A control system for a tractor having a transmission with a hydraulic drive circuit in which a hydraulic pump supplies pressurised fluid to a hydraulic motor. The control system controls an operating condition of an implement attached to the tractor and said control system comprises a pressure sensing means which senses the pressure in the hydraulic drive circuit and provides a signal which is indicative of the current pull force necessary to pull the implement. The control system further comprises a control means which receives the pressure signal and a second signal relating to the speed of the tractor and adjusts the current position of the implement to a new position when said pressure signal varies. The new position lies within a pre-determined position range dependent on the second signal in order to maintain an optimal, yet safe operating condition of the implement.
