Why do bike tires lose air when sitting in the garage for a long time?
In: Physics
Former bike mechanic of 5 years here.
Most air is lost through the rubber of the tube and tire. Rubber has teeny tiny little pores all over its surface and is not capable of creating a perfect seal.
Rubber works good enough for things that don’t need a perfect seal – only a “very good” seal – like gaskets and tires. Gaskets don’t hold static pressure for extended periods of time, and with bike and car tires it’s expected that you’ll just put air in from time to time.
A high pressure bike tire like on higher-end road bikes can lose up to 20psi/day and it’s totally normal.
As for the other comment on here, it’s true the valve seals aren’t perfect. But the huge majority of air lost is actually straight through the tubes and tires, not the valves.
Edit: I should have said it can lose 20psi on the FIRST day. As the internal pressure goes down, less air is being pushed out. The rate of air loss decreases as internal pressure decreases. But it is always losing air until inside pressure = outside pressure = no difference = flat.
All tires loose air when sitting for a long time. The seals on the valves aren’t perfect and air escapes through them little by little.
Another thing going on is that in the winter when the bike sits and it gets cold, molecules tend to shrink when cold, allowing them to escape easier through barriers due to their smaller size. Bike tires are always flat after winter…
Latest Answers