JustAdam

I have not used air in any of my 3 vehicles for over a year.

Check it out - I use Nitrogen. Really.
It will allow you to keep the same pressure in your tires regardless of the temperature outside.

What do you use in your tires?<ul><li><a href="http://www.suburbantire.com/tires/nitrogen.htm">Nitrogen tires!</a></li></ul>

PanTTher

jk

JohnLZ7W

It's a neat idea but I've got an air-compressor in the trunk... can't do that with nitrogen.

JustAdam

That is what we call MODTIME - lol

JohnLZ7W

Hmm, maybe run my nitrous system to the tires and the engine?

OldSchool AG

What a rip. Air is 78% nitrogen anyway.

<a href="http://encarta.msn.com/encyclopedia_1741500785/Air.html">AIR</a>

OldSchool AG

I know that according to the industry, the oxygen leaks out 3X faster than the nitrogen. I don't feel like doing the math, but replacing the 21% of oxygen in the air I pump into my tires with nitrogen isn't going to give me much more time between pressure checks.

But hey... the hype surrounding this does allow Ingersoll-Rand to sell this <a href="http://www.irco.com/pressroom/newsatir/is/58711.html">nifty nitrogen tire-filling system</a>.

With the "3X faster" stat, they are counting on customer stupidity, thinking that AIR = OXYGEN. Bzzzt, wrong, thanks for playing.

poet

that an oxygen molecule leaks thru faster than a nitrogen molecule due to the size of the atoms.

For this calculation, you need to know the void space (gaps between molecules) in galvanized rubber relative to the size of N2 and O2 molecules.

I would guess that different brands of tires have different sized void spaces. For example, if a jar is filled with marbles, the void space is large and air could pass through quickly; however, if the jar were filled with sand, it would take longer for the air to pass through the void space.

My guess is that they are looking at the largest possible void space in their calculation. With that said, a Nitrogen molecule is about 15% larger at most than an Oxygen molecule.

And I would argue that if the oxygen leaves quicker, then each time you fill your tire, you should have a lower ratio of O2 to N2 in your tire.

Aslo, they never state what the rates of diffusion (evaporation of N2 and/ or Oxygen through the rubber) are across their worst case scenario tire.

This ends our lesson for the day. ;-)

OldSchool AG

in my line of work, it doesn't pay to think that much about it. "Directionally correct" they call it. ;-) I was figuring a 300% faster leakage (their stat) for the oxygen molecules, of which a tire filled with "regular air" from the atmosphere is 21%. Point taken that each subsequent refillage the mixture would seem to become less oxygen rich, further negating the need for the Nitrogen filling gimmick.

poet

This probably matters if you are in NASCAR and replace tires often. But for the long term tire, air is all it need bear!

I'm a chemical engineer, so in my line of work... it pays to be detailed. Well detailed within a 10% margin of error. ;-P