How long to put the air in?
Give the tyre size and what the compressor delivers. The air volume comes from the sidewall marking, so you can tell whether a small inflator is worth the wait.
What this assumes
- The volume is given as a range because a tyre size cannot pin it down. The upper figure treats the chamber as a square-cornered ring between rim and tread, which it cannot exceed; the lower figure treats it as a round-sectioned ring that fits inside, which it cannot be smaller than. The truth sits between the two.
- Published methods that produce one number apply an empirical fill factor. None is used here, because a borrowed constant would be invisible behind a confident-looking answer. If you know the real volume, enter it and the range disappears.
- The inflator is assumed to deliver its rated free air throughout. Small 12V inflators slow down markedly as pressure rises, so treat their figures as optimistic.
- Air warms as it is compressed into the tyre, so the pressure settles back slightly as it cools. Set final pressures on a cold tyre.
- Nothing here says what pressure a tyre should be at. That comes from the placard on the door pillar or the handbook.