Abstract: Method and apparatus for tensioning an endless, inextensible, elastomeric ground engaging belt into frictional driven engagement with a driver wheel structure, oscillatably supporting an axle on which an idler wheel structure associated with the drive wheel structure is mounted, and accommodating recoil of the idler wheel structure. Such associated wheel structures are arranged on each lateral side of a vehicular main frame and are entrained by the ground engaging belt. The idler wheel structures are rotatably mounted on opposite ends of the axle extending laterally relative to the main frame. The axle is oscillatably mounted to the main frame about an oscillation axis parallel to the vehicle's longitudinal axis to accommodate uneven terrain and about a vertical axis to permit substantially independent recoil of the respective idler wheel structures.