Shimano XTR M971 Rear Derailleur, Top Normal (Long Cage)
There's a good reason why you'll find the XTR Rear Derailleur aboard just about every top-end off-roader. It's super light, durable and shifts like a dream. This cold-forged-aluminum rear derailleur is stiffer than ever and boasts smooth, light-action shifting. The 11-tooth pulleys alternate link contact, reducing wear and smoothing pedaling.
Chain-wrap capacity: up to 43 teeth.
Largest cog this derailleur can handle: 34 tooth
Weight: 197 grams
Top Normal means that the derailleur spring assists shifts to the smaller cassette cogs, which is the way most rear derailleurs work.