Pneumatic tire

A pneumatic tire comprises a tread portion with a tread surface; four main grooves in the tread surface of the tread portion, extending in a tire circumferential direction; and a center land portion, middle land portions adjacent to the center land portion on either side in a tire lateral direction, and shoulder land portions outwardly adjacent to the middle land portions in the tire lateral direction formed by the main grooves. The main grooves have a wave-like shape with a constant groove width in the tire circumferential direction and with periodic oscillation.

TECHNICAL FIELD

The present technology relates to a pneumatic tire that can provide enhanced wear resistance performance while maintaining braking performance on wet road surfaces.

BACKGROUND ART

The conventional pneumatic tire described in Japanese Unexamined Patent Application Publication No. 2014-076764, for example, is designed to improve both wet performance (braking performance on wet road surfaces) and noise performance (anti-external noise performance). This pneumatic tire includes a plurality of wave-shaped circumferential grooves extending in the tire circumferential direction with left and right groove walls having a wave-like shape with a wavelength and an amplitude, and at least one row of wave-shaped land portions defined by adjacent wave-shaped circumferential grooves. The shape of the left and right groove walls of the wave-shaped circumferential grooves have identical wavelengths but with a phase difference. The groove wall on the wave-shaped land portion side of one of the left and right wave-shaped circumferential grooves that define the row of wave-shaped land portions has an amplitude that is greater than that of the groove wall on the wave-shaped land portion side of the other wave-shaped circumferential groove.

The conventional heavy duty pneumatic tire described in Japanese Unexamined Patent Application Publication No. 61-175104, for example, is designed to improve both wet performance (braking performance on wet road surfaces) and uneven wear resistance performance. This heavy duty pneumatic tire includes a tread that includes at least three main grooves extending in the tire circumferential direction in a zigzag manner that define the tread in the tire lateral direction, shoulder ribs located at least one the outermost sides in the tire lateral direction, and second ribs inwardly adjacent to the shoulder ribs that divide the main grooves. The ridge lines of the shoulder ribs and the second ribs that face the main grooves located outward in the tire lateral direction have a smaller zigzag pitch and amplitude.

In the pneumatic tire of Japanese Unexamined Patent Application Publication No. 2014-076764 described above, the left and right groove walls of the wave-shaped circumferential grooves are disposed with a phase difference, and the groove wall on the wave-shaped land portion side of one of the left and right wave-shaped circumferential grooves that define the row of wave-shaped land portions has an amplitude that is greater than that of the groove wall on the wave-shaped land portion side of the other wave-shaped circumferential groove. As a result, the groove width varies between being wide and being narrow. This leads to the land portion rigidity of the tread portion being non-uniform, and a decrease in wear resistance performance. In the heavy duty pneumatic tire of Japanese Unexamined Patent Application Publication No. 61-175104 described above, the ridge lines of the shoulder ribs and the second ribs that face the main grooves located outward in the tire lateral direction have a smaller zigzag pitch and amplitude. The resulting difference in rigidity may adversely affect uneven wear. Additionally, the corner portions formed by the zigzag shape of the main grooves may experience uneven wear.

SUMMARY

The present technology provides a pneumatic tire that can provide enhanced wear resistance performance while maintaining braking performance on wet road surfaces.

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

a tread portion;

four main grooves extending in a tire circumferential direction in a tread surface of the tread portion; and

a center land portion, middle land portions adjacent to the center land portion on either side in a tire lateral direction, and shoulder land portions outwardly adjacent to the middle land portions in the tire lateral direction formed by the main grooves;

the main grooves having a wave-like shape with a constant groove width in the tire circumferential direction and with periodic oscillation.

According to the pneumatic tire, the main grooves have a shape with periodic oscillation. This increases the overall width of the main grooves to provide good drainage properties, and allows braking performance on wet road surfaces to be maintained. Additionally, according to the pneumatic tire, the main grooves have a constant groove width in the tire circumferential direction. This allows the rigidity of the land portions (which form the main grooves) near the main grooves to be made uniform, and wear resistance performance to be improved.

A pneumatic tire according to an embodiment of the present technology may have a configuration wherein,

a vehicle inner/outer side orientation when the pneumatic tire is mounted on a vehicle is designated; and

the middle land portion on the vehicle inner side is provided with an auxiliary groove, the auxiliary groove having a narrower groove width than the main grooves and extending in a linear manner in the tire circumferential direction.

According to the pneumatic tire, the vehicle inner side greatly contributes to drainage properties, and so by the middle land portion on the vehicle inner side being provided with the auxiliary groove extending in a linear manner in the tire circumferential direction, good drainage properties can be provided, and thus the braking performance on wet road surfaces can be improved. Furthermore, the auxiliary groove has a narrower groove width than the main grooves. Thus, a decrease in the rigidity of the middle land portion can be suppressed, and wear resistance performance can be improved.

A pneumatic tire according to an embodiment of the present technology may further comprise

a plurality of through lug grooves disposed in the tire circumferential direction; the plurality of through lug grooves each intersecting the tire circumferential direction and continuously passing through the center land portion and the middle land portion on the vehicle outer side, and opening to the main groove on the vehicle outer side of the middle land portion on the vehicle outer side at a first end, passing through the main groove on the vehicle inner side of the center land portion, and terminating within the middle land portion on the vehicle inner side at a second end without reaching the auxiliary groove.

According to the pneumatic tire, the through lug grooves are disposed running continuously through the center land portion and the middle land portion on the vehicle outer side. This connects the center main grooves and the shoulder main grooves on the vehicle outer side. As a result, good drainage properties can be provided, and braking performance on wet road surfaces can be improved. Furthermore, the through lug groove terminates within the middle land portion on the vehicle inner side without reaching the auxiliary groove. This allows a decrease in rigidity of the middle land portion on the vehicle inner side to be suppressed and wear resistance performance to be improved.

A pneumatic tire according to an embodiment of the present technology may have a configuration wherein,

the shoulder land portions are provided with a plurality of shoulder land portion lug grooves that intersect the tire circumferential direction disposed in a row in the tire circumferential direction, the plurality of shoulder land portion lug grooves each terminating without reaching the main groove inward of the shoulder land portion in the tire lateral direction.

According to the pneumatic tire, the shoulder land portion lug grooves provide good drainage properties in the shoulder land portions, and the terminating ends within the shoulder land portion allow a decrease in rigidity of the shoulder land portion to be suppressed and wear resistance performance to be improved.

A pneumatic tire according to an embodiment of the present technology may have a configuration wherein,

the plurality of shoulder land portion lug grooves each communicate with the main groove inward of the shoulder land portion in the tire lateral direction via a communication narrow groove that has a narrower groove width than the plurality of shoulder land portion lug grooves.

According to the pneumatic tire, the communication narrow grooves provide good drainage properties and allow braking performance on wet road surfaces to be improved. Additionally, the communication narrow grooves have a narrower groove width than the shoulder land portion lug grooves. This allows a decrease in rigidity of the shoulder land portions to be suppressed and wear resistance performance to be improved.

A pneumatic tire according to an embodiment of the present technology may further comprise

a lug narrow groove in which a lug groove and a narrow groove are present disposed between the shoulder land portion lug groove and the communication narrow groove.

According to the pneumatic tire, the lug narrow grooves are disposed between the shoulder land portion lug grooves and the communication narrow grooves. This allows excessive changes in rigidity at the communicating portion between the shoulder land portion lug grooves and the communication narrow grooves to be suppressed, and wear resistance performance to be improved.

A pneumatic tire according to an embodiment of the present technology may further comprise

a shoulder land portion narrow groove disposed between pairs of the plurality of shoulder land portion lug grooves adjacent in the tire circumferential direction, the shoulder land portion narrow groove intersecting the tire circumferential direction and having a narrower groove width than the plurality of shoulder land portion lug grooves.

According to the pneumatic tire, the shoulder land portion narrow grooves provide good drainage properties and allow braking performance on wet road surfaces to be improved. Additionally, the shoulder land portion narrow grooves have a narrower groove width than the shoulder land portion lug grooves. This allows a decrease in rigidity of the shoulder land portions to be suppressed and wear resistance performance to be improved.

A pneumatic tire according to an embodiment of the present technology may have a configuration wherein,

the shoulder land portions are provided with a recessed portion at outer ends in the tire lateral direction; and

the shoulder land portion narrow groove terminates at the recessed portion at an outer end portion in the tire lateral direction.

According to the pneumatic tire, the outer end portions of the shoulder land portion narrow grooves in the tire lateral direction terminate at the recessed portions. This prevents loads acting on the outer end portions of the shoulder land portion narrow grooves in the tire lateral direction, and allows a decrease in rigidity of the shoulder land portions to be suppressed and wear resistance performance to be improved.

A pneumatic tire according to an embodiment of the present technology may have a configuration wherein,

the lug grooves comprise a chamfer at an opening portion.

According to the pneumatic tire, the lug grooves are formed with the chamfers on the opening portions. This allows a decrease in rigidity of the land portions near the lug grooves to be suppressed and wear resistance performance to be improved.

A pneumatic tire according to an embodiment of the present technology may have a configuration wherein,

a vehicle inner/outer side orientation when the pneumatic tire is mounted on a vehicle is designated;

a middle land portion narrow groove that intersects the tire circumferential direction is disposed in the middle land portion on the vehicle outer side, the middle land portion narrow groove communicating with the main groove on the vehicle inner side of the middle land portion at a first end and terminating within the middle land portion at a second end without reaching the main groove on the vehicle outer side of the middle land portion; and

a center land portion narrow groove that intersects the tire circumferential direction is disposed in the center land portion, the center land portion narrow groove communicating with the main groove on the vehicle inner side of the center land portion at a first end and terminating within the center land portion at a second end without reaching the main groove on the vehicle outer side of the center land portion.

According to the pneumatic tire, the middle land portion narrow grooves and the center land portion narrow grooves provide good drainage properties and allow braking performance on wet road surfaces to be improved. Additionally, by the middle land portion narrow grooves and the center land portion narrow grooves terminating within the respective land portions, a decrease in rigidity of the land portions can be suppressed and wear resistance performance can be improved.

A pneumatic tire according to an embodiment of the present technology may have a configuration wherein,

the tread portion has an asymmetrical pattern in the tire lateral direction; and

a difference in groove area ratio between the two regions on either side of a tire equatorial plane in the tire lateral direction is within 2%.

According to the pneumatic tire, the rigidity and the drainage properties of the land portions located in the two regions on either side of the tire equatorial plane in the tire lateral direction can be made uniform, and the effect of enhancing wear resistance performance can be significantly provided while maintaining braking performance on wet road surfaces.

A pneumatic tire according to an embodiment of the present technology may have a configuration wherein,

the shoulder land portions comprise recessed portions at an outer end in the tire lateral direction;

the recessed portions are formed in two rows in the tire lateral direction, a laterally inner row with two of the recessed portions in the tire circumferential direction and a laterally outer row with three of the recessed portions in the tire circumferential direction; and

the recessed portions of the laterally outer row have a larger diameter than those of the laterally inner row.

According to the pneumatic tire, the recessed portions can improve the appearance of the outer ends of the tread portion in the tire lateral direction.

A pneumatic tire according to an embodiment of the present technology can provide enhanced wear resistance performance while maintaining braking performance on wet road surfaces.

DETAILED DESCRIPTION

Embodiments of the present technology are described in detail below based on the drawings. However, the present technology is not limited to these embodiments. Constituents of the embodiments include elements that can be easily replaced by those skilled in the art and elements substantially the same as the constituents of the embodiments. Furthermore, the modified examples described in the embodiments can be combined as desired within the scope apparent to those skilled in the art.

FIG. 1is a meridian cross-sectional view of a pneumatic tire according to the present embodiment.FIG. 2is a plan view of a tread portion of the pneumatic tire according to the present embodiment.FIG. 3is an enlarged cross-sectional view of a main groove of the pneumatic tire according to the present embodiment.FIG. 4is an enlarged cross-sectional view of a lug groove of the pneumatic tire according to the present embodiment.FIG. 5is an enlarged cross-sectional view of a narrow groove of the pneumatic tire according to the present embodiment.FIG. 6is an enlarged cross-sectional view of a lug narrow groove of the pneumatic tire according to the present embodiment.

Herein, “tire radial direction” refers to the direction orthogonal to the rotation axis (not illustrated) of a pneumatic tire1. “Inward in the tire radial direction” refers to the direction toward the rotation axis in the tire radial direction. “Outward in the tire radial direction” refers to the direction away from the rotation axis in the tire radial direction. “Tire circumferential direction” refers to the circumferential direction with the rotation axis as the center axis. “Tire lateral direction” refers to the direction parallel with the rotation axis. “Inward in the tire lateral direction” refers to the direction toward a tire equatorial plane (tire equator line) CL in the tire lateral direction. “Outward in the tire lateral direction” refers to the direction away from the tire equatorial plane CL in the tire lateral direction. “Tire equatorial plane CL” refers to the plane orthogonal to the rotation axis of the pneumatic tire1that passes through the center of the tire width of the pneumatic tire1. “Tire width” is the width in the tire lateral direction between components located outward in the tire lateral direction, or in other words, the distance between the components that are the most distant from the tire equatorial plane CL in the tire lateral direction. “Tire equator line” refers to the line along the tire circumferential direction of the pneumatic tire1that lies on the tire equatorial plane CL. In the present embodiment, the tire equator line and the tire equatorial plane are both denoted by reference sign CL.

As illustrated inFIG. 1, the pneumatic tire1is mainly used on passenger vehicles and includes a tread portion2, shoulder portions3on opposite sides of the tread portion2, and sidewall portions4and bead portions5continuing in that order from the shoulder portions3. The pneumatic tire1also includes a carcass layer6, a belt layer7, and a belt reinforcing layer8.

The tread portion2is made of rubber material (tread rubber), is exposed on the outermost side of the pneumatic tire1in the tire radial direction, and the surface thereof constitutes the contour of the pneumatic tire1. The outer circumferential surface of the tread portion2is a tread surface21that mainly comes in contact with a road surface when the tire runs.

The shoulder portions3are portions located outward in the tire lateral direction on both sides of the tread portion2. Additionally, the sidewall portions4are exposed on the outermost sides of the pneumatic tire1in the tire lateral direction. The bead portions5each include a bead core51and a bead filler52. The bead core51is formed by a bead wire, which is a steel wire, wound into an annular shape. The bead filler52is a rubber material that is disposed in the space formed by an end of the carcass layer6in the tire lateral direction folded back at the position of the bead core51.

The end portions of the carcass layer6in the tire lateral direction are folded back around the pair of bead cores51from inward to outward in the tire lateral direction, and the carcass layer6is stretched in a toroidal shape in the tire circumferential direction to form the framework of the tire. The carcass layer6is constituted by a plurality of coating-rubber-covered carcass cords (not illustrated) disposed in alignment at an angle with respect to the tire circumferential direction that conforms with the tire meridian direction. The carcass cords are made of organic fibers (for example, polyester, rayon, and nylon). At least one carcass layer6is provided.

The belt layer7has a multilayer structure in which at least two belts71,72are layered. In the tread portion2, the belt layer7is disposed outward of the carcass layer6in the tire radial direction, i.e. on the outer circumference thereof, and covers the carcass layer6in the tire circumferential direction. The belts71and72each include a plurality of coating-rubber-covered cords (not illustrated) disposed in alignment at a predetermined angle with respect to the tire circumferential direction (for example, from 20° to 30°). The cords are made of steel or organic fibers (for example, polyester, rayon, and nylon). Moreover, the belts71and72overlap each other and are disposed so that the direction of the cords of the respective belts intersect each other.

The belt reinforcing layer8is disposed outward of the belt layer7in the tire radial direction, i.e. on the outer circumference thereof, and covers the belt layer7in the tire circumferential direction. The belt reinforcing layer8includes a plurality of coating-rubber-covered cords (not illustrated) disposed in alignment in the tire lateral direction substantially parallel (±5°) with the tire circumferential direction. The cords are made of steel or organic fibers (for example, polyester, rayon, and nylon). The belt reinforcing layer8illustrated inFIG. 1is disposed so as to cover end portions in the tire lateral direction of the belt layer7. The configuration of the belt reinforcing layer8is not limited to that described above. Although not illustrated in the drawings, a configuration may be used in which the belt reinforcing layer8is disposed so as to cover the entire belt layer7. Alternatively, for example, a configuration with two reinforcing layers may be used, in which the inner reinforcing layer in the tire radial direction is formed larger than the belt layer7in the tire lateral direction so as to cover the entire the belt layer7, and the outer reinforcing layer in the tire radial direction is disposed so as to only cover the end portions of the belt layer7in the tire lateral direction. In another example, a configuration with two reinforcing layers may be used, in which both of the reinforcing layers are disposed so as to only cover the end portions of the belt layer7in the tire lateral direction. In other words, the belt reinforcing layer8overlaps with at least the end portions of the belt layer7in the tire lateral direction. Additionally, the belt reinforcing layer8is constituted of a band-like strip material (having, for example, a width of 10 mm) wound in the tire circumferential direction.

For the pneumatic tire1according to the present embodiment, the vehicle inner/outer side orientation when the pneumatic tire1is mounted on a vehicle is designated. In other words, when the pneumatic tire1is mounted on a vehicle, the orientation with respect to the inner side and the outer side of the vehicle in the tire lateral direction is designated. While the designated orientation is not illustrated in the drawings, the orientation is indicated, for example, by an indicator provided on the sidewall portion4. For the pneumatic tire1, the side facing the inner side of the vehicle when mounted on the vehicle is referred to as a “vehicle inner side” and a side facing the outer side of the vehicle is referred to as a “vehicle outer side”. Note that the designations of the vehicle inner side and the vehicle outer side are not limited to cases where the tire1is mounted on a vehicle. For example, rims have an orientation with respect to the inner side and outer side of the vehicle in the tire lateral direction. Thus, when the pneumatic tire1is mounted on a rim, the orientation with respect to the vehicle inner side and the vehicle outer side in the tire lateral direction is designated.

As illustrated inFIGS. 1 and 2, in the pneumatic tire1as described above, four main grooves22extending in the tire circumferential direction are formed in the tread surface21of the tread portion2.

The main grooves22include two center main grooves22A disposed adjacent to the center in the tire lateral direction on either side of the tire equatorial plane CL and shoulder main grooves22B disposed outward of the center main grooves22A in the tire lateral direction. Additionally, five land portions23are formed by the main grooves22in the tread surface21. The land portions23include a center land portion23A disposed between the center main grooves22A and on the tire equatorial plane CL; middle land portions23B disposed between the center main grooves22A and the shoulder main grooves22B and outwardly adjacent to the center land portion23A in the tire lateral direction; and shoulder land portions23C disposed outward of the shoulder main grooves22B in the tire lateral direction, outwardly adjacent to the middle land portions23B in the tire lateral direction, and outermost in the tread portion2in the tire lateral direction.

The main grooves22(22A,22B) have a wave-like shape with periodic oscillation and a constant groove width W1in the tire circumferential direction. The wave-like shape of the main grooves22can be such that a groove bottom22aillustrated inFIG. 3has a linear shape in the tire circumferential direction and groove walls22bhave periodic oscillation such that the groove width W1is constant in the tire circumferential direction. Alternatively, the wave-like shape of the main grooves22can be such that the groove bottom22aand the groove walls22billustrated inFIG. 3have periodic oscillation such that the groove width W1is constant in the tire circumferential direction. In the present embodiment, as illustrated inFIG. 3, the main grooves22are formed with a chamfer22con the opening edges. The groove width W1of the main grooves22is the opening width to the tread surface21. Thus, the groove width W1of the main grooves22with the chamfer22cis the groove width W1between the outer edges of the chamfers22c. As illustrated inFIG. 3, the center main grooves22A of the main grooves22has a groove width W1ranging from 5 mm to 12 mm and a groove depth D1ranging from 4 mm to 8 mm. The shoulder main grooves22B have a groove width W1ranging from 3 mm to 6 mm and a groove depth D1ranging from 4 mm to 8 mm. The groove width W1of the center main grooves22A is greater than that of the shoulder main grooves22B. For example, the groove width W1of the shoulder main grooves22B ranges from 10% to 50% of the groove width W1of the center main grooves22A. This is preferable to maintain the drainage properties of the center main grooves22A and to ensure the rigidity of the land portions23around the shoulder main grooves22B. Additionally, as illustrated inFIG. 2, the center main grooves22A of the main grooves22have a central line22dof oscillation located a distance L1outward from the tire equatorial plane CL in the tire lateral direction, the distance L1being a distance ranging from 20% to 30% of a ground contact width TW. The shoulder main grooves22B have a central line22dof oscillation located a distance L2outward from the tire equatorial plane CL in the tire lateral direction, the distance L2being a distance ranging from 60% to 70% of the ground contact width TW. This is preferable to maintain the drainage properties of the center main grooves22A and to ensure the rigidity of the land portions23around the shoulder main grooves22B. The edge shape and dimensions of the land portions23in the tire lateral direction can be determined depending on the oscillation and position in the tire lateral direction of the main grooves22.

Herein, “ground contact width TW” refers to the width of the ground contact region in the tire lateral direction. Additionally, the outermost edges of the ground contact region in the tire lateral direction are referred to as ground contact edges T.FIG. 2illustrates the ground contact edges T as being continuous in the tire circumferential direction. The ground contact region is the region where the tread surface21of the tread portion2of the pneumatic tire1comes into contact with a dry road surface, when the pneumatic tire1is mounted on a regular rim, inflated to the regular internal pressure, and loaded with 70% of the regular load. “Regular rim” refers to a “standard rim” defined by the Japan Automobile Tyre Manufacturers Association Inc. (JATMA), a “design rim” defined by the Tire and Rim Association, Inc. (TRA), or a “measuring rim” defined by the European Tyre and Rim Technical Organisation (ETRTO). “Regular internal pressure” refers to “maximum air pressure” defined by JATMA, a maximum value given in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or “INFLATION PRESSURES” defined by ETRTO. “Regular load” refers a “maximum load capacity” defined by JATMA, the maximum value given in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, and a “LOAD CAPACITY” defined by ETRTO.

In the pneumatic tire1according to the present embodiment, the middle land portion23B on the vehicle inner side is provided with an auxiliary groove24extending in a linear manner in the tire circumferential direction. The auxiliary groove24has a narrower groove width than the main groove22with the smallest groove width W1. The auxiliary groove24is centrally disposed between the center main groove22A and the shoulder main groove22B that form the middle land portion23B on the vehicle inner side. The auxiliary groove24divides the middle land portion23B on the vehicle inner side into rib land portions adjacent in the tire lateral direction. The auxiliary groove24has a groove width ranging from 1 mm to less than 3 mm and a groove depth ranging from 4 mm to 8 mm.

In the pneumatic tire1according to the present embodiment, the land portions23are provided with lug grooves25and narrow grooves26that intersect the tire circumferential direction. The lug grooves25provided in the center land portion23A are referred to as center land portion lug grooves25A, the lug grooves25provided in the middle land portions23B are referred to as middle land portion lug grooves25B, and the lug grooves25provided in the shoulder land portions23C are referred to as shoulder land portion lug grooves25C. The narrow grooves26provided in the center land portion23A are referred to as center land portion narrow grooves26A, the narrow grooves26provided in the middle land portions23B are referred to as middle land portion narrow grooves26B, and the narrow grooves26provided in the shoulder land portions23C are referred to as shoulder land portion narrow grooves26C. The narrow grooves26that communicate with a terminating end of one of the lug grooves25and connect to one of the main grooves22or the auxiliary grooves24are referred to as communication narrow grooves26E. Additionally, in the pneumatic tire1according to the present embodiment, a lug narrow groove27is provided where both the lug groove25and the narrow groove26are present and connected.

As illustrated inFIG. 4, the lug groove25includes groove walls25bformed with a chamfer25cfrom the opening portion in the tread surface21to a groove bottom25a. The lug groove25has a groove width W2ranging from 2 mm to 4 mm and a groove depth D2less than that of the main grooves22and the auxiliary groove24ranging from 2 mm to 6 mm. As illustrated inFIG. 5, the narrow groove26includes groove walls26bformed from the opening portion in the tread surface21to a groove bottom26ain the tire radial direction. The narrow groove26has a groove width W3ranging from 0.4 mm to 1.0 mm and a groove depth D3less than that of the main grooves22and the auxiliary groove24ranging from 3 mm to 6 mm. As illustrated inFIG. 6, the lug narrow groove27includes the lug groove25and the narrow groove26formed in the groove bottom25aof the lug groove25in the extension direction of the lug groove25. The sum of the groove depth D2of the lug groove25and the groove depth D3of the narrow groove26makes an overall groove depth of 6 mm or less, less than that of the main grooves22and the auxiliary groove24. Additionally, the groove depth D3of the narrow groove26of the lug narrow groove27is preferably 70% or greater of the overall groove depth (D2+D3) of the lug narrow groove27including the lug groove25.

The center land portion lug grooves25A provided in the center land portion23A are disposed in the tire circumferential direction. The center land portion lug grooves25A communicate at both ends with the center main grooves22A that form the center land portion23A and divide the center land portion23A into a plurality of blocks disposed in a row in the tire circumferential direction. Note that in the present embodiment, the center land portion lug grooves25A are composed overall of the lug narrow grooves27where both the lug grooves25and the narrow grooves26are present.

The middle land portion lug grooves25B provided in the middle land portion23B on the vehicle outer side are disposed in the tire circumferential direction. The middle land portion lug grooves25B communicate at both ends with the center main groove22A and the shoulder main groove22B that form the middle land portion23B on the vehicle outer side and divide the middle land portion23B on the vehicle outer side into a plurality of blocks disposed in a row in the tire circumferential direction. Additionally, the middle land portion lug grooves25B provided in the middle land portion23B on the vehicle outer side communicate at one end with the shoulder main groove22B that forms the middle land portion23B on the vehicle outer side and terminates there. Note that in the present embodiment, the middle land portion lug grooves25B provided in the middle land portion23B on the vehicle outer side are composed overall of the lug narrow grooves27where both the lug grooves25and the narrow grooves26are present.

The middle land portion lug grooves25B provided in the middle land portion23B on the vehicle inner side communicate at the first end with the center main groove22A that forms the middle land portions23B on the vehicle inner side and terminates at the second end within the middle land portion23B on the vehicle inner side without reaching the auxiliary groove24. Accordingly, the middle land portion23B on the vehicle inner side is formed as a rib-like land portion. Note that in the present embodiment, the middle land portion lug grooves25B provided in the middle land portion23B on the vehicle inner side are, at the terminating end portion, lug narrow grooves27where both the lug grooves25and the narrow grooves26are present. The communication narrow groove26E extends from the narrow groove26of the lug narrow groove27and communicates with the auxiliary groove24.

The middle land portion lug grooves25B disposed in the middle land portion23B on the vehicle outer side and the center land portion lug grooves25A disposed in the center land portion23A are disposed such that in a plan view they are one groove that passes through the center main groove22A on the vehicle outer side, with both ends at the center main groove22A between the middle land portion23B on the vehicle outer side and the center land portion23A facing one another. The center land portion lug grooves25A provided disposed the center land portion23A and the middle land portion lug grooves25B disposed in the middle land portion23B on the vehicle inner side are disposed such that in a plan view they are one groove that passes through the center main groove22A on the vehicle inner side, with both ends at the center main groove22A between the center land portion23A and the middle land portion23B on the vehicle inner side facing one another. Thus, the middle land portion lug groove25B provided in the middle land portion23B on the vehicle outer side, the center land portion lug groove25A provided in the center land portion23A, and the middle land portion lug groove25B provided in the middle land portion23B on the vehicle inner side constitute one through lug groove25E that passes through the center main grooves22A. In other words, a plurality of the through lug grooves25E are disposed in the tire circumferential direction. The through lug grooves25E intersect the tire circumferential direction and continuously pass through the center land portion23A and the middle land portion23B on the vehicle outer side. Also, the through lug grooves25E open to the shoulder main groove22B on the vehicle outer side of the middle land portion23B on the vehicle outer side at the first end, pass through the center main groove22A on the vehicle inner side of the center land portion23A, and terminate within the middle land portion23B on the vehicle inner side at the second end without reaching the auxiliary groove24.

The shoulder land portion lug grooves25C disposed in each of the shoulder land portions23C are disposed in a row in the tire circumferential direction and intersect the tire circumferential direction. The shoulder land portion lug grooves25C open at the first end to a design end E, which is the outer end of the tread surface21of the tread portion2in the tire lateral direction, and terminate at the second end within the shoulder land portion23C without reaching the shoulder main groove22B located inward of the shoulder land portion23C in the tire lateral direction. Accordingly, the shoulder land portions23C are formed as rib-like land portions. Note that in the present embodiment, the shoulder land portion lug grooves25C provided in the shoulder land portions23C are, at the terminating end portion, lug narrow grooves27where both the lug grooves25and the narrow grooves26are present. The communication narrow groove26E extends from the narrow groove26of the lug narrow groove27and communicates with the shoulder main grooves22B. Additionally, terminating end portions of the shoulder land portion lug grooves25C, which are lug narrow grooves27, are disposed on the ground contact edges T.

Herein, design end E refers to the outermost end of the tread portion2in the tire lateral direction disposed outward of the ground contact edge T in the tire lateral direction, and is the outermost end of the tread portion2in the tire lateral direction where grooves are formed. InFIG. 2, the design end E is illustrated as being continuous in the tire circumferential direction. In other words, in the tread portion2, when the tire is placed on a dry, flat road surface, the region from the ground contact edge T to the design end E is a region which does not typically come into contact with the ground.

Note that the shoulder land portion lug grooves25C provided in the shoulder land portions23C terminate within the shoulder land portions23C and are separated from the through lug grooves25E described above. However, the first end of the through lug groove25E, i.e. the end of the middle land portion lug groove25B provided in the middle land portion23B on the vehicle outer side that communicates with the shoulder main groove22B, is disposed on an extension of the end portion where the shoulder land portion lug groove25C provided in the shoulder land portion23C on the vehicle outer side terminates within the shoulder land portion23C. Additionally, the second end of the through lug groove25E, i.e. the end of the middle land portion lug groove25B provided in the middle land portion23B on the vehicle inner side, is disposed on an extension of the end portion where the shoulder land portion lug groove25C provided in the shoulder land portion23C on the vehicle inner side terminates within the shoulder land portion23C. In other words, the lug grooves25that include the shoulder land portion lug grooves25C provided in the shoulder land portions23C and the through lug grooves25E (the middle land portion lug grooves25B of the middle land portion23B on the vehicle outer side, the center land portion lug grooves25A of the center land portion23A, and the middle land portion lug grooves25B of the middle land portion23B on the vehicle inner side) are disposed on a smooth, continuous curved line CU that crosses the land portions23A,23B,23C between the outer ends (design ends E) of the tread portion2in the tire lateral direction. Curved line CU refers to a line having only tangent lines with an angle ranging from 40° to 90° with respect to the tire lateral direction.

The center land portion narrow grooves26A of the narrow grooves26provided in the center land portion23A are disposed between pairs of the center land portion lug grooves25A adjacent in the tire circumferential direction and intersect the tire circumferential direction. The center land portion narrow grooves26A communicate with the center main groove22A on the vehicle inner side of the center land portion23A at the first end, and terminate within the center land portion23A at the second end without reaching the center main groove22A on the vehicle outer side of the center land portion23A.

The middle land portion narrow grooves26B provided in the middle land portion23B on the vehicle outer side are disposed between pairs of the middle land portion lug grooves25B adjacent in the tire circumferential direction and intersect the tire circumferential direction. The middle land portion narrow grooves26B communicate with the center main groove22A at the middle land portion23B at the first end, and terminate within the middle land portions23B at the second end without reaching the shoulder main groove22B at the middle land portion23B.

The middle land portion narrow grooves26B provided in the middle land portion23B on the vehicle inner side are disposed between extensions of pairs of the middle land portion lug grooves25B adjacent in the tire circumferential direction and intersect the tire circumferential direction. The middle land portion narrow grooves26B communicate at both ends with the shoulder main groove22B at the middle land portion23B and with the auxiliary groove24. Thus, the middle land portion narrow grooves26B provided in the middle land portion23B on the vehicle inner side divide a portion of the middle land portion23B between the shoulder main groove22B and the auxiliary groove24into a plurality of blocks disposed in a row in the tire circumferential direction.

The shoulder land portion narrow grooves26C provided in the shoulder land portions23C are disposed between pairs of the shoulder land portion lug grooves25C adjacent in the tire circumferential direction and intersect the tire circumferential direction. The shoulder land portion narrow grooves26C communicate with the shoulder main grooves22B at the first end and terminate at the second end within the shoulder land portions23C near the outer ends of the tread portion2in the tire lateral direction (design ends E), extending beyond the ground contact edges T.

Note that the shoulder land portions23C are provided with recessed portions28near the outer ends of the tread portion2in the tire lateral direction (design ends E). The recessed portions28have a circular dimple shape and are formed between pairs of the shoulder land portion lug grooves25C adjacent in the tire circumferential direction in two rows in the tire lateral direction, a laterally inner row28awith two recessed portions28in the tire circumferential direction and a laterally outer row28bwith three recessed portions28in the tire circumferential direction. Additionally, the recessed portions28of the laterally outer row28bhave a larger diameter than those of the laterally inner row28a. The shoulder land portion narrow grooves26C provided in the shoulder land portions23C terminate at the recessed portions28at the second ends. In the present embodiment, the shoulder land portion narrow grooves26C terminate at the recessed portion28of the laterally outer row28bcentrally located in the tire circumferential direction.

In such a manner, the pneumatic tire1according to the present embodiment is provided with four main grooves22in the tread surface21of the tread portion2, each extending in the tire circumferential direction. The main grooves22form the center land portion23A, the middle land portions23B adjacent to the center land portion23A on either side in the tire lateral direction, and the shoulder land portions23C outwardly adjacent to the middle land portions23B in the tire lateral direction. The main grooves22have a wave-like shape with a constant groove width in the tire circumferential direction and with periodic oscillation. The vehicle inner/outer side orientation when the pneumatic tire1is mounted on a vehicle may be designated.

According to the pneumatic tire1, the main grooves22have a wave-like shape with periodic oscillation. This increases the overall width of the main grooves22to provide good drainage properties, and allows braking performance on wet road surfaces to be maintained. Additionally, according to the pneumatic tire1, the main grooves22have a constant groove width in the tire circumferential direction. This allows the rigidity of the land portions23(which are formed by the main grooves22) near the main grooves22to be made uniform, and wear resistance performance to be improved.

Preferably, for the pneumatic tire1according to the present embodiment, the vehicle inner/outer side orientation when the pneumatic tire1is mounted on a vehicle is designated, and the auxiliary groove24is provided in the middle land portion23B on the vehicle inner side, the auxiliary groove24having a narrower groove width than the main grooves22and extending in a linear manner in the tire circumferential direction.

According to the pneumatic tire1, the vehicle inner side greatly contributes to drainage properties, and so by the middle land portion23B on the vehicle inner side being provided with the auxiliary groove24extending in a linear manner in the tire circumferential direction, good drainage properties can be provided, and thus the braking performance on wet road surfaces can be improved. Furthermore, the auxiliary groove24has a narrower groove width than the main grooves22. Thus, a decrease in the rigidity of the middle land portion23B can be suppressed, and wear resistance performance can be improved.

Preferably, the pneumatic tire1according to the present embodiment includes a plurality of the through lug grooves25E disposed in the tire circumferential direction. The through lug grooves25E intersect the tire circumferential direction and continuously pass through the center land portion23A and the middle land portion23B on the vehicle outer side. Also, the through lug grooves25E open to the shoulder main groove22B on the vehicle outer side of the middle land portion23B on the vehicle outer side at the first end, pass through the center main groove22A on the vehicle inner side of the center land portion23A, and terminate within the middle land portion23B on the vehicle inner side at the second end without reaching the auxiliary groove24.

According to the pneumatic tire1, the through lug grooves25E are disposed running continuously through the center land portion23A and the middle land portion23B on the vehicle outer side. This connects the center main grooves22A and the shoulder main grooves22B on the vehicle outer side. As a result, good drainage properties can be provided, and braking performance on wet road surfaces can be improved. Furthermore, the through lug groove25E terminates within the middle land portion23B on the vehicle inner side without reaching the auxiliary groove24. This allows a decrease in rigidity of the middle land portion23B on the vehicle inner side to be suppressed and wear resistance performance to be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the shoulder land portions23C are provided with the shoulder land portion lug grooves25C that intersect the tire circumferential direction in a row in the tire circumferential direction, the shoulder land portion lug grooves25C terminating without reaching the shoulder main groove22B inward of the shoulder land portion23C in the tire lateral direction.

According to the pneumatic tire1, the shoulder land portion lug grooves25C provide good drainage properties in the shoulder land portions23C, and the terminating ends within the shoulder land portion23C allow a decrease in rigidity of the shoulder land portion23C to be suppressed and wear resistance performance to be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the shoulder land portion lug grooves25C communicate with the shoulder main groove22B inward of the shoulder land portion23C in the tire lateral direction via the communication narrow groove26E, which has a narrower groove width than itself.

Furthermore, according to the pneumatic tire1, the communication narrow grooves26E provide good drainage properties and allow braking performance on wet road surfaces to be improved. Additionally, the communication narrow groove26E have a narrower groove width than the shoulder land portion lug grooves25C. This allows a decrease in rigidity of the shoulder land portions23C to be suppressed and wear resistance performance to be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the lug narrow grooves27in which the lug grooves25and the narrow grooves26are present are disposed between the shoulder land portion lug grooves25C and the communication narrow grooves26E.

According to the pneumatic tire1, the lug narrow grooves27are disposed between the shoulder land portion lug grooves25C and the communication narrow grooves26E. This allows excessive changes in rigidity at the communicating portion between the shoulder land portion lug grooves25C and the communication narrow grooves26E to be suppressed, and wear resistance performance to be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the shoulder land portion narrow grooves26C are disposed between pairs of the shoulder land portion lug grooves25C adjacent in the tire circumferential direction. The shoulder land portion narrow grooves26C intersect the tire circumferential direction and have a narrower groove width than the shoulder land portion lug grooves25C.

According to the pneumatic tire1, the shoulder land portion narrow grooves26C provide good drainage properties and allow braking performance on wet road surfaces to be improved. Additionally, the shoulder land portion narrow grooves26C have a narrower groove width than the shoulder land portion lug grooves25C. This allows a decrease in rigidity of the shoulder land portions23C to be suppressed and wear resistance performance to be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the shoulder land portions23C are provided with recessed portions28at the outer ends in the tire lateral direction, and the shoulder land portion narrow grooves26C terminate at the recessed portions28at the outer end portion in the tire lateral direction.

According to the pneumatic tire1, the outer end portions of the shoulder land portion narrow grooves26C in the tire lateral direction terminate at the recessed portions28. This prevents loads acting on the outer end portions of the shoulder land portion narrow grooves26C in the tire lateral direction, and allows a decrease in rigidity of the shoulder land portions23C to be suppressed and wear resistance performance to be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the lug grooves25are formed with the chamfers25con the opening portions.

According to the pneumatic tire1, the lug grooves25are formed with the chamfers25con the opening portions. This allows a decrease in rigidity of the land portions near the lug grooves25to be suppressed and wear resistance performance to be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the vehicle inner/outer side orientation when the tire is mounted on the vehicle is designated; and the middle land portion narrow grooves26B that intersect the tire circumferential direction are disposed in the middle land portion23B on the vehicle outer side. The middle land portion narrow grooves26B communicate with the center main groove22A on the vehicle inner side of the middle land portion23B at the first end and terminate within the middle land portion23B at the second end without reaching the shoulder main groove22B on the vehicle outer side of the middle land portion23B. The center land portion narrow grooves26A that intersect the tire circumferential direction are disposed in the center land portion23A. The center land portion narrow grooves26A communicate with the center main groove22A on the vehicle inner side of the center land portion23A at the first end and terminate within the center land portion23A at the second end without reaching the center main groove22A on the vehicle outer side of the center land portion23A.

According to the pneumatic tire1, the middle land portion narrow grooves26B and the center land portion narrow grooves26A provide good drainage properties and allow braking performance on wet road surfaces to be improved. Additionally, by the middle land portion narrow grooves26B and the center land portion narrow grooves26A terminating within the respective land portions23B,23A, a decrease in rigidity of the land portions23B,23A can be suppressed and wear resistance performance can be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the tread portion2has an asymmetrical pattern in the tire lateral direction, and the difference in groove area ratio between the two regions on either side of the tire equatorial plane CL in the tire lateral direction is within 2%.

Herein, “groove area ratio” is defined as groove area/(groove area+ground contact area) expressed as a percentage. “Groove area” is the total opening area of all of the grooves in the contact patch (ground contact region). Additionally, the groove area and the ground contact region are the regions measured when the pneumatic tire1is mounted on a regular rim, inflated to the regular internal pressure, and loaded with 70% of the regular load.

According to the pneumatic tire1, the rigidity and the drainage properties of the land portions located in the two regions on either side of the tire equatorial plane CL in the tire lateral direction can be made uniform, and the effect of enhancing wear resistance performance can be significantly provided while maintaining braking performance on wet road surfaces. Note that the groove area ratio is preferably higher on the vehicle inner side which contributes more to drainage properties.

Preferably, in the pneumatic tire1according to the present embodiment, the recessed portions28are formed at the outer ends of the shoulder land portions23C in the tire lateral direction. The recessed portions28are formed in two rows in the tire lateral direction, the laterally inner row28awith two recessed portions28in the tire circumferential direction and the laterally outer row28bwith three recessed portions28in the tire circumferential direction. The recessed portions28of the laterally outer row28bhave a larger diameter than those of the laterally inner row28a.

According to the pneumatic tire1, the recessed portions28can improve the appearance of the outer ends of the tread portion2in the tire lateral direction. Note that the portion where the recessed portions28are formed are portions located outward from the ground contact edges T in the tire lateral direction and do not normally come into contact with a dry road surface. As such, they do not affect the running of the vehicle.

The pneumatic tire1according to the present embodiment is provided with the tread portion2, four main grooves22in the tread surface21of the tread portion2, each extending in the tire circumferential direction. The main grooves22form the center land portion23A, the middle land portions23B adjacent to the center land portion23A on either side in the tire lateral direction, and the shoulder land portions23C outwardly adjacent to the middle land portions23B in the tire lateral direction. The main grooves22have a wave-like shape with periodic oscillation. The lug grooves25are disposed in the land portions23A,23B,23C in a row in the tire circumferential direction and intersect the tire circumferential direction. The lug grooves25are disposed on the smooth, continuous curved line CU that crosses the land portions23A,23B,23C between the outer ends of the tread portion2in the tire lateral direction.

According to the pneumatic tire1, the main grooves22have a wave-like shape with periodic oscillation. This increases the overall width of the main grooves22to provide good drainage properties, and allows braking performance on wet road surfaces to be maintained. Additionally, according to the pneumatic tire1, the lug grooves25are disposed on the smooth, continuous curved line CU that crosses the land portions23A,23B,23C between the outer ends of the tread portion2in the tire lateral direction. This allows good drainage properties to be provided between the land portions23A,23B,23C, and braking performance on wet road surfaces to be maintained. Furthermore, the lug grooves25are disposed on the smooth, continuous curved line CU that crosses the land portions23A,23B,23C between the outer ends of the tread portion2in the tire lateral direction. This allows an excessive difference in rigidity between the land portions23A,23B,23C in the tire lateral direction to be suppressed. Thus, wear resistance performance can be improved.

Preferably, in the pneumatic tire1according to the present embodiment, a plurality of the lug grooves25on the same curved line CU communicate with a main groove22at both ends.

According to the pneumatic tire1, better drainage properties is provided between the land portions23A,23B,23C, and braking performance on wet road surfaces can be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the vehicle inner/outer side orientation when the tire is mounted on the vehicle is designated. The lug grooves25include the through lug grooves25E disposed in the tire circumferential direction that continuously pass through the center land portion23A and the middle land portion23B on the vehicle outer side. Also, the through lug grooves25E open to the shoulder main groove22B on the vehicle outer side of the middle land portion23B on the vehicle outer side at the first end, pass through the center main groove22A on the vehicle inner side of the center land portion23A, and terminate within the middle land portion23B on the vehicle inner side at the second end.

According to the pneumatic tire1, the through lug grooves25E are disposed running continuously through the center land portion23A and the middle land portion23B on the vehicle outer side. This connects the center main grooves22A and the shoulder main grooves22B on the vehicle outer side. As a result, good drainage properties can be provided, and braking performance on wet road surfaces can be improved. Furthermore, the through lug groove25E terminates within the middle land portion23B on the vehicle inner side. This allows a decrease in rigidity of the middle land portion23B on the vehicle inner side to be suppressed and wear resistance performance to be improved.

Preferably, in the pneumatic tire according to the present embodiment, the shoulder land portions23C are provided with the shoulder land portion narrow grooves26C between pairs of the shoulder land portion lug grooves25C adjacent in the tire circumferential direction that intersect the tire circumferential direction. The shoulder land portion narrow grooves26C communicate with the shoulder main groove22B inward of the shoulder land portion23C in the tire lateral direction at the first end and terminate within the shoulder land portion23C at the second end. The middle land portions23B are provided with the middle land portion narrow grooves26B between pairs of the middle land portion lug grooves25B adjacent in the tire circumferential direction that intersect the tire circumferential direction. The middle land portion narrow grooves26B communicate with one of the main grooves22(the center main groove22A or the shoulder main groove22B) at the middle land portion23B at the first end and terminate within the middle land portion23B at the second end without reaching the other main groove22(shoulder main groove22B or center main groove22A) at the middle land portion23B. The center land portion23A is provided with the center land portion narrow grooves26A between pairs of the center land portion lug grooves25A adjacent in the tire circumferential direction that intersect the tire circumferential direction. The center land portion narrow grooves26A communicate with one of the center main grooves22A at the center land portion23A at the first end and terminate within the center land portion23A at the second end without reaching the other center main groove22A at the center land portion23A.

According to the pneumatic tire1, the narrow grooves26A,26B,26C are disposed in the respective land portions23A,23B,23C, and communicate with a main groove22at the first end and terminate within the corresponding land portion23A,23B,23C at the second end. This allows good drainage properties to be provided, and allows a decrease in rigidity of the land portions23A,23B,23C to be suppressed and braking performance on wet road surfaces be maintained. Thus, wear resistance performance can be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the vehicle inner/outer side orientation when the tire is mounted on the vehicle is designated; and the middle land portion narrow grooves26B that intersect the tire circumferential direction are disposed in the middle land portions23B. The middle land portion narrow grooves26B communicate with one of the main grooves22at the middle land portion23B (the center main groove22A or the shoulder main groove22B) at the first end and terminate within the middle land portion23B at the second end without reaching the other main groove22at the middle land portion23B (shoulder main groove22B or the center main groove22A). The center land portion narrow grooves26A that intersect the tire circumferential direction are disposed in the center land portion23A. The center land portion narrow grooves26A communicate with one of the center main grooves22A at the center land portion23A at the first end and terminate within the center land portion23A at the other end without reaching the other center main groove22A at the center land portion23A. The ratios A1, A2, A3satisfy the relationship A1<A2<A3, where A1is the ratio between a lateral dimension RW1of the middle land portion23B on the vehicle inner side and a lateral dimension GW1of the middle land portion narrow grooves26B provided in the middle land portion23B on the vehicle inner side, A2is the ratio between a lateral dimension RW2of the center land portion23A and a lateral dimension GW2of the center land portion narrow grooves26A provided in the center land portion23A, and A3is a ratio between a lateral dimension RW3of the middle land portion23B on the vehicle outer side and a lateral dimension GW3of the middle land portion narrow grooves26B provided in the middle land portion23B on the vehicle outer side.

According to the pneumatic tire1, the ratios between the lateral dimensions of the land portions23and the lateral dimensions of the narrow grooves26increase in order from the vehicle inner side to the vehicle outer side. In other words, the lateral dimensions of the narrow grooves26are greater relative to the lateral dimension of the corresponding land portion23from the vehicle inner side toward the vehicle outer side. As a result, the narrow grooves26on the vehicle inner side, which may include many grooves to contribute to drainage properties, have smaller lateral dimensions than those on the vehicle outer side. This allows an extreme difference in rigidity between the center land portion23A and the middle land portions23B to be suppressed. Thus, wear resistance performance can be improved.

Preferably, in the pneumatic tire1according to the present embodiment, the vehicle inner/outer side orientation when the tire is mounted on the vehicle is designated. The middle land portion narrow grooves26B that intersect the tire circumferential direction are disposed in the middle land portions23B between pairs of the middle land portion lug grooves25B adjacent in the tire circumferential direction. The center land portion narrow grooves26A that intersect the tire circumferential direction are disposed between pairs of the center land portion lug grooves25A adjacent in the tire circumferential direction. The ratios B1, B2, B3satisfy the relationships B2<B1and B2<B3, where B1is a shortest distance B1of the middle land portion narrow grooves26B to the predetermined curved line CU in the middle land portion23B on the vehicle inner side, B2is a shortest distance of the center land portion narrow grooves26A to the curved line CU in the center land portion23A, and B3is a shortest distance of the middle land portion narrow grooves26B to the curved line CU in the middle land portion23B on the vehicle outer side.

According to the pneumatic tire1, the distance of the narrow grooves26from the lug grooves25in the center land portion23A has a magnitude relationship opposite to that of the middle land portions23B on either side. As a result, an extreme difference in rigidity between the center land portion23A and the middle land portions23B can be suppressed. Thus, wear resistance performance can be improved.

EXAMPLES

In the examples, performance tests for wear resistance performance and braking performance on wet road surfaces were performed on a plurality of types of pneumatic tires of different conditions (seeFIGS. 7A-7C).

In these performance tests, pneumatic tires having a tire size of 205/55R16 were assembled on 16×6.5 J rims, inflated to the regular internal pressure (200 kPa), and mounted on a test vehicle (1600 cc, front engine front wheel drive sedan passenger vehicle).

Wear resistance performance was evaluated by driving the test vehicle described above on a test course with a dry road surface for 5000 km and then measuring the wear of the land portions via the amount of main groove remaining. Then, the measurement results were expressed as index values with the value of the Conventional Example being defined as the reference (100). In this evaluation, larger values indicate less wear, which is preferable.

Braking performance on wet road surfaces was evaluated by measuring the braking distance of the test vehicle from a speed of 100 km/h on a wet road surface test course with a water depth of 1 mm. Then, the measurement results were expressed as index values with the value of the Conventional Example being defined as the reference (100). In this evaluation, larger values indicate less braking distance, which is preferable.

InFIGS. 7A-7C, the pneumatic tires that were used as the test tires had a configuration including five land portions formed by four main grooves on the tread surface, the land portions including the center land portion disposed on the tire equatorial plane CL, the middle land portions disposed adjacent to the center land portion on the two sides in the tire lateral direction, and the shoulder land portions disposed adjacent to the middle land portions on the outer sides in the tire lateral direction.

The pneumatic tire of the Conventional Example indicated inFIGS. 7A-7Cinclude main grooves that oscillate in a wave-like manner with a non-constant groove width.

The pneumatic tires of Examples 1 to 12 include main grooves that oscillate in a wave-like manner with a constant groove width. The pneumatic tires of Examples 2 to 12 include an auxiliary groove. The pneumatic tires of Examples 3 to 12 include an integral through lug groove, formed by the lug grooves of the center land portion and the middle land portion on the vehicle outer side communicating with the main grooves at both ends and the lug grooves of the middle land portion on the vehicle inner side communicating with a main groove at the first end. In the pneumatic tires of Examples 4 to 12, the lug grooves of the shoulder land portions terminate within the land portions without communicating with the main grooves. In the pneumatic tires of Examples 5 to 12, the lug grooves of the shoulder land portions communicate with the main groove via the communication narrow grooves. In the pneumatic tires of Examples 6 to 12, the lug narrow grooves are disposed between the lug grooves of the shoulder land portions and the communication narrow grooves. In the pneumatic tires of Examples 7 to 12, the narrow grooves of the shoulder land portions communicate with the main groove. In the pneumatic tires of Examples 8 to 12, the narrow grooves terminate at one of the recessed portions disposed in the shoulder land portion. In the pneumatic tires of Examples 9 to 12, the opening portions of the lug grooves are formed with the chamfers. In the pneumatic tires of Examples 10 to 12, the narrow grooves of the center land portion and the middle land portions terminate within the land portion at one end portion without communicating with a main groove. In the pneumatic tires of Examples 11 and 12, the tread portion has an asymmetrical pattern in the tire lateral direction, and the difference in groove area ratio between the two regions on either side of the tire equatorial plane in the tire lateral direction is within 2%, with the vehicle inner side having a higher groove area ratio. In the pneumatic tire of Example 12, the recessed portions disposed in the shoulder land portions are formed in two rows in the tire lateral direction, the laterally inner row with two recessed portions in the tire circumferential direction and the laterally outer row with three recessed portions in the tire circumferential direction. The recessed portions of the laterally outer row also have a larger diameter than those of the laterally inner row.

As can be seen from the test results shown inFIGS. 7A-7C, the pneumatic tires of Examples 1 to 12 provided enhanced wear resistance performance while maintaining braking performance on wet road surfaces.