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Today I was clumsy and managed to hit my carbon fork against a fence while lifting the bike over it. There's just a tiny ding, almost not visible without a magnifier and superficial scuffs around it. Although I try to avoid things like this, I mean it's practically not possible to never get a scratch or anything inside a carbon frame or fork, right?

So when do you need to worry and ask your LBS for further diagnosis? I mean in this case I honestly would feel stupid to ask, but nevertheless I'm concerned a little. How do you handle things like this?

magnified scratch tiny scratch/indentation

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    Does this answer your question? What do I do when I am unsure if damaged carbon fiber is safe to use or needs replacing or repairing?
    – mattnz
    Commented Jun 10, 2023 at 21:15
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    In a way, it does. But the devil is still in the details. How to decide if damage should be observed or possibly even professionally assessed? In my case, the fork hit a wooden fence, so suffered a blunt impact. But visible damage is minimal. How are you supposed to know whether internal layers of carbon have not been damaged? Personally, this material just gives me a headache. Quote from the article: Damage to carbon items is frequently not visible at the surface. However, an impact, even a fairly soft one, might lead to a delamination below the surface that later grows into a larger failure.
    – conste
    Commented Jun 10, 2023 at 21:37
  • Carbon fiber is black. So that's the color you're going to see in damage.
    – Therac
    Commented Jun 11, 2023 at 11:52
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    @conste - Given liability law in most countries, does anyone honestly think a bike part manufacturer will risk selling something so fragile a light knock on a fence post will do enough damage kill someone? My advice is if you think carbon is that fragile, buy an alloy bike and some cotton wool. A large part of any manufacturers social license to operate is they don't kill their customers.
    – mattnz
    Commented Jun 11, 2023 at 19:27

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Although one cannot make a definitive judgement based off a few photos, I think in this case it is exceedingly safe to say that this damage is not a problem. Scraping your bike against a fence is unlikely to deliver enough energy to risk damage, and the scratch is very shallow anyways. It's barely made it through the paint layer--the primer is still there. Rest assured that your fork is strong enough to handle a lot more than that. Hospitals would be filled with cyclists if a 2mm scratch was enough to fatally wound their bikes.

Also, I question the ability of the average LBS to evaluate carbon for damage. They might have more experience than the customer, but ultimately without X-rays, ultrasound, etc they can't say for sure either.

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  • This underscores how I interpreted this damage and wanted to treat it. Basically in a way of doing nothing except checking it every once in a while. I just find it irritating that there is so much panic and confusion about carbon fiber damage. Like I said, I think things like this just can't be prevented on a day to day basis so I would feel weird asking a mechanic about it. I just always slightly wonder if the impact that caused the scratch could have left internal damage as well. With carbon fiber, you just never really know.
    – conste
    Commented Jun 11, 2023 at 13:29
  • @conste A lot of it is indeed just panic and confusion. I'd like to repeat my catchphrase: "carbon fiber is not a high explosive". Yeah, you gotta treat it with some level of respect, but it's not like a porcelain dish that'll shatter the second you look at it wrong. From my understanding, barring freak accidents, you have to reach a certain impact force threshold in order to risk delamination. Scratching your bike hardly even counts as an impact. And yeah, the uncertainty is there, but that's kinda just the nature of freakishly lightweight, high-performance mechanical parts.
    – MaplePanda
    Commented Jun 12, 2023 at 0:05
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Could asking the manufacturer be an option here? They do test their forks for things like this, right? Could they provide details about what kinds of forces and impacts, outside normal use, is the fork designed to whitstand?

I believe, in engineering, products often get tested for situations outside normal use. And there should always be a safety margin. A fork that puts the rider's life in danger after being scratched a little should not be allowed to be on the market.

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  • I have not tried this, but I suspect mainstream manufacturers do not have the necessary equipment. Most manufacturers have their bikes made overseas, with QC probably done on the factory floor. I doubt they have the ultrasound equipment to detect delaminations. No harm asking, naturally.
    – Weiwen Ng
    Commented Jun 11, 2023 at 12:18

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