Abstract: A pneumatic power assist mechanism for supporting heavy truck tires during nstallation on or removal from a truck or similar vehicle. The mechanism comprises an inflatable pillow that can be pressurized to slightly elevate a tire cradle means to a position in which the tire weight is transferred from the vehicle axle to the cradle means. The cradle means is slidably guided for transporting the cradled tire laterally toward or away from the vehicle. In a preferred embodiment the cradle means consists of two rollers that are oriented to permit rotation of the heavy tire about its axis, as for example when it is necessary to align holes in the wheel with studs projecting from the axle.