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Yesterday I saw something like a crack in the carbon fork of my roadbike. Now I don't have any clue if this is a really a crack or just the paint. Maybe someone can help me or tell me how to find out. Thanks! Fork Fork2

EDIT: Thanks again for all your answers. I took the bike to my dealer, he communicated it to the TREK warranty department and I got a brand new fork. No bigger problems, just some e-mails and pictures (from the dealer, he also sent the broken fork in). Thumbs up TREK!

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    Second photo looks like a scratch, top photo looks like a crack. Did you crash at any time? Do you park it in a shared rack ? ie, is there a probable cause ? – Criggie May 31 '18 at 10:28
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    No Crash, nothing like that. I even do not lean it somewhere where it does not stand properly. It was no "rough" tour or something. Just a normal ride. – Obl Tobl May 31 '18 at 10:30
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    Looks suspect anyway. Take it to the place where you bought it or to some qualified Trek retailer. As a preliminary test: remove the wheel and let your index fingernail flick against either fork-leg, listen for the sound. Don't ride until thoroughly checked – Carel May 31 '18 at 11:24
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    Looks to me like a joint between the assembled pieces. Whether it's a problem or not is hard to tell. – Daniel R Hicks May 31 '18 at 12:01
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    Out of curiosity @Carel, what sound are you listening for? On the bright side Obl, replacing a fork is relatively cheap... – Sam May 31 '18 at 15:12
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On the surface it doesn't look good, but I wonder if there is a reinforcement wrap for the brake posts, with an unfinished edge). There are some informal ways to try and confirm whether the structural carbon has been damaged.

'Carbon usually has a very crisp sound to it [when tapped] and when it’s damaged the tone changes completely,' says John Hansell of Yorkshire-based Fibre-Lyte, which offers a full inspection and repair service for carbon frames.

-- How to assess a cracked carbon frame

Others will argue that this is a difficult method, or that it only tends to work when the damage is already very visible. Typically, I would tap with a solid object (e.g., smooth end of a screw driver), with a consistent force. Tapping with your fingers might not work well. There may also be pitch changes where the underlying material has change (e.g., many frames bond aluminum to carbon at places such as drop outs, steer, etc). The tone to listen for is a dull thud.

As suggested by David Richerby you could compare and contrast the sound of the potentially damaged area against the other fork leg (which I assume does not show any signs of damage) to see if are any notable differences in sound when tapped.

Another technique I have been told to try when inspecting used frames was to squeeze in the area around suspected damage. If the carbon feels "softer" it is a sign of structural damage.

None of these techniques are definitive, as it requires you to essentially "read tea leaves" some can do it, some miss signs others pick up on.

The definitive answer would be to scan the carbon (e.g., X-ray) to look for anomalies or damage. This however would likely cost more than the bike is worth and requires access to a skilled technician who can correctly interpret the results. Thermal scanning may be another option in this realm, but I don't know the availability of this technique, or whether it has been validated.

Ultimately, you may need to send the frame into Trek's warranty department and allow them to assess and replace if required, they do have a good warranty department.

  • Thanks for your answer. I tried it with a coin, sounds the same as on the other side of the fork. But I will take it to a Trek dealer to be sure. Maybe it's a warranty case and the fork can be replaced. – Obl Tobl Jun 1 '18 at 8:20
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    @OblTobl in addition to a warranty (which you should qualify for as there is clearly some type of defect) manufacturers will also have a crash replacement policy, where they discount replacement frame/fork. The brands want you to continue riding their wears. – Rider_X Jun 1 '18 at 14:06
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I'm sorry to say that looks like a crack rather than a scratch.

Bike looks quite new (I notice the dual pivot calipers), but I believe Trek's lifetime warranty covers CF frames and forks beyond 5 years anyway.

  • Ok the warranty calms me a little bit. The bike is almost new, not even two years. – Obl Tobl May 31 '18 at 11:49
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    If under 2 years you are definitely good according to the warranty. Just take it back to your Trek LBS and start the process. – Argenti Apparatus May 31 '18 at 11:53
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    Doesnt a warranty, even lifetime, cover only factory damages, not those caused by extensive usage? – 9ilsdx 9rvj 0lo Jun 1 '18 at 10:11

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