The shimano crm80 single chainring for xt m8000 30t 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 this all aids holding the chain firmly on uneven terrain while keeping chain noise and drag to a minimum and increases durability shimano crm80 single chainring for xt m8000 30t features hollow gear construction for optimized rigidity l