Info 250w bike on the throttle only sample

Andy88

Esteemed Pedelecer
Nov 6, 2016
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Ayrshire
I hope I've posted this in the right section, the short video helped me see exactly how much pulling power a 250w front hub motor has.

The rider is 120 KG. Enjoy hope it helps potential buyers.

 
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Rohloffboy

Esteemed Pedelecer
Sep 1, 2015
315
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62
North West.
Yep, it's always good to see these kind of real world tests, I am quite confident that a legal 250w motor will be more than adequate for my needs, although I will be going for a Crank Drive.
 
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Deleted member 4366

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You need to have a lot of understanding to make sense of that test. Don't expect any bike with a 250w hub-motor to behave the same.

The main point is that his motor maxes out (not limited) at 25 km/h in a 20" wheel, which means it's a 230 rpm motor. That is very slow for a motor in a 20" wheel. That is a typical speed for a 250w hub motor that's used in 26" wheels, which would have about 75% of the torque and would stall out on that steep hill because it would be running at lower rpm out of its efficient zone.

If you want good climbing ability, any small hub-motor can give it if you use small wheels. As I've said before, even the tiniest motor (200w Q85) can get a 100kg rider up a 15% hill without pedalling if you put it in a Brompton with 16" wheels.

You don't need much power to go up hills slowly, but most hub-motors are designed for faster speeds, which means that they have very low efficiency at low speed, so can't produce the power when you need it most. If you choose a motor with the right maximum RPM, you can get full power for climbing.

As an example, take a typical 26" wheeled bike with a typical 230 rpm motor, typical 15A controller and 36v battery (40v charged). A steep hill can drag the speed down to 6 mph. That's 30% of its maximum RPM, at which point its efficiency will be about 45%, so you get 15 x 40 x .45 = 270 watts of assistance.

The same motor in a 20" wheel at the same speed will have an efficiency of about 60% and give 360w of power, which is 33% more.
 
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