A variable speed ratio transmission comprises a support structure, an input member, an output member and a plurality of planet wheels which are supported rotatably on the support structure and which receive the movement from the input member. Each of the planet wheels comprises a connecting rod which is rotatably connected thereto in the region of a first end thereof and which supports at an opposite end thereof a unidirectional connection wheel which entrains in rotation the output member. The transmission further comprises a variation device for the spacing between the pivot axis of the connecting rods and a respective rotation axis of the planet wheels.