I'm a believer - increased gas mileage by 15%

[Grateful11]

I tried this with my Scion xA. I went from driving mostly 70mph to driving 65-67mph and my mileage went from about 38.5 to 42mpg.

[olnacl]

The only exception I found to the faster means worse gas mileage was a 1976 - 5 speed Vega hatchback that I bought new. The speed limit was 55 then and I discovered over the course of a 4000 mile trip that fuel economy was better at 70 mph than at 55 by some considerable amount. I further discovered that by using only 4th gear, the mileage at 55 equated the mileage at 70 using 5th gear. When I returned from the trip I changed the rear end ratio so RPMs at 55 in 5th were approximately the same as running 70 in 5th previously. Fuel economy increased noticibly. Did I make back the cost of the rear gear change in fuel savings? No, but the car was much peppier at all driving speeds and that was worth the cost.
Bottom line is that a small engine needs to operate in the sweet spot of RPMs to be reallly fuel efficient. The car, as shipped from the factory, was lugging in 5th gear at 55, thus sacrificing performance and fuel economy.