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Old 07-25-07, 09:29 PM   #1
russell88
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Pavement vs. Carbon Fiber Fork?

I know this question has been asked many times, but I've yet to find my exact situation. Today I layed my road bike down on its side at what I estimate was about 10-12 mph. I have a carbon fiber fork, and I've heard the horror stories about catastrophic failures of damaged CF. I'm not sure exactly what component impacted the ground. However, I cannot spot any damage whatsoever to the fork. No cracks or paint chips whatsoever, and I was clipped in so my upper leg and hip absorbed most of the impact. I've gone over the bike pretty thoroughly, and the only noticeable damage was that the impact knocked the brake hood at an angle (quick fix). I tried the tap test on the fork, but I really don't know what to look for. So here is my question:

- What is the likelihood that, with no visible damage to fork, front tire, spokes or rim, that the carbon fiber was in fact damaged in the crash?

- If it is unlikely that there is any damage, should I keep the fork and ride it anyway?

I'll be taking it in to the shop that sold it to me to have it checked out when I can find the time, just trying to find out what I'm in for (college student so my budget is tight)

Thanks for any help
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Old 07-25-07, 10:17 PM   #2
baiskeli
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I'd have it checked out by a competent bike shop (which it sounds like you are already doing)but chances are that it is fine. Carbon fiber is not as delicate as people make it out to be (I have a Carbon fiber fork and once laid the bike down at 17 MPH, cracking my wrist and getting some serious road rash. I did have a shop check it out and it was fine). In that crash my hand, hip, shoulder and helmet took the brunt of the impact.

In total I've had that same fork for about 7 years (Reynolds Ouzo Pro) and its been on two frames and through 3 crashes (one sort of serious and 2 minor ones).
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Old 07-26-07, 06:32 AM   #3
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It's probably fine if you don't see cracks or chips, but if you're worried, have a shop look it over.
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Old 07-26-07, 06:38 AM   #4
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My feeling on carbon fiber is that it is for racing, good for a one time use, and should be replaced after a crash. Visable damge or not. The way that it fails is SO catastrophic that it is too much a risk to reuse it.
Keep in mine if it were to fail, it would be under high load ( fast descent, hard braking, hard cornering), and it would fail in an instant with no warning.
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Old 07-26-07, 07:08 AM   #5
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Quote:
Originally Posted by russell88 View Post

- What is the likelihood that, with no visible damage to fork, front tire, spokes or rim, that the carbon fiber was in fact damaged in the crash?

- If it is unlikely that there is any damage, should I keep the fork and ride it anyway?

I'll be taking it in to the shop that sold it to me to have it checked out when I can find the time, just trying to find out what I'm in for (college student so my budget is tight)

Thanks for any help
I've worked with carbon fiber composites, I've tested them in the lab, etc. I would not ride on a CF fork that's impacted the ground. No way.

The problem is that the stresses in that kind of material aren't always visible, so eyeballing it won't work. Tap test won't really work either - finding stresses in CF materials require much more sophisiticated equipment than that.

And as you've heard, when CF fails, it's often catastrophic (ie, road-eating) failure.

I'd say, given the distribution of damage (hip and brake hood), there's probably a very good chance that the fork is fine. The only problem is that if the thing fails, you could end up shopping for Polident with the over-60 crowd.

If it were me, it would annoy the hell out of me since the thing is probably fine, but I don't think I'd ride it if there's even a scratch on it. The only way I'd keep it is if I could convince myself that it didn't take *any* impact at all - in other words, if you slid a bit and all the parts that hit the ground have road rash but the fork, tire, and rim are all fine, then I might be reasonably certain that it's untouched. Even then, if I could get a decent fork at a good price, I might swap out just for the peace of mind.

On a similar note, I wouldn't buy a used CF fork.
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Old 07-26-07, 07:58 AM   #6
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I've mentioned before that I have had steel and aluminum parts fail in the same instantaneous manner that posters on these forums often suggest is unique to carbon parts. I've had an over-fatigued steel frame sheer completely in half when I stood to climb, no warning, in less than a second.

I'm still using a CF mountain bike handlebar that I've crashed repeatedly on over eight years. It might fail. But it can't fail any faster than the aluminum one that I snapped off some years ago.

So yes, it *might* fail instantly and hurt you. But so might everything else.

I'd just ride it.
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Old 07-26-07, 08:02 AM   #7
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If a carbon fork fails while riding, it is likely to fail instantly. Carbon does not bend when a tube fails, it snaps like a pretzel...not good.

Before you ride the bike again, get it out in bright sunlight. Get a magnifying glass, and look over the fork inch by inch. Look for hairline cracks, deep scratches or gouges. Then, take the bike to the dealer, and have the dealer inspect the fork.

If you or the dealer find hairline cracks, deep scratches or gouges, the fork should be replaced. Consider an "upgrade" to a steel fork. If you damage a steel fork in a crash, usually the dealer can re-align it, and you are good to go.
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Old 07-26-07, 08:22 AM   #8
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I've mentioned before that I have had steel and aluminum parts fail in the same instantaneous manner that posters on these forums often suggest is unique to carbon parts. ...
I have had three cranks fail, one (1970 aluminum Sugino Mighty Compe) in a potentially catastrophic manner. I have heard of numerous potentially dangerous chain link separations, though I have never experienced one personally. I have broken two otherwise undamaged steel frames, but neither event was safety-related. I have read the familiar cautionary tales of Viscount "forks of death" and aluminum AVA "stems of death." I have broken two rear axles, one solid and one quick-release, but again without concern for my safety.

However, the prospect of fork failure, be it steerer tube separation or abrupt blade failure, scares me enough that I personally choose not to ride carbon fiber forks and that I advocate careful and frequent safety inspections of all forks.
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Old 07-26-07, 08:42 AM   #9
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I have to say that I've tried to brake a basic carbon fork before. We had it off the bike (it was being replaced because the owner saw some cracking in the clear coat) and we threw it as hard as we could at the ground, jumped on it to bend the legs in and tried to pull the legs apart. Stuff that would have destroyed a steel fork (although in a much less catastrophic way). Eventually we clamped it in a vice and took turns swinging at it with our 4' steel leverage bar until one of the legs snapped off.

After that I'll have to say that I generally have more trust in carbon. I've never trusted anything designed for racing (steel, Al or carbon) so I wouldn't recommend commuting on a $3000 carbon bike (racing stuff isn't designed to handle daily use for long periods of time (years)), but I wouldn't have a problem using some more utilitarian carbon stuff. Just keep an eye on it like you would any other parts. Always take any paint cracks or deep scratches seriously regardless of the material and always closely inspect every part of your bike after a crash.
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Old 07-26-07, 04:01 PM   #10
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It's rather unlikely that the fork hit anything if you just "fell". If the bike falls on a substantially flat surface, its next to impossible for the fork blades to suffer an impact. This is probably why you don't see any marks.

Is the fork "full carbon" or does it have a metal steer tube? If your handlebars suffered obvious serious impact, there is the possibility that the steerer was over stressed at the stem-headtube area. If it's a carbon steer tube, this is obviously not good!

It is quite likely that your fork is undamaged, but I would recommend that you inspect it, or have a reputable shop check it out and explain the circumstances to them.

Good luck,

Ed
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