James' wrote:
I begg to differ. But to each his own. ;-)
The pressure will be higher when the tire is supporting the TC. If you want to imagine a free body diagram, simplify things and consider a TC resting on one big tire. If you take the TC and the truck off, it's supporting no weight - it does not have to exert any force on the axel to keep the TC in static equilibrium. Air is a compressible fluid - pressure will increase when the tire bears a load because it's the "pushing back" of the air that keeps the TC from falling.
clicky
The pressure doesn't increase to support the load, the contact area to the ground does. force = PSI * area. The tire simply changes shape to accommodate and create this larger area. The tire can only increase in pressure if it loses volume. The loaded tire ends up very slightly out of round and the change in volume (if any) is so miniscule that you won't be able to measure a change in pressure.
Sorry for furthering the off-topic discussion.
