poorly designed internal brake cable routing

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Foghat
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by Foghat

Ribble’s Sportive Azzurro frame has a very poorly designed internal rear brake cable routing, causing an irritatingly stiff cable action that even the otherwise slickly-running latest Shimano polymer cabling cannot counter.

The cause of the high friction is the inner cable rubbing the inside of the top tube along the entire length of the internal run. For some reason, the frame designer thought a curved top tube that results in this ridiculous rubbing is a good idea – see the photo below for the curvature (although the photo doesn’t do justice to the extent of the curvature and its impedance of the inner cable).

Now, if Ribble had designed the routing so that there was a full-length run of outer that could be fed through the frame, there wouldn’t be a friction problem – full-length Shimano polymer cables run exceptionally smoothly in my experience, even with tight bends. Unfortunately, the outer cable entry points are fitted with stops that enforce the use of an interrupted outer cable run. The outer sections are all cut properly and are not restricting cable movement. I’ve removed the basic metal ferrules that Ribble fitted and replaced them with long-nosed ones; this has improved things very slightly, but the friction is still unacceptably high – not least because it ruins the modulation capability of the superb Ultegra 6800 brake, and causes an enormous force-required imbalance between the front and rear brake levers. I expect the cable will also wear a groove into the tube that will get deeper over time and eventually compromise the frame.

So I’m minded to execute some rectification on the ill-thought-out design – namely drilling the outer cable stops at the entry and exit points such that a full-length outer can be used. Before doing so, it makes sense to canvas opinion on the feasibility, pitfalls and techniques for doing this.

The entry point has a moulded shape and no covering plate – i.e. it is just a moulded angled hole in the carbon fibre tube with the stopping point fixed in the frame. The exit point is a fair-sized covering plate with a fixing bolt, and this presumably covers a larger non-angled hole and presumably can be removed; I assume the stop is part of the plate.

So I’m considering enlarging the entry and exit holes with an appropriately sized bit and feeding the full-length outer through instead. The fact that the exit point has a removable plate should mean locating the end of the outer and getting it to exit shouldn’t be a major problem.

I would be interested to hear from anyone who’s done something similar on carbon tubing, plus any comments on methods and potential problems.

Thanks.

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eric
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by eric

Sounds like it needs some plastic cable liner.

sungod
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by sungod

my thought also

see if you can feed some 2mm id ptfe tubing through, it might run smoother than the channel in the frame, and should also introduce less friction than running a length of outer through there

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Calnago
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by Calnago

If you can fit some of those rubber cable "donuts" in there, that might be a way to go as well.
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rpenmanparker
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by rpenmanparker

If you aren't prepared to send the frame back, then just dooo eet. Just drill the thing. My steel frame has a full length internal rear brake cable and it works like a champ.
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wingguy
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by wingguy

Foghat wrote:Ribble’s...


That's about all you had to say.

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dwaharvey
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Location: USA

by dwaharvey

Definitely worth trying the liner before taking a drill to anything and voiding your warranty. Should be able to get some PTFE liner from your LBS.

lone wheeler
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by lone wheeler

wingguy wrote:
Foghat wrote:Ribble’s...


That's about all you had to say.



:lol: :lol: :lol:

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