roadfix

I've never experienced an O ring problem and I've been using CO2's since the mid nineties.

Blaireau

I ride on Armadillo tyres with oversized thorn resistant tubes, heavy as hell, yes --but I don't even have to worry about the whole Co2. vs Pump debate :-) ...I could ride on a flat in the unlikely event I had one
Bonus: some of the weight gained by the tyres and chambers is lost by ditching the pump/Co2. apparatus....

humble_biker

It's not a race. I carry a very small pump, two tubes, Park tool patches, and two CO2 cartridges. No way am I walking or hitching a ride. Or anybody I ride with, or see on the road stranded. Unless I'm training, then I can't stop to help. Don't want my heart rate to fall below 185bpm. <;^)
Incidentally CO2 is compressed air, meaning that when it exits the cartridge and enters the tube it expands to larger than the normal CO2 molecule(!). It usually takes the molecules around 24 hours to shrink to normal size. That is why you will have a flat or soft tire the next day after using CO2.

khuon

?!?!?!?!?!?!?!?!?!?! WHAT ?!?!?!?!?!?!?!?!?

roadfix

That was my reaction too.....

DrPete 

Uh, no. Just no.

Talewinds

OHHHH MYYYYYY GODDDDDDDD!
Probably majored in the arts.

merlinextraligh

CO2 does leak out of a tube faster than ambient air which is mostly nitrogen. However, that isn't the explanation for why.

DrPete 

Damned infernal shrinking molecules...

Boss Moniker

CO2 isn't air, merely a component of air (carbon dioxide), that accounts for like 2% by volume. Air is primarily Nitrogen (like 78%, but I forget the actual figures), and Oxygen. I don't know where you got that description, but it appears to be wrong on all counts (although I'm no expert).

The Co2 in the canisters is compressed under pressure to a liquid, so as it expands it absorbs heat. Each molecule doesn't "expand", merely the spaces in between, when the CO2 goes from a high pressure environment to a lower one.

Of course, this doesn't necessarily explain why the C02 leaks quicker than anything else. I'm relatively certain air isn't a molecule (merely a gaseous mixture), so we can't really compare the "sizes" of molecules.

And you know, the O-ring failure might be a result of the ring being cooled rapidly as the Co2 flows by, which would dry it out and crack it. I guess oiling it heavily with silicone or something might help, or just keep a spare packet of o-rings that you use once each.

khuon

I suppose I should say something insightful rather than simply reacting...

Okay. Let's start with the Ideal Gas Law which is:


Where:

• P = Pressure
• V = Volume
• n = number of moles
• R = Universal gas constant
• T = Temperature

We assume for now that this is a closed system which is not entirely true as we will see later. Thus we have:


Now n is a constant and is fixed (ncyl = ntube) as of course is R, thus our relationship becomes:


Initially Pcyl > Ptube. As the gas from the cylinder flows into the tube, Ptube starts to go up and Pcyl starts to decrease. However, bear in mind that Vtube also increases. Because Vcyl is fixed, in order to preserve the relationship, Tcyl must decrease. This is why the cylinder gets cold.

The gas expands from a smaller volume in the cylinder to a larger volume in the tube. The ratio of this expansion combined with the initial pressure in the cylinder directly governs the final pressure inside the tube when everything has come to equilibrium. The molecules of the gas do not expand or shrink. The space between them does. All molecular sizes are governed by the composition of their atoms and their atomic bonds.

Now we come to why tyres filled with CO2 go flat faster than with air. CO2 molecules are more permeable and soluable in butyl rubber than other molecules in air. Thus when a tube is filled with air, the CO2 molecules will tend to permeate and leak through the rubber faster than the other components of other gases in the air. This leaves other gasses such as Nitrogen and Oxygen (amongst others) to linger around longer. When a tube is filled with just CO2, the rate of leakage is the same as that of the CO2 leaking out through the tube filled with air but since there's only CO2 to leak, the tube will go flat faster.

BTW, CO2 doesn't necessarily leak through rubber faster because of its size but because of how the molecules in rubber attract CO2 better than Oxygen or Nitrogen. As a result, the CO2 permeates the rubber which then swells and thus allows more molecules to escape.

Note - Writing equations with vBcodes sucks!

roadfix

Thanks, now I understand why my coke goes flat sitting out after a couple of hours....

DieselDan

Always carry a pump. For all you weight weenies out there, a pump can weight less then 1 lb., but the bike weight upwards of 16-23 pounds, which you will have to carry or push with the flat, when you don't carry a pump.

DrPete 

Not completely--maybe if you ask nicely khuon will put together a nice summary of vapor pressure and gases in solution.

Phantoj

Hey, you anti-CO2 guys, have you ever experienced a mechanical failure of the pump you've brought along? That would be equally incapacitating.

I've always been a pump user, but I'm thinking about switching over to CO2, not so much for the weight, but because it's quite a bit smaller. Where's a good place to put a pump on a modern road bike?

'nother

I'm pro-CO2, but I have experienced a mechanical failure on a pump...it was the impetus for me switching to CO2

Surferbruce

well sure, all mechanical things can fail, but i'm going off experience. one time i can handle but twice, same thing, is enough to change my habits. the title of post probably should've been "done w/ co2 as my only means...". i'm sure next time i'm in the shop i'll more closely inpect the nozzle designs on the inflators, and if i see something that looks better will probably try it, but only along with a pump out on the road.

DrPete 

Genuine Innovations has a pretty cool device out called the "Second Wind" that's basically a CO2 system with an integrated backup pump. Only pumps to a max of 90 psi, but it's enough to limp home.

This was the 1st link to come up: https://www.performancebike.com/shop/....cfm?SKU=16497

Then you'll never be stranded, even when your CO2 molecules shrink

Al1943

That's why I switched to CO2 back in '98, bought a CF bike that had no pump pegs. Now I'd never go back.

Al

DrPete 

The jersey pocket.

I have a Silca 2-step Alloy pump that's ridiculously small and works really well. I take it with me on my rides further from civilization, or if the team car (AKA Mollie, my fiancee) isn't available for support in the event of a CO2 failure.

CyLowe97

...And take an extra 5 minutes to get the tire pumped up, while the CO2 user is a mile down the road....

I've got a combo Genuine Innovations Second Wind [as mentioned by Dr. Pete above]. The pump is small, but enough to get the tire inflation started so that an inexpensive unthreaded 12g CO2 can finish the job, or can hand pump it just enough to ride should I for some reason run out of CO2. And it fits in the saddle bag or jersey pocket, no problem.

curiouskid55

Hey here's another possibillity based solely on conjecture (nothing). The valve freezes and expands when the CO2 is released . When you tighten it, it is still cold. When it warms up to ambinet it is a little loose and does not hold pressure as effectively.

GP 

How do you maintain the o-ring in the inflator? Dab of silicone grease?

Pedal Wench

I use the Crank Brother's Power Pump. It fits into a small saddlebag with no problems. Used it yesterday to help out some stranded cyclists who used up both of their CO2 cartridges on a tire they pinched while replacing.

Doid23

I'm sorry, I've got to be honest, his explanation was a lot more fun than yours. I'm sticking with the expanding molecule explanation.