Pneumatic tire with tread having circumferential grooves

A pneumatic tire having at least one outer region circumferential main groove extending continuously in a circumferential direction of a tire and disposed in an outer region of a tread surface which faces outward of a tire equator with respect to a vehicle,

• said outer region circumferential main groove being a straight groove such that each of ridge lines at which groove wall surfaces on both sides of said groove intersect with said tread surface extends straight in the circumferential direction,
• each of said groove wall surfaces comprising a gently-inclined upper wall surface portion which extends downwardly from each of said ridge lines at an angle θ1 of 40 to 60° with respect to a normal line to the tread surface, and a steeply-inclined lower wall surface portion which is continuous with a lower end of said upper wall surface portion and extends up to a groove bottom at an angle θ2 smaller than said angle θ1,
• said lower wall surface portion including projections disposed at intervals in the circumferential direction, said projections having a triangular cross section and projecting from said lower wall surface portion toward a groove width center with a slope surface extending from said lower end of said upper wall surface portion up to said groove bottom at an angle θ3 which is not greater than said angle θ1 but is greater than said angle θ2,
• at least one inner region circumferential main groove extending continuously in the circumferential direction is disposed in an inner region of said tread surface which faces inward of the tire equator with respect to a vehicle, and
• said inner region circumferential main groove being formed into a rectangular wave-like zigzag groove such that each of ridge lines at which wall surfaces on both sides of the grooves intersect with the tread surface, comprises a first ridge line portion located on a groove width center side and extending straight in the circumferential direction and a second ridge line portion located outside of said first ridge line portion and extending straight in the circumferential direction.