The group then established a design process based on their theoretical work as follows. First, the lengths of the thigh and lower leg of the rider are measured. Second, the contours of GTI and GSI are drawn using the lengths of the thigh and lower leg. Third, the optimum region is found according to the requirements of GTI and GSI, as shown in Figure 3. Finally, the design is taken from the optimum region and is verified.
After many years' research on the optimum design of a bicycle, scholars have established applicable empirical formulas. This research project explored a new way to optimize the design of bicycle parameters. The innovation of this work is the provision of a calculation method having a mechanical perspective. In this project, the structure of the human body (thigh and lower leg) and the crank length and seat height of the bicycle were mechanized. A double-crank-and-rocker mechanism was thus obtained as the bicycle–rider mechanism. From a mechanism perspective, a method to optimize the design of the crank and seat height of a bicycle according to different lengths of a person's thigh and lower leg was proposed. In this manner, a "customized bicycle" is realized. The result of the paper is useful for matching bicycles to athletes, bicycle manufacturing, and the design of cycling robots. This project was supported by a grant from the National Natural Science Foundation of China (grants 51075222 and 51135008) and a grant from Tsinghua University Student Research Training.