Like a car, the size, strength and power of an e-bike’s motor and battery can vary greatly from model to model. Even changing one component in the drive system can drastically change how it performs.
The below list of variables and terms are how e-bike manufacturers describe their motor and battery systems. By grasping them, you can get a rough picture of how a given bike might perform (at least on paper).
- Torque is the rotational force produced by the motor, usually measured in Newton meters (Nm). On an e-bike, torque is particularly important for acceleration and going up hills.
- Volts are, in essence, a measure of electrical pressure inside a battery. The measure is commonly explained using this analogy: If a battery is a water tank, the voltage would be the water pressure built up inside. The higher the pressure inside the tank (or volts inside a battery), the quicker water (electricity) will flow from the tank (battery) and at higher volumes. To sum it up: The higher an e-bike battery’s voltage, the more power is available to the motor and quicker.
- Amps (short for ampere) is the basic unit used to measure electrical current. What this describes is the constant rate of flow of electricity out of a battery. The higher the amperage, the more electricity is flowing.
- Amp hours: Going back to the water analogy, amp hours describe the size of the water tank. The larger the tank — or, in the case of e-bikes, the larger the battery — the more water there is for use. This unit of measurement tells you exactly how much amperage a battery can sustain for one hour. For example, a 10Ah rated battery can expend 10 amps of power in an hour before it’s drained. That rate can also be accelerated or decelerated, so the same battery can expend 20 amps in a half-hour or 5 amps over two hours.
- Watts (often shortened to just a “w”) are to e-bikes what horsepower is to cars. It’s a measure of how much power the motor produces. The three-class system in the U.S. allows e-bikes to sustain up to 750w, though many motors can produce short bursts much higher than that. For context, a typical professional road cyclist might average between 300w and 400w during a race, so e-bike motors are plenty strong.
- Watt hours (Wh for short) describes how much energy is available in a battery for exactly one hour. A battery rated for 480Wh, for example, is going to have a battery capable of producing 480 watts for exactly one hour before it runs out. Combine that with a 750w motor, the legal maximum in the U.S., and that same battery would be able to run the motor at max throttle for about two-thirds of an hour before it runs dead.
So why do these terms matter? Because added together and applied to specific e-bike drive systems, the above concepts can help you get an idea of what a bike’s motor and battery are theoretically capable of.
But, don’t put too much faith in a bike’s spec sheet. Measures like amp hours and watt hours can be deceiving, and variables like temperature or the number of hills on your ride can wildly affect the performance of a bike’s motor and battery. When it comes to truly knowing how a bike will perform, there’s no substitution for actually riding it.