PURPOSE: To improve stability and controllability free from a substantial drop in running performance on a rough road, due to the tread pattern of a tire, and further free from the partial abrasion thereof at high-speed travel, regarding a rib-lag type tread pattern.

CONSTITUTION: When the breadth of a flat section from a tread end to the zigzag neutral line of a nearby main groove, is taken at (a), and the circumferential pitch of lags determined by a gap between adjacent cut grooves 4 at (b), a relationship of 0.27×W2≤(a)×(b)≤0.82W2, and 1.40≤(b)/(a)≤3.6 is established with reference to the half-breadth W of the tread, in the case of three main grooves. Also, a relationship of 0.42×W2≤(a)×(b')≤1.11W2, and 1.40≤(b')/(a)≤3.6 in the case of two main grooves.