[beatr911]

Try documenting each and every tank with notes and post them to this site to see a graphical representation. Nobody gets a straight 30 mpg every time. I suspect you'll begin to see some trends that you can then exploit to your favor. If you can also have your wife document when she fills, she will be more aware and might change her driving habits for the better as well.

Not that it's necessarily the case with your experience but I've noticed something about variable driving habits or the difference between drivers. Possibly it could explain at least some of the non-variability you or others are seeing.

If I drive the entire tank with good technique and only have a very occasional outburst of speeding fun (like once or twice) the tank mileage doesn't suffer. If I drive like an idiot the entire tank and hypermile for say only a single commute, I'll get idiot mileage. The moral is the tank mileage is the average of the driving technique used over the entire tank and small variations don't affect mileage much itether good or bad. For your driving 30 mpg is it. Wayne Gerdes would probably be able to squeak 37mpg out of it but he can drive on the extreme edge of hypermiling.

I use this to my advantage. Hypermile 95% and have some fun for the 5% or so. I still think driving is fun and don't want to make it all about maximum mpg.

The other comments are probably spot on about gearing and aerodynamics. It could very well be that the mpg of the high drag body at speed equals the city mileage. Maybe the car needs some repair in order for it to reach it's potential.

In the '80s I had a Kawasaki GPz 550 that always seemed to get 60 mpg. Gentle all city driving or backroad strafing at WOT and 100% braking. Didn't seem to matter. Tank after tank. Looking back I didn't know about hypermiling and probably could have done better in some modes of driving. I also didn't document it, just figured it in my head at the pump. I suspect the figuring in the head was the bigger problem.