A steering wheel system for a semi-trailer is described. The system uses a retractable encoded system releasably connected to a kingpin, a mechanical steer driving system translating the rotation of the kingpin to a hydraulic system, and a non-circular cogged system driven by the hydraulic system adapted to steer the wheels. A hydraulic generator system powered by the rotation of the wheels is used to decrease the electric energy required by the hydraulic system. Other improvements are also present to increase security, decrease weight and improve time expectancy of the components.