- Drivetrains on e-bikes with strong mid motors are subject to enormous constant load. Based on that fact, KMC offer specific e-bike chains and sprockets for Bosch motors and internal gear hubs. Specifically designed for Bosch E-Bike systems, the KMC Narrow chainring is a perfect solution for replacing or upgrading your current front sprocket. By incorporating KMC into your drive train you can vastly increase useage and ensure a mileage of over 3,500km. * 1/2" X 11/128" or 1/8" * For Bosch II Systems * Chromoly Black