Yes, we want to talk about gas.
Why? Well, nitrogen might be more popular in road car applications now to extend tyre life, prevent wheel corrosion, improve fuel economy and all sorts of other nonsense, but what about on track?
We Kutukans have now been running on nitrogen-filled tyres since mid 2008. So forgive us if we feel qualified to report on whether it works or not.
The official AA line on nitrogen is this:
The air we breath (and the normal compressed air used to inflate tyres) contains 78% Nitrogen, 21% Oxygen and 1% other gases.
Purified nitrogen has been used to inflate tyres on aircraft and racing cars for many years, but now some tyre specialists are offering nitrogen inflation for ordinary car and van tyres.
The advantages of using nitrogen in specialist applications are clear
For passenger car applications the main claims seem to be
Leakage can occur through the tyre's inner liner but can also occur through the valve, punctures, or failure of the seal between tyre and wheel rim. Pure nitrogen might leak more slowly through the liner, but regular checks of tyre condition and pressures will still be essential.
Corrosion of the tyre through use of normal compressed air alone is most unlikely because only the outer tread band of a car tyre contains steel – the amount of moisture reaching it from the inside is minimal.
Changing to nitrogen involves removing all the air which is already in the tyres and then re-inflating them with purified compressed nitrogen. There will be a one-off charge per tyre but once filled with nitrogen any future top-ups would also have to be with nitrogen if any advantages are to be maintained.
Overall, while accepting the possibility of purified nitrogen being of benefit in certain applications, we don't think that the cost and possible inconvenience are justified for normal passenger car use.
but why bother for track use?
Well, the key is there, pressure variation. It is alleged that nitrogen is more stable than pure air.
Is it more stable, really?
Well, actually, yes. And no.
Obviously getting your tyres to maintain pressure for as long as possible, as evenly as possible, gives you an advantage on track, especially on more racy rubber.
The theory is nitrogen will expand less and give less variation. In practice, we believe that it expands nearly as much as air. There isn't a lot in it, and more importantly we don't think it's the gas itself that is the key here, but the moisture content.
BUT, our tyres are remarkably predictable. For a given pressure we can tell you in advance what they will measure after 5 hot laps, and that is a big help. They do still put on pressure though, don't think that you set them to 40psi and come hell or high water they'll stay there, that's complete bunk.
But that predictability is a great advantage, pressures can be accurately set and relied on, and it applies every time to each car, we're no longer guessing, and we won't get one tyre putting on random pressure we cannot explain.
The truth to it, we think, is simply that by using a cylinder of BOC's finest nitrogen, we are getting pure, dry gas with no hint of water in it. Water is your enemy, it is THAT that expands like crazy when your tyres get hot and sends your pressures wonky.
When your tyre guy fits your rubber, and probably picks the airline out of a puddle, his air supply is as water-rich as the air outside. He may have a water trap fitted, but that doesn't do the job. It varies from tyre to tyre, car to car, and from day to day. Using a dry gas eliminates much of this uncertainty. You could use dried air and probably get the same result, but where do you get that from?
We reckon it is only nitrogen selected because it doesn't support combustion, and for racing cars that's helpful, but you could use anything that eliminates the water.
No, filling your rims with silica gel isn't a good plan.
So yes, there is an advantage to nitrogen, with a little care you can eliminate some of the tyre pressure guesswork, but you do still have to set your pressures properly to begin with.
There are downsides to it. Cost, faffing about, and space.
Space? Yes, you need to cart a honking great cylinder about. And cost, it's not just the gas, it's the BOC account to go with it, bottle rental etc. Probably £50 per season for this little perk.
Faffing? Well, you don't just fill the tyre. You fill it, purge it, and refill, to get rid of the air and water that was already in there. Faff.
Oh, and daft as it sounds, you need to outfit your tow vehicle with "compressed gas" warning stickers. No, really!
Should I do it?
How serious are you? For those doing a lot of test miles and looking for a consistently-performing, predictable setup, ie you folks who are gathering a lot of data, yes.
If you're a "what track is this one again?" type, no.
No, there are no pictures here. What pictures could you possibly want for this? A photo of a cylinder? A periodic table with an arrow? Tell you what, here is a photo of some pure nitrogen:
OK, fine, have a periodic table. Christ.