Motorcycle Driveline Stability in a Minimal Model Including Roll Angle During a Braking Maneuver

A minimal, three degrees of freedom model for the rear of a racing motorcycle is developed to study the effects of roll angle on the stability of the driveline mode, also known as “chatter”, under a heavy braking maneuver. It is found that the added roll angle degree of freedom does not play a large role in the unstable mode, but its addition to the linearized equations of motion does add to the instability of the system. This is attributed to the working point of the tire tangential forces changing as more lateral force is introduced. The mode becomes unstable during the given maneuver with a frequency of around 19 Hz. Power analysis reveals the source of instability, and that the longitudinal tire force gradients can change the stability by changing the phase relationship of the longitudinal force and slip velocity. Eigenvalue sensitivity analysis shows that splitting the rear-hop and driveline mode frequencies also leads to stability, and so does reducing the chain-to-swingarm angle.