The Shimano XT SM-CRM81 Single Chainring features Dynamic Chain Engagement (DCE) is used to hold the chain and help prevent chain jump out. This is achieved by using a broader and taller tooth profile in conjunction with a special hooked leading edge and alternate profiled tooth shaping. This provides superior chain retention, lower driving sound, increased durability and drag to a minimum. Shimano XT SM-CRM81 Single Chainring Features Hollow gear construction for optimized rigidity, lightweight and durability Durable teeth using a plated steel construction supported by a carbon composite (CFRP) carrier body Dyna-Sys11 HG-X11 11-speed chain compatible Available in 30T/32T/34T