JTM wrote:See "Range for Speed" on the Swedish BMW owners site
I find no mention of the ambient temperature during these tests. The 2 range vs. speed posts were in March and early May, so ambient temperatures were likely in the 40's, but they could have been in the 30's or 50's as well. There was a mention of preheating which suggests that the ambient temperature was relatively low which could have reduced the measured ranges but probably didn't significantly affect the percentage differences in range at different speeds. However, air density and thus aerodynamic drag are higher at colder temperatures.
The range vs. speed graph indicates a 62 mile range at a constant 62 mph which is certainly lower than many of us experience at higher temperatures, presumably. Also, the range vs. speed appears to be an almost linear relationship which is a little surprising considering that the power required to push a car through air is proportional to the square of the speed. As a result, I would expect the range at 74 mph (120 kph) to be a fourth that at 37 mph (60 kph), but it was measured to be just slightly less than half, so something else must be going on.
I recall that Tony Williams was able to drive an i3 for ~88 miles at a constant 62 mph over a standard flat circular course in Orange County at temperatures in the low 70's and with little wind. So using Tony's range at 62 mph and the measured 20% less range at 74 mph vs. 62 mph, one could probably reasonably extrapolate that Tony's range might have been 88 x 0.8 = 70 miles at 74 mph.