To reduce blowouts of a rear-wheel tire by making a nail thrown by a front-wheel tire hardly stick in the rear-wheel tire.

Respective tread positions of the tires 14, 15 of the right/left rear wheels RR, RL are arranged inside in the vehicle-width direction from tread positions of the tires 12, 13 of the right/left front wheels FR, FL by not less than a dimension T in the vehicle-width direction of the tires 12, 13.