Abstract
Because of difficulty in measurement and recording of the motion of running motor-cycle, the quality of its stability has so far been discussed merely through the feeling test. In this paper, by using a new test equipment for in-door test, the stability, especially "hands off" stability, of motorcycle is quantitatively examined as are the effects of several factors such as longitudinal and vertical position of center of gravity amounts of trail, caster and moment of inertia about the steering axis. And also, the authors succeeded in confirming the results of in-door test by comparing with those of practical road running test. Finally the basic principle for designing motor-cycles from a view point of stability is established.