Abstract: An apparatus for quickly positioning a tubeless tire on a corresponding wheel rim includes a retractable nozzle associated with a valve member mobile in a substantially cylindrical chamber under the action of compressed air and against another predetermined pressure lower than that pressure which causes its movement, this valve member opening at the end of its movement in the chamber to enable said air to reach this nozzle, the cylindrical chamber being connected to a vessel containing a predetermined quantity of air at the higher pressure, between this chamber and the vessel there being provided valve means preferably operated by a pedal.