There is one concern I have for getting gas consumption readings, similar to Metro and his tail extension:
1) The car
without the under body smoothing panels and tail extension
2) The car
with them both attached
The Insight has lean burn, and I'm wondering if the car without the aero aids will actually be able to get into lean burn at 55 to 60 mph on an old country road that is flat enough for this. Once in lean burn, the car would need to able to stay there for at least one mile.
Of course, this would need to be repeatable in both directions and for several iterations.
I live near the Interstate as well, but the A-B-A testing would all have to be done in the wee hours of the night, and it takes about 1.5 hours just to jack up the car high enough to be able to remove all the body panels from underneath the car. And they are held on with lots of fasteners.
Now imagine doing this for three test sessions (A-B-A), and getting all this done in one day while there is little traffic on the road, and the atmospheric conditions have not changed much!!
I do however, think that driving at a constant speed will give better results than coast down testing, again similar to Metro.
Jim.