I have a Shimano FD-TX50. How should I adjust it?
A front derailer is a bit more complicated than it looks, and can be quite complex to adjust if you're starting from zero -- just having installed the unit.
There are five (and a half) adjustments --
- Height, sliding up and down the seat tube.
- Rotation around the seat tube.
- Low limit
- High limit
- Cable tightness
Generally height is such that the derailer, when in "high gear" position, is just a millimeter or two above the teeth of the large ring.
Generally rotation is such that the long arm of the derailer is parallel to the large ring (though it's tricky finding the right reference point on the derailer). But very slight adjustments (particularly rotating clockwise slightly as viewed from above) may improve shifting.
Derailers differ in terms of whether they spring out, to the largest ring, or spring in, to the smallest ring. If it springs out, place the shifter in the position for the largest ring, adjust the barrel adjuster until it's just about all the way screwed together, then pull the cable tight, force the derailer in until it's just off the high limit, and tighten the cable clamp. (Getting this right the first time takes practice, so don't cut the cable short until you're confident everything is correct.) (For a "springs in" derailer you essentially do the opposite.)
Next adjust the high and low limits until the derailer centers over the high and low rings when those gears are selected. Finally, adjust the barrel adjuster so that the derailer centers over the center ring when selected. Double check the high and low.
Once you have it this far you need to crank the bike on a stand and see how it shifts. Fine adjustment of the limits and cable tightness may be required.
The cable will stretch some over the first few hours and days of use, so fine-tuning of the barrel adjuster may be required.