raised from a tread base portion,
wherein
each of the blocks has.

According to an embodiment of the present invention, said vertical cross section is that at a center position in the tire axial direction of the block.

According to an embodiment of the present invention, in the vertical cross section of the block, when a first straight line is drawn from the first edge to a position on the first side wall surface which is separated radially inwardly from the first edge by <NUM>% of the radial height of the block, the angle α of the first straight line is not more than <NUM> degrees with respect to a straight line drawn normally to the ground contacting top surface at the first edge.

According to an embodiment of the present invention, the ground contacting top surface has a second edge extending in the tire axial direction on the toe side in the tire rotation direction, wherein each of the blocks has a second side wall surface extending radially inwardly from the second edge, and in the vertical cross section, the second side wall surface is inclined toward the toe side in the tire rotation direction from the second edge toward the inside in the tire radial direction.

According to an embodiment of the present invention, in the vertical cross section, the angle β of a second straight line drawn from the second edge to a position on the second side wall surface separated radially inwardly from the second edge by <NUM>% of the block height, with respect to a straight line drawn normally to the ground contacting top surface at the second edge is larger than the angle α of a first straight line drawn from the first edge to a position on the first side wall surface separated radially inwardly from the first edge by <NUM>% of the block height, with respect to a straight line drawn normally to the ground contacting top surface at the first edge.

According to an embodiment of the present invention, the angle β is in a range from <NUM> to <NUM> degrees.

According to an embodiment of the present invention, the blocks include a crown block disposed on the tire equator, and the first edge of the crown block is formed in a V shape convex toward the toe side in the intended tire rotation direction.

According to an embodiment of the present invention, the angle of the first edge of the crown block with respect to the tire axial direction is in a range from <NUM> to <NUM> degrees.

According to an embodiment of the present invention, the blocks include a middle block located axially outside the crown block, and the first edge of the middle block is substantially located on a virtual straight line extended axially outwardly from the first edge of the crown block.

In the tire for running on rough terrain according to the present invention, the traction performance on rough terrain is further improved by the above configuration.

The present invention is suitably applied to a tire for a motorcycle, but may be applied to tires for passenger cars, heavy duty vehicles and the like. Further, the present invention can be applied to not only pneumatic tires but also non-pneumatic tires so called airless tires.

<FIG> is a partial plan view of a tread portion of a tire for running on rough terrain showing a conceptual simple example of the block according to the present invention.

According to the present invention, the tire <NUM> for running on rough terrain has an intended tire rotational direction N specified therefor.

The tire <NUM> comprises a tread portion provided with blocks <NUM> raised from a tread base portion 2R.

<FIG> shows the top view of a conceptual simple example of the block <NUM>.

According to the present invention, the planar shape of the block <NUM> is not limited to such example, and various shapes may be adopted.

Each of the blocks <NUM> has: a ground contacting top surface <NUM> having a first edge 10e extending in the tire axial direction on the heel side in the intended tire rotation direction N; and a first side wall surface <NUM> extending radially inwardly from the first edge 10e.

The shape of the ground contacting top surface <NUM> of the block <NUM> is not limited to the one shown in <FIG>, and various shapes may be adopted.

<FIG> is a cross-sectional view of the block <NUM> taken along line A-A of <FIG>.

This cross-sectional view shows a vertical cross section parallel to the tire circumferential direction.

This vertical cross section is at the mid position of the block <NUM> in the tire axial direction.

In the vertical cross section, the first side wall surface <NUM> comprises a radially outer portion <NUM> and a radially inner portion <NUM> as shown in <FIG>.

The radially outer portion <NUM> extends substantially straight and radially inwardly from the first edge 10e, while inclining toward the toe side in the intended tire rotation direction N at an inclination angle with respect to a straight line "n" drawn normally to the top surface <NUM> at the first edge 10e.

The radially inner portion <NUM> extends from the radially outer portion <NUM> to the tread base portion 2R in an arc shape.

<FIG> schematically show how the block <NUM> can be deeply pierced into the ground (f) in chronological order.

In the first side wall surface <NUM>, as shown in <FIG>, the force due to the tire rotation is applied to the radially outer portion <NUM> as a rotational force with the arc-shaped radially inner portion <NUM> as a fulcrum, and can exert an increased shear force. As a result, the first side wall surface <NUM> can be deeply pierced into the ground (f).

Here, the expression "extend substantially straight" means to extend parallel to not only a perfect straight line having an infinite radius of curvature but also an arc line having a radius of curvature of at least <NUM>.

As shown in <FIG>, the length H1 in the tire radial direction of the radially outer portion <NUM> is in a range from <NUM>% to <NUM>% of the block height Ha of the block <NUM> in the tire radial direction from the ground contacting top surface <NUM> to the tread base portion 2R.

Since the length H1 is <NUM>% or more of the block height Ha, the radially outer portion <NUM> can be deeply pierced into the ground (f).

Since the length H1 is <NUM>% or less of the block height Ha, the radially inner portion <NUM> is suppressed from becoming smaller, and the rigidity of the radially inner portion <NUM> is maintained high, so the first side wall surface <NUM> is suppressed from falling to the toe side of the intended tire rotation direction N.

Further, such first side wall surface <NUM> suppresses the radially inner portion <NUM> from cracking or chipping.

Therefore, the block <NUM> according to the present embodiment of the invention can improve the traction performance on rough terrain and can sustain this effect for a long time.

Further, such block <NUM> enhances the instantaneous force on rough terrain.

From such view points, the length H1 of the radially outer portion <NUM> is preferably not less than <NUM>%, but preferably not more than <NUM>% of the block height Ha of the block <NUM>.

In this application including specification and claims, various dimensions, positions and the like of the tire <NUM> refer to those under the normal state of the tire unless otherwise noted.

The normal state is such that the tire is mounted on a standard wheel rim and inflate to a standard pressure but loaded with no tire load.

The standard wheel rim is a wheel rim officially approved or recommended for the tire by standards organizations, i.e. JATMA (Japan and Asia), T&RA (North America), ETRTO (Europe), TRAA (Australia), STRO (Scandinavia), ALAPA (Latin America), ITTAC (India) and the like which are effective in the area where the tire is manufactured, sold or used.

The standard pressure is the air pressure for the tire specified by the same organization in the Air-pressure/Maximum-load Table or similar list, i.e. the "maximum air pressure" in JATMA, the "Inflation Pressure" in ETRTO, the maximum pressure given in the "Tire Load Limits at Various Cold Inflation Pressures" table in TRA or the like.

In the present embodiment of the invention, the radially inner portion <NUM> has a single radius of curvature.

Since such radially inner portion <NUM> relaxes the stress concentration acting on the radially inner portion <NUM>, the traction performance is further enhanced.

The radially inner portion <NUM> may be formed by an arc having a multi-radius curvature.

The radius of curvature R1 of the radially inner portion <NUM> is set in a range from <NUM> to <NUM>.

Since the radius of curvature Rs is <NUM> or more, the stress concentration acting on the radially inner portion <NUM> is reduced.

Since the radius of curvature R1 is <NUM> or less, the rigidity of the radially inner portion <NUM> is maintained high.

When the radially inner portion <NUM> is formed by a plurality of arcs having different radii of curvature, the radius of a circle passing through three points: the radially outermost end, the radially innermost end, and the intermediate point therebetween (not shown) of the radially inner portion <NUM> is adopted as the radius of curvature of the radially inner portion <NUM>.

In the above-mentioned vertical cross section of the block <NUM>, the angle α of a first straight line X1 is preferably not more than <NUM> degrees with respect to the straight line "n" drawn normally to the top surface <NUM> at the first edge 10e, wherein the first straight line X1 is a straight line drawn from the first edge 10e to a position P1 on the first side wall surface <NUM> which is separated radially inwardly from the first edge 10e by <NUM>% of the block height Ha of the block <NUM>.

Thereby, the rigidity of the block <NUM> is ensured, and the first side wall surface <NUM> can be deeply pierced into the ground.

If the angle α is small, the amount of mud excavated during shearing may be small.

From such a viewpoint, the angle α is preferably not less than <NUM> degrees, but preferably not more than <NUM> degrees, more preferably not more than <NUM> degrees.

The ground contacting top surface <NUM> of the block <NUM> has a second edge 10i extending in the tire axial direction on the toe side in the intended tire rotation direction N as shown in <FIG>, and
the block <NUM> has a second side wall surface <NUM> extending radially inwardly from the second edge 10i as shown in <FIG>.

In the above-mentioned vertical cross section, the second side wall surface <NUM> is inclined toward the toe side in the intended tire rotation direction N, while extending radially inwardly from the second edge 10i.

Such second side wall surface <NUM> increases the rigidity of the block <NUM> and prevents the block <NUM> from falling toward the toe side in the intended tire rotation direction N when the block <NUM> contacts with the ground.

The second side wall surface <NUM> in this example comprises a first portion <NUM> extending radially inwardly from the second edge 10i, a second portion <NUM> extending radially inwardly from the first portion <NUM> while inclining more gently than the first portion <NUM>, and a third portion <NUM> extending radially inwardly from the second portion <NUM> to the tread base portion 2R.

Each of the first portion <NUM> and the second portion <NUM> extends linearly.

The third portion <NUM> is curved in an arc shape.

The third portion <NUM> is curved concavely.

The length H2 in the tire radial direction of the first portion <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the block height Ha of the block <NUM>.

The length H3 in the tire radial direction of the second portion <NUM> is larger than the length H2 in the tire radial direction of the first portion <NUM>.

The length H3 in the tire radial direction of the second portion <NUM> is
preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the block height Ha of the block <NUM>.

The radius of curvature R2 of the third portion <NUM> is larger than the radius of curvature R1 of the radially inner portion <NUM> of the first side wall surface <NUM>.

Thereby, the collapse of the block <NUM> at the time of contacting with the ground is further suppressed.

Although not particularly limited, the radius of curvature R2 of the third portion <NUM> is preferably not less than <NUM>, more preferably not less than <NUM>, but preferably not more than <NUM>, more preferably not more than <NUM>.

In the above-mentioned vertical cross section of the block <NUM>, the angle β of a second straight line X2 with respect to a straight line "n" drawn normally to the top surface <NUM> at the second edge 10i, is preferably set to be larger than the above-mentioned angle α, wherein
the second straight line X2 is a straight line drawn from the second edge 10i to a position P2 on the second side wall surface <NUM> separated radially inwardly from the second edge 10i by <NUM>% of the block height Ha.

In order to effectively derive the above-mentioned function, the angle β is preferably not less than <NUM> degrees, more preferably not less than <NUM> degrees, still more preferably not less than <NUM> degrees, but preferably not more than <NUM> degrees, more preferably not more than <NUM> degrees, still more preferably not more than <NUM> degrees.

<FIG> shows a more specific example of a tread portion <NUM> of the tire <NUM> according to the present invention.

In the present embodiment of the invention shown in <FIG>, the above-described block <NUM> is modified and provided as crown blocks <NUM> disposed on the tire equator C and middle blocks <NUM> disposed axially outside the crown blocks <NUM>.

In the present embodiment of the invention, the tread portion <NUM> is further provided with shoulder blocks <NUM> disposed axially outside the middle blocks <NUM>.

In the present embodiment of the invention, the tread portion <NUM> or tread pattern is line-symmetrical with respect to the tire equator C.

In the present embodiment of the invention, each of the crown blocks <NUM> and the middle blocks <NUM> is provided with the above-described first side wall surface <NUM> comprising the radially outer portion <NUM> and the radially inner portion <NUM>, and the above-described second side wall surface <NUM>.

When running straight, mainly the crown blocks <NUM> and the middle blocks <NUM> contact with the ground, therefore, the tire <NUM> of the present embodiment of the invention is improved in the traction performance when running straight in particular.

The first edge 10e on the heel-side of the crown block <NUM> is formed in a V shape convex toward the toe side in the intended tire rotation direction N.

Since such crown block <NUM> can exert a large shearing force against mud, the traction performance is improved.

An angle θ1 of the first edge 10e with respect to the tire axial direction is preferably not less than <NUM> degrees, more preferably not less than <NUM> degrees, but preferably not more than <NUM> degrees, more preferably not more than <NUM> degrees. The angle θ1 is that of a straight line drawn from each of the axially outer ends e1 of the first edge 10e to the intermediate position e2 in the tire axial direction of the first edge 10e. The axially outer ends e1 are located on the heel side than the intermediate position e2.

In the present embodiment of the invention, the intermediate position e2 is located on the tire equator C.

In such crown block <NUM>, the mud excavated by the first edge 10e can be collected at the center of the crown block <NUM> in the block width direction, and a larger shearing force can be exerted.

Each of the crown blocks <NUM> comprises
a crown block main portion <NUM> formed in a V shape convex toward the toe side in the intended tire rotation direction N, and crown fin portions <NUM> protruding from the crown block main portion <NUM> toward the toe side in the intended tire rotation direction N.

In the crown block <NUM>, when the crown block main portion <NUM> contacts with the ground, the crown fin portions <NUM> suppresses the crown block main portion <NUM> from collapsing toward the toe side, and the mud digging force is maintained. Thereby, the traction performance is improved.

For each crown block <NUM>, only two crown fin portions <NUM> are provided.

<FIG> is a top view of the crown block <NUM>. As shown, the first edge 10e comprises.

The first intermediate portions 15c are inclined at a larger angle with respect to the tire axial direction than the first outer portions 15a and the first inner portion 15b.

Each of the first outer portions 15a and first intermediate portions 15c extends linearly.

The first inner portion 15b is bent at the intermediate position e2 into a V shape.

The axially inner edge portions 16A are connected with each other at the toe-side end 16i of the second edge 10i. The connected axially inner edge portions 16A are bends in a V shape.

Each of the axially outer edge portions 16B extends linearly in this example.

In the present embodiment of the invention, each of the two crown fin portions <NUM> is formed in a parallel quadrilateral shape in the top view of the block.

The crown fin portions <NUM> in this example each have an outer edge 21e in the block width direction, an inner edge 21i in the block width direction, a heel-side edge 21a on the heel side in the intended tire rotation direction N, and a toe-side edge 21b on the toe side in the intended tire rotation direction N.

The outer edge 21e and the inner edge 21i extend in parallel with the tire circumferential direction in this example.

The heel-side edge 21a is positioned on the heel side of the second edge 10i.

Each of the first edge 21a and the second edge 21b extends in parallel with the outer edge portion 16B.

The inner edge 21i, the outer edge 21e, the heel-side edge 21a and the toe-side edge 21b define the radially outer surface 21A of the crown fin portion <NUM>.

In this embodiment of the invention, as shown in <FIG>, the radially outer surface 21A is positioned radially outside the ground contacting top surface <NUM> of the crown block main portion <NUM>.

However, the radially outer surface 21A may be positioned in the same radial height as the ground contacting top surface <NUM> of the crown block main portion <NUM>.

As shown <FIG> and <FIG>, the outer edges 21e of the crown fin portions <NUM> are located on the inside in the block width direction of the axially outer ends 20e of the crown block main portion <NUM>.

Since such crown block <NUM> maintains the deformation of the crown fin portions <NUM> and facilitates ejection of mud clogged between the crown fin portions <NUM>, therefore, the edge effect of the inner edge portion 16A of the crown block main portion <NUM> is increased in particular.

The distance Lb in the tire axial direction between the outer edge 21e of the crown fin portion <NUM> and the axially outer end 20e of the crown block main portion <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the width W1 in the tire axial direction of the crown block main portion <NUM>. Thereby, the deformation of the crown fin portions <NUM> is ensured, and the effect of ejecting mud is enhanced.

As shown in <FIG>, the connection portion K between the crown block main portion <NUM> and the crown fin portion <NUM> is provided with a shallow groove <NUM> for promoting deformation of the crown fin portion <NUM> on the connection portion K side.

Such shallow groove <NUM> helps to smoothly eject the mud clogged between the crown fin portions <NUM>.

The shallow groove <NUM> extends from the inner edge portion 16A to the outer edge portion 16B of the crown block <NUM> so as to surround the connection portion K.

In this example, the shallow groove <NUM> extends along a part of the outer edge 21e, the heel-side edge 21a and a part of the inner edge 21i.

Such shallow groove <NUM> allows the crown fin portions <NUM> and the crown block main portion <NUM> to move almost independently from each other to increase the deformation of the crown fin portion <NUM>, so the traction performance on rough terrain is further enhanced.

In this example, the shallow groove <NUM> extends in a U shape open toward the heel side.

<FIG> is a cross-sectional view taken along line B-B of <FIG>. As shown, the groove depth d1 of the shallow groove <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the block height Ha of the crown block <NUM>.

The width W3 (shown in <FIG>) of the shallow groove <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the width W1 in the tire axial direction of the crown block main portion <NUM>.

Thereby, the above-mentioned action is effectively exhibited, and the rigidity of the crown fin portions <NUM> and the crown block main portion <NUM> is maintained, and large shear forces are ensured.

It is preferable that a distance Ld in the tire circumferential direction between the most heel-side end 25e of the shallow groove <NUM> and the second edge 10i is not more than <NUM>% of a length L2 in the tire circumferential direction of the crown block main portion <NUM>.

Thereby, the rigidity of the crown block main portion <NUM> in the tire circumferential direction is maintained, and the effect of suppressing the collapse of the crown block <NUM> when contacting with the ground is highly exhibited.

The width W1 in the tire axial direction of the crown block main portion <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the developed tread width TW (shown in <FIG>).

The developed tread width TW is the distance between the tread edges Te measured in the tire axial direction along the tread surface of the tread portion <NUM>.

<FIG> shows the top view of the middle block <NUM> and its vicinity.

As shown, in the present embodiment of the invention, the middle block <NUM> is inclined to the heel side in the intended tire rotation direction N from the inside toward the outside in the tire axial direction.

The middle block <NUM> in this example comprises.

The middle block main portion <NUM> has a pair of third edges <NUM> respectively extending from both ends e3 of the first edge 10e toward the toe side in the intended tire rotation direction N.

The pair of third edges <NUM> are a third inner edge 32a adjacent to one of the crown blocks <NUM> in the tire axial direction, and a third outer edge 32b adjacent to one of the shoulder blocks <NUM> in the tire axial direction.

In this example, the middle fin portion <NUM> includes.

The outer middle fin portion 31A is directly connected to the middle block main portion <NUM>.

The axially outer edge <NUM> of the outer middle fin portion 31A and the third outer edge 32b of the middle block main portion <NUM> extend in a straight line.

The inner middle fin portion 31B is connected to the middle block main portion <NUM>, and along the junction between them, a middle shallow groove <NUM> is formed.

The axially inner edge <NUM> of the inner middle fin portion 31B and the third inner edge 32a of the middle block main portion <NUM> extend in a straight line across the middle shallow groove <NUM>. Since the deformation of the inner middle fin portion 31B is promoted by the middle shallow groove <NUM>, the mud clogged between the middle fin portions <NUM> can be smoothly removed.

The middle shallow groove <NUM> has a heel-side groove edge 36a which extends in the longitudinal direction of the groove and forms a part of the second edge 10i of the middle block <NUM>.

The groove width W4 of the middle shallow groove <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the groove width W3 of the shallow groove <NUM> of the crown block <NUM>.

The groove depth (not shown) of the middle shallow groove <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the block height (not shown) of the middle block main portion <NUM>.

The axial width W5 of the middle block main portion <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the developed tread width TW.

As shown in <FIG>, the first edge 10e of the middle block <NUM> is substantially located on a virtual straight line X3 corresponding to an axially outward extension of the first edge 10e of the crown block <NUM>.

Here, the expression "substantially located on a virtual straight line" means not only that the first edge 10e of the middle block <NUM> coincides with the virtual straight line, but also that the maximum distance Le in the tire circumferential direction between the first edge 10e of the middle block <NUM> and the virtual straight line X3 is not more than <NUM>.

As a result, the first edge 10e of the middle block <NUM> and the first edge 10e of the crown block <NUM> function as one long edge, and a large shearing force is exhibited to enhance the traction performance.

<FIG>is a top view of one of the shoulder blocks <NUM>.

As shown, the shoulder block <NUM> in this example is formed in a generally quadrilateral shape, more specifically trapezoidal shape in its top view.

The ground contacting top surface 7a of the shoulder block <NUM> has an axially outer edge <NUM>, an axially inner edge <NUM>, a toe-side edge <NUM>, and a heel-side edge <NUM>.

The axially outer edge <NUM> extends in the tire circumferential direction, and in this example, forms a part of the tread edge Te.

The axially inner edge <NUM> extends in the tire circumferential direction in this example.

The toe-side edge <NUM> extends in parallel with the tire axial direction from the axially outer edge <NUM> toward the axially inner edge <NUM> in this example.

The heel-side edge <NUM> extends from the axially inner edge <NUM> to the axially outer edge <NUM> while inclining with respect to the tire axial direction, for example, toward the intended tire rotation direction N in this example.

Each of the shoulder blocks <NUM> is provided with a shoulder shallow groove <NUM> in this example.

As shown in <FIG>, the shoulder shallow groove <NUM> extends in a V shape in the top view of the shoulder block <NUM>.

Such shoulder shallow groove <NUM> promotes the deformation of the shoulder block <NUM>, and helps to eject the mud clogged between the shoulder block <NUM> and the adjacent middle block <NUM>.

The shoulder shallow groove <NUM> is composed of a circumferential portion <NUM> extending in the tire circumferential direction, and an axial portion <NUM> extending in the tire axial direction.

The circumferential portion <NUM> extends at an angle of not more than <NUM> degrees with respect to the tire circumferential direction.

The axial portion <NUM> extends at an angle of more than <NUM> degrees with respect to the tire circumferential direction.

In this example, the circumferential portion <NUM> extends in parallel with the tire circumferential direction from the toe-side edge <NUM> toward the heel side in the intended tire rotation direction N, and ends within the shoulder block <NUM>.

In this example, the axial portion <NUM> extends from the axially inner edge <NUM> toward the outside in the tire axial direction, and is connected to the end of the circumferential portion <NUM>. The axial portion <NUM> extends in parallel with the heel-side edge <NUM>.

Such shoulder shallow groove <NUM> further promotes deformation of the shoulder block <NUM>.

The groove width W6 of the shoulder shallow groove <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the axial width W7 (<FIG>) of the shoulder block <NUM>.

The groove depth of the shoulder shallow groove <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the block height of the shoulder block <NUM> measured from the ground contacting top surface to the tread base portion 2R.

The axial width W7 of the shoulder block <NUM> is preferably not less than <NUM>%, more preferably not less than <NUM>%, but preferably not more than <NUM>%, more preferably not more than <NUM>% of the developed tread width TW.

It is preferable that the tread rubber (not shown) by which the above-mentioned blocks <NUM> to <NUM> are formed has a rubber hardness of not less than <NUM> degrees, and not more than <NUM> degrees.

Here, the rubber hardness means the durometer A hardness measured at a temperature of <NUM> degrees C according to the Japanese Industrial Standard (JIS) K6253.

While detailed description has been made of a preferable embodiment of the present invention, the present invention can be embodied in various forms within the scope of the appended claims.

Based on the tread pattern shown in <FIG>, pneumatic tires for a rear wheel of a motorcycle for running on rough terrain were experimentally manufactured as test tires (Working example tires Ex. <NUM> and Comprehensive example tires Ref.<NUM>-Ref.<NUM>).

Specifications of the test tires are shown in Table <NUM>.

The test tires were tested for the traction performance, instantaneous power performance, and overall performance, using a 450cc motorcycle for motocross competition having the following rim sizes and tire sizes.

In the test, the rear tire was changed, but the front tire was not changed and an identical tire was used. (tire pressure: <NUM> kPa).

The traction performance, instantaneous power performance and overall performance when the above-mentioned motorcycle was run on rough terrain covered with mud were evaluated by the test rider.

Here, the "traction performance" is an evaluation made by the test rider, of the responsiveness of acceleration when the accelerator was opened during running straight and cornering at a constant speed (or the smoothness of acceleration when the speed was further increased from a state where the speed was already sufficiently increased).

The "instantaneous power performance" is an evaluation made by the test rider, of the responsiveness of acceleration when the accelerator was opened during running straight and cornering at low speed (or the smoothness of acceleration when the speed was increased from a state where the speed was low).

The "overall performance" is an evaluation made by the test rider, of the smoothness of running when accelerating during straight running and cornering, and the comfort of the handle response.

The test rider evaluated each performance on a ten-point scale, and the results are shown in Table <NUM>.

Claim 1:
A tire (<NUM>) for running on rough terrain for which an intended tire rotational direction (N) is specified, and which comprises a tread portion (<NUM>) provided with blocks (<NUM>) raised from a tread base portion (2R),
wherein
each of the blocks (<NUM>) has
a ground contacting top surface (<NUM>) having a first edge (10e) extending in the tire axial direction on the heel side in the tire rotation direction (N), and
a first side wall surface (<NUM>) extending radially inwardly from the first edge (10e),
characterized in that
in a vertical cross section of the block (<NUM>) along the tire circumferential direction, the first side wall surface (<NUM>) comprises
a radially outer portion (<NUM>) extending substantially straight and radially inwardly from the first edge (10e), while inclining toward the toe side in the intended tire rotational direction (N), and
a radially inner portion (<NUM>) extending from the radially outer portion (<NUM>) to the tread base portion (2R) while curving in an arc shape, and
a length (H1) in the tire radial direction of the radially outer portion is in a range from <NUM>% to <NUM>% of a height (Ha) of the block (<NUM>) measured in the tire radial direction from the ground contacting top surface (<NUM>) to the tread base portion (2R),
and the radius of curvature (R1) of the radially inner portion (<NUM>) is in a range from <NUM> to <NUM>.