A variable-speed belt drive includes at least: two substantially parallel shafts; two variably interspaced flange pulleys, one driving, the other driven, each carried by a shaft and interconnected by the belt, the flanges of the driving pulley being movably mounted in a variably interspaced manner via a speed variation device including control elements for bringing the flanges of the driving pulley closer together, and control assisting elements including a cam formed by two coaxial plates having sliding-contact inclined ramps, one plate being rotatably fixed to the movable flange of the driving pulley, the other being rotatably fixed to the shaft carrying the driving pulley, the distance between the plates becoming wider in the direction of the flanges of the driving pulley coming together under the effect of the transmitted torque; and elements formed by a simple spring for recalling the flanges of the driven pulley in the close position.