I'm trying to remember what kind of shifters you have on your flat bars, so I may be completely off here.
Has anyone explained "trimming" the derailleur to you?
Indexed brifters have pretty much one click or two half clicks and BOOM the front der is where it is gonna be. Some of the bar shifters have lots and lots of clicks, and your front der has several choices of where it can be. They act almost like friction shifters.
For sake of illustration, assume here I'm talking about a bar shifter with infinite clicks, or friction shifters:
Whaling the shifter to one extreme or the other pops the chain onto the big or small ring, and the derailleur cage (if the limiter screws are set just so) is pretty much out of the way of the chain as you merrily zip through the rear cassette. (assuming here you are not cross-chaining, which I know you know about)
The middle ring can get kind of exciting, because the cage can be centered on the ring, or more toward the big ring, or more toward the small ring. The chain can be merrily whipping through the cage in the middle ring and rub against the cage sides if it is too far one way or the other. If it is a bit too far one way or the other, the chain will rub as you shift the rear der and the line of the chain changes.
There is nothing wrong with the shifter or the der. This is just how it works. It has an arc of travel. At each end of the arc there is a ring ready and waiting. Somewhere in the middle of the arc is the middle ring. You get the chain onto the middle ring, and if you hear chain hitting der cage, you finesse the cage away from the running chain by moving the der a smidgen. (on my twist shifts, it was a couple tiny clicks, on my trigger shifts it was one click, on my friction shifts it is a smidgen) That trims the derailleur.
Here's your experiment for the day:
Take the bike out, ride around, shift into the middle ring. Get off the bike. Look at the chain, see where it sits relative to the two sides of the der cage. Now, move your left shifter a smidgen. See how the cage moves but the chain is still on the middle ring? Move that cage until the inside plate is touching the chain. Now move it until the outside plate is touching the chain. Now move it until it is centered. Get on the bike again. Ride a few yards. Does it make noise? Shift up and down the cassette. If it makes noise, move the left der a smidgen. If that causes MORE noise, move the left der the other way TWO smidgens. Voila! You've trimmed your front derailleur!
Of course, if you can't move the front der a smidgen and eliminate the noise you get from changing rear cogs.... then what I've just told you is useless and your shop needs to give you a hand.
But maybe it would be useful for someone else.
Last edited by KnottedYet; 08-08-2010 at 05:09 AM.
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