In a parallel hybrid motorized bicycle, such as the aforementioned 1897 invention by Hosea W. Libbey, human and motor inputs are mechanically coupled either in the bottom bracket, the rear wheel, or the front wheel, whereas in a (mechanical) series hybrid cycle, the human and motor inputs are coupled through differential gearing. In an (electronic) series hybrid cycle, human power is converted into electricity and is fed directly into the motor and mostly additional electricity is supplied from a battery.
Bicycles have long been one of the most popular modes of transportation and, in a time where environmental friendless and health are top of mind, the popularity of bicycles shows no signs of slowing down. For many bicycle enthusiasts, an electric bike is the best of both worlds (get where you're going faster and not winded) and with a range of choices and designs available, we've helped narrow down the best models on the market today.
Gearing: none (many hub motors, one motor revolution = one wheel revolution), fixed gear reduction for more torque, varies when geared motor drives the chain through the bicycle gears which increases torque about 50% (in low gear) for better hill-climbing and offers better top-end speed (in high gear) than direct drive systems using motors of similar wattage.
More powerful pedelecs which are not legally classed as bicycles are dubbed S-Pedelecs (short for Schnell-Pedelecs, i.e. Speedy-Pedelecs) in Germany. These have a motor more powerful than 250 watts and less limited, or unlimited, pedal-assist, i.e. the motor does not stop assisting the rider once 25 km/h has been reached. S-Pedelec class e-bikes are therefore usually classified as mopeds or motorcycles rather than as bicycles and therefore may (depending on the jurisdiction) need to be registered and insured, the rider may need some sort of driver's license (either car or motorcycle) and motorcycle helmets may have to be worn. In the United States, many states have adopted S-Pedelecs into the Class 3 category. Class 3 ebikes are limited to <=750 watts of power and 28 mph.
For many bikes, battery range is more important that total power (because they're all pretty powerful). You want a bike that delivers a range long enough for your rides at the power levels you want. Most e-bikes will have three to five levels of assist kicking in anywhere from 25 percent of you pedal power to 200 percent boost. Consider how fast the battery takes to recharge, especially if you'll be using your bike for long commutes.