General Overview of Electric Bikes or eBikes
The first question we when talking to someone new to electric bikes is, “Do I have to pedal?” The short answer is “yes”.
Pedal-assist eBikes do not do the work for you, instead they add to the work you do so that you go further and faster with the same effort. Of course this does make it easier to cruise and climb hills, however think of it more like having a coach rather than cheating. EBikes allow you to pedal comfortably while covering more ground, climbing hills, or enjoying your commute. In reality you may get better quality exercise in a given amount of time because your relaxed mindset gives no voice to self-imposed limitations, just like having a coach!
Riding a bicycle gets you outside breathing fresh air, is good exercise, and it’s fun! eBikes add to this by rewarding your efforts with a higher average speed, more hill climbing capability, and more practicality.
Most eBikes can go 30-50 miles on a single charge, while some models can easily achieve 80-100 miles or more. Small changes in your eBike’s set up can greatly effect its efficiency. It is important that when your eBikes is newly assembled that all bearings are properly adjusted, wheels are aligned and true, and that the bike fit and ergonomics are comfortable for you. Before a ride make sure the battery is fully charged and locked to the bike, and be sure your tires are properly inflated. Low tire pressure wastes a lot of energy and can significantly decrease the distance you go on a charge.
Ebike motors fall into two categories: Hub- Drive and Mid-Drive.
Hub-drive motors are very powerful and simple because the rear wheel is the motor. Hub-drives commonly have both pedal-assist and throttle operation. Hub motors fall into two basic categories as well; direct- drive hub motors and geared hub motors.
With direct-drive hub motors the hub is literally the motor, meaning that the motor is turning the same speed as the wheel. If you are riding along at 20mph, the wheel is turning at about 260rpm, and therefore the motor is also turning at about 260 rpm. Direct drive hub motors are the only motor capable of regeneration. With a geared hub motor, the motor is inside the hub, and there are gears between the motor and the hub shell. This allows the motor to turn faster than the wheel, making it much more efficient. Both types of hub-drives are typically a 48 volt system with a 500 watt motor (more on electrical specifications below).
Mid-drive implies that the motor is in the middle of the bike and the motor turns the cranks. Mid drives are very efficient because the gears of the bicycle also serve as a transmission for the motor. Mid drive motors are made by some of the biggest tech companies in the world including Bosch, Shimano, Yamaha, and Panasonic. They are typically 36 volt systems and 250-350 watt motors.
Even though mid-drives use less powerful motors, they are more capable because of the way they use that power. In the world of electronics greater efficiency equals smaller batteries, less weight, and lower operating temperatures.
Understanding Electrical Specifications
(Doing our best to demystify all the ratings and numbers)
Voltage is the most important specification in an electrical system. Voltage is the electrical pressure in the circuit, which is supplied by the battery (or in your home, the wall socket). The entire electrical system is designed to operate correctly and efficiently at a specific voltage. It’s easy to visualize voltage like water pressure in a pipe. Increase the pressure and more water will flow, but at some point the pipe may burst!
Amperage (Amps) is the amount of electrical current flowing through the system. The electrical circuit and motor are designed to handle the current that will flow at a specific voltage. If you increase the voltage, more current will flow, but things will heat up and this can damage components. Just like in the example above, the wiring and motor are designed to handle a maximum amount of pressure, which will safely conduct the electrical current that will flow at that pressure.
Power (Watts) is the amount of work being produced. To determine the power you multiply the amount of current flowing (amps) by the amount of pressure (volts) behind this flow, or watts = amps x volts.
Watts(power) = Amps(current) x Volts(pressure)
Battery capacity is measured in amp-hours (Ah). This is like measuring the amount of gas your car can hold, but in this case it is how many amps of current the battery can provide continuously for one hour. So a 14Ah battery will provide 14 amps of current continuously for one hour and then need a recharge. If you take energy out of the battery slower it will last longer. A 14Ah battery can also supply one amp of current continuously for 14 hours.
The total amount of power (or work) that a battery can supply is measured in Watt-hours (Wh). This is also what the power company charges you for in your home, except in thousands of watt-hours, or kilowatt-hours (kWh). To calculate watt-hours you multiply the amp-hour capacity of the battery by its voltage. If you know that a battery is 36 volts and it holds 14 amp-hours, multiply 36 by 14 which equals 504 watt-hours.
Many mid-drive manufacturers specify the total power of their batteries in watt-hours. For example the Bosch PowerPack 500 is a 500 watt-hour battery. If you divide 500 watt-hours by 36 volts you see the Bosch PowerPack 500 is also a 14 amp-hour battery.
Many hub-drive manufacturers specify the capacity of their batteries in amp-hours. If you have a 48 volt hub-drive system with a 14 amp-hour battery, multiply 48 by 14 to get a total battery power of 672 watt-hours!
The difference in the efficiency of a mid-drive compared to a hub drive is indirectly represented by the total power of the batteries they typically come with. The hub motor consumes more power so larger capacity batteries are used to match the range of a lesser powered mid-drive. This is not to discredit hub drive systems; they are very powerful, reliable, allow the use of a throttle, and are excellent for all types of smooth surface riding (including dirt paths and recreational off-road riding). In fact a small lightweight hub drive system with a small battery is the choice for many high-end e-road bikes. The minimal system can be added to a lightweight high performance bicycle and give the rider a little extra boost for their effort. This makes the ride much more exciting without adding a lot to the basic bicycle.