Tuesday, June 15, 2010
Thoughts about eBike Range Measurement
As I've been testing new ebikes, and planning more tests in the future, I've been trying to think of the best gauge of range. It's a common question among people shopping for ebikes, and it's one of most often asked of me by the e-curious. Usually, battery capacity is measured in amp-hours; I've also seen measurements in watt-hours and "up to" mile ranges. Amp-hour is a fairly straightforward metric, but it's mile range I've been thinking about; after all I don't want a 10ah battery, I want an effective range. A range estimate usually includes caveats such as "if you pedal as well, and work more at starts and stops, you could get up to XX miles out of a charge". If I never actually turned the motor on, I would get an infinite range from a single charge. But that's not why we ride ebikes, is it?
My current thinking is that the best measure of range is a "worst case scenario" (hereafter WCS). Put another way, if I do as little work as possible and use the battery as much as possible, what's the lowest range I can expect?
Upper distance measurements proffered by ebike manufacturers often have a lot of caveats (flat route, 150lb rider, full tires). Instead of applying these caveats in order to get to that upper range, I like to think of it as applying the caveats to extend the WCS range.
Finally, don't forget, if you ride an ebike, you'll eventually ride on a dead battery. The best way to prevent this is ABC - "Always Be Charging". Your battery will thank you!
And finally-finally, what's your assist type (pedal assist only, pedal assist/throttle combo, throttle only, other), voltage, amp-hours, and WCS scenario range? My primary ride is throttle/36v/10ah, and I get about 18 miles, WCS. Throw your answer in comments, please!
Shortly after publishing this, I found an iPhone app "Ebike Calculator" that claims to calculate ebike range. Sadly, it's for a later version of the iPhone software than I have, so I can't attest to its accuracy. Anyone have a newer iPhone want to download it and check it out? It's free!