Here you will find a discussion of E-Bike motor types.
A geared hub motor has internal gears inside the hub casing. Its a permanent fixed gear, there is no shifting. Geared motors tend to be smaller and have more torque than a direct drive hub motor. An added advantage of the geared hub motor is that its free spinning and so doesnt create any added drag when the motor is not being used. Bafang do a number of geared brushless e-bike motors.
A direct drive hub motor is similar in appearance to a geared motor although its larger in size. There is no gearing , a revolution of the motor equates to a revolution of the wheel. In theory a direct drive motor should provide higher top speeds but has less torque than a geared motor. One advantage of a direct drive motor is that it is possible to use regenerative braking which charges the battery when going downhill or braking.
Many low end electric bikes use hub motors as they are cheap to buy. An electric bike conversion kit using a hub motor can be bought from Ebay for as little as £130. As the popularity of E bikes increases so the techonology improves mid drive crank motors are used more on bike in the more mid / high price ranges.
Mid Drive Motors
A mid drive motor, as the name suggests is mounting the centre of the bike at the bottom bracket. The motor drives the crank and so utilises the existing gearing of the bicycle. The downside is that there may be more wear and tear on the drivetrain of the bike.
This mid positioning gives the bike better stability and balance as the weight of the bike is in the centre. Due to the increased development from large manufacturers, mid drive motors now offer better performance than their hub motor counterparts. The performance of these motors is better than hub motors. As a mid range motor utilises the existing drive chain you can use the normal bike gears to go up hills etc.
Friction motors work by rubbing against the tyre.
There is also another way to turn your normal bike into an electric bike. Of course you can buy a kit and mount either a hub or a mid-drive motor, but you can also mount – directly to your seatpost – a friction motor. This system generate energy through a battery that makes a roller turning on your wheel and propel the bike forward.
The advantage of friction motors is that they are easy to fit and they work on most types of bikes. The downside is they will wear the tyre and may also suffer problems in wet weather conditions.
An example of a e bike friction motor is the GBoost System.