The different types of Electric Bicycle Motor
What is the difference between a direct drive hub motor and a geared hub motor on an e-bike?
The geared and gearless terms refer to the way power is transferred from the motor to propel the bike forward. In practice, this distinction usually applies to in-wheel motors (located in the center of the wheel) rather than mid-drives (located around the pedal crank) - the vast majority of mid-drives are geared motors.
Overview of Geared Hub Motors
Geared hub motors use a gear system inside the hub to transmit the rotational force of the motor to the hub and wheel. It's easiest to see in the typical cheap hub motor in the picture above. The central gear, which is fixed to the rotating motor, turns to the hub through a series of other gears (called planetary and ring gears, but that doesn't matter...).
The main point to understand is that the gears inside the hub reduce the rapid speed at which the motor turns, allowing the wheel to turn at a more suitable speed. Motors like to turn fast, much faster than the wheels of your bike, hence the need for gearing. Geared hub motors are the most common and economical form of the hub motor.
Gearless (Direct Drive) In-Wheel Motor Overview
Yes, you guessed it, a gearless hub motor has no gears inside the hub! As you can see in the picture above, the hub in a gearless system is the motor itself. The bundle of copper wires you see is part of the stator on the right. When the motor controller pulls current from the battery into the wires, the stator becomes an electromagnet. In the hub shell on the left, are permanent magnets that force the stator to turn when energized, by subtly attracting and repelling the magnets at the right time. There are no gears involved - just magnetism - hence the gearless moniker.
While this might sound like the ideal solution - why introduce extra gearing in the hub if it isn't needed? - It's not as simple as we explain in the pros and cons section below.