CO2 canisters

Paul Boyd said:

I've just bought some of the above (plus the trigger thingy) primarily
because I'm lazy and don't like pumping tyres in the pouring rain
after a puncture, or pumping up MTB tyres with a mini-pump!

Just curious - what sort of pressures should I expect from a 16g
cartridge on, say, 26x1.95 or 700c x 32 tyres?

Sorry I haven't got any figures at the moment for those sizes, but I know
from experience that, from flat, one 16g cartridge inflates a 700x28 enough
to ride comfortably and safely (hard enough to resist pinch punctures). The
same should be true for 700x32. I'm not sure about 26x1.95.

If you want higher pressure, you can use a second cartridge, or put some air
in first with a pump. It's a good idea to have a pump as backup anyway. It
can be one of the extremely small and light ones.

There is practically no limit to the pressure you can get in a bike tyre
when using multiple catridges, or some air first.

Hold the cartridge upright for maximum yield.

Quoted message said:

Quoted message said:

Oh yeah, I bought them from wiggle ;-)

No comment ;-)

~PB

Paul Boyd said:

I've just bought some of the above (plus the trigger thingy) primarily
because I'm lazy and don't like pumping tyres in the pouring rain
after a puncture, or pumping up MTB tyres with a mini-pump!

Just curious - what sort of pressures should I expect from a 16g
cartridge on, say, 26x1.95 or 700c x 32 tyres?

Oh yeah, I bought them from wiggle ;-)

IIRC 12G is about right for a 700x23, so 16 sounds ok for a 32. I'd say
about 30-40psi in a 1.95. These are fairly wild guesses mind.

Doki said:

IIRC 12G is about right for a 700x23, so 16 sounds ok for a 32. I'd
say about 30-40psi in a 1.95. These are fairly wild guesses mind.

16g gets a 700x23 to about 100 psi, from flat.

~PB

Paul Boyd said:

I've just bought some of the above (plus the trigger thingy) primarily
because I'm lazy and don't like pumping tyres in the pouring rain after
a puncture, or pumping up MTB tyres with a mini-pump!

CO2 leaks out of rubber really fast. OK for emergencies though, and
you'll get about 30psi in the 1.95 tyres.

Paul Boyd said:

I've just bought some of the above (plus the trigger thingy) primarily
because I'm lazy and don't like pumping tyres in the pouring rain after
a puncture, or pumping up MTB tyres with a mini-pump!

Just curious - what sort of pressures should I expect from a 16g
cartridge on, say, 26x1.95 or 700c x 32 tyres?

Oh yeah, I bought them from wiggle ;-)

I find 700c x 32 inflate fully to ride condition with one 16g cartridge,
although I inflate the tube a little with a pump to facilitate fitting
the tyre.

If you haven't used them before, you may have fun the first time. Just
remember to wear gloves or wrap a buff or something round your hand
before releasing the gas.

--
Brian G
www.wetwo.co.uk

Thanks to all for the responses! I've bought one of those trigger
holder things that the canister fits into so shouldn't be a problem with
freezing hands.

I would take a mini-pump as well but plan on not needing it! The bit
about CO2 leaking through rubber was interesting though. I suppose the
answer is to deflate the tyres back home then re-inflate with my track pump.

As far as pressures go - I'm amazed!

--
Paul Boyd
http://www.paul-boyd.co.uk/

Zog The Undeniable said:

Paul Boyd said:

I've just bought some of the above (plus the trigger thingy) primarily
because I'm lazy and don't like pumping tyres in the pouring rain
after a puncture, or pumping up MTB tyres with a mini-pump!

CO2 leaks out of rubber really fast. OK for emergencies though, and
you'll get about 30psi in the 1.95 tyres.

Not out of my tyres it does not. Helium and Hydrogen might but I don't
thing CO2 does.

--chris

Chris Gerhard said:

Zog The Undeniable said:

CO2 leaks out of rubber really fast. OK for emergencies though, and
you'll get about 30psi in the 1.95 tyres.

Not out of my tyres it does not. Helium and Hydrogen might but I don't
thing CO2 does.

CO2 escapes from tyres quicker than air does. You may not notice it so much
with wider or thicker tyres that are less porous and so take longer to
deflate than skinny lightweight racing ones.

It makes sense anyway to replace CO2 in your tyre with air as soon as
practicable.

~PB

Pete Biggs said:

Chris Gerhard said:

Zog The Undeniable said:

CO2 leaks out of rubber really fast. OK for emergencies though, and
you'll get about 30psi in the 1.95 tyres.

Not out of my tyres it does not. Helium and Hydrogen might but I don't
thing CO2 does.

CO2 escapes from tyres quicker than air does. You may not notice it so much
with wider or thicker tyres that are less porous and so take longer to
deflate than skinny lightweight racing ones.

It makes sense anyway to replace CO2 in your tyre with air as soon as
practicable.

Wow I learn something new every day. CO2 permeates through the rubber
despite being a larger molecule.

Thanks

Pete Biggs said:

Chris Gerhard said:

Zog The Undeniable said:

CO2 leaks out of rubber really fast. OK for emergencies though, and
you'll get about 30psi in the 1.95 tyres.

Not out of my tyres it does not. Helium and Hydrogen might but I don't
thing CO2 does.

CO2 escapes from tyres quicker than air does. You may not notice it so much
with wider or thicker tyres that are less porous and so take longer to
deflate than skinny lightweight racing ones.

Pete, that sounds like Bad Science to me (although I've got not facts
at my finger tips to back it up). How are the inner tubes fitted to
wider tyres less porous than those fitted to narrow tyres? Butyl tubes
excepted.

Quoted message said:

It makes sense anyway to replace CO2 in your tyre with air as soon as
practicable.

Yes, it's more dense.
--

Tim

I understand very little of what's being discussed
but for some reason it's fascinating.

(Jon Thompson, urs)

Tim Hall said:

Quoted message said:

CO2 escapes from tyres quicker than air does. You may not notice it
so much with wider or thicker tyres that are less porous and so take
longer to deflate than skinny lightweight racing ones.

Pete, that sounds like Bad Science to me (although I've got not facts
at my finger tips to back it up). How are the inner tubes fitted to
wider tyres less porous than those fitted to narrow tyres? Butyl tubes
excepted.

More of a case of Bad Writing. There are two separate issues:

1) Thicker tyres and tubes are less porous than thin ones. I'm referring
to the thickness of the tyre casing and inner tube material here. Even
though a tyre (ordinary type) would not hold pressure if it contained no
inner tube (due to the poor seal at the beads and any holes caused by
punctures), it still affects the rate of deflation as it somewhat blocks the
pores of the tube.

2) A wide tyre takes longer to go flat than a narrow one when the porosity
of the material is the same, and both are initially inflated correctly.
It's to do with volume and surface area.

Often the two factors are combined as well. Often wide tyres are thick and
fitted with heavy inner tubes, whereas narrow ones are more often thin and
fitted with ultralight (thin) tubes, so the difference can be dramatic.
Some tyre & tube combinations need topping up every few days (or even every
day with latex tubes), whereas others hold good pressure for weeks.

~PB

Chris Gerhard said:

Wow I learn something new every day. CO2 permeates through the rubber
despite being a larger molecule.

CO2 does escape from the inner tube. Otherwise it would be a wonder gas for
cyclists and used routiney by many of us instead of just for emergencies.
Not having to top your tyres up would be convenient! You'd never have to
pump your tyres up exccept after a puncture or tyre replacement. But sadly,
that is not the case.

Since I'm not a scientist I had forgotton how CO2 escapes from tyres. I
just knew that it did - and faster than air does. It's a well-known fact,
actually. I don't really understand anything. I just know a few things :-)

A quick Google finds some good detail:

QUOTE - - - - - - - - - - - - - -

It's not porosity that causes latex tubes to lose air.

About 80% of the atmosphere is N2, 20% is 02, and a smidgen is CO2.
(Plus milli-smidgens of a few other rare gases.)

These gases are soluble in both butyl and latex rubber:

http://www.madsci.org/posts/archives/may98/895552329.Ch.r.html

As that short article explains, CO2 is about 15 times as chemically
soluble in rubber as N2. That's why tubes inflated with CO2 cartridges
lose "air" so quickly compared to tubes inflated with 80% N2 from a
hand pump.

Just as CO2 is much more soluble than N2, latex is much more
chemically soluble than butyl. So expensive latex tubes lose gases
much more quickly than ordinary butyl tubes. It's not a mechanical
matter of "pores" being larger in latex--it's a chemical process in
which latex is more reactive.

In the process, the gases are attracted to the rubber and are drawn
into it, between its atoms. There's less pressure on the other side of
the tube, so that's where the gas atoms come out of solution.
Eventually, the tire goes flat.

This is why party balloons filled with helium last longer when they
have that shiny metal foil coating. Neither the rubber nor the metal
have "pores" like the pores in our skin, and the size of the gas atoms
doesn't matter. It's just that the gases are chemically soluble in
rubber, but not in metal.

- Carl Fogel, rec.bicycles.tech, http://tinyurl.com/2do6uc

END QUOTE - - - - - - - -

I believe that porosity is relevant to tyres inflated with air, though. The
thickness of the tube and tyre is relevant to air and CO2 anyway, regardless
of porosity, so my "bottom lines" still stand.

As well as the deflation issue, CO2 is also quite corrosive to rubber and
some synthetics and can "rot" it. I'm not really sure if this is a
practical concern for inner tubes. If it is, it's another reason to replace
with air sooner rather than later.

~PB

Paul Boyd said:

I would take a mini-pump as well but plan on not needing it!

Great plan! Why didn't I think of that? :-)

--
Dave...

Tim Hall said:

Pete Biggs said:

Chris Gerhard said:

Zog The Undeniable wrote:
>
> CO2 leaks out of rubber really fast. OK for emergencies though,
> and you'll get about 30psi in the 1.95 tyres.

Not out of my tyres it does not. Helium and Hydrogen might but I
don't thing CO2 does.

This is what a little knowledge of science does for you :-)

Quoted message said:

Quoted message said:

CO2 escapes from tyres quicker than air does. You may not notice it
so much with wider or thicker tyres that are less porous and so take
longer to deflate than skinny lightweight racing ones.

Pete, that sounds like Bad Science to me (although I've got not facts
at my finger tips to back it up). How are the inner tubes fitted to
wider tyres less porous than those fitted to narrow tyres? Butyl tubes
excepted.

It was wrong to mention porosity in relation to CO2. Sorry about that. Now
corrected in my reply to Chris. Size and thickness is still relevant
though.

Quoted message said:

Quoted message said:

It makes sense anyway to replace CO2 in your tyre with air as soon as
practicable.

Yes, it's more dense.

And it escapes more quickly.

~PB

Chris Gerhard said:

Wow I learn something new every day. CO2 permeates through the rubber
despite being a larger molecule.

Surprisingly it does. See table IV in this link. <http://
www.apainfo.com/pdf/permeability.pdf>

Butyl rubber is more than 17 times more permeable to CO2 than to air.

--
Dave...

I scribbled:

Quoted message said:

I believe that porosity is relevant to tyres inflated with air, though.

I'm not sure it is, actually. Nevermind.

~pb

Chris Gerhard said:

Zog The Undeniable said:

CO2 leaks out of rubber really fast. OK for emergencies though,
and you'll get about 30psi in the 1.95 tyres.

Not out of my tyres it does not. Helium and Hydrogen might but I
don't thing CO2 does.

CO2 is quite a mobile gas. It does escape quite quickly through most
rubber - if you're piping it you use a special tube (which is a more
rigid plastic).

regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|

Brian G said:

Paul Boyd said:

I've just bought some of the above (plus the trigger thingy) primarily
because I'm lazy and don't like pumping tyres in the pouring rain after
a puncture, or pumping up MTB tyres with a mini-pump!

Just curious - what sort of pressures should I expect from a 16g
cartridge on, say, 26x1.95 or 700c x 32 tyres?

Oh yeah, I bought them from wiggle ;-)

I find 700c x 32 inflate fully to ride condition with one 16g cartridge,

Same with 26"x2.2. Although the volume is greater the working pressure is
lower, so one cartridge does the trick.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; this is not a .sig

In article <[email hidden]>, Paul Boyd
usenet.is.worse@plusnet says...

Quoted message said:

I've just bought some of the above (plus the trigger thingy) primarily
because I'm lazy and don't like pumping tyres in the pouring rain after
a puncture, or pumping up MTB tyres with a mini-pump!

Just curious - what sort of pressures should I expect from a 16g
cartridge on, say, 26x1.95 or 700c x 32 tyres?

Let's try to calculate it from what we remember of O Level science and
maths. :-)

CO2 has density 1.977 g/l at S.T.P. so your 16g is 16/1.977 = 8 litres
at STP.

A 26x1.95 tube is roughly a torus where R = (559+50)/2 and r = 25, so
its volume (2 * pi^2 * R * r^2) is about 2 * 9.87 * 305 * 625 = 3.76
litres

The ideal gas law states PV = nRT and in this case nRT is constant (once
the CO2 has warmed up to ambient temperature again) so P1 * V1 = P2 * V2
so P1 * V1 / V2 = P2

8 litres x 1 atm / 3.76 litres = 2.12 atm and 1 atm = 14.7 PSI so the
cartridge will inflate to about 31 PSI.

That seems rather low to me - we need to knock off 1 atm to allow for
ambient pressure. On that basis using two 16g cartridges would get 44
PSI, which seems much more reasonable to me.

Do the same for 700x32C and we get 1.65 litres and 57 PSI, for 700x23C
it's 0.84 litres and 125 PSI, which is somewhere near Pete Biggs'
experience.

Of course I'm assuming that the tube is completely empty before the CO2
is injected, and that none is lost in the process, neither of which is
particularly realistic - that would go some way to account for the
differences.