Abstract: A variable tread vehicle includes first and second parallel horizontal rails which are connected to a frame and extend in a direction which is transverse to the direction of movement of the vehicle. First and second movable carriages are movable on sections of the track formed by the rails. A first drop axle is connected to and extends downward from the first movable carriage, and a second drop axle is connected to and extends downward from the second movable carriage. Connected near the lower ends of the first and second drop axles are first and second wheels of the vehicle. The first and second movable carriages are moved on the track by first and second threaded drive shafts, which are driven by hydraulic motors. By controlling the hydraulic motors, the operator can drive the first and second movable carriages outward to increase the spacing between the first and second wheels, or can drive the first and second movable carriages inward to decrease the spacing between the first and second wheels.