Electric Bike Mid drive Systems (Bottom Bracket Systems)
Mid drives geared systems vs hub motors
May 01, 2014
Hub motors systems do not utilize the benefits of the gears on the bike. The mid drives are much more efficient.
Bafang BBSO2, 750W mid-drive electric bike motor
U.S. Distributor: http://www.electricbike.com/bafang-bbso2-750w-mid-drive/
Here is an example of a mid-drive that is fairly noisy.
Benefits of a mid drive over a hub motor
- Climbs steep hills MUCH better than a hub motor. There are videos of mid drives climbing stairs…(a feat nearly impossible to do on a hub motor electric bike).
- Places the weight of the motor low and centralized in the frame (instead of a heavy hub in the rear wheel) which means a better balanced feel.
- The motor can use the bikes gears, so the RPMs stay up in it’s efficient range = More range per battery-Ah.
- Keeping the motor in it’s best RPM range means lower peak-amps drawn from the battery.
- Giving the motor some gears to use, also means you can get a broader range of performance from a smaller and lighter motor.
- Easy to change a flat tire with no hub motor.
- No more broken spokes from hitting a pothole with a heavy hub motor in the wheel.
Drawbacks of a mid drive:
- Often more expensive than a simple hub-motor.
- Some mid-drives are noisier than a hub, a direct-drive hub with a sinewave controller is especially quiet.
- Mid-drive kits are more complex to install than a simple hub.
- Shifting a mid drive electric bike can be a real pain. With a hub motor bike, the only reason to use gears is to get the right pedal cadence which usually means just staying in high gear.
- Mid drives are generally not as well suited for flat land street commuting as hub motor bikes.
- Mid drives are not as stealthy as most hub motor bikes.
- If you want a super powerful electric bike (over 2000 watts) you have better and more reliable options from hub motor kits.
- Mid drives have more moving parts and therefore tend to be less reliable than most hub motor kits.
Most mid-drives (chain-drives) are noisy because of the chain on the sprocket and the internal gears. BaFang has this problem solved using a composite and wide gear internally.
Electric motors: the losses are the square of the current. Example: if you use 4 times the current to get up a hill, you in fact use 16 times the heat and energy looses. This describes hub motors which have a significant loss due to increased current demands because they are not geared efficient as a mid drive hookup which utilizes the same gears which allows you to more easily trek up a hill or incline. More torque needed to climb (hub drives) = more current = heated motor.