# Optimal cable housing length



## serpico7 (Jul 11, 2006)

I'm cutting brake and derailleur cables and housing for a new build and trying to figure out the optimal housing lengths.

Park Tools writes:
_The less the drag on the cables, the better for the shifting and braking. Too short of housing will cause it to kink and bind, making even more friction. As a rule of thumb, try to size the housing so it is as short as possible but it still enters the stops and barrel adjusters in a straight approach. For the rear derailleur housing, note especially how the housing enters the barrel adjuster._

Sheldon Brown writes:
_The Four Commandments of Cable Routing:

1. The handlebars must be able to turn as far as they can in both directions without being limited by a cable pulling taut. Instead, the turning limit must be set by the handlebar bumping into the top tube or by the brake arm or reflector bracket bumping into the down tube.

2. No wrong direction bends (For example: as the rear brake cable leaves the top tube and makes the bend down toward the caliper, it should make a smooth transition from parallel to the top tube to parallel to the seat stays. If the cable bends up from the top tube before bending down toward the seat stays, it is probably too long. If the cable curves out past the caliper, then bends back at an angle more vertical than the seat stays, it is certainly too long.

3. The bends that cannot be avoided should be made as wide (gradual) as possible,

4. Cable housings should be as short as they can be without violating the above rules._

They're suggesting similar lengths, but why is Sheldon focused on leaving so much cable that the bars bump the frame? I think the extra rear brake cable housing I've got might be causing mushy braking (everything is brand new - cables, housing, shifters, calipers), but if I cut it shorter it might stop the bar just before it would hit the top tube.


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## Kerry Irons (Feb 25, 2002)

*Cross purposes*

The recommendation to have enough casing to allow the bars to hit the frame serves both to give you gentle bends and to prevent damage to bar tape and maybe even prevent pulling the casing out of the brake lever in a sharp twist of the bar. You might get a little less cable friction with shorter casing, but not much. The extra long casing of concern is the one that goes past the seat post, not up front.


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## Mel Erickson (Feb 3, 2004)

I generally like casing long enough to allow the bars to touch the TT but I've made them shorter. I think it's important for the housing to look right as well as perform properly. Sometimes casing long enough to allow the bars to touch the TT just looks too long and messy when the wheel is centered. You'll never have a reason or need to rotate your bars that much so shorter housing is ok if you need it for a clean front end. It's highly unlikely that housing lengths that stop the bars short of the TT (say three inches) will cause any problem. I think the most likely problem would be increased cable rub on the head tube and marred paint.


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## serpico7 (Jul 11, 2006)

I cut the derailleur cables a little too short for TT contact, but the bends are gentle and it looks good. I guess if my bars are ever turned sharply enough to yank out the housing, I'll probably be on the floor and the cabling will be the last thing I'm worried about.


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## drewmcg (Sep 19, 2005)

Some bikes (like my old Biacchi) have one contiguous brake housing running from the handle to the rear caliper. Sheldon Brown's Pt. 2 re. rear cable housing is NOT directed at this situation, but rather the (more common, now) situation of a split housing, where the front part of the rear brake housing runs from the brake lever to a stop on the front of the top tube, bare wire runs the length of the top tube, and a rear section of housing runs from another cable stop (forward of the seat) to the rear caliper.

It sounds like you might have one, contiguous cable. In that instance, set the length as short as you can such that when you turn the handlebars from side to side, they do not cause the rear brakes to engage toward the rim.


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## serpico7 (Jul 11, 2006)

drewmcg said:


> It sounds like you might have one, contiguous cable. In that instance, set the length as short as you can such that when you turn the handlebars from side to side, they do not cause the rear brakes to engage toward the rim.


Nope. It's split housing.


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