Process for activating an axle lift device of a semi-trailer motor vehicle

The system is used especially on a three-axle semi-trailer to minimize tire scrub with excessive friction and wear on tight curves. The system has a sensor measuring the angle between the tractor vehicle and the semi-trailer, and when the angle reaches a given value, the axle lifting mechanism is actuated. The semi-trailer may have air springs. An overload arrangement is incorporated. On a continuously twisty section of road the front axle of the semi-trailer may be permanently lowered.