What is the max torque?

Many ebike motor suppliers provide torque data for their ebike assist motors. For the torque to be a useful metric to compare assist motors, it must be measured the same way on the ebikes. 

However, some ebike motor manufacturers measure the torque not on the motor but on the output gear of the motor drive. While others measure the torque on the output of the bike’s gear system (on the driven wheel. Then the torque measured is only valid in the lowest/lightest gear position. 

In addition, different wheel size makes a direct comparison of torque invalid to quantify the level of assist provided by a specific motor solution. For example a torque of 100 Nm gives 40% more assist power on a bike with 0.5 m diameter 20 inch (47-406) wheels, compared to an ebike with regular sized bicycle wheels (40-622). 

The conclusion is that the difference in methods of measuring torque, and the way torque becomes part of propelling force makes it impossible to compare only “motor torque” on equal terms.

If you really want to compare data from different motor suppliers and wheel sizes, there is a good way to do that: Since the assist power is used to help propel a vehicle, converting torque into propulsion force will enable direct comparison on equal terms.

So, to really compare assist power, you would need to know:

  1.  the (peak) motor torque in Newton meter (Nm) as measured on the bike’s wheel, not anywhere else, and 
  2. the wheel diameter in meter (m). 

The maximum assist force is then: F = torque  / radius = torque * 2 / diameter

Examples:

FRIKAR provides 57 Nm in peak per motor, and our wheel diameter is 0.5 m:

Fassist(max)= 57 Nm * 2 / 0.5 m = 228 N

For a regular ebike with 60 Nm on the rear wheel , with 0.7 m diameter wheels:

Fassist(max)= 60 Nm * 2 / 0.7 = 171 N

A final comment: 

On FRIKAR 57 Nm is the maximum we can provide on the assist motor. As we also have an electronic gear providing power from the cyclist to the wheels, that uses the same type of motor as used on the assist motor, we can in total provide 456 N of propulsion force to the vehicle when going uphill. With a total mass of 200 kg, gravitation of 9.81 m/s2, the maximum theoretical hill we can climb is 23.2%. However, there will be friction and airdrag so we say that the maximum hill you should be able to climb is 18% with a fully loaded FRIKAR.

More about torque on ebike motors.