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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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.
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.