What Does the Shimano R8170 Ultegra Di2 Left Lever Do?

The ST-R8170 left lever is the front brake and left-side shift control for Shimano's 12-speed Ultegra Di2 hydraulic disc brake system. The lever integrates two distinct systems into a single unit: the BR-R8170 hydraulic disc brake caliper with a 2-piston design for consistent, powerful stopping power, and the Di2 wireless shift interface that sends electronic shift signals without a physical cable connection to the derailleur. The brake side uses Shimano's SERVO-WAVE technology, which varies the leverage ratio through the lever stroke to deliver an initial quick pad pickup followed by increasing power as braking force builds, creating a more intuitive feel compared to linear-ratio hydraulic systems. The result is precise modulation at light braking intensities with full stopping power available when needed.

The wireless Di2 platform removes shift cables entirely from the front lever while maintaining Shimano's characteristically reliable and fast electronic actuation. The ST-R8170 is sold as a single left unit and pairs with the right ST-R8170 lever to complete the Ultegra Di2 12-speed system. It is compatible with the full Ultegra R8100 and R8150 Di2 ecosystem including the RD-R8150 rear derailleur and FD-R8150 front derailleur. The BR-R8170 caliper is flat-mount and mounts to standard flat-mount disc brake frame mounts. For road cyclists building or upgrading to a complete Ultegra Di2 wireless hydraulic disc system, the ST-R8170 left lever is the correct front-side component.