PURPOSE: To make both traction and biased abrasion proof improve by forming both side walls of main grooves arranged to both sides of the equator of a tire respectively in zigzag like, while specifying a relation of sizes, between respective repetitive pitches and between point heights.

CONSTITUTION: A pair of main grooves G1 extending in peripheral direction are arranged at both sides of the equator C of a tire on a tread surface 2 of the tire in a range of a distance of 0.075-0.275 times tread width from the equator C of the tire. Respective main grooves G1 are connected together with lateral grooves (g) inclined to the tire axis direction in an angle of 0-50°. Meanwhile, respective groove walls on the equator side and the tread end side of each main groove G1 are respectively formed in zigzag like on upper parts of respective grooves. Moreover, a repetitive pitch PQ on the upper part of the equator side groove is set smaller than a repetitive pitch PS on the upper part of the tread end side groove. Still more, a point height KQ of the upper side of the equator side groove is set larger than a point height KS of the upper side of the tread end side groove.