The Shimano XTR BR-M9100 Disc Brake disc brake assembly is an ideal example of the priorities of XC-racers and XC-trail riders. Featuring light weight, ample power, tremendous feel and modulation, with tool required reach adjust and better overall action, and stiffer overall high load braking than M9000, this is a superb lightweight dual piston hydraulic disc braking system. Most XC racers don't require massive power and willingly trade off the weight differential versus the heavier trail 4-piston M9120 version.

Think of this M9100 disc brake as an advanced and refined version of the 9000 series. Visually and functionally it is largely the same, and maintains the simple one-way mineral fluid bleeding system. Most of the refinements aren't easily seen, but felt in hard driving performance. This is really one of the simplest disc braking systems on the market, but one that maximizes it's impeccable construction and premium materials through pure engineering. From the lever pivot point, adjustment system, and lever shape, to the sleek magnesium barrel master cylinder, every aspect of the lever appears minimalist, yet highly effective. The lever is lightweight, stiff carbon fiber, with an ideal tactile feel for one or two finger use. The mounting hardware is also aluminum- lightweight and stout in the direct clamp or I-Spec Evo mode.

The M9100 Post Mount Hydraulic Disc calipers feature aluminum mono-body construction with two 22mm ceramic pistons. Shimano's lightweight K03Ti Resin with titanium back plate (no fins) are optimal for dry race conditions. The fixing bolts are titanium and the center-style pad axle is aluminum. A stiffer, more responsive narrow channel SM-BH90-SS hydraulic housing is used. Shimano calculates the average weight of the assembly (plus an MT900 rotor- not included) at 314 grams, give or take based on hose length; about 26 grams lighter than it's 9000 series predecessor.