OldeRider

Something I found out the hard way. A tire aired up with a CO2 cartridge will leak down in about 2-3 days, they're only for getting you home. My LBS informed me of this after the fact, guess I should have read the instructions.

SilentShifter

I found out the same thing when I went on a short vacation. Was a little concerned that the tube I just replaced was flat again - LBS informed me otherwise. Now when I have to use the CO2, I deinflate when I get home and fill with regular air.

CO2, it will get you home, but not much else.

HillRider

I used to wonder about this because CO2 has a higher molecular weight than air so it should, by pure diffusion, leak out of a tube slower. Obviously it doesn't, so why not?

Well, the answer seems to be that CO2 is more soluble in butyl or latex rubber than air so it makes it's way through the tube wall faster.

I do what SilentShifter recommends. I use CO2 to fix the flat, then replace it with air after I get home.

RockyMtnMerlin

Hmm; this has never happened to me. I thought that the whole thing sounded kind of "urban mythy" so I did some research. I mean why would CO2 leak out of an inner tube faster than air (which is mostly nitrogen)? I found that a CO2 molecule is larger than a nitrogen atom. That made me think that this may be bogus because how could a larger molecule (an oxygen atom bonded to either side of a carbon atom) pass through the rubber of the inner tube (or latex for that matter) more easily than a single smaller atom of nitrogen. Even if the CO2 is soluble (i.e breaks down into its component atoms), they (oxygen and carbon atoms) are still both larger than nitrogen atoms. So I called a professor friend of mine at the local university and he said that it sure sounded like an urban myth to him. My take is that the patch was probably not completely secured and that caused the further loss of air.

Nessism

CO2 DOES leak out faster. I can't give you an scientific explaination but I know it's true.

LapDog

I would argue with anyone about this, probably to the point of extreme embarassment.

But it has happened to me several times. Air up the flat while on the road. The next day the tire is flat. Pump it up with a regular pump and the tire stays inflated forever!

So who has the info as to why!

Mentor58

I suggest that in the best BF traditions, we can attempt to solve this one of two ways. The first is the basic "Yes it does", "No it doesn't", "Yes it does", "No it doesn't", "YESS", "NOOO", "You are an idiot", "You are a nose-picking Monkey". After that, it goes down hill quickly.

Second way, get 2 identical tubes, (now I know that this is a very small sample, and not proof, but should prove the point). Mount each, inflate one with AIR and the other with CO2 to identical levels. Check pressures at 12 hour intervals. Then reverse the situation, fill the first with CO2, the second with Air. Repeat the measurements. This should show at what rate the two vary. This would be better with a number of tubes and a statistical analysis performed on the results, but this should work quick and dirty.

Just an idea. I don't use CO2, so I'm not capable of running this experiment.

Steve W.
Who would open the box, but he doesn't know if the cat is alive or dead.

supcom

I have done a semi-controlled experiment that proves well enough for me that CO2 leaks out of a tire faster than air. I inflated two tires of the same construction containing the same type of tube (27x1-1/4). One was inflated with a single 12g CO2 cartridge; the other pumped up to the same pressure as the CO2 filled tire using a floor pump. It should be noted that experience with the two tires was that they each lost air pressure at approximately the same rate. The initial pressure of each was approximately 62 psi. The bike used for the experiment was parked and not moved during the entire test. Both valves were oriented at the top of the wheel and plastic valve caps were installed on the valve stems.

After 24 hours, the pressure was checked in each tire, being careful to not let any more air escape than necessary to perform the checks. The CO2 filled tire had dropped approximately 9 psi; the air filled tire dropped only 2 psi.

Subsequent pressure measurements were made over the next couple days. As time passed, the disparity between the CO2 filled tire and the air filled tire became greater.

I am confidant in concluding that CO2 leaks out of a typical bicycle tire more rapidly than air.

It should be noted that in my test, the starting pressures were about half of the typical road tire pressure. This was all that a small CO2 cartridge would inflate a 27 inch tire, yet the leakage was still 9 psi in 24 hours. I would expect that the leakage for a tire filled with only CO2 at 120 psi to be double that from 62 psi, or 18 psi drop in 24 hours.

Al1943

Yes it leaks out faster, I thought that was common knowledge. I've seen it in print more than once. I've also seen the solubility explaination on forums more than once.
My wife had a flat recently (her second in 10 years). I filled the tube/tire on the road with CO2 and forgot to replace it with air. Two days later I noticed it was totally flat so I pulled the tube out, put some air in it and held it under water- no leaks. The next day I remembered the CO2. I pump all tires with air before every ride, they never go completely flat with air, even when left unused for months. CO2 goes flat in 2 or 3 days.

Al

2manybikes

I know this is a really, really, bad idea, but............

We could go to the Innovations (the company that sells the stuff) web sight, or read the instructions. That would tell us that the molecules are smaller and leak out of the tube faster.

Sorry, I know real men don't read instructions. I apologize.

RockyMtnMerlin

Okay, I went to the Innovations website and looked for their info on molecule size. I only spent about 20 minutes reading but could not find it. Where is it? FWIW I also emailed Innovations and posed the question to them (both about molecule size and the general question about deflation). If they answer (no matter the outcome) I will post it in this thread.

zip22

yeah, i can't find it anywhere on the website either. i even watched all the movies. sorry 2manybikes, i think you're smart aleck response backfired.

supcom

The leak rate is not an issue of molecule size. I don't think there is any question that a CO2 molecule is larger than an N2 or O2 molecule. Besides, it's hardly in Innovations best interest to volunteer that using their product will result in a flat tire a couple days later!

2manybikes

It was on there 10 years ago. When I find something I'll post it.

NoRacer

Maybe we should send this one in to "Myth Busters".

2manybikes

Innovations actually pointed out that you need to refill the tire later with air, as it would leak out faster. I have no idea about the molecule size, I'm just repeating what I read from innovations, years ago. At one point the web site claimed that the co2 came from a volcanic source, at another point they claimed it was taken from the air. I don't see that on the web site now either. Call them up.

jscott

Molecular Size N2 smallest, O2 next CO2 biggest.

The loss of CO2 through the rubber is called permeation. CO2 permeates the rubber faster since it is more soluble in the rubber than the N2 and O2.

This is because it is a polar molecule (slightly positve on one end and negative on the other end). This allows the CO2 to wiggle into the rubber better. (good science eh).

This effect is well known and used to separate CO2 from many gases. High CO2 permeability is common to alot of polymers.

cyccommute 

CO2 is a nonpolar molecule. Because it is a linear molecule, the dipole moment is zero. In fact, everything in the system- tube, N2, 02 and CO2 - is nonpolar. There are other interactions on a molecular level that occur that allow the CO2 to pass through the rubber faster than the other gasses. Size of molecule is also not a contributing factor.

jscott

your dreaming

cyccommute 

The term is "you're dreaming" which comes from the contraction of you (an objective personal pronoun) and are (a state of being) as in "you are dreaming". "Your" is a possesive personal pronoun which implies dreams that I have as in "in your dreams". But since you don't know what my dreams are, I fail to see where "your dreaming" applies.

Obviously, since your grasp of chemistry is about as good as your grasp of grammar, you might want to bone up on both since it's obvious that you need work on both.

jscott

CO2 bond angle 92.5 degrees

cyccommute 

"The linear geometry with two identical oxygen atoms attached to a center carbon gives rise to a special effect. The molecule is symmetrical. There are partial charges seen from the difference in the electronegativities. The electrostatic potential shows a blue (partially positive) color for carbon and shows a red (partially negative) color for both oxygen atoms. However, the symmetrical nature of the bonds has the overall effect of canceling the dipole, therefore the molecule is non-polar."

From https://www.elmhurst.edu/~chm/vchembo...inorganic.html

No carbon/oxygen compound makes a bond angle of 92.5 degrees.

2manybikes

Slammed to the floor! 2 points .

Surferbruce

without a doubt co2 leaks out faster. there. done.

Jason Curtiss

No - we can't be done yet!

It's the adiabatic inflation process combined with the warming of the CO2 after inflation that causes the tire to go flat.