A tractor-trailer combination includes a semitrailer tractor having a front axle and at least one drive axle having a predefined nominal axle load, a semitrailer having a first axle and at least one second axle, and an axle load adjusting device, which has an axle center height drive for the first axle enabling the axle load acting on the drive axle to be changed by adjusting a center height of the first axle, that can automatically switch into a starting assistance mode in which the second-axle axle load is increased to a starting-assistance axle load that is always below a predefined maximum axle load. An axle center height controller is adapted to automatically detect actuation of an off-road starting sensing device, and increase the second-axle axle load to an off-road starting axle load that is greater than the maximum axle load if the off-road starting sensing device is actuated.