Originally Posted by Paul Dennis
At the pressures and temperatures tyres work at the variation in pressure with temperature must be pretty much the same for nitrogen and air filled tyres since the gas behaves more or less ideally. I'm not sure what the advantages of nitrogen are.....may be very low water content
It is the water content.
Nitrogen is dry, so 0% water, so the rate of pressure rise with heat is always constant and a known variable.
Air always contains a % of water vapour so the rate of pressure rise with heat isn't a known constant.
On a road car it makes no difference at all.
And unless you are running a low single seater it makes little difference to a race car either.
Remember that air is 78% Nitrogen anyway.