I finally got new rear tires for the Focus. The previous owner went to used tire places and when I bought the car, it had larger diameter tires on the front and really big tires on the back that were off an SUV. The effect of the taller gearing since it is front wheel drive, made the car impossible on hills so the first thing I did was replace the fronts, it help tremendously, better gas mileage and lowered the front of the car an inch.
Its snow season and the old Bridgestones on the back slipped all over in the snow, I replaces the fronts with Kuhmo Solus' and the all season design digs right in in the snow and they handle great. So time came to replace the rears, they also got the Kuhmo Solus' and what a change from day to night, the stance of the car is lower, the back of the car sits almost 2 inches lower, getting rid of the Stink Bug effect, so today I have to drive into D.C. and I will see how it feels. Already driving home it handles flat, I can't wait to take a couple of mountain roads, plus with the lower flatter stance, I should get a better aerodynamic effect and better mpg.
I love your "stink bug effect" description! Doubt it will change your mileage noticeably, however. My wife used to have an AT Focus. We got high 20s mpg on long freeway trips at 70 mph. When I slowed down to 60 mph, the mileage jumped to 36 mpg. Try it on your next highway trip.