> The amount of energy required to travel the same distance is not linear to speed, at all. If it were linear, speed would have no effect on efficiency. > Pow

> The amount of energy required to travel the same distance is not linear to speed, at all. If it were linear, speed would have no effect on efficiency. > Power from engines ... But their efficiency can't improve with v^-3, so air friction wins. Just check the consumer reports on cars' fuel efficiency. Optimum efficiency is around 80km/h for most cars.