Moral first: check your tire pressure.

My car decided I'd let it go too long without checking and sure enough, the tires needed air and one was a bit lower than the others. Nothing too drastic, so there's no wild leak or anything, but a bit annoying to find a gas station (I was a bit far from home) with a working air pump in the dark and have to pay $1.50 for air.

Moral again: check your tire pressure.

 

Similar thing happened to me. My MINI sat for several weeks while I was in the hospital. When I started it up again and went for a drive I got the flat tire warning. However, it only appeared after the tires had warmed up. It seems that the discrepancy wasn't detectable when they were cold.

 

I use nitrogen in ALL my tires, seldom loses any pressure even when sitting for long periods of time.

Also holds pressure better at cruising speeds.

 

I use helium in ALL my tires. Makes my cars float like the Delorean in Back to the Future.