Why do race cars use nitrogen in their tires?

One commonly cited answer is that the pressure won’t vary as much with temperature.  But as was demonstrated earlier, this is not the case; nitrogen’s pressure-vs-temperature curve is virtually identical to that of air, even air that isn’t completely dry.  And the pressures aren’t that high (typically 20-40 psi), so fire/explosion safety isn’t a major concern.  The best answer I’ve heard so far is that race teams already have bottles of dry nitrogen on hand for servicing suspension components; having a separate air compressor around for filling tires would be a redundant waste of space and money.

Not only that, but there may be a new reason soon, if not already, for the widespread use of nitrogen in race car tires, even among amateur racers: sponsorship from nitrogen vendors who want to be able to point to racers and say “see, they’re using it, you should too!”