Pneumatic tire with tread including circumferential grooves having inclined fine grooves

1. A pneumatic tire having a tread surface in which two circumferential direction main grooves continuous in a tire circumferential direction are arranged on each of left and right sides of a tire center, and land portions are defined by the circumferential direction main grooves as ribs or blocks having lug grooves, wherein

a plurality of fine grooves are provided only in each of right and left walls of each of the circumferential direction main grooves, the fine grooves being inclined in a radial direction to the tire circumferential direction at an angle of 20° to 70°, the fine grooves being provided in regions along the circumferential direction main groove, covering at least 50% of the entire circumference thereof in total,

in each of the two circumferential direction main grooves on tire shoulder sides, the fine grooves in the right wall and the fine grooves in the left wall are inclined to the tire circumferential direction in the same direction in a plan view in a tire radial direction, and

in each of the two circumferential direction main grooves on a tire center side, the fine grooves in the right wall and the fine grooves in the left wall are inclined to the tire circumferential direction in directions opposite to each other in a plan view in the tire radial direction,

wherein the fine grooves extend from the tread surface toward the bottom of the circumferential direction main grooves;

groove walls of each circumferential direction main groove are inclined to a normal direction of the tread surface at an angle of 7° to 13°, and

wherein each of said circumferential direction main grooves has a see through structure.

2. The pneumatic tire according to claim 1 , wherein

a width of each of the fine grooves is set to 0.4 mm to 0.6 mm, and

an interval between each adjacent two of the fine grooves is set to 1 mm to 5 mm.

3. The pneumatic tire according to claim 2 , wherein the inclined angle of each fine groove to the tire circumferential direction is set to 35° to 55°.

4. The pneumatic tire according to claim 1 , wherein

each center line of a circumferential direction main groove on the tire center side is located in a region between lines shifted from the tire center respectively by 5% and 15% of a tire contact width on the corresponding side, and

each center line of a circumferential direction main groove on the corresponding shoulder side is located in a region between lines shifted from the tire center respectively by 25% and 40% of the tire contact width on the corresponding side.

5. The pneumatic tire according to claim 1 , wherein

each circumferential direction main groove on the tire center side has a groove width set to 4% to 6% of the tire contact width, and

each circumferential direction main groove on the corresponding shoulder side has a groove width set to 115% to 125% of the groove width of each circumferential direction main groove on the tire center side.

6. The pneumatic tire according to claim 1 , wherein a groove area ratio in the tread surface is 30% to 50%.

7. The pneumatic tire according to claim 1 , wherein a groove area ratio of the lug grooves in the tread surface is 5% to 20%.

8. The pneumatic tire according to claim 1 , wherein

in each of the two circumferential direction main grooves on the tire shoulder sides, the fine grooves in the right wall and the fine grooves in the left wall have the same inclined angle in a plan view in the tire radial direction, and

in each of the two circumferential direction main grooves on the tire center side, the fine grooves in the right wall and the fine grooves in the left wall have different inclined directions line-symmetric with respect to a main groove center line in a plan view in the tire radial direction.

9. The pneumatic tire according to claim 1 , wherein the pneumatic tire is a mud and snow tire.