i use the 2x VESC 4.12 for a dual hub motor (from diyeboard, the 75kV).
Since i have 90mm wheels i should theoretical reach 53,4kmh, with 95% duty cycle 50,7kmh at full voltage (42V, 10S3P).

But i only reach ~37kmh with full battery. And while im cruising in this speed the VESC App shows that the motor only get a small current (<10A) and around 350W.

Do you have a idea what could be the limiting problem? Battery current and motor current limits are much higher.

Weighted is just a guess that you input, if you say your loaded speed is x, and your load speed is 85% just make x*0.85

For to actually calculate the weighted speed you have to first calculate the force required to overcome all losses, calculate the torque for that force and from then the current needed in each motor, and then calculate all voltage drop across all components