In this paper, a pedaled, self-balanced, personal mobility vehicle named Legway, is developed. The vehicle is structurally similar to a pedaled unicycle but uses a brushless DC (BLDC) hub motor as its main driving wheel. For this one-wheel vehicle, it is intended that the unstable longitudinal dynamics is stabilized by a feedback control system but the lateral balancing and steering are manually controlled by the rider via a passive steering mechanism. The steering mechanism consists of a main pulley, a timing belt and a pair of cables, springs, tension-adjusting devices, and idle pulleys. Research efforts are devoted to the dynamic analysis and design optimization of the proposed passive mechanism. The target is to enhance the controllability of the steering and handling control so that the rider can operate the vehicle more effortlessly.