PURPOSE: To prevent a locally deep rut from being made by a vehicle moving on soft or weak ground, by causing the distances between the centers of the tread portions of three or more axles to differ from each other so that the loci of moving wheels of the vehicle are not overlapped with each other.

CONSTITUTION: Wheels W1,...W8 are provided on four axles coupled to the frame 1 of a vehicle, so that the distance between the tread centers of the wheels on the front and the rear axles is set at X1 and that between the tread centers of the wheels on the other intermediate axles is set at X2 which is smaller than X1. These distances X1, X2 are related to the width of the tires of the wheels as X1-X2≥B. As a result, three or more wheels do not take the same locus nor overlapped loci when the vehicle moves straightly.