Abstract: An inflator for pneumatic tires that uses compressed gas. The inflator has a housing 10, a cartridge 12 of compressed gas that communicates through a passage 20 of the housing, and a valve chuck 14 connected to the passage and constructed to fit over and seal about a tire valve stem. The passage has a tubular member 50 with a restrictive orifice 60 that produces a pressure drop to the flow of gas. The valve chuck has a rotatable nut 64 that compresses an annular gasket 22 to provide a seal with the valve stem. A clamp removably secures the inflator to the underside of a bicycle seat.