a standard model truck or trailer having a rear load bearing axle with two side - by - side pneumatic tires mounted on wheels at both ends of the axle is provided . a further set of like side - by - side rear wheels with pneumatic tires are connected to the vehicle &# 39 ; s main frame by depending carriers pivoted thereto . the rear wheels are rearwardly biased by a compression spring and may be selectively moved forwardly or rearwardly in an arc about their pivotable connection by a hydraulic piston and cylinder arrangement . an endless tread - type track can be mounted around the succeeding pairs of tires on either side . each track has two or more parts dovetailed at the ends held together by a spring steel rod inserted in openings therethrough , each opening being defined by a polygonal tube which receives the rod whereby it cannot rotate . the rod is maintained in place by a detent member . a slightly curved plate , rectangular as seen in plan , pivoted from supports depending from frame forward of at least the rearmost wheels , extends rearwardly centrally between the wheels to where a hydraulic cylinder and piston assembly connects it to the frame to lift the wheels simultaneously for installing the tracks . they are installed by decreasing the distance between the wheels through the hydraulic arrangement and , when in place , by releasing pressure in the connected hydraulic piston and cylinder assembly whereby the compression spring tensions the wheels against them .