The ST-R8170 is where Shimano's second-generation semi-wireless Di2 story lives at the Ultegra tier, and for most riders it's the practical entry point into 12-speed electronic road. You get the same shifting architecture Shimano put in Dura-Ace R9270 — wireless communication from the levers to the rear derailleur, a wired connection from the rear derailleur to the front derailleur and central battery, and Bluetooth setup through the E-TUBE app. The differences between R8170 and R9270 come down to materials and finish rather than function: shift speed, button layout, and hood shape all carry across.

Ergonomically these are a real departure from the R8070 hoods they replace. Shimano raised the peak of the hood and reshaped the transition into the bar, which gives you more to hang onto when you're climbing out of the saddle and a flatter perch when you're riding on the tops. The reach on the brake lever is bolt-adjustable with a 2mm hex, and free stroke is separately adjustable using the same tool, so you can dial the lever position to your hand size without shimming or swapping parts. The lever blade itself is aluminum and the body is carbon composite, which is where the weight sits relative to previous mechanical Ultegra hoods.

Braking is Servo Wave, which changes the leverage ratio through the stroke — light initial engagement to bring the pads to the rotor, then a firmer ratio once you're actually slowing the bike. Paired with BR-R8170 flat mount calipers and Shimano mineral oil, the modulation is genuinely one of the strong arguments for staying on Shimano hydraulics rather than switching platforms. The master cylinder connects via SM-BH90-JK-SSR hose, which is sold separately and needs to be cut to length for your frame's routing.... Read More