Stability of Motorcycles Under Acceleration and Braking

A comprehensive study of the effects of acceleration and braking on motorcycle stability is presented. This work is based on a modified version of the dynamic model that was first presented in (Sharp & Limebeer, 2000), and is thought to be the most comprehensive motorcycle dynamic model in the public domain. Extensive use is made of both nonlinear and linearized models. The models are written in LISP and make use of the multibody modelling package AUTOSIM (Autosim 2.5+, 1998). There is novelty in the way in which control systems have been used to control the motorcycle drive and braking systems in order that the machine maintains desired rates of acceleration and deceleration. The results show that the wobble mode of a motorcycle is significantly destabilized when the machine is descending an incline, or braking on a level surface. Conversely, the damping of the wobble mode is substantially increased when the machine is ascending an incline at constant speed, or accelerating on a level surface. This probably accounts for the pleasing stable “feel” of the machine under firm acceleration. Except at very low speeds, inclines, acceleration and deceleration appears to have very little effect on the damping or frequency of the weave mode. Nonlinear simulation have quantified the known difficulties to do with rear tyre adhesion in heavy braking situations that are dominated by rear wheel braking.