Inertial and Modal Properties of Racing Motorcycles

The dynamic behavior of a racing motorcycle depends on the inertial characteristics of the vehicle, which is considered as a rigid body, and on the power-train characteristics. In particular, the center of mass position and moments of inertia around the roll and yaw axes give information about handling characteristics. The modes of vibration of the vehicle in motion (capsize, weave and wobble), which determine motorcycle stability, depend on rigid body properties and tire characteristics, but can also be influenced by mass and flexibility distributions. The inertial properties of super sport motorcycles were identified using a special inertia tester machine that made it possible to measure the inertia moments around different axes without moving the vehicle. The results regarding the moments of inertia around the roll, pitch and yaw axes and roll/yaw products of inertia are showed here. The structural modes of vibration, natural frequencies and damping ratios of the motorcycle were identified, because they highlight the influence of mass and flexibility distributions on dynamic behavior. The modal analysis was carried out using the impulsive technique on the whole vehicle. The structural modes identified in static conditions are here compared with the motorcycle's modes of vibration that take place in motion. Results are then discussed in terms of stability and handling.