I'd be surprised if this didn't come up, but why is it CO2 that is used for inflating tires? As opposed to say air or laughing gas or helium.

Apologies if this is a schoolboy question.

Cheers

Chris

1) non toxic (unless in high concentrations)
2) cheap
3) I think it's easily compressible as it probably liquifies under a little pressure, whereas nitrogen (equally cheap and non toxic) would probably require much higher pressures to get enough in the cartridge
4) helium is expensive and would quickly leak out

Mostly 3) I think, however propane is also used in some of the larger cylinders.

But would helium filled tyres offer a weight saving?

Cheap, easily available. Also – the canisters are actually the same ones they use for fizzing drinks, to save on cost.

But would helium filled tyres offer a weight saving?

yes, several grammes…

How about laughing gas? I buy a lot of containers of that and they're cheaper. I've just never had a non-threaded dispenser handy.

but why is it CO2 that is used for inflating tires

I used compressed air pretty much exclusively TBH 😀

3) I think it's easily compressible as it probably liquifies under a little pressure

Shame on you Simon, didn't they teach you anything at school?
CO2 does not liquify (at all).
It transitions from gas directly to solid and vice versa, without existing in a liquid state (sublimation).

Didn't they teach you anything?
It's only at normal atmospheric pressure that CO2 doesn't do a liquid state, and sfb does mention pressure!

CO2 does not liquify (at all).

True at atmospheric pressure but not true in general

Pressure in a CO2 cartridge is 800-1000psi = around 60-70bar so just about forming a liquid phase at cool-ish room temperatures.

really ecky thump?
i didnt know that!

could you get tablets of CO2 to drop in your valve stems then? like O2 pills in that gerry anderson comic i cant think of the name of…. "X2"?

boogger – ya got me there

What's more, the very reason CO2 is used is the relative ease of turning it into a liquid using pressure!

… slinks off to hide in shame

Co2 is used as said previously its easily compressed into a liquid, air is not used as to compress enough air would need a more sturdy cylinder as it is not so easily liquefied.

Nitrogen is even more difficult to use in a liquid form and as for NOx im not sure who would supply it as its only manufactured in the UK by BOC who wont sell to anyone other than medical ie not to the motorsport industry.

Helium you must be kidding it would cost a fortune , the only reason we still fill balloons with it is that medical has to be ultra pure and boil off from these cant be condensed so its used in balloons. Plus its a finite resource

well, I'm glad to be vindicated! So, adding more gas to the cylinder won't take the pressure above the critical pressure at its temperature – though that will go up due to the latent heat released by condensation ?

Plus its a finite resource

yes, helium atoms travel faster than the escape velocity of the planet at the temperature at the top of the atmosphere so are lost to space 🙁

Well to be honest theres no way anyone would every take the tiny percentage out of the air , all the stuff in the UK comes from LPG fields in the US.

simonlovesrocks – Member

Well to be honest theres no way anyone would every take the tiny percentage out of the air , all the stuff in the UK comes from LPG fields in the US.

Not strictly true. About 85% of the helium produced comes from the US but most of the UK stuff comes from Poland, Russia and Algeria. BOC have recently opened up a new plants in Australia and Qatar too.

Solid CO2 is dry ice, used by many ice-cream vans and theatres.
So I guess you could get a dry ice "sand" that could be forced into tyres…
Controlling the pressure might be an art, though