The motor that powers an electric bike is usually located in one of two possible places; either in one of the hubs or in the bottom bracket area. There are pros and cons to both:
HUB MOTOR
Hub-based motors tend to be smaller, lighter and less powerful so are often found on commuter or hybrid style bikes although they have also been adopted for some lower-powered road bikes in order to take advantage of their lighter weight. As there is no need to manufacture the frame with room for a motor in it, the frame and the bike can look more subtle and elegant than the alternatives. If the motor is located in the front hub then the steering and traction can be affected a little and, whether positioned front or rear, removing the wheel can be a little more difficult. At slow speeds hub motors can struggle a touch as they drive the wheel directly rather than with the benefit of gearing, but operate better when spinning at higher speeds.
BOTTOM BRACKET MOTOR
Bikes that site the motor in the bottom bracket area (sometimes called mid-motor or crank motor) have to have a frame that has been designed specifically to house it, so can look bulky and heavy, but as it can be larger than a hub motor it can also be more powerful. Mountain bikes, in particular, utilise this form of motor, but it can also be found in many powerful electric road or gravel bikes as well as some hybrids. As the motor is connected to the crankset, it is more likely to be spinning quickly and efficiently to help drive the bike, but the added torque can cause extra wear on the chain and drivetrain.
THE TYPES OF BATTERY USED IN ELECTRIC BIKES
Key to an electric bike’s performance and range is its battery. Measured in watt hours (Wh), the bigger the battery’s output, the greater the range that the bike will have, all other things being equal, but this power comes at the cost of size, weight and charge time. Most modern electric bikes use Lithium-Ion batteries as they offer the best performance and range for their weight and don’t need to be fully discharged before recharging. Batteries are usually between 300-700Wh, although some bikes can have additional range extender batteries added to the system for longer rides.
RACK-MOUNTED BATTERY
The main location for the battery on an electric bike is either in the downtube of the frame or on a rack at the back of the bike. The rack-mounted option is the simplest for the manufacturer and allows easy access to the battery for removal or recharging but raises the bike’s centre of gravity and means that the rack might not be able to be used for luggage as well. Typically it is less expensive commuter or hybrid style bikes that mount the battery in this way.
DOWNTUBE BATTERY
The more prevalent battery placement option is to design the bike’s frame around a battery that is mounted in, or forms part of, the downtube; this solution is much neater than rack mounting and keeps the extra weight low down on the frame for better handling. Some of these downtube batteries can be removed from the bike without the need for tools for charging in the house or to save weight if electric assistance isn’t required on a particular ride.