A transmission control circuit (101-112) for a vehicle measures an efficiency factor for the variable transmission. It also measures the actual output speed of the transmission and the torque of the engine. These factors are combined with other measurements to select the transmission ratio and the engine speed etc. in order to achieve maximum efficiency, minimum emission products etc. The control takes into account engine torque and speed, torque reserve, fuel usage etc. The transmission has a continuously variable ratio for optimum effect.
