It is important to keep in mind that an e-bike (and a motorcycle) are a "brick" aerodynamically. That is, e-bikes have a very high drag coefficient, like 0.5 or more. There is not much you can do about it, besides things that are unacceptable to most bicycle riders like enclosures and recumbent riding position, etc. You could also go slow. :-)

Most e-bike drive systems these days are amazingly efficient. Like 85% or better. That remaining 10 or 15% really won't make that much difference in the range and performance. The main "inefficiency" is aerodynamic and is unavoidable _if_ you want to stick with a conventional looking bicycle that you ride in the conventional position.

Bill D.

On 5/30/2017 10:28 AM, Lee Hart via EV wrote:
ken via EV wrote:
I have a Bike E with a 20" rear wheel I want to put a 36 volt at 500 to
1000 watt hub motor there but I want it RPM effecint  for 20 mph. where
do i find such a wheel at reasonable price.

I also have a Bike-E, and have thought of electrifying it. But its handling is such that I wouldn't feel comfortable with such a big motor. Keeping it down to 20 mph is a good idea!

Note that PM motor efficiency tends to peak strongly near full power. At light load, they are much less efficient, because you have full magnetic losses all the time. So it may be better efficiency-wise to use a smaller motor and gearing to achieve the best speed/efficiency tradeoff.

My Bike-E has a 7-speed rear hub, and of course a very long chain. My thought was to mount the motor under the seat, with a freewheel sprocket to the chain. That way, it gets the benefit of the gearing. The freewheel means you're not spinning the motor when it's not being used while pedaling.

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