Abstract: A drive mechanism is described that provides a speed ratio that is infinitely variable between predetermined limits. Coaxial driving and driven shafts carry discs formed with frusto-conical friction surfaces arranged face-to-face with control spheres in frictional engagement with these surfaces and equidistantly distributed round the discs. Each control sphere has an annular groove in which rolling elements of a rolling bearing run. Each bearing is mounted on one face of a control segment formed on the opposite face with an arcuate surface which rolls on the base of a groove in an adjusting ring, concentric with the shafts, when the adjusting ring undergoes axial movement.