Rear derailluer housing length??

[johnniecakes]

Over the weekend I was starting the year end cleaning and maintenance and noticed that the rear derailleur cable housings all have about a 2 ½ inch radius from the frame stop to the derailleur adjuster. I really never thought about it before nor have I ever asked any professional mechanics about it. Is there a formula for determining the correct length of this housing? What say the wise sages??

[ultraman6970]

IMO it depends a lot of the frame and the brand of the group you are setting up.

Campagnolo IME need a longer cable than shimano groups, if the frame is tricky with the position of the bosses then sometimes it is a must to go longer in the casing to avoid friction.

About the length size, I do it by eye...

[peanutgallery]

Shimano is pretty easy, just enough so as to not put a kink in it and it pulls smoothly. MTB is a straight shot more or less when working with the newer stuff

SRAM, go long. Long enough that folk will take note. Make sure you route the cable properly too before you clamp it down

[Ralph]

I tend to go a little on the long side when I recable new. Then a year later, when I dissemble and clean, will usually trim a little off, and use the old housing and even cable if i can. Just trim off some. I use stuff a long time as long as it works. Might even cross under down tube first go around, then uncross the second year, if frame allows.

[jemoryl]

With 10-spd Campy I find that it is not wise to use anything shorter than what comes with the Campy cable kit. I've had poor results when cutting this piece. Also, I notice the black plastic coating seems to crack at the bend after awhile.

[oldpotatoe]

Over the weekend I was starting the year end cleaning and maintenance and noticed that the rear derailleur cable housings all have about a 2 ½ inch radius from the frame stop to the derailleur adjuster. I really never thought about it before nor have I ever asked any professional mechanics about it. Is there a formula for determining the correct length of this housing? What say the wise sages??

TLAR, That Looks About Right. Long enough that the housing enters the barrel adjuster straight, not angled up (too short) or down(too long) altho too long is hardly ever a problem.

[carpediemracing]

I read somewhere that with SRAM you have to go long, like a huge loop. It looks almost ridiculous but whatever, it's supposed to be better.

I use Campy (10s) but with Nokons for their anti-burst properties when routing tighter bends. With them I go short as possible, so a touch shorter than the stock Campy housing length. No worries about the spiral wound wire coming out of a Nokon. That happened with every one of my Campy housings leading to the rear derailleur.

I'm curious if Nokons or other segmented housing would reduce the SRAM length requirements. The long loop has to be friction related or derailleur angle related, and Nokons have more consistent and very low friction (a few times I've clicked a new install and then thought, "··· did I forget to install the actual cable??" and then I check and the cable has been installed) and don't tug on derailleurs like a spiral wound housing.

[christian]

Shimano and Campy I like to go long enough that the circumference of the loop leads directly into the stop on the derailleur. In practice, that means a longer loop for Campy due to derailleur geometry. I've heard with SRAM it's better to go really really long. No experience there.