Patent Description:
<CIT> discloses a pneumatic tyre with a tread portion having a designated mounting direction to a vehicle, the tread portion being provided with outer shoulder lateral grooves and inner shoulder lateral grooves. In a pneumatic tyre, the intersections of the groove edges of the outer shoulder lateral grooves and the outboard tread edge, and the intersections of the groove edges of the inner shoulder lateral grooves and the inboard tread edge are provided at different positions in the tyre circumferential direction.

<CIT> discloses a tyre according to the preamble of claim <NUM>. Similar tyres are known, for example, from <CIT>, <CIT>, <CIT> or <CIT>.

In the above-mentioned pneumatic tyre, the block edges facing the shoulder lateral grooves of the shoulder blocks is slippery with respect to the ground when the vehicle drives or brakes. As a result, there is a problem that heel-and-toe wear (hereinafter may be referred to as "H&T wear") in which the block edges wear at an early stage is likely to occur.

The present invention has been made in view of the above circumstances and has a major object to provide a tyre capable of preventing uneven wear such as H&T wear.

In one aspect of the present invention, a tyre includes a tread portion including axially spaced first and second tread edges that are axially outermost edges of a ground contacting patch of the tyre which occurs under a condition such that a <NUM>% standard tyre load is applied to the tyre placed under a normal state, wherein the normal state is such that the tyre is mounted onto a standard wheel rim and inflated to a standard pressure, a first shoulder land portion including the first tread edge, and a first shoulder circumferential groove located inwardly in a tyre axial direction of and adjacent to the first shoulder land portion and extending continuously in a tyre circumferential direction, wherein the first shoulder land portion is provided with a plurality of first shoulder lateral grooves extending from the first shoulder circumferential groove across the first tread edge, each of the plurality of first shoulder lateral grooves has a pair of first groove walls, and the pair of first groove walls is provided with a pair of first chamfer portions that extends from the first shoulder circumferential groove to a first location beyond the first tread edge. The pair of first chamfer portions has a chamfer width reducing outwardly in the tyre axial direction and terminates at the first location, the first shoulder lateral grooves comprising a pair of non-chamfered groove edges that extends outwardly in the tyre axial direction from the first location of the pair of first groove walls.

An embodiment of the present invention will be explained below with reference to the accompanying drawings. <FIG> is a development view of a tread portion <NUM> of a tyre <NUM> according to an embodiment. As illustrated in <FIG>, the tyre <NUM> according to the present embodiment, for example, is a pneumatic passenger car tyre, especially being a summer tyre. Note that the present invention is not limited to such an aspect and may be used for all-season tyre, heavy-duty tyre, and the like.

The tyre <NUM> according to the present embodiment, for example, includes the tread portion <NUM> having a designated mounting direction to a vehicle. In the present embodiment, the mounting direction to a vehicle is indicated by characters or marks on the sidewall portion, etc. (not shown), for example. Further, the tread portion <NUM>, for example, has an asymmetric pattern (i.e., the tread pattern being not line-symmetrical with respect to the tyre equator C). Alternatively, the tyre <NUM> may be mounted on a vehicle in an unspecified direction, and the tread portion <NUM> may be configured as a symmetrical pattern.

The tread portion <NUM> includes axially spaced first tread edge T1 and second tread edge T2. The tread portion <NUM> according to the present embodiment has a designated mounting direction to a vehicle such that the first tread edge T1 is located on the outside of a vehicle when mounted on the vehicle and the second tread edge T2 is located on the inside of the vehicle when mounted on the vehicle. The first tread edge T1 and the second tread edge T2 are axially outermost edges of a ground contacting patch of the tyre which occurs under a condition such that the tyre <NUM> placed under a normal state is grounded on a plane with a <NUM>% standard tyre load at zero camber angles. The first tread edge T1 and the second tread edge T2 are close to the actual ground contact edges of the tread portion <NUM> when a vehicle is being stopped or traveling straight at a constant speed. Thus, the area located axially inwardly of the first and second tread edges T1 and T2 is always in contact with the ground unless the ground contact pressure becomes excessively low. On the other hand, areas around the first tread edge T1 and the second tread edge T2 tend to have a large change in ground contact pressure.

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

As used herein, the "standard pressure" is a standard pressure officially approved for each tyre by standards organizations on which the tyre 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 used herein, the "standard tyre load" is a tyre load officially approved for each tyre by standards organizations in which the tyre is based, wherein the standard tyre load is the "maximum load capacity" in JATMA, the maximum value given in the above-mentioned table in TRA, and the "Load Capacity" in ETRTO, for example. If a tyre is not based on the standards, or is a non-pneumatic tyre, the standard tyre load refers to the load acting on the tyre when the tyre is under a standard mounting state. The "standard mounting state" refers to a state in which the tyre is mounted on a standard vehicle according to the purpose of use of the tyre, and the vehicle is stationary on a flat road surface while being able to run.

The tread portion <NUM> includes a plurality of circumferential grooves <NUM> extending continuously in the tyre circumferential direction between the first tread edge T1 and the second tread edge T2, and a plurality of land portions divided by the circumferential grooves <NUM>. The tyre <NUM> according to the present embodiment is configured as a so-called five-rib tyre in which the tread portion <NUM> has five ribs divided by four circumferential grooves <NUM>. Note that the present invention is not limited to such an aspect, and the tyre may be configured as a so-called four-rib tyre in which the tread portion <NUM> has four ribs divided by three circumferential grooves <NUM>, for example.

The circumferential grooves <NUM>, for example, include a first crown circumferential groove <NUM>, a second crown circumferential groove <NUM>, a first shoulder circumferential groove <NUM> and a second shoulder circumferential groove <NUM>. The first crown circumferential groove <NUM> and the second crown circumferential groove <NUM> are disposed such that the tyre, heavy tyre equator C is arranged therebetween. The first shoulder circumferential groove <NUM> is disposed between the first crown circumferential groove <NUM> and the first tread edge T1. The second shoulder circumferential groove <NUM> is disposed between the second crown circumferential groove <NUM> and the second tread edge T2.

In the present embodiment, the circumferential grooves <NUM> extend straight in the tyre circumferential direction. Alternatively, the circumferential grooves <NUM> may extend in a zigzag manner.

A distance L1 in the tyre axial direction from the tyre equator C to the first crown circumferential groove <NUM> or the second crown circumferential groove <NUM> is in a range of from <NUM>% to <NUM>% of the tread width TW, for example. A distance L2 in the tyre axial direction from the tyre equator C to the first shoulder circumferential groove <NUM> or the second shoulder circumferential groove <NUM> is in a range of from <NUM>% to <NUM>% of the tread width TW, for example. Note that the tread width TW is a distance in the tyre axial direction from the first tread edge T1 to the second tread edge T2 under the normal state.

Preferably, a groove width W1 of the circumferential grooves <NUM> is at least <NUM>. In some preferred embodiments, the groove width W1 of the circumferential grooves <NUM> is in a range of <NUM>% to <NUM>% of the tread width TW.

The land portions, at least, include a first shoulder land portion <NUM> including the first tread edge T1. In addition, the land portions according to the present embodiment include a second shoulder land portion <NUM> including the second tread edge T2.

Further, the land portions according to the present embodiment include a crown land portion <NUM>, a first middle land portion <NUM> and a second middle land portion <NUM>. The crown land portion <NUM> is defined between the first crown circumferential groove <NUM> and the second crown circumferential groove <NUM>. The first middle land portion <NUM> is defined between the first crown circumferential groove <NUM> and the first shoulder circumferential groove <NUM>. The second middle land portion <NUM> is defined between the second crown circumferential groove <NUM> and the second shoulder circumferential groove <NUM>.

<FIG> is a partial enlarged perspective view of the first shoulder land portion <NUM> of <FIG>. <FIG> is a partial enlarged view of the first shoulder land portion <NUM> of <FIG>. As illustrated in <FIG> and <FIG>, the first shoulder land portion <NUM> is provided with a plurality of first shoulder lateral grooves <NUM> extending from the first shoulder circumferential groove <NUM> across the first tread edge T1.

<FIG> is a cross-sectional view taken along the line A-A of <FIG>. As illustrated in <FIG>, each first shoulder lateral groove <NUM> has a pair of first groove walls <NUM>. The pair of first groove walls <NUM> is provided with a pair of first chamfer portions <NUM> inclined with respect to an outer surface of the first shoulder land portion <NUM>. In addition, as illustrated in <FIG>, in a tread plan view, the pair of first chamfer portions <NUM> extends from the first shoulder circumferential groove <NUM> to a first location beyond the first tread edge T1. The tyre <NUM> according to the present invention can prevent uneven wear such as H&T wear by adopting the above configuration. The reason for this is presumed to be the following mechanism.

In the present invention, the pair of first chamfer portions <NUM> tends to exert a uniform contact pressure on the groove edges on both sides of the first shoulder lateral grooves <NUM>, and thus H&T wear is effectively prevented. In particular, since the pair of first chamfer portions <NUM> extends beyond the first tread edge T1, uneven wear is effectively prevented in the vicinity of the first tread edge T1 where the change in the acting ground pressure is large. In the present invention, it is presumed that such a mechanism can effectively prevent uneven wear such as H&T wear.

In the present invention, due to the pair of first chamfer portions <NUM>, the ground pressure acting on the first shoulder land portion <NUM> may be equalized. By such an action, the first shoulder land portion <NUM> can properly generates a cornering force and improve steering stability at lane changes and gentle curves.

Hereinafter, a more detailed and preferred configuration of the present embodiment will be described. Note that each configuration described below shows a specific aspect of the present embodiment. Thus, the present invention can exert the above-mentioned effects even if the tyre does not include the configuration described below. Further, even if any one of the configurations described below is applied independently to the tyre of the present invention having the above-mentioned characteristics, the performance improvement according to each additional configuration can be expected. Furthermore, 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 illustrated in <FIG>, a chamfer width W2 of the first chamfer portions which is measured along an outer surface of the first shoulder land portion <NUM> is in a range of from <NUM> to <NUM>, for example. Preferably, the chamfer width W2 of the first chamfer portions is equal to or more than <NUM>% of a width W3 (shown in <FIG>) in the tyre axial direction of the ground contact surface of the first shoulder land portion <NUM>, more preferably equal to or more than <NUM>%, and preferably equal to or less than <NUM>%, more preferably equal to or less than <NUM>%.

A chamfer depth d1 of the first chamfer portions <NUM>, for example, is in a range of from <NUM> to <NUM>. An angle θ1 of inclined surfaces 18a of the pair of first chamfer portions <NUM> with respect to the tyre normal is in a range of from <NUM> to <NUM> degrees, for example. Note that the above-mentioned tyre normal is a virtual straight line that passes through the groove edge of the first shoulder lateral grooves <NUM> and extends at a right angle to the outer surface of the first shoulder land portion <NUM>.

As illustrated in <FIG>, the pair of first chamfer portions <NUM> terminates at the first location E1 beyond the first tread edge T1 in the tyre axial direction. The first location E1 is a location within <NUM> from the first tread edge T1.

In a tread plan view, each first chamfer portion <NUM> includes a constant-width portion <NUM> having a constant chamfer width, and a variable-width portion <NUM> having a chamfer width varying in a longitudinal direction of the first shoulder lateral groove <NUM>. The constant-width portion <NUM>, for example, extends axially outwardly from the first shoulder circumferential groove <NUM> to a location just before the first tread edge T1. The variable-width portion <NUM> is connected to the constant-width portion <NUM> and extends across the first tread edge T1. The variable-width portion <NUM> has a chamfer width reducing continuously toward outwardly in the tyre axial direction. Thus, uneven wear around the ends of the first chamfer portions <NUM> can be prevented effectively.

In order to ensure the above effects, a length L3 in the tyre axial direction of the variable-width portion <NUM> is preferably in a range of from <NUM>% to <NUM>% of the width W3 in the tyre axial direction of the ground contacting surface of the first shoulder land portion <NUM>.

Each first shoulder lateral groove <NUM> includes a pair of non-chamfered groove edges <NUM> that extends outwardly in the tyre axial direction from the first location E1 of the pair of first groove walls <NUM>. The non-chamfered groove edges <NUM> mean that the first groove walls <NUM> and the ground contacting surface of the first shoulder land portion <NUM> are directly connected to each other to form edge components that scratch the ground and increase the frictional force when grounding.

In the present embodiment, in a situation where the contact pressure acting on the first shoulder land portion <NUM> increases during braking and an area outside in the tyre axal direction from the first tread edge T1 comes into contact with the ground, the non-chamfered groove edge <NUM> comes into contact with the ground, increasing the frictional force in the tyre circumferential direction, for example. Thus, the non-chamfered groove edges <NUM> can help to improve braking performance on dry and wet roads.

As illustrated in <FIG>, in the present embodiment, the first location E1 is a location within <NUM> from the first tread edge T1. In other words, the distance L4 from the first tread edge T1 to the non-chamfered groove edges <NUM> is equal to or less than <NUM>. This makes it easier for the non-chamfered groove edges <NUM> to come into contact with the ground during braking, and a large frictional force can be obtained.

A length of the non-chamfered groove edges <NUM> which is a periphery length in a view when the tread portion <NUM> is developed on a plane, for example, is in a range of from <NUM>% to <NUM>% of the width W3 in the tyre axial direction of the first shoulder land portion <NUM>. The non-chamfered groove edges <NUM> having such a length can help to improve braking performance effectively.

<FIG> illustrates a cross-sectional view taken along the line B-B of <FIG>. As illustrated in <FIG>, at least one of the first shoulder lateral grooves <NUM> is provided with a first tie-bar <NUM> where a groove bottom thereof raises locally. The first tie-bar <NUM> according to the present embodiment is arranged in an inner end portion in the tyre axial direction of the at least one of the first shoulder lateral grooves <NUM>. The first tie-bar <NUM> can enhance rigidity of the first shoulder land portion <NUM>, improving steering stability.

A length L6 in the tyre axial direction of the first tie-bar <NUM>, for example, is preferably in a range of from <NUM>% to <NUM>% of the width W3 (shown in <FIG>) of the ground contacting surface in the tyre axial direction of the first shoulder land portion <NUM>. When the length in the tyre axial direction of the first tie-bar <NUM> changes depending on the position in the tyre radial direction, the length L6 is measured by the center position of the first tie-bar <NUM> in the tyre radial direction. In addition, a minimum groove depth d3 on the first tie-bar <NUM>, for example, is in a range of from <NUM>% to <NUM>% of the maximum groove depth d2 of the first shoulder lateral groove <NUM>. Such a first tie-bar <NUM> can improve steering stability while ensuring drainage performance of the at least one of the first shoulder lateral grooves <NUM>.

As illustrated in <FIG>, a pitch length P1 in the tyre circumferential direction of the first shoulder lateral grooves <NUM>, for example, is in a range of from <NUM>% to <NUM>% of the width W3 in the tyre axial direction of the ground contacting surface of the first shoulder land portion <NUM>. Thus, steering stability on dry roads and wet performance can be improved in a well-balanced manner. Note that a pitch length P1 is a length in the tyre circumferential direction between axially innermost ends of the groove centerlines of circumferentially adj acent two first shoulder lateral grooves <NUM>.

In some more preferred embodiments, the first shoulder land portion <NUM> includes a plurality of first shoulder blocks <NUM> divided by the plurality of first shoulder lateral grooves <NUM>. In addition, no sipes nor grooves are provided on the first shoulder land portion <NUM> except for the plurality of first shoulder lateral grooves <NUM>. Such a first shoulder land portion <NUM> can have high rigidity and can further improve steering stability.

<FIG> illustrates a partial enlarged view of the second shoulder land portion <NUM>. As illustrated in <FIG>, the second shoulder land portion <NUM> is provided with a plurality of second shoulder lateral grooves <NUM>. The plurality of second shoulder lateral grooves <NUM> extends from the second shoulder circumferential groove <NUM> across the second tread edge T2.

Each of the second shoulder lateral grooves <NUM> includes a pair of second groove walls 31a. In addition, the pair of second groove walls 31a is provided with a pair of second chamfer portions <NUM> that extends from the second shoulder circumferential groove <NUM> to a second location E2 beyond the second tread edge T2. As a result, steering stability and uneven wear resistance can further be improved by the same mechanism as described above.

Note that the second chamfer portions <NUM> have substantially the same configuration as the first chamfer portions <NUM>. Thus, the configuration of the first chamfer portions <NUM> described above can be applied to the second chamfer portions <NUM>, and the description thereof is not repeated. The pair of second chamfer portions <NUM> terminate at the second location E2 in the tyre axial direction. The second location E2 is a location within <NUM> from the second tread edge T2. In addition, the pair of second groove walls 31a includes a pair of non-chamfered groove edges <NUM> arranged axially outwardly of the second location E2. As a result, the braking performance can further be improved.

A pitch length P2 in the tyre circumferential direction of the second shoulder lateral grooves <NUM>, for example, is in a range of from <NUM> to <NUM>% of the pitch length P1 in the tyre circumferential direction of the first shoulder lateral grooves <NUM>.

<FIG> illustrates a cross-sectional view taken along the line C-C of <FIG>. As illustrated in <FIG>, at least one of the second shoulder lateral grooves <NUM> is provided with a second tie-bar <NUM> where a groove bottom thereof raises locally. The second tie-bar <NUM> according to the present embodiment is arranged in an inner end portion in the tyre axial direction of the at least one of the second shoulder lateral grooves <NUM>.

A length L7 in the tyre axial direction of the second tie-bar <NUM>, for example, is preferably in a range of from <NUM>% to <NUM>% of a width W4 (shown in <FIG>) of the ground contacting surface in the tyre axial direction of the second shoulder land portion <NUM>. In addition, a minimum groove depth d5 on the second tie-bar <NUM>, for example, is in a range of from <NUM>% to <NUM>% of the maximum groove depth d4 of the second shoulder lateral groove <NUM>. Such a second tie-bar <NUM> can improve steering stability on dry roads and wet performance in a well-balanced manner.

Comparing the first tie-bar <NUM> (shown in <FIG>) provided in the at least one of the first shoulder lateral grooves <NUM> with the second tie-bar <NUM> provided in the at least one of the second shoulder lateral grooves <NUM>, the length in the tyre axial direction of the first tie-bar <NUM> is preferably greater than the length in the tyre axial direction of the second tie-bar <NUM>. Such an arrangement of tie-bars relatively increases rigidity of the first shoulder land portion <NUM> and can help to exert excellent steering stability.

On the other hand, the groove depth at the first tie-bar <NUM> is preferably greater than the groove depth of the second tie-bar <NUM>. Thus, drainage performance of the at least one of the first shoulder lateral grooves <NUM> can be ensured, and wet performance of the tyre can be maintained.

As illustrated in <FIG>, the second shoulder land portion <NUM> includes a plurality of second shoulder blocks <NUM> divided by the plurality of second shoulder lateral grooves <NUM>. In the present embodiment, an area of the ground contacting surface of one of the first shoulder blocks <NUM> (shown in <FIG>) is preferably greater than an area of the ground contact surface of one of the second shoulder blocks <NUM>. Specifically, the above-mentioned area of one of the first shoulder blocks <NUM> is preferably in a range of from <NUM>% to <NUM>% of the above-mentioned area of one of the second shoulder blocks <NUM>. As a result, excellent steering stability can be exhibited while maintaining uneven wear resistance.

The second shoulder blocks <NUM> are provided with a plurality of shoulder sipes <NUM> extending along the plurality of second shoulder lateral grooves <NUM>. In the present embodiment, the second shoulder lateral grooves <NUM> and the shoulder sipes <NUM> are arranged alternately in the tyre circumferential direction. As used herein, "sipe" shall mean an incision that has a narrow width and a width between inner wall surfaces facing with each other is equal to or less than <NUM>, more preferably <NUM> to <NUM>. Note that an opening of sipe may be provided with a chamfer portion that defines an opening width more than <NUM>. In addition, note that a bottom of sipe may be provided with a flask shaped groove that has a width more than <NUM>.

The shoulder sipes <NUM>, for example, extend from the second shoulder circumferential groove <NUM> across the second tread edge T2. Such shoulder sipes <NUM> can suppress distortion of a ground contacting surface of the second shoulder land portion <NUM>, preventing uneven wear thereof.

Preferably, each shoulder sipe <NUM>, for example, includes a shallow bottom portion (not illustrated) at an inner end portion in the tyre axial direction. A depth of the shallow bottom portion, for example, is in a range of <NUM>% to <NUM>% of the maximum depth of the shoulder sipe <NUM>.

<FIG> illustrates a partial enlarged view of the tread portion <NUM> including the first middle land portion <NUM>, the crown land portion <NUM> and the second middle land portion <NUM>. As illustrated in <FIG>, the first middle land portion <NUM> is provided with a plurality of first middle sipes <NUM> and a plurality of second middle sipes <NUM> which are arranged alternately in the tyre circumferential direction. The first middle sipes <NUM>, for example, traverse the first middle land portion <NUM> entirely in the tyre axial direction. The second middle sipes <NUM>, for example, extend from the first crown circumferential groove <NUM> and terminate to have closed ends 42a within the first middle land portion <NUM>.

The first middle sipes <NUM>, for example, are inclined in a first direction (upward to the right in <FIG>) with respect to the tyre axial direction. Preferably, an angle of the first middle sipes <NUM> with respect to the tyre axial direction is greater than an angle of the first shoulder lateral grooves <NUM> with respect to the tyre axial direction, and is in a range of <NUM> to <NUM> degrees, for example. Such first middle sipes <NUM> can provide frictional force not only in the tyre circumferential direction, but also in the tyre axial direction.

<FIG> illustrates a cross-sectional view taken along the line D-D of <FIG>. As illustrated in <FIG>, the first middle sipes <NUM> each include a main portion 41a and a pair of chamfer portions <NUM> connected to the main portion 41a and having a width greater than that of the main portion 41a. Preferably, an opening width W5 of the chamfer portion <NUM> is greater than the chamfer width W2 (shown in <FIG>) of the first chamfer portions <NUM> of one or more first shoulder lateral grooves <NUM>. Thus, the wear of the first shoulder land portion <NUM> and the first middle land portion <NUM> may progress uniform, and uneven wear resistance may be improved.

As illustrated in <FIG>, a pitch length P3 of the first middle sipes <NUM> in the tyre circumferential direction is preferably greater than the pitch length P1 of the first shoulder lateral grooves <NUM> (shown in <FIG>). Specifically, the pitch length P3 is in a range of from <NUM>% to <NUM>% of the pitch length P1. This structure can help to suppress uneven wear of the first middle land portion <NUM>.

As illustrated in <FIG>, axially outer ends of the first middle sipes <NUM>, which are located on the first shoulder circumferential groove side, overlap respective projected regions in which axially inner ends of the first shoulder lateral grooves <NUM> are expanded in parallel with the tyre axial direction onto the first shoulder circumferential groove <NUM>. Thus, the first shoulder lateral grooves <NUM> tend to open easily when grounding, resulting in improving wet performance.

As illustrated in <FIG>, the second middle sipes <NUM> are inclined in the first direction with respect to the tyre axial direction. Preferably, the second middle sipes <NUM> extend along the first middle sipes <NUM>. In the present embodiment, the angle difference between the second middle sipes <NUM> and the first middle sipes <NUM> is equal to or less than <NUM> degrees. In addition, a length L8 in the tyre axial direction of the second middle sipes <NUM> is preferably in a range of from <NUM>% to <NUM>% of a width W6 in the tyre axial direction of the ground contacting surface of the first middle land portion <NUM>.

<FIG> illustrates a cross-sectional view taken along the line E-E of <FIG>. As illustrated in <FIG>, each second middle sipe <NUM>, for example, includes a pair of sipe walls that connected to the ground contact surface of the first middle land portion <NUM> directly to form a pair of sharp edges. The second middle sipes <NUM> can provide a large friction force using the edges, helping to improve braking performance.

As illustrated in <FIG>, the crown land portion <NUM> is provided with a plurality of the crown lateral grooves <NUM>. The crown lateral grooves <NUM>, for example, extend from the second crown circumferential groove <NUM> and terminate to have closed ends 45a within the crown land portion <NUM>. The crown lateral grooves <NUM>, for example, are inclined in the second direction (downward to the right in <FIG>) which is opposite to the first direction with respect to the tyre axial direction. An angle of the crown lateral grooves <NUM> with respect to the tyre axial direction, for example, is in a range of from <NUM> to <NUM> degrees. Such crown lateral grooves <NUM> can exert frictional force in a direction different from that of the first middle sipes <NUM>, and braking performance can be further improved.

The crown lateral grooves <NUM>, for example, do not traverse the tyre equator C, and do not traverse the center location in the tyre axial direction of the crown land portion <NUM>. A length L9 in the tyre axial direction of the crown lateral grooves <NUM> is preferably smaller than the length L8 in the tyre axial direction of the second middle sipes <NUM>. Specifically, the length L9 of the crown lateral grooves <NUM> is in a range of from <NUM>% to <NUM>% of a width W7 in the tyre axial direction of the crown land portion <NUM>. The crown lateral grooves <NUM> can improve wet performance while maintaining uneven wear resistance.

The second middle land portion <NUM> is provided with a plurality of third middle sipes <NUM> and a plurality of the fourth middle sipes <NUM> which are arranged alternately in the tyre circumferential direction. The third middle sipes <NUM> and the fourth middle sipes <NUM> traverse the second middle land portion <NUM> entirely in the tyre axial direction. The third middle sipes <NUM> and the fourth middle sipes <NUM>, for example, are inclined in the first direction with respect to the tyre axial direction. An angle of the third middle sipes <NUM> with respect to the tyre axial direction and an angle of the fourth middle sipes <NUM> with respect to the tyre axial direction are preferably in a range of <NUM> to <NUM> degrees.

The third middle sipes <NUM> each, for example, have the same cross-sectional shape as the first middle sipes <NUM> shown in <FIG>. That is, each third middle sipe <NUM> includes a main portion and a pair of chamfer portions having a greater width than the main portion. The third middle sipes <NUM> can suppress uneven wear of the second middle land portion <NUM>.

The fourth middle sipes <NUM> each, for example, have the same cross-sectional shape as the second middle sipes <NUM> shown in <FIG>. That is, the fourth middle sipes <NUM> includes a pair of sipe walls that connected to the ground contact surface of the second middle land portion <NUM> directly to form a pair of sharp edges. The fourth middle sipes <NUM> can provide a large friction force. In the present embodiment, the above-mentioned third middle sipes <NUM> and the fourth middle sipes <NUM> which are arranged alternately in the tyre circumferential direction can improve uneven wear resistance and braking performance in a well-balanced manner.

As illustrated in <FIG>, axially outer ends of the third middle sipes <NUM>, which are on the second shoulder circumferential groove <NUM> side, overlap respective projected regions in which axially inner ends of the second shoulder lateral grooves <NUM> are expanded in parallel with the tyre axial direction onto the second shoulder circumferential groove <NUM>. Thus, the second shoulder lateral grooves <NUM> tend to open easily when grounding, resulting in improving wet performance.

While the particularly preferable embodiments in accordance with the present invention have been described in detail, the present invention is not limited to the illustrated embodiments, but can be modified and carried out within the scope of the claims.

Tires having a size of <NUM>/50R18 and a tread pattern shown in <FIG> were prototyped based on the specifications in Table <NUM>. As a comparative example, a tyre having a tread pattern shown in <FIG> was also prototyped. As illustrated in <FIG>, in the tyre of comparative example, no chamfer portions are provided on the first shoulder lateral grooves (a) and the second shoulder lateral grooves (b). Note that the tyre of comparative example has the substantially same tread pattern shown in <FIG> except for the above chamfer structure. For each test tyre, uneven wear resistance, steering stability and braking performance were tested. The common specifications and test methods for each test tyre are as follows.

After traveling a certain distance on the above test vehicle, the wear state of the first shoulder lateral grooves and the second shoulder lateral grooves (the degree of uneven wear such as H&T wear) was visually checked. The test results are indicated in Table <NUM> using a score with the wear state of the comparative example as <NUM>. The larger the value, the better the uneven wear resistance is.

Steering stability of the above test vehicle when traveling on a dry road surface was evaluated by the driver's sensuality. The test results are indicated in table <NUM> using a score with steering stability of the comparative example as <NUM>. The larger the value, the better the steering stability is.

The braking performance when driving on dry and wet roads with the above test vehicle was evaluated by the driver's sensuality. The test results are indicated in Table <NUM> using a score with braking performance of the comparative example as <NUM>. The larger the value, the better the braking performance is.

Claim 1:
A tyre (<NUM>) comprising:
a tread portion (<NUM>) comprising:
axially spaced first and second tread edges (T1, T2) that are axially outermost edges of a ground contacting patch of the tyre (<NUM>) which occurs under a condition such that a <NUM>% standard tyre load is applied to the tyre (<NUM>) placed under a normal state, wherein the normal state is such that the tyre (<NUM>) is mounted onto a standard wheel rim and inflated to a standard pressure;
a first shoulder land portion (<NUM>) including the first tread edge (T1); and
a first shoulder circumferential groove (<NUM>) located inwardly in a tyre axial direction of and adjacent to the first shoulder land portion (<NUM>) and extending continuously in a tyre circumferential direction,
wherein
the first shoulder land portion (<NUM>) is provided with a plurality of first shoulder lateral grooves (<NUM>) extending from the first shoulder circumferential groove (<NUM>) across the first tread edge (T1),
each of the plurality of first shoulder lateral grooves (<NUM>) has a pair of first groove walls (<NUM>), and
the pair of first groove walls (<NUM>) is provided with a pair of first chamfer portions (<NUM>) that extends from the first shoulder circumferential groove (<NUM>) to a first location beyond the first tread edge (T1), and
characterized in that the pair of first chamfer portions (<NUM>) has a chamfer width reducing outwardly in the tyre axial direction, and
the pair of first chamfer portions (<NUM>) terminates at the first location, the first shoulder lateral grooves (<NUM>) comprising a pair of non-chamfered groove edges (<NUM>) that extends outwardly in the tyre axial direction from the first location of the pair of first groove walls (<NUM>).