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I'm new to carbon fiber in general. The other day my fork scraped up on some concrete. I'm not too worried if it's a scratch; however, I am worried if it means the fork is a goner. I've posted a picture of the damage. Also to add, the paint is about 2-3mm thick and I couldn't feel too much of a groove within the actual carbon fiber. It was merely a scratch and if I had to assume at the worst then .5mm deep into the carbon fiber portion.

Thank you for whoever answers!

enter image description here

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    Scratch is definitely through the paint and into the CFC. The question is, is it deep enough to affect the strength?
    – Argenti Apparatus
    Commented Jul 25, 2019 at 15:01
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    Questions like this are why Carbon Frames make me nervous. Saving a couple pounds doesn't make sense if you're always worried about your frame breaking.
    – SurpriseDog
    Commented Jul 26, 2019 at 2:28
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    Is it actually 'paint' or rather a coloured layer of resin intended to protect the carbon?
    – Carel
    Commented Jul 26, 2019 at 9:14
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    Perhaps look into how much a replacement fork is, and weigh that cost against your peace of mind?
    – Andrew Henle
    Commented Jul 26, 2019 at 13:02
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    So the LBS said that I should not worry about it too much. My riding style is not too rough to begin with; however, in a couple of months I will look into buying a new fork -- assuming it is cheaper (or equal) than getting this fork repaired. I have also opened a ticket with the bike manufacturer to see if I can buy a replacement fork from them (or maybe get one free considering it is still under warranty). Lastly, I have also contacted Calfee to get a quote on repairs. I will update with whatever happens. Thank you for everyone who took the time to answer. I greatly appreciate it.
    – Grundlebear
    Commented Jul 26, 2019 at 13:47

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Personally, I'd put some clear (UV stable) epoxy over it and not worry any more about it.

My MTB has a carbon rear triangle and I had a landing go sideways (literally) when the knobs on the rear tire kicked hard left and started grinding through the clear coat and down through the CF. I stopped the bike as quickly as I could, re-aligned the rear wheel and kept riding. I didn't have time to have it repaired before MTB National Championships last year so I raced it just like that and still finished 9th. I then got some quotes and had it repaired by Calfee earlier this year. It looks and feels even stronger than it did prior to the repair.

enter image description here

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    At the rear, maybe. At the front, never. Any breaking is potentially lethal and there will be no warning signs.
    – Carel
    Commented Jul 25, 2019 at 20:39
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    @Carel If the exposed section were any larger or any deeper, I'd agree. As it is though, the underlying CF is barely exposed, much less compromised. All this kerfufle is much ado about nothing and people need to worry a little less over superficial scratches in paint and resin. That gouge from my reply above was raced on a rigid, hardtail singlespeed over the rocks, roots, and trails of Snowshoe, WV and placed me 9th in the National Championships... That's WAY more concerning than what the OP posted.
    – jc allen
    Commented Jul 26, 2019 at 14:45
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I wouldn't pitch the fork just yet until you get a professional assessment at a bike shop. You could gently tap on the fork for several centimeters around the wound and listen for a change in the quality of the tone nearer the scratch. If present I wouldn't ride until a better assessment is completed. That said, neither would I call this little test reason enough for comfort if nothing was heard.

Here's an interesting trick I recently read about. Apparently, helicopter mechanics use this technique to fill/repair chips in rotor blades. If one takes liquid cyanoacrylate glue ("super glue," "Krazy glue," etc.) Fills the basin of a scratch or chip and then immediately sprinkles a generous coating of baking SODA onto the wet glue, it dries and hardens in seconds. The resulting dried cyanoacrylate-baking soda filler is extremely hard, sandable and paintable.

I've used this trick when I want a super glue application to be dry almost immeadiately. An improvised chain tool pin I fashioned from a screw tip bit has been held securely within the threaded pusher of the tool. Still solid after a half-dozen chain breaks

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  • Does it make any difference that rotor blades are subject to tensile load, while fork works under compression (I may be wrong and a bicycle fork works under tensile forces, too, please correct me if I am wrong)?
    – EarlGrey
    Commented Jul 26, 2019 at 9:58
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    Bicycle forks and frames are under both TENSILE (stretching force) and COMPRESSIVE (squeezing force) forces. The load through different areas of the fork vary from tensile to compressive forces. Either way, laminate carbon fiber has an ultimate tensile strength of 1600MPa (mega-Pascals) whereas acrylic is <100MPa so the repair is still likely to be the weak point.
    – Jeff
    Commented Jul 26, 2019 at 11:07

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