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Old 08-15-2011, 11:40 AM   #31 (permalink)
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If the rate of leakage of oxygen is significantly greater than nitrogen then after a few fills most people will end up at 95+% nitrogen anyway provided they don't let their tires drop more than a few PSI, and if they're letting their pressure drop more than a few PSI anyway they shouldn't be worrying about what they're putting in their tires.

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Note also that if you fill and top off with air, the percentage of N2 will gradually increase over time; at first you lose about half O2 and half N2, but you top off with a mixture of 78% N2 and 22% O2. So if you fill your tires with air and they initially lose about a psi a month, then after a year of this, it’s down to mostly N2 inside the tire, and the leakdown rate should slow down. For many motorcyclists, tires don’t make it through a season before replacement, so the effect is negligible; but if your car tires last four years, then by using air in them you’ve actually gotten about 3/4 of the benefit of a N2 fill, without the expense.
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Old 08-15-2011, 01:40 PM   #32 (permalink)
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Originally Posted by roflwaffle View Post
If the rate of leakage of oxygen is significantly greater than nitrogen then after a few fills most people will end up at 95+% nitrogen anyway provided they don't let their tires drop more than a few PSI, and if they're letting their pressure drop more than a few PSI anyway they shouldn't be worrying about what they're putting in their tires.



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Okay - this is going directly into unicorn territory here. I very severely doubt that the tires themselves are somehow acting as oxygen sieves.
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Old 08-15-2011, 02:25 PM   #33 (permalink)
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...ah-h-h, but atomic-level molecules are sneaky...the little ones sneak "in & out" faster than the big ones:

AIR = 100.00%.....28.966 MW
_N2 = 78.084%.....28.013 MW
_O2 = 20.946%.....31.999 MW
_Ar = _0.934%.....39.948 MW
H20 = _0.400%.....18.020 MW (water vapor)
_He = _0.000524%.._4.000 MW
_H2 = _0.000055%.._2.020 MW

Last edited by gone-ot; 08-15-2011 at 06:05 PM.. Reason: added Helium (He) and Hydrogen (H2)
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Old 08-15-2011, 05:13 PM   #34 (permalink)
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Okay - this is going directly into unicorn territory here. I very severely doubt that the tires themselves are somehow acting as oxygen sieves.
Yep. You want to see a sieve at work, a previous poster suggested helium. I bet a tire is great for leaking helium.
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Old 08-15-2011, 05:44 PM   #35 (permalink)
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Or hydrogen, just make sure to keep it someplace it can't do any damage. Anyway, if the nitrogen leaks slower than the oxygen then refills will automagically increase the amount of nitrogen and decrease the overall leakage rate, and if they both leak at about the same rate it's a moot point to begin with.
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Old 08-15-2011, 06:21 PM   #36 (permalink)
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Or hydrogen, just make sure to keep it someplace it can't do any damage.
Heck, let's just go for broke - let's test using HHO or Brown's Gas or something...
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Old 08-15-2011, 06:42 PM   #37 (permalink)
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The point of using H2, or any smaller gas, is that you could measure the leakage rate and quantitatively show that different gases or gas mixtures leak out at different rates.
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Old 08-15-2011, 06:54 PM   #38 (permalink)
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My point was that I wanted to see something explode.

Heh.
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Old 08-15-2011, 08:27 PM   #39 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
...ah-h-h, but atomic-level molecules are sneaky...the little ones sneak "in & out" faster than the big ones:

AIR = 100.00%.....28.966 MW
_N2 = 78.084%.....28.013 MW
_O2 = 20.946%.....31.999 MW
_Ar = _0.934%.....39.948 MW
H20 = _0.400%.....18.020 MW (water vapor)
_He = _0.000524%.._4.000 MW
_H2 = _0.000055%.._2.020 MW
Accordingly, at the end of a few years of leakage, we'll have a tire full of Argon and Oxygen? Cool! Helium would be interesting if it weren't prone to leaking out of tires... they fill some bicycle frames with it. Maybe they can cure some of the weight problems of run-flats with helium... reduce weight by 0.01 pounds a corner...
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Old 08-16-2011, 03:37 AM   #40 (permalink)
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Unicorn wind blows opposite of normal wind.
I've just realised this is the reason I have such bad results when drafting them.

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