Pneumatic radial tires including a fork-shaped groove

A pneumatic radial tire having a tread portion and a tread pattern in the tread portion, the tread pattern including in a ground contact area of the tread portion a plurality of main slant grooves, the main slant grooves bordering on a center of the pattern and extending in a gradually expanding direction from bottom toward top viewed from a front of the tire at a state of mounting of the tire on a vehicle and opening to an end of the tread portion;

• each of said main slant grooves being comprised of a steeply slant segment being located in a region near the pattern center and having an inclination angle of 0.degree.-30.degree. with respect to a circumferential direction of the tire and a gently slant segment smoothly connected to the steeply slant segment and being located in a region near a side end of the tread portion without crossing any other grooves and having an inclination angle of 60.degree.-90.degree. with respect to the circumferential direction, wherein a fork-shaped groove is bifurcated from the steeply slant segment of each of the main slant grooves at a position between the pattern center and a position which is located a distance of 1/4 of a width of the tread portion from the pattern center and extended toward each end of the tread portion and provided with at least two branch groove segments, each of the two branch segments opening to the end of the tread portion without crossing any other grooves, a land portion being defined for each of the main slant grooves between the main slant groove and the fork-shaped groove and having an included angle of 5.degree.to 40.degree. and a land portion being defined for each fork-shape groove between the branch groove segments of the fork-shaped groove and having an included angle of 5.degree.-40.degree., each of the land portions including a tapered zone having an end and a surface height of the tapered zone of each of the land portions is gradually decreased toward the end of the tapered zone.