Shimmy Phenomenon on Steering System of Two-Wheeled Vehicles.

Abstract

The shimmy that appears in two-wheeled vehicles has been regarded as a self-exited vibration, but this has yet to be clearly proven. Here, we provide experimental and theoretical analyses based on three experiments. It is found that the shimmy phenomenon can be clearly defined by the experimental analyses. It is impossible for previous theoretical models to describe the shimmy phenomenon. Therefore, we propose a new tire model which includes the dynamics of side force and self-aligning torque. From the results of the theoretical analyses, it is found that the model describes the shimmy phenomena not only qualitatively but also quantitatively. Furthermore we analyze the influence of the design parameters of the tire and their main influences on shimmy. Consequently, it is clarified that cornering stiffness, tire lateral and torsional rigidity, relaxation length of lateral displacement of contact patch, tire lateral damping and moment of inertia around the steering axis all have strong influences on shimmy.