A two- or three-wheeled self-propelled motor vehicle. Power is usually supplied by an internal combustion engine of one or more cylinders with either air or liquid cooling, although electric-powered motorcycles have been built. Transmissions commonly have four or five forward speeds; motorcycles with automatic transmissions have been commercially available, but have not achieved great popularity. Some three-wheeled motorcycles are equipped with a reverse gear. Power is transmitted from the transmission to the rear wheel by either a roller chain, a belt, or a shaft drive.