Power assisted steering systems provide a gear reduction of approximately 25:1 between a steering wheel and a steering mechanism and approximately 625:1 between an electric motor and a steering mechanism. The system is back-driveable from the steering mechanism. In one embodiment, the gear reduction is provided primarily by three planetary gear sets, with the remainder provided by axis transfer gearing. In another embodiment, the gear reduction is provided primarily by a cycloidal gear set, with the remainder provided by axis transfer gearing.