Experimental Analysis of Rider Motion in Weave Conditions

Motorcycle dynamics is characterized by the presence of modes of vibration that may become unstable and lead to dangerous conditions. In particular weave mode shows large yaw and roll vibrations of the rear frame and out of phase oscillations of the front frame about the steering axis. The presence of the rider influences the modes of vibration, since the mass, stiffness and damping of limbs modify the dynamic properties of the system; moreover at low frequency the rider can control vibrations. Up to now very few experimental results dealing with rider’s behavior in the presence of weave are available. This lack is due to the difficulty of carrying out measurements on the road and of reproducing the phenomena in laboratory. This paper deals with a research program aimed to measure the oscillations of rider’s body on a running motorcycle in the presence of weave vibrations. First testing equipment is presented, it includes a special measurement device that is able to measure the relative motion between the rider and the motorcycle. Then the road tests carried out at increasing speed (from 160 to 210 km/h) are described and best fitting methods are used for identifying the main features of measured vibrations. The last section deals with the analysis of experimental results. The characteristics of the motion of the vehicle and of the rider (below and above the threshold of instability) are described in terms of amplitudes and relative phases. These results may be useful for validating numerical simulations.