Experimental Study of Motorcycle Transfer Functions for Evaluating Handling

The transfer functions of a motorcycle, especially that between roll angle and steering torque, qualify input-output characteristics - that is, motion produced as a function of steering torque - and are closely related to ease of use and handling. This paper describes the measurement of the transfer functions of a typical sports motorcycle, resulting from data collected in slalom tests. These functions are then compared to analytical transfer functions derived from known models in the literature. The comparison shows fair to good agreement. Lastly, the formation of steering torque is analysed and the observed transfer functions are interpreted in this framework. It is shown that gyroscopic effects are mostly responsible for the lag between steering torque and roll angle, and that there is a velocity for which the various terms that combine to form steering torque cancel each other out, yielding a 'maximum gain condition' for torque to roll transfer function which drivers rated 'good handling'.