PURPOSE: To improve the performance of wet tires by arranging the centers of a pair of tires to be furnished at the front and the rear on the same straight line that is in parallel with an advance direction, making at the same time the zigzag grooves of the main grooves of the rear side tire coincide with the straight groove positions of the main grooves of the front side tire.

CONSTITUTION: A zigzag groove 2A is formed at the center portion of a front side tire TA toward an advance direction, and straight grooves 1A are provided on its right and left, and the positions of the straight grooves 1A are made to be the ones that divide the maximum width SW of the tire into approximately three equal parts. Meanwhile, in the case of the rear side tire TB, a straight groove 1B is provided at the center portion, and zigzag grooves 2B opposite to the two straight grooves 1A of the front side tire are provided on its right and left, and in addition, straight grooves 11B are provided on their outsides. Water on a road surface wrapped in by means of the straight grooves of the front side tire is instantly repelled off to the outer part of a tire road surface, and the rear side tire whose main grooves are of a zigzag shape, conducts traveling on the road surface where water has become scarce, so the performance of traction is improved.