Abstract: A four-wheel drive agricultural tractor with independently steered ground engaging wheels supporting a flat, extensible load supportive frame includes an operator's cab that is adapted to face the direction of travel. Mounted under the frame is an internal combustion engine, clutch, and transmission which are individually controllable from the cab. A system of shafts and gears couple motive power from the transmission to pairs of wheels and a system of hydraulic steering motors are controllable from the cab for effecting either coordinated or crab steering. Fabricated of box-girders, the frame includes fixed and slidable portions that are mutually displaceable by hydraulic rams located within the frame to vary the wheelbase and tread of the tractor. The frame also includes an articulated hinged member at each end carrying a hydraulic stabilizer.