Shimano XTR FD-M985 Dyna-Sys Front Derailleur - Double $99.95
This XTR Dyna-Sys Double Front Derailleur FD-M985 is specifically designed for use with Shimano's XTR Race Double Crankset and XTR 10-speed HG-X chain. The reason for the exclusivity is that the cage is shaped accordingly. It's shorter than the cage on the triple compatible version. So while either derailleur can accommodate a 42t large chainring, this FD-M985 XTR derailleur won't work well with the 24t small ring as the chain would drag across the cage bridge in many gear options on the cassette.
It's quite similar to the last generation 970 XTR derailleur, though the cage is a bit different. They don't cut the XTR logo into the outermost plate any longer. Instead their time is spent notching the inner plate to remove extra material and save a few grams. And for what it's worth, Shimano's top swing derailleurs always tickle the scale a few grams lighter than their traditional counterparts, and this one's no exception. The limit screws are angled to the outside to make adjustment easier on many of today's complex rear suspension designs.
The Shimano XTR Double Front Derailleur FD-M985 is a top swing design and is available with two mounting options -- Multi-Clamp (28.6/31.8/34.9mm) and E-Type. The Multi-Clamp uses plastic shims to accommodate the two smaller seat tube diameters. The E-Type can be mounted from the bottom bracket shell using the included plate, or it may be mounted directly onto some frames or swingarms in what is commonly referred to as a low-direct mount.
What community has to say
You said this double front "won't work as...
You said this double front "won't work as well with the 24T small ring" but Shimano offers the double chain rings in the 24-38 combination on the M785 crank set. So I'm not sure what you're talking about.
- Familiarity: I've put it through the wringer
Absolutely no regrets. Performs perfectly.