All Belting used on standard Low Profile Belt Conveyors has a minimum pulley diameter recommendation.  This diameter is based on the belt sustaining a given number of flexure cycles over the pulley before surface fatigue (fine fractures) has occurred.  As the pulley diameter increases from this minimum value, the surface stress decreases and fatigue life is increased.  A common End Drive Conveyor will have (2) flexure cycles per complete belt cycle.  A center drive conveyor, however, can induce (5) or (6) flexure cycles per complete belt cycle, two of which involve more severe reverse flexing.  This would mean that the center-drive would have a fatigue life of one-third or less than the end-drive, if both were the same length, and speed. Speed has a direct influence on belt fatigue life, and should not be higher than required.  Pulley diameters near the belt minimum pulley diameter should be avoided especially on center drive and higher speed conveyors, if extended fatigue life is desired.