On steering wobble oscillations of motorcycles

Abstract

The paper is aimed at an improved understanding of steering wobble oscillations of motorcycles through simulation. The background to the problem is discussed first. Then, an existing mathematical model of a manoeuvring motorcycle and rider is extended to include a yaw freedom for the upper body of the rider. The rider upper body and arm structural parameters are chosen in the light of newly published results from the testing of human subjects in a driving simulator, with forced motion of the steering wheel by means of an electric motor. Results show that steering wobble oscillations grow more vigorously as their amplitude increases beyond a few degrees of steering and that the stabilizing influence of the rider's tensing his/her muscles in response to a growing wobble problem is small. The work supports the idea that any machine which has a very lightly damped wobble mode at some operating condition may be made unstable by an unusual set of initial conditions and that the natural response of the rider to the problem will be largely ineffective. This idea is closely aligned with anecdotal accounts from general motorcycle usage.