Shimano is entering a new world with the RD-M972 XTR Shadow Rear Derailleur. Not only does this share the paradigm-shifting design of the XT Shadow rear derailleur with the amazing blingy good looks of previous XTR bits, but it is the first time Shimano has introduced carbon fiber to their rear derailleur.

Yes, carbon fiber. It deserves the requisite oooohs and ahs. The cage on the XTR rear derailleur is made of the good stuff. The reason for the change is simple -- weight reduction (though you could probably make a solid argument for sex appeal). Yes, it's pretty cool, but a 182g rear derailleur is really light, like hanging parallelogram light, like pre-indexing light, like road light. It's as if Shimano is shooting for a 15lbs fully-functional full-suspension cross-country bike.

The big deal with the Shadow design is that by changing the derailleur pivot point, the changer moves faster easier, and is better protected in a crash because it barely protrudes past the quick release bolt when the chain is in the biggest gear.

The Shimano XTR RD-M972 Shadow rear derailleur is offered in two sizes: GS (mid-cage) and SGS (long-cage). In all cases, the max cogset that can be used is an 11-34. The difference is that the mid cage size has a 33 tooth total capacity while the long cage takes 45 tooth total. All XTR rear derailleurs have sealed 11-tooth upper and lower jockey wheels. The spring in the derailleur yields Shimano's traditional "light action" gear changes. 182g (long cage). MSRP $239.99.