[FreedomPoster]

Wind resistance goes up with the square of the speed. I suspect it would be a lot more than a 10% reduction in range.

[Tell It Right]

It's been decades since I tested it. So maybe I'm behind times. But in my then new 1991 Ranger I saw only a 10% reduction in mpg between driving 60 mph vs 80 mph. I'd say about 3/4ths of my driving was on the highway. And I did it for 2 weeks each.

As a college student I was experimenting to see if the gas savings was worth it. But as a full time worker (while going to college) I determined that my time was more valuable than saving 10% in on $1.20-ish per gallon.