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jebrick(at)comcast.net
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 Posted: Sun Jan 11, 2009 5:55 am Post subject: Nitrogen in Tires |
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Previous thread under "Old subject revisited"
I filled my tires with nitrogen a while back and they don't leak down
anymore... not much anyway, what a blessing. At the same time, I replaced my
inner tubes with Michelin Airstop tubes, so I'm not sure how much to credit
nitrogen for the improvement.
Curt Bryan also put nitrogen in his tires with the same result...very little
leak down. But he too botched the experiment by further tightening the valve
cores just to make sure they didn't leak.
Consumer Reports did a study on this by inflating 31 pairs of tires of
various models to 30 psi. One of each pair had nitrogen, the other air. They
were set outside for one year and then rechecked. They found that on average
the air filled tires dropped 3.5 psi, while the nitrogen filled tires
dropped 2.2 psi; a difference of 1.3 psi. Yes they were careful to measure
pressure at the same temperature, etc., etc. I assume they were tubeless
tires... not sure how that would make a difference but maybe it would. But
even if you have a much greater pressure loss due to actual tire use,
landing or braking technique, or whatever; there is only a 4.3 (four point
three) percent difference in air vs nitrogen. Hardly even measurable it
would seem.
http://blogs.consumerreports.org/cars/2007/10/tires-nitrogen-.html
Airliners and race cars use nitrogen too:
Air is a mixture of gases, not a gas in itself like oxygen or nitrogen;
there is no such thing as a molecule of air. Air is 78% Nitrogen, 21%
Oxygen, and 1% other stuff such as argon, carbon dioxide, neon, helium,
hydrogen, methane and krypton, not to mention a huge list of pollutants and
water vapor. The presence of water vapor in the air naturally dilutes or
displaces the other air components as its concentration increases. Water
vapor expands and contracts with temperature changes at a much greater rate
than air. NASCAR teams use nitrogen because it allows them to more
accurately predict tire pressure fluctuation. Nitrogen fluctuates with
temperature change, but it does so less than when water vapor is present.
The FAA requires nitrogen in all commercial aircraft tires to eliminate the
potential for water vapor from freezing at high altitudes. Also, nitrogen,
unlike oxygen, is not corrosive (no oxidation) and will not support
combustion.
If you want to rummage around on the internet you can look into molecular
weights, permeability coefficients, Fick's Law of Diffusion, Henry's Law of
Solubilities, Graham's Law of Effusion, and other fascinating gobbledygook,
to find out that O2 permeates faster through rubber than does N2. So if that
is true, and you keep filling your tires with air, and the oxygen keeps
leaking out faster than nitrogen, wouldn't you eventually end up with mostly
nitrogen anyway?
jb
RV-4
Tacoma
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nukeflyboy
Joined: 05 Jan 2008
Posts: 162
Location: Granbury, TX
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| Posted: Mon Jan 12, 2009 11:10 am Post subject: Re: Nitrogen in Tires |
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Exactly. There are a host of reasons to use nitrogen per the previous note, none of them have to do with leak rate, and non are particularly pertinent to RV-10s. It's one of those things that you can do if you want (ie, does no harm) but is of dubious value and not worth the effort and expense.
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Dave Moore
RV-6 built and sold
RV-10 built and flying |
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vbhisey
Joined: 28 Jun 2007
Posts: 2
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| Posted: Sun Feb 01, 2009 5:06 am Post subject: Re: Nitrogen in Tires |
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If water vapor is the problem, wouldn't it be easier to just get the water vapor out during compression of the air? It's a fairly straightforward process. Scuba divers use it all the time while filling up their tanks with air.
... my 2c
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