A tire includes a tread portion. The tread portion has a main groove extending continuously in a tire circumferential direction, and a land portion adjacent to the main groove. The land portion has lateral grooves extending from the main groove in a tire axial direction. Each of the lateral grooves has a first portion communicating with the main groove, and a second portion connected to the first portion. The first portion has a larger groove width than the second portion and has a smaller groove depth than the second portion.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a tire having lateral grooves provided on a tread portion.

Description of the Background Art

Japanese Laid-Open Patent Publication No. 2016-64726 discloses a tire including middle land portions formed between shoulder main grooves and center main grooves. Each middle land portion has middle lug grooves each including a wide-width portion and a narrow-width portion having a smaller groove width than the wide-width portion. The wide-width portion has a first end of the middle lug groove located at the main groove, and extends toward the inside of the land portion. The narrow-width portion is connected to the wide-width portion via a step portion and has a second end of the middle lug groove. Each middle lug groove has a groove width that gradually decreases from the first end toward the second end. Such a middle lug groove has a large edge component and snow column shearing force, and also smoothly discharges snow held within the groove, to the main groove.

Moreover, the middle lug grooves include first middle lug grooves each having the first end located at the shoulder main groove, and second middle lug grooves each having the first end located at the center main groove, and the first and second middle lug grooves are alternately provided in the tire circumferential direction. Such middle lug grooves ensure the stiffness of the middle land portion in a well-balanced manner in the tire axial direction. Therefore, this type of tire has improved ice and snow road performance and steering stability on a dry road (hereinafter, sometimes simply referred to as “steering stability”).

However, in recent years, global warming has progressed, so that opportunities to drive on dry roads have been increasing as compared to those on ice and snow roads. Therefore, for such tires, further improvement of steering stability with ice and snow road performance maintained is required.

The present invention has been made in view of the above-described problem, and a main object of the present invention is to provide a tire that is capable of improving steering stability while maintaining ice and snow road performance.

SUMMARY OF THE INVENTION

The present invention is directed to a tire including a tread portion, wherein the tread portion has a main groove continuously extending in a tire circumferential direction, and a land portion adjacent to the main groove, the land portion has lateral grooves extending from the main groove in a tire axial direction, each of the lateral grooves has a first portion communicating with the main groove, and a second portion connected to the first portion, and the first portion has a larger groove width than the second portion and has a smaller groove depth than the second portion.

In the tire according to the present invention, preferably, the first portion includes a main body part having a first depth and a sub part having a second depth smaller than the first depth, and the main body part and the sub part are aligned in the tire circumferential direction.

In the tire according to the present invention, the first portion preferably includes a groove wall formed in a step shape by the main body part and the sub part.

In the tire according to the present invention, the main body part of the first portion preferably has a groove width equal to that of the second portion.

In the tire according to the present invention, each of the lateral grooves preferably has a terminal end within the land portion.

In the tire according to the present invention, the land portion preferably has sipes extending from the terminal end.

In the tire according to the present invention, preferably, the land portion has circumferential recesses that are provided at a corner portion between a tread surface of the land portion and a groove wall of the main groove and that extend in the tire circumferential direction, and each of the circumferential recesses communicates with a first side in the tire circumferential direction of the first portion of the lateral groove.

In the tire according to the present invention, the first portion preferably has a main body part having a first depth, and each of the circumferential recesses communicates with the main body part of the first portion of the lateral groove.

In the tire according to the present invention, preferably, the land portion has chamfers that are provided at the corner portion between the tread surface of the land portion and the groove wall of the main groove, that extend in the tire circumferential direction, and that are recessed less than the circumferential recesses, and each of the chamfers communicates with a second side in the tire circumferential direction of the first portion of the lateral groove.

In the tire according to the present invention, preferably, the tread portion has a crown land portion, a pair of middle land portions adjacent to the crown land portion, and a pair of shoulder land portions adjacent to the middle land portions and provided at endmost tread edge sides, and the land portion is formed as the pair of middle land portions.

In the tire according to the present invention, preferably, each of the middle land portions has, as the lateral grooves, first middle lateral grooves each having the first portion at the crown land portion side, and second middle lateral grooves each having the first portion at the shoulder land portion side, and the first middle lateral grooves and the second middle lateral grooves are alternately provided in the tire circumferential direction.

In the tire according to the present invention, preferably, the tread portion specifies how the tire is to be oriented when mounted to a vehicle, the middle land portions include an outer middle land portion located at an outer side of the vehicle when the tire is mounted on the vehicle, and, in the outer middle land portion, the second middle lateral grooves are formed without facing the first portions of the first middle lateral grooves in the tire circumferential direction.

In the tire according to the present invention, preferably, the outer middle land portion has outer middle sipes extending in the tire axial direction, and a length in the tire axial direction of each outer middle sipe is 125% to 150% of a length in the tire axial direction of each of the first middle lateral grooves and the second middle lateral grooves provided to the outer middle land portion.

In the tire according to the present invention, a length in the tire axial direction of each of the first middle lateral grooves and the second middle lateral grooves is preferably 50% to 75% of a width in the tire axial direction of the outer middle land portion.

In the tire according to the present invention, preferably, the tread portion specifies how the tire is to be oriented when mounted to a vehicle, the middle land portions include an inner middle land portion located at an inner side of the vehicle when the tire is mounted on the vehicle, and, in the inner middle land portion, the second middle lateral grooves are formed so as to face the first portions of the first middle lateral grooves in the tire circumferential direction.

In the tire according to the present invention, the land portion is preferably formed as the crown land portion.

In the tire according to the present invention, the land portion has lateral grooves each of which has a first portion communicating with the main groove and a second portion connected to the first portion. Generally, the stiffness of a region, adjacent to the first portion, of the land portion is lower than the stiffness of a region, adjacent to the second portion, of the land portion. In each of the lateral grooves of the present invention, the first portion has a larger groove width than the second portion and has a smaller groove depth than the second portion. The land portion having the lateral grooves including the first portion having a smaller groove depth as described above has a reduced difference between the stiffness of the region adjacent to the first portion and the stiffness of the region adjacent to the second portion, and thus can exert effective friction force on a road surface over a wide range of the tread surface of the land portion. Moreover, the first portion having a larger groove width smoothly discharges snow or ice (water may be contained) held within the second portion, to the main groove. Therefore, the tire according to the present invention is capable of improving steering stability while maintaining ice and snow road performance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG.1is a partial development of a tread portion2of a tire1according to the present embodiment.FIG.1shows a tread portion2of a pneumatic tire for a passenger car as a preferred embodiment. However, the present invention can be applied to a pneumatic tire for a two-wheeled automotive vehicle and a heavy-duty pneumatic tire, and also to tires in the other categories.

As shown inFIG.1, the tread portion2of the present embodiment has main grooves3continuously extending in the tire circumferential direction, and a land portion4adjacent to the main grooves3. The land portion4of this embodiment is demarcated by the main grooves3,3provided at both sides in the tire axial direction. The land portion4is not limited to such a mode, and may be demarcated, for example, by the main groove3and a tread edge Te (shown inFIG.4). For the main grooves3and the land portion4, known modes can be selected as appropriate.

The land portion4of this embodiment has lateral grooves5extending from the main grooves3in the tire axial direction. Such lateral grooves5have snow column shearing force and exhibit ice and snow road performance.

The lateral grooves5of the present embodiment are inclined relative to the tire axial direction. The lateral grooves5are, for example, aligned in the tire circumferential direction. In the present embodiment, the respective lateral grooves5are inclined in the same direction.

FIG.2is a perspective view of the lateral groove5.FIG.3(a)is a cross-sectional view taken along a line A-A inFIG.1, andFIG.3(b)is an end view as seen from a line B-B inFIG.1. As shown inFIG.1toFIG.3(b), the lateral groove5includes a first portion6that communicates with the main groove3, and a second portion7that is connected to the first portion6. The first portion6has a larger groove width than the second portion7and has a smaller groove depth than the second portion7. The land portion4having the lateral grooves5each including the first portion6having a smaller groove depth as described above, has a reduced difference between the stiffness of a region4sadjacent to the first portion6in the tire circumferential direction and the stiffness of a region4tadjacent to the second portion7in the tire circumferential direction. Thus, the land portion4can exert great friction force on a road surface over a wide range of a tread surface4hof the land portion4. In addition, the first portion6having a larger groove width maintains smooth discharge of snow or ice held within the second portion7. Therefore, such a tire1is capable of improving steering stability while maintaining ice and snow road performance.

The first portion6includes a main body part6A having a first depth da, and a sub part6B having a second depth db smaller than the first depth da, and the main body part6A and the sub part6B are aligned in the tire circumferential direction. The sub part6B of such a first portion6keeps the stiffness of the region4sof the land portion4high, and thus the first portion6improves the steering stability. In addition, the main body part6A exerts great snow column shearing force.

In the present embodiment, the second depth db of the sub part6B is preferably 60% to 85% of the first depth da of the main body part6A. If the second depth db of the sub part6B is less than 60% of the first depth da of the main body part6A, or if the second depth db of the sub part6B is greater than 85% of the first depth da of the main body part6A, imbalance in stiffness between the respective regions4sand4tmay occur, resulting in failure to effectively exert the above-described action.

When the second depth db of the sub part6B is equal to the first depth da of the main body part6A, that is, when the first portion6is not divided into the main body part6A and the sub part6B, snow or ice within the second portion7is smoothly discharged from the main body part6A and the sub part6B.

The first portion6includes a groove wall8formed in a step shape by the main body part6A and the sub part6B. Such a groove wall8increases snow column shearing force. The groove wall8includes, for example, a first groove wall8a, a second groove wall8b, and a third groove wall8c. In the present embodiment, the first groove wall8aextends in the tire radial direction so as to be connected to a groove bottom6sof the main body part6A, and forms a groove wall of the main body part6A. In the present embodiment, the second groove wall8bextends from the tread surface4hof the land portion4inward in the tire radial direction, and forms a groove wall of the sub part6B. In the present embodiment, the third groove wall8cconnects the first groove wall8ato the second groove wall8b, and forms a groove bottom of the sub part6B. The groove wall8is not limited to such a mode.

The groove width w1of the main body part6A of the first portion6is preferably equal to the groove width w2of the second portion7. Accordingly, an excessive reduction in the stiffness of the land portion4is inhibited. In the present embodiment, the main body part6A has a first groove edge6cextending in the tire axial direction. A groove edge5aat a first side f1in the tire circumferential direction of the lateral groove5is formed, for example, by the first groove edge6cand a groove edge7aat the first side f1in the tire circumferential direction of the second portion7such that one smooth line (arc) is drawn. Accordingly, snow within the second portion7is smoothly discharged to the main groove3side. In the present specification, the first side f is defined as a direction to the main body part6A side as seen from the sub part6B, and a second side f2is defined as a direction to the sub part6B side as seen from the main body part6A. In the present specification, the groove width of each lateral groove5is a width parallel to the tire circumferential direction.

The sub part6B includes a second groove edge6dextending from the main groove3in the tire axial direction, and a third groove edge6ethat connects the second groove edge6dto a groove edge7bat the second side12in the tire circumferential direction of the second portion7and that extends in the tire circumferential direction. Accordingly, a groove edge5bat the second side12in the tire circumferential direction of the lateral groove5is formed in a crank shape by the second groove edge6d, the third groove edge6e, and the groove edge7bof the second portion7.

In order to exert such action effectively, each lateral groove5is preferably formed in the following mode. The first depth da of the main body part6A is preferably 50% to 80% of the groove depth d1of the second portion7. The length L2in the tire axial direction of the first portion6is preferably 15% to 45% of the length L1in the tire axial direction of the lateral groove5. The groove width w2of the second portion7is preferably 75% to 95% of the groove width W3of the first portion6. The length L2bin the tire axial direction of the sub part6B is preferably 80% to 120% of the length L2ain the tire axial direction of the main body part6A. In the present embodiment, the length L2bin the tire axial direction of the sub part6B is equal to the length L2ain the tire axial direction of the main body part6A.

In the present embodiment, each lateral groove5has a terminal end5ewithin the land portion4. Such a lateral groove5keeps the stiffness of the land portion4high. In the present embodiment, the terminal end5eis provided to the second portion7.

In the present embodiment, the land portion4has sipes10extending from the terminal ends5e. Such sipes10each increase deformation of the lateral groove5and effectively push and discharge snow or ice within the groove when the lateral groove5comes into contact with the ground. In addition, the sipes10scratch an ice road surface to generate traction. The sipes10enhance the ice and snow road performance. In the present embodiment, the sipes10extend in a straight manner. The sipes10can take various modes such as a wavy manner and a zigzag manner.

In the present embodiment, each sipe10connects the main groove3to the lateral groove5. Accordingly, the ice and snow road performance is kept high. The sipe10is not limited to such a mode, and, for example, may have a terminal end (not shown) within the land portion4. In the present specification, a sipe is defined as a cut having a width less than 1.5 mm and is distinguished from a groove having a width equal to or greater than 1.5 mm.

The sipe10preferably has a depth d3smaller than the groove depth d1of the second portion7of the lateral groove5, and the depth d3is further preferably 20% to 40% of the groove depth d1. If the depth d3of the sipe10is less than 20% of the groove depth d1of the second portion7, deformation of the lateral groove5may be reduced, and thus it may be impossible to keep the ice and snow road performance high. If the depth d3of the sipe10is equal to or larger than the groove depth d1of the second portion7, the stiffness of the land portion4may be decreased, and thus the steering stability may deteriorate.

The land portion4has circumferential recesses12that are provided at a corner portion k between the tread surface4hof the land portion4and a groove wall3eof the main groove3and that extend in the tire circumferential direction. In the present embodiment, each circumferential recess12includes a wall portion12aextending from the tread surface4hinward in the tire radial direction, and a bottom portion12bthat extends from the inner end in the tire radial direction of the wall portion12aalong the tread surface4hand that is connected to the groove wall3e. Such a circumferential recess12exerts snow column shearing force. The circumferential recess12is not limited to such a mode.

In the present embodiment, the circumferential recess12has a width w4in the tire axial direction of 1.0 to 3.0 mm. The circumferential recess12has, for example, a depth d4in the tire radial direction of 1.0 to 3.0 mm. The length L4in the tire circumferential direction of the circumferential recess12is preferably 20% to 40% of a pitch P in the tire circumferential direction between the lateral grooves5.

The circumferential recess12communicates with the first side f1in the tire circumferential direction of the first portion6of the lateral groove5. That is, the circumferential recess12communicates with the main body part6A having a first depth da, and thus effectively discharges snow or ice within the groove in cooperation with the main body part6A.

The land portion4has chamfers14provided at the corner portion k between the tread surface4hof the land portion4and the groove wall3eof the main groove3, and the chamfers14extend in the tire circumferential direction and are recessed less than the circumferential recesses12. In the present embodiment, each chamfer14is formed as a surface inclined more gently relative to the tire radial direction than the groove wall3eof the main groove3. Such a chamfer14exerts scratching force on a road surface while maintaining the stiffness of the corner portion k, thereby enhancing the steering stability and the ice and snow road performance in a well-balanced manner. For example, the chamfer14may be formed as a linear flat surface as shown inFIG.3(a), or may be formed as an arc surface that projects outward in the tire radial direction.

Such a chamfer14preferably has a width w5in the tire axial direction of equal to or greater than 0.5 mm and less than 1.0 mm. In addition, the chamfer14preferably has, for example, a depth d5in the tire radial direction of equal to or greater than 0.5 mm and less than 1.0 mm.

In the present embodiment, each chamfer14communicates with the second side f2in the tire circumferential direction of the first portion6of the lateral groove5. The chamfers14are provided, for example, at the corner portion k excluding the lateral grooves5and the circumferential recesses12. Accordingly, the above-described action is effectively exerted. The land portion4of the present embodiment has corner portions k at both sides in the tire axial direction, and the circumferential recesses12and the chamfers14are provided at each corner portion k.

FIG.4is a development of the entirety of the tread portion2having the lateral grooves5shown inFIG.1toFIG.3(b). As shown inFIG.4, the tread portion2of this embodiment has a plurality of main grooves3. The main grooves3include a pair of shoulder main grooves3A located at the endmost tread edge Te sides, and a pair of crown main grooves3B adjacent to the inner sides in the tire axial direction of the respective shoulder main grooves3A.

Accordingly, the land portion4has, for example, a crown land portion4A, a pair of middle land portions4B adjacent to the crown land portion4A, and a pair of shoulder land portions4C adjacent to the middle land portions4B and provided at the endmost tread edge Te sides. In the present embodiment, the crown land portion4A is demarcated between the pair of crown main grooves3B. In the present embodiment, each middle land portion4B is demarcated between the crown main groove3B and the shoulder main groove3A. In the present embodiment, each shoulder land portion4C is demarcated between the shoulder main groove3A and the tread edge Te.

The “tread edges” Te are defined as ground contact positions at both endmost sides in the tire axial direction when a normal load is applied to the tire1, in a normal state where the tire1is mounted to a normal rim (not shown) and inflated to a normal internal pressure and no load is applied to the tire1, such that the tire1is brought into contact with a plane at a camber angle of 0 degrees. In the normal state, the distance in the tire axial direction between both tread edges Te is defined as a tread width TW. Unless otherwise specified, dimensions of components of the tire and the like are values measured in the normal state.

The “normal rim” is a rim that is defined, in a standard system including a standard on which the tire is based, by the standard for each tire, and is, for example, the “standard rim” in the JATMA standard, the “Design Rim” in the TRA standard, or the “Measuring Rim” in the ETRTO standard.

The “normal internal pressure” is an air pressure that is defined, in a standard system including a standard on which the tire is based, by the standard for each tire, and is the “maximum air pressure” in the JATMA standard, the maximum value indicated in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, or the “INFLATION PRESSURE” in the ETRTO standard. In the case where the tire is for a passenger car, the normal internal pressure is 180 kPa.

The “normal load” is a load that is defined, in a standard system including a standard on which the tire is based, by the standard for each tire, and is the “maximum load capacity” in the JATMA standard, the maximum value indicated in the table “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in the TRA standard, or the “LOAD CAPACITY” in the ETRTO standard. In the case where the tire is for a passenger car, the normal load is a load corresponding to 88% of the load described above.

In the present embodiment, the land portion4having the above-described lateral grooves5is formed as the pair of middle land portions4B. Greater contact pressure acts on the middle land portions4B than on the shoulder land portions4C. During turning, greater lateral force acts on the middle land portions4B than on the crown land portion4A. By providing the lateral grooves5to the middle land portions4B on which relatively great contact pressure and lateral force act as described above, it is possible to effectively exert action to enhance the steering stability while maintaining the ice and snow road performance.

Each middle land portion4B has, as the lateral grooves5, first middle lateral grooves20each having a first portion6at the crown land portion4A side, and second middle lateral grooves21each having a first portion6at the shoulder land portions4C side. Accordingly, great snow column shearing force can be exerted, and snow or ice within the grooves can be discharged to the crown main groove3B and the shoulder main groove3A.

The first middle lateral grooves20and the second middle lateral grooves21are alternately provided in the tire circumferential direction. Accordingly, the stiffness in the tire circumferential direction of each middle land portion4B can be ensured in a well-balanced manner in the tire axial direction.

In the present embodiment, the tread portion2specifies how the tire1is to be oriented when mounted to a vehicle. Accordingly, the tread edges Te of the present embodiment include an outer tread edge To located at the outer side of the vehicle when the tire1is mounted on the vehicle, and an inner tread edge Ti located at the inner side of the vehicle when the tire1is mounted on the vehicle.

In the present embodiment, the shoulder main grooves3A include an outer shoulder main groove3alocated at the endmost outer tread edge To side, and an inner shoulder main groove3blocated at the endmost inner tread edge Ti side. In addition, the crown main grooves3B include an outer crown main groove3cadjacent to the endmost outer shoulder main groove3a, and an inner crown main groove3dadjacent to the endmost inner shoulder main groove3b.

The respective middle land portions4B include an outer middle land portion4alocated at the outer tread edge To side, and an inner middle land portion4blocated at the inner tread edge Ti side. The respective shoulder land portions4C include an outer shoulder land portion4clocated at the outer tread edge To side, and an inner shoulder land portion4dlocated at the inner tread edge Ti side.

FIG.5is a development of the outer middle land portion4a. The outer middle land portion4ais generally a land portion4on which greater lateral force acts than on the crown land portion4A and the inner middle land portion4b(shown inFIG.4) during turning, and thus keeping the stiffness of the outer middle land portion4ahigh is effective for improving the steering stability. Thus, as shown inFIG.5, in the outer middle land portion4a, the second middle lateral grooves21are formed without facing the first portions6of the first middle lateral grooves20in the tire circumferential direction. The stiffness of such an outer middle land portion4ais kept high, and thus the steering stability is enhanced. The distance L6in the tire axial direction between an inner end21aat the inner tread edge Ti side of the second middle lateral groove21and an inner end22aat the outer tread edge To side of the first portion6of the first middle lateral groove20is preferably 4% to 10% of the width Wa in the tire axial direction of the outer middle land portion4a.

From the same viewpoint, in the outer middle land portion4a, the first middle lateral grooves20are preferably formed without facing the first portions6of the second middle lateral grooves21in the tire circumferential direction. In the outer middle land portion4a, the distance L7in the tire axial direction between an inner end20aat the outer tread edge To side of the first middle lateral groove20and an inner end22bat the inner tread edge Ti side of the first portion6of the second middle lateral groove21is preferably larger than the distance L6in the tire axial direction. That is, in the present embodiment, a region Sb where the distance L7is taken is located outward in the tire axial direction of a region Sa where the distance L6is taken, and thus greater lateral force acts on the region Sb. Therefore, by making the distance L7larger than the distance L6, the steering stability can be further enhanced. From such a viewpoint, the distance L7is preferably 10% to 20% of the width Wa in the tire axial direction of the outer middle land portion4a.

In order to further improve the steering stability while further maintaining the ice and snow road performance, the length L8in the tire axial direction of each of the first middle lateral grooves20and the second middle lateral grooves21of the outer middle land portion4ais preferably 50% to 75% of the width Wa in the tire axial direction of the outer middle land portion4a.

The outer middle land portion4aof the present embodiment has outer middle Sipes24extending in the tire axial direction. In the present embodiment, each outer middle sipe24extends from the main groove3and terminates within the outer middle land portion4a. Such an outer middle sipe24inhibits an excessive reduction in the stiffness of the outer middle land portion4a.

The outer middle sipes24include, for example, first outer middle sipes24aconnected to the outer shoulder main groove3a, and second outer middle sipes24bconnected to the outer crown main groove3c. Accordingly, the stiffness of the outer middle land portion4acan be ensured in a well-balanced manner in the tire axial direction.

The number of the first outer middle sipes24ais smaller than the number of the second outer middle sipes24b. Accordingly, the stiffness of a region Sc at the outer side in the tire axial direction of the outer middle land portion4aon which relatively great lateral force acts is kept higher than the stiffness of a region Sd at the inner side in the tire axial direction of the outer middle land portion4a. Thus, the steering stability is improved.

Each outer middle sipe24is formed such that the length L9in the tire axial direction of the outer middle sipe24is larger than the length L8in the tire axial direction of each of the first middle lateral grooves20and the second middle lateral grooves21provided to the outer middle land portion4a. Accordingly, the above-described action is effectively exerted. For example, the length L9in the tire axial direction of the outer middle sipe24is preferably 125% to 150% of the length L8in the tire axial direction of each of the first middle lateral grooves20and the second middle lateral grooves21.

Each outer middle sipe24communicates only with the chamfer14without communicating with the circumferential recess12. Such an outer middle sipe24inhibits a reduction in the stiffness of the outer middle land portion4a.

FIG.6is a development of the inner middle land portion4b. As shown inFIG.6, in the inner middle land portion4b, the second middle lateral grooves21are formed so as to face the first portions6of the first middle lateral grooves20in the tire circumferential direction. Generally, relatively smaller lateral force acts on the inner middle land portion4bthan on the outer middle land portion4a. Thus, even when the stiffness of the inner middle land portion4bis reduced to be lower than that of the outer middle land portion4a, the influence of such a reduction on the steering stability is small. Thus, by making the second middle lateral grooves21and the first portions6of the first middle lateral grooves20face each other in the tire circumferential direction, that is, overlap each other in the tire circumferential direction, greater snow column shearing force can be obtained, and maintenance of the ice and snow road performance is promoted. The distance L10in the tire axial direction between an inner end21bat the outer tread edge To side of the second middle lateral groove21and an inner end22cat the inner tread edge Ti side of the first portion6of the first middle lateral groove20is preferably 10% to 20% of the width Wb in the tire axial direction of the inner middle land portion4b.

From the same viewpoint, in the inner middle land portion4b, the first middle lateral grooves20are preferably formed so as to face the first portions6of the second middle lateral grooves21in the tire circumferential direction. In the inner middle land portion4b, the distance L11in the tire axial direction between an inner end20bat the inner tread edge Ti side of the first middle lateral groove20and an inner end22dat the outer tread edge To side of the first portion6of the second middle lateral groove21is preferably smaller than the distance L10in the tire axial direction. That is, in the present embodiment, a region Sf where the distance L11is taken is located outward in the tire axial direction of a region Se where the distance L10is taken, and thus greater lateral force acts on the region Sf. Thus, by making the distance L11smaller than the distance L10, the stiffness of the region at the outer side in the tire axial direction of the inner middle land portion4bcan be maintained, and the steering stability can be further enhanced. From such a viewpoint, the distance L11is preferably 4% to 10% of the width Wb in the tire axial direction of the inner middle land portion4b.

In order to further improve the steering stability while further maintaining the ice and snow road performance, the length L12in the tire axial direction of each of the first middle lateral grooves20and the second middle lateral grooves21of the inner middle land portion4bis preferably 70% to 95% of the width Wb in the tire axial direction of the inner middle land portion4b.

The inner middle land portion4bof the present embodiment has inner middle sipes25extending in the tire axial direction. In the present embodiment, each inner middle sipe25crosses the inner middle land portion4b. Such an inner middle sipe25exerts great friction force on an ice road surface.

In the present embodiment, each inner middle sipe25communicates with the circumferential recess12. Accordingly, when the circumferential recess12comes into contact with the ground, deformation of the circumferential recess12is promoted, and snow or ice within the circumferential recess12is smoothly discharged.

FIG.7is a development of the crown land portion4A. As shown inFIG.7, the land portion4having the lateral grooves5each having the first portion6and the second portion7may be formed as the crown land portion4A. The crown land portion4A is a land portion4on which great contact pressure acts. Thus, the lateral grooves5provided to the crown land portion4A exert great snow column shearing force.

The lateral grooves5include first crown lateral grooves27each having a first portion6that communicates with the outer crown main groove3c, and second crown lateral grooves28each having a first portion6that communicates with the inner crown main groove3d. In the present embodiment, the first crown lateral grooves27and the second crown lateral grooves28are alternately provided in the tire circumferential direction. Accordingly, the stiffness in the tire circumferential direction of the crown land portion4A can be ensured in a well-balanced manner in the tire axial direction.

In the crown land portion4A, the second crown lateral grooves28are formed without facing the first portions6of the first crown lateral grooves27in the tire circumferential direction. Similarly, the first crown lateral grooves27are formed without facing the first portions6of the second crown lateral grooves28in the tire circumferential direction. The stiffness of such a crown land portion4A is kept high, and thus the steering stability is enhanced. The distance L13in the tire axial direction between an inner end28aat the outer tread edge To side of the second crown lateral groove28and an inner end22eat the inner tread edge Ti side of the first portion6of the first crown lateral groove27is preferably 10% to 20% of the width Wc in the tire axial direction of the crown land portion4A. The distance L14in the tire axial direction between an inner end27aat the inner tread edge Ti side of the first crown lateral groove27and an inner end22fat the outer tread edge To side of the first portion6of the second crown lateral groove28is preferably 10% to 20% of the width Wc in the tire axial direction of the crown land portion4A.

The length L15in the tire axial direction of each lateral groove5provided to the crown land portion4A is not particularly limited, but is preferably 50% to 75% of the width Wc in the tire axial direction of the crown land portion4A.

The crown land portion4A of the present embodiment has crown sipes30extending in the tire axial direction. In the present embodiment, each crown sipe30crosses the crown land portion4A. Such a crown sipe30exerts great friction force on an ice road surface.

In the present embodiment, each crown sipe30communicates with the circumferential recess12. Accordingly, when the circumferential recess12comes into contact with the ground, deformation of the circumferential recess12is promoted, and snow or ice within the circumferential recess12is smoothly discharged.

FIG.8is a development of the outer shoulder land portion4c. As shown inFIG.8, the outer shoulder land portion4cof the present embodiment has outer shoulder lateral grooves32extending from the outer shoulder main groove3atoward the outer tread edge To side.

In the present embodiment, each outer shoulder lateral groove32includes a first outer portion33extending in the tire axial direction at the outer tread edge To side, and a second outer portion34that connects the first outer portion33to the outer shoulder main groove3aand that has a smaller groove width than the first outer portion33. Such an outer shoulder lateral groove32reduces the difference in stiffness between a region R1, near the second outer portion34, having relatively low stiffness and a region R2, near the first outer portion33, having relatively high stiffness. Accordingly, the outer shoulder land portion4cprovides uniform friction force over a wide range to a road surface, and thus improves the steering stability.

The length L16in the tire axial direction of the second outer portion34is preferably 20% to 40% of the width Wd in the tire axial direction of the outer shoulder land portion4c.

In the present embodiment, the outer shoulder land portion4chas circumferential recesses36, and chamfers37that are recessed less than the circumferential recesses36. In the present embodiment, the circumferential recesses36and the chamfers37are provided at a corner portion k1between a tread surface4kof the outer shoulder land portion4cand a groove wall3fof the outer shoulder main groove3a. Each circumferential recess36is, for example, connected to the second outer portion34. Each chamfer37is, for example, connected to the second outer portion34or the circumferential recess36.

The circumferential recesses36are formed in the same manner as the circumferential recesses12described with reference toFIG.1toFIG.3(b), and thus the detailed description thereof is omitted. The chamfers37are also formed in the same manner as the chamfers14described with reference toFIG.1toFIG.3(b), and thus the detailed description thereof is omitted.

In the present embodiment, the outer shoulder land portion4chas outer shoulder sipes40extending in the tire axial direction. In the present embodiment, the outer shoulder sipes40include first outer shoulder sipes40A and second outer shoulder sipes40B. Each first outer shoulder sipe40A of the present embodiment terminates at both ends thereof within the outer shoulder land portion4c. Each second outer shoulder sipe40B has an inner end located outward of the first outer shoulder sipe40A in the tire axial direction, and extends to the outer tread edge To. Such outer shoulder sipes40maintain the ice and snow road performance while inhibiting an excessive reduction in the stiffness of the outer shoulder land portion4c.

FIG.9is a development of the inner shoulder land portion4d. As shown inFIG.9, the inner shoulder land portion4dof the present embodiment has inner shoulder lateral grooves42extending from the inner shoulder main groove3btoward the inner tread edge Ti side.

In the present embodiment, each inner shoulder lateral groove42has a tie bar43raised at a groove bottom thereof. Such a tie bar43inhibits a reduction in the stiffness of the inner shoulder land portion4dand enhances the steering stability. The tie bar43is connected to the inner shoulder main groove3b. Accordingly, the difference in stiffness between the inner and outer portions in the tire axial direction of the inner shoulder land portion4dis reduced, and thus the steering stability can be further enhanced.

The length L17in the tire axial direction of such a tie bar43is, for example, preferably 10% to 25% of the width We in the tire axial direction of the inner middle land portion4b. A tie bar depth (not shown) from a tread surface4nof the inner shoulder land portion4dto an outer surface43eof the tie bar43is preferably 25% to 45% of the groove depth (not shown) of the inner shoulder main groove3b.

In the present embodiment, the inner shoulder land portion4dhas circumferential recesses46, and chamfers48that are recessed less than the circumferential recesses46. In the present embodiment, the circumferential recesses46and the chamfers48are provided at a corner portion k2between the tread surface4nof the inner shoulder land portion4dand a groove wall3kof the inner shoulder main groove3b. Each circumferential recess46is, for example, connected to the inner shoulder lateral groove42. Each chamfer48is, for example, connected to the inner shoulder lateral groove42or the circumferential recess46.

The circumferential recesses46are formed in the same manner as the circumferential recesses12described with reference toFIG.1toFIG.3(b), and thus the detailed description thereof is omitted. The chamfers48are also formed in the same manner as the chamfers14described with reference toFIG.1toFIG.3(b), and thus the detailed description thereof is omitted.

In the present embodiment, the inner shoulder land portion4dhas inner shoulder sipes50extending in the tire axial direction. In the present embodiment, the inner shoulder sipes50include first inner shoulder sipes50A and second inner shoulder sipes50B. Each first inner shoulder sipe50A of the present embodiment extends from the inner shoulder main groove3boutward in the tire axial direction and terminates within the inner shoulder land portion4d. Each second inner shoulder sipe50B has an inner end located outward of the first inner shoulder sipe50A in the tire axial direction, and extends to the inner tread edge Ti.

Although the tire according to the embodiment of the present invention has been described in detail above, the present invention is not limited to the above specific embodiments, and various modifications can be made to implement the present invention.

EXAMPLES

Tires with a size of 215/60R 16 having the basic pattern inFIG.4were produced as sample tires on the basis of specifications in Table 1, and were tested for ice and snow road performance and steering stability. The common specifications and the test method for all the sample tires are as follows.

Ice and Snow Road Performance/Steering Stability

The sample tires were mounted to all the wheels of a front-wheel-drive vehicle having an engine displacement of 1500 cc, under the following conditions, and a test driver drove the vehicle on a test course with an ice and snow road surface and on a test course with a dry asphalt road surface. Sensory evaluation was made by the test driver for running characteristics regarding handling responsiveness, traction, grip performance, and the like at that time. The results are indicated as scores with the result of Comparative Example 1 being regarded as 100. A higher numerical value indicates that the result is better.

As a result of the test, it was confirmed that the tires of the examples exhibit good steering stability, while maintaining ice and snow road performance, as compared to the tires of the comparative examples.