Performance of mobility is highly dependent on the gravitational environment Some researchers have proposed novel locomotion methods for extremely small terrestrial bodies like asteroids. Hopping is a possible method under micro-gravity. It is not proved, however, that the proposed method of locomotion is optimum for a given level of gravity. The purpose of this paper is to analyze which level of gravity is optimum for each mechanism, and which mechanism or parameter is optimum for each level of gravity. First, a classification of locomotion mechanism is described. Next, the speed of hopping and wheeled robots is compared. Finally, some simulation studies are performed to analyze the detailed mobility of wheeled robots.