The Reverend

I personally think even on a very humid morning the difference you get from moisture in the tire is nominal.

Erik's right, I'm a lawyer, not a chemist, but the 1psi variance example IfixVWs gave isn't holding up in my courtroom. Way way way way too many uncontrolled variables to call 1psi significant proof of anything.

Does it make a difference in a theoretical setting to have dry verses "damp" air - yes. Is it worth going out of your way to keep N2 around for your tires - not unless you've got tolerance levels for your setup that rival a top Formula 1 team. And even then, I'd say use whatever dry compressed gas you find in the pits as long as it's not hydrogen or oxygen (fire hazards).

Kermdaddy

I'm a little rusty on my chemical engineering but under real conditions you would have to use the modified Raoult's Law and Excess Gibbs Energy equation which I tried to paste in here but it would not work. This requires a lot of things that I can't remember how to do. So I will try to do the problem this weekend and let you know what I come up with. For the ideal gas solution it would break into the ratio of P1/P2 = n1T1/n2T2. The ideal gas law constant would cancel out because it is a constant. The volume of the tire does not change so it to can be dropped. I would drop the moles of each gas because Nitrogen has a molecular weight of 28 g/mol. Air has an average molecular weight of 28.9 g/mol. This is only about a 3% difference. When you look at the vast number of moles required to fill a tire, the numbers would become almost the same. We then have P1/P2 = T1/T2. So if you change the temperature then you would have the change the pressure. If you are using Nitrogen you might get a 3% less change. I have not really thought about the "dry" part of it yet. Air is 78% nitrogen 21% oxygen. The rest is composed of CO2 and water. At approx 85 degrees F and 60% humidity there are 110 grains of moisture in the air. This is a very small number when compared to the huge percentage of pure gas. I doubt it will have very much affect on your pressure.

Sorry for thinking out loud, but my .02 is that N2 in tires is I would not waste your money on paying for something you get 78% of for free. I could be wrong I made a C in my senior level engineering thermodynamics class. If i can remember how to do all that crap or find the spreadsheat on my computer this weekend I will post the result. But this is a free country and if you think that N2 is better, it is cheap enough to go for it man!

macr88

The main problem isn't really the air coming from the compressor it's most
likely the amount of soapy water they use to lube the bead. It is a proven
fact that a moister free tire will maintain a more consistent rise in pressure.
It won't eliminate the rise but it sure can lessen the amount depending on
the amount of moister.

The tankless compressors are the worst at introducing moister into your tire.
A compressor with a tank is better and one with two depending on piping
is even better. next would be a water/oil seperator. then an air dryer and
finally nitrogen. So you can see why they use nitrogen. It's all about the $$$..

So basically filling your tires with nitrogen isn't going to help unless all
the moister is removed from the tire. The only way to do this is put it into
a deep vacuum. Been there done that and it aint worth it.. Maybe if I was
racing for a million bucks..

Hope this helps

mikegarrison

No, you are correct. Any dry gas will do. (Well, pure oxygen would be very bad because the tires would catch fire. So any fairly inert dry gas will do.)

Since the air is 80% N2, it is relatively easy to get a lot of cheap, dry N2. Any dry gas (including dry air) would do just as well, though.

rlaifatt

I like helium .

twohoos

Looks like everyone has a piece of the puzzle, but nobody's put it together. Here's the deal: Nitrogen offers a single benefit -- predictability. Race teams can predict cold-to-hot pressure changes more precisely, and more repeatably, with dry N2 than with ambient air.

Yes, all pure gases, as somebody pointed out, will obey PV-nRT; N2 is no different. But water vapor is less predictable (it's not a "gas"; the gaseous form of water is steam, which of course is only generated above 100C). So if the air has an unknown (or even known) humidity level, it's harder to set pressures in the pits so that the tire will behave as desired on track. There are potentially some corrosion or tire-bead concerns, but those are secondary by far.

And yes, you could use pure oxygen, helium, or any other gas, but N2 is of course by far the cheapest, since ambient air is mostly N2, plus it's not a flammability risk and is entirely benign to humans.

Voodoo_S2K

But that is the thing, Nitrogen isn't in the real world any more predictable that regular air. Maybe in a test lab with ultra precise measuring equipment and controlled variables, it might make a difference.

mikegarrison

Yes it is. Dry N2 is available almost anywhere, for quite reasonable prices.

l8brakr

Conclusion: If it's free/cheap and available use it. If it's not and you can't/don't want to make room for it in your track budget than don't worry about it.

BrianZ