This study investigated the rollover behaviors in turning of the tricycle with two front wheels and one rear wheel by neural paralysis. According to the analysis, the researcher fixed radius of gyration and made ride in steady-state turning to obtain the rollover threshold speed of the tricycle. Then we drew different parts of the rollover behaviors with a compuer program, Solidworks. We also decided the steering mechanisms sizes with VB.NET. In Automatic Dynamic Analysis, the researcher identified the rollover problems of the tricycle with the of Mechanical System software (ADAMS). During the researcher, we obtained the highest rollover threshold speed value of the sampling tricycle, and then we adjusted the width, the length of the tricycle. Later on, we adjusted the mass center height of human sizes and the initial rollover threshold speed the tricycle. After getting the best range of rollover threshold speed of the tricycle, the researcher decided appropriate length and height of the bicycle. Finally, we compared rollover behaviors of several different size of new tricycles with the sampling tricycle.