content: Tesla hasn't released any actual data sheets for their motors; So, take everything I say with a grain of salt. In my experience 3 phase motors tend to be most efficient around 4000 rpm. We use gearing to put that range where most people do their driving which is around 60 mph or 100 kph. So, theoretically the motor would be running most efficiently at 60 mph. However, wind resistance roughly squares with speed. Meaning that if you're going 10 mph and have 10 newtons of wind resistance than going 20 mph means you now have 100 newtons of wind resistance. So, to answer your question the motor is not operating at peak efficiency, but because of the reduced drag less power is required to go the same distance even factoring in the motor efficiency loss.