Was thinking about this earlier after seating a tubeless tyre with a CO2 cartridge. I then deflated it and reinflated it with air because apparently CO2 is bad for sealant.

Why are compressed gas cartridges filled with CO2 and not air?

I think you can fit more CO2 into the same space at lower pressure, therefore it’s safer.

Nitrogen would make more sense?
They sell it as an upgrade for car tyres as it leaks out more slowly (larger molecules?)

Safer in a fire?

I’ve always wanted it to be helium

Are the cartridges not the same ones as used in the food industry for putting bubbles into things ie sodastream and the like? Hence they are already being made in quantity thus are chaep. doing air cartridges would only be for bike use and thus be much more expensive

I don’t know for sure but thats what I have thought

Is CO2 bad for sealant per se? I always assumed it was to do with the intense cooling effect of depressurising all that gas. Ie it would be the same effect whether using CO2, air or anything else. Happy to be proven wrong.

Is CO2 bad for sealant per se? I always assumed it was to do with the intense cooling effect of depressurising all that gas. Ie it would be the same effect whether using CO2, air or anything else. Happy to be proven wrong.

I think it is. The latex emulsion in sealant is stabilised using ammonium hydroxide (in some, not all) to increase the pH. Using pure Co2 will mean more is dissolved into the water and lower the pH when it forms carbonic acid.

A quick google of the original question suggest CO2 is used because the canisters are steel for strength and compressed air would be corrosive since it would still contain water and oxygen. CO2 is relatively cheap and cheaper than changing the container or otherwise protecting it with a coating.

Why are compressed gas cartridges filled with CO2 and not air?

Because the CO2 liquifies under pressure which means you can fit *much* more gas volume in a cartridge.

Nitrogen would make more sense?
They sell it as an upgrade for car tyres as it leaks out more slowly (larger molecules?)

I’m worried about all that nitrogen polluting the atmosphere 😉

I thought that all gasses became liquid when pressurized .

Don’t worry, unlike normal air it doesn’t leak out, that’s the whole point.

Ramsey Neil – Member
I thought that all gasses became liquid when pressurized

Depends how much you pressurised it. Imagine if it happened to your air sprung forks or even your tyres at full compression.

Don’t worry, unlike normal air it doesn’t leak out, that’s the whole point

<breathes sigh of relief>

Hang on -wtf– that sigh was 74% nitrogen!

What have you been doing? You’re supposed to put it in your tyres, not your lungs. Though I suppose your lungs will leak less than if you’d filled them with air.

I’m just wondering if I can monetise it. Does it matter if the other 26% is a mixture of garlic and beer?

Depends how much you pressurised it.

..and also the temperature. Above the critical temperature for a gas, no amount of pressure will liquify it. Critical temperature for air is ~ -140°C.

CO2 has convenient properties for storing as a liquid at room temperature, and is cheap and fairly inert.

Don’t get me started on nitrogen in car tyres. Air is mostly nitrogen. If your tyre deflates I’m assuming it’s not nitrogen leaking out, you then top up with air, again most of which is nitrogen, so what’s now in your tyre is mostly nitrogen.

Nitrogen N2 two atoms of 14 particles
Oxygen O2 two atoms of 16 particles
Co2 3 atoms 2×12 + 1×16

So size is a no, however for very high performance applications the compression of nitrogen will be more predictable than air due to it being pure.

People don’t put nitrogen in car tyres to stop it leaking out. They use it because it’s more stable under temperature changes. Tyre pressure stays consistent despite circuit temperature, tyre deformation etc. This means handling is more predictable and tyres last longer.

Putting nitrogen in your road car tyres is like riding to work on your TT bike on the aero bars.

Are the cartridges not the same ones as used in the food industry for putting bubbles into things ie sodastream and the like? Hence they are already being made in quantity thus are chaep. doing air cartridges would only be for bike use and thus be much more expensive

Nope. Because science.

The cartridge technology looks to be the same as for the ones used for air guns etc. They are made out of steel, does that need to be food grade as well as the CO2 they are filled with? Sodastream use big re-usable cartridges though. The dinky ones used in old-fashioned soda syphons are the same size as the air gun/ tyre filling ones.

People don’t put nitrogen in car tyres to stop it leaking out. They use it because it’s more stable under temperature changes. Tyre pressure stays consistent despite circuit temperature, tyre deformation etc. This means handling is more predictable and tyres last longer.

Look up Charles’s Law, then something on how marketing works.

Same as selling snow to Eskimos. Brilliant piece of maketing genius that I wish I’d thought up.

If you want ultimate control, exclude as many variables as possible. In f1 that makes sense. In a nova Sri less so

I don’t think those CO2 cartridges contain liquid, do they? They’d last a hell of a lot longer if they did I think.

My local tyre fitters speak very highly of helium.

I can’t tell if people are arguing or agreeing with each other on this thread. Going back to bed.

I have a degree in Chemistry…. but it is from such a long time ago that I can’t remember any of it. So I’m going go and have a bit of toast and a cuppa. I don’t think anyone can argue with those facts.

My local tyre fitters speak very highly of helium.

😆

That definitely won’t work. Molecule’s way too small. Tyres would be flat in a matter of days. I’ve got some helium at work 😥

My local tyre fitters speak very highly of helium.

In a very high squeaky voice, or from a great height?

My local tyre fitters speak very highly of helium.

😆

Except a nitrogen molecule is bigger than an oxygen molecule, which does account for lower diffusion rates (I’m not sure if that’s all there is to it, but it certainly contributes). Hence tyres filled with nitrogen do lose pressure slower than those filled with air, which is sufficient for Kwik Fit to make their claims even if the difference is marginal.

CO2 is apparently soluble in rubber, which is why it leaks faster than nitrogen or oxygen.

Loosing pressure isn’t the thing though, if your selling on that then your mad (to idiots) it’s predictable behaviour your after

Indeed – are none of you lot old enough to remember the original CO2 inflators which did use the unthreaded sodastream cartridges – which I presume is why CO2 was used originally at least.

The predictable behaviour is nonsense too. Air is 80% nitrogen so air is just as stable as nitrogen near as damn it. Whatever that means. I suspect nobody else does they just say it because they’ve been told it and it sounds cool “yeah, my tyre pressure are so stable because of the nitrogen”

The nitrogen in car tyres came from motorsport and the reason they fill tyres with nitrogen is for convenience. They don’t want to rely on the air supply provided by the circuit so they bring their own and nitrogen is cheap.

The co2 cartridges are not made specifically for bike applications. They are used for many other applications so co2 is convenient, cheap and contains no oxygen so no fire risk in some applications where fire might be an issue. So no specific reason in relation to bikes as to why it is co2.

CO2 is apparently soluble in rubber, which is why it leaks faster than nitrogen or oxygen.

That’s interesting. One of my Ground Control 2.1s was found to be quite low in pressure before its first few rides.. guess which one wouldn’t seal and needed CO2?

Surely motorsport teams will need a compressor for their tools and so compressed air will be essentially free and guaranteed available? I thought it was the water (humidity) in air that is alleged to cause minor pressure variations.

Nitrogen cartridges are available that fit CO2 inflators too, they’re controlled though because of the yoof.

Apologies if I’ve missed someone else saying this.

Also, from experience co2 filled tyres do lose pressure quicker than air filled.

[video]https://youtu.be/bCnWvMleVD0[/video]

17 minutes! You must be joking

Nitrogen is better than air as it contains no water. So Nitrogen will behave more like an ideal gas than air. The risk being that if you set the pressure when the air is cold the tyre might contain liquid water. As the tyre warms up the water evaporates and the pressure rises faster then it would with dry air or nitogen

No idea if this matters in the real world

I’m sure the Co2 in a cartridge is a liquid. It is easier to liquify than nitrogen