To provide a pulley apparatus for a belt drive that is self-tensioning for the transmission of rotary mechanical power in fixed and variable speed applications.

The pulley apparatus (100) of a belt drive includes a first and a second pulley means (110, 120) and a belt bearing means (130). First pulley means (110) is fixed coaxial to the power shaft (160) and has a first pitch setting means (141). Second pulley means (120) is coaxially rotatable relative to the first pulley means (110) and has a second pitch setting means (142). Belt bearing means (130) maintains a gross bearing surface to bear the belt (180) at a pitch (140) by a cooperation with the two pitch setting means (141, 142). Transmission of power loads the pulley apparatus (100), thereby the second pulley means (120) is induced by the loading to rotate relative to the first pulley means (110) in the opposite direction.