Why do tires slowly lose air? From what it seems, they are sealed and shouldn’t really be letting anything in or out, but they still need to be refilled every now and then.

Question

I understand pressure changes as heat changes, but even in the same season you will still lose a slight amount of pressure.

In: 141

Answer 1

Rubber isn’t actually air tight. It’s just mostly air tight. When you are talking air that is made up of just atoms and very, very small and simple molecules, the very large molecules of the rubber don’t seal well enough that a few atoms can squeeze through occasionally.

Rubber at the molecular level is somewhat like weaved cloth. Where the rubber doesn’t quite weave together perfectly atoms can pass. The more pressure in the tire, the more the flaws get exposed and the more energy there is to push the tiny molecules in the air through.