Join Date: Feb 2004
Location: St Peters, Missouri
Bikes: Rans Rockst (Retro rocket) Rans Enduro Sport (Retro racket) Catrike 559, Merin Bear Valley (beater bike).
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Originally Posted by spinerguy
First: When replacing a standard double cranks (shimano ultegra) with a compact double (shimano ultegra), do I need to shorten the chain? All other things being equal.
1. You may or may not find it necessary to shorten your chain. Assuming you are keeping the same rear cassette you're only taking 3 chainring teeth out of the equation and only about 1/2 of them are engaged at one time so that cuts the difference to 1 1/2 teeth. You can't shorten your chain by 1 1/2 links. If your chain was on the long side of the tolerance range before, you'll need to shorten your chain by 1" (2 links). If your chain was on the short side of the range previously, you'll want to leave it the same length.
If it was my bike, I'd resize it using the big/big method. Break the chain and wrap it around the big chainring and biggest cog bypassing the derailleur. Figure the shortest place you could rejoin the chain and add 1" (2 links) to that.
If you don't want to break the chain, you might try the little/little chain sizing method. After you install the compact crankset, shift into the little/little combination. If your derailleur is capable of taking up all of the chain slack without the chain rubbing on itself or sagging, you're good-to-go.
2. Lay your bike on it's side with the exit hole for the brake cable on the bottom. Thread a long piece of wire through the entrance hole and watch for it at the exit (a little flashlight helps). When you see the wire, snare it with something and use it to pull the brake cable through the frame.
Next time, leave the brake housing in place and use it to guide the new brake cable through. Then pull the old housing out and use your new brake cable to guide the new housing through the frame.
Last edited by Retro Grouch; 05-22-09 at 07:28 PM.