flat belts made from joined hides were first on the scene, however modern flat belts are of composite construction with cord reinforcement. They are particularly suitable for high speeds. V-belts comprise cord tensile members located at the pitchline, embedded in a relatively soft matrix which is encased in a wear resistant cover. The wedging action of a V-belt in a pulley groove results in a drive which is more compact than a flat belt drive, but short centre V-belt drives are not conducive to shock absorption. Wedge belts are narrower and thus lighter than V-belts. Centrifugal effects which reduce belt-pulley contact pressure and hence frictional torque are therefore not so deleterious in wedge belt drives as they are in V-belt drives. Modern materials allow cut belts to dispense with a separate cover. The belt illustrated also incorporates slots on the underside known as cogging which alleviate deleterious bending stresses as the belt is forced to conform to pulley curvature. Cogging should not be confused with the teeth on . . . . Synchous timing belt drives are positive rather than friction drives as they rely on gear- like teeth on pulley and belt enabled by modern materials and manufactureing methods. They are mentioned here only for completeness - we shall not examine them further. If a single V-belt is inadequate for power transmission then multiple belts and corresponding multi- grooved pulleys are necessary - this pulley is equipped with a tapered bush for axle clamping without the stress concentration associated with a key. The rather extreme short-centre drive on the left illustrates a problem with multiple belts - how to ensure equitable load sharing between flexible belts whose as-manufactured dimensional tolerances are significanty looser than those of machined components .
function. The main load- carrying elements are the tensile members, often in tEach component of a V-belt performs a particular he form of longitudinally stiff rayon cords located near the centroidal axis of the belt's cross-section, embedded in a relatively soft elastomeric matrix whose main purpose is to channel the load from the contacts with the groove sides into the tensile members.