co2 in tyres?

[yostumpy]

I would be a big fan of Helium. Great on the hills!

As a monatomic gas it would leak even faster....

Well this takes me back a ways. About 20 years ago, i used to go mountain biking in the not so local woods, in winter, at night. No mean feat when you consider, rigid bikes and candle lamps! Anyway, one night, in 'apres mud' mode in t'pub, I mentioned the fact that hellium in the tyre would be an interesting experiment. Well you can imagine the laughter and p... mickey taking that ensued. Not detered, I contacted the R&D dept at BOC gas, and explained my plight to an interested chap. Leave it wi' me lad. About a week later, I got a phone call, and was told the results. Yes it leaks, especially out of butyl tubes, but one chap in the r&d was a keen cyclist, and he brought in some latex tubes to try. That wasn't really successful either, BUT they had listened to me, and actually tried it out, which I found quite pleasing.

[Mick F]

Are all the canisters of the same capacity? And is it a case of using one and throwing it away, or do you like get 3 or 4 fills? If so, how do you know how much gas remains in the canister?

You only get one shot per canister. Usually get you up to 100+ psi on a skinny road tyre from a 16g cartridge.

You get a couple of shots from my 16g canisters. Enough to fill two 23mm tyres to max pressure. I've tried it as an experiment.
In fact, when I've used one and not needed the rest of the gas, I've just stowed it away in my saddle pouch. The pressure is still there a week later, but I won't rely on it, so I replace it anyway.

Some years ago I went on a Grand Tour of Scotland, England and Wales (1,400miles in three weeks) and didn't bother with my pump but used CO2 to top my tyres up every day or two. At that time I wasn't aware that CO2 "leaks" away so I was topping them up pointlessly as I'd have been better off with my pump.

I was being lazy.

[Dachshund90]

Thank you everyone for the replies, very helpful and greatly appreciated

[sreten]

Hi,

CO2 is not smaller than N2 or O2 and won't go down faster than air.

At -42C @ 1atm it doesn't just liquify it goes directly
to a solid, hence you get dry ice, CO2 sublimates.

CO2 needs less pressure than N2 or O2 to be stored in a non
gas phase and therefore its enclosures are the cheapest
of the three, and why its the most prevalent.

rgds, sreten.

[Brucey]

despite its molecular size it turns out that CO2 diffuses through rubber at a rate substantially higher than either O2 or N2.

MickF reported this observation (i.e. that CO2 filled tyres went down more quickly) and frankly I was sceptical, and for similar reasons. However a little digging around showed good data that supported Mick's observations.

The best explanation is perhaps that the CO2 molecule is very polar, so finds it easy to bond loosely with, and then diffuse through, the structure of rubber.

cheers

[Mick F]

Yes, it's a Chemistry thing and not a Physical thing.

You would think that CO2 molecules being "huge" wouldn't go through rubber, but it ain't like that at all. Nowt to do with size.

There's a long thread on here somewhere that I dug up the last time this subject came up. CJ reckoned on the Physics being correct about the size of the CO2 molecules, but he was corrected by one our members explaining the Chemistry.

Whatever the reason, do your own experiment and see that CO2 goes down VERY prematurely. It'll last a day or so, so there's no need to worry if you get a puncture early in a ride. Fill up with normal air at your leisure within the next 24hrs and don't panic about it.

[trull]

Filling with nitrogen gas would be good, apparently oxygen diffuses more quickly through a rubber tyre. So as air is c.80% N and 18% 02, you could stay at optimum pressure for longer. I'm sure Myth busters did a experiment on breathing air from submerged car tyres which showed you would not get enough oxygen .

[Urticaria]

I noticed that CO2 is about a hundredfold more soluble in certain silicone oils than the other components of air. Perhaps the same is true for butyl rubber?
I wonder whether an innertube could become saturated with CO2 such that it ceases to deflate? Could do the experiment by measuring the pressure in a tyre, and topping up every day.
Possibly, though, if the CO2 can migrate in a sufficient depth, it can migrate out the other side of the inner tube, and be lost.

Looking up the bond lengths of C=O, O=O, and N≡N, it doesn't seem true that CO2 is the smaller molecule. Its polarized nature probably enables it to be absorbed so readily.

If going away on tour, you could try putting some real ale in your innertube to provide a daily top up, or if you have schrader valves, popping in a few baked beans for a methane lift?

[easyroller]

CO2 is not smaller than N2 or O2 and won't go down faster than air.

rgds, sreten.

You've obviously never used a CO2 canister to fill your tyres then...

[Richard D]

FWIW, I had a puncture on last week's group ride (the first for 12 months), and used a CO2 inflator. At least one person commented on how quickly it enabled me to get moving again. Five days later, that same tube was very soft - far too soft to ride on. I'd wondered if the advice to refill the tyre with air after a CO2 fill was necessary, and it clearly is.

[Mick F]

Yes.
It's amazing how fast you can inflate them.

I honestly believe it's not worth the effort of pumping when you can use CO2 so conveniently. Just imagine fiddling with a pump when you're tired or in a hurry, and imagine the effort required in pouring rain and wind.

CO2 is fantastic, and I do not understand why people seem to poo-poo the idea. So long as you re-inflate at your leisure when you get home, CO2 is perfect.

[Brucey]

if you ride in a group and you have a decent pump you may feel (or indeed are) obligated to loan it out whenever there is a puncture and someone else is struggling. I wonder how many CO2 cartridges you would have to carry to be sure that you were not going to run out?

Most people I know carry a pump as well anyway, in which case you may as well carry a good one rather than a piece of junk that you are not actually happy to use. My record is about 12 punctures in a single ride BTW, prior to which I would have scorned the mere idea of having more than about two.

With some tyre/rim combinations they don't always fit right and about one time in three you need to deflate the tyre and reseat it before inflating it again. That would get pretty old, pretty quickly, with CO2 cartridges.

Another way of looking at it is that if the CO2 leaks out anyway, all you are doing is postponing pumping the tyre up. You still need to own and use a pump, and using CO2 just means you need another gadget and you need another consumable -something cycling is otherwise blissfully free of- to stock and worry about.

CO2 is best suited to triathletes, MTBers and others who are obliged to fix their own punctures ASAP, or those who can't or won't use a pump.

cheers

[[XAP]Bob]

A small compressor at home could easily be the "long term" solution, with canisters as "get you home".

On long rides I'll often pack the track pump - why take anything smaller?

[jb]

Punctures are very rare for me these days but when I have, its usually resulted in me needing to inflate the tyre two or three times due to there being more than one hole. The time taken to pump up a road tyre is pretty much insignificant.

[Mick F]

My record is about 12 punctures in a single ride

I don't think I've had as many as twelve punctures in my whole LIFE.

I commuted for YEARS and only had one circa 1987. I never bothered carrying a pump so had to walk home.

I remember my first puncture. I was thirteen and distraught that my front tyre went down and Dad had to show me how to repair it. Next one was years later, maybe 16years old. Next, I was in my twenties commuting to Devonport from home in Plymstock but it was only a slow one. Don't think I had another one until as late as 2007.

Funny, I can remember these things? I can remember them because they are rare events.