Differences in Ebike Motor Performance

[Sailormannn]

A question on performance output and info from bike manufacturers on performance.

Noticed at least manufacturer who cites similar torque ratings for different watt rated motors 750/500 made by Bafang. Not sure what role the controller plays in determining peak power output, but is it possible to get the same performance out of motors or are numbers being inflated.

Example. The Bafang Geared Hub Motor on the RadRover 5 sold by Rad Power Bikes in the US is rated by Rad as 750w with 80 Nm of torque while the Canadian model is 500w but rated with the same 80 Nm of torque. Presume the lower wattage motor on the Canadian model is to align with legal requirements in Canada where most provinces limit motor size to a max 500 watts.

Is the info from Rad too good to be true or are the differences so small it doesn’t matter.

 

[AHicks]

I think this is a great question. Struggling with this concept as well (how a 750w and a 500w could have the same amount of torque, all else being equal). Would like to see if RAD's answer to it, to see if
it makes any sense, or not.

 

[Art Deco]

Pay attention to where the torque is generated and at what rpms. Watts don't matter much, except to generate torque, and if I need to pedal at 90 or 100 rpms to get it, it's useless for me.

 

[AHicks]

So you are saying that the 500w in this case, may actually be capable of 80nm, but the cadence necessary to achieve that mark would be nearly impossible to achieve?

 

[Iridebikez]

I imagine Rad is using the controller to tune the same motor for different markets to achieve different nominal watt numbers. Or in this case, de-tuning the motor for the Canadian market. But if they're starting with the same motor, they don't have to limit the torque, so both have the same 80nm.

All that said, watts are like horsepower in cars. 750w is equal to one horsepower. You can think of how car manufacturers are able to tune the same ICE engine to achieve different horsepower and torque curves for different vehicles and markets. But the curves will look very different for electric motors because they're torque monsters. For those of us who live the United States of Pound Feet, 80nm is 59 lb/ft of torque! The Bafang BBSHD and Ultra mid-drive motors have about 1500w nominal (2hp) and 160nm of torque, or almost 120 lb/ft! I've owned cars with less torque and you can strap that thing to a bicycle...it still blows my mind.