Investigations of Motorcycle Mid-Corner Instability Using a Three Degree-of-Freedom Minimal Model

A minimal three degrees of freedom model is developed and used to investigate unstable modes during high roll angle and acceleration maneuvers. During high roll angle maneuvers, it is found that there are unstable modes in the 6 Hz to 9 Hz range. The modes share similar characteristics to that of the unstable driveline or “chatter” mode found in braking maneuvers, except at a lower frequency caused by the higher inertia about the roll axis, which is the facilitating factor to the tire vertical oscillations. Power analysis shows that a combination of tire frictional characteristics and governing relationships can lead to a phase lag between tire forces and tire slip velocities that causes to instability, and eigenvalue sensitivity analysis shows which modeling parameters have the most effect on the stability boundaries.