Abstract: A modular vehicle system consisting of a rear propulsion device and a variety of different front-end assemblies that can be attached to the rear propulsion device to create different types of motorized vehicles. The rear propulsion device contains a frame, an engine mounted to that frame and a drive wheel that is driven by the engine. The front-end assemblies contain a frame, a steering fork element and a steering mechanism for turning the steering fork element. The steering fork supports either a front wheel or a ski. The frame of the front-end assembly attaches to the frame of the rear propulsion device in order to create a vehicle upon which a person can sit. At any time, the front-end assembly can be exchanged with another of a different configuration in order to change the physical characteristics of the resultant vehicle.