Calculating miles or range added per hour depends on the efficiency of the car. It is really not the best way to calculate. The better way is to calculate kw added per hour. If the car is more efficient, then one will get more range even though the input is the same. My Chargepoint Flex, plugged into a 50 amp circuit and delivering 40 amps, delivers 9.1 kw/hr. If one gets 4.6 miles per kw on 19 inch wheels, this is ~42 miles per hour. However, if one has 21 inch wheels, even though I am filling the battery at the same rate, the miles per hour will be less.