9 Speed Mountain Bike Rear Derailleurs

Choose from the two major brands Shimano or Sram. Cage length is an important factor when choosing a rear derailleur. Proper cage length is determined by the maximum size cassette cog which the derailleur can handle plus the tooth-difference capacity of the entire drivetrain. Shimano offers rear derailleurs with short (GS) or long (SGS) cages. Sram offers also medium length cages in addition to short and long cages.

Shimano derailleurs are further divided into standard (top-normal) and RapidRise (bottom-normal) models. RapidRise was more commonly used for Shimano's discontinued Dual Control integrated shift/brake levers. However, it could also be used on conventional levers, but the shifters function reverse of traditional shifitng. To shift to a smaller cog you use your thumb instead of your index finger. Another common option on Shimano rear derailleurs is their Shadow technology. Shadow rear derailleurs are designed to sit closer towards the frame to help prevent damage to the derailleur in the event of a crash.

Double check the compatibility of your shifters when selecting a rear derailleur. SRAM 9 speed rear derailleurs are not compatible with Shimano shifters due to their different cable pull ratio.