TheShimano Alivio RD-M3100-SGSrear derailleur is perfect for 2×9- as well as 3×9-speed MTB riding. Its low profile Shadow RD design avoids not only damage from rocks, but also improves shifting performance. The Top Normal rear derailleur accepts cassettes with a maximum range of 11 to 36 teeth. The guide and tension pulley of the long SGS cage feature 11 teeth each.