figure 13.4 illustrates a portion of the timing-belt drive. The teeth are coated with nylon fabric. The tension member, usually steel wire, of timing-bel is positioned at the belt pitch line. The pitch length therefore is the same regardless of the backing thickness. Note that, as in the case of gears. The circular pitch p is the distance, measured on the pitch circle, from a point on the tooth to a corresponding point on an adjacent tooth. Since timing-belt, no initial tension is necessary and a fixed center drive may be used at any slow or fast speed. The disadvantages are the cost of the belt, the necessity of grooving the sprocket, and the dynamic fluctuations generated at the belt-tooth meshing frequency