dose not stretch or slip and hence transmits power at a constant angular velocity ratio. This permits timing belts to be employed for many applications requiring precise speed radio, such as a driving an engine camshaft form the crankshaft. Toothed belts also allow the use of small pulleys and small ares of contact. They are relatively lightweight and can efficiently operate at speeds up to at least 16,000 fpm. A timing belt fits into the grooves cut on the periphery of wheels or sprockets, as shown in Figure 13.3. The sprockets come in sizes form 0.60-in. Diameter to 35.8 in. And with teeth numbers ranging form 10 to 120. the efficiently of a toothed belt drive ranges form about 97 to 99%