So far my best average MPG is 42.92. 40% urban 60% freeway, no A/C, no passenger, speeds no greater than 65mph, RPM’s below 3000, recommended tire pressure and using premium fuel. I averaged 37.9 mpg with A/C 50% of the time, with a passenger 50% of the time and same driving habits. My worse average mpg is 34.7 when going 70-85mph on the freeway and accelerating above 3000rpm’s from the start using the A/C 50% of the time. I think the key to get the best mileage on the smart, is to keep the rpm's below 3000 as much as possible and limit A/C usage. As for the K&N air filter, I’m not sure if it does increase mpg’s as others claim, but waiting to see what ScanGauge users are getting with the k&n air filters compared to stock.