The Shimano Dura-Ace BR-RS9170 Flat Mount Hydraulic Disc Brake caliper is an upgrade of braking performance on all counts. The primary goals were to make this brake smaller, lighter, and better on all fronts. Shimano succeeded. They also had a secondary goal, to make these easier to operate, easier to set up, easier to install a wheel. They succeeded on that front as well.
The caliper possesses a lower profile. This means it hides better from the wind behind the fork and is less of an obstacle to the wind when mounted on stays. It still utilizes Shimano’s Flat Mount system for attaching to frames. Despite the smaller size, the caliper dissipates heat better.
The two-piston design has been refined for a better balance of power and modulation. While the pistons self-adjust, they also retreat farther back for more rotor clearance. With this design, slight frame flex won’t cause rotors to hit the pads, and an imperfect seating of the wheel or slightly mis-aligned rotor won’t cause annoying and performance-robbing brake rub. The pads have also been improved. The edges are chamfered to better assist guiding in the brake rotors.
Bleeding is easy. Gravity does the trick. Open the valve and it comes out.
The calipers weigh approximately 256g each, or 515g for the pair. They come with the caliper and pads. You’ll need to supply the hydraulic hose(s) and fluid. If you buy the levers at the same time, the hoses and fluid come with the levers.
Rotors need to be purchased separately. Shimano recommends their SM-RT900 rotors, which are available in both 140mm (SS) and 160mm diameters (S).
These calipers are sold individually, so you need to specify front or rear or front and rear.
The Shimano Dura-Ace BR-RS9170 Flat Mount Hydraulic Disc Brake caliper is the first brake Shimano has deemed worthy of the Dura-Ace label. The effort shows.