loss of pressure over time

Why do tires/basketballs/footballs/volleyballs lose pressure when left unused - but not as quickly when used regularly?

They do?

Anecdotal experience suggests they do. I’ve used cars for months without having to re-pressurize tires, but they go pretty limp left unused for a couple of weeks. It’s possible it was just perception, I don’t have data to back up this claim. Others haven’t noticed this?

Did you actually check the gauge pressure in the unused tires, or are you just noticing the visual deformation of the tire that occurs after you’ve let the car sit for a month or two? Because the latter isn’t really pressure-related.

Nope, I haven’t made actual measurements to support what I said earlier. The visual deformation is not related to pressure?

Well, it is related to pressure (obviously, if you let the air in the tires out, the effects will be much more dramatic), but what you’re probably noticing is the tire rubber yielding to continual application of force on one side only. Your contact patch is probably going to be about the same as a fresh tire, but the edges are going to be sharper & more noticeable.

I had an old truck that I drove about once a week. Often when I went out to start the truck one or more tire were low.

I moved to a house a few hundred yards away. It has been six years now and I have never see a low tire.

Go figure.