The Ideal gas law says there are no difference between different gases regarding temperture vs pressure relationship. Many people use that as an argument for that air works just as fine as nitrogene.
However, if the gas contains moist, the number of mol of gas changes when the water changes state between liquid and vapor. The Ideal gas law also says pressure is relative to number of mol of gas and the amount of vapor a gas can carry is relative to temperature. So with a gas containing moist, the pressure relationship to temperature is not linear!
Any gas can carry moist, even nitrogen. The difference is that nitrogen is produced by cooling air, removing any possible moist. Diving air is also completely dry for the same reasons.
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| Air for divers and tyres |
So my conclusions are that any dry gas is more predictable than humid air. Dry air works just as good as dry nitrogene. The benefit with a completely dry gas is a linear temperature-pressure relationship. Remember that you have four wheels and the chance you have exactly the same amount of moist in all of them is not very likely.
With that said, I did try nitrogen once instead of my normal gas-station air and couldn't find that much difference, but I tend to drive a handful of laps and then check and re-adjust my tyre pressures over and over. For those who have to start a race with cold tyres I can clearly see the benefit.
To be able to fill a tyre with nitrogen or dry air you must do it several times before all humid air is out. With stiff side-walls and low tyre pressure it not easy to get all out.
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