A friction Drive or friction engine is a type of transmission that, instead of a chain and sprockets, uses 2 wheels in the transmission to transfer power to the driving wheels. This kind of transmission is often used on scooters, mainly go-peds, in place of a chain.
An example of this system is in an early Turicum automobile. The Turicum's friction drive consisted of a flat steel disc coupled directly to the engine. This primary disc subsequently drove a smaller leather covered wheel oriented normal to its surface. Assuming a constant rotational velocity on the primary wheel, the angular velocity on the disc's surface will increase proportionally to the distance from the center of rotation. Therefore, positioning the smaller wheel at different points along the larger wheel's surface varies the gear ratio. Furthermore, since there are no limitations beyond the minimum and maximum positions, the gear ratios are infinitely adjustable.
The problem with this type of drive system is that they are not very efficient. Since the output wheel (leather covered wheel) has width, the area of contact is spread across various radii on the primary disc. Consequently, since the angular velocity varies as radius varies, the system must overcome these variances. The compromise is slippage of the leather to metal contact area which creates friction, which in turn converts much of the energy transfer of this system into heat. Heat generation also requires a cooling system to keep the transmission working effectively.
Automobiles using this drive system included the Anglo-Dane, the Arista, the Armadale, the Astra, the Allvelo, the Bukh & Gry, the Crown 12HP Model Two (1905-1906), the Davis Totem, the Ner-a Car, the Cartercar and the Turicum.
Plymouth Locomotive Works's first three models, the AL, BL and CL were equipped with a friction drive.