Tuesday, April 8, 2008

Derailleur

I upgraded my front derailleur from Shimano 440 to Shimano Ultegra looking to improve front derailleur performance. I did not really experience much of an improvement. Is it worth upgrading the flat handle bar Shimano 440 shifter to a Shimano 660 shifter to improve front derailleur shifting performance or am I simply looking to improve something that really cannot noticeably be further improved? Thanks.

********************************

Maybe you just don't know how to adjust it right.Even poorly adjusted DA won't shift well. Too many folks think upgrading a FD is the answer to poor adjustment.


Read through the Park Tool front derailleur adjustment page (http://www.parktool.com/repair/readhowto.asp?id=75) carefully. Once you understand it, start adjusting. If you're unsure in your abilities, you may not want to start loosening your derailleur clamp yourself (meaning: have this performed by your LBS). Once you loosen that clamp, there's really no equivalent to an "undo" command that will get you back where you started.


Between the FD angle and the height, though, I would submit that here's where faster FD shifting can be found (at least sought) . . . providing your cable tension, chainline, etc., are correct to begin with.

You also may want to obtain a copy of John Forester's Effective Cycling (http://www.amazon.com/exec/obidos/tg/detail/-/0262560704/qid=1125240855/sr=8-1/ref=pd_bbs_1/103-5539992-0539848?v=glance&s=books&n=507846). There's a section on 'Derailleur Theory and Expert Adjustment' that gives a bit more information and a few more tricks to try.

***********************



The adjustments actually comes AFTER you've got the derailleur positioned optimally on the frame relative to the crank. That Park Tool guide is one of the best procedures.

1. First, make sure you have the proper bottom-bracket spindle. Measure the distance between the centerline of the seat-tube to the center between the chainrings. Derailleurs designed for doubles want this distance between 35-45mm.

2. Then, make sure the height of the derailleur has the outer-cage just 1.0-2.0mm above the teeth on the big-chainring. I find that 1.5mm works way, way better than 3.0mm.

3. Next comes the lateral rotation of the derailleur. Notice that the Park Tool guide has you setting the chain in the biggest gear (big-ring in front, smallest cog in back). Then they have you rotate the derailleur so that the outer cage is parallel to the chain not the chainrings. That's a tiny difference, but it makes a HUGE difference in shifting performance. Most shops train their employees to set the outer-cage to be parallel with the chainring because it allows them to make consistent adjustments, but it's a consistenly mediocre adjustment. Follow the Park guide and set the outer-cage parallel to the chain the biggest gear. This adjustment is SO important that Shimano even makes a pre-rotated/pre-bent outer-cage on their newer derailleurs with the little step that kicks out at the bottom of the cage. This has the same effect as rotating the rear of the cage outwards even when shops stubbornly keep the face of the cage parallel to the chainring.

4. Finally, the trick that really helps shifting from the small chainring to the big one is to bend the tip of the inner cage outwards a little. About 3-4mm from parallel to the outer-cage should do. If you look at the newer Shimano derailleurs, you'll see that they have a built-in bump that has the tip of the inner-cage aimed towards the outside. This helps guide the chain up from the small ring to big-ring.

FINALLY, once all these physical adjustments are made, you can mess with cable-tension and limit-screws.

No comments: