Nitrogen is used because it has less parts per million of water than compressed air. It gives a more predictable pressure increase over a given tire temp.
Nitrogen and oxygen = Air
nitrogen
Nitrogen
It's nitrogen.
Nitrogen.
Nitrogen
Nitrogen, because it is an inert gas.
nitrogen
Most pro racing teams are using pure Nitrogen gas in their tires. This has the main advantage of minimising pressure changes as the tire warms up. It will also not feed a fire in a post crash fire.
I think it is Nitrogen. The normal air mixture pumped into regular road cars is not efficient at high speeds and will lose pressure easily. If that happens there could be catastrophic consequence at high speed. That is why they use nitrogen If you pump nitrogen into the tires of your regular road car, you need not check tire pressure for 3 months.
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Nitrogen