Air suspension system for a vehicle with at least one front steering axle, at least one rear drive axle and a trailing axle in front of or behind the drive axle, having an electronic control and regulating unit, an operating unit which can be actuated by way of a vehicle driver and is connected to the electronic control and regulating unit, a plurality of switching valves (16, 19, 22, 25) which are connected to the electronic control and regulating unit, and in each case one pressure sensor which is connected to the electronic control and regulating unit for the measurement of the pressures in the supporting bellows (2, 4; 3, 5) of the at least one drive axle and the trailing axle, the electronic control and regulating unit being set up: - to check, in a "pressure ratio regulation" regulating mode, on the basis of the current supporting bellows pressures, whether relieving of the trailing axle is possible, without overloading the at least one drive axle as a result, - if this is the case, to switch over automatically into an "optimum traction" regulating mode, and, - in the "optimum traction" regulating mode, to increase the pressure in the supporting bellows (2, 4) of the at least one drive axle by way of actuation of the switching valves, and to lower the pressure in the supporting bellows (3, 5) of the trailing axle as far as a parameterized residual pressure, in order, as a result, to bring about a load displacement to the at least one drive axle by way of relieving of the trailing axle, without exceeding the maximum permissible axle load of the at least one drive axle, and without undershooting the minimum permissible axle load of the trailing axle, characterized by in each case one pressure sensor (S2, S4; S3, S5), which is connected to the electronic control and regulating unit, on each of the supporting bellows (2, 4; 3, 5) of the at least one drive axle and the trailing axle, and by an electromagnetic 3/2-way valve which is arranged together with the switching valves (16, 19, 22, 25) in a valve block, the input of which 3/2-way valve is connected to a compressed air source, the first output of which 3/2-way valve is connected to a ventilating device, and the second output of which 3/2-way valve is connected to the inputs (17, 20, 23, 26) of four electromagnetic 2/2-way valves (16, 19, 22, 25), of which the outputs (18, 21) of a first and a second electromagnetic 2/2-way valve (16, 19) are connected to a first supporting bellows and a second supporting bellows, respectively, of the at least one drive axle, and the outputs (24, 27) of a third and fourth electromagnetic 2/2-way valve (22, 25) are connected to a third supporting bellows and to a fourth supporting bellows, respectively, of the trailing axle. - to check, in a "pressure ratio regulation" regulating mode, on the basis of the current supporting bellows pressures, whether relieving of the trailing axle is possible, without overloading the at least one drive axle as a result, - if this is the case, to switch over automatically into an "optimum traction" regulating mode, and, - in the "optimum traction" regulating mode, to increase the pressure in the supporting bellows (2, 4) of the at least one drive axle by way of actuation of the switching valves, and to lower the pressure in the supporting bellows (3, 5) of the trailing axle as far as a parameterized residual pressure, in order, as a result, to bring about a load displacement to the at least one drive axle by way of relieving of the trailing axle, without exceeding the maximum permissible axle load of the at least one drive axle, and without undershooting the minimum permissible axle load of the trailing axle, characterized by in each case one pressure sensor (S2, S4; S3, S5), which is connected to the electronic control and regulating unit, on each of the supporting bellows (2, 4; 3, 5) of the at least one drive axle and the trailing axle, and by an electromagnetic 3/2-way valve which is arranged together with the switching valves (16, 19, 22, 25) in a valve block, the input of which 3/2-way valve is connected to a compressed air source, the first output of which 3/2-way valve is connected to a ventilating device, and the second output of which 3/2-way valve is connected to the inputs (17, 20, 23, 26) of four electromagnetic 2/2-way valves (16, 19, 22, 25), of which the outputs (18, 21) of a first and a second electromagnetic 2/2-way valve (16, 19) are connected to a first supporting bellows and a second supporting bellows, respectively, of the at least one drive axle, and the outputs (24, 27) of a third and fourth electromagnetic 2/2-way valve (22, 25) are connected to a third supporting bellows and to a fourth supporting bellows, respectively, of the trailing axle.