Pneumatic tire including zig-zag subgrooves

A pneumatic tire having a tread surface including:

• two or three main grooves, which extend in the circumferential direction of said tire, in a central ground contacting region alone of the tread surface of said tire, the rotational direction of which is designated to one direction,
• at least one rib, which extends in the circumferential direction of said tire, between said main grooves, and
• a plurality of sub-grooves, which respectively extend from the both sides of said main grooves outward in the widthwise direction of said tire up to at least the ground contacting ends of said tire, at a predetermined pitch in the circumferential direction of said tire,
• wherein said sub-grooves are formed in zigzag lines inclined with the inner end portions thereof positioned on the forward side with respect to the rotational direction of said tire and not communicating with said main grooves, each of said sub-grooves extends in a zigzag line so as to have three to five bent portions,
• land portions separated by said sub-grooves are communicated,
• each of said sub-grooves is formed by connecting sub-groove portions together in series via said bent portions,
• an angle of inclination .alpha. with respect to the widthwise direction of said tire of an odd-numbered sub-groove portion counted from an inner end of each sub-groove being set larger than an angle of inclination .beta. of an even-numbered sub-groove portion,
• said angle of inclination .alpha. of said odd-numbered sub-groove portion is 45.degree.-90.degree., and said angle of inclination .beta. of said even-numbered sub-groove portion being 0.degree.-30.degree.,
• narrow grooves are provided which extend from odd-numbered sub-groove portions of each sub-groove in widthwise outermost positions to forward positions in the rotational direction of said tire in both the left and right sides of the tread surface with respect to the tire center line, said narrow grooves not communicating with adjacent sub-grooves, each narrow groove having a width smaller than a width of said sub-groove.