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PostPosted: Mon Sep 12, 2011 7:01 am 
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Joined: Thu Apr 01, 2010 10:24 am
Posts: 595
I know this has been round the forums a couple of times before.

My brother was using Corima Aero carbon clinchers on our recent trip to Mt Ventoux. On the first descent of the holiday he got half way down and realised the braking was pulsing like hell. We stopped and I checked the brake tracks but couldn't see anything obvious to the human eye as they were a bit grabby. They pulsed a little bit before anyway (as most carbon wheels do). We kept on going - hitting over 90 kph on the next section down. We stopped again and checked it out - It was an 'oh sh*t' moment when I discovered that the rim had melted and totally warped and the tyre was barely hanging on!
If that had gone when we were hammering down the climb, my brother would have had a face full of tarmac. Anyway needless to say, the wheel is trashed - it was the rear one and the front is fine. We went to the bike shop in Malaucene and they replaced it there and then with a Mavic Aksium for a great price - so we were very lucky. He also gave us some replacement pads for the front wheel as he said they're less likely to build up so much heat. We were using Swisstop yellows before-hand.
My Zipp 404s were absolutely fine and performed very well with no problems. I'd like to add also that me and my brother are confident at descending - we are not on the brakes all the time and use our brakes properly.

Coincidentally, I had a hunch before the holiday that we shouldn't try descending on carbon clinchers, and that we should use a different wheelset for that - as I was already aware of the potential problems they have. However we didn't get our act together in time and we just hoped they'd be okay, as we have descended with those wheels on Ventoux once before.

Learn from our mistake guys, please be careful!


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PostPosted: Mon Sep 12, 2011 8:07 am 
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Joined: Sat Jul 24, 2010 9:41 pm
Posts: 28
It's more a function of how you ride, not the wheelset. I can ride down 7-8% grades all day long and control my speed by sitting up in the wind, only braking for a moment into corners. I find it difficult to believe you generated high enough temps to melt the epoxy and weren't dragging the brakes. I believe epoxy resin has a melting point somewhere around 200C or 400F, that's pizza cooking temps.


Last edited by OnTheRivet on Mon Sep 12, 2011 8:16 am, edited 1 time in total.

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PostPosted: Mon Sep 12, 2011 8:15 am 
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Posts: 1048
You were lucky. If I had a Euro for every puncture I've seen on Zipp 404's riding Alpine descents I'd be a very wealthy man indeed.

Just leave the deep section stuff at home - or ride tubs.


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PostPosted: Mon Sep 12, 2011 8:32 am 
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Posts: 595
On Ventoux there are a lot of cars and they're slow compared to bikes. You have to brake for them until it is safe to overtake - I'm sure that might've contributed. Other than that, we were hardly on the brakes at all except braking for the hairpins and tighter bends.

My Zipp 404s are tubs, so they were fine - like I said - sorry I forgot to mention they were tubulars.

Anyway, I am never going to buy or recommend them again. Carbon clinchers are rubbish anyway even if they don't melt - they weight a ton and all the ones I've tried feel dead on the road. But that's just my opinion.


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PostPosted: Mon Sep 12, 2011 9:31 am 
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Very strange that the rear one would melt before the front one though, it gets only a fraction of the breaking force, for the balance point moving forward when braking, all the more on a descent.

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PostPosted: Mon Sep 12, 2011 10:33 am 
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Location: Denmark
The Corimas are an old construction. (good rims, though) But their heat management is not on current standards. The best new Carbon Clincher rims like LW, Zipp, ENVE are much more resistant to heat than older models.
Also, IME, the SwissStop pads are not up to par with other offerings. I can easily feel the difference from eg. the ENVE pads on both my LW's and ENVE wheels I have. The rims are considerably less hot with those pads, compared to the SwissStop. (better modulation as well, but that's an other case)


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PostPosted: Mon Sep 12, 2011 1:00 pm 
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Location: Melbourne,Australia
Carbon Clinchers are fine for decending but not on these type of slopes, u also need to make sure ur not dragging the brakes and just come off and on allowing the rim to cool

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PostPosted: Mon Sep 12, 2011 1:20 pm 
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Location: Slovenia---that forest land
i ride every day my reynolds strike 2011.
even 10% descents with hard corners they survived. breaking is much better than on Zonda wheels with duraace rubber pads. On reynolds i am useing oriinal blue reynolds pads. swiss stop sucks! Breaking surface is after around 5k km still as new. I ride them on atack/force inflitated 9,5bars.

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PostPosted: Mon Sep 12, 2011 1:46 pm 
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Location: Aix en Provence
I would never ride any carbon clincher. No way down Ventoux. And BTW, you are not supposed to use swissstop yellow on Corima, only cork.

Glad your brother is OK.


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PostPosted: Mon Sep 12, 2011 2:05 pm 
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Posts: 595
Well to start off I'm very glad most of you other guys are having far better experiences. I can now see why people still bother to manufacture and market carbon clinchers.
Also thanks for your concern for my brother. I think he plans on getting tubs for his next wheelset anyway.
Just a mistake on our part really in several ways and we learnt the hard way!


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PostPosted: Mon Sep 12, 2011 3:12 pm 
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Posts: 813
Location: NYC
wassertreter wrote:
Very strange that the rear one would melt before the front one though, it gets only a fraction of the breaking force, for the balance point moving forward when braking, all the more on a descent.



+1...very strong evidence that he was riding his brakes down the slope, using the rear as a drag brake. Whenever I see these sort of missives I have to wonder who really is at fault: rider or equipment?
EM3

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PostPosted: Mon Sep 12, 2011 3:25 pm 
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Location: London
I agree.

Maybe the rear brake was set up real close to the rim. (or maybe the brake got twisted round). Rider could then have been inadvertently riding the back brake by just resting fingers on the levers.

Either way. It seems astronomically unlikely that the rear would overheat before the front unless he was riding the brake.

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PostPosted: Mon Sep 12, 2011 4:28 pm 
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Joined: Thu Mar 26, 2009 2:19 pm
Posts: 86
Sounds to me like your bro is using his rear brake and not his front enough. You should be using the front for about 70% and the rear for 30% these are approximate. Secondly I have descended at speeds upwards of 65-70mph with hard braking and never had over heating issues. Like mentioned earlier use air resistance as this can save you from massive amounts of breaking especially when you would normally build the largest amounts of heat, that being higher speeds say above 50ish. Another thing is to pulse the brakes on long braking stretches normally do 2-3 seconds on 2 seconds off oscillating from front to rear will allow you to stay on the brakes while still slowing. Braking late will also build excessive heat due to higher friction and thermal dissipation properties as carbon is poor compared to aluminum.

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PostPosted: Mon Sep 12, 2011 7:46 pm 
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Location: Brighton, UK
Have you checked that Swissstop Yellow pads are approved to be used with that specific rim?

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PostPosted: Mon Sep 12, 2011 7:52 pm 
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Joined: Sun Oct 05, 2008 8:09 pm
Posts: 1326
Location: Aix en Provence
StradaJon wrote:
Have you checked that Swissstop Yellow pads are approved to be used with that specific rim?

as I said above they are not.


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