Abstract: An electro-hydraulic auxiliary drive system providing power to the non-driven steerable wheels of an agricultural tractor utilizing hydraulic power in a parallel circuit from a pressure compensated pump which varies torque supplied to the auxiliary system by sensing the relative speed between the front and rear wheels and increases the torque to the auxiliary system when a set percentage of slip is determined between the front and rear wheels. The steerable wheels are driven by hydraulic motors connected in parallel through a flow divider valve and supplied by a variable displacement pressure compensated pump. When the electronic control receives an indication of slip from the main drive wheels it energizes a solenoid causing the pressure compensation level of the variable displacement pump to increase the torque output of the auxiliary drive system, with the percentage of slip being proportional to the increased torque.