The top motor is rated at 3.0 MH while the bottom is 1.85. That being said, the top motor needs 69v to compared to 48v on the lower motor. So, if you ran both at 48v, the top motor is slightly handicapped at higher RPM, but if ran at 60v, the lower motor would run hotter. It's kind-of a toss-up between the two.
IIRC, the tried and true formula is square root of the motors MH rating times 32 equals the sweet spot in volts to feed the controller to maximize the speed while reducing the motors heat.
That formula has been around a long time and controllers can morph what is powering the motor to reduce heat, so you should be able to go above that a little bit.
For example the top motor.
Sqrt(3.0)*32=55
And the bottom motor
Sqrt(1.85)*32=43
So, the top motor needs 55/43 or about 1.3x higher voltage supplying the controller for a fair comparison between the two motors.
That means the top motor needs about 60v to compare with the bottom motor at 48v.
I hope that this helps.
John Z
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