Speed reducer and method of assembling such a reducer

A speed reducer comprising a shaft extending along a longitudinal axis, two rolling bearings arranged around the shaft, the two rolling bearings each comprising a radially outer ring, a radially inner ring and rolling elements arranged between the radially outer and inner rings, characterized in that it comprises a preload system positioned in the gap between the two rolling bearings, the preload system comprising:

• two spacer elements each in bearing engagement with one of the rings of the rolling bearings,
• at least one elastically deformable element interposed between the two spacer elements, said at least one elastically deformable element is configured to be able to occupy a first prestressed state and a second at least partially relaxed state,
• the preload system being designed such that the transition of said at least one elastically deformable element from the first state to the second state causes a unidirectional rotational movement of each spacer element with respect to the other so as to generate, by a wedge effect, a preload in the rolling bearings.