Abstract: A pneumatic radial tire has a tread pattern having a pair of straight main grooves each having a width equal to 8-13 percent of a ground contact width W of the tire and extending in parallel on opposite sides of an equator of the tire, a plurality of lug grooves extending across shoulder regions formed on the outersides of the pair of main grooves from the pair of main grooves outwardly toward the ends of the ground contact surface of the tire to form in cooperation with the main grooves successive rows of blocks, and a plurality of V-shaped sub-grooves in the shoulder regions spaced at a predetermined pitch apart in the circumferential direction of the tire and extending divergently with respect to the direction of reverse rotation of the tire, wherein the ratio of a distance W1 between respective centers of the main grooves to the ground contact width W is in the range of 0.2.ltoreq.W1/W.ltoreq.0.4; an angle .alpha.

Abstract: Two or three main grooves, which extend in the circumferential direction of a tire, are provided in the central ground contacting region alone of a tread surface of the tire the rotational direction of which is designated to one direction, and at least one rib extending in the circumferential direction of the tire is formed between the main grooves. A plurality of sub-grooves respectively extending from the both sides of the main grooves outward in the widthwise direction of the tire up to at least the ground contacting ends of the tire are arranged at a predetermined pitch in the circumferential direction of the tire in such a manner that the sub-grooves formed in zigzag lines are inclined with the inner end portions thereof positioned on the forward side with respect to the rotational direction of the tire. The sub-grooves do not communicate with the main grooves but communicate with land portions separated by the sub-grooves.