A motorized bicycle is a bicycle with an attached motor or engine and transmission used either to power the vehicle unassisted, or to assist with pedalling. Since it sometimes retains both pedals and a discrete connected drive for rider-powered propulsion, the motorized bicycle is in technical terms a true bicycle, albeit a power-assisted one. Typically they are incapable of speeds above 52 km/h (32 mph); however, in recent years larger motors have been built, allowing bikes to reach speeds of upwards of 113 km/h (70 mph).
Powered by a variety of engine types and designs, the motorized bicycle formed the prototype for what would later become the motor driven cycle.