Originally Posted by Mike_TX

Hmmm ... that wasn't my experience on my 3500-mile trip. In fact, my wife and I discussed the fact that at 80mph on the interstate I got 29-30 mpg and when we took some secondary highways at 65-70mph I got closer to 27-28. Not a huge difference, but enough to notice.

And BTW - it wasn't because of traffic or little towns slowing us down - much of the secondary stuff was in the wastelands of Nevada (between Las Vegas and Tonopah, where there's little or nothing). I WAS afraid of police lurking out there, though, just to snare over-confident drivers, so I stuck to the lower speeds.

Fuel economy v. speed is a complex science, having to do with gearing, coefficient of drag, engine optimization and other factors. It's not a slam-dunk to say higher speeds automatically translate to lower gas mileage. I recall my BMW's actually got better mileage at 80-85 than at 65-70, too!

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Originally Posted by PatsSoxfan

Mike,

I have no idea why you were getting better gas mileage at higher speeds. But in my experience, I know for a fact that when I am going 65 or 70 as opposed to 80 or 85, I get better gas mileage. It is not just on this recent trip that I have noticed this but on every trip that I have taken with the LS. I wonder if your situation has anything to do with the dryness of the air and altitude. I seem to recall from many years ago when we took a trip to the Desert Southwest and the southern Rockies that my gas mileage was amazingly good for that car (Mustang, Mach 1).