Shimano builds Ultegra and Dura-Ace on identical Di2 platforms, which means the ST-R8170 lever uses the same wireless protocol, the same Servo Wave brake technology, and the same E-Tube Project app as its more expensive sibling. The weight difference between them is about 20 grams per lever, and the Dura-Ace version uses titanium hardware where Ultegra uses steel. Everything else that matters for how the levers actually work is shared between the two groupsets. For most riders, that makes this Ultegra lever the more sensible choice.

The shifters communicate wirelessly via Bluetooth Low Energy to the derailleurs, sending commands to the BT-DN300 battery which then relays them to the front and rear derailleurs through thin SD300 wires. No junction boxes sit near the cockpit anymore, and no shift wires need to route through integrated bars and stems. Each lever runs on a CR1632 coin cell battery that Shimano estimates will last 1.5 to 2 years under normal use. When the battery eventually dies, swapping takes less than a minute with just a coin to pop the cover.

Servo Wave brake technology changes the mechanical advantage of the lever throughout its stroke. Initial travel moves the pads toward the rotor quickly with minimal lever effort, then the leverage ratio increases once the pads make contact. This creates more usable range for modulating braking force, which Shimano describes as a wider control area for finer adjustments when feathering through corners or managing speed on descents. The brake levers feature 16.4mm of reach adjustment, letting riders with smaller hands position the blade closer to the bar for confident single-finger braking from the drops or hoods.... Read More