e*thirteen Helix Race Carbon e*spec Crankset – 165mm BOSCH SX-Brose S Mag-TQ HPR50 21.5mm Offset Black. Helix Core cranks provide an e-bike drivetrain upgrade with high-end features and aesthetics at an exceptional value. Forged for e-Enduro strength with alloy self-extractor bolts pedal washers and molded impact boots. 24mm ISIS interface models are compatible with Bosch Gen 4 Brose S Mag TQ Fazua Yamaha Maxon and Specialized Brose motor systems. Available in short lengths from 155mm for improved pedal clearance.