Carbon Clincher Rims

mroli

Right - I know that this is a contentious point, but I thought I would share recent experiences with Carbon Clincher rims. I have just got back from cycling in Croatia and on the 4th day, we climbed up the HC Mt Jura in the Biokovo national park. Conditions were dry and cold - snow at the top and about 8 degrees at the top. No problems going up, but on the way down my mates inner tube blew and he pulled over to a halt sharpish. This is what has happened to his carbon clincher rim:



As you can see, the rim has completely split. this in turn made the inner tube blow. Luckily he was on a straight section of road (as we were going well over 40mph in parts). The rims were non-branded carbon rims, he was using Reynolds blue brake pads and both were fairly new. This happened 4km into a 24km decent (road markings confirmed this) and my mate is an experienced cyclist who has climbed in the Alps and Pyrenees.



I have nothing against carbon rims - I have tubs and clinchers with them, but I would definitely NOT use either for prolonged descents where your rims would heat up. This failure could have had pretty bad consequences and he is lucky they blew where they did. TBH, I'm querying riding them all after seeing this!

Obviously there is going to be some difference between brands etc (for instance another rider had enve clinchers on and got down fine), but his £500 (bought and made in UK) clinchers were not up to the job. We had the fun job of removing his wheels (front and back) and pads and swapping them over to Al rims and pads (Mavic Aksiums) - which were fine for the remaining 20km of descent.

Happy to answer any questions.

drlodge

Glad you were able to swap the wheels over and continue. I'll be keeping by carbon *tubular* and aluminium clincher wheels then.

ugo.santalucia

And the "no brand" brand has to remain secret for the usual Sicilian code of silence in vogue on the forums?

mroli

Only "no brand" because they were not labelled and I do not know where they came from - they were 40mm clinchers and that's all I know. My mate had them built up for him by a wheelbuilder. Will ask him for further details...

Grill

40mm is an odd size, 38mm perhaps? The fact that they're unbranded leads me to believe that they're cheapy Chinese jobbies. Nothing wrong with that except it's unlikely that they have a brake track that's designed to cope with heat.

Carbon clinchers are fine for most (certainly no descents in the UK are going to challenge them), but I stick to tubs for the big stuff.

Monty Dog

There's a reason the likes of P-X don't do carbon clinchers - just hybrid alloy carbon. I've broken enough carbon tubular rims to know there are limits to carbon as a rim material - highly stressed U-sections being one of them.

mercia_man

I've just come back from holiday in France. I rode up Ventoux from Bedoin and saw dozens of other riders. Interestingly, only one had carbon rims. Everyone else, including me, was playing it safe with alloys. Worrying about whether carbon clinchers would melt on the descent would spoil the experience for me.

mfin

mroli wrote:

Conditions were dry and cold - snow at the top and about 8 degrees at the top.

It might have been a temperature problem, I don't know about carbon but aluminium can get affected by low temperatures.

ugo.santalucia

mfin wrote:

It might have been a temperature problem, I don't know about carbon but aluminium can get affected by low temperatures.

Except even those cars fitted aluminium bodywork and engine parts seem to do pretty well over the average Ontario winter, when the temperature drops to -20 to -40 for three months

I don't know where you got this information and it might relate to extreme temperatures, certainly not 8 degrees. Remember airliners, largely made of aluminium alloy, happily fly at -50 C, which is the typical temperature at 35,000 feet.

As for carbon fibre, it's nothing magic, it's a fabric mixed with a resin. The fibre is largely unaffected by temperature, in fact carbon can withstand any temperature you can think of from - 100 and lower to well in excess of a thousand degrees. The resin however is a lot more temperature sensitive, not much on the low side, but rather on the high side. You can take any epoxy thermoset you have at home (a rigid plastic mug, for instance) and stick it in the oven at 200 degrees and see what happens... au contraire, if you put it in the freezer at - 18 none of the mechanical properties is affected

mfin

Sorry you took time to type that Ugo, I know the range of temperatures people cycle in won't affect aluminium or carbon whatsoever!