Classic mountain bike rear derailleurs could reach and handle any gear combination on the market. Newer slim ultra-light rear derailleurs can be limited in what they can handle. The M610 Deore 10-speed Shadow rear derailleur harkens back to that old school design. Able to handle a 36 tooth ring in the back and a 22 tooth gear spread in the front, you can still run your triple crankset and huge cassette with ease. The Shadow design lets the cage of the derailleur sit tucked away under the cassette rather than poking out where an errant stick or rock can easily take it out. This plus the longest 10-speed cage in the Shimano catalog makes this derailleur ready for anything!