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I have noticed that the seat stay eyelet for my rack has developed a crack. I'm not sure if this is just in the veneer or if it's cracked the actual carbon fibre too. I only installed the rack a few days ago so I'm wondering if I may have overtightened the screw.

enter image description here

Does anyone know if this means my frame is toast?

Cheers!

For reference, here is the undamaged seatstay:

enter image description here

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  • Can you post a photograph of the other side for comparison? It looks like the screw is pulling out from the frame, and if it is I'd think that's a bad sign.
    – Andrew Henle
    Commented Jul 12 at 11:24
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    Hi thanks for your reply. Here is a pic of the other side. It also seems to be jutting out a bit so I'm not sure how normal that is imgur.com/a/jayrmru
    – Harry
    Commented Jul 12 at 11:33
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    Suggest you remove the rack completely. If any chips fall off, look and see if they're carbon or metal or paint flakes. If its anything except paint, stop using this rack on this bike.
    – Criggie ♦
    Commented Jul 12 at 11:58
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    @Criggie the rack was a later fitment and the frame is 4 years old now. I have emailed BH asking about warranty/repair options but I'm not getting my hopes up. Also waiting to hear back from a carbon repair workshop to see my options
    – Harry
    Commented Jul 12 at 12:37
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    How much weight have you been putting on the rack?
    – Paul H
    Commented Jul 12 at 18:29

1 Answer 1

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Every place you thread a screw into a carbon frame, they bonded an aluminum insert in. It looks like the carbon surrounding the insert has cracked and the insert is pulling out of the frame. That is, it's not just a crack in the paint or clear coat.

While we're on the subject of damage in general, you need a torque wrench. However, I'm not saying you over-torqued the bolt. This looks more like the rack pulling the insert out, and it isn't really the sort of damage I'd expect a well-manufactured frame to have. I would seek a warranty replacement if available.

If not, you could seek a carbon repair expert's opinion. They'll probably render one for free anyway, so you could start there.

If not economically repairable, ask the repairer if you could ride the frame without the rack and monitor if the crack propagates. The crack may not extend to the load-bearing part of the structure, and it might not propagate into that area. I'd obviously not be happy with this, and you will be without the rack that you obviously wanted. Also, you would do this at your own risk. That said, if your seatstay cracks, you can still ride the bike home. If that were your fork and it cracked, that would be instant loss of control.

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    Overtightening the mounting screw shouldn't affect the carbon fiber at all - I'd think that would just put a compressive force on the insert itself. The only way I could see overtightening itself causing cracking in the carbon fiber matrix is if the compressive force were enough to significantly distort the insert. But that doesn't rule out twisting or sideways forces on the insert by the tightening operation from cracking the carbon fiber matrix. Given the way the side of the insert-supporting bulge in the seat stay is cracked outward, I suspect a sideways force on the mount is the cause.
    – Andrew Henle
    Commented Jul 12 at 16:31
  • most carbon forks that have eyelets for racks have a pretty (IMHO) restrictive weight limit on them. I'd wager the same could be said about rear racks (I'm front-basket kind of guy, so I'm not sure)
    – Paul H
    Commented Jul 12 at 18:29
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    FWIW some carbon frames, including contemporary ones, do have rivnuts that are installed the "normal" way, by compression with a rivnut tool, no glue.
    – Nathan Knutson
    Commented Jul 14 at 6:52
  • Carbon doesn't bend well. In fact it can be quite brittle when overstressed. What I see is an insert that has been put under too much torque and compressed the carbon fiber and caused the initial crack down the side of the insert, and that continued around the insert until you get what you have. Left unrepaired you may have a serious issue in the future.
    – some dumb guy
    Commented Jul 14 at 14:55
  • @NathanKnutson To me it actually does look like a rivnut setup. In the first pic you can kinda see the ridges around the outside.
    – MaplePanda
    Commented Jul 17 at 5:22

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