How does wheel size affect hub motor ebike performance?

[Brummie]

Thinking out loud... ebike performance must be affected by wheel size (both in torque/acceleration & top speed) because the wheel size is effectively part of the overall eGearing?
Does anyone know of a detailed guide to this please?

 

[Woosh]

Thinking out loud... ebike performance must be affected by wheel size (both in torque/acceleration & top speed) because the wheel size is effectively part of the overall eGearing?
Does anyone know of a detailed guide to this please?

that depends on what you call performance.

Factors to consider:

1) maximum motor output in Watts
2) Maximum torque
3) Noload RPM

These factors are not affected by the wheel size.
Don't pay much attention to the noload speed that is shown on your LCD. That gives a false impression because a bigger wheel will translate to higher 'headline' speed at the same RPM when off the ground. As soon as that wheel touches the ground, it's the same ground speed as a smaller wheel.

There is a perceptible difference when climbing steep gradient because the conversion yield drops with the RPM. A larger wheel runs more slowly, therefore is less efficient than a smaller wheel. That difference translates to a win for the smaller wheel on steep hills.

 

[Deleted member 4366]

For any given hub-motor, torque is inversely proportional to wheel diameter/circumference.

You can get a good understanding of all these things by playing with the simulator.

http://www.ebikes.ca/tools/simulator.html

 

[Woosh]

For any given hub-motor, torque is inversely proportional to wheel diameter/circumference.

but what the rider sees is the speed, the same motor at same current gives the same speed.
You may see a small difference in the road surface friction loss, large wheels tend to have narrower tyres and less friction loss, that translates into a small gain in speed.
eg the default simulator settings shows 41kph maximum speed @ 26". If you change it to 700C, it shows 42.3kph.
It's down to friction loss.