The objective of this study is to investigate the dynamic characteristics and optimize the required power of an electric bicycle equipped with a semi-automatic transmission. In this simulation, we analyze the dynamic characteristics and operating characteristics of an electric bicycle at each gear ratio based on the effects of input parameters such as gear-speed, frontal area, and slope grade by using Matlab-Simulink. Through this simulation, an analysis is conducted to maximize the power generation of the electric bicycle. The simulation results show that the required power can be optimized by changing the key parameters mentioned above. In addition, a model-based control study is conducted to control the bicycle speed under the effects of gear-speed and slope grade. We also conduct an experiment on a real road and analyze the dynamics and required power of the electric bicycle. The experimental results agree well with the simulation results at each transmission ratio. This combination of simulations and experiments provides a useful method to estimate the power requirements for the motor of an electric bicycle.