My favourite derailer Shimano XT M750

An awesome CX derailer and will even go to 36 teeth.

Do you like using drop bars off road?
Do you like using large rear sprockets?
Do you use Shimano?


See below my favourite derailer. Its my favourite for many reasons.

1. It is very robust
2. It has a lot less moving parts than the more recent designs that have (a) clutches and (b) sacrifical mounts that don't actually sacrifice themselves because the derailer construction is too light to actually take a hit anyway, plus they introduce two much thinner areas to develop play in instead of one wider more robust one.
3. It works on a wide variety of drive trains.
4. It works with large sprockets on the back, up to 36 teeth anyway.
5. Its cheaper than a more high-end MTB derailer (which isn't road compatible anyway; dynasys 10 isn't) and you might well find one in your LBS's bin, you will have to look hard though because there will be a pile of shimano shadow derailers on top of it !!

These are the three bikes I am using this derailer on currently with indexing.
An 8 speed MTB
A 9 speed cyclocross bike with 9 speed durace road shifters
A 10 speed MTB with 10 speed durace road shifters

It will also work on a 5, 6, 7 and 9 speed MTB setup.
So 5-9 MTB and 9-10 road.

Why  is the 9-10 road important?
Because if you are a tourer, or monster-cross or cyclo cross rider and you like big hills you may want to use a derailer that works on sprockets up to and over 34 cogs. This derailer will do that. It came out in 1999 but was supersed with the bottom normal derailer in 2003. That flopped, and with egg on their face Shimano relaunched an identical 1999 derailer again in 2005.  Another good to reason to use one is because they are dirt cheap, and even though I have used them for at least 3 years of cyclo-cross I have never come close to tearing one off. How many people can say that?

Most people matching MTB derailers to integrated road brake/shifters (Americans call them "brifters") use SRAM, because for 10 speed at least, SRAM road talks to MTB, and you can go 1x with a clutch derailer on the back. I think this compatibility may have changed with 11 speed. Other people spare themselves the grief and use friction bar-end shifters which may suffice for touring but would suck big time in CX.

Best derailer ever. 255 grams. 

This guy also makes a 9/10 speed long cage derailer for touring.
http://sunxcd.net/rearder/

Read what Sheldon Brown said about derailers and marketing hype.