There are different systems on the market using a mid-drive pedal-assist or a rear/front wheel assist motor. The rear/front wheel assist systems mostly give you the option of having a throttle so you don’t necessarily have to pedal. The motor is either in the front or the rear wheel (hub).
Mid-drive systems like Bosch or Shimano STEPS provide power through the cranks of the bike and enhance your pedal stroke – so you must be pedalling to engage the assist.
Mid-drive systems now make up approximately 90% of the e-bike market, Bosch is a worldwide leader in the category. Their mid-drive system is light weight, centrally located on the bike, and the direct power is extremely efficient. With 4 different drive units, and various battery options, Bosch makes systems for electric bikes which are designed for recreational riding, commuting, off road riding and even cargo bikes.
The Bosch e-bike system offers a 4 tiered assist system and the batteries are made up of lithium ion cells, with a high quality monitoring system.
Similar to Bosch, Shimano makes a mid-drive system for e-bike manufactures to use when designing electric bikes. Shimano's systems are very lightweight, and smooth riding. With the drive unit placed around the crank, the bicycles centre of gravity is quite low. The 3 tiered controller system gives you the option to run low, medium or high assist levels, or run the bike without assist.