Mid-Drive Motors Demystified
Mid-drive systems good for climbing long steep hills because they can leverage the lower gears of the bike and keep their rpm’s in an efficient range without getting “bogged down” like a hub motor. This is a good feature if you ride in areas that have consistently long and steep hill climbs.
These motors can also leverage the higher gears of the drivetrain to cruise along at high speeds on flat or inclined roads.
Since the motor is at the cranks of the bike, it provides for a low and centered weight distribution. When the battery is mounted in the center of the bike it adds to great weight distribution which is good for the handling of the bike as well as making it easier to lift onto a car rack or carry upstairs.
Removing the front or rear wheel is easy because there are no motor wires or hardware to remove when compared to a hub motor. The bike can use almost any wheel type along with quick releases front and rear.
Most mid-drive systems use a chain, cogs, and derailleur drivetrain. Some systems are compatible with internally geared hubs and belt drives. The E2 Drives combine the mid drive motor with a “gearbox” at the cranks.
A mid-drive system can use a throttle and/ or cadence or torque sensor pedal assist.
Some mid drives are quite sophisticated with sensors that measure the pedal power, wheel speed, and crank speed to provide assist that blends with the rider’s power to create a very intuitive ride feel.
There are also sensors that will reduce power when the system senses that the rider is going to shift gears to make the shift smoother.
In addition, there are some mid drives that are integrating with electronic shifting systems.
Since the power is being transferred through the drivetrain of the bike, the drivetrain components (chain, cogs, derailleur, etc.) will experience increased wear. The higher power systems will add significantly more wear and those components may need to be replaced on a more frequent basis.
In order to keep the mid-drive motor operating efficiently the rider needs to shift gears properly when climbing hills or cruising along the flat roads.
Some mid-drive systems will reduce the power when shifting for a smoother ride. Other systems may not have sensors to detect shifting and that can lead to abrupt shifts when the motor is applying full power.
A majority of mid-drives systems only have a single chain-ring. This limits the gear range to a rear cog-set or internally geared hub. For most general riding conditions this is not a big issue because the motor is capable of compensating for the missing gear range. Also, the gear range of most rear cog-set or IGH tends to be pretty wide on most bikes these days.
Most of the popular mid-drive systems are only available on complete e-bikes with specific frame mounts. There are not many mid-drive retrofit kits available currently but we may see more on the horizon.
Mid-drive systems experience frequent damage to rims (spoke pulls) due to the high torque generated by electric motors.
If the system fails it can not be removed or bypassed and the bike basically becomes unusable until it has been repaired.
If you already own a conventional bike that you enjoy riding, you will need to purchase a whole new bike to benefit from a mid-drive system since a mid-drive system cannot be easily installed on a typical bike frame.
Mid-drive systems also tend to be amongst the more expensive types of systems available today.