My 2018 Specialized Epic Comp (Aluminum) has a 24 mm threaded bottom bracket. If I remove the bottom bracket will I be able to route the cable housing down the down tube (there is an opening in the frame for a cable housing), around the top of the cavity where the bottom bracket was and up the seat tube?

Or will there be some sort of tube or housing where the BB was that will still prevent me from routing the cable housing up the seat tube?

  • Are you asking whether there are orifices between the frame tubes and the bottom bracket shell to actually admit the cable from the down tube into the shell, and then up the seat tube? I think there have to be holes so that water can drain out. – Kaz Aug 28 '19 at 19:12
  • Seems like a bad idea. The cable will have too sharp a bend in it & will be subject to wear from the BB, plus you'd have to drill holes in the frame to allow the cable to enter/exit. – Daniel R Hicks Aug 28 '19 at 20:15
  • 2
    a 2018 frame was likely designed for internal routing. assuming that's the case, you won't need to remove your BB to route the cable. the bike's owner's manual will explain how to route the cable. – Paul H Aug 28 '19 at 21:17
  • forums.mtbr.com/specialized/… has a good discussion. If you go ahead and do it, come back here and answer your question. – mattnz Aug 29 '19 at 4:02

I've never run a cable this way, but I would imagine that it depends on the bottom bracket. (You already know that, which is why you're asking!)

Here's a quick look at a bunch of different models of cartridge style bottom brackets from Google Images:

screenshot of a Google Image Search page containing 15 photos of different brands and sizes of cartridge style bottom brackets

From this quick look, we can see that there is a differential between the internal diameter of the bottom bracket shell (into which you screw the ends of the bottom bracket) and the diameter of the bottom bracket cartridge's "waist". For some bottom brackets, like the third and fourth ones in the second row (Velo Orange and RPM respectively), that diff is pretty small, so there won't be a lot of room between the cartridge and the frame. For the top left and top right ones (Sugino 75 and Shimano UN55) there appears to be more room. Whether it would be enough to run cable housing without putting too much pressure on it, I can't say - again, it would depend on your particular bottom bracket.

If you were able to replace the bottom bracket with the old cup-and-cone style, there'd almost definitely be room, but I can't imagine it'd be easy to find one that fit your particular bike :)

If this is your bike, I found an instruction manual that will help. One of the instructions says to "Work the housing over the bottom bracket shell and up the seat tube until it exits at the top of the seat tube", which indicates that yes, your particular bottom bracket should accommodate this cable run. Note that according to those instructions, you run the cable itself first and then to run the housing over it, which is a bit counterintuitive but it makes sense once you absorb the whole process.

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