Initially, when I was shopping for my e-bike I thought that the most important factor to increase my range would be the size of my battery. So I wanted the biggest battery I could find, in my case 840 watt hours. It only made sense to me that the bigger the battery the farther it would take me.
While it’s true that a higher capacity battery would take you farther if everything else remains constant, the vast majority of a battery’s power is used to move the air around you unless you’re climbing a steep hill. To make matters worse, as speed increases the power needed to overcome air resistance increases with the square of the velocity
Since the power needed to increase speed is not linear,
For example, based on data from Cycling Power (road-bike.co.uk) and other sources, it takes about 120 watts to ride at 15.6 mph. However, it would take about twice the power (250 watts) to increase the speed to 20 mph and more than six times the power (about 750 watts) to reach 28 mph.
In terms of range,
- Increasing speed from 15.6 mph to 20 mph will reduce range by about 50%.
- Increasing speed from 15.6 mph to 28 mph will reduce range by a staggering 85%.
Before choosing what e-bike class is right for you, consider if speed or range is the most important factor to you. You can’t have both. If range is the most important factor, I would opt for a class 1 over a class 3. This will optimize your range and reduce the temptation to be seduced by speed. If speed is your biggest concern a class 3 is the only bike that will provide assistance beyond 20 mph.