Nitrogen is the only thing that the Costco’s up here are using now. Interesting that a lot of the tire shops are going to N2 now…

umm… the Big O Tires down the block fills all tires all the time with
N2.

As a full time racer I can assure you nitrogen is the way to go and there are many reasons to use it. Moisture that is found in compressed air tends to cause tires to heat up faster and pressures raise as well. Controlling tire pressure/heat is very important when racing on tracks. We also use compressed nitrogen bottles to run our air tools. Not only does the absence of moisture help out air tools but the work much faster as well which is a great advantage during endurance races when tenths of a seconds spent in the pits are everything. Furthermore there is no need to wait for a generator to run an air compressor. That’s why all pro team use it.

Since air is 70%+ N2, it shouldn’t make much difference… I don’t know about CO2

Doesn’t really seem to make a difference while you’re driving. But, you have to refill it A LOT less.