Automobiles steer by imposing a steer angle between the front and rear wheels. Broadly speaking, the response of the vehicle is related to that angle; the automobile is a "position-controlled" system in normal use.
Bikes steer by controlling roll angle. However roll angle is not directly manipulated by the handlebars in the same way as steer angle in an automobile. Rather it is influenced indirectly by applying roll moments to the machine. These roll moments in turn come from side forces at the wheels, which are closely related to steering torques. Thus the bike is a "force-controlled" system in which the actual position of the handlebars is free.[citation needed]
