I've been a casual observer of this forum for a few weeks. I ran across it when I was doing a Google search for aerodynamic devices. My interest (obsession?) with automotive aerodynamics has ben primarily race car focused, but more recently I have directed it in the fuel economy direction. I have found a number of the projects here very interesting, and hope that I can add an occasionally helpful comment.
To commute with, my wife and I share an '98 Saturn SL2 automatic and an '06 Chrysler PT Cruiser. I had made some aero changes to my '91 Nissan Sentra SE-R and saw somw mileage improvements. I had to sell that car about a year ago because of my growing family (two boys, 4 and 2 months). Until February I was commuting 33 miles each way to work (Olmsted Township to Euclid, for anyone familiar with Cleveland) and ANY fuel savings were welcome. Since most of the commute was ~65 mph interstate, highway mileage has been my main interest. I now work 5 miles from my house (driving less does indeed lower your gas consumption ). So, while my mileage improvement interest remains, it is not a crucial as it was.
So far, I see 2 mph highway improvement on the Saturn due to aero changes (+ another 1 mpg from K&N air filter). I made more extensive changes to the PT prior to a recent vacation to Myrtle Beach (740 miles each way), and saw a significant difference there.
Oh, and I also have an '83 Mustang GL V-8 that I am turning into a weekend race car. Obviously my interest here is not mileage, but downforce and drag.
It is great to find other people who understand physics (you can't make big SUVs more fuel efficient through legislation) and have genuine interest in improving mileage. Yay!
Glad to see another aero nerd join the fray. I'm a rank amateur, but I find the topic of aero (for reducing Cd) fascinating, and have been reading as much as I can about it this year.
Also, if you peruse my posts, you'll find I'm not shy about getting out the cardboard and duct tape to improve my car's figures. I'm satisfied with my in-town mileage, primarily through driving technique - it's the highway stuff that needs work, and aero benefits most there, on top of technique.
Please tell us about the aero changes you made to your cars.