HP and RPMs

[SAcharlie]

Is this a reasonable rule for motors.

A motor produces its max horsepower at half its max rpms while at half the volts of a given voltage system.

An example of a 48volt system is where the motor runs 4000rpm at 48v pulling 5amps.
Now you load the motor down to were it is only turning 2000 rpm but you are telling the controller to feed 48v.
At 2000rpm the motor only wants 24v, so the controller feeds 24v and converts the excess into amps.