Pneumatic tire

A pneumatic tire includes a first block formed by first lug grooves defining a first land portion that is defined by a first main groove and a second main groove. The first block includes: a first circumferential narrow groove extending in the tire circumferential direction with at least one end communicating with one of the first lug grooves, a set of two lateral narrow grooves extending in the tire width direction with one end communicating with the first main groove, a first lateral auxiliary groove extending in the tire width direction with a first end communicating with the second main groove and a second end communicating with the first circumferential narrow groove, the second end of the first lateral auxiliary groove being disposed at a position in the tire circumferential direction between end portions of the set of first lateral narrow grooves proximal to the first circumferential narrow groove.

TECHNICAL FIELD

The present technology relates to a pneumatic tire and particularly relates to a pneumatic tire capable of improving braking performance on wet road surfaces and snowy road surfaces in a compatible manner and uneven wear resistance performance.

BACKGROUND ART

Generally, all-season pneumatic tires used all year round are required to have excellent running performance (for example, braking performance) on various road surfaces such as dry road surfaces, wet road surfaces, and snowy road surfaces, as well as having excellent uneven wear resistance performance. In the art, pneumatic tires designed to achieve good performance in a compatible manner in two areas among such various areas are known. Examples include a pneumatic tire that includes, in a tread surface, two circumferential grooves extending in the tire circumferential direction arranged side by side in the tire width direction, and lateral grooves disposed in land portions formed between the circumferential grooves, the lateral grooves extending in the tire width direction from the circumferential grooves.

For example, Japanese Unexamined Patent Application Publication No. 2012-126214A describes a pneumatic tire designed to improve the running performance on snowy road surfaces while maintaining the steering stability performance on dry road surfaces. The pneumatic tire includes two circumferential grooves formed in a land portion, and lateral grooves including narrow grooves and/or sipes that extend the entire width of the land portion, the lateral grooves having a zigzag shape. Japanese Unexamined Patent Application Publication No. 2013-107492A describes a pneumatic tire designed to achieve good drainage performance and steering stability performance in a highly compatible manner. The pneumatic tire includes two circumferential grooves; a land portion formed therebetween; first inclined grooves extending in the tire width direction at an incline from one of the circumferential grooves and terminating within the land portion; second inclined grooves extending in the tire width direction at an incline from the other circumferential groove and terminating within the land portion, the first inclined grooves and the second inclined grooves being alternately disposed in the tire circumferential direction; first circumferential sipes extending in the tire circumferential direction from the end portion of the first inclined groove in the land portion to an intermediate portion of the second inclined groove; and second circumferential sipes extending from the intermediate portion of the second inclined groove along an extension line of the first circumferential sipes and terminating within the land portion.

The pneumatic tires described in Japanese Unexamined Patent Application Publication Nos. 2012-126214A and 2013-107492A described above may achieve good performances in a compatible manner especially in terms of the two performances mentioned above. However, extending this to enhance another performance so that good performances in three areas are achieved in a compatible manner is difficult. In other words, in the pneumatic tire of Japanese Unexamined Patent Application Publication No. 2012-126214A, by arranging the lateral grooves across the whole width of the land portion with a zigzag shape, quadrangular blocks formed by two lateral grooves extending in the same direction are formed into triangular blocks by being divided at an incline by the lateral grooves extending in a different direction. Thus, the rigidity of the land portion decreases and the uneven wear resistance performance become insufficient. The pneumatic tire of Japanese Unexamined Patent Application Publication No. 2013-107492A includes the first circumferential sipes and the second circumferential sipes. However, as these sipes extend in the tire circumferential direction, the edge effect they provide is insignificant. As a result, the braking performance on snowy road surfaces is insufficient.

SUMMARY

The present technology provides a pneumatic tire capable of improving braking performance on wet road surfaces and snowy road surfaces in a compatible manner and uneven wear resistance performance.

A pneumatic tire according to an embodiment of the present technology includes:

a first main groove and a second main groove that extend in a tire circumferential direction formed in a tread portion side by side in a tire width direction;

a first land portion defined between the first main groove and the second main groove;

a plurality of first lug grooves that extend in the tire width direction disposed in the first land portion at intervals in the tire circumferential direction, each of the plurality of first lug grooves communicating with the first main groove and the second main groove at both ends; and

a plurality of first blocks formed by the plurality of first lug grooves defining the first land portion;

each of the plurality of first blocks comprising:

a first circumferential narrow groove that extends in the tire circumferential direction with at least one end communicating with one of the first lug grooves,

a set of two lateral narrow grooves that extend in the tire width direction with one end communicating with the first main groove,

a first lateral auxiliary groove that extends in the tire width direction with a first end communicating with the second main groove and a second end communicating with the first circumferential narrow groove, the second end of the first lateral auxiliary groove being disposed at a position in the tire circumferential direction between end portions of the set of first lateral narrow grooves proximal to the first circumferential narrow groove.

In an embodiment of the present technology, as described above, in the first land portion, the first blocks defined by the first lug grooves are further divided by the first circumferential narrow grooves, the first lateral narrow grooves, and the first lateral auxiliary grooves. This can improve the snow traction and the braking performance on snowy road surfaces. Additionally, the drainage performance expected to be provided by the first circumferential narrow grooves, the first lateral narrow grooves, and the first lateral auxiliary grooves can improve wet performance. Furthermore, by the set of two lateral narrow grooves and the first lateral auxiliary groove being arranged as described above, a reduction in block rigidity can be suppressed, and uneven wear caused by a difference in rigidity between adjacent blocks can be suppressed.

In an embodiment of the present technology, the second main groove preferably has a smaller groove width than the first main groove. By setting the groove widths of the first main groove and the second main groove in such a manner, the rigidity of the land portions on either side of the second main groove can be ensured, and steering stability can be improved.

In an embodiment of the present technology,

the set of lateral narrow grooves are preferably inclined so that a distance between one another increases from an end portion of the lateral narrow grooves proximal to the first main groove toward an end portion proximal to the first circumferential narrow groove, and form an angle α that ranges from 10° to 50°. By arranging the set of lateral narrow grooves in this manner, the lateral narrow grooves provide an effective edge effect. As a result, block rigidity is maintained, uneven wear is suppressed, and braking performance on snowy road surfaces is improved.

In an embodiment of the present technology, an angle β formed by the first circumferential narrow groove and the first lateral auxiliary groove is preferably 45° or greater. By the first circumferential narrow groove and the first lateral auxiliary groove being disposed in such a manner, the angle formed by the first circumferential narrow groove and the first lateral auxiliary groove is prevented from being too acute, and uneven wear caused by slipping can be suppressed.

In an embodiment of the present technology,

in each of the plurality of first blocks, an area of a region with the largest area out of five regions divided by the first circumferential narrow groove, the set of lateral narrow grooves, and the first lateral auxiliary groove is preferably equal to or less than 1.7 times an area of a region with the smallest area. By dividing the block in such a manner, the difference in rigidity between adjacent blocks is reduced, and uneven wear can be suppressed.

An embodiment of the present technology preferably further includes:

a third main groove that extends in the tire circumferential direction at a position outward from the second main groove in the tire width direction, the third main groove having a larger groove width than the second main groove;

a second land portion defined between the second main groove and the third main groove disposed side by side in the tire width direction;

a plurality of second lug grooves that extend in the tire width direction disposed in the second land portion at intervals in the tire circumferential direction, each of the plurality of second lug grooves communicating with the second main groove and the third main groove at both ends;

a plurality of second blocks formed by the plurality of second lug grooves defining the second land portion, each of the second blocks including:

a second lateral auxiliary groove that extends in the tire width direction with one end communicating with the second main groove. By providing the second lateral auxiliary groove in the second block formed by further providing the third main groove and the second lug grooves, drainage performance provided by the second lateral auxiliary groove can be obtained while the rigidity of the second blocks can be maintained and wet performance can be improved. By the first lateral auxiliary groove and the second lateral auxiliary groove opening to the second main groove disposed on the outer side with respect to the vehicle when the tire is mounted on the vehicle, wet performance can be increased.

In this embodiment, each of the plurality of second blocks preferably includes a second circumferential narrow groove that extends in the tire circumferential direction and intersects the second lateral auxiliary groove. By further providing the second circumferential auxiliary groove, the rigidity of the second blocks is brought close to that of the first blocks with the difference in rigidity between first blocks and second blocks adjacent in the tire width direction decreasing. As a result, the ground contact pressure of the first blocks and the second blocks can be made uniform and uneven wear can be suppressed.

In an embodiment of the present technology,

the first main groove is preferably disposed on an inner side of the second main groove with respect to a vehicle when the tire is mounted on the vehicle. By disposing the first main groove and the second main groove in such a manner, the rigidity of the land portions on either side of the second main groove on the outer side with respect to the vehicle when the tire is mounted on the vehicle can be ensured, and steering stability can be further effectively improved.

Note that in an embodiment of the present technology, the narrow grooves are fine grooves with a groove width of from 0.4 mm to 1.5 mm, for example. Additionally, the auxiliary grooves are grooves with a groove width greater than that of the narrow grooves of 1.6 mm or greater, for example, but less than that of the main grooves.

In an embodiment of the present technology, the angle formed by two grooves (for example, the angle α formed by the set of lateral narrow grooves or the angle β formed by the first circumferential narrow groove and the first lateral auxiliary groove) are measured using a straight line (reference line) that connects the midpoint in the groove width direction at the starting point of the groove and the midpoint in the groove width direction at the end point of the groove.

DETAILED DESCRIPTION

Configurations according to embodiments of the present technology are described below in detail with reference to the accompanying drawings.

The reference sign CL inFIG. 1denotes the tire equator. A pneumatic tire according to an embodiment of the present technology includes an annular tread portion1that extends in the tire circumferential direction, a pair of sidewall portions2disposed on both sides of the tread portion1, and a pair of bead portions3disposed inward of the sidewall portions2in the tire radial direction.

A carcass layer4extends between the left-right pair of bead portions3. The carcass layer4includes a plurality of reinforcing cords extending in a tire radial direction, and is folded back around a bead core5disposed in each bead portion3from a vehicle inner side to a vehicle outer side. Additionally, bead fillers6are disposed on the periphery of the bead cores5, and each bead filler6is enveloped by a main body portion and a folded back portion of the carcass layer4. In the tread portion1, a plurality of belt layers7,8(two layers inFIG. 1) are embedded on the outer circumferential side of the carcass layer4. Each belt layer7,8includes a plurality of reinforcing cords inclined with respect to the tire circumferential direction, the direction of the reinforcing cords of the different layers intersecting with each other. In the belt layers7,8, the inclination angle of the reinforcing cords with respect to the tire circumferential direction is set in the range, for example, of 10° to 40°. In addition, a belt reinforcing layer9is provided on the outer circumferential side of the belt layers7,8. The belt reinforcing layer9includes organic fiber cords oriented in the tire circumferential direction. In the belt reinforcing layer9, the angle of the organic fiber cords with respect to the tire circumferential direction is set, for example, to from 0° to 5°.

The present technology may be applied to such a general pneumatic tire; however, the cross-sectional structure thereof is not limited to the basic structure described above.

In the embodiment illustrated inFIG. 2, a first main groove11and a second main groove12are provided in the tread portion1on either side of the tire equator CL of the tread portion1in the tire width direction. Additionally, a third main groove13is disposed outward of the second main groove12in the tire width direction and a fourth main groove14is disposed outward of the first main groove11in the tire width direction. A first land portion21is defined by the first main groove11and the second main groove12, a second land portion22is defined by the second main groove12and the third main groove13, and a third land portion23is defined by the first main groove11and the fourth main groove14. Additionally, shoulder land portions24,25are disposed outward of the third main groove13and the fourth main groove14located outermost in the tire width direction and defined thereby. Note that in the example illustrated, the outer shoulder land portion24is disposed on the outer side with respect to the vehicle (OUT side in the drawing) when the tire is mounted on the vehicle, and the inner shoulder land portion25is disposed on the inner side with respect to the vehicle (IN side in the drawing) when the tire is mounted on the vehicle.

In the first land portion21, a plurality of first lug grooves31that extend in the tire width direction and communicate with the first main groove11and the second main groove12at both ends are disposed at intervals in the tire circumferential direction. The first land portion21is defined into a plurality of first blocks41by the plurality of first lug grooves31. In the second land portion22, a plurality of second lug grooves32that extend in the tire width direction and communicate with the second main groove12and the third main groove13at both ends are disposed at intervals in the tire circumferential direction. The second land portion22is defined into a plurality of second blocks42by the plurality of second lug grooves32. In a similar manner, in the third land portion23, a plurality of third lug grooves33that extend in the tire width direction and communicate with the first main groove11and the fourth main groove14at both ends are disposed at intervals in the tire circumferential direction. The third land portion23is defined into a plurality of third blocks43by the plurality of third lug grooves33.

Furthermore, in the outer shoulder land portion24, a plurality of outer shoulder lug grooves34A that extend in the tire width direction are disposed at intervals in the tire circumferential direction. The outer shoulder lug grooves34A terminate within the land portion at the inner end portion in the tire width direction and open outward in the tire width direction at the outer end portion in the tire width direction. In the outer shoulder land portion24, outer shoulder auxiliary grooves34B that link the terminating ends of the outer shoulder lug groove34A located inward in the tire width direction and the main groove (third main groove13) are disposed. Additionally, the outer shoulder land portion24is defined into a plurality of outer shoulder blocks44by the plurality of outer shoulder lug grooves34A and the outer shoulder auxiliary grooves34B. In the inner shoulder land portion25, a plurality of inner shoulder lug grooves35that extends in the tire width direction are disposed at intervals in the tire circumferential direction. The inner shoulder lug grooves35communicate with the main groove (fourth main groove14) at the inner end portion in the tire width direction and open outward in the tire width direction at the outer end portion in the tire width direction. The inner shoulder land portion25is defined into a plurality of inner shoulder blocks45by the plurality of inner shoulder lug grooves35.

A first circumferential narrow groove51A that extends in the tire circumferential direction, a first lateral narrow groove51B that extends in the tire width direction, and a first lateral auxiliary groove51C that extends in the tire width direction are formed in each of the first blocks41. The first circumferential narrow groove51A communicates with the first lug groove31at at least one end (both ends in the example illustrated). Additionally, in the example illustrated, the first circumferential narrow groove51A extends while curving with respect to the tire circumferential direction. The first lateral narrow groove51B is formed as a set of two grooves, both communicating with the first main groove11at a first end. Note that in the example illustrated, the second end of the first lateral narrow groove51B does not communicate with the first circumferential narrow groove51A described above and terminates within the first block41. The first lateral auxiliary groove51C communicates with the second main groove12at a first end and communicates with the first circumferential narrow groove51A at a second end. Additionally, the second end of the first lateral auxiliary groove51C (the end portion on the side that communicates with the first circumferential narrow groove51A) is disposed at a position in the tire circumferential direction between the end portions of the set of the lateral narrow grooves51B described above proximal to the first circumferential narrow groove51A.

A second circumferential narrow groove52A that extends in the tire circumferential direction, and a second lateral auxiliary groove52B that extends in the tire width direction are formed in each of the second blocks42. Additionally, in the example illustrated, a second lateral narrow groove52C that extends in the tire width direction from the end portion of the second lateral auxiliary groove52B is provided. The second circumferential narrow groove52A communicates with the second lug groove32at one end (both ends in the example illustrated). Additionally, in the example illustrated, the second circumferential narrow groove52A extends while curving with respect to the tire circumferential direction. The second lateral auxiliary groove52B communicates with the second main groove12at a first end and terminates within the second block42at the second end. The second lateral narrow groove52C communicates with the terminating end of the second lateral auxiliary groove52B on one side, extends in the extending direction of the second lateral auxiliary groove52B, and communicates with the third main groove13at the other end.

A third circumferential auxiliary groove53A that extends in the tire circumferential direction, and a third lateral narrow groove53B that extends in the tire width direction are formed in each of the third blocks43. The third circumferential auxiliary groove53A communicates with the third lug grooves33at both ends. Additionally, in the example illustrated, the third circumferential auxiliary groove53A extends with a zigzag shape bending at a partway portion in the tire circumferential direction. The third lateral narrow groove53B is formed as a set of two grooves, a third lateral narrow groove53Ba and a third lateral narrow groove53Bb. The third lateral narrow groove53Ba communicates with the fourth main groove14and the first main groove11at both ends. The third lateral narrow groove53Bb communicates with the fourth main groove14at one end and terminates within the third block43without reaching the first main groove11at the other end. The set of third lateral narrow grooves53B both intersect the third circumferential auxiliary groove53A. In particular, as in the example illustrated, the third lateral narrow groove53Ba and the third lateral narrow groove53Bb intersect with two linear portions positioned on either side in the tire circumferential direction of a bent-back portion (portion that extends in a linear manner) of the third circumferential auxiliary groove53A.

Outer shoulder narrow grooves54A are disposed in the outer shoulder blocks44. The outer shoulder narrow grooves54A each include two portions that extend in the tire width direction and communicate with the third main groove13at one end and terminate within the outer shoulder land portion at the other end, and a portion that extends in the tire circumferential direction in a manner so that the other ends of the two portions are joined. The portions that extend in the tire width direction each include a zigzag shaped region on the surface of the outer shoulder block44. Furthermore, an outer groove54B is disposed outward in the tire width direction of the portion that extends in the tire circumferential direction. The outer groove54B extends in the tire circumferential direction with a zigzag shape bending at a partway portion in the tire circumferential direction, does not communicate with the outer shoulder lug grooves34A at either end and terminates within the outer shoulder block44.

In a similar manner, outer shoulder narrow grooves55A are disposed in the inner shoulder blocks45. The outer shoulder narrow grooves55A each include two portions that extend in the tire width direction and communicate with the fourth main groove14at one end and terminate within the outer shoulder land portion at the other end, and a portion that extends in the tire circumferential direction in a manner so that the other ends of the two portions are joined. The portions that extend in the tire width direction each include a zigzag shaped region on the surface of the inner shoulder block45.

In an embodiment of the present technology, as described above, in the first land portion21, the first blocks41defined by the first lug grooves31are further divided by the first circumferential narrow grooves51A, the first lateral narrow grooves51B, and the first lateral auxiliary grooves51C. The edge effect provided by these grooves can improve the snow traction and the braking performance on snowy road surfaces. Additionally, the drainage performance expected to be provided by the first circumferential narrow grooves51A, the first lateral narrow grooves51B, and the first lateral auxiliary grooves51C can improve wet performance. Furthermore, by the set of two first lateral narrow grooves51B and the first lateral auxiliary groove51C being arranged as described above, a reduction in block rigidity can be suppressed, and uneven wear caused by a difference in rigidity between adjacent blocks can be suppressed.

In such a configuration, by at least one end of the first circumferential narrow groove51A communicating with a first lug groove31, the effect described above can be obtained, and preferably both ends communicate with the first lug grooves31as illustrated. When the first circumferential narrow groove51A terminates within the first block41without communicating to the first lug grooves31, sufficient snow traction and drainage performance is not obtained. Additionally, the first circumferential narrow groove51A may extend in the tire circumferential direction in a linear manner. However, by extending in a curved manner as illustrated, a more effective edge effect can be obtained, which is advantageous in improving snow performance.

As described above, the first lateral narrow groove51B is a set of two grooves. When only one was provided, the first blocks41are not sufficiently divided, which makes sufficiently improving snow traction difficult. When three or more first lateral narrow grooves51B are provided, the first blocks41are too narrowly divided. As a result, block rigidity significantly decreases, and the desired effect cannot be obtained.

As illustrated inFIGS. 2 and 3, the first lateral narrow grooves51B may terminate within the first block41without communicating with the first circumferential narrow groove51A. However, they preferably communicate with the first circumferential narrow groove51A as illustrated inFIG. 4. In this configuration, the first circumferential narrow groove51A, the first lateral narrow groove51B, and the first lateral auxiliary groove51C are connected. This improves the flow of water between the grooves, and further improves drainage performance.

The set of first lateral narrow grooves51B are preferably inclined so that the distance between one another increases from the end portion proximal to the first main groove11toward the end portion proximal to the first circumferential narrow groove51A. Specifically, an angle α formed by the set of first lateral narrow grooves51B preferably ranges from 10° to 50°. By arranging the set of first lateral narrow grooves51B in this manner, the first lateral narrow grooves51B provides an effective edge effect. As a result, block rigidity is maintained, uneven wear is suppressed, and braking performance on snowy road surfaces is improved. When the angle α is less than 10°, the set of first lateral narrow grooves51B are substantially parallel. This makes a decrease in land portion rigidity difficult to sufficiently suppress. When the angle α is greater than 50°, at least one of the first lateral narrow grooves51B is too closely orientated with the tire circumferential direction, making an appropriate edge effect difficult to obtain.

To provide an effective edge effect, the set of first lateral narrow grooves51B are preferably curved as illustrated. Specifically, in the example illustrated, the first lateral narrow grooves51B each include a portion that extends in a linear manner and communicates with the first main groove11, a portion that communicates with this portion and curves with a convex shape facing one way in the tire circumferential direction of the first block41, and a portion that communicates with the end of this portion and curves with a convex shape facing an opposite way in the tire circumferential direction of the first block41.

The first lateral auxiliary groove51C extends in a linear manner in the tire width direction and does not curve like the first circumferential narrow groove51A or the first lateral narrow grooves51B. The first lateral auxiliary groove51C has a groove width that gradually increases as it extends from inner end portion in the tire width direction of the first block41toward the outer end portion in the tire width direction. By having such a shape, good drainage performance can be obtained.

As described above, the first lateral auxiliary groove51C communicates with the first circumferential narrow groove51A and is disposed at a position in the tire circumferential direction between the end portions of the set of first lateral narrow grooves51B proximal to the first circumferential narrow groove51A. When the first lateral auxiliary groove51C is disposed in the tire circumferential direction of end portions of the first lateral narrow grooves51B proximal to the first circumferential narrow groove51A, at least one of the portions of the first block41defined by the first lateral auxiliary groove51C becomes excessively small. As a result, the rigidity of this portion decreases, and uneven wear becomes difficult to suppress.

At the point where the first lateral auxiliary groove51C and the first circumferential narrow groove51A communicate, an angle β formed by the first circumferential narrow groove51A and the first lateral auxiliary groove51C can be set to 45° or greater, for example. By the first circumferential narrow groove51A and the first lateral auxiliary groove51C being disposed in such a manner, the corner portion formed by the first circumferential narrow groove51A and the first lateral auxiliary groove51C is prevented from being too acute, and uneven wear caused by slipping can be suppressed. When the angle β is less than 45°, the corner portion formed by the first circumferential narrow groove51A and the first lateral auxiliary groove51C becomes significantly acute, which makes uneven wear difficult to suppress.

Three types of grooves, the first circumferential narrow groove51A, the set of two first lateral narrow grooves51B, and the first lateral auxiliary groove51C described above, are formed in the first block41. If any one of these grooves are missing, then the effects described above cannot be sufficiently obtained.

The first block41is divided into five regions41a,41b,41c,41d,41eas illustrated (seeFIG. 5) by the first circumferential narrow groove51A, the set of two first lateral narrow grooves51B, and the first lateral auxiliary groove51C as described above. The region out of the five regions with the largest area (region41bin the example illustrated) preferably has an area 1.7 times the area of the region with the smallest area (region41din the example illustrated). By dividing the first block41appropriately in such a manner, the difference in rigidity between adjacent blocks is reduced, and uneven wear can be effectively suppressed. When the area of the region with the largest area is greater than 1.7 times the area of the region with the smallest area, the difference in rigidity between adjacent blocks increases significantly, and uneven wear becomes difficult to suppress. Note that the five regions41a,41b,41c,41d,41eare determined in a manner similar to how the angles are measured using a straight line (reference line) that connects the midpoint in the groove width direction at the starting point of the groove and the midpoint in the groove width direction at the end point of the grooves that define the regions. The area is the area of the first block41(the road contact surface not including the grooves) divided by the reference line. Additionally, in a configuration in which the first lateral narrow grooves51B terminate without reaching the first circumferential narrow groove51A, as illustrated inFIG. 5, the regions are determined to be sectioned by the reference line of the first lateral narrow grooves51B extended to the first circumferential narrow groove51A.

In an embodiment of the present technology, the first circumferential narrow groove51A, the set of two first lateral narrow grooves51B, and the first lateral auxiliary groove51C are formed as described above in at least the first blocks41, and the inclination angle of the grooves, the area of the regions that divide the grooves, and other characteristics are set. However, the configuration of portions other than the first blocks41are not limited by the embodiment described above. In other words, if at least the first block41have the configuration described above, excellent wet performance and snow performance can be obtained, and uneven wear especially of the first blocks41can be suppressed.

However, in an embodiment of the present technology, as in the tread pattern ofFIG. 2described above, the first main groove11is preferably disposed on the inner side of the second main groove12with respect to the vehicle when the tire is mounted on the vehicle and the third main groove13is preferably disposed outward (on the outer side with respect to the vehicle when the tire is mounted on vehicle) of the second main groove12. By having such a configuration, the rigidity of the land portions on either side of the second main groove12disposed on the outer side with respect to the vehicle when the tire is mounted on the vehicle can be ensured, and steering stability can further effectively be improved. Furthermore, in a configuration with the main grooves disposed as such, the groove width of the second main groove12is preferably less than the groove width of the first main groove11. By setting the groove widths of the first main groove11and the second main groove12in such a manner, the rigidity of the land portions on either side of the second main groove12can be ensured, and steering stability can be improved.

In a tire with the configuration for the main grooves described above, the second blocks42preferably have the configuration described above. In other words, the second circumferential narrow groove52A that extends in the tire circumferential direction and the second lateral auxiliary groove52B that extends in the tire width direction are preferably provided. Providing the second circumferential narrow groove52A and the second lateral auxiliary groove52B in such a manner is advantageous because good wet performance, snow performance, and uneven wear resistance performance can be achieved in a compatible manner.

In particular, by providing the second lateral auxiliary groove52B, drainage performance provided by the second lateral auxiliary groove52B can be obtained while the rigidity of the second blocks42can be maintained and wet performance can be improved. By the first main groove11and the second main groove12having the configuration of the example illustrated, the first lateral auxiliary groove51C and the second lateral auxiliary groove52B open to the second main groove12disposed on the outer side with respect to the vehicle when the tire is mounted on the vehicle. As a result, wet performance can be increased.

In the example illustrated, the second lateral narrow groove52C extends in the tire width direction from the end portion of the second lateral auxiliary groove52B. By further providing the lateral narrow groove52B in such a manner, the second block42is divided by the second lateral auxiliary groove52B and the second lateral narrow groove52C. As a result, wet performance can be further effectively improved.

Additionally, by providing the second circumferential narrow groove52A, the rigidity of the second blocks42is brought close to that of the first blocks41with the difference in rigidity between first blocks41and second blocks42adjacent in the tire width direction decreasing. As a result, the ground contact pressure of the first blocks41and the second blocks42can be made uniform and uneven wear can be suppressed.

The second circumferential narrow groove52A may extend in the tire circumferential direction in a linear manner; however, it preferably extends in a curved manner as illustrated. This allows wear resistance performance to be improved.

The third circumferential auxiliary groove53A formed in the third land portion23preferably extends in the tire circumferential direction with a zigzag shape, and has a smaller groove width than the first main groove11, the second main groove12, the third main groove13, and the fourth main groove14as illustrated. By the third circumferential auxiliary groove53A having such a configuration, the edge effect provided by the zigzag shape produces an effect of improving the braking performance on snowy road surfaces and collapsing in the tire width direction at the third land portion23can be prevented. As a result, the rigidity of the third land portion23can be improved, and the steering stability on dry road surfaces can be improved.

The outer shoulder narrow grooves54A and the inner shoulder narrow grooves55A provided in the outer shoulder blocks44and the inner shoulder blocks45, in particular, preferably extend in the tire width direction with a zigzag shape as illustrated. By the outer shoulder narrow grooves54A and the inner shoulder narrow grooves55A having such a configuration, at the outer shoulder blocks44and the inner shoulder blocks45, the braking performance on snowy road surfaces provided by the edge effect is improved, and collapsing of the outer shoulder blocks44and the inner shoulder blocks45in the tire circumferential direction can be prevented. As a result, block rigidity can be improved and steering stability on dry road surfaces can be improved.

EXAMPLES

Thirteen types of pneumatic tires, Conventional Example 1, Comparative Example 1, and Examples 1 to 11 were manufactured. The manufactured pneumatic tires had a tire size of 205/55R16 91V, the cross sectional shape illustrated inFIG. 1, the tread pattern illustrated inFIG. 2as a base, and set with the values listed in Table 1 for the following parameters: presence of first circumferential auxiliary groove, type of groove that opens to the inner side with respect to the vehicle when the tire is mounted on the vehicle (vehicle inner side), type of groove that opens to the outer side with respect to the vehicle when the tire is mounted on the vehicle (vehicle outer side), angle α formed by the set of lateral narrow grooves, angle β formed by the first circumferential narrow groove and the first lateral auxiliary groove, the ratio of the area of the region with the smallest area of the five regions divided by the first circumferential narrow groove and the set of lateral narrow grooves and the first lateral auxiliary groove to the area of the region with the largest area (largest area/smallest area ratio), groove width of the first main groove, groove width of the second main groove, presence of the second lateral auxiliary groove, presence of the second circumferential auxiliary groove.

Note that the Comparative Example 1 has substantially the same tread pattern as Example 1; however, the groove that opens to the vehicle inner side (first lateral narrow groove in an embodiment of the present technology) is an auxiliary groove with a groove width greater than the narrow grooves.

The 13 types of pneumatic tires were evaluated for wet performance, snow performance, and wear resistance performance by the evaluation methods described below, and the results are also shown in Table 1.

Wet Performance

The test tires were mounted on wheels with a rim size of 16×6.5 JJ, inflated to an air pressure of 200 kPa, and mounted on a front wheel drive passenger vehicle (test vehicle) with an engine displacement of 1.6 L. A driving test was performed by a test driver on a wet road surface test course with a 1 mm deep film of water. The distance (braking distance) was measured from the point where the brakes were applied at an initial speed of 100 km/h to the point where the vehicle came to a stop. The evaluation results were expressed, using the inverse value of the measurement value, as index values with the results of Conventional Example 1 being defined as 100. Larger index values indicate shorter braking distances on wet road surfaces and superior wet performance.

Snow Performance

The test tires were mounted on wheels with a rim size of 16×6.5 JJ, inflated to an air pressure of 200 kPa, and mounted on a front wheel drive passenger vehicle (test vehicle) with an engine displacement of 1.6 L. A driving test was performed by a test driver on a compacted snow road surface test course. The distance (braking distance) was measured from the point where ABS braking was applied at an initial speed of 40 km/h to the point where the vehicle came to a stop. The evaluation results were expressed, using the inverse value of the measurement value, as index values with the results of Conventional Example 1 being defined as 100. Larger index values indicate shorter braking distances on snowy road surfaces and superior snow performance.

Wear Resistance Performance

The test tires were mounted on wheels with a rim size of 16×6.5 JJ, inflated to an air pressure of 200 kPa, and mounted on a front wheel drive passenger vehicle (test vehicle) with an engine displacement of 1.6 L. After the vehicle was driven for 50000 km at an average speed of 80 km/h, the difference in degree of wear was measured. The evaluation results were expressed, using the inverse value of the measurement value, as index values with the results of Conventional Example 1 being defined as 100. Larger index values indicate less difference in degree of wear and superior wear resistance.

As is clear from Table 1, Examples 1 to 11 all achieved improved snow performance and uneven wear resistance performance in a compatible manner while maintaining wet performance to a high degree. Comparative Example 1 included an auxiliary groove as the groove that opens to the vehicle inner side (expressed from a different perspective, the groove width of the first circumferential narrow groove is excessively large), thus uneven wear resistance performance deteriorated.