Abstract: Disclosed herein is a vehicle testing apparatus comprising a pair of brake clipers operable in response to the application of pressure fluid for applying torque in opposition to driving torque delivered by the driving wheels of a vehicle operating at a given speed, a force sensor for sensing differential in the driving and applied torque, a control for generating a signal representative of the torque differential, and a pressure regulator for maintaining the applied torque at a constant magnitude by regulating the pressure of the fluid applied to the brake calipers.