dbex

How much different is the pressure of a tire that is mounted on the car from the pressure off the car, without the car weighing it down?

Just trying to make sure that if I measure tire pressure before the wheels go on and it's OK, that I'm not suddenly going to be riding on the rims once the wheels are mounted. I'd think that the 4000 lbs of the car (spread over 4 tires) would raise the internal pressure somewhat, but how much (if at all)? There's a reason I'm not a scientist.....

thks
Dave

Jet Jockey/A4 Pilot

They remain the same.

BergeyRPI

The pressure is the pressure. The weight on the wheels is totally independent of the pressure. The only way to change the pressure would be to compress the tire in all directions. Then you'd have the same pounds of air acting on a smaller area. Therefore, pounds/square-inch would be higher.

dbex

I'm an idiot. Thanks guys.

Jet Jockey/A4 Pilot

Idiot! I think you are being too hard on yourself.

DiscerningInfusco

Your thinking along an intuitive line... the reality is as BergeyRPI says it is. The only pressure that'll increase is that of the tire (in the contact patch) on the ground it rests. It is transfered pressure... the internal pressure doesn't not change in magnitude, thus it acts as a solid body. However, the distribution of the internal tire pressure does change significantly (as the air is want to bud out of the sidewalls, thus compression in the vertical direction). Good question by the way.

dbex

For some reason, I had it in my head that the sidewalls weren't flexible, when obviously they are. Duh.