Smaller wheel diameter can give you up to 8 miles more range

General Discussion about electric bicycles.
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morph999
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Smaller wheel diameter can give you up to 8 miles more range

Post by morph999 » Feb 26, 2010 8:16 pm

I was using Swbluto's ebike calculator and fooling around with variables. Did you guys know that the difference between a 20" rim and a 26" rim is like 8 miles of range. It says the 20" rim can give you 8 miles more range. That's incredible. It's a couple mph slower but has more range.

I found out that it takes a 60 amp controller and 100 volts on a 5303 hub motor to go 53 mph. And it predicted my top speed for my current bike to the tenth of a decimal. It also predicted my range almost to the mile. Here's the calculator, if you want to play with it...it's still on the forum in a thread but here it is again...thanks Swbluto

http://www.mediafire.com/?lgj4zy2mz44

It works on Windows XP. I can verify that.

swbluto
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Re: Smaller wheel diameter can give you up to 8 miles more range

Post by swbluto » Feb 26, 2010 8:21 pm

Thanks, but just a reminder, it's only an approximation (A surprisingly good one in many cases). The tenth of a decimal, in retrospect, is a bit of a fib. It can't predict things that accurately and I don't think anything can.

Anyway, it's surprising how much speed can affect range. A 5 mph difference between 20 and 25 mph on my scooter is the difference between 12 miles and 20 miles. :shock: It's pretty surprising how incredibly fast wind losses increase with speed. Also, a smaller wheel is likely to allow the hub motor to operate more efficiently by spinning faster, which makes for more range.

morph999
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Re: Smaller wheel diameter can give you up to 8 miles more range

Post by morph999 » Feb 26, 2010 9:45 pm

Well, I ran my bike and got 27.9 mph and then I did the calculation and it said the same thing. Ok, maybe it's just a coincidence but I was surprised.

It might be more accurate than you think. Before I even looked at the calculator, I had estimated my range with 10AH to be 18 miles and it gave me 19 mile range. That's pretty impressive.

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Russell
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Re: Smaller wheel diameter can give you up to 8 miles more range

Post by Russell » Feb 26, 2010 11:42 pm

I think it’s actually easier to predict the distance you’ll get from a battery if you don’t pedal or if you are traveling at a speed where your input becomes almost meaningless. For instance with a given battery my range can be all over the map depending on how much I contribute and whether my average speed is 17, 18 or 19 mph. If however I rode at full throttle all of the time and didn’t contribute much I would expect my range to be more easily predictable. When you go with a powerful ebike ridden like a motorscooter it ends up being no different predicting range from a battery than it does predicting range from a tank of gas for the scooter.

-R
Jeep Comanche Trekking Bike w/YOUE geared motor, 42 lbs + 15 lb rear trunk bag w/12S 16Ah LiPo battery, tools, etc., 21A controller, 700 x 40C tires. 27 MPH.


My other E-Bikes: Nashbar Steel Flatbar

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dogman dan
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Re: Smaller wheel diameter can give you up to 8 miles more range

Post by dogman dan » Feb 27, 2010 8:40 am

My 5500 miles experience has taught me that slowing down even 1 mph yeilds an amazing amount more range. So if the 20" wheel is even a little bit slower range would increase a lot. Also , the small wheel would lug less on starts, so that would help too.

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Re: Smaller wheel diameter can give you up to 8 miles more range

Post by JEB » Feb 27, 2010 11:09 am

On a 6 mile run, same place every time (to stores) I found that if I used 100% battery power it would take 1amp hour per mile @ 24 volts. or 6amp hours for the run. On a sunny day when I was not in a hurry, peddeling away from every stop, and running 12 to15mpr instead of full throttle (20~mph), only 3 amp hours were used for the same trip. Lots of savings using the same wheel size.

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Re: Smaller wheel diameter can give you up to 8 miles more range

Post by swbluto » Feb 27, 2010 11:20 am

Yes, everybody, pedaling helps but the amount of extra range that affords depends on the speed, although more technically, the output power.

If you're going 20 mph, and you can pedal such that *without* a motor you can sustain 15 mph, you can greatly increase the range by pedaling. This is because pedaling would contribute more than half of the needed power to sustain 20 mph so you'd cut the battery-only power by over half.

If you're going 40 mph, and you normally pedal 15 mph unassisted, your increase in range from pedaling is practically nothing. This is because pedaling contributes less than 10%, and most likely less than 5%, of the needed output power.

If you're going 15 mph, and you can pedal normally going 15 mph, your "battery range" approaches infinity while pedaling. Who needs a motor? :)

So, like russell was saying, pseudo-motor-scooters don't really benefit much from this technique unless they really want to slow down, but "pedal pushers" can benefit a lot from it, depending on their desired speed and how much power they want to contribute. I'm already looking at a trip on my scooter that's about 20 miles in distance, and it's clear I'll have to go slower to make it, but if I were to take a bike, that range could extend significantly with pedal power. The only thing is that my bikes' ergonomics suck, so I'd get a recumbent for the trip (But that also introduces its own complications).

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Re: Smaller wheel diameter can give you up to 8 miles more range

Post by Rifle » Feb 27, 2010 5:57 pm

I always hear going slow adds a lot of range, but I have yet to experience that. Maybe it's that in situations that I ride slower I tend to start and stop more. Or maybe increased range w/ slower speed only applies to people that pedal?
2807 9c front hub. 48v 20ah Ping. 12s2p Lipo.

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