Multibody Efficiency Analysis of Chain Drives in Racing Motorcycles

In racing motorcycles, the maximization of power transmission from the engine to the rear wheel is one of the critical aspects for improving the performance. Therefore, it is important to improve as much as possible the efficiency of the chain drive, consisting of a front sprocket on the output shaft of the transmission and a rear sprocket connected to the rear wheel, linked by a roller chain. In this study, a multibody model of a chain drive of a racing motorcycle involving high rotational speeds is developed and validated. The energy losses are analyzed, highlighting their dependency on working conditions, and the efficiency is studied as a function of number of teeth on the sprockets, mounting of the chain and sprockets, selected speed ratio, and chain pitch. As a result, it is found that the efficiency is improved by a larger number of teeth with an equal speed ratio, by reducing the chain pitch (while keeping the sprocket diameters constant), and by larger diameter sprockets (in every working condition, including those of high rotational speeds, in contrast to findings in previous literature). Variations in clearances in the chain influence the efficiency, while variations of center distance between sprockets is not influential if the clearances are kept constant.