Max duty cycle – determines after which RPM VESC won’t drive the motor faster anymore. If you exceed this value you can still brake, however. (But if you brake at more than 100% duty cycle you might kill your ESC) (Use this value instead of Max ERPM to set a speed limit on your board.)
Max duty cycle current limit start – determines the max duty cycle mulitplier (as of FW 5.3. On earlier firmwares this was an absolute value for the duty cycle) at which the ESC will decrease current from as you reach max duty cycle.
For example, with the default values of 95% duty cycle and 85% duty cycle current limit start, and full throttle on the remote:
- From 0% to 81% duty cycle (0.95 x 0.85) the ESC will drive your motors with the max current it can (based off of motor current and battery current, depending on the duty cycle).
- From 81% to 95% duty cycle, the ESC will gradually decrease the motor current you try to drive your motors with. At 95% it will limit you to 0A, and at 81% you still have full power. Whether this limiting is done as a cap to absolute motor current (I hope not lol), or a multiplier of whatever you’re inputting from the throttle, I do not know.
Obviously at 0A your board is going to decelerate, so your board will naturally even out somewhere between 81% and 95% duty cycle. If you want to squeeze out every bit of top speed out of your board, you might want to decrease this gap or eliminate it entirely, just be careful of the sudden power loss as you approach max duty cycle. This is why I personally overgear my boards so that my theoretical max speed is higher than what I actually want to ride at.
(And yes, since from 5.3 onwards duty cycle current limit start is a multiplier, you can set it to whatever you want. I recommend 90% or lower, but feel free to set it to 100% to disable this safety feature completely. I personally set it to 80% on torquey setups to make sure I don’t kill myself from the otherwise sudden power loss as I hit top speed 
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