Pneumatic tire

A pneumatic tire has a tread portion provided with an asymmetrical tread pattern and comprising an inboard shoulder land portion, an inboard shoulder main groove, an inboard middle land portion, an inboard crown main groove, a center land portion, an outboard crown main groove, an outboard middle land portion, an outboard shoulder main groove, and an outboard shoulder land portion. The inboard middle land portion is provided with inboard middle axial grooves extending from the inboard shoulder main groove and each comprising a main portion and a turnback portion. The inboard shoulder land portion is provided with inboard shoulder sipes extending from the inboard shoulder main groove.

BACKGROUND OF THE INVENTION

The present invention relates to a pneumatic tire, more particularly to an asymmetrical tread pattern capable of improving noise performance without sacrificing wet performance and steering stability.

In general, pneumatic tires for example passenger tires are provided in the tread portion with tread grooves such as circumferential grooves and axial grooves.

If tread grooves are increased in the volume in order to improve wet performance of the tire, there is a problem such that the rigidity of the tread portion is decreased and the steering stability is deteriorated. Further, air tube resonance becomes liable to occurs when the groove volume is increased, therefore there is a problem such that noise performance is deteriorated. Thus, the wet performance is contradictory to the noise performance and steering stability.

In order to solve such contradictory problem, Japanese Patent Application Publication No. 2003-285610 discloses a pneumatic tire in which a circumferentially continuously extending rib is formed on each side of a circumferential groove to isolate the circumferential groove.

In such a pneumatic tire, however, there is room for simultaneous improvement in the steering stability, wet performance and noise performance.

SUMMARY OF THE INVENTION

It is therefore, an object of the present invention to provide a pneumatic tire in which the noise performance can be improved without sacrificing the wet performance and the steering stability.

According to the present invention, a pneumatic tire comprises

a tread portion provided with a tread pattern of left-right asymmetry and having an outboard tread edge and an inboard tread edge,

the tread pattern comprising circumferentially continuously extending main grooves which are an inboard shoulder main groove, an inboard crown main groove, an outboard crown main groove, and an outboard shoulder main groove, whereby the tread portion is axially divided into an inboard shoulder land portion between the inboard shoulder main groove and the inboard tread edge, an inboard middle land portion between the inboard crown main groove and the inboard shoulder main groove, a center land portion between the inboard crown main groove and the outboard crown main groove, an outboard middle land portion between the outboard crown main groove and the outboard shoulder main groove, and an outboard shoulder land portion between the outboard shoulder main groove and the outboard tread edge, wherein

the width of the outboard shoulder main groove is smaller than the width of the inboard shoulder main groove,

the inboard middle land portion is provided with a plurality of inboard middle axial grooves arranged circumferentially of the tire at intervals,

each of the inboard middle axial grooves comprises a main portion which extends from the inboard shoulder main groove toward the tire equator, while inclining with respect to the tire axial direction to one tire circumferential direction, and a turnback portion which extends from the main portion toward the other tire circumferential direction and terminates within the inboard middle land portion,

the inboard shoulder land portion is provided with a plurality of inboard shoulder sipes arranged circumferentially of the tire at intervals, and

each of the inboard shoulder sipes extends from the inboard shoulder main groove to the inboard tread edge.

In the present invention, since the tread pattern is of left-right asymmetry (asymmetry about the tire equator), the mounting position of the tire (the inside and outside of the tire) is specified. Thus, the tread portion has the outboard tread edge to be positioned away from the center of the vehicle body and the inboard tread edge to be positioned close to the center of the vehicle body. For example, the sidewall portion to be located on outside when installed on the vehicle is provided with an indication such as “outside”, and the sidewall portion to be located on inside is provided with an indication such as “inside”.

According thereto, in this application including specification and claims, the terms “outboard” and “inboard” are used toward the outboard tread edge and inboard tread edge, respectively, to refer relative positions in the tire axial direction.

The terms “axially inner”, “axially inward” and the like are used toward the tire equator, and

the terms “axially outer”, “axially outward” and the like are used toward the tread edge in order to refer relative positions in the tire axial direction.

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

The normally inflated unloaded condition 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 undermentioned normally inflated loaded condition 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.

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

The tread width TW is the width measured under the normally inflated unloaded condition, as the axial distance between the tread edges Te determined as above.

Getting back to effects of the pneumatic tire according to the present invention, since the tread portion is provided with the wide inboard shoulder main groove and the narrow outboard shoulder main groove, the rigidity of the tread portion is increased in an outboard part subjected to larger loads during cornering in comparison with an inboard part, therefore, the steering stability during cornering can be improved. Further, since the turnback portions of the inboard middle axial grooves reduce the axial rigidity of the inboard middle land portion to allow relatively large deformation during running, thereby the occurrence of standing wave in the inboard shoulder main groove is hindered by the deformed groove sidewall, and the generation of air tube resonance sound from the inboard shoulder main groove is prevented to improve the noise performance. Further, the inboard shoulder sipes can improve the wet performance. As a result, the noise performance can be improved without sacrificing the wet performance and the steering stability.

The pneumatic tire according to the present invention may further include the following features (1)-(7):

(1) the turnback portion extends parallel with the tire circumferential direction;

(2) the number of the inboard shoulder sipes is more than the number of the inboard middle axial grooves;

(3) the inboard middle land portion is provided with a plurality of inboard middle sipes arranged circumferentially of the tire at intervals, and each of the inboard middle sipes extends axially outwardly from the inboard crown main groove and terminates within the inboard middle land portion;
(4) the axial outer ends of the inboard middle sipes are located axially outside the turnback portions;
(5) the outboard shoulder land portion is provided with a non-grooved rib-like part extending circumferentially of the tire and disposed adjacently to the outboard shoulder main groove;
(6) the inboard middle axial grooves have a width, and the inboard crown main groove and the outboard crown main groove have a width more than the width of the inboard middle axial grooves;
(7) the inboard crown main groove has a width, and the outboard crown main groove has a width same as the width of the inboard crown main groove.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings.

As well known in the art, a pneumatic tire comprises a tread portion2whose outer surface defines the tread and which is provided with a tread pattern, a pair of axially spaced bead portions mounted on bead seats of a rim, a pair of sidewall portions extending between the tread edges and the bead portions, a carcass extending between the bead portions through the tread portion and the sidewall portions, and a tread reinforcing belt disposed radially outside the carcass in the tread portion.

According to the present invention, the tread portion2is provided with

a pair of circumferentially continuously extending crown main grooves9disposed one on each side of the tire equator C, and

a pair of circumferentially continuously extending shoulder main grooves10disposed axially outside the respective crown main grooves9.

Each of the crown main grooves9and shoulder main grooves10extends straight and has a constant width. However, it is also possible that the crown main grooves9and the shoulder main grooves10are configured as a zigzag or wavy groove. Further, the groove width may be varied along the groove length.

The crown main grooves9are

the inboard crown main groove9ihaving a width W1 and

the outboard crown main groove90having a width W2. Preferably, the width W1 and the width W2 are set in a range of from 0.10 to 0.15 times the tread width TW in order to provide a good wet performance without deteriorating the rigidity of the tread crown region.

It is preferable that the width W1 is the same as the width W2 in order to improve the drainage in the tread crown region.

The shoulder main grooves10are

the inboard shoulder main groove14having a width W3 and

the outboard shoulder main groove15having a width W4. Preferably, the widths W3 and W4 are less than the width of the crown main groove9in order to increase the pattern rigidity in the tread shoulder region subjected to a large load during cornering and thereby to improve the steering stability.

The width W4 of the outboard shoulder main groove15is less than the width W3 of the inboard shoulder main groove14. The width ratio W4/W3 is preferably set in a range of not more than 0.85, more preferably not more than 0.82, but not less than 0.75, more preferably not less than 0.78 in order to increase the pattern rigidity in an outboard tread part whose contribution to the improvement in the steering stability is higher, than in an inboard tread part, and thus to further improve the steering stability.

By the above-mentioned main grooves9and10, the tread portion2is axially divided into

a center land portion11between the inboard crown main groove9iand the outboard crown main groove9o,

a pair of middle land portions12between the crown main grooves9and the shoulder main grooves10, and

a pair of shoulder land portions13between the shoulder main grooves10and the tread edges Te.

It is preferable that the axial width W5 of the center land portion11is set in a range of not less than 0.10 times, more preferably not less than 0.12 times, but not more than 0.16 times, more preferably not more than 0.14 times the tread width TW in order to provide steering stability without deteriorating the wet performance.

The center land portion11is provided with a plurality of inboard center axial grooves25extending from the inboard crown main groove9itoward the tire equator C and arranged circumferentially of the tire at intervals, and a plurality of outboard center axial grooves26extending from the outboard crown main groove90toward the tire equator C and arranged circumferentially of the tire at intervals in order to improve the drainage in the tread crown region.

All the inboard center axial grooves25extend substantially straight from the inboard crown main groove9itoward the tire equator C, while inclining with respect to the tire axial direction to one circumferential direction in order to reduce the rigidity at the inboard edge11iof the center land portion11and thereby hinder the generation of air tube resonance sound in the inboard crown main groove9i, without deteriorating the wet performance.

Each of the inboard center axial grooves25continues to a center sipe27and terminates within the center land portion11.

The center sipe27inclines with respect to the tire axial direction and terminates within the center land portion11not to make the rigidity of the center land portion11insufficient.

All the outboard center axial grooves26extend from the outboard crown main groove90toward the tire equator C, while inclining with respect to the tire axial direction to one circumferential direction, and terminate within the center land portion11.

It is preferable that the outboard center axial grooves26have an axial length shorter than the inboard center axial grooves25in order to relatively increase the rigidity at the outboard edge11oof the center land portion11and thereby improve the steering stability.

It is desirable that all of the inboard and outboard center axial grooves25and26are inclined in the same direction, and

preferably the inclination angles with respect to the tire axial direction are identical.

It is preferable that the inboard center axial grooves25and the outboard center axial grooves26are arranged such that an extension of the widthwise center line25cof each of the inboard center axial grooves25passes through the width of one of the outboard center axial grooves26, and

an extension of the widthwise center line26cof each of the outboard center axial grooves26passes through the width of one of the inboard center axial grooves25in order to optimize the rigidity distribution in the center land portion11and thereby improve the uneven wear performance.

The above-mentioned middle land portions12are the inboard middle land portion16having an axial width W6 and the outboard middle land portion17having an axial width W7. It is preferable that the axial width W6 is more than the axial width W5 of the center land portion9, and the axial width W7 is more than the axial width W5.

The axial widths W6 and W7 are preferably set in a range of not less than 1.18 times, more preferably not less than 1.20 times, but not more than 1.26 times, more preferably not more than 1.24 times the axial width W5 in order to relatively increase the rigidity of the middle land portion12subjected to a larger load than the center land portion11during cornering and thereby improve the steering stability during cornering. Thus, such inboard middle land portion16and outboard middle land portion17can improve the steering stability without sacrificing the wet performance.

The inboard middle land portion16is provided with

inboard middle axial grooves20arranged circumferentially of the tire at intervals, and

inboard middle sipes28arranged circumferentially of the tire at intervals.

The inboard middle axial grooves20are each composed of a main portion21extending from the inboard shoulder main groove14toward the tire equator C, while inclining with respect to the tire axial direction to one circumferential direction, and

a turnback portion22extending toward the other circumferential direction from the main portion21and terminating within the inboard middle land portion16.

Such main portion21and turnback portion22reduce the rigidity in an axially outside part of the inboard middle land portion16, in particular, the rigidity of the corner39formed between the main portion21and the turnback portion22.

Thereby, during running, the axially inner groove-sidewall face14iof the inboard shoulder main groove14can make larger axial deformation than the axially outer groove-sidewall face14o. As a result, the occurrence of standing wave in the inboard shoulder main groove14is hindered, and the generation of air tube resonance sound from the inboard shoulder main groove14can be prevented.

Since the axial grooves20having such configuration are disposed in the inboard middle land portion16not subjected to large loads during cornering, the noise performance can be improved without deteriorating the steering stability.

The main portion21of the inboard middle axial groove20is substantially straight from its axially outer end at the inboard shoulder main groove14to its axially inner end at the midpoint of the axial width of the inboard middle land portion16.

If the angle θ1 of the main portion21with respect to the tire circumferential direction becomes small, there is a possibility that uneven wear occurs in the inboard middle land portion16. If the angle θ1 becomes large, there is a possibility that the axial rigidity of the inboard middle land portion16can not be suitably reduced.

Therefore, the angle θ1 of the main portion21is preferably set in a range of not less than 50 degrees, more preferably not less than 55 degrees, but not more than 70 degrees, more preferably not more than 65 degrees with respect to the tire circumferential direction.

If the axial length L1 of the main portion21becomes short, there is a possibility that the rigidity of the inboard middle land portion16can not be suitably reduced. If the axial length L1 becomes long, there is a possibility that the rigidity of the inboard middle land portion16is excessively reduced and the steering stability is deteriorated. Therefore, the axial length L1 of the main portion21is preferably set in a range of not less than 0.40 times, more preferably not less than 0.45 times, but not more than 0.60 times, more preferably not more than 0.55 times the axial width W6 of the inboard middle land portion16.

The width t1 of the main portion21is set in a range of from 2.5 to 3.5 mm for example from a point of view of the rigidity of the inboard middle land portion16and the drainage.

If the angle θ2 formed between the main portion21and the turnback portion22becomes small, there is a possibility that uneven wear occurs in the inboard middle land portion16. If the angle θ2 becomes large, there is a possibility that the rigidity of the inboard middle land portion16can not be suitably reduced.

Therefore, the angle θ2 formed between the main portion21and the turnback portion22is preferably set in a range of not less than 50 degrees, more preferably not less than 55 degrees, but not more than 70 degrees, more preferably not more than 65 degrees.

Preferably, the turnback portion22extends parallel with the tire circumferential direction in order to suitably reduce the axial rigidity of the inboard middle land portion16.

If the circumferential length L2 of the turnback portion22becomes short, there is a possibility that the wet performance is deteriorated. If the circumferential length L2 becomes long, there is a possibility that the rigidity of the inboard middle land portion16is excessively reduced and the steering stability is deteriorated.

Therefore, the circumferential length L2 of the turnback portion22is preferably not less than 0.5 times, more preferably not less than 0.55 times, but not more than 0.7 times, more preferably not more than 0.65 times the axial length L1 of the main portion21.

The width t2 of the turnback portion22is set in a range of from 2.0 to 3.0 mm for example for the rigidity of the inboard middle land portion16and the drainage.

The corner39formed between the main portion21and the turnback portion22is preferably chamfered.

Also the corner41formed between the inboard shoulder main groove14and the main portion21is preferably chamfered.

Such chamfer40can prevent uneven wear and a tear starting from the corner.

All the inboard middle sipes28extend straight axially outwardly from the inboard crown main groove9iand terminate within the inboard middle land portion16in order that the sipes effectively exert their edge effect without largely decreasing the rigidity of the inboard middle land portion16, and thereby the wet performance is improved without sacrificing the steering stability.

If the axial length L3 of the inboard middle sipes28becomes short, there is a possibility that the wet performance can not be effectively improved. If the axial length L3 becomes long, there is a possibility that the steering stability is deteriorated.

Therefore, the axial length L3 of the inboard middle sipes28is preferably not less than 0.40 times, more preferably not less than 0.50 times, but not more than 0.70 times, more preferably not more than 0.60 times the axial width W6 of the inboard middle land portion16.

The axial outer ends28eof the inboard middle sipea28are preferably located axially outside the turnback portions22in order to further improve the wet performance.

The inboard middle sipes28and the main portions21are preferably inclined in the same direction. Preferably, the inclination angle θ3 of the inboard middle sipes is set in a range of not less than 50 degrees, more preferably not less than 55 degrees, but not more than 70 degrees, more preferably not more than 65 degrees with respect to the tire circumferential direction.

Such inboard middle sipes28can distribute the circumferential rigidity of the inboard middle land portion16in a well balanced manner from the axially inside to the axially outside to thereby improve the steering stability.

The outboard middle land portion17are, as shown inFIG. 4, provided with

a plurality of outboard middle axial grooves29arranged circumferentially of the tire at intervals and extending from the outboard crown main groove90into the outboard middle land portion17, and

a plurality of outboard middle sipes30arranged circumferentially of the tire at intervals and extending from the outboard shoulder main groove15into the outboard middle land portion17.

All the outboard middle axial grooves29are inclined with respect to the tire axial direction to one circumferential direction. The outboard middle axial grooves29extend substantially straight.

Each of the outboard middle axial grooves29continues to a middle auxiliary sipe31and terminates within the outboard middle land portion17.

The middle auxiliary sipe31extends parallel with the outboard middle axial groove29and terminates within the outboard middle land portion17.

Such middle auxiliary sipes31can exert their edge effect without substantially reducing the rigidity of the outboard middle land portion17, therefore, it is possible to simultaneously pursue the wet performance and the steering stability.

The width of the outboard middle sipe30is smaller than the width of the outboard middle axial groove29.

The closed ends of the outboard middle sipes30are located axially outside the closed ends of the middle auxiliary sipes31. In the tire circumferential direction, the outboard middle sipes30are located between the outboard middle axial grooves29, in other words, they are staggered.

Such outboard middle sipes30can improve the wet performance while maintaining the rigidity in an axially outer part of the outboard middle land portion17in a well balanced manner.

The above-mentioned shoulder land portions13are the inboard shoulder land portion18and the outboard shoulder land portion19.

Preferably, the axial width W8 of the inboard shoulder land portion18is more than the axial width of the center land portion11and more than the axial width of the middle land portion12in order to provide rigidity in the tread shoulder region and improve the steering stability.

The axial width W8 is preferably not less than 1.30 times, more preferably not less than 1.35 times, but not more than 1.50 times, more preferably not more than 1.45 times the axial width W6 of the inboard middle land portion16in order to improve the steering stability while maintaining the wet performance.

The inboard shoulder land portion18is as shown inFIG. 5provided with a plurality of inboard shoulder sipes23extending from the inboard shoulder main groove14to the inboard tread edge Te, in this example axially outwardly beyond the inboard tread edge Te in order to improve the road grip performance of the inboard shoulder land portion18during wet running.

Such inboard shoulder sipes23exert their edge effect to improve the wet performance. The inboard shoulder sipes23do not largely reduce the rigidity of the inboard shoulder land portion18since their width is smaller than the width of the inboard middle axial grooves20. Accordingly, the axially inner groove-sidewall face14ican make larger deformation than the axially outer groove-sidewall face14o, and the generation of air tube resonance sound in the inboard shoulder main groove14can be effectively suppressed.

Each of the inboard shoulder sipes23is composed of an axially inner part33extending axially outwardly from the inboard shoulder main groove14while inclining with respect to the tire axial direction to one circumferential direction,

an axially outer part34extending axially inwardly from the inboard tread edge Te while inclining with respect to the tire axial direction to one circumferential direction same as the axially inner part33, and

a curved portion35connecting between the axially inner part33and the axially outer part34and curved in an arc shape.

The inboard shoulder sipe23having such configuration exerts its edge effect in the tire circumferential direction as well as the tire axial direction, and it is possible to improve wet performance.

The width t3 of the inboard shoulder sipe23is preferably set in a range of not less than 0.15 times, more preferably not less than 0.18 times, but not more than 0.25 times, more preferably not more than 0.22 times the width t1 of the main portion21of the inboard middle axial groove20in order to improve the wet performance without deteriorated the steering stability.

The number of the inboard shoulder sipes23in the inboard shoulder land portion is preferably more than the number of the inboard middle axial grooves20in the inboard middle land portion in order that the occurrence of standing wave in the inboard shoulder main groove14can be effectively prevented to improve the noise performance, and further, the edges are increased to improve the wet performance.

In order to effectively derive such advantageous effects, the number of the inboard shoulder sipes23is preferably not less than 1.6 times, more preferably not less than 1.7 times, but not more than 2.4 times, more preferably not more than 2.3 times the number of the inboard middle axial grooves20.

Since the outboard shoulder land portion19is subjected to larger loads during cornering in compare with the inboard shoulder land portion18, it is preferable that the axial width W9 of the outboard shoulder land portion19is more than the axial width W8 of the inboard shoulder land portion18as shown inFIG. 1andFIG. 6.

If the axial width W9 of the outboard shoulder land portion19becomes small, there is a possibility that the steering stability is deteriorated. If the axial width W9 becomes large, there is a possibility that the wet performance is deteriorated.

Therefore, the axial width W9 is preferably not less than 1.04 times, more preferably not less than 1.06 times, but not more than 1.12 times, more preferably not more than 1.10 times the axial width W8.

The outboard shoulder land portion19includes an axially inner non-grooved rib-like part36and an axially outer grooved annular part37.

The inner non-grooved rib-like part36is not provided with any void such as groove, sipe, slot and the like and extends continuously in the tire circumferential direction. The non-grooved rib-like part36is located adjacently to the outboard shoulder main groove15.

Such non-grooved rib-like part36can improve the noise performance, and can provide rigidity for the outboard shoulder land portion19to improve the steering stability.

The grooved annular part37is provided with grooves and/or sipes.

In the grooved annular part37in this example, a plurality of axially-extending outboard shoulder sipes38are arranged circumferentially of the tire at intervals.

The outboard shoulder sipes38are slightly curved.

Such outboard shoulder sipes38can exert their edge effect without substantially reducing the axial rigidity of the outboard shoulder land portion19, therefore, the wet performance can be improved while maintaining the steering stability.

As shown inFIG. 7as another embodiment of the present invention, the above-mentioned outboard middle axial grooves29may be configured in the same manner as the inboard middle axial grooves20, namely, the groove29has

a main portion extending from the outboard crown main groove90into the outboard middle land portion17, and inclined with respect to the tire axial direction to one circumferential direction, and

a turnback portion extending toward the other circumferential direction from the main portion and terminating within the outboard middle land portion17.

Such outboard middle axial grooves29can prevent the generation of air tube resonance sound in the outboard crown main groove90in the same way as explained above in connection with the inboard middle axial groove20.

Further, as shown inFIG. 7, the above-mentioned inboard center axial grooves25may be configured in the same manner as the inboard middle axial grooves20, namely, the groove25has a main portion extending from the inboard crown main groove9itoward the tire equator C while inclining with respect to the tire axial direction to one circumferential direction, and a turnback portion extending toward the other circumferential direction from the main portion and terminating within the center land portion11.

In the above-mentioned embodiments shown inFIG. 1andFIG. 7, all of the main portions21of the inboard middle axial grooves20, the inboard center axial grooves25(inFIG. 7, their main portions), the outboard center axial grooves26(inFIG. 7, their main portions), the outboard middle axial grooves29, the axially outer parts34of the inboard shoulder sipes23, the inboard middle sipes28, the center sipe27, the middle auxiliary sipes31, the outboard middle sipes30, and the outboard shoulder sipes38are inclined with respect to the tire axial direction to the same direction.

Comparison Tests

Pneumatic tires of size 215/60R16 (rim size 16×6.53) having specifications shown in Table 1 were prepared and tested for the wet performance, steering stability, and noise performance.

Embodiment tire Ex. 1 had the tread pattern shown inFIG. 1.

Embodiment tire Ex. 2 had the tread pattern shown inFIG. 7.

Embodiment tires Exs. 3-11 had tread patterns modified based on the tread pattern shown inFIG. 1.

Comparative example tire Ref. 1 had the tread pattern shown inFIG. 8, wherein all the crown main grooves and shoulder main grooves had an identical groove width, each of the center land portion, inboard middle land portion and outboard middle land portion had no turnback portions, and the inboard shoulder sipes terminated without reaching the inboard tread edge.

Comparative example tires Refs. 2-11 had tread patterns modified based on the tread pattern shown inFIG. 8.

A test car (2400 cc front-wheel drive passenger car) provided on all four wheels with test tires (tire pressure 220 kpa) was run along a 100 meter radius circle on an asphalt road partially provided with a 10 mm depth 20 m long water pool, and the lateral acceleration (lateral G) during running in the water pool was measured at the front wheels, gradually increasing the speed entering into the water pool, to obtain the average for the speed range of from 50 to 80 km/h.

The results are indicated in Table 1 by an index based on Comparative example tire Ref. 4 being 100, wherein the larger is better.

The above-mentioned test car was run on a dry asphalt road in a test course, and the test driver evaluated steering stability based on the handle response, rigidity, grip and the like.

The results are indicated by an index based on Comparative example tire Ref. 2 being 100, wherein the larger the index number, the better the steering stability.

According to the “Test Procedure for Tire Noise” specified in Japanese JASO-C606, the test car was coasted for 50 meter distance at a speed of 60 km/h on an asphalt road surface of a straight test course, and

the maximum noise sound level dB(A) (pass-by noise) was measured with a microphone set at 1.2 meter height from the road surface and 7.5 meter sideways from the running center line in the midpoint of the course.

The results are indicated by an index based on Comparative example tire Ref. 2 being 100, wherein the larger the index number, the smaller the pass-by noise.

From the test results, it was confirmed that, according to the present invention, the noise performance can be improved without sacrificing the wet performance and the steering stability.