Understanding Electric Bikes

It’s pretty obvious that one of the most important components of an electric bicycle is the electric motor. The motor is what turns the electrical energy from your battery into movement. Today we’ll be looking at different types of electric hub motors, so you can understand what makes them different, how they work, and ultimately, which type is best for you.

In the electric bicycle industry, two types of hub motors dominate: direct drive (gearless) motors, and geared hub motors. In a nutshell, both types of motor do the same thing – they spin, and they use magnets to get the job done. The difference lies in the innards, specifically how the motor gets the force generated inside the motor outside.

Direct Drive (or Gearless) Hub Motors

The direct drive hub motor is much simpler than the geared hub motor design. To put it simply, a direct drive hub motor just spins the outer shell of the motor (including the wheel) around the axle.

The axle of the motor is part of a larger disc inside the motor, which is surrounded with copper windings. This inner part is called the “stator” because it is static – it doesn’t move. The outer part, which includes the shell and is attached to the rest of the wheel, is lined with magnets. This is called the “rotor” because it is the part that rotates.

By sending a current through the copper windings in the stator, the stator artificially induces a magnetic field. Manipulating this current allows the stator to force the magnets on the rotor to move – moving the wheel with it!

A picture of the insides of a direct drive hub motor.
This is what a direct drive motor looks like on the inside. Notice the copper wire coils surrounding the stator. (source)

Geared Hub Motors

The core difference between direct drive and geared hub motors is that geared hub motors have an additional planetary gear system. The rotor doesn’t turn the outer casing, but the inner part of the planetary gear system. The planetary gear system then turns the outer casing, along with the wheel.

Example of a planetary gear system.
Example of a planetary gear system. In a geared hub motor, the rotor is the centre gear, and the shell is rotated like the outer gear is. (source)

This might seem redundant, but the gearing makes it so that for each rotation of the wheel, the motor has spun many more times. Inside, the motor is constantly spinning at very high speeds. This allows the motor to operate at its optimal speeds, maximizing efficiency, without requiring the outer casing to rotate as quickly.

What does this mean?

Direct drive hub motors are fundamentally simpler, resulting in a more durable design with fewer small, moving parts. On top of that, direct drive motors can reach higher top speeds and run more quietly than their geared counterparts. The flipside of this is that direct drive hub motors are bigger and heavier. You simple need more space to get more power. This means less battery efficiency – you won’t go as far on one of these. Also, the lack of gearing means you have to deal with more resistance while pedaling.

Geared hub motors, on the other hand, are a clever but more complex design. The many moving parts make it slightly louder, and will eventually wear down, so they won’t last as long as direct drive hub motors do. They also won’t reach the same top speeds as direct drive. In exchange for speed, geared motors produce more torque – helping you get up and over hills and accelerate faster. The geared design is also more compact, allowing geared hub motors to be smaller and lighter than direct drive motors, and also be more power-efficient. There is also less resistance when pedaling.

FeatureDirect DriveGeared
Speed
Torque
Size
Weight
Efficiency
Durability
Noise
Resistance

Which one should I get?

Currently, geared hub motors are becoming more and more common. The smaller, lightweight body, and improved torque and efficiency have made it the most practical choice for daily usage in a variety of situations. Under standard Victorian laws, electric bicycles have a wattage limit of 200W of power for standard electric bicycles and 250W for pedal-elecs (always make sure to check your local laws, as they may differ). At this wattage, the advantages of direct drive motors aren’t very significant, so geared motors end up being more popular here.

However, if you want speed and a motor durable enough to carry heavy loads for a long time, a direct drive motor might be the best choice for the job. Just remember to comply with your local regulations!