An electric vehicle drive system has several asynchronous electrical machines (11,12) each coupled to drive wheel (13,14), a polyphase supply unit (2) and a regulator (6) which uses a reference signal (SR) which represents the speed of one of the wheels. In traction mode each wheel is continually monitored for slip. If one wheel slips and at least another doesn't a speed signal (NM1,NM2) is selected for the non slipping drive wheel which turns the quickest, or if all the wheels slip a change signal (NF1) is used to produce the reference signal (SR). This first change signal represents the speed of a drive wheel immediately before it starts to slip. In the braking mode, where the electrical machines are driven by the wheels each wheel is continually monitored for locking. In the selection stage if at least one wheel is locked a speed signal is selected (NM1,NM2) which corresponds to the drive wheel which turns the quickest. If all the wheels are locked a second change signal (NF1) is used to produce a reference signal (SR) which represents the speed of a drive wheel immediately before locking.