Dangerous tube blow outs - DA 7850 50mm Carbons

[Dr_Mutley]

Hi All,
im after some thoughts on 2 recent blow outs I've had with my above DA 50mm rims. Both times have been after moderate, but short decents, and luckily both at low speed at the bottom. Ive had 2 in the past week.

First tube rupture (ie 6" blowout) was a vredestein tube and second was a Conti ultra race tubes. I'm 90kgs and the first rupture occurred running 120psi, and the second running slightly less, 115psi. When decending I have been riding my rear brakes a little as not to drop the group too far back, so I'm assuming these blowouts are heat related. I have checked the inside of the wheel, and there doesn't appear to be anything fouling the tube. If there was, I would think that it would just cause a flat anyway, not a catastrophic failure like Ive experienced.

One thing I haven't checked is the reliability of the pressure gauge on my relatively new Topeak track pump. I am pretty confident that this isn't an issue, and that I am not running excessive pressures. I try to run my pressures a little higher (110 to 120psi) due to my weight. I don't want to buckle or destroy a rim on a pot hole or train track or the likes.

I am assuming the problem is just heat related, generated from riding the brakes a little, and having my pressures rise due to expansion.

Anything I'm missing guys? Luckily til now it's been my rear. I really don't want to lose my front at speed and do a jens bought face plant into the tarmac at speed.

[rustychisel]

not enough info, good doctor. Pix would help.

We're talking clinchers on carbon rims, yeah? What tyres, how old, how well seated on the rims? How did the 'catastrophic' experience manifest itself, blow tyre off the rim, or tyre popped up and off then the tube blew. Have you examined brake pads to ensure they're absolutely set correctly? Are you sure they're good pads for those rims? What riding conditions? How hot?

Most things are guess work but a lot can be learned from precise information and careful examination of the offending items. And yeah, if I were you I'd want to do everything I could to get to the bottom of the matter too.

[alex]

do you ride the brakes a lot?

thats the only thing i can think of

unless it is a hot day and you have too much pressure (inaccurate guage as you suggested)...

[twizzle]

Every blowout I have personally seen has been due to the tyre not being fully under the clincher edge when inflated - which is why I now partially inflate and then work my way around the tyre pushing it back/down to ensure the tube isn't pinched and the retaining bead is properly in place. I've only screwed it up once myself, but the front started bulging as the tyre was coming off the rim and I worked out what it was before it blew.

[drubie]

I'd be tempted to turn that tyre inside out and inspect it for glass filled cuts, and be careful about re-mounting it like Twizzle says - some rims and some tyres are just a bad match. Anything easy to put on (i.e. with generous beading) is always a bit of a worry as when you inflate them, they can ride up the clinch inside without you noticing.

I had one do this the other day - front wheel got bumpier and bumpier as I rode. It didn't blow but it was very unpleasant until remounted at my destination.

(and if it's a gatorskin, they're designed to chew up tubes )

[petal665]

Are you using the blue plastic rim tape that came with the wheels? If so, get rid of it and buy some cloth rim tape. It may have no relation to your problem but I can't stand that plastic stuff.

[MichaelB]

Wasn't there an issue with the rim tape supplied for these rims, and Shimano adviswed to use a new tpe )or was it supplied with veloplug type inserts and they suggested to ditch them and use the Shinmano tape ?

Cheers

Michael B

[Dr_Mutley]

not enough info, good doctor. Pix would help.

We're talking clinchers on carbon rims, yeah? What tyres, how old, how well seated on the rims? How did the 'catastrophic' experience manifest itself, blow tyre off the rim, or tyre popped up and off then the tube blew. Have you examined brake pads to ensure they're absolutely set correctly? Are you sure they're good pads for those rims? What riding conditions? How hot?

Most things are guess work but a lot can be learned from precise information and careful examination of the offending items. And yeah, if I were you I'd want to do everything I could to get to the bottom of the matter too.

Sorry for the brief OP.. was at breakky, typing it out on the iphone... i will post some pics tonite

Conti GP 4000s Black Chilli clinchers, brand new 8 weeks ago, done about 1750kms, put them on when i got the new DA wheels outta the box.

Problem manifested itself by a sudden blow out. No preceeding warning to suggest a bead or the like had unhooked itself from he rim, or anythign was bulging or the like. As far as i am aware this is behaving like a tube explosion, without any preceeding tyre issue.

Brake pads I am assuming are probably ultegra or DA standard black pads. I am assuming they are stock from new (they are on the below cervelo in my sig - an RS 2008 model) I have kept a close eye on them and minutely adjusted them as necessary. The rear has about 50% left in them (i thnk). Prior to this happening, i had ordered a set of Koolstop Black to replace them with when the time came. I may do that now sooner rather than later.

Riding conditions: first blowout at low 20s temp, and yesterday was in the Coast to Coast ride here in Adelaide at 9am in the hills. Therefore i would at a guess say again the ambient temp woulda been about 20deg. Both times when changing the tube the rim was warm, but not uber hot or anything.

[Dr_Mutley]

do you ride the brakes a lot?

thats the only thing i can think of

unless it is a hot day and you have too much pressure (inaccurate guage as you suggested)...

yeah i am a bit of a brake rider. Both times i had ridden the rears more than usual so i wouldnt drop anyone. I wouldnt say i was riding them excessively, as i would of still averaged 60kmh + down the decents, and by no means were the decents monsterous. U, being an adelaie fella, is probably familiar with the C2C course. This blowout occurred not long after climbing lofty, and then on the fast downhill section thru picadilly and on the way thru under the freeway at Mt Barker. First blowout occured at the hairpin at the bottom of the decent after baskeet range, on the way out to Lobethal.

Every blowout I have personally seen has been due to the tyre not being fully under the clincher edge when inflated - which is why I now partially inflate and then work my way around the tyre pushing it back/down to ensure the tube isn't pinched and the retaining bead is properly in place. I've only screwed it up once myself, but the front started bulging as the tyre was coming off the rim and I worked out what it was before it blew.

Thanks Mr T.
AFAIK the tyre stayed hooked on the rim. I am pretty sensitive to vibrations etc and certainly had no preceeding warnings. I am usually pretty particular when fitting tyres, and always firstly partially inflate the tube as not to pinch it, then fit the tyre, and further partiallly inflate to hook the tyre. after full inflation i always thorughly inspect to ensure proper seating of the tyre.

I'd be tempted to turn that tyre inside out and inspect it for glass filled cuts, and be careful about re-mounting it like Twizzle says - some rims and some tyres are just a bad match. Anything easy to put on (i.e. with generous beading) is always a bit of a worry as when you inflate them, they can ride up the clinch inside without you noticing.

I had one do this the other day - front wheel got bumpier and bumpier as I rode. It didn't blow but it was very unpleasant until remounted at my destination.

(and if it's a gatorskin, they're designed to chew up tubes )

Certainly nothing inside the tyre fouling the tube.

[Dr_Mutley]

Are you using the blue plastic rim tape that came with the wheels? If so, get rid of it and buy some cloth rim tape. It may have no relation to your problem but I can't stand that plastic stuff.

yep

[bunchridefinder]

+1
I replaced the Blue Plastic tape that came with my Shimano wheels (I was having a similar problem) with the cloth type and hav'nt had a problem since.

[Dr_Mutley]

+1
I replaced the Blue Plastic tape that came with my Shimano wheels (I was having a similar problem) with the cloth type and hav'nt had a problem since.

U were having tubes exploding with a noise like a large calibre gun going off??

Hmmmm will have to order some cloth rim tape, when I order a replacement tyre

[bunchridefinder]

+1
I replaced the Blue Plastic tape that came with my Shimano wheels (I was having a similar problem) with the cloth type and hav'nt had a problem since.

U were having tubes exploding with a noise like a large calibre gun going off??

Hmmmm will have to order some cloth rim tape, when I order a replacement tyre

Nah, for me it was a slow flat - which happened every time i used the wheels (racing). Checked the tyres, checked the rims for sharp points, nothing.

Since I've changed the rim strip no flats!

[Dr_Mutley]

+1
I replaced the Blue Plastic tape that came with my Shimano wheels (I was having a similar problem) with the cloth type and hav'nt had a problem since.

U were having tubes exploding with a noise like a large calibre gun going off??

Hmmmm will have to order some cloth rim tape, when I order a replacement tyre

Nah, for me it was a slow flat - which happened every time i used the wheels (racing). Checked the tyres, checked the rims for sharp points, nothing.

Since I've changed the rim strip no flats!

ahhh thanks for the clarification BRF.... seems different to what ive experienced then. I havent had any such pinch or penetrative flats or the like from the rim tape, but will certainly replace the strips anyway now i know this is likely to be a problem at some point.... cheers....

[Mikka]

A quick comment .. intended as helpful. For a 90kg rider .. I'd consider those tubes underinflated. Pressures should be dictated by riding weight. I've found my tyres wear quite differently now I adjust the pressures as per this article. They also handle impacts differently ... Maybe this will help somehow... Tyre Pressures and Tire Drop ..

[alex]

This blowout occurred not long after climbing lofty, and then on the fast downhill section thru picadilly and on the way thru under the freeway at Mt Barker. First blowout occured at the hairpin at the bottom of the decent after baskeet range, on the way out to Lobethal.

yep i know it, its not really a long enough descent to overheat a rim i wouldnt think though it is quite fast! (and fun)

[trailgumby]

Do they have an alloy or carbon brake track? If alloy, does it contact the tube? Did the tube failure occur in the same location relative to the valve, or somewhere different?

I'm thinking that the rims being carbon are perhaps not giving the alloy clincher sectoin in contact with the tube much assistance to dissipate the heat. Consequently the temperature rise is a lot more sudden than would otherwise be the case.

If they are full carbon, including bead track, disregard the above: I'd be looking for a protruding sharp object, or a crack.

My understanding of the conventional wisdom for rim brakes is that you shouldn't ride them. Better to let the bike run a bit, and then apply them with a good effort. Rinse and repeat to allow them cooling time between brake applications. (I use discs, so less of an issue for me.)

You may laready be doing this: mount your tures with the sidewall logo next to the valve. This helps you identify where any offending object might be hiding in your tyre when you next have a puncture.

[fixie]

I have been following this thread and also another here on this forum. I have given it much thought without much insight or resolution.

Tubes exploding on rims seems to be a periodically reported phenomenon. It has happened a lot on Tandems during alpine descents in Europe where the Alps are.

Generally for a tube to explode some of the tube must be unsupported, ie outside the tyre rim containing space.

This normally happens when the tyre is not correctly seated so that the hook can do its job of providing a radial restraint to the casing. If there is even the smallest gap, the tube will find it and explode. The problem is made more difficult because while rims are accurately made, tyres are not. If the tyre is so loose on the rims that the bead is not below the hook all of the way round, failure is inevitable. That explains why the gentleman with the Bontrager tyre had no problems until he changed brands. Il Padrone recognised the same problem and has sensibly chosen to offload the oversize tyre. The other issue that can happen even if the tyre is a tight fit. Even if the tyre is a tight fit and very difficult to get onto the rim, it is imperative that it be seated correctly if the tube is not to explode.

Exploding tubes were a phenomenon before hooked rims were invented. They commonly happened with Tandems due to overheating on long descents. On these rims what I believe happens is that the pressure in the tyre rises in accordance with Boyle's law (PV = RT) and eventually the pressure is sufficient to stretch the bead enough to allow a small gap above or close to the edge of the rim. On nonhook rim tyres the bead is an essential part of the tyre retaining mechanism. There are not the same clinching forces and because the inside of the rim is not angled inwards, but is angled slightly outwards, it is easy for the tyre to try and slip off.

In summary: It may be incorrect assembly and it may be poor tyres. specifically tyre fit. It may be brand related or just model related. I have been personally fortunate but when I discovered that my Rubino Pros 23 measured 25 and that I could take them off the rim without a tyre lever, I have been very circumspect. So far no problems.

Here is a link to a CTC Technical page where there is discussion of similar problems.

[petal665]

I have been personally fortunate but when I discovered that my Rubino Pros 23 measured 25 and that I could take them off the rim without a tyre lever, I have been very circumspect.

I can take all my tires off the rim without tire levers, apart from on my Neutrons, they even require levers to get them back on.

[Dr_Mutley]

hi all... thanks for all the replies... will go thru and consider them tomorrow...

just thought i would throw up some pics tonite....


Some pics of the first blowout... the split in the tube measures about 160mm.
For reference purpposes, the valve is 80mm






Some pics of the brake alignment and pads. The are set a little high, but still well clear of the tire etc...













Example of the tire well seated on the rim, which is consitent all the way around, both sides




SOme pics of the looseness of the tyre on the rim. These can be removed, and reinstalled without tire levers. They however seat well on the rim

[petal665]

Maybe you should just give me the 7850 C50's and buy yourself the RS80 C50 clinchers when they come out.

[twizzle]

Ditch the tyres. Try Michelin - I find them an absolute pr-ck to R & R on all of my rims.

FWIW, in regards to people blowing off tyres under braking, it's all about the quantity of water in the air in the tyres. When moist air gets really hot, the pressure increase can be enormous. But carbon fibre is an interesting beast - it's not a good conductor of heat, which is why you need special brake pads to deal with it, so descending on carbon is safer than on an alloy rim.

[petal665]

FWIW, in regards to people blowing off tyres under braking, it's all about the quantity of water in the air in the tyres. When moist air gets really hot, the pressure increase can be enormous.

You are talking about the air (not just the rim surface) heating up to over 100°C. I don't think that happens.

[twizzle]

FWIW, in regards to people blowing off tyres under braking, it's all about the quantity of water in the air in the tyres. When moist air gets really hot, the pressure increase can be enormous.

You are talking about the air (not just the rim surface) heating up to over 100°C. I don't think that happens.

Water vapour exists down to about -40C, but starts to rise noticeably after 0C. If you have water in the tubes (pumped up with high humidity on a warm day or used a compressor without a water trap) you can get big increases in pressure as the vapour displaces air. The conversion factor is 1650:1, ie. 1ml of water will make 1650ml of water vapour. The effect tops out at 100C.

To quote Jobst Brandt :

The high temperature blow-off seems to be a combination of effects
that include primarily increased pressure from heating and the
softening and slipperiness of the tire bead that heat causes. In any
case, enough tandem riders have overheated tires that exploded off the
rim, that it is a known phenomenon. Because we don't know the
temperature of the air in the tire that exploded, we can't make an
estimate of the pressure. One thing is certain from my experience and
measurements I have made, is that the rim gets hotter than 120 deg C
and that steam can be generated from water inside a hollow rim. I
don't know how hot a tandem rim gets.

[petal665]

1ml of water makes 1650ml of water vapour at 0kPag, not 110psig (758kPag).

Additionally, if you take air at 27°C and 90% relative humidity and compress it to 110psig, it gets hot.
When you cool it down to 27°C again you get liquid water forming.
At the same volume (your tire) and constant pressure you need to heat the air in the tire back up to 64°C to vapourise all the water.
Once this has happened, any increase in temperature will increase the pressure.

The question is, how hot does the air in your tires get and at what pressure does your tire blow off?