Tuesday, June 16, 2020

E-bike Range: How far can I go?



One of the most common questions anyone asks about an e-bike is "How far can I go on a single charge?" While this sound like a simple question, a variety of factors go into this calculation and the most accurate response anyone can give is "it depends".

Micah Toll is an e-bike writer and rider and he dives into the various considerations in detail in an article at:

https://electrek.co/2020/06/12/how-far-can-an-electric-bicycle-really-go-on-a-charge/

Now Micah is a very experienced e-bike enthusiast and he is a fan of going fast, powerful motors and throttles. As he admits, he's not a fit cyclist but he does a pretty good job in his article of trying to get into the fit cyclist perspective. But that is fundamentally not the perspective he comes from when it comes to e-bikes.

Alan Scholz, Bike Friday's founder, and myself do come from the fit cyclist perspective. We're both in our sixties now and have been lifelong cyclists. Our approach to e-bikes, and hence Bike Friday's approach, is to keep things as light as possible. We figure that the motor is there to be an assist to human muscle power, not a replacement for it. Therefore, Bike Friday builds Class 1 e-bikes (with no throttle).

Now much of the e-Bike industry has a "weight be damned, you've got a motor" philosophy and in the industry one quick rule of thumb is that they will quote an ebike as using about 20 WattHours per mile. Micah ups that number to 25 for his style of riding but in his article he does an experiment of riding at a very low assist level, laying off the throttle and putting in a lot of human power into his ride. Doing this he was able to only use 3.1 WattHours per mile on a 29 mile ride. But he admits he was exhausted at the end of that ride and doesn't recommend riding at that level every day.

Now Alan and I do ride pretty much every day we're nerds so we've used recording Watt meters to tell us how many WattHours per mile we are using. Alan and I have remarkably similar results. On a recent moderately hilly ride, with my e-assist set to levels 2 or 3 (out of 5), I used 214.7 WattHours to go 37.7 miles. My arage speed was not super fast but not turtle slow either, I averaged 13.6 mph. My bike has a modest 250 Watt motor and a 12.5 AmpHour 36 Volt battery. On my ride the maximum peak power the motor put out was 151.9 Watts (for a short time on the steepest climb).

Now let's do some math. 214.7 WattHours  total divided by 37.7 miles tells me that I used an average of 5.69 WattHours per mile. This was not at a "grind myself into the ground" pace effort. This is my standard, "I'm going on a bike ride" pace. My battery has total capacity of 36 Volts times 12.5 AmpHours which equals 450 WattHours. Therefore based on this sample ride I would estimate my e-bike's range to be 450 WattHours divided by 5.69 Watt Hours per mile which equals just a bit over 79 miles.

Now again, I can't stress enough that your mileage will vary. Going up hills takes much more power than riding on flat terrain. Heavier bikes and riders use more power than lighter folks.

Our Bike Friday travel bikes use airline legal LiGo batteries from Grin Technologies. Each LiGo holds 99 Watt Hours. Our bikes typically ship with 3 or 4 LiGo batteries. So let's say I have a customer who uses 10 Watt Hours for each mile they travel. That person would have a range of just under 30 miles for a 3 LiGo system or 40 miles if they opted for 4 LiGos. And some of our customers buy multiple sets of LiGos to increase their range.

The "How Far Can I Go?" question is a complicated one. A lot of folks trying to sell you something will give you an easy, optimistic and probably wrong answer. The longer answer is "it depends" and I hope Micah's article and this one give you the information you need to determine what the true answer is for you.

Keep 'em rolling,

Kent Peterson
Eugene, OR USA

4 comments:

Tony Licuanan said...

Very nice Kent. Thanks for that.

WMdeR said...

It is amazing that our elite athletes burn themselves to the ground for 50w peak output changes. A 250w supplement for an hour turns this burro into a world-class cyclist. We obviously don't use that power for sporting fraud, but to add to the already astonishing seven-league boots a safety bike gives us. Thank you for describing, documenting, and normalizing a technology I would have dismissed as driving a moped.

Best Regards,

Will
William M deRosset
Fort Collins CO USA

Wheelsall said...

I think that electric bicycles are mainly an auxiliary function, which is assisted in human conditions, rather than pure electric driving. Help the rider to travel longer distances.

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