Bicycle Mechanics - CO2 in Tubes. Does it seep?

My lbs guy told me that I shouldn't leave C02 in a tube because the molecules are smaller and they will seep out of the tube itself. He said after using C02 to make an emergency repair, that i should deflate the tire and re-air it when i get home.

True or False?

Just asked a phd chemist he says that CO2 is the same size or larger than O2. He drew out the molecules but I don't have the little squiggles on the keyboard.
I have used CO2 carts for inflating and have not noticed them going down any faster.

My lbs guy told me that I shouldn't leave C02 in a tube because the molecules are smaller and they will seep out of the tube itself. He said after using C02 to make an emergency repair, that i should deflate the tire and re-air it when i get home.

True or False?

Good ol' air does the same thing. Seep out of the tube/tire, that is. Nature of the rubber beast.

I'm no chemist, but air has a variety of molecules, not just O2. I think thatthe majority of air is Nitrogen. I would guess that they are varying sizes and that some of them would make their way out of the tire anyway you look at it. Pump 'em up before every ride and it's a non-issue.

Did the guy at the LBS say that he had a degree in chemistry?

Did the guy at the LBS say that he had a degree in chemistry?

No. But he was mixing something up in the back of the shop that smelled sort of funny. :D

This dead horse has already been beaten ;) http://www.bikeforums.net/showthread.php?postid=1838493#post1838493, and beaten http://www.bikeforums.net/showthread.php?t=152657&highlight=co2+tubes.

CO2 is bigger than most air molecules, however a high concentration of CO2 inside a tube forms a steep chemical gradient that may cause more CO2 to escape than what comes in. I've heard anectdotally from a number of cyclists who notice that their CO2-inflated tubes drop pressure faster than those pumped with normal atmospheric air.

Didn't we just cover this? Yes it leaks out faster, much faster, I'll let someone else explain why. CO2 works great to get you through the ride, but then it should be replaced with air.

Al

Oops. I just saw that it's already been discussed. That's what I get for opening thsi thread 45 minutes before actually reading it.

Damn you tabbed browsing! Damn you!

The short answer is that CO2 leaks out of tubes significantly faster than compressed air. I have personally tested this under somewhat controlled conditions and proven beyond a reasonable doubt that this is so.

Why this is the case, I cannot say. But good data beats a good theory every time.

The other answer would be, "What difference does it make?". Which is also a question. I top my tires off every time I ride so it does not really matter how low they are. Unless, of course, they are completely flat, then it is time for a tube.

co2 is evil. my tires only have 370 parts per million, though next year they will have 372, but maybe less if george bush gets shot.