title_body: Is it a good practice to use a throttle limit of 90% for racing builds? I had read somewhere that it's a good idea to set a throttle limit of 90% for racing.  The reason given was that, in the last 10% of the throttle, the cost/benefit ratio for power to thrust would not be worth it.  Is there any truth to this?  If so, what is the recommended throttle limit for any build/all builds?
upvoted_answer: The reason why this is recommended for racers is likely due to the fact that during these high-throttle punches, the voltage of the battery sags from the load and so more current is pulled from the battery to increase the motor RPM.
  
  Power is equal to VI when V is voltage and I is current, which can be rewritten (by substitution of Ohm's law V = IR in for V) as I^2 * R. This means that if more current is drawn to compensate for a voltage sag, the power consumed by the motors increases by a greater amount because the resistance of the circuit is constant. (for all intents and purposes) For example, in the hypothetical scenareo that twice the current is drawn, four times the power would be consumed. This results in quicker battery drain.
  
  The 10% figure that you've heard isn't a hard line, but rather just a suggestion based on experience with miniquad hardware and its capabilities. This recommendation isn't just specific to racing; all quads would benefit from the efficency (energy extraction from the battery) boost from rarely using the top XX% of the throttle range. However, this is often more important in racing scenareos where it is often necessary to make the most of the energy in the battery pack you're using because you've selected the smallest and lightest one possible and need as much energy as you can get to complete the course in record time.