A pulley drive system such as for an electric motor drive (3), comprising an endless belt (5) trained around a driving pinion (1) and a driven pulley (4, 104). A tensioning arrangement (9) is provided for acting on a stretch of the belt (5) between the driving pinion (1) and the driven pulley (4, 104) to increase the tension in the belt (5). The driven pulley is arranged without full meshing engagement with the section of the toothed belt (5) in contact therewith, whereby slip can occur between the belt (5) and the driven pulley (4, 104) upon start-up of the drive system before the drive pinion (1) and the driven pulley (4, 104) reach synchronous rotational speeds.
