It does not seem to matter what we do or how fast we drive, we still get anywhere from 15 to 18 and we get an occational 20 plus in the Columbia River Gorge if the wind is at our back! My husband drove 65 to 70 mph from Portland, Or to Slab City, Ca. We were able to do this because we have a new engine. With all the stimulus money for roads, there is a lot of new pavement out there. It is an RVers dream.