Question on CO2 cartridges

joker77

Was out for a spin on Wednesday evening, had a slow puncture so decided to change the tube. Replaced the tube, all done, went to inflate and used a CO2 cartridge in the mini pump I have. It was a screw in one, so screwed it in to break the seal, then screwed out a little until it was all used. The valve was white and frozen looking after, tyre nice and hard. Too hard though? That's the question.

Went on for another few Kms, came out onto the N11 at Kilmacanogue heading towards Bray. Was tearing down the N11, when tyre blew out. It was shredded a little in the tyre wall, I really don't think I went over anything, think it just blew.

So my question is - with CO2 cartridges - should you use the whole thing to inflate the tube? Could it have over inflated to cause the blowout?
The mini pump I have has no way to tell the psi...

DirkVoodoo

A 16g cartridge will fill a standard 700x23 road tyre to about 130 PSI.

I suggest either not using the whole thing, letting some air out, buying a portable gauge or buying 12g cartridges which should get you to about 100 PSI.

CheGuedara

AFAIK most cartriges are set to inflate a 700cx23 to 100 to 110psi which shouldn't burst a tyre unless something is wrong.

There may have been something up with the tyre (may have lost its seating during the rapid inflation?) or even the tube to cause a blow out but I'd be surprised if excessive CO2 was the culprit

Edit: +1 on what Dirk says re. pressure gauges, picked digital one up in halfords for small change and it's small enough to fit in back pocket/saddle bag if requires. Handn't figured for the larger cartrige size either - one to watch for alright

joker77

Strange one alright, cheers for the heads up on the 130 though, didn't know that.

DirkVoodoo

I'll have to verify that, gimme a minute or two.

EDIT: Yes, I think it's about 130 PSI although my methods may be suspect.

Dr_Colossus

DirkVoodoo wrote: »

I'll have to verify that, gimme a minute or two.

EDIT: Yes, I think it's about 130 PSI although my methods may be suspect.

Is that 130 psi immediately after inflation when the CO2 is still cold and compressed in the tube, how about 1/2 hour later after a bit of a spin and the tire and CO2 inside warms up a little, would the pressure increase much/significantly? Care to give a pressure reading again Dirk?

DirkVoodoo

P1V1 =P2V2

P1 is atmospheric pressure, 14.7PSI
V1 is the volume of the uncompressed CO2 at STP given from the ideal gas law. Number of moles is 16/44 giving a volume of 8.15L.

P2 is what we want.
V2 is the volume of the tube which is approximated by a toroidal shape. Volume of a torus is 2*pi^2*R*r^2 where r is the radius and R is the distance from the axis of rotation. I got about 0.913 L for a 700x23 tyre, but again this is all very rough and like you say I'm probably wrong.

Anyway, P2 = P1V1/V2

=> (14.7)(8.15)/(0.913)

= 131.22 PSI

Again, might be totally wrong. That's the inflation pressure assuming no losses, I don't know what the rate of CO2 permeation through a butyl tube is.

EDIT: I'm leaving myself wide open for public decimation. I reckon Lumen will spot a glaring error somewhere

Lumen

DirkVoodoo wrote: »

I reckon Lumen will spot a glaring error somewhere

Yes, you have too much time on your hands. Empiricism FTW! :pac:

DirkVoodoo

My initial 130PSI was based on what the manufacturers of these CO2 pumps say by the way. It inflates to 130PSI. That could be enough to pop the bead off the rim, it happened to me before. Easy to miss and would cause a blowout similar to what the OP reported.

DirkVoodoo

Lumen wrote: »

Yes, you have too much time on your hands. Empiricism FTW! :pac:

That took 12 minutes according to my post and edit record

niceonetom

Jesus, I'm having leaving cert flashbacks here.

When you said your methods might be suspect I thought you'd gone and filled a tyre with a fresh canister and then used a track pump to measure the resulting pressure. Not maths.

joker77

DirkVoodoo wrote: »

My initial 130PSI was based on what the manufacturers of these CO2 pumps say by the way. It inflates to 130PSI. That could be enough to pop the bead off the rim, it happened to me before. Easy to miss and would cause a blowout similar to what the OP reported.

Sorry for the ignorance, but can you describe what you mean by this?

DirkVoodoo

Well, when I did it once there was a massive bulge in the sidewall, you can either see it (which I did) or feel it when you ride (which has happened before).

At any rate, 130 PSI would be at the limit for a lot of clincher tyres.

joker77

Cheers Dirk, what I thought but wanted to be sure.

I'd say that's what it was, the bead not fully set and the bubble causing the blowout. Will be more careful in future not to over inflate.

Have ordered a new set of GP4000s, should arrive next week, in the meantime I've stuck an old Armadillo on it for the weekend spin.

As a bit of an aside, I've had a fair bit of trouble with Conti tubes - anyone else? I got a batch of 5 a while ago, 3 of which were faulty so sent back (the fault was in the valve - it wouldn't open and when forced, the whole valve part unscrewed from the pipe). Then recently, with the new batch (the replacements), I've had 2 slow punctures which I reckon is a valve issue as well.

Have opted for Schwalbe tubes instead. Aside over

DirkVoodoo

Yeah all my conti tubes have leaky valves. Fine when they are closed but even unscrewed a little they leak air.

blorg

DirkVoodoo wrote: »

Well, when I did it once there was a massive bulge in the sidewall, you can either see it (which I did) or feel it when you ride (which has happened before).

At any rate, 130 PSI would be at the limit for a lot of clincher tyres.

I have had it happen to me before also and it has been improper seating of the bead rather than pressure. Sometimes it happens immediately on inflation with the track pump (bang there and then) but at least once it only happened 10km into a ride. Was an issue I had mainly with Conti GP4000s IIRC.

While 130 is over the recommended max for some road tyres it is not very much over the max. The lowest rating I have seen is 116PSI, most are 120-145PSI. You certainly don't need 130 PSI in a 700x23c tyre but I think it unlikely to cause your tyre to blow off.

DirkVoodoo

I think max for GP4000 is 120 PSI though? Does going over the PSI recommendation increase the likelihood of a tyre unseating itself?

Lumen

blorg wrote: »

While 130 is over the recommended max for some road tyres it is not very much over the max.

I posted this a while back. It was Zipps excuse for not having a carbon clincher, before they had a carbon clincher.

Zipp wrote:

Q: How come Zipp hasn't come out with a full carbon clincher rim yet?

A: The short answer is that we don't really want to have a full carbon clincher on the market. The reasoning behind this is that the technology has not yet advanced to make available reliable, durable, safe full carbon clinchers. Carbon is a wonderful material and everyday more is learned about how to work with it. However, at this point in time, no one has learned enough to overcome the three main forces a clincher rim has to overcome. The first force is an outward force on the clincher bead exerted by the pressure of the tire. The second hurdle to overcome is the tremendous heat generated by heavy braking. The final force to overcome is impact. Consider the following scenario. You start a ride with a tire pressure of 160 psi. Your ride takes you up into the mountains and (obviously) down the other side. On the way back down, you will be braking heavily occasionally. It is not uncommon for the surface of a carbon rim to reach temperatures in excess of 250 degrees Fahrenheit (121 C). With this increase in temperature, your tire pressure has suddenly gone to almost 200 psi. This excessive pressure forces the clincher beads apart. This force compromises the impact resistance since the beads are no longer parallel, but rather bowed outward. If the wheel takes a hit, the impact will sheer the sidewall of the rim off causing the tire to blow off. Granted, this scenario requires many variables to come into place which simply will not happen 99% of the time. However we have been able to replicate this failure in our testing and have decided that it is not yet feasible to produce a full carbon clincher rim and have devoted our focus to producing lightweight, durable carbon/alloy clincher rims that, on average, only weigh about 75 grams more than their full carbon counterparts.

Putting aside the lame excuses, I imagine that Zipp would know what sort of pressures are required to blow off a properly seated tyre, and 130psi is not even close.

Lumen

Funnily enough, I can no longer find the statement "The short answer is that we don't really want to have a full carbon clincher on the market" on Zipps website.