A timing belt, timing chain or cam belt is a part of an internal combustion engine that controls the timing of the engine's valves. Some engines use timing gears. The term "timing belt" is also use for the more general case of any flat belt with integral teeth. Such belts are used for power transmission or to interchange rotary motion and linear motion, where either high loads or maintaining a specific drive ratio are important. A common non-automotive application is in linear positioning systems. Such belts have also been used in efforts to make a cleaner, lower-maintenance bicycle transmission, but have never become popular in this application.