Abstract: In cross-country vehicles where it is desirable to change the pressure in the pneumatic tires of the vehicle to fit the terrain, means are provided for changing the pressure on the tires without leaving the seat of the vehicle. The means provided in this disclosure comprise a source of compressed air, air control valves for each wheel of the vehicle, control keys including a magnetic valve, etc., for venting air from or forcing air to the tires, all somewhat similar to the arrangement disclosed in (Ger) DE-OS No. 2,141,553 but the sensitive throttle added to the latter disclosure is omitted and instead, a relief valve is provided for the air control valve of the wheels whereby the venting time is shortened and less of the apparatus as a whole is maintained under high pressure.