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PostPosted: Mon Oct 05, 2009 3:40 pm 
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Joined: Tue Jul 25, 2006 5:53 pm
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Location: San Jose, CA
Warning: Long post (because I've never seen anybody share this issue and the context needs to be thorough)

This past weekend I participated in Levi's Granfondo and had a wonderful time. Amazing roads, people, support and weather for a terrific ride that took me through parts of California that I would otherwise not have ever seen.

One of the sights I thought I'd never see was my beloved Edge Composite 68 carbon clinchers fail under me while riding. These have been a bomb-proof wheel set since day one. 20/24 spokes, WI hub up front, Powertap in the rear with CX-Ray spokes. An absolute dream. My 88kg's have had nothing but great times on these wheels.

I've learned with these wheels that under heaving braking on steep descents you must exhibit caution. You can't ride the brakes and just think you'll be fine when you get to the bottom. I learned this on a very short and steep 20% descent last fall when I had a latex tube blow out. Yes, I was on the brakes the whole way down and should have known better, but thankfully no harm was done to the wheel or myself. Lesson learned, at least I thought...

Some of the descents of the Granfondo were pretty steep and around blind corners. With being unfamiliar with the roads, I made sure I was cautious. Cautious, but also considerate of the fact that I didn't want to overheat the brakes. I didn't experience any problems over the first 60 miles. The rims weren't squealing nor were the rims overheating.

This all changed as I descended down Meyers Grade Road (photo from http://www.steephill.tv's route preview). The day of the 'fondo was just as perfect as this picture.Image

The descent was made a bit more technical from the 20+mph wind blowing from off the ocean to the right. The signs at the top warn riders that you're about to descend an 18% grade and caution is required. As had been the norm for the descents up until this point, I made sure I descended safely and with the goal of keeping all equipment in tact. To put this is relation to other riders, I was descending just as fast as others with the exception of a former MTB pro who kept bombing past me on descents (I would then pass him on climbs).

Toward the bottom third of this descent I felt a very bad pulsation in the front brake lever. I looked down at the front wheel to see if there was something wrong but there wasn't anything visibly bad. But it was scary to see the fork flexing back and forth under braking; it probably was oscillating at least an inch when I had the front brake applied heavily.

I got to the bottom of the descent and my teammate pulled over a few seconds later to see how I was doing. I spun the front wheel and it got stuck. It wasn't clear to me what happened. I opened the brakes up to let the wheel spin more freely. At this point I saw the issue. Initially it looked like the sidewall of my Rubino Pro had bulged out and was rubbing the break pads (yellow Swiss Stop). But to my surprise it actually was a deformity of the braking area of the rim! I had somehow managed to melt the carbon.

I was able to limp back through the rest of the ride, but took it very slow on corners and was only able to use about 10% of the braking power from the front. When I got home I took the tire off the wheel and noticed the damage was much worse. I thought only one side of the rim had melted. Come to find out it was on both sides. In the picture you'll see how each side of the clincher flares out.

Image

Thankfully I kept the rubber down, but I'll be on the phone with Edge to discuss the details around the failure and what we can do going forward.


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Posted: Mon Oct 05, 2009 3:40 pm 


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PostPosted: Mon Oct 05, 2009 3:56 pm 
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I am not surprised.

Given the amount of heat that braking can bring, something would have to happen eventually.

My guess is the rim(the clincher) beads are or were not formed quite right. And when the pressure built up from the heat, it caused the rim beads to expand outwards to allow for it. It looks like the valve hole is near or right where it happened. If that is the case, the valve area is more reinforced than any other area of the tube. Given this, it would expand with out blowing.

What was the pressure of the tire? I am betting they will ask that question second, after, did you crash and are you hurt?

You are very lucky. I had a tire blow from excessive braking and I went down hard on a 40mph+ hill. It pretty much sucked like you wouldn't believe! lol

Good luck with the warranty of the rim. I hope they take care of it.


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PostPosted: Mon Oct 05, 2009 4:02 pm 
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Location: San Jose, CA
The tires were 25mm Rubino Pro's running around 115 psi. The carbon expansion on the rim is about as far away from the valve hole as possible (valve at 12 o'clock, carbon failure at 5 o'clock). Luckily no crash.


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PostPosted: Mon Oct 05, 2009 4:14 pm 
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Location: Northern California
Thanks for the report. I've got Edge 68 clinchers on my tandem, and if I am not hyper-vigilant careful I will share the same fate.


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PostPosted: Mon Oct 05, 2009 4:18 pm 
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Ok, I couldn't tell if it was the valve hole or a spoke hole.


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PostPosted: Mon Oct 05, 2009 4:25 pm 
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Two things
1) I want to live where you live....
2) Glad you are okay but concerned to hear of your mishap - please let us know what Edge say

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PostPosted: Mon Oct 05, 2009 4:43 pm 
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It's not unusual for any carbon clincher to do this when over inflated and especially when over heated as the heat increases the pressure even more.
I've seen quite a few of these do this, not just Edge but also Reynolds and Corimas.
Good luck with a claim, I suspect they will tell you you over inflated it.

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PostPosted: Mon Oct 05, 2009 4:52 pm 
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legs 11 wrote:
It's not unusual for any carbon clincher to do this when over inflated and especially when over heated as the heat increases the pressure even more.
I've seen quite a few of these do this, not just Edge but also Reynolds and Corimas.

Do you think that carbon rims with an aluminum braking surface are less susceptible to rim melting?


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PostPosted: Mon Oct 05, 2009 4:57 pm 
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Yes, they cerainly are stronger with an alloy brake track, they are often rather heavy though.
With an alloy brake track, you basically have an alloy clincher with a faired in cover.
I do think it's a better option though if you really must have a deep clincher.
That must be a bummer to have a rim breakage like that. :(
Just a few thoughts about this type of faliure, I don't think you should really define it as a rim 'melting' as the material hasn't actually melted......it's just caused by over inflation and the same thing can happen on an overheated alloy rim as well.
The problem comes about when you have say....110psi in there, ride a long technical descent like in the high Alps or somewhere like that and the heating of the rim and inner tube is substantial enough to push the pressure over the safe limit.
We've had the same discussion on the board when the LEW clincher was released a couple of years back, the thicker side walls that LEW devised were intended to minimise this effect by spreading the heat away from the bead bed where the tyre sits.

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Last edited by legs 11 on Mon Oct 05, 2009 5:16 pm, edited 1 time in total.

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PostPosted: Mon Oct 05, 2009 5:04 pm 
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Looks like the heat caused the resin to soften. I had this same arguement with another weenie "engineer wannabe" who insists the epoxies are thermoset and cannot be affected by heat. Whatever...no customer will ever know what is the "terminal" temperature on these carbon parts so it's impossible for you to know how to regulate things like braking, etc.

Carbon fiber is great in certain applications but it still has it's limits for now. Bummer on the rim, hope they replace it for you.


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PostPosted: Mon Oct 05, 2009 5:16 pm 
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Edge has great CS. I'll be curious to see what happens.

Try some Bontrager cork pads- they seem to heat up less than the SS yellows.

I don think horses for courses applies though- you are quite heavy at almost 200 lbs and 20% descents on 68mm carbon clinchers with 20mph gusting cross winds is not my idea of safe, esp when you had similar concerns with brakes overheating in the past.

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PostPosted: Mon Oct 05, 2009 5:26 pm 
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tmanley wrote:
(valve at 12 o'clock, carbon failure at 5 o'clock).


The carbon didn't fail, the rider did. You might think you were taking care of that rim, but you have cooked the crap out of it. Good luck on the warranty.

I just don't get carbon clinchers, such a contradiction in terms. Either get a good race (tubs) wheel or a good training wheel (alloy rim) trying to have both by paying for carbon clinchers, you end up with things like this, the delicacy of carbon and the weight of alloy. Worst of both worlds.


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PostPosted: Mon Oct 05, 2009 5:31 pm 
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Location: Phoenix, AZ
coloclimber wrote:
Edge has great CS. I'll be curious to see what happens.

Try some Bontrager cork pads- they seem to heat up less than the SS yellows.


That doesn't make sense; the heat generated will always be the same. You're converting momentum into heat, and since the brake pad doesn't affect momentum, the heat is the same no matter what pad you use. The only way one pad could "heat up less" than another is if the pad itself were a (significantly) better conductor of heat. Cork pads aren't going to conduct heat any better than Swiss Stop pads.

Maybe your cork pads are not stopping you as quickly, thereby allowing more time for heat to dissipate from the rim and reducing peak temperatures. However, you can get the same effect with Swiss Stop pads--just don't grab the levers as hard.

Cheers,

Jason


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PostPosted: Mon Oct 05, 2009 5:36 pm 
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tmanley wrote:
The tires were 25mm Rubino Pro's ....


A $20 tire on a $2k+ wheelset?? bad tmanley, bad..... :wink:

If you really want to enjoy carbon wheels, I agree with some of the others, get yourself some tubulars.
Hope Edge takes care of you.


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PostPosted: Mon Oct 05, 2009 5:42 pm 
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My thought is the rim beads in that area, and most likely in the rest of rim, are light on material. Which caused heat to build up more. It took less time for it to "cook" than the rest of the rim brake track.


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Posted: Mon Oct 05, 2009 5:42 pm 


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