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Is it safe to ride? Will jb weld fill do the trick?

Seems like this damage was caused by a to wide tire rubbing the frame. I don’t see any fibers exposed to be honest(but I might not know what I’m looking for). Adding closeup’s

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  • Have you put a smaller sized tyre on this bike? Or is the damage continuing? I'd also slap a reminder sticker on saying something like "max tyre size 28mm" or whatever you know fits.
    – Criggie
    Commented Jul 19, 2022 at 22:13
  • 1
    no no, it's not continuing, god forbid. This was not done by me and as far as I know damage was done some time ago - not widening since.
    – Soks
    Commented Jul 19, 2022 at 22:23

4 Answers 4

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I'm not a carbon repair expert, but that looks too deep to diy repair with a bit of filler to me.

If this were my frame i'd send it off to a carbon repair specialist to be checked.

If I were going to attempt a repair myself i'd use something like fiberfix wrap - although this would come at the cost of some tyre clearance.

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  • Thanks. Its 1mm deep
    – Soks
    Commented Jul 19, 2022 at 13:45
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Is this inside the chainstay?

I count 4 to 5 layers abraded through. These look like thin layers, consistent with the many plies of lightweight uni cloth used in bikes these days. (I home build carbon fiber bikes and that's all with dry cloths with much thicker tows.) That's why fibers don't look evident, they're very small -- and also, they've been abraded away as with fine sandpaper, so you wouldn't expect to see something like a busted matchstick.

Fillers won't accomplish anything if this damage matters, except maybe to provide a sacrificial layer for more abrasion.

If it were my bike, and this is all the damage, I'd have zero qualms about removing the parts, taking the finish off about 3-5 cm all around and reinforcing this spot with a layer of 6-9ish oz uni parallel to the stay with some plain weave over the top, tightly wrapped in green stretch cling (Home depot packing department) and poked with a sewing pin to let the excess epoxy drip out. (Backward electrical tape works, but not nearly as well.) I'd put a small extra patch of uni the size of the damage right into that spot as the first layer, then go from there.

But it's not my bike of course, and I have all that stuff on-hand.

I think many "can I ride this damaged carbon" threads are overly cautious, but if this were my bike, I also probably wouldn't ride it without patching it. The research I read on bike frame forces before making mine showed that the forces on a drive-side chainstay are actually mostly opposing tension along the chain line, that is, it bows like a potato chip, axle moving right as the chain yanks when you pedal. (Imagine the chain is a bowstring and the chainstay is a bow.) That means the carbon in the chainstay's job is, on the outside of the stay, compression and on the inside (where you have this damage) tension.

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  • thank you very much. yup it's a chainstay. Damage was done by too wide tire and mud rubbing the rear triangle…I will be fixing this thing but in about two months, I just want some confirmation if this will hold "easy rides", meaning no races until summer ends
    – Soks
    Commented Jul 19, 2022 at 22:15
  • I doubt you'd break it outright, but that's just a guess. You could potentially work that into a crack, I suppose, and then you'd have a bit more of a job to fix it. In my experience breaking carbon fiber parts, they don't just suddenly let go. They announce their increasing decrepitude with unprecedented flexibility, creaks, groans, etc. But I'm a skinny guy who just tours and rides for fun. YMMV.
    – user36575
    Commented Jul 19, 2022 at 23:42
  • Thank you. I have setup a repair with professional repair company. I won’t be risking. They have counted 6 to 7 layers abraded, and said basically same as you, that it would hold for touring rides(my original plan was to keep it during summer, but scratch that) but any serious stress on that area = broken rear triangle. Thay charge me ~120usd for carbon fix + painting and some extra for transport, comparing to the eventuality of getting 'gravel face*' - no brainer :) *when you slow down with your face
    – Soks
    Commented Jul 20, 2022 at 13:31
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This looks like it’s definitely through the paint and into at least one layer of carbon.

I’m surprised you didn’t notice.

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  • It wasn’t me who done the damage. ;/ is this actual carbon-carbon, or resin? I don’t see any fibers, ca glue won’t stick, it’s all smooth and rounded. No cracks etc. anyway I’ve sent email to some repair shops. As far as know this was done some time ago and not worsen since
    – Soks
    Commented Jul 19, 2022 at 14:39
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I got the frame back some week ago. Perfect job by the repair shop. Not even a scratch left in the place of those massive damage marks.

They charged me 280USD (converted from my local currency) for repair, stripping and building back bike and for the paint job. Very pleased by how it ended up!

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  • 1
    Thank you for the follow-up and closure. Did you paint it to match ? What size tyres are you running now - 25mm?
    – Criggie
    Commented Aug 29, 2022 at 22:09
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    it was painted by the repair shop to match the original paint. 38c
    – Soks
    Commented Aug 31, 2022 at 9:34

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