Carbon Fork crack

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oilboy123

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Dec 5, 2003
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I have Motobecane Grand Record.
I just noticed what appear to be fine cracks where the fork tubes meet the crown.

Motobecane claims a lifetime warranty. I can't for the life of me get a hold of them or Kenesis (maker of the fork).
No one answers the phone, or my e-mail. That really #@$%! me off.
mad.gif
 
I did this with a set of wheels although I did buy them from a local dealer. Shimano has NO way to contact them on-line to even ask about a warranty. I started going to another bike shop and they offered to send the wheel back to Shimano in CA to have it re-built (I kept breaking spokes, 5 or 6 so far). They took care of the paperwork and got me taken care of, even though the wheel was "technically" out of warranty.

I would definitely pursue it through a local dealer.
 
I did get in contact with a guy at Portland, Oregon Kenesis. He said it could be a glue joint.

I told him I will moving to Salem, Oregon soon. My parents live North of Seattle.
I will drop buy and have them take a look at it when I pass through Portland.
 
1 thing that kills carbon forks is car carriers that have a 1 size fits all fork spacing that stresses the fork beyond it's flexibility. Combined with the stress of going down the road (on the car) the 2 can combine to stress the component. CF is wonderful stuff but isn't always as tough as some people think.
 
Well I rode my bike up the Soledad Mountain in San Diego when I lived their.

The steep way down I did about 55 mph coasting. That is by far the fastest I have ever gone on a bike it was kinda scary.
On a motorcyle or car it seems like nothing.

That would not be a good time for a fork to shear off.........
This was before I saw the reputed crack. I will keep an eye on it.
 
Originally Posted By: wileyE
1 thing that kills carbon forks is car carriers that have a 1 size fits all fork spacing that stresses the fork beyond it's flexibility. Combined with the stress of going down the road (on the car) the 2 can combine to stress the component. CF is wonderful stuff but isn't always as tough as some people think.

???

ALL road forks are spaced 100mm.
carbon is great, but I don't like it in a fork. the cracks may just be in the clearcoat, but who knows? it can't be repaired, just replaced, and no one is going to do a stress analysis on it to find out what is wrong.

I don't like carbon forks.
 
A friend of my has had his all carbon forks break twice while racing. first time was slow and no big deal. the second time was while pushing hard going around a corner. the steerer broke and he went down hard. he had rash on half his face and body.
 
But if the fork mount (actual block) is smaller than the spacing, then, when you tighten the skewer, you could be stressing the fork.
 
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On the History channel show call Shockwave, which "amazing" survival footage. Some guy set a bike speed record but doesn't remember it because his carbon fiber frame snapped at over 100. It took him 5 years to recover.
 
Carbon fiber is an iffy choice of material in critical applications. It was a carbon fiber vertical stabilizer that cracked bringing a plane down in NY shortly after 9/11.
 
Originally Posted By: Kestas
Carbon fiber is an iffy choice of material in critical applications. It was a carbon fiber vertical stabilizer that cracked bringing a plane down in NY shortly after 9/11.


The reason the CF pieces broke was due to PILOT ERROR, not simply because the pieces were made from carbon fiber. Aluminum or steel would likely have failed, too, given what the pilot was doing before that crash.
 
140 km/h. The fork went on the second run. He was on a mountain bike (if we are speaking about the same one). I'm sure that the heat generated by that speed had a lot to do with that fork failure. I don't think that (short of a mtc shock) there is a mtn bike front suspension capable of those kinds of speeds.
 
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I think that one of the problems with CF is that if some level of primary damage occurs that does not result in a failure it is harder to see by just visual inspection. Then, if there is some form of secondary impact it is more likely to simply 'let go' without warning than a metal part would.
 
That's the one. It was an old volcano, worse than sand. They said the reason the head tube broke was from the extra force from the ground leveling out.
 
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