The main issue is that the efficiency curve of a electric motor is fairly flat once it gets >60% load[0]. There is a small hump typically around 60-80% output t

The main issue is that the efficiency curve of a electric motor is fairly flat once it gets >60% load[0]. There is a small hump typically around 60-80% output that is most efficient, but its only a few percent at best, so not worth the cost of a high torque transmission as adding a few extra batteries to cover the loss at slow speeds is much cheaper. When cost is no object (eg: racing) you see transmissions so they can get peak power for longer. Even in a application that I was involved in where power was ~$200/Watt, fixed gearing was chosen as the extra weight of the transmission made the whole system less efficient than what was gained by the transmission. [0]: http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1004&context=bae_fac http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?articl... (Its for Irrigation pumps, but still in the same class of power output as cars)