A driving mechanism with a driving pulley having a V-shaped circumferential groove and a driven pulley having a V-shaped circumferential groove. A flexible endless member having chamfered flanks interconnects and spans the pulleys. The diameter of the pulleys can be varied automatically and stepless with regard to each other so that different transmission ratios can be obtained. The flexible endless member consists of one or more layers of steel belts arranged with a mutual play that is greater than 0.3 X the thickness of the belt and smaller than 1.8 X the thickness of the belt.