4

Internally routed brake and shift cables pass through the bottom bracket (from the down tube to a chainstay), where—if they're slack—they will rest against the frame and away from the spindle, but where—if they're taut—they risk touching the continuously turning spindle. Or vice-versa if the cables are above the spindle.

If they do touch the spindle, then sooner or later the housing will be worn off, with the potential for an unpleasant incident such as leakage of brake fluid inside the frame.

What methods are being used to stop internally routed cables from touching the turning spindle? Is it ever the case, for instance, that the spindle is itself in a housing that does not rotate?

Related
3
  • BTW as the title refers to cables, I didn't address brake hoses. They're not under tension and can be formed into a nice curve. They're also pretty robust, to the point that I'd be more worried about the spindle. I've seen what grit trapped in that area (on a road bike) can do
    – Chris H
    Commented May 9, 2023 at 12:16
  • @ChrisH But structurally they pose the same risk. Shift and brake cables have tension, but only a relative tension between the cable and the housing. The housing itself is not taut. It will happily take, for example, these lavish low-curvature turns from handlebar to frame. What am I missing?
    – Sam7919
    Commented May 9, 2023 at 14:50
  • internally routed cables are often bare, or just in a slick but lightweight sleeve. If you've got a full housing with internal routing, as on my 2010 GT hybrid (RIP), you can guide the bend how you like, within reason. With something like a 2021 Synapse, the RD cable at least is unsupported inside the frame. That was a bit of a shock when I said "why don't we detour to mine and swap out that fraying derailleur cable, it will only take a few minutes" - how wrong I was! And now I have a Topstone with presumably the same setup.
    – Chris H
    Commented May 9, 2023 at 15:00

2 Answers 2

8

The bottom bracket housing.

I'm not saying there has never been a fairly high-end housingless design out there, but all bottom brackets I've worked on, or can find pictures of easily, have a non-rotating housing. In many sealed designs it's a necessary part of getting the bearing preload right.

The only time I've seen a bare spindle is on cheap kids' bikes with single piece cranks, and these won't have internal cables. BMXs also apparently use such BBs at times.

4
  • So the common wording is that if it's specified as a "hollow (crank) spindle" then the risk of contact between moving and stationary parts is there, but otherwise, if it's merely a (crank) spindle, then it does have a housing, and we can determine that from the specs; is that about right?
    – Sam7919
    Commented May 7, 2023 at 11:34
  • 1
    @Sam even a hollow spindle/axle (Shimano use the latter term; the distinction is a matter of opinion) still runs in a housing. See for example these Dura Ace exploded views in which the term used is "inner cover". The only bike where I've done much with internal routing used a very similar Hollowtech 105 crankset, again with a housing. Now I'm curious about what I've got on my new endurance/gravel bike - external bearings, 105 drivetrain, but 46/30 crankset which isn't listed as an option for the normal 2x11 105
    – Chris H
    Commented May 7, 2023 at 12:03
  • 1
    On my Rose X-Lite 4 2018 road bike carbon frame the spindle is exposed. These bearings are pressed into the frame and then the SRAM DUB crankset is inserted. The cables run underneath it with enough separation (and a liner).
    – Michael
    Commented May 7, 2023 at 12:40
  • 1
    @Michael that's the sort of counter example I was expecting to see. Assuming it's internally routed, have you seen enough inside to add an answer with how that frame protects the cable? The liner alone won't do much. Of course it's a little easier with electronic shifting as the cable isn't under tension (in fact, electronic shifting is probably an answer by itself, due to the extra design flexibility it offers).
    – Chris H
    Commented May 7, 2023 at 12:43
3

For my Rose X-Lite 4 2018 carbon road bike: There is a small plastic hatch underneath the bottom bracket. The cables are protected by a liner and run “over” this plastic hatch which keeps them separated from the crankset spindle. The front derailleur cable is even redirected upwards by the hatch.

I’ll try to take some photos later. I’ve found this photo online: https://www.rennrad-news.de/forum/attachments/1654235287608-jpeg.1094658/ (the left cable is the front derailleur cable going up to the derailleur and it is missing the liner)

1
  • That's clever if slightly cheating, to bring the cable outside just for a bit where it bends
    – Chris H
    Commented May 7, 2023 at 13:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.