I believe that but for me and my 70-75 range I haven't seen a noticeable difference. Lot of factors at play here- hilly/flat terrain (mine is somewhat hilly), driving style, Cd of the car closed up vs. windows down I'm sure varies pretty wildly per vehicle. One of the things I've come to love about the 1 is how nice and relatively quiet it stays with windows down and roof tilted. I prefer some added aero drag over noticeable driveline drag (maybe in the 35 I wouldn't
I drove home the most efficient way today windows up vent on and trip mpg stuck at the proverbial 30.1 same as it was at the start- I reset every tank and turn in a consistent 29.3-30.5 indicated that generally ends up being ~.5mpg optimistic.