Pneumatic tire

1. A pneumatic tire, comprising:

a tread surface;

a plurality of circumferential main grooves formed on the tread surface and extending in a tire circumferential direction;

a plurality of lug grooves formed on the tread surface and extending in a tire lateral direction;

a plurality of blocks defined by the lug grooves on both sides in the tire circumferential direction and by the circumferential main grooves on at least one end portion in the tire lateral direction; and

narrow grooves formed in the blocks;

wherein the narrow grooves comprise a plurality of bent portions, a circumferential narrow groove extending in the tire circumferential direction and a lateral narrow groove extending in the tire lateral direction;

each of the blocks includes only a single one of the lateral narrow groove;

the circumferential narrow groove being provided as a plurality of circumferential narrow grooves, and each of the blocks comprises a plurality of intersection points where the plurality of circumferential narrow grooves intersect the lateral narrow groove; and

the circumferential narrow grooves and the lateral narrow groove have a same groove width;

the intersection points are spaced apart from one another in the tire lateral direction; and

each of the circumferential narrow grooves terminate at the intersection points without extending beyond the lateral narrow groove.

2. The pneumatic tire according to claim 1 , wherein

the bent portions are each positioned between the intersection points in the tire lateral direction, and

the lateral narrow groove opens to at least one of the circumferential main grooves.

3. The pneumatic tire according to claim 2 , wherein

the narrow grooves open to the respective lug grooves defining both sides of one of the blocks in the tire circumferential direction, and thus comprise two opening portions;

a distance W 3 in the tire lateral direction between one of the two opening portions and, among both ends of the one of the blocks in the tire lateral direction, an end portion near the opening portion is within a range of 0.15≤(W 3 /WB)≤0.40 with respect to a width WB of the one of the blocks in the tire lateral direction, and

a distance W 4 in the tire lateral direction between the other of the two opening portions and, among both ends of the one of the blocks in the tire lateral direction, an end portion near the opening portion is within a range of 0.15≤(W 4 /WB)≤0.40 with respect to the width WB of the one of the blocks in the tire lateral direction.

4. The pneumatic tire according to claim 3 , wherein

the narrow grooves have a groove depth d 1 within a range of 0.05≤(d 1 /d 2 )≤0.50 with respect to a groove depth d 2 of the circumferential main grooves.

5. The pneumatic tire according to claim 4 , wherein

the narrow grooves have a groove depth d 3 of the circumferential narrow grooves within a range of 0.5≤(d 3 /d 4 )≤0.8 with respect to a groove depth d 4 of the lateral narrow groove.

6. The pneumatic tire according to claim 5 , wherein

the narrow grooves comprise two of the intersection points, and

an angle β 1 between the narrow grooves that intersect at one of the intersection points and an angle β 2 between the narrow grooves that intersect at the other of the intersection points are within ranges of 70°≤β1≤90° and 70°≤β2≤90°, respectively.

7. The pneumatic tire according to claim 6 , wherein

the narrow grooves comprise two of the bent portions, and

a bend angle α 1 at one of the bent portions and a bend angle α 2 at an other of the bent portions are within ranges of 90°≤α 1 ≤120° and 90°≤α 2 ≤120°, respectively.

8. The pneumatic tire according to claim 7 , wherein

the blocks are configured so that a plurality thereof are aligned in the tire circumferential direction, forming block rows,

the tread surface is provided with a plurality of the block rows aligned in the tire lateral direction, and

the narrow grooves are formed in the blocks of the plurality of block rows.

9. The pneumatic tire according to claim 8 , wherein

the tread surface is provided with six of the block rows, and

the narrow grooves are formed in at least the blocks of four block rows, among the six block rows, other than the two block rows positioned on both end sides in the tire lateral direction.

10. The pneumatic tire according to claim 9 , wherein

the pneumatic tire has a specified rotation direction, and

the bent portions bend such that a portion of the narrow grooves positioned outward from the bent portions in the tire lateral direction is configured to bend further in directions positioned on a trailing side in a tire rotation direction than a portion positioned inward from the bent portions in the tire lateral direction.

11. The pneumatic tire according to claim 1 , wherein

the narrow grooves open to the respective lug grooves defining both sides of one of the blocks in the tire circumferential direction, and thus comprise two opening portions;

a distance W 3 in the tire lateral direction between one of the two opening portions and, among both ends of the one of the blocks in the tire lateral direction, an end portion near the opening portion is within a range of 0.15≤(W 3 /WB)≤0.40 with respect to a width WB of the one of the blocks in the tire lateral direction, and

a distance W 4 in the tire lateral direction between the other of the two opening portions and, among both ends of the one of the blocks in the tire lateral direction, an end portion near the opening portion is within a range of 0.15≤(W 4 /WB)≤0.40 with respect to the width WB of the one of the blocks in the tire lateral direction.

12. The pneumatic tire according to claim 1 , wherein

the narrow grooves have a groove depth d 1 within a range of 0.05≤(d 1 /d 2 )≤0.50 with respect to a groove depth d 2 of the circumferential main grooves.

13. The pneumatic tire according to claim 1 , wherein the narrow grooves have a groove depth d 3 of the circumferential narrow grooves within a range of 0.5≤(d 3 /d 4 )≤0.8 with respect to a groove depth d 4 of the lateral narrow groove.

14. The pneumatic tire according to claim 1 , wherein

the narrow grooves comprise two of the intersection points, and

an angle β 1 between the narrow grooves that intersect at one of the intersection points and an angle β 2 between the narrow grooves that intersect at the other of the intersection points are within ranges of 70°≤β1≤90° and 70°≤β2≤90°, respectively.

15. The pneumatic tire according to claim 1 , wherein

the narrow grooves comprise two of the bent portions, and

a bend angle α 1 at one of the bent portions and a bend angle α 2 at an other of the bent portions are within ranges of 90°≤α1≤120° and 90°≤α2≤120°, respectively.

16. The pneumatic tire according to claim 1 , wherein

the blocks are configured so that a plurality thereof are aligned in the tire circumferential direction, forming block rows,

the tread surface is provided with a plurality of the block rows aligned in the tire lateral direction, and

the narrow grooves are formed in the blocks of the plurality of block rows.

17. The pneumatic tire according to claim 16 , wherein

the tread surface is provided with six of the block rows, and

the narrow grooves are formed in at least the blocks of four block rows, among the six block rows, other than the two block rows positioned on both end sides in the tire lateral direction.

18. The pneumatic tire according to claim 1 , wherein

the pneumatic tire has a specified rotation direction, and

the bent portions bend such that a portion of the narrow grooves positioned outward from the bent portions in the tire lateral direction is configured to bend further in directions positioned on a trailing side in a tire rotation direction than a portion positioned inward from the bent portions in the tire lateral direction.

19. The pneumatic tire according to claim 1 , wherein the lateral narrow groove includes the plurality of bent portions between the intersections of the circumferential narrow grooves with the lateral narrow groove in the tire lateral direction.

20. The pneumatic tire according to claim 1 , wherein the intersections of the circumferential narrow grooves with the lateral narrow groove are between the bent portions of the lateral narrow groove in the tire lateral direction.

21. The pneumatic tire according to claim 1 , wherein the intersection points are spaced apart from one another in the tire circumferential direction.

22. A pneumatic tire, comprising:

a tread surface;

a plurality of circumferential main grooves formed on the tread surface and extending in a tire circumferential direction;

a plurality of lug grooves formed on the tread surface and extending in a tire lateral direction;

a plurality of blocks defined by the lug grooves on both sides in the tire circumferential direction and by the circumferential main grooves on at least one end portion in the tire lateral direction; and

narrow grooves formed in the blocks;

wherein the narrow grooves comprise a plurality of bent portions, a circumferential narrow groove extending in the tire circumferential direction and a lateral narrow groove extending in the tire lateral direction;

the bent portions are located on a single one of the narrow grooves and are spaced away from any intersections of any of the narrow grooves with the single one of the narrow grooves;

the lateral narrow groove and the circumferential narrow groove being configured so that at least one thereof is provided in a plurality and comprises a plurality of intersection points where the one intersects the other;

the circumferential narrow groove and the lateral narrow groove have a same groove width;

the intersection points are spaced apart from one another in the tire lateral direction; and

each narrow groove of the plurality of the lateral narrow groove or the circumferential narrow groove terminates at the intersection points without extending beyond the intersection points.