The Shimano Di2 XTR M9250 wireless long cage derailleur paired with a standard 10-51t M9200 cassette (cassette sold separately) gives riders and racers the speed range and robustness to tackle every trail on the mountain. With built-in Automatic Crash Recovery an impact-deflecting shape and simple covered-pulley solutions this derailleur stands up to harsh trail impacts and still retains its lightning-quick shifting speed and top-level performanceWireless Di2 paired with HYPERGLIDE+ technology result in smooth precise and instantaneous shiftsWide link structure skid-plate design durable carbon plate and solid pulley add robustness and longevityAutomatic Impact Recovery function instantly returns the derailleur motor to its original position after impactShadow ES provides a slimmer stronger evolution of Shimano's pioneering chain-stabilizing Shadow conceptWedge shape of Shimano's most survivable rear derailleur to-date avoids more direct impacts and smoothly glances off rocks if there is a hitTucked safely inside an enclosed space the battery won't budge even in rough terrain while remaining completely removable for charging