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

Companies that make liquid products in plastic containers routinely do stability studies to figure out how much product is lost to the atmosphere over time. Even though the volume of lost material is small, it’s not zero, and for some products can be enough to affect the chemical makeup/potency/concentration etc. of the product. Plastics and rubber are porous, just not very. This is one reason for expiration dates on drug products. In addition in the case of a tire there’s also a sealing surface that isn’t perfect either.