Chainrings, kits and service parts for mid-drive systems.
Mid-drive motors sit at the bottom bracket and drive the bike's chain, so they multiply torque through the gears the same way your legs do. That is why they climb so well and why cargo bikes and serious commuters favor them. It also means the drivetrain does more work: chains, chainrings and cassettes wear faster than on a hub-drive bike, and the parts that attach to the motor are often specific to that motor family rather than standard bike parts.
The aftermarket is dominated by Bafang's BBS01, BBS02 and BBSHD kits and their accessories, alongside a smaller set of other conversion motors, while factory mid-drives from Bosch, Shimano, Yamaha and Brose are mostly dealer-serviced and use their own chainrings and covers. Whichever you own, the first thing to identify is the exact motor model, because chainrings, spider adapters, gear sensors, controllers and displays are typically model-specific. The second is your frame's bottom bracket shell width, since conversion kits are sold in a few shell lengths and a kit that is too short or too long will not clamp securely.
Chainline is the detail people underestimate. A mid-drive's chainring sits in a fixed spot, and if it does not line up reasonably with the cassette the chain will drop or wear out quickly; offset chainrings and narrow-wide teeth exist precisely to fix that. Electrically, mid-drive kits are closed systems, so stick to parts made for your motor and confirm compatibility with the seller. Mismatched electrical parts can damage a controller or battery; if you are unsure what you have, an E-Bike Assessment is the safe next step.
