Originally Posted by
bobotech
Totally agreed.
Just to clarify for others who might wander into this thread, I am posting a picture of a pair of roughly identical caged derailleurs. The one of the left is an road bike Ultregra FD-6503 and the one on the right is an actual FD-R443. You will see the cages are pretty identical however the main difference is the distance between the pivot point and the cable attachment points. Look at the orange line in between the yellow lines on the Ultregra derailleur and note the short distance between the yellow lines and compare to the much longer orange line in between the yellow lines on the FD-R443 derailleur. That is what makes the FD-R400 series rather special. It allows someone who wants road bike gearing (note the large cages on both of the derailleurs, designed for 48t and higher) but who wants to use mountain bike shifters which pull a lot more cable. Almost all other mountain bike derailleurs are designed for 46t and lower big rings on the front.
Perfect illustration
The mountain-bike hardcore weight weenies sometimes use road FDs for their low weight. To get the correct pull ratio, they use bolt-on extenders like Speen (
PDF file) that move the cable anchor point farther from the pivot. If you happen to have a really good road derailleur and want to use it, there may be a Speen adapter that would do it.