A small, typically gasoline-powered engine mounted above the rear bicycle wheel and employing a roller to transmit power directly to the tire constitutes this type of propulsion system. A simple centrifugal clutch engages the roller with the tire when the engine reaches a certain speed, propelling the bicycle forward. Variations exist, including some models using a friction wheel against the front tire.
This straightforward design offers several advantages. Its simplicity translates to ease of installation and maintenance, often requiring minimal tools and mechanical expertise. The relatively low cost compared to other motorized bicycle options makes it an attractive entry point. Historically, such systems have provided a readily available and affordable means of motorized transport, particularly in areas with limited access to more complex vehicles.