MaXJohnson said:If you're talking about the freeway, the minimum posted speed of 45 MPH will return the best mileage.
ymmv
Try that without getting run over. I've had to limp a few cars home (over heating, would miss fire if you gave it too much gas, slipping transmission) going 45-55 mph on the interstate and, even though I stayed in the right lane, everyone was riding my ass, flashing their lights at me, etc. Truckers are by far the worst about it.
If I'm trying to get good gas mileage, I go 65-70. I'm barely even touching the gas pedal and turning under 2000 RPMs. I did that one trip and I got 22 mpg on my '95 4.0l AW4/231 XJ. My XJ is at stock height and I'm only running 235s on it though.