Patent ID: 8496036

Claim:
A pneumatic tire including a tread portion provided with a pair of crown circumferential grooves which extend continuously and straightly in the tire circumferential direction on both sides of the tire equator to provide a center land portion between them, wherein said crown circumferential grooves comprise an inner crown circumferential groove which is located on the inside of the tire equator with respect to a vehicle when a tire is fitted to the vehicle, and an outer crown circumferential groove which is located on the outside of the tire equator with the fitted tire, a plurality of curved oblique grooves are provided in said center land portion at intervals in the tire circumferential direction, wherein each curved oblique groove extends obliquely from its outer end which opens at said outer crown circumferential groove, toward the inner side of the vehicle over the tire equator, turns toward the outer side of the vehicle at a closest approach location that the curved oblique groove makes the closest approach to said inner crown circumferential groove, and further extends obliquely up to its inner end located in said center land portion, said respective curved oblique grooves are connected with each other through connecting groove portions each extending in the tire circumferential direction from said inner end to an adjacent curved oblique groove adjoining in the tire circumferential direction, and said center land portion has a center rib which is defined by said connecting groove portions, portions of said curved oblique grooves each portion extending between said connecting groove portions, and said inner crown circumferential groove, and said center rib extends continuously in the tire circumferential direction while repeating increase and decrease of its axial width, and has a ratio of the maximum width to the minimum width within the range of 2.0 to 4.0, wherein said inner crown circumferential groove is a straight groove in which: respective ridge lines at which both groove walls intersect with the tread surface, extend straight in the circumferential direction, the groove wall on the tire equator side includes a mildly-inclined upper wall portion which extends downward from the ridge line at an angle θ 1 of 50 to 70° with respect to the normal line to the tread surface, and a steeply-inclined lower wall portion which is continuous with the lower edge of said upper wall portion and extends up to a groove bottom at an angle θ 2 smaller than said angle θ 1 , and said upper wall portion extends in the circumferential direction with repeating increase and decrease of its axial wall width, and has the maximum wall width at a location at which the width of said center rib becomes minimum.