Shimano XT M773 Shadow 10 Speed Rear Derailleur
If Shimano's new 10 speed shifters are the biscuits of Dyna-Sys, their new 10 speed rear derailleur is the gravy and you can't have one without the other.
The all-new RD-M773 rear derailleur uses Shimano's proven Shadow design to give it a very low profile to keep it out of harm's way. A reworked cage and pulley combo are optimized for the larger 10 speed cassette and narrower chain. The RD-M773 is a traditional style derailleur and is not made in a Rapid Rise version.
The RD-M773 is offered in both a long and a mid cage version. The long cage will allow you to take full advantage of the astounding gear range of the Dyna-Sys platform. Riding in a 42/36 combo is no problem.
If you're going to run a single ring or a double with a bash guard, the mid cage would be a good option. The largest gear combination it can accommodate is a 32 while in the 36 tooth cog.
Please note that the RD-M773 is designed for 10 speed only. It is not meant for use with 9 speed components.
The long cage tips our scale at 237g. The mid is a little lighter at 235g.