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When you fill your tire with a CO² cartridge you are obviously putting CO² into it. When you use a pump you are putting air into it. Are there significant temperature variations that may lead to poor or better performance when using one or the other?

For instance, if you fill a tube with CO² and another with Air at same temperature and then the temperature rises 10°F, will one be more likely to explode than the other? What precautions must be taken when using one vs the other?

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4 Answers 4

up vote 15 down vote accepted

This is a debate that gets picked up on every bicycle forum known to man (okay, that might have been exaggerating a bit). Typically you start to ask the question when you notice that the morning after you have used your CO2 cartridge, your tyre is ridiculously low.

By no means am I a chemist but, as it has been explained to me, CO2 and butyl are more soluble than N2/O2 and butyl. Most tubes are constructed from butyl (fancy pants cyclists will sometimes use Latex tubes, haha). Due to the increased solubility you can expect that a CO2 inflated tyre will need re-inflating sooner than one you pump up by hand.

http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html

While the explanation above is dealing w/ escape from balloons I am going to assume that we can take that information and apply it to our discussion.

Now, if i am incorrect (which I often am) please let me know!

I just noticed I didn't tackle the temperature issue. I do know that temperatures exceeding 50 degrees celcius (above 125 farenheit) can result in the potential for ... explosive fun, in regards to CO2 canisters.

http://www.stayfill.com

This company has a proprietary gas blend that won't leak from your tubes apparently ... ... ...

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+1 for pointing out the high permeability of CO2 in rubber. –  darkcanuck Sep 6 '10 at 20:56
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+1 for "fancy pants" –  Joe Philllips Sep 7 '10 at 5:04
    
Since you mention temperature, what is the normal operating temperature of a tire? It must be higher than air temperature, due to friction on the ground and from the brakes. Can you expect 'fun time' if you fill your tire to a certain psi then go maybe 5-10 miles? –  JFA Mar 9 at 22:34

The air we breathe is made up of 78% nitrogen (N2) and 21% oxygen (O2), with trace gases making up the rest. So the easiest comparison is between N2 and CO2. N2 is less dense than CO2 but otherwise they're very similar (to your tires) unless you somehow find yourself riding in temperatures near their liquidation points -- in which case you have bigger things to worry about.

As far as pressure changes go, they should both follow the ideal gas law which states that the pressure in your tire has a direct relationship to the temperature of the gas inside it. The density of the air molecules doesn't matter, just how many there are. Whether its N2 or CO2, that relationship remains the same.

So to answer your question, a 10degF change should affect the pressure of a CO2-filled tire about the same as an N2-filled tire. I'm curious about the higher density though, that would mean that a CO2-filled tire will have more rotating mass...

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CO2 is smaller molecule than N2 (so it'll escape more easily). One of the problems with H2 as a fuel source, apparently, is that it's so small that it tends to leak from pipes/pipelines/containers. –  ChrisW Apr 15 '11 at 2:21

at normal temperatures (human life temperatures) and pressures all gases behave about the same with temperature variation. Check out this article and the pressure tests of air, CO2, and nitrogen at the end:

http://www.powertank.com/truth.or.hype/

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Welcome to Bicycles.SE. Would you consider editing your answer, expanding it to summarize a few of the most relevant points from your link? –  amcnabb Jun 26 '13 at 4:01

I have never noticed a significant difference between the two. CO2 is great on a ride because using mini pumps, well, it just isn't fun.

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