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What is the general consensus on filling tyres with air or Nitrogen? Air is 78% Nitrogen anyway so is it worth filling with pure Nitrogen or not?

Costco did my tyres and they are nitrogen filled. Can't say I've noticed any difference, other than the pressures never seem to go down. Didn't know there was a nitrogen option, other than Costco, which leads to the next question; if they are nitrogen filled and they need topping up......do you go air or back to Costco?

There's a big market for Oxygen, which when extracted from air (at low temperatures as a liquid) leaves Nitrogen as that has a lower boiling point.
They could presumably just vent it to the atmosphere. It's a clever marketing ploy to sell a waste product at a premium price IMHO.
As noted above, top up with air, it's almost 4/5ths Nitrogen anyway.....

Hi,

Offered free its no bad thing.

Its positive points are that it's not as subjective to expansion through the heat ranges as Atmospheric air, meaning its best suited to a track environment as it will save doing multiple pressure checks throughout a session. It also has a larger molecular size than oxygen so when compared to atmospheric air it will "escape" less meaning less top ups at the garage pump.

In short, if its free take it, if is not don't waste your money.

Craig.

I seem to recall a few discussions around this being a load of BS and making no difference from a performance point of view. But less air escaping is a nice bonus.

Unless they will vacuum the tyre like they do when refilling an AC system so its devoid of all air and fill with pure nitrogen then yeah why not. All ive seen is once tyre is fitted then fill with nitrogen. Dont see the point

Indeed, pretty pointless.
Normal air pressure at sea level is about 14psi, so pumping up with pure nitrogen to say +28psi (probably a bit low, but bear with me) will add twice as much gas as is already there.
So any non-nitrogen will be diluted to a third of the original level - roughly 22% down to 7%. It will never get to as low as 5%.
Net effect is that the gas inside the tyre will increase from 78% nitrogen to 93%/94%. There will still be some oxygen, water vapour, argon etc. in there.

If you really wanted near-pure nitrogen in there you would need to repeatedly inflate and deflate to flush the other gases out. Assuming a degree of over-inflation each time to give a four-fold reduction then 5 cycles would reduce it by about a factor of 1000...….. maybe that's what they do to racing tyres?

A case of unnecessary up selling !