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

Gas molecules sneak past the seal between the rim and the wheel. No seal is perfect. A flaw wide enough for a single molecule to pass at a time is enough for the tire to eventually deflate.

Some molecules (such as hydrogen and helium) are small enough to pass directly (albeit slowly) between molecules which form the container, which makes storing these elements in their gaseous state a challenge. This is why hydrogen and helium are usually stored as cryogenic liquids.