Power useage and pulley size

[Desertprep]

With a non-hub motor, how do the power requirements of a motor change based on the size of gears or pulleys used in the drive train? and power drain? by changing the size of a pulley I can give a bike a top speed that is 10% or 25% higher...or 15% lower. What is the effect on power usage?

 

[spinningmagnets]

You may gain some effieciency by using a different pulley ratio set, but it also may require you to use a motor with a different kV (RPM per volt applied).

Take an imaginary example to an extreme. If you chainged your front chainring to a 100-tooth, could that allow you to pedal your bike to 50-MPH? It is just as hard for an electric motor to drive a heavy load in low RPMs as it is for people. At low RPMs with a heavy load, much of your battery energy is converted to waste heat.

Then again, if changing a pulley set will give you 10% higher speed, that may be worth it to you, even if it causes your battery to last a 10% shorter distance due to excess energy converted to waste heat.

 

[Desertprep]

Thanks! So should the pulley size based on the power curve of the motor AND the chemistry of the battery?