Abstract: A variable speed power transmission belt drive apparatus wherein a pair of asymmetric cross section drive belts are utilized in conjunction with complementary sheaves, including a pair of axially adjustably spaced outer sheaves and an intermediate sheave. The outwardly facing side faces of the intermediate sheave are substantially planar and substantially perpendicular to the axis of the shaft on which the pulley is mounted. The inwardly facing surfaces of the outer sheaves are conical and the side surfaces of the belts are complementary to the confronting faces of the sheaves. Fluid pressure structure is provided for applying substantially equal forces to the speed-adjusting sheaves in effecting the speed-adjusting operation. In the illustrated embodiment, the angled surfaces of the belts and outer sheaves extend at an angle in the range of approximately 5.degree. to 30.degree.