In article .com,
says...

Propane is liquid. (LP = Liquid Propane) (Now who is the idiot?)
Liquid is a big difference from air.

Actually, it's not. A liquid is only a liquid because of temperature
and pressure combination. IOW, you can take any gas, compress it
enough, and it will become liquid.

Not *any* gas. There is no liquid phase of helium at room
temperature at any pressure.


However, that website that John
posted does prove I am wrong. I just wonder how much weight is added
to a 15" tire when 32 lbs of air is added.

You can figure it out if you know the volume of the tire.

Sure, 32psi is about 2ATM, so it will weight twice that of air at
0ATM (note: differential pressures). Air is mostly N2 and O2, so
it has a weight of, say 30g/mole (O2 is 32g/mole, N2 is 28g/mole).
At STP there are 22.4moles/l so that's about 375g/l. So, at 2ATM a
tire will weight about 750grams per liter of tire volume more than
it will deflated. That doesn't sound like it's going to to take a
tremendously accurate scale to measure. ;-)

--
Keith