Originally Posted by chas58

Keep in mind that the majority of hub motors use an older screw on type. Typically these are 7 speed with the smallest tooth being 14 teeth (although there are some other (non Shimano) alternatives that are not of the best quality).

If you want to use the more modern Cassette hubs (where the cassette slides on to splines on the hub), you need one of the newer CST designs, and that takes a little more searching for (look for Bafang CST for instance).

EM3ev is a useful site with good information. As you can see, the MAC motor can be built with different voltages and power ranges. It is the controller that determines the current (AMPS = torque) and the battery that determines speed (Volts = speed). Amps X Vots = Power. To further complicate things, the winding (Turns) in the motor also determine speed, so it is important that the motor/battery/controller are matched together. Otherwise you could get a motor that turns too fast and ends up burning out.

Keep in mind that a "high torque" motor (low number of turns on the wiring) does not really have more torque than a "high speed" motor. Their torque and power is about the same (with the same controller and battery). Its just that the "high speed" motor will not be able to provide a lot of low speed torque without burning up, while the "high torque" motor can operate efficiently at low speeds, but will have a lower top speed.