Aerodynamically, there's no way a Smart Car can get 40MPG at 80MPH... My Scanguage tells me as much (and yes, I have checked it's averaged readings against the fuel pump gallons delivered). Maybe if you drafted a semi going down the highway, but then they don't cruise that fast. But, I noted that there's a marked increase in fuel efficiency if I slow down to 60 MPH, which might get me into that MPG ballpark (my Scangauge would read in the high 30's)... Unfortunately, that's too slow for traffic in my typical routes. Drivers are far too impatient and will ride your ass in the slow lane if you drive at 60...Upping the tire pressures didn't help the MPG's, but driving with the windows closed did. I'm lucky to get 30MPG at the cruising speeds out here normally aspirated (no turbo). On the tollroads, it's literally pedal to the metal -- right against the downshift switch -- the whole way... I might upshift into 5th to lower the revs a bit and save gas, but that's about it... And, that's sitting in the slow land being passed by practically everything -- Ford Transits, MBZ Sprinters, diesel pickup trucks, Daewoo's, you name it. The lowest MPGs I ever had was between 18 and 19 boosting to 1Bar when I had a SFR Stage III turbo installed. Even then, I could be right up against the speed limiter and still get passed by gardeners in their little mini pickup trucks -- rakes and week whackers flapping in the wind... Still, I really miss that turbo -- had to remove it for smog inspection when the car reached 6 years old... Alas, my "new" Smart 451 (got it with 42 miles on the clock) was registered by Car2Go San Diego back in 2015, so even "new" Kalifornia thinks it's a 3 years old car. I'm hesitant to install the turbo on it as I'd have to remove it in just a few years for a smog inspection.... In some states, engines under 1 liter are not subject to any inspections... Alas, Kalifornia isn't one of those states...