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PostPosted: Tue Feb 28, 2012 10:00 pm 
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Hi everyone,

My Renovo frameset finally arrived last week and I plan to start building it up this weekend. I have built up several bikes in the past, but I would like to do this one by the book.

On all my previous builds I always used the cable length that looked nice. The same goes for the bend to the rear derailleur. I was hoping some of you could inform me as to what the right cable length should be for my next build and what the right bend should be to rear derailleur. I was also wondering what the correct placement of the shift indicator should be in the right shift cable. Some pictures would also be great.

The groupset I will be using is a DA 9-spd groupset.

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PostPosted: Tue Feb 28, 2012 11:42 pm 
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Cables pass ideally through a housing with no friction. On that basis, to the greatest extent you can minimize friction through the housing, in this case tight bends, sharp angles, or excessive housing, the shifting will typically be optimized.

So in essence the best length is the one that has the shortest path without introducing any overly tight bends. Also make sure to rotate the bars and check the path and length at both left and right extremes before you cut.


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PostPosted: Wed Feb 29, 2012 1:02 am 
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Good question, SWijland.

Can someone show us some bike pictures of proper cable length?

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PostPosted: Wed Feb 29, 2012 1:19 am 
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Look on the Sheldon Brown website. http://sheldonbrown.com/cables.html There are simple explanations on how to set cable length.

Unfortunately, there is no "formula" and the exact length is judgement-based, and two cabling jobs on the same frame might be slightly different, but both excellent in that they are within the parameters of "proper cable housing length". Also, aesthetics comes in to play in that some of us will try to minimize housing length while still adhering to the principles.

Two general principles that I think are emphasized in Sheldon's articles and in my own experience are: (like someone else has already said), make the curves as sweeping as possible, but no longer than necessary. Too tight = too much friction. Excessive length = too much friction. But there's some leeway of course in what functions well. This is where my personal aesthics happens to come into play. I will fudge on the side of shorter housing length - as much as I can while still maintaining good smooth functioning - just because I like the looks of smaller loops better. If I get a bike (either new or used) that looks to me like it's got excessve housing lengths, I'll take it apart and shorten them.

I think that many shops err on the side of excessive housing length for a couple of reasons - one, it's less likely to cause problems than too-short length and two, they just go with whatever cable "set" they have, if they happen to be using a set, and don't trim it. My shop/factory built tandem, and my wife's small-framed shop/factory built road bike both had ridiculously long cable housings. Some are several inches longer than they need to be and actually violated the second principle (read on!).

The other general principle is, wherever a cable ends a sweep and sets into a cable housing stop, it should be going straight in - should have finished its sweep so it's going directly in line with the cable stop before it actually enters it. If it's too long or too short, it will tend to insert into the stop at an angle causing excessive friction.

As an example of this, many people cut their rear derailleur housing too short so that it comes into the derailleur cable stop at an angle. Sram RD's , compared to Shimano, need quite a large loop to accomplish this and they look odd to people who are used to the fairly tight loop that can work with Shimano. This is fairly subtle to look at and see and doesn't smack you on the side of the head as being wrong unless you're aware of it. (look closely at the photos in Sheldon's articles focusing on the actual place the cable housing enters the stop).

Anyway, there's no straight formula, you need to understand the simple principles as described in Sheldon Brown's article (and others, of course) and then cut your cables as you judge - probably erring on the long side and then trimming if you're not happy with how it looks.


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PostPosted: Wed Feb 29, 2012 3:10 am 
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There is a magic number for the rear mech cable.
292mm, I you use this length you will never have a issue

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PostPosted: Wed Feb 29, 2012 3:24 am 
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:thumbup: :goodpost: :exactly:

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PostPosted: Wed Feb 29, 2012 3:29 am 
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I don't really know and I copy the old, or other bikes and make it slightly longer. They say SRAM needs to be longer to shift well but I am not really sure how long, some would make it so big it look ridiculous and I rather due with a little less smooth shifting.
But as a rule it is supposed to loop big enough so it go straight into the RD


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PostPosted: Wed Feb 29, 2012 8:17 am 
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@Camilo: thanks for the explanation and tips!

All I need to know now is where to put the gear indicator... Is it supposed to come right after the shifter or does it work better / look better when I put a little bit of cable between the gear indicator and the shifter?

Image

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My Renovo R1 wooden bike project and the reason for my passion for all that is wood.

Check it out: the most amazing vintage Colnago, Merckx and Pinarello collection


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PostPosted: Wed Feb 29, 2012 9:15 am 
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Joined: Fri Jun 03, 2011 9:12 pm
Posts: 503
Location: Riverside
Here's my front cable housing lengths, they're pretty much the shortest I could make them and still have enough bend

Image

actually, my rd housing might be a tad short


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