Designed for the extremes of downhill racing and freeride disciplines, the Saint RD-M820 Rear Derailleur remains crisp-shifting and noticeably free of drivetrain noise when you're plunging into formidable downhills at high rates of speed and sending bigger features at the freeride park. Since downhill riders tend to push things to the absolute limit, the engineers at Shimano designed it with a low-profile skid plate that minimizes damage in the event of a nasty crash. Another cool feature, its silent bump stopper employs a vibration-absorbing piece of urethane that keeps your drivetrain running silently on aggressive downhills. One of its best features is the ability to switch between widely spaced mountain bike cassettes and short-block road cassettes with its mode converter. This allows you to run a 10-speed cassette that's tightly spaced for less jump between gears on downhill runs or give your freeride bike a bit more gear range when you actually need to pedal back uphill. It'll work with 10-speed road cassettes of 11 to 23, 11 to 25, and 11 to 28-teeth, as well as 10-speed mountain bike cassettes of 11 to 32, 11 to 34, and 11 to 36-teeth. Alloy construction maintains high levels of strength without the massive weight penalty you've come to expect from downhill-specific components. Fluorine-coated link pin bushings create silky-smooth shifts across all ten gears. Moreover, it's packing Shimano's Shadow Plus technology, which prevents the chain from violently slapping around when you're plunging downhill at high rates of speed. Shadow Plus engages with a switch that keeps it in a semi-rigid position while you're riding, switching off when you need to move the derailleur out of the way for repairs and wheel swaps.