On Mon, 2 Feb 2009 20:15:34 -0800 (PST), TimR
wrote:

Do you think the weight of the car has anything to do with the
inflation pressure?

Many years ago I watched a mechanic check the pressure on my tires
while the car was up on a lift, the wheels hanging loose.

I asked him if he was sure the pressure would be correct once the car
was on the ground and the weight of the car was on them. There was a
reason for this - I was a high school kid, working a summer job. I'd
loaded a trailer too full at work and blown a tire, and got my butt
chewed good by the foreman.

The mechanic when he got done laughing called me a moron and told me
of course the pressure would be the same in the air or on the ground.
Okay, but I wanted him to recheck once the car was down. He got the
same reading and laughed some more at this dumb high school kid.
Still not sure he was right, though.


Well, the tire will have a higher PSI on the ground than when the
vehicle is suspended in the air, but not much. A regular tire
pressure gauge may not be sensitive enough to show the pressure
differences.