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April 29, 2017
One of the questions we often get from customers is how the different types of electric bike motors work, and which is the best.
In this post, we discuss each of the three major types of ebike motors, mid-drive, hub (front and rear), and all-in-one designs, and talk about their various applications.
Mid-drive motors (also known as mid-motors) are centrally located around the bottom bracket of the bike frame; that's the cylindrical shell at the bottom center of the frame that houses the crankset.
Placing a motor in this location is ideal, since it provides for a low and centered distribution of weight. This is useful when riding your ebike, but also helps when the bikes are being lifted into cars, boats or airplanes, or carried up a flight of stairs.
Mid-drive motors provide the greatest amount of power, and are ideal for long, steep climbs, because they are able to leverage the lower gears of the bike and keep the RPMs in an efficient range without getting bogged down.
They also work well when traveling at higher speeds on flat or inclined roads or pathways, as they are capable for leveraging the higher gears of the bike.
Most mid-drive systems use a chain, cogs, and derailleur drivetrain, and some systems are compatible with internally geared hubs and belt drives. Some of the more sophisticated mid-drive systems have sensors that measure pedal power, wheel speed and crank speed, to automatically provides levels of assist that blend with the rider’s own powering, creating a very intuitive ride feel.
There are also sensors that can reduce power when the system senses that the rider is slowing down and shifting gears, making the speed transition very smooth. Some of the most sophisticated mid-drive systems are electronically integrated with shifting systems.
Mid-drive systems are powerful, and therefore place a great deal of stress on the drivetrain. This can add the wear and tear of these components (chain, cogs, derailleur, etc.) and way require that they be replaced more frequently.
A great example of a well-engineered ebike with a mid-drive motor is the Bakcou Mule electric mountain bike, which features a 1000W Bafang Ultra mid-drive. The Mule is featured in the Ultimate Guide to Fat Tire Electric Bikes.
The hub is the centermost part of a wheel. The hub is the part of the wheel where the spokes attach to and the part that includes the axle or quick release, which attach the wheel to the bicycle.
As the name suggests, hub motors are actually built into the hub of the wheel (front or rear), and may include internal gears. Hub motors are the most common types of electric motors on ebikes.
While hub motors are not exceedingly heavy, their placement in the front or rear wheel will affect the overall weight distribution and balance of the bike.
Direct drive hub motors use the whole hub shell, while geared hub motors are smaller, and use planetary gears to drive the hub shell. In addition, we are starting to see a number of all-in-one electric wheel systems, which house all of the electric bike components in the hub or wheel, including the motor, battery and controller.
To understand how a typical brushless DC motor actually works, take a look at this instructive video.
The following section discusses the various pros and cons for each of the major hub motor types.
Because of its forward location in the front wheel, a front wheel hub has the effect of pulling the ebike forward. One of the main benefits of the front hub motor is that it creates an effective all-wheel-drive system (it drives or pulls the front wheel forward, while you are powering the rear wheel by pedaling).
This type of power combo is really useful when trudging through uneven surfaces such as snow or sand. However, front hub motors have a tendency to feel bogged down on long steep climbs.
Another benefit of the front wheel placement of the hub motor is that it allows for a variety of bike drivetrains to be used to power the rear wheel. This includes the traditional chain-driven gear cassettes with derailleurs, or internally-geared hubs driven with a chain or belt drive. Many riders prefer belt drives because they do not require grease and are thus much cleaner than chains.
Also, unlike rear hub motors, front hub motors are relatively easy to remove from the bike, since they do not connect to a chain or belt drive system. This is useful if you need to fix a flat tire, or if you want to change out the powered hub for a conventional front wheel.
The forward location of the front hub motor also helps to distribute the overall weight of ebikes which have batteries located on a rear rack or behind the seat post.
Front hub motors tend to be less powerful than rear hub motors, typically in the 250 watt to 350 watt range). One reason for this is that in the forward location, the only support the motor gets is from the front fork, whereas a rear hub motor is supported by the structural platform of the seat and chain stays. For this reason, if you are looking at hub motors, make sure the bike itself comes with sturdy forks, larger spokes and strong rims, especially for higher-powered models.
Front hub motors typically have a throttle and/or cadence sensor pedal assist configuration. Torque sensor systems, which sense the amount of energy you are using to move the pedals, are more common in mid-drive and rear hub motors.
In contrast to front hub motors which pull the bike forward, rear hub motors have the effect of pushing the bike forward; because conventional (non-electric) bikes also push forward when exerting energy through pedaling, the rear hub motor feels more familiar to most riders.
Rear hub motors come in a wide range of power options, from about 250 watts all the way 1000 watts, which is made possible by a structural platform (seat and chain stays) that can handle the high torque from the motor.
In a rear hub motor configuration, there is less tendency for the rear wheel to spin out when riding over gravel or other uneven surfaces, when compared to front wheel drives. They can also be setup to provide electric power with a throttle and/or cadence or torque sensor pedal assist.
One thing to consider before buying an ebike with a rear hub motor is the fact that they can be a little cumbersome to install or remove, because you will need to work around the gear cassette and derailleur (unless, of course, the hub motor is internally geared).
Also, rear hub motor powered ebikes may tend to bog down on long, steep climbs when compared to mid-drive ebikes (but less so when compared to front hub motor drives).
Make sure when shopping for a rear hub motor ebike that it has larger spokes and sturdy rims, which are needed to handle the extra torque.
While not as common as hub or mid-drive motors, some ebikes come equipped with all-in-one wheels, where the motor, electric battery and controller are all housed within the front or rear wheel. The pulling effect of front hubs motors, and the pushing effect rear hub motors, described above, would also apply to all-in-one configurations.
All-in-one systems are typically easy to install, and can be found as aftermarket add-ons for conventional bicycles. However, with all the weight of the motor and battery combined in one location, rather than distributed across the frame of the bike, these types of systems are typically less balanced than other ebikes.
Because all-in-one systems house the battery and motor together, excessive heat from the motor can affect the performance and lifespan of the battery. Some higher end bikes with all-in-one systems have addressed this issue with proper insulation, but a buyer should review each system on a case-by-case basis.
Whichever motor you decide is right for you, alway make sure that you buy your ebike from a reputable supplier who warranties their products. And it should go without saying, please always wear a bicycle helmet, even for the shortest rides in the safest places. Thank you.
ps - to learn more about the pros and cons of hub drives vs. mid drive motors, check out his informative video from the guys at Blue Monkey Bicycles...
And if you wondering about us, check out our About Us video ;)
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