Shimano

Dura-Ace ST-R9170 Di2 Hydraulic STI Lever

Shimano's Di2 drivetrain continues its evolution and with the release of the Dura-Ace ST-R9170 Di2 Hydraulic STI Lever & Disc Brake Caliper, an entirely new hydraulic disc brake system comprising STI shift/brake levers and new flat-mount calipers. Previous versions of the top-tier Di2/Hydro levers and calipers were handled by the ST-R785 set, a model that wasn't confined to a group and most likely a place holder until the UCI decided its stance on road bike disc brake use in competition. This marks the first time we see hydraulic disc brakes under the Dura-Ace moniker and we couldn't be happier. Shimano's excellent E-Tube project offers customizable shifting set-up so no matter your cycling discipline, you are fully in control in how you program your shifting. Sold as individual right and left levers, the levers include specific BR-R9170 flat mount brake calipers and hydraulic hose kits.

Shimano's Di2 shifting is the gold-standard in which all other shifting is compared, so we're understandably excited that a hydraulic disc brake option now exists that proudly wears the Dura-Ace badge. Mating superior all-weather braking power and modulation with the industry's best shifting creates the most desirable components for your current drop bar bike or your next dream build.

The ergonomics of the new 9170 hydraulic lever are nothing short of phenomenal. The lever is much slimmer than before and is very similar to the silhouette of the non-hydro Di2 and mechanical versions of 9100. Shimano also worked on making the clicks more positive, which provides great feedback when operating the levers in freezing conditions with thick gloves, during a muddy 'cross race, or over washboard gravel roads. The ability to integrate satellite buttons for climber and sprinter shifters carries over from previous versions, but the new textured hoods provide excellent cushion and grip when you're shifting at the levers. They also simply disappear when we're riding.

We're not surprised that Shimano waited until the Dura-Ace version to include the flat-mount brake calipers. By doing so, Shimano was able to drop weight while increasing power and offering even more of the highly vaulted modulation. The caliper is very low-profile and the finish matches the rest of the Dura-Ace group. One of our favorite things about Shimano brakes is that they use mineral oil, which is safer for the environment and won't harm your frame's finish.

Though its proprietary mineral oil is more heat-resistant than standard DOT options, Shimano still worked hard to keep operating temperatures low. No one wants to carry around large heavy rotors on the road, so the brand looked at design and the materials used on the rotors, pads, and pistons to keep temps in check. The resin pads are super quiet and offer Dura-Ace-grade modulation, and the aluminum fins dissipate heat quickly and allow you to run smaller diameter rotors without the fear of overheating or fading on long descents. Ceramic pistons act as a heat sink to shield the caliper and fluid from the heat generated by the pads, and an aluminum core draws the heat away from the face of the stainless steel rotor.

Flat mounts are becoming the standard on newer 'cross, road, and gravel framesets, and most of the ones coming through the doors at Competitive Cyclist have them. In the wind tunnel, flat mounts have less of an impact on aerodynamic performance versus post mount, so if you're fretting about drag as a deciding factor, worry no more. Rotors are sold separately and the IceTech versions in 140 or 160mm are highly recommended.

The new E-tube Di2 system allows for a completely custom shifting setup. To take advantage of this system you will need to use a BM-DN100 or BT-DN110 battery and the EW-WU101 ANT/BLE wireless connector to connect to your tablet or phone. Each shift lever is programmable to operate either derailleur and you can choose if you want that button to upshift or downshift. Shimano also adds SyncroShift which helps to manage sequential shifting with two options. In fully synchronized mode, the front derailleur will automatically shift up or down based on the position of the rear derailleur and the set ratios you determine in the app. In semi-syncronization mode, you will still shift front and rear derailleurs normally but after a front shift is initiated, the rear derailleur will upshift or downshift depending on the direction of the front shift to keep cadence optimal and allow you to focus on pedaling and not gear ratios.