(The U.F.O. at a picnic pull-off on the 1000 Islands Parkway, along the shore of the mighty and lovely St Lawrence River. I parked here to remove/reinstall the tail for A-B-A testing. That's upper N.Y. State in the far distance on the opposite side.)
I just got back from testing on my usual route - jumped at the chance to go this afternoon because the conditions were near perfect.
I did A-A-A-B-B-B-A-A bi-directional runs, where A=tail, B=no tail.
Results show: 9.7% better MPG at 80 km/h (50 mph) with the tail.
Happy, happy!
