Carbon clinchers - warping under extreme braking? Discuss...

epo-aholic

In my never ending quest for a pair of deep section clinchers i was about set on going for carbon clinchers with a carbon clincher if that makes any sense, rather than an aluminium braking service if you follow?

Anyway, just had a short discussion with a well-known wheelbuilder who says he wont touch them until he's satisfied they are safe and not likely to warpi under prolonged braking.

Has anyone seen this or heard this first hand? I feel i need to read up on this a bit before i plunge.........

Cheers

moonshine

From zipp website - I've bought a set of carbon tubs from derek at wheelsmith based on zipps comments on carbon clincher technology available on the Market at present.


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

epo-aholic

moonshine
Very interesting reading.........

cheers

pontarlier_pete

Thanks for that. I've always used clinchers in the mountains as I was worried about tub glue, maybe I've been getting it wrong.

Wappygixer

I've been contemplating carbon wheels for few weeks now.
I cant see carbon clinchers working to well without an alloy braking surface but htis then adds weight.
Now I'm looking at tubs which wont have the same issues with tyre pressures but will still get very hot with braking.
I'm not that fast anymore so the areo effect wont help me any but they do look nice.

moonshine

As far as I know, the issue with carbon clinchers with alu rims is of heat build up on long descents, and the inner tube pops if it comes into contact with the alloy braking surface.

Tubs don't have this problem , but carbon rims generate a lot ofheat and aren't as efficient in dissipating heat( can hey up to 250c ) which can soften glue. The tubes won't pop as they dont ttouch the rim.

Glue softening is only a real issue on alpine length descents tho.

I'll try mine in Majorca in April .

moonshine

And go easy on the brakes!