Quote Originally Posted by Rob Edge View Post
Nitrogen at higher percentages will suffocate you. This is what happens to people at altitude where the air is described as thin due to the lower percentage of oxygen and higher percentage of nitrogen. Nitrogen is used in tyres due to it being more temperature stable. It has a much lower expansion rate than air as it is heated.
Not so. The coefficient of expansion of all gasses is the same provided that the gas is not at a pressure or temperature close to a phase change (condense, evaporate, or solidify). This is easily verified using google.

There is some controversy over the use of Nitrogen in tyres and I have not been able to find any satisfactory explanation other than for tyres used in extreme conditions. Aircraft tyres run at typically 200 psi and at that pressure oxygen becomes much more reactive - this might also be the case for truck tyres. For car tyres = snake oil.

Racing car tyres run at very low pressures and I have been unable to understand why they use N - even the thermal conductivity of N and air are very nearly the same. It may be that they have always done it this way.