It ought to work with any car, and the worse the mileage, the larger the percentage increase even a small increase would be. I'm just now trying some of the tactics with my 2008 Honda Fit, but my primary use for the car is city commuting, so there's not much benefit to be had. Still, EPA says it's rated at 28mpg city, and I'm pretty regularly exceeding that by 1-2mpg. On a 5 mile commute where half the trip is warming up and half the time is creeping along or sitting still, it's not bad. On the highway, I've gotten nearly 40mpg just by setting the cruise control on the speed limit (70mph), and keeping tire pressures at 38psi. No magic there, just common sense. The little 1.5L engine has a VTEC feature that activates at 3500rpm, and 70mph is about 3200, and that was the largest single benefit I saw. Tire pressure is well below the max, but high enough to help protect the small-ish tires.

Aerodynamics is something that can benefit any car, especially our old Mopar bricks. It's hard to make my Valiant any slicker than it is, so drafting a semi or other large box is about the only way to reduce aero drag. And you don't have to be on the bumper of the box to get the benefit, just somewhere in the wake. The more common version of drafting is to sit about 1 second back, and before anyone says that's dangerous, 1 second = 88 feet @ 60mph. That's at least 5 car lengths in my Valiant, and nearly 7 Fit-lengths. Incorporating 1-sec drafting, I know of at least 2 Fit owners who have pulled over 55mpg from cars identical to mine. My question is, how do they keep some fool from pulling in to that space? Around here, if you're more than a couple car lengths back, some idiot is going to take that space as they try to blast down the road.

Nutshell, drive more smoothly, keep your tires inflated, and take advantage of natural aerodynamics, and you should see noticible improvements.

Clair