The Shimano 105 ST-R7170-L is the left dual-control lever for hydraulic disc brakes and Di2 electronic front shifting on 2×12-speed road bikes. It suits riders upgrading to wireless electronic shifting on Shimano 105 R7100 series groupsets, paired with FD-R7150 front derailleur and BR-R7170 caliper (not included). Compatible with drop bars (23.8-24.2mm clamp) and flat-mount front forks, it uses wireless Di2 connectivity for front shifts without cables, keeping the cockpit clean. Requires SM-BH90-J-SSR or SM-BH90-JK-SSR hoses and Shimano mineral oil for braking. Two CR1632 batteries per lever last 3.5-4 years. Reach and free stroke adjustment allow fit tweaks via hoods; customize buttons with E-TUBE app. No satellite shifter port or hidden hood buttons, and wired shifting not supported.