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I have an Avid BB5 front disk brake on my 20" trials bike, and when I bought it from a shop that claims to specialize on trials bicycles, it had a pretty long front brake hose (80 cm/30"). The arch that the hose makes on its way from lever to the caliper is pretty wide, possibly making the force transition through the cable rather inefficient.

enter image description here

Nevertheless, I rode like this for a couple of years, and now that I finally decided to overhaul the brake and put new hose and cable on it, I'd like to ask this: does the arch the cable makes affect front brake performance in any serious way? I now have a Jagwire keb-sl linear strand hose, which they claim to be compressionless, so the cable probably doesn't flex much anyway. But I still want as much power from the brake as possible, so I'd like to know if making the hose shorter (and therefore more straight) will make braking any better.

And if it will, are there any potential downsides or compromises in doing that? I don't do barspins or tailwhips, neither do I plan to, so frame movement is probably not a limitation. But maybe there is some other kind of reasoning behind this setup that I'm not aware of?

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    Have you ever caught the brake hose in the tread of your front tyre? Have you considered a Potts mod ?
    – Criggie
    Sep 5, 2022 at 12:21
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    @Criggie yes I have at first, and solved that by using the zip-tie which you can see on the right leg of my forks. As for Potts - no, I haven't considered it. I'm content with my current setup
    – acalabash
    Sep 5, 2022 at 12:25

2 Answers 2

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Yes it probably affects brake performance but not by much.

Right now you have about 180° of direction change because you go “out” and down (+90°) and then back “in” (+90° = 180°) even though you could go down with single, gentle 90° bend.

I don’t think it makes a huge difference with good, new, clean cables and housing.

To quote http://www.killasgarage.bike/uncategorized/cable-routing-and-friction/ :

The radius doesn’t matter. The total length doesn’t matter. Only total change in direction and coefficient of friction.

enter image description here

To quote his conclusions:

• Route cables to minimize total change in direction.

• Try to pre-form a tight but smooth curve in the cable housing near the derailleur to minimize the bowing effect that results in greater total direction change. My friend Brian suggested that a heat gun might be useful. If I see you riding with a zip-tie on your cable to hold it in to 180 degrees, I’ll laugh at you. Use clear packing tape. 🙂

• Don’t arbitrarily oil derailleur and brake cables. It may actually increase friction.

• Apply this information to derailleur and brake cables all over the bike.

• Appreciate SRAM’s recent mountain bike derailleur designs where the cable enters the derailleur more vertically than to the rear.

• Try not to lose sleep over this, because modern bicycle cable systems work very well. These tweaks will make only a very marginal, probably not discernable, difference.

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  • I've no idea why someone would use clear packing tape over cable ties, and that makes me wonder about the rest of his conclusions. It's flimsy and won't last long in sunlight before the glue and plastic both degrade and you're left with just a mess. It's not even very good in sustained wet conditions. There are stronger repair tapes which would be slightly better but it's still better use something actually designed to constrain cables
    – Chris H
    Sep 5, 2022 at 13:55
  • @ChrisH: I’m with you on that piece of advice.
    – Michael
    Sep 5, 2022 at 13:56
  • @ChrisH I think the quip about clear packing tape was a joke
    – Paul H
    Sep 7, 2022 at 22:15
  • @PaulH maybe, without knowing the original author's style (and how they tend to use smileys) it's hard to tell. The context of reading it here, where answers tend to be straight, doesn't help
    – Chris H
    Sep 8, 2022 at 5:33
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    @jimchristie From my understanding, the simple capstan equations do not perfectly represent Bowden cables due to their rigidity, but the correcting factor is fairly small and the general idea of the "less angle is better" mantra seems to be correct.
    – MaplePanda
    Oct 5, 2022 at 18:26
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Compressionless brake housing is good at allowing only minimum friction buildup with the housing wrapped even multiple times around the steerer, presuming it was set up long enough to do so. The bike in the picture shows a setup that is intended to take advantage of this.

If you will never do barspins etc, then yes it's better to make the housing as short as possible while still avoiding abrupt bends and preventing kinks from when the bars do get turned at extreme angles. With compressionless, the difference in power transmitted is extremely marginal. In the absolute sense, yes it does eat some input force that would otherwise go to the brake, but it doesn't really matter between the different ways you might set up a front brake for barspins vs not. What you do get from making it shorter is less of a hazard of the housing snagging on something.

If it were spiral brake housing, that's completely different. Spiral housing eats input force and movement with excess length and curvature. Length of straight runs of housing are not a major concern, but excessive curves are. Under braking force, the gaps in those coils have to close up before power reaches the braking surface, which eats a lot of input force and movement.

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