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

The surface of the rim may not be perfectly smooth, it could have corrosion or dirt, allowing a partial seal but not a very good one. The valve where you fill the tire is designed to open/close so of course this is another thing that is *supposed* to seal but it can get dirty or just wear out with time and usage.

A good tire shop should clean the rim as part of the process of installing a tire, and should possibly replace the valve with every tire change. But with tire pressure sensors built into many newer valves it is more expensive and complicated to do that. This is a common cause of a leak that is faster than you’d expect from a normal tire, but not as fast as a giant hole in the tire.