Cable outer, full or "broken"?

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mattsccm
Posts: 5101
Joined: 28 Nov 2009, 9:44pm

Cable outer, full or "broken"?

Post by mattsccm »

Context. 2 bikes, near identical cable routing to rear disc brake. Via top tube then seat stay.
1 has a full length outer the other has exposed inner along the TT. all other things being equal, which would you thing was more efficient?
I would go with the exposed version thinking that the give in the extra 2 ferrules would be more than made up for by the compression of 18" of outer in the full length version. Only just though. The inner on the full length outer version is about 2cm longer due to slightly different placing of brake mount and top tube cable stops.
Practically though the one with an exposed bit of cable is noticeably more sponging and ineffective.
Hmm
Assuming identical preparation ( and I am damn sure it is) what am I missing?
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531colin
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Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Cable outer, full or "broken"?

Post by 531colin »

?alignment of the caliper & pads to the disc?
?where the arm is when the brake is "off" ?
stewartpratt
Posts: 2566
Joined: 27 Dec 2007, 5:12pm

Re: Cable outer, full or "broken"?

Post by stewartpratt »

Same calipers? Same levers? No friction in either of these?

Do you have rubber seals on the ferrules? More could add some friction.

Both sets of cables clean and fresh? More ferrules means more points for water and muck to get in - on your setup the prime culprit would be the final section near the caliper, where water will run down the cable and could get into the outer.
Brucey
Posts: 44522
Joined: 4 Jan 2012, 6:25pm

Re: Cable outer, full or "broken"?

Post by Brucey »

prep quality on the cable outer ends; they must be ground square and fitted with good quality ferrules. You can get linered ferrules (e.g. jagwire) these days which give a really smooth feel.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Valbrona
Posts: 2696
Joined: 7 Feb 2011, 4:49pm

Re: Cable outer, full or "broken"?

Post by Valbrona »

Brucey wrote:prep quality on the cable outer ends; they must be ground square and fitted with good quality ferrules. You can get linered ferrules (e.g. jagwire) these days which give a really smooth feel.


Yeah, the child labourers in Vietnam that built your bike have never seen a new pair of cable cutters.
I should coco.
mattsccm
Posts: 5101
Joined: 28 Nov 2009, 9:44pm

Re: Cable outer, full or "broken"?

Post by mattsccm »

Ah, but I built them up and all but used a set square on the ends of the outers. I even touch them with a grinder. Convinced I am loosing efficiency with the two part outer some how. Planning to swap the bar/cable set up but leave the brake caliper in place.
BigG
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Joined: 7 Jun 2010, 4:29pm
Location: Devon

Re: Cable outer, full or "broken"?

Post by BigG »

The frictional losses in the horizontal length of cable will be negligeable. However, the split cable with an exposed wire central piece will have a shorter Bowden cable. Even the best cable outers compress slightly under load and the shorter length of the split one will give a less spongy brake with a slightly shorter lever travel for the same brake movement. A split cable is certainly my preference.
mattsccm
Posts: 5101
Joined: 28 Nov 2009, 9:44pm

Re: Cable outer, full or "broken"?

Post by mattsccm »

That's what is irritating me. The split cable isn't working as well. Got to be "give" in the ferrules.
Brucey
Posts: 44522
Joined: 4 Jan 2012, 6:25pm

Re: Cable outer, full or "broken"?

Post by Brucey »

sometimes the shorter lengths of cable housing are forced to have tighter bends and often don't have smooth bends near the cable stops, either. That is why I like the lined ferrules.

The Jagwire ones are a snug fit on the cable housing, have a reasonably square bottom, and can be turned down to be an exact fit in a frame boss so that there isn't a sudden kink in the cable. If you are not using these or similar you can easily be losing a bit there.

BTW did you try the back to back experiment?

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
reohn2
Posts: 45159
Joined: 26 Jun 2009, 8:21pm

Re: Cable outer, full or "broken"?

Post by reohn2 »

I have both set ups on three different bikes.
The split/exposed inner bike runs along the TT and has three lengths of outer(it's a tandem)one from lever to TT one short one to bypass the captain seat tube and one from just in front of the stokers seat tube to the caliper.
The other two bikes(solos) run uninterrupted outers from brake lever to caliper along the down tube over the top of the BB and along the chainstay.
All three use BB7 calipers and all three are very good stoppers thought the tandem has 203 rotors and the solos 160's.
So IMO if all things are equal there shouldn't be a problem with either set up IMO.
I the brake is spongy on one bike and I could find out why,I'd first swop calipers over to prove/disprove calipers then set to work on the cables if the calipers were ok.
Sponginess seems to suggest outer cable compression.
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"All we are not stares back at what we are"
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Binkyboy
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Joined: 29 Oct 2010, 5:05pm

Re: Cable outer, full or "broken"?

Post by Binkyboy »

Have you just tried a good look?
By that I mean get someone to squeeze the lever and watch what happens at the various points as the cable transfers the force from lever to brake.
You will be able to see something squashing or bending more on one bike than the other and that will give you the clue.

I have had, and still have, both types of outer and can't really say I've ever noticed any difference. BUT the differences I have noticed are in the brake callipers themselves. Some are definitely stiffer than others.
Valbrona
Posts: 2696
Joined: 7 Feb 2011, 4:49pm

Re: Cable outer, full or "broken"?

Post by Valbrona »

Anyone want to add anything to this old thread the subject of which I am interested in?

Thanks.
I should coco.
reohn2
Posts: 45159
Joined: 26 Jun 2009, 8:21pm

Re: Cable outer, full or "broken"?

Post by reohn2 »

Non other than my bikes weren't built by child labourers :)
-----------------------------------------------------------
"All we are not stares back at what we are"
W H Auden
Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Cable outer, full or "broken"?

Post by Brucey »

the other thing that may have escaped comment thus far is that the caliper mounting may be responsible. If the caliper is slightly twisted or offset, it can't clamp the disc square on unless something twists/bends, and the twisting gives a spongy feel at the lever.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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