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Wheel scratched carbon seat tube

Hi everyone,

Recently my wheel scratched my carbon seat tube as it loosened at the end of my ride. Was wondering if it is safe to ride.

Imgur has 4 images, 2 are below link

Thanks in advance!

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    How did the wheel come loose at the end of the ride? That's a separate problem to be fixed.
    – Criggie ♦
    Commented Apr 14 at 22:34
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    Worth a read: bicycles.stackexchange.com/questions/76022/…
    – mattnz
    Commented Apr 15 at 0:36
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    @Criggie, I assume the rear axle was not bolted in completely. The ride was ~140km and I had shifting issues for the entire ride but didn't think much of it. Literally 200m from my house, at the last corner, the rear axle bolt loosened. Assume it was simply due to vibrations
    – xigoL
    Commented Apr 15 at 9:14

2 Answers 2

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I don't see any frayed carbon fibers, nor any cracks propagating from the worn area. I've raced on a bike with much worse tire rub on its seat stay - again, with no frayed carbon fibers or cracks - and I was 90+ kg and I'd routinely hit 1800W in sprints.

Any loss in strength from wearing off any of the matrix - if you even did wear any of it off - should negligible.

Assuming this is a road bike and not something like a downhill bike or otherwise subjected to extra stresses, just paint it with some clear nail polish or similar to seal it, check it for cracks regularly, and ride on.

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    In the first photo I think you can see an exposed or even abraded carbon layer.
    – Michael
    Commented Apr 15 at 6:01
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For reference, this answer offers general guidance on what to do if you're not sure if a carbon frame is cracked. That answer contains some photographs of abrasion damage from the infamously muddy 2023 Unbound Gravel race. In that race, people got routed through some extremely muddy sections. By the end of the race, some people had the mud abrade through many layers of their carbon frames.

In this case, I'm not 100% certain from the photos, but one option is watchful waiting, as generally recommended in the answer. I would consider this to be something like a small dent on a light but not super-light metal frame. That would be elevated concern, but not enough to scrap the frame. It looks like a few layers of carbon got abraded through. It also looks like this may be a seatstay, and I believe those take relatively little load. If it's a chainstay, there's more force transmitted through it, so I would be more watchful and I would try to consult a carbon repair expert. This obviously isn't as bad as the damage some bikes took at Unbound, but because carbon derives its strength from all the layers being present, it bears watching.

I don't honestly know for sure what to look out for. Cracks propagating from the abrasion would be one, and this is what I'd look for on a metal bike, but carbon may not fail the same way. You can also gently squeeze the carbon structure around the abrasion. It should be solid. If it starts to give way, stop and find a carbon repair expert.

Note that ultralight carbon frames should probably not be squeezed like this. This isn't the case here, I'm talking about frames that have warnings not to sit on the top tube.

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  • It is indeed the seatstay. What would you advice watching out for, when testing through time. Softness in the seatstay, or bending or something else?
    – xigoL
    Commented Apr 15 at 9:19
  • @xigoL check for cracks developing. Also, when you very lightly squeeze a carbon tube, it’s rigid. If it’s cracked internally, you’ll perceive some movement. The structure might lose rigidity. Those are potential checks. You could also consider asking a carbon repairer to take a look, if you have one local.
    – Weiwen Ng
    Commented Apr 15 at 19:20

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