[s-cars] Tire Pressures

[bob.rossato at att.net]

> That's why I use nitrogen to fill  my tires, does not fluctuate with
> temperature.
> 
> Mark S

All else being equal, any gas will increase in pressure with a corresponding increase in temperature.

The Ideal Gas Law is defined as:

PV=nRT

where:
P = pressure
V = volume
n = # moles of gas
R = constant
T = temperature

If we assume a constant volume for the tire (yes I know it will change slightly but for all intents and purposes it is the same), if temperature goes up then pressure has to go up.

The reason nitrogen is used in racing is that it is dry, as typically provided, so the crew can accurately predict the expected pressure rises because they don't have the additional variable of moisture in the gas causing a greater pressure increase as it heats up and evaporates.  Or put another way, tires filled up with Houston ambient air in August will have a greater pressure rise for a given temperature rise than tires filled with ambient air in Pheonix.

Bob