How You Can Turn Your Bicycle Into An E-Bike

Every electric system you put on a bicycle is going to add weight. Mid-drive motors mitigate the effects of that extra weight because the added weight is sprung mass, and there is no extra rotational mass (via CJ Pony Parts). Mid-drive motors also benefit from the transmission system on a standard mountain bike. Since the chain runs from the motor output to the rear transmission, any force applied by the motor receives the same mechanical advantage as pedaling would. The motor acting through the gears on the rear wheel makes a mid-drive far more versatile. If you’re on a steep hill, you can shift into a lower gear to get more torque, and if you’re on a flat, you can shift into a higher gear for more speed — all without sacrificing efficiency of the motor.

Mid-drive motors aren’t perfect, though, and the main drawback is that they require a bit more mechanical know-how than a hub motor. For starters, there’s often a little more setup required. Instead of simply slotting in a new wheel, attaching a chain, and connecting the wires, mid-drives also require removing the bottom bracket and replacing it with the motor — a task that requires a special bottom bracket removal tool. Mid-drives also increase drivetrain wear, meaning replacement parts will be in order sooner (via Electric Travel).

While mid-drive motors take home the win in terms of efficiency and performance, hub motors are a neat package, and are often more than enough for the average commuter e-bike. Mid-drive motors also lose the cost competition in a bad way. While the aforementioned 1000 W Bafang mid-drive motor kit came in at around $530, a similar hub motor kit comes in at around $370. The penalty of mid-drive performance is cost and complexity.