The influence of tire characteristics on Shimmy stability

Heron José Dionísio¹; Fabio Mazzariol Santiciolli¹; Jony Javorski Eckert¹; Eduardo dos Santos Costa¹; Franco Giuseppe Dedini¹

¹ State University of Campinas

doi:10.20906/CPS/COB-2015-0363

Resumo

The Shimmy phenomenon can be described as a self-excited oscillation of the front part of a motorcycle around its steering axis. It has been studied since the beginning of the twentieth century due to its effect in system stability and passengers' safety. Beside motorcycles, this phenomenon can occur in some carriages and aircraft landing gear. The system oscillation can be stable or unstable depending on the system characteristics and its work conditions. It is known that Shimmy stability is affected by the fork and handlebars stiffness, the trail and the speed of the system, the wheel bearings clearance and the tire characteristics. Podgorski and other authors propose mathematical models known as front wheel system models that make possible the analysis of the Shimmy behavior and the factors that affect it. In this paper, it is analyzed the tire stiffness and damping influence on Shimmy stability using the mathematical model presented by Podgorski. First, the model was implemented MATLAB. Then, the values of stiffness and damping coefficients were varied in a range of 30% to 200% of their respective original values. Finally, two graphics were plotted to show the Shimmy stability curve behavior. According to these graphics, increasing the value of tire stiffness coefficient causes an increase at the stable region of the graphic regardless of the trail and the speed of the system. On the other hand, when the value of tire damping coefficient increases, the stable region of the graphic also increases for low speeds, but it decreases for high speeds. It shows the importance of tire characteristics on Shimmy behavior and possible ways of avoid that the system works in unstable conditions.

Palavras-chave: Shimmy; Tire; Simulation