Pneumatic tire including main slant grooves and auxiliary grooves

A pneumatic tire comprising;

• a tread portion divided into two regions at a center of a tread pattern, and a plurality of main slant grooves arranged in at least one of the two regions at substantially equal intervals in a circumferential direction of the tire, each of the main slant grooves being comprised of a steep slope segment extending from a position of the pattern center or the vicinity thereof toward a side of an end of the tread pattern at a relatively small inclination angle with respect to a plane inclusive of the circumference of the tire and a gentle slope segment extending from the steep slope segment at a relatively large inclination angle with respect to the plane to the end of the tread pattern or to open at a ground contact end of the tread, and a plurality of land portions defined by adjoining two main slant grooves in said at least one of the two regions, a single steeply slant auxiliary groove communicating to the adjoining two main slant grooves and extending at a relatively small inclination angle with respect to the plane in the same direction as in the main slant groove and a gently slant auxiliary groove disposed between the adjoining two main slant grooves and extending from the steeply slant auxiliary groove to the end of the tread pattern or to open at the ground contact end of the tread substantially in parallel to the main slant groove being arranged in a tread side zone wherein, said at least one of the two regions is equally divided by a phantom line parallel with the pattern center into a tread central zone and the tread side zone, a land portion is further divided by the arrangement of these auxiliary grooves into a central land part and several shoulder land parts, said central land part of the land portion has a shape such that a side wall facing the steeply slant auxiliary groove is pushed out in an arc-shaped form toward the ground contact end of the tread, and groove widths of the gentle slope segment of the main slant groove facing a side wall of the shoulder land part, the steeply slant auxiliary groove and the gently slant auxiliary groove are approximately equal and are within a range of 40-80% of a groove width of the steep slope segment of the main slant groove facing the side wall of the central land part.