There are prior art speed variators which have a driving wheel that engages, by rolling, on the outer surface of a conical bell-shaped body (driven unit) in such a way that it can slide along the axis of the bell-shaped body to vary the radius of the circumference traveled by the wheel on the bell-shaped body, thus varying the gear ratio. In these variators, the axes of rotation of the bell-shaped body and the wheel are parallel.
Disadvantageously, in conventional variators of the type just described, in the contact area between the wheel and the bell-shaped body, micro-slippages are created which result in a dissipation of power, penalising the overall performance of the reduction stage. Such slippages are mostly caused by a kinematic coupling which is not optimum between the wheel and the bell-shaped body.
Moreover, the local deformability of the wheel and/or the bell-shaped body generates hysteresis cycles which have the effect of dissipating a further fraction of the power transmittable.