Jim, I tried to input some of your data into the aero and rolling resistance tool
https://ecomodder.com/forum/tool-aer...resistance.php
However, I don't know some of the variables, such as your final weight and such.
When you have a moment, can you input some of the data to get a rough estimate of the final cD ?
BTW, If i understand correctly, a tail like this would only show an increase of 4.3 MPG on a car like mine that got 42 MPG at that same speed you traveled.
( And likely much less, since each cars body shape is different )
I'm a bit confused when you all say you are getting over 80 -90 mpg when traveling at 56 mph.
Stock, your car got around 55 -60 mpg at that speed, correct ?
Is the 80 -90 -100+ mpg using tricks, like coasting, or coasting with the engine turned off ?