Most bicycles have front mounted, brushless, permanent magnet hub motors. Some models have rear mounted hub motors.
Some motors have brush and armature.
Maximum current is 20 Amps and safe 30 Volts at the regulator. Battery recharging is 4 to 6 hours. Wheel hub speed is 250 r.p.m. The hub motor will accept up to 450 Watt overloading. Actual speed averages 18 miles per hour but depends on wind, weight, grade and surface.