I'm not quite sure what you're asking, but the motor speed constant kV is used to tell you how fast it will go at a particular voltage, depending on load. kV is approximately RPM/Volt. If you don't know the kV, you can determine it experimentally, by applying full throttle to the motor and measuring it's RPM. THen divide the RPM by the voltage applied.
If you want to play around with it, and see the relationships, you can go to http://ebikes.ca/simulator
and pick a motor, then try different battery voltages, etc., and see what happens. Read the instructions below the graph area for what everything is and does and how to use it.
If you mean something else, let us know and we can try to help.