Tcc1999

So I read this and thought, what is he talking about, how could nitrogen, with a slightly smaller mass than oxygen be a bigger molecule than oxygen (N2 v. O2, that is)? If anyone else is curious here's a "relatively" simple explanation - note though that it is from "getnitrogen.org" so give it whatever credence you think appropriate.

http://www.getnitrogen.org/pdf/graham.pdf


Oh, and in regard to the original tire pressure question. While unlikely, a bad TPMS sensor could also be at fault. Easy to check though with a good tire gauge.

997s07

The reasons are complicated but can be distilled down to a few basic ideas. Not getting into the quantum mechanics of atoms - let's take as fact that atoms are overwhelmingly pure space >99%. As the atomic number (number of protons, and mass) increases the "pull" on the electrons increases disproportionately, causing the volume to contract and therefore become smaller. The above is only true for a set of progressively added protons. So take this explanation to be true only for N2 and O2.

eg991

Sounds temperature related, especially as all four tires seem to be losing pressure proportionally.

worf928

The primary reason Nitrogen is used by races teams is that it doesn't have moisture in it. Air from your garage compressor has a lot of moisture in it. It's the moisture content that changes the pressure/temperature dynamics far away from pv=nrt (or whatever.)

I'll just leave this here...

http://www.tirerack.com/tires/tirete...jsp?techid=191

stratocaster69

Good article, thanks! I have a good tire gauge and opt for that route (:

Tcc1999

This may be wholly true but I like the elegance of quantum mechanics of O2 and N2 atoms (if not the comparative bizzare nature of quantum anything) as an explanation better.

997s07

While not quantum mechanics (but more physical chemistry) the ideal gas law PV = nRT, can be divided by nRT on both sides giving PV/nRT=1. An ideal gas would behave in such a way to always have the above ratio equal to 1. The pics below show the deviations for some gases.




Nitrogen is pretty close to 1 under all conceivable pressures. And yes, water deviates very badly. But I'll sell a bridge in Brooklyn to anyone who thinks they can get anhydrous nitrogen in their tires without the equipment that F1 uses.

Bethtamm

This is a problem related to temperature.

LexVan

This. Low moisture content. Not that crappy moisture laden air from the local gas station.

The other primary reason is that N is a non flammable gas.

worf928

Interesting. 'splain please. A lot of organizations have a nitrogen tank, a regulator and an inline dryer and expect dry nitrogen out of it. I'm not buying your bridge but I might like a view from a distance...

997s07

Sure, I'll try.

All tanks have regulators, no open valves at those pressures are practical.

Inline driers are pretty much useless for a couple reasons. The desiccant they use (CaCl2 typically) is not as efficient as others but good enough IF the gas is passed over it more than once. The tanks that AirGas or BOC deliver are very wet. Same for other companies. Furthermore, the dessicants get inoperable quickly, being fully capacitated. Most consumer "organizations" probably are not concerned with changing them.

Nitrogen generators are better, but not much better (nevermind if nitrogen is being generated in humid environments).

You want dry N2? Pass it through a desiccant a few times at cold temperatures.

Hope this 'splains it. Let me know if you want the bridge.

GSIRM3

I only use certified German air in my tires, and rotate it quarterly. Rotational mass is much lower and acceleration times and gas mileage greatly improved. The German air fully complies with the Ideal Gas Law and other stringent environment regulations, and is fully ISO certified.

mtony

I think the Michelins hold their N2 better than the P Zeros do.

worf928

This follow-up is not purely academic. I'm interested in getting an N2 cylinder for various automotive purposes (except putting N2 in my tires except, perhaps, for long-term storage.)

What do you consider very wet? I'm looking at Praxair's spec sheet:

http://www.praxair.com/~/media/praxa...4631.pdf?la=en

what's 'wet'? 5 ppm? 1 ppm?

studlee

yes....cold weather equals lower tire pressure.