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I just want to share a recent observation, but I have to pose it as a question.

A person showed me an FSA Gossamer 30mm hollow crank spindle broken into 2 parts. The break looked almost as good as a machined cut from a lathe. He explained that his frame has internal routing of the gear cables, and that having changed the rear gear cable some time ago, eventually the gear cable wire had sawed through firstly the plastic sleeve cover, then finally the spindle.

Rather an expensive lesson learned here, in that he needs to replace at least the right crank c/w integral spindle. I just wanted to document the occurrence which may help others in future.

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    Before this gets deleted as "not a question", have a look at pardo.net/bike/pic. The maintainer of that site might be interested.
    – ojs
    Jan 25, 2021 at 11:48
  • @ojs Link's not working
    – user430
    Jan 25, 2021 at 11:57
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    That is interesting. I have rephrased the title to phrase it more as a question. You can revert it if you choose using the edit function, but I think the current wording clarifies the issue, and also phrases it as an actual question.
    – Weiwen Ng
    Jan 25, 2021 at 15:35
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    @Michael Steel cable vs aluminum spindle.
    – Andrew Henle
    Jan 25, 2021 at 21:02
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    @Jeff Shimano is the only hollow-type crank manufacturer to my knowledge that uses steel.
    – MaplePanda
    Jan 14, 2022 at 15:32

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As clarified in comments, this frame appears to have a 30mm spindle crank with a bare derailleur cable somehow routed internally through the bottom bracket. I surmise that maybe the cable didn’t cut all the way through the spindle, but it might have abraded through the spindle enough to cause a stress riser and later a fracture.

While I haven’t worked on internally cabled frames, my understanding is that most current designs should use full internal housing, I.e. cable housing is pushed through openings in the frame, rather than leaving bare cable. I am not sure how the routing was done on this frame. I am also a bit surprised to hear that bare cable was rubbing against the spindle. If you aren’t routing full housing through the frame, I would imagine there has to be a cable stop to keep the cable under tension. If the frame was designed so that the cable was actually in contact with the BB sleeve, then that does seem like a very elementary error. Basically, I have not heard of this particular issue, and I am surprised by it. It sounds like something might be missing from the story.

While I’m not a frame designer, it does seem like many metal BSA shells with a 30mm spindle would have little room for internal cables or wires. Frame designers may choose to route hydraulic hoses externally at the BB, I.e. the hoses enter the down tube, then exit around the BB, and either re-enter at the chainstay or just get zip tied to the chain stay. One example is the 2021 Trek Domane aluminum bike, photo below from a review by Cyclingtips.

enter image description here

In general, if you have housing against bare metal or carbon, then if the latter is moving, you introduce the risk of fretting. With some current generation frames with fully internal cables/hoses that are routed against the fork steerer, I wonder if this will become an issue over time. At least some bike reviews on Cyclingtips have raised this as a possible issue, although I forget which ones. That could be solved by putting some sort of foam or rubber insulation against the house or cable housing.

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    Probably due to sloppy or incompetent craftsmanship from whoever assembled the bike.
    – Carel
    Jan 25, 2021 at 16:30
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    I've got internal cable routing on my hybrid that goes down inside the downtube, out, and back into the chainstay. Erroneously skipping the out-and-back-in could explain it passing the BB with no clearance as none was designed in. Mine is fully housed and the entry points aren't designed to be end stops, but I've also seen internal routing of bare cables. So a coincidence of unusual design and flawed installation could do this. Once it wore through the shell (through fretting), it would gain some slack and the gears wouldn't work, but if retightened would abrade the rotating axle quickly.
    – Chris H
    Jan 25, 2021 at 16:37
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    @Chris H My MTB’s old frame used to have internal bare cabling. Trying to feed the cable through internally mounted cable stops was one of the worst bike-related jobs I’ve ever done. For the 2020 model Trek thankfully moved to a full-length housing design, which is probably cheaper to manufacture anyways.
    – MaplePanda
    Jan 25, 2021 at 19:35
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    @MaplePanda you have my sympathy. Mine was difficult enough. The internal bare cables I've seen were on a 2000s cheap copy of a 90s MTB, but they're probably used to save weight on something fancier as well
    – Chris H
    Jan 25, 2021 at 21:04
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    @MaplePanda Trying to feed the cable through internally mounted cable stops was one of the worst bike-related jobs I’ve ever done. Yep. I got a TT frame cheap because someone had removed the rear shift cable and no one could figure out how to rethread it. "How hard can it be?", I asked myself as I paid for it. Ummm, really REALLY hard. If it hadn't occurred to me to finally try running a stranded copper wire through the frame backwards, fishing it through the front entry hole, soldering with a really thin solder joint to the shifter cable to pull it through I'd still be doing it
    – Andrew Henle
    Jan 25, 2021 at 21:08

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