Patent Description:
There has been known a tire provided in the tread portion with a circumferential groove, and two rib-shaped land portions adjacent to each other across a circumferential groove, wherein side wall surfaces of the respective two rib-shaped land portions which are facing each other through the circumferential groove, are each provided with a protrusion protruding toward the other of the side wall surfaces and extending in the tire circumferential direction. (See, Patent Document <NUM>) Patent Document <NUM>: <CIT>;
<CIT> discloses a tire comprising the features according to the preamble of claim <NUM>. <CIT> discloses a tire having a tread portion which comprises first and second circumferential grooves disposed on each side of a tire equator and which is further provided with a third circumferential groove extending in the tire circumferential direction and disposed between the first and second circumferential grooves.

The tire disclosed in Patent Document <NUM> is required to be further improved in drainage performance,.

It is therefore, a primary object of the present invention to provide a tire having excellent drainage performance even in the last stage of tread wear life.

According to the present invention, a tire comprises a tread portion provided with: a first circumferential groove and a second circumferential groove each extending in the tire circumferential direction; and lateral grooves connecting between the first circumferential groove and the second circumferential groove,
wherein
the first circumferential groove is a zigzag groove, and comprises a radially outer first portion having a smallest groove width, and a radially inner second portion which is positioned inside the first portion in a tire radial direction and is wider in groove width than the first portion.

With respect to a tire equator, the second circumferential groove is disposed outside the first circumferential groove in the tire axial direction.

It is preferable that the first circumferential groove comprises first approximate portions at which the first circumferential groove is closest to the second circumferential groove, and of which depth is not more than a depth of the second circumferential groove.

It is preferable that the lateral grooves are connected to the first approximate portions.

It is preferable that the second circumferential groove comprises second approximate portions closest to the first circumferential groove, and the lateral grooves are connected to the second approximate portions.

The tread portion may comprise a first land portion disposed on one side of the second circumferential groove which side is the first circumferential groove side, and a second land portion disposed on the other side of the second circumferential groove which side is opposite to the first circumferential groove side, and
it is desirable that the lateral grooves extend from the first land portion across the second circumferential groove and terminate within the second land portion.

It is preferable that the groove width W1 of the radially outer first portion is <NUM> to <NUM>.

It is preferable that the radially inner second portion has a largest groove width W2 of from <NUM> to <NUM>.

It is preferable that the largest groove width W2 of the second portion is <NUM> to <NUM> times the groove width W1 of the first portion.

It is preferable that the shortest distance H2 in the tire radial direction from the groove bottom of the first circumferential groove to the radially inner end of the first portion is in a range from <NUM>/<NUM> to <NUM>/<NUM> times the depth H1 of the first circumferential groove. (<NUM>/<NUM> =< H2/H1 =< <NUM>/<NUM>).

It is preferable that the first circumferential groove comprises a third portion which is disposed outside the first portion in the tire radial direction, and in which the groove width is gradually increased toward the outside in the tire radial direction.

It is preferable that the tread portion is further provided with first sipes extending from the first circumferential groove to the second circumferential groove.

It is preferable that the first circumferential groove is disposed on each side of the tire equator, and
the tread portion is further provided with a third circumferential groove extending in the tire circumferential direction and disposed between the first circumferential grooves.

It is preferable that the tread portion is further provided with second sipes extending from the third circumferential groove to the first circumferential grooves.

The tread portion may be provided with reinforcing layers including a radially outermost layer, and it is desirable that the radially outermost layer extends in the tire axial direction so that the axially outer edges thereof are respectively located axially outside axially outermost circumferential grooves.

Therefore, in the tire according to the present invention, the drainage performance in the last stage of tread wear life is ensured by the radially inner second portion of the first circumferential groove. Further, the lateral grooves promote water flow from the first circumferential groove to the second circumferential groove, and improve the drainage performance.

The present invention can be applied to pneumatic tires for heavy duty vehicles, passenger cars, motorcycles and the like. Further, the present invention may be applied to non-pneumatic tires so-called airless tires.

Hereinafter, taking a pneumatic tire for heavy duty vehicles an example, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<FIG> is a cross-sectional partial view of a tire <NUM> as an embodiment of the present invention taken along the tire equatorial plane including the tire rotation axis (not shown) under a normal state of the tire.

In the case of a pneumatic tire, the normal state of the tire is a normally inflated unloaded state such that the tire is mounted on a standard wheel rim and inflate to a standard pressure but loaded with no tire load.

The undermentioned normally inflated loaded state is such that the tire is mounted on the standard wheel rim and inflated to the standard pressure and loaded with the standard 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 and the standard tire load are the maximum air pressure and the maximum tire load for the tire specified by the same organization in the Air-pressure/Maximum-load Table or similar list. For example, the standard wheel rim is the "standard rim" specified in JATMA, the "Measuring Rim" in ETRTO, the "Design Rim" in TRA or the like. The standard pressure is 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. The standard load is the "maximum load capacity" in JATMA, the "Load Capacity" in ETRTO, the maximum value given in the above-mentioned table in TRA or the like. In case of passenger car tires, however, the standard pressure may be uniformly defined by <NUM> kPa.

In this application including specification and claims, various dimensions, positions and the like of a pneumatic tire refer to those under the normally inflated unloaded state of the tire unless otherwise noted.

The tread edges TE1 and TE2 are the axial outermost edges of the ground contacting patch of the tire which occurs under the normally inflated loaded state when the camber angle of the tire is zero.

The tread width TW is the width measured under the normally inflated unloaded state, as the axial distance between the tread edges TE1 and TE2 determined as above.

The tire <NUM> in this embodiment comprises a tread portion <NUM>, a pair of axially spaced bead portions <NUM> each with a bead core <NUM> therein, a pair of sidewall portions <NUM> extending between the tread edges TE1 and TE2 and the bead portions <NUM>, a carcass <NUM> extending between the bead portions <NUM>, and a tread reinforcing belt <NUM> disposed radially outside the carcass in the tread portion <NUM>.

The bead core <NUM> is formed by winding a steel wire into a polygonal cross section, for example.

The carcass <NUM> is composed of at least one ply 6A of cords rubberized with topping rubber. As to the carcass cords, for example, steel cords and organic fiber cords such as polyester fibers, nylon fibers, rayon fibers, polyethylene naphthalate fibers, aramid fibers and the like may be employed.

The carcass ply 6A extends between the bead portions <NUM> through the tread portion <NUM> and the sidewall portions <NUM>, and is secured to the bead cores <NUM>. The carcass <NUM> in this example consists of a single carcass ply 6A, but the carcass <NUM> may be composed of a plurality of the carcass plies 6A.

The belt <NUM> is composed of one or more plies, in this example, four plies 7A, 7B, 7C and 7D, each made of parallel cords rubberized with a topping rubber. For the belt cords of the belt plies 7A, 7B, 7C and 7D, high modulus cords such as steel cords are preferably used.

On the outside in the tire radial direction of the belt <NUM>, a band may be provided. The band is composed of at least one ply of at least one organic fiber cord arranged at a small angle, for example, not more than <NUM> degrees, with respect to the tire circumferential direction. The band ply may be of a so-called jointless ply structure formed by spirally winding a rubberized cord or several parallel cords embedded in rubber in a ribbon-shape, or of a spliced ply structure formed by splicing both ends of a strip of rubberized parallel cords.

<FIG> shows a part of the tread portion <NUM> of the tire <NUM> in the present embodiment. The tread portion <NUM> is provided with a first circumferential groove <NUM> and a second circumferential groove <NUM> each extending circumferentially of the tire, and lateral grooves <NUM> connecting between the first circumferential groove <NUM> and the second circumferential groove <NUM>.

The first circumferential groove <NUM> is a zigzag groove of which widthwise center line extends in the tire circumferential direction in a zigzag manner. Here, the zigzag groove includes a repeatedly sharply bent groove made up of linear groove segments, and a repeatedly smoothly curved groove, for example like a sine-wave.

<FIG> shows a cross section taken along line A-A in <FIG>. As shown, the first circumferential groove <NUM> comprises a first portion <NUM> defined as having the smallest groove width, and a second portion <NUM> which is larger in the groove width than the first portion <NUM>. The second portion <NUM> is located inside the first portion <NUM> in the radial direction of the tire.

In the present embodiment, the first circumferential groove <NUM> has a cross-sectional shape like a flask shape or teardrop shape. Due to such cross-sectional shape, even when the tread portion <NUM> is subjected to a large load, the stress applied to the side walls of the land portions, namely, the side walls of the first circumferential groove <NUM> is relaxed.

The first portion <NUM> of the present embodiment is opened at the tread surface. Therefore, in the initial stage of tread wear life, the first circumferential groove <NUM> appearing in the tread surface is its first portion <NUM>. The first portion <NUM> may be closed by the load applied to the tread portion <NUM>, and thereby the rigidity of the tread portion <NUM> in the tire axial direction is increased. Since the first portion <NUM> of the present embodiment extends in the tire circumferential direction in a zigzag shape, the land portions on both sides of the first portion <NUM> engage with each other, therefore, the rigidity of the tread portion <NUM> in the tire circumferential direction is also increased.

On the other hand, as the wear of the tread portion <NUM> progresses, the position of the tread surface moves inward in the radial direction of the tire, and the opening of the first circumferential groove <NUM> changes from the first portion <NUM> to the second portion <NUM>. Since the opening width of the first circumferential groove <NUM> is increased as the tread wear progresses,
the drainage performance is maintained at high levels even in the last stage of tread wear life (for example, the groove depth of the remaining first circumferential groove <NUM> is <NUM>).

Further, as shown in <FIG>, the lateral grooves <NUM> improve the drainage performance of the tread portion <NUM> and enhances the cornering performance during running in wet conditions. The first circumferential groove <NUM> and the second circumferential groove <NUM> are communicated with each other via the lateral grooves <NUM>. Therefore, the lateral grooves <NUM> promote water flow from the first circumferential groove <NUM> to the second circumferential groove <NUM> to improve the drainage performance of the tread portion <NUM>.

As the first circumferential groove <NUM> extends zigzag, it has first approximate portions at which the first circumferential groove <NUM> is closest to the second circumferential groove <NUM>. It is preferable that the first approximate portions <NUM> have a depth D1 not more than the depth D2 of the second circumferential groove <NUM>. By setting the depth D1 equal to or less than the depth D2, the water in the first circumferential groove <NUM> easily flows into the second circumferential groove <NUM> through the lateral grooves <NUM> during running in wet conditions, and the retention of water in the first circumferential groove <NUM> is suppressed. Therefore, the drainage performance is improved. Further, the rigidity of the tread portion <NUM> in the tire axial direction is increased. Furthermore, the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance performance of the tire <NUM> is improved.

It is preferable that the depth D1 of the first approximate portions <NUM> is not less than <NUM>% of the depth D2 of the second circumferential groove <NUM>. When the depth D1 is more than <NUM>% of the depth D2, the water flow in the first circumferential groove <NUM> becomes good, and the drainage performance in the last stage of tread wear life is improved especially.

It is preferable that the depth D3 of the lateral grooves <NUM> is set in a range from <NUM>% to <NUM>% of the depth D1 of the first approximate portion <NUM>. When the depth D3 is more than <NUM>% of the depth D1, the water in the first circumferential groove <NUM> easily flows into the lateral grooves <NUM>, and the retention of water in the first circumferential groove <NUM> is suppressed, and the drainage performance is improved. In addition, the drainage performance in the last stage of tread wear life is improved. On the other hand, when the depth D3 is less than <NUM>% of the depth D1, the rigidity of the tread portion <NUM> in the tire circumferential direction is increased. Further, the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance performance of the tire <NUM> is improved.

It is preferable that the lateral grooves <NUM> are connected to the first approximate portions <NUM> of the first circumferential groove <NUM>. Since such flow paths from the first circumferential groove <NUM> to the second circumferential groove <NUM> formed by the lateral grooves <NUM> are shorter, the water in the first circumferential groove <NUM> easily flows into the second circumferential groove <NUM> during running in wet conditions, and the drainage performance is improved. Further, the water in the first circumferential groove <NUM> easily flows into the lateral grooves <NUM> during running in wet conditions, and the drainage performance is improved.

It is preferable that the second circumferential groove <NUM> is a zigzag groove of which widthwise center line extends in the tire circumferential direction in a zigzag manner. As a result, the cornering performance during running in wet conditions can be improved.

As the second circumferential groove <NUM> extends zigzag, it comprises second approximate portions <NUM> at which the second circumferential groove <NUM> is closest to the first circumferential groove <NUM>. It is preferable that the lateral grooves <NUM> are connected to the second approximate portions <NUM> of the second circumferential groove <NUM>. Since such flow paths from the first circumferential groove <NUM> to the second circumferential groove <NUM> formed by the lateral grooves <NUM> becomes shorter, the water in the first circumferential groove <NUM> easily flows into the second circumferential groove <NUM> during running in wet conditions, and the drainage performance is improved. Further, the water in the lateral grooves <NUM> easily flows into the second circumferential groove <NUM> during running in wet conditions, and the drainage performance is improved.

It is preferable that the distance L1 in the tire circumferential direction between the adjacent first and second approximate portions <NUM> and <NUM> is set in a range from <NUM> to <NUM>. When the distance L1 is more than <NUM>, the inclination angle of the lateral grooves <NUM> with respect to the tire axial direction becomes large, and the flow of water existing in the lateral grooves <NUM> is promoted. When the distance L1 is less than <NUM>, the rigidity in the tire axial direction of the tread portion <NUM> is increased. Further, the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance performance of the tire <NUM> is improved.

It is preferable that the lateral grooves <NUM> extend linearly. As a result, the water flow in the lateral grooves <NUM> becomes smooth during running in wet conditions. Further, the length of the lateral groove <NUM> becomes short, and the water in the first circumferential groove <NUM> easily flows into the second circumferential groove <NUM> during running in wet conditions. As a result, the drainage performance is improved.

The tread portion <NUM> comprises a first land portion <NUM> on one side of the second circumferential groove <NUM> which side is the first circumferential groove <NUM> side, and a second land portion <NUM> on the other side of the second circumferential groove <NUM> which side is opposite to the first land portion <NUM>. The first land portion <NUM> is defined between the first circumferential groove <NUM> and the second circumferential groove <NUM>.

It is preferable that the lateral grooves <NUM> extend from the first land portion <NUM> across the second circumferential groove <NUM> and terminates within the second land portion <NUM>. That is, in the present embodiment, the lateral grooves <NUM> each have a portion <NUM> extended into the second land portion <NUM>. By providing such extended portion <NUM> into the second land portion <NUM>, the drainage performance in the second land portion <NUM> is improved.

As shown in <FIG>, the groove width W1 in the first portion <NUM> is preferably <NUM> to <NUM>. When the width W1 is <NUM> or more, water easily flows from the first portion <NUM> to the second portion <NUM> during running in wet conditions, and sufficient drainage performance can be easily ensured. On the other hand, since the width W1 is <NUM> or less, when a load is applied to the tread portion <NUM> in the initial stage of tread wear life, the first portion <NUM> is likely to be closed by the ground contact pressure, and the rigidity of the tread portion <NUM> in the tire axial direction is increased. Further, the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance performance of the tire <NUM> is improved.

The largest groove width W2 occurring in the second portion <NUM> is preferably set in a range from <NUM> to <NUM>. When the largest groove width W2 is more than <NUM>, the width of the first circumferential groove <NUM> can be easily secured even in the last stage of tread wear life, and sufficient drainage performance can be easily secured. On the other hand, when the largest groove width W2 is less than <NUM>, the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance performance of the tire <NUM> is improved.

It is preferable that the largest groove width W2 is set in a range from <NUM> to <NUM> times the groove width W1. Since the width W2 is twice or more of the width W1, the groove width of the first circumferential groove <NUM> can be easily secured even in the last stage of tread wear life, and sufficient drainage performance can be easily secured. Since the width W2 is <NUM> times or less of the width W1, the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance performance of the tire <NUM> is improved.

In the first circumferential groove <NUM> of the present embodiment, it is more preferable that the width W1 is <NUM> or more, the width W2 is <NUM> or more, and the width W2 is twice or more of the width W1. With such first circumferential groove <NUM>, it is possible to easily secure sufficient drainage performance even in the last stage of tread wear life. Further, it is desirable that the width W1 is <NUM> or less, the width W2 is <NUM> or less, and the width W2 is <NUM> times or less the width W1. Thereby, the rubber volume of the tread portion <NUM> is easily secured by the first circumferential groove <NUM>, and the wear resistance performance of the tire <NUM> is improved.

It is preferable that the shortest distance H2 in the tire radial direction from the groove bottom of the first circumferential groove <NUM> to the first portion <NUM> is set in a range from <NUM>/<NUM> to <NUM>/<NUM> times the depth H1 of the first circumferential groove <NUM>, namely, a condition: <NUM>/<NUM> =< H2/H1 =< <NUM>/<NUM> is satisfied.

When the H2/H1 is <NUM>/<NUM> or more, the groove volume of the second portion <NUM> can be easily secured, and sufficient drainage performance in the last stage of tread wear life can be easily secured. When the H2/H1 is <NUM>/<NUM> or less, the rigidity of the tread portion <NUM> in the tire axial direction is increased in the initial stage of tread wear life. Further, the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance performance of the tire <NUM> is improved.

In the first circumferential groove <NUM> of the present embodiment, it is more preferable that the largest groove width W2 is set in a range from <NUM> to <NUM> times the groove width W1, and a condition: <NUM>/<NUM> =< H2/H1 =< <NUM>/<NUM> is satisfied. When the width W2 is twice or more of the width W1 and the H2/H1 is <NUM>/<NUM> or more, it is possible to easily secure sufficient drainage performance in the last stage of tread wear life. When the width W2 is <NUM> times or less of the width W1 and the H2/H1 is <NUM>/<NUM> or less, the rubber volume of the tread portion <NUM> is easily secured, and the wear resistance performance of the tire <NUM> is improved.

It is preferable that the second circumferential groove <NUM> has a groove width W3 (shown in <FIG>) in a range from <NUM>% to <NUM>% of the tread width TW (shown in <FIG>).

When the width W3 is <NUM>% or more of the tread width TW, the drainage performance is improved. On the other hand, when the width W3 is <NUM>% or less of the tread width TW,
the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance performance of the tire <NUM> is improved.

It is preferable that the lateral grooves <NUM> each have a groove width W4 in a range from <NUM> to <NUM>. When the width W4 is <NUM> or more, the flow of water from the first circumferential groove <NUM> to the second circumferential groove <NUM> becomes good, and the drainage performance is easily improved. On the other hand, when the width W4 is <NUM> or less, the rigidity of the tread portion <NUM> in the tire circumferential direction is increased. Further, the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance of the tire <NUM> is improved.

<FIG> shows a modified example 10A of the first circumferential groove <NUM>. The configurations of the first circumferential groove <NUM> described above can be adopted for portions of the first circumferential groove 10A not described below.

The first circumferential groove 10A comprises a third portion <NUM> located radially outside the first portion <NUM>. In the third portion <NUM>, the groove width is gradually increased toward the outside in the tire radial direction. The third portion <NUM> increases the volume of the first circumferential groove 10A in the initial stage of tread wear life. The third portion <NUM> increases the amount of water flowing from the first portion <NUM> to the second portion <NUM>. As a result, the drainage performance is improved.

It is preferable that the largest groove width W2 in the second portion <NUM> is larger than the largest groove width W5 in the third portion <NUM>. As a result, the groove volume of the first circumferential groove 10A can be easily secured in the second portion <NUM>, and sufficient drainage performance in the last stage of tread wear life can be easily secured.

A set of the first and second circumferential grooves <NUM> and <NUM> and the lateral grooves <NUM> may be formed plurally in the tread portion <NUM>. Further, the first and second circumferential grooves <NUM> and <NUM> and the lateral grooves <NUM> may be employed in combination with other grooves.

<FIG> shows a tread portion 2A which is a modification of the tread portion <NUM> shown in <FIG>. The above-described configurations of the tread portion <NUM> may be adopted for portions of the tread portion 2A not described below.

The tread portion 2A is provided, on each side of the tire equator CL, with a pair of the first and second circumferential grooves <NUM> and <NUM>, and
the second circumferential groove <NUM> is disposed axially outside the first circumferential groove <NUM>. As a result, the ground contact pressure in the portion around the first circumferential groove <NUM> becomes higher than the ground contact pressure in the portion around the second circumferential groove <NUM>, so the first portion <NUM> is likely to be closed in the initial stage of tread wear life, and the rigidity of the tread portion <NUM> in the tire axial direction is increased.

Further, the tread portion 2A is provided with a third circumferential groove <NUM> extending in the tire circumferential direction and disposed between the two first circumferential grooves <NUM>.

In this embodiment, the third circumferential groove <NUM> is located on the tire equator CL. With such third circumferential groove <NUM>, the drainage performance in the crown portion of the tread portion 2A is enhanced.

In this embodiment, the tread portion 2A when not yet worn, functions as a four-rib tread pattern axially divided by the two second circumferential grooves <NUM> and the one third circumferential groove <NUM>, and the wear resistance performance is improved. On the other hand, in the last stage of tread wear life, the tread portion 2A functions as a six-rib tread pattern axially divided by the two first circumferential grooves <NUM>, the two second circumferential grooves and the one third circumferential groove <NUM>, and the drainage performance during running in wet conditions is improved.

It is preferable that the groove width W6 of the third circumferential groove <NUM> is set in a range from <NUM>% to <NUM>% of the tread width TW. When the groove width W6 is <NUM>% or more of the tread width TW, the drainage performance of the tread portion <NUM> is enhanced. On the other hand, when the width W6 is <NUM>% or less of the tread width TW, the rubber volume of the tread portion <NUM> is easily secured. As a result, the wear resistance performance of the tire <NUM> is improved.

Each of the first land portions <NUM> is provided with first sipes <NUM> extending from the first circumferential groove <NUM> to the second circumferential groove <NUM>. The first sipe <NUM> is a narrow groove having a groove width of <NUM> or less, which is closed by the ground contact pressure of the tire <NUM>.

The first sipes <NUM> exert an edge effect and enhances traction performance during running in wet conditions. In the present embodiment, the first sipes <NUM> each extend in a zigzag shape, therefore, when the first sipe <NUM> is closed and the opposite sipe walls are engaged with each other, the rigidity of the first land portion <NUM> is increased.

<FIG> shows a cross section of the tread portion 2A. It is preferable that the depth D5 of the third circumferential groove <NUM> is larger than the depth D4 of the third approximate portions <NUM>. By setting the depth D5 larger than the depth D4, the drainage performance of the tread portion <NUM> is enhanced.

The third land portion <NUM>, which is defined between the third circumferential groove <NUM> and each of the first circumferential grooves <NUM>, is provided with second sipes <NUM> extending from the third circumferential groove <NUM> to the first circumferential groove <NUM>. The second sipe <NUM> is a narrow groove having a width of <NUM> or less, which is closed by the ground contact pressure of the tire <NUM>.

The second sipes <NUM> exert an edge effect and enhances traction performance during running in wet conditions. In the present embodiment, the second sipes <NUM> each extend zigzag, therefore, when the second sipe <NUM> is closed and the opposite sipe walls are engaged with each other, the rigidity of the third land portion <NUM> is increased.

The third circumferential groove <NUM> extends zigzag, therefore, it has fourth approximate portions <NUM> at which the third circumferential groove <NUM> is closest to the first circumferential groove <NUM>. It is preferable that the second sipes <NUM> are connected to the respective fourth approximate portions <NUM>.

As the first circumferential groove <NUM> extends zigzag, it has third approximate portions <NUM> at which the first circumferential groove <NUM> is closest to the third circumferential groove <NUM>. It is preferable that the second sipes <NUM> are connected to the respective third approximate portions <NUM>. As a result, the second sipes <NUM> become short, and the rigidity of the third land portion <NUM> is increased.

The tread portion 2A is provided with a plurality of reinforcing layers <NUM> stacked in the tire radial direction. In the case of the tire <NUM> provided with only the belt <NUM>, the belt plies 7A, 7B, 7C and 7D constituting the belt <NUM> correspond to the reinforcing layers <NUM>. In the case of the tire <NUM> provided with the belt <NUM> and a band layer disposed on the radially outer side of the belt <NUM>, the belt plies and the band layer correspond to the reinforcing layers <NUM>.

In the tread portion 2A, it is desirable that axially outer edges 9E of the radially outermost layer of the reinforcing layers <NUM> (in the present embodiment, the radially outermost belt ply 7D) are located axially outside the respective first circumferential grooves <NUM>. By extending the radially outermost reinforcing layer <NUM> to the axially outer sides of the first circumferential grooves <NUM>, the rigidity of the tread portion <NUM> is increased, and as a result, the drainage performance is improved, and the cornering performance during running in wet conditions is improved.

In the tread portion 2A, it is desirable that axially outermost edges 9E of the reinforcing layers <NUM> are located axially outer sides of the respective axially outermost circumferential grooves (in the present embodiment, the second circumferential grooves <NUM>). By extending the reinforcing layers <NUM> to the axially outer sides of the second circumferential grooves <NUM>, the rigidity of the tread portion <NUM> is further increased. As a result, the drainage performance is further improved, and the cornering performance during running in wet conditions is enhanced.

<FIG> and <FIG> show a tread portion 2B which is a modification of the tread portion 2A shown in <FIG> and <FIG>. The above-described configurations of the tread portion 2A can be adopted for portions of the tread portion 2B not described below.

The tread portion 2B is provided, on each side of the tire equator, with a pair of the above-described first circumferential groove 10A and the second circumferential groove <NUM>. As shown in <FIG>, the first circumferential groove 10A comprises the third portion <NUM> radially outside the first portion <NUM>. The groove width in the third portion <NUM> gradually increases toward the outside in the radial direction of the tire. Thus, the third portion <NUM> enhances the drainage performance of the first circumferential groove 10A in the initial stage of tread wear life.

While detailed description has been made of preferable embodiments 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 of size <NUM>/70R22. <NUM> were experimentally manufactured and tested for wet performance in the initial stage and the last stage of tread wear life. In order to reproduce the tread portion in the last stage of tread wear life, the tread rubber was removed by buffing the tread surface so that the groove depth of the second circumferential groove became <NUM>. Specifications of the test tires are listed in Table <NUM>. Specifications not listed in Table <NUM> are common to all the test tires. The test methods are as follows.

The respective test tires were mounted on all wheels of a test vehicle. Using the test vehicle, a wet performance test was carried out under the tire load of <NUM>% of the standard load. In the test, twenty test drivers ran the test car on a wet road surface of a tire test course covered with about <NUM> to <NUM> depth water, and each test driver evaluated the cornering performance into five ranks. For each test tire, the total value of the rank numbers evaluated by the twenty test drivers was calculated. The calculated total values of the respective test tires are indicated in Table <NUM> by an index based on comparative example tire <NUM> being <NUM> and rounded so as to become a multiple of <NUM>, wherein the larger the value, the better, the wet performance. Specifically, if the number below the first place of the total value was <NUM> or more and less than <NUM>, it was rounded down to <NUM>, if <NUM> or more and less than <NUM>, it was rounded to <NUM>, and if <NUM> or more, it was rounded up to <NUM>.

As is clear from Table <NUM>, it was confirmed that the working example tires were significantly improved in the wet performance as compared with the comparative example tires.

Based on the basic pattern shown in <FIG>, pneumatic tires of size <NUM>/70R22. <NUM> were experimentally manufactured, and tested for wet performance and wear resistance in the last stage of tread wear life. Specifications of the test tires are listed in Table <NUM>. Specifications not listed in Table <NUM> were common to all the test tires. The test methods were as follows.

In the same manner as explained above, wet performance test was carried out on each test tire. The results are indicated in Table <NUM> by an index based on working example tire <NUM> being <NUM> and rounded so as to become a multiple of <NUM>, wherein the larger the value, the better the wet performance.

The amount of wear of each test tire was measured after running for a predetermined distance using the above-mentioned test vehicle.

The results are indicated in Table <NUM> by an index based on working example tire <NUM> being <NUM> and rounded so as to become a multiple of <NUM>, wherein the larger the value, the better the wear resistance.

Based on the basic pattern shown in <FIG>, pneumatic tires of size <NUM>/70R22. <NUM> were experimentally manufactured and tested for wet performance and wear resistance in the last stage of tread wear life. Specifications of the test tires are listed in Table <NUM>. Specifications not listed in Table <NUM> were common to all the test tires.

In the same manner as explained above, wet performance test was carried out on each test tire.

The results are indicated in Table <NUM> by an index based on working example tire <NUM> being <NUM> and rounded so as to become a multiple of <NUM>, wherein the larger the value, the better the wet performance.

In the same manner as explained above, the amount of wear of each test tire was measured.

Based on the basic pattern shown in <FIG>, pneumatic tires of size <NUM>/70R22. <NUM> were experimentally manufactured and tested for wet performance in the last stage of tread wear life. Specifications of the test tires are listed in Table <NUM>. Specifications not listed in Table <NUM> were common to all the test tires. The test methods are as follows.

Based on the basic pattern shown in <FIG>, pneumatic tires of size <NUM>/70R22. <NUM> were experimentally manufactured and tested for wet performance in new condition and wear resistance. Specifications of the test tires are listed in Table <NUM>. Specifications not listed in Table <NUM> were common to all the test tires. The test methods are as follows.

Based on the basic pattern shown in <FIG>, pneumatic tires of size <NUM>/70R22. <NUM> were experimentally manufactured and tested for wet performance in the last stage of tread wear life and wear resistance.

Specifications of the test tires are listed in Table <NUM>. Specifications not listed in Table <NUM> were common to all the test tires. The test methods are as follows.

Based on the basic pattern shown in <FIG>, pneumatic tires of size <NUM>/70R22. <NUM> were experimentally manufactured and tested for wet performance in the last stage of tread wear life and wear resistance. Specifications of the test tires are listed in Table <NUM>. Specifications not listed in Table <NUM> were common to all the test tires. The test methods are as follows.

Based on the basic pattern shown in <FIG>, pneumatic tires of size <NUM>/70R22. <NUM> were experimentally manufactured and tested for wet performance in the last stage of tread wear life and wear resistance. Specifications of the test tires are listed in Table <NUM>. Specifications not listed in Table <NUM> were common to all the test tires. The test methods are as follows.

Claim 1:
A tire (<NUM>) comprising a tread portion (<NUM>) provided with a first circumferential groove (<NUM>) and a second circumferential groove (<NUM>) each extending in the tire circumferential direction, and lateral grooves (<NUM>) connecting between the first circumferential groove (<NUM>) and the second circumferential groove (<NUM>),
wherein
the first circumferential groove (<NUM>) is a zigzag groove, and comprises a radially outer first portion (<NUM>) having a smallest groove width, and a radially inner second portion (<NUM>) which is positioned inside the first portion (<NUM>) in a tire radial direction and is wider in groove width than the first portion (<NUM>),
characterized in that
with respect to a tire equator (CL), the second circumferential groove (<NUM>) is disposed outside the first circumferential groove (<NUM>) in the tire axial direction.