mrblue

Hi,

I am going to be replacing (upgrading) my handlebars, stem, and brakes, on my road bike. I figured since I am going to be doing all that I might as well replace all the cables, too, since they're pretty old and fraying.

My question is: When installing new derailleur cable, particularly for the front, how much slack/tension is desirable, in the cable? In other words, how do you do it? What techniques, tips, and/or tricks, do you use?

thanks.

Retro Grouch 

The trick is to make sure your chain and your shifter are both in the smallest sprocket position. Pull the cable until it's just taut (I use my needle nose pliers) and tighten the cable clamp on your derailleur. You may find that you need to use a barrel adjuster to fine tune your cable tension but most of the time I don't.

dsbrantjr

These are my recommended procedures for front and rear derailleur: Park Tool Co. » ParkTool Blog » Front Derailleur Adjustments Park Tool Co. » ParkTool Blog » Rear Derailler Adjustments (derailleur)

Start at the beginning and do not skip any steps. There are no guidelines for cable "tension", which is actually a misnomer, you are adjusting the cable LENGTH with the adjuster, the derailleur provides the tension. The length is adjusted for correct indexing and the tension is what the derailleur provides.

FBinNY 

While we speak of tension in cables, that's actually a misnomer. The tension is determined by the derailleur return spring, and cannot be changed. What we control is the length which determines the position or trim of the FD when the lever is clicked.

The length is set according the trim on the larger chainring, so that it upshifts crisply, and trims with the outer plate of the cage just clearing the chain when on the smallest rear sprocket. That ensures that you can get the maximum use of various rear sprockets without (or before) rubbing on the inner plate.

The inner chainring trim is set with the inner limit screw, and the cable slack there will be whatever it is.

BTW- as long a you're doing the job consider adding an inline adjuster (if there's no adjuster anywhere else) to make adjusting trim easier.

rydabent

Fb +1

FBinNY 

We maybe should start a charity drive to get warm coats for those poor souls in the netherworld.

fietsbob

not binding when you turn the handlebars seems important. to me.

mrblue

Thanks for the input, everyone!

Now that I have my nomenclature correct, how much cable length is desirable when installing a new derailleur cable (in terms of front derailleurs)? Retro Grouch mentioned pulling the cable taut then tightening the clamp. Is this leaving enough length to allow the derailleur to shift into the larger chainring?

FBinNY 

Read the second paragraph of my earlier post (no4). The goal is to optimize shifting and trim on the larger chainring. You can get very close (often good enough to quit) by correctly trimming the cage for the inner ring with the limit, and pulling out all the slack, then clamping. However it's hard to pull out the slack completely so many experienced mechanics use a pencil to jam the FD in a partly shifted position than pull out the slack. (takes some eye and touch to get consistent results.

If you have a 4th hand cable pulling tool, you can use it to shift to high, set the trim via the tool, then clamp there.

The difficulty of precisely clamping the cable at the right length is why I suggest using some kind og barrel adjuster. This allows you to get it close and clamping, then precisely dialing in the ideal trim.

mrblue

Thanks everyone!

I replaced the derailleur cables without a problem. As a matter of fact, once I went to adjust the trim there was very little adjusting necessary.

speedy25

You learned well! Glad to hear of your success. Hopefully you also lubed those cables when you installed them.

-SP