reif

So I was last week on Tenerife and I did the mandatory climb from coast to Teide caldera(about 40km, 2,2km vertical). I was using my new chinese carbon wheelset (50mm carbon clinchers, for the first time) that I had bought from Miracle trade.

The climb went well but on the way back, pretty soon, like after a few kilometers the rear brake starts to make some noise. I stopped to check the brakes and the wheel and then noticed that there is a bump on the rear rim. Green line indicates where the rim sidewall should be.



I don't think that my braking was excessive but I suppose that the friction heat might have softened that spot and then the tire pressure pushed that part out. Either that or then the wheel is just crap.

So what do you think that my options are? Could this be fixed? Or should I get another rim? Or maybe a non-carbon wheelset? I'm going to contact Miracle Trade but somehow I have a feeling they won't be too cooperative. But I'll report if I can get an answer from them.

jimc101

Light strong cheap pick two, this still hold true.

Would only ever go for branded products like this from a reputable manufacture who can provide aftersales support.

Carbon is not the best material for Clincher rims, Aluminum is still the best material for this application.

For fixing, depends on the rim ERD, if you can find another to swap with that's fine, otherwise probably scrap, doubt Miracle Trade will be too much help, but may be wrong, then there is the shipping cost back to them to think of

reif

I do agree with that now.

I took the tire out and here are two more pictures:



So the damage is actually on both sides. I wonder if this could be partially fixed with heat and pressure? At least I could get some riding before I get a replacement. My local routes are quite flat so there's no prolonged braking in here.

Kimmo 

Man, that's poo. Looks like one part of the rim warmed up and expanded a tad for whatever reason, which then caused a runaway positive feedback cycle, and bam. Massive bulge. At a guess, I'd say the resin of the matrix simply can't stand the heat... or the rim was contaminated during manufacture. I suspect the latter, since I'd expect your front rim should have been getting hotter.

I'd be pushing pretty hard for a replacement.

It'll always be true, cause 'light' is a relative term; what's light these days won't be considered quite so snazzy after another decade of engineering progress. If time machines existed, you could break that rule, except I suspect they'd be horrifically expensive to run...

motobecane69

1. Dont try to fix it yourself
2. BE thankful you didn't get hurt
3. see if they will give you a replacement. I've actually heard of good customer service from some of these asian ebay sellers. I've been using a set of "no name" carbon bars and stem for a few months now with great success. You could have simply gotten a defective rim which can happen from any manufacturer but it certainly is unsettling. There is nothing worse than not feeling confident in your equipment in ANY sport

timg7

The fact that the rim has failed on both sides simultaneously is a bit hard to explain. I assume these are all-carbon rims, including the braking surfaces?

Check the inside edge of the rim-wall and under the rim-tape. Can you see how the material has failed? Is there any sign of cracking or splintering, or is it a smooth plastic deformation?

dabac

Heat shouldn't really be much of a consideration. At least I've never heard of thermoplastics being used to infuse a CF cloth. Prepreg CF might be cured at elevated temperatures, but that's a one-way ticket. All the "normal" laminating resins I can think of have a fairly decent window of allowable temperature range to work in once cured.

reif

Yes, they are.

Here's another close-up:



No cracking, no splintering. To me it just looks like the sidewalls are melted.

timg7

How very odd. The spoke-hole is also distinctly misshapen. Epoxy shouldn't melt, and carbon shouldn't bend (not permanently anyway). Makes me wonder what exactly these wheels are made of.

jeepr

No failures in any other spots on the rim? I am not a carbon expert, but with a failure in one spot I would think a manufacturing problem. Either a bulge in that spot causing it to heat up there, or a spot that didn't get manufactured properly.

Looigi

Just guessing here, but since in on both sides in one spot around the, I'd suspect a problem either with inconsistent mix or curing of the resin... Like at that point they got to the bottom of the pot and it wasn't mixed thoroughly, or there was a cold spot there when cured.

reif

Nope. And the wheel is still 100% true, expect for those blown out sidewalls.

I must admit, I just tried to melt a cut out carbon steerer tube with a lighter(outside, using a respirator). And no, it didn't melt or bend.

himespau 

is that red line in the picture a crack where the sidewall is separating from the bottom part of the rim?

Mr IGH

Just be sure your dental, health and life insurance is current. No, seriously, are you joking? I'd never buy off-brand CF, your post about this rim is all the proof I need.

reif

Not a crack, it is part of rim tape.

furballi

Looks like you've hit the curb with that area.

himespau 

Whoops, guess my eyes weren't quite open yet this morning.

reif

Asphalt was in pretty good condition at the top part of Teide where this happened.

HillRider

Lennard Zinn did a fairly extensive test of new name-brand carbon rims in a recent issue of VeloNews based on previous poor results with braking efficiencey and rim strength under heat loads in the past. He reported the newer rims were much better but he was testing very high-line wheels and carbon specific brake pads.

BCRider

Laminating epoxy resins don't actualy melt and run when very hot but they do get soft and could easily allow this sort of deformation given the pressure in the tires. Chances are there was a slight out of spec bulge at that point to begin with that produced a higher pressure pulse at that point which led to the heating.

If the supplier doesn't come through with a replacement and you want to have a go at fixing it you'll need to clamp the rim between two big plates and warm it slowly and watch for the side walls coming back inwards then allow it to cool fully while clamped.

And no more long or steep hills for these wheels even if the replacement comes through or you manage to re-form the rim.

reif

Thanks for a good answer. This seems like a probable cause for this malfunction.

This was something I was planning to try out if I can't get a replacement for the rim. The malfunction is still far from catastrophic failure so it would seem silly to throw away the wheel just for this.

Yes, this is where I learnt my lesson. Carbon wheels might be otherwise ok but these kind of extended steep descents with lots of braking is just asking for trouble.

FastJake

I was just talking to a buddy this weekend who works for Zipp. He said that because carbon doesn't dissipate heat as well as aluminum, the rims can get very hot during steep descents under heavy braking. You're lucky you didn't blow a tire. I wouldn't have a problem running a Chinese carbon rim, but I would switch to an Al rim for anything mountainous. No carbon rim will dissipate heat like Al, and you still run the risk of blowing/melting tires.

Bianchigirll 

Caveat Emptor! atleast your wheel did not fold over

miamijim

But you could have hit something last week.......

What tire pressure do you run?

furballi

There are indentations/deformations at the top of the left and right rim flanges, about 1" long. Classic sign of impact on a hard object. The pads do not make contact with those areas. Has nothing to do with epoxy glue.