How to know the real range of an electric bike?
The range of your ebike depends on a few characteristics. First, the energy contained in your battery. This is not your battery’s voltage on its own, nor its Ah capacity on its own, but the two multiplied together: Voltage x Capacity in Ah. This gives you the energy carried by the battery of your bike in Wh. For example, the FX’s standard battery carries 314Wh which corresponds to a potential consumption of 314W for one hour or 157W for 2 hours and so on.
Most ebike motors for road use have a continuous power of 250W, a peak power of 500W and a max speed of 25km/h. This means that upon accelerating, and for short periods of time, the motor will pull up to 500W of power from the battery, let’s say for a maximum of 10 seconds after which it will pull a constant 250W until the bike reaches 25km/h. Going back to our Physics of ecycling article, we can calculate how much power is consumed at 25km/h for a person of 75kg on an asphalt road:
We get a drag of 20N and a rolling resistance of 0.38N. This means that when riding your ebike at a constant speed of 25km/h you have to compensate for about 20.38N of force acting against your forward movement. Power is equal to force multiplied by velocity and 25km/h corresponds to approximately 7m/s. This gives a necessary power consumption of 142W to maintain this speed of 25km/h. Now, although part of the magic of bicycles is being able to enjoy great free wheel, which allows to ride power free without decelerating too fast, all periods of acceleration consume up to 500W. In addition, during these periods, the bike’s speed is lower than 25km/h. We have found through multiple tests and experiments that a factor of 20% represents well these losses.
Eventually, we can write that (Capacity (Wh) * Velocity (km/h)) / (Power Consumed (W) * Loss Factor) = Expected Range (km):
- For a battery of 314Wh, this gives a range of 313*25/(142*1.2) = 46km
- For a battery of 374Wh, this gives a range of 374*25/(142*1.2) = 55km
- For a battery of 482Wh, this gives a range of 482*25/(142*1.2) = 71km
These values depend on your weight, style of riding and environmental conditions (temperature, assist level, acceleration, free wheeling, etc) but give a very reasonable approximation of what to expect. We are working on an online calculator, taking all these variables into account, that will be available on our website very soon. In the meantime, this will give you a very good idea of what’s real and what’s not. For example, a battery capacity of 220Wh will only give you about 32km at an average pace, not more like some would like you to think 😉