Aspects of the invention relate to a method comprising: determining an output torque at a wheel of a vehicle mounted to a test apparatus comprising an external motor, the output torque being in response to a command; determining a correction factor based on the output torque and at least one coefficient associated with a reaction of a component of the vehicle and/or of the test apparatus to an applied torque at the vehicle; and controlling the external motor to apply the correction factor to the wheel of the vehicle.