Rear derailleur for bicycles or similar vehicles

A rear derailleur for bicycles and similar vehicles, of the type which comprises a top bracket (1) fixed to the bicycle and a bottom bracket (2) carrying a chain guide (3), these brackets (1) and (2) being connected by a linkage system (4-5) making a deformable parallelogram linked to an operating cable (C) integral with a lever, this cable working in conjunction with a fixed part (1a) of the derailleur, in particular the top bracket and a fixing point (8) on a moving part, wherein it has, at the fixed part which takes the cable, a facility (9) for moving at will the supporting and return point (A) of the cable to change the angle (.alpha.) which the cable makes so as to increase or reduce the extent of transverse movement of the parallelogram for the same extent of angular movement of the lever.