So I just finished up testing the new addition to the rear.
I tested at both 60mph (constant) and 70mph (constant). Both times, no A/C, radio and full exterior lights on, wet roads after a storm, no rain. 6mph winds out of the SSE.
The test circuit is a 4mi segment separated into a 2mi East->West, and a 2mi return
60mph:
A: WITH REAR MODIFICATION
A1: 51.0, 52.5 =51.75
A2: 50.8, 52.6 =51.7
A3: 51.2, 52.3 =51.75
A Total AVG: 51.73mpg
B1: 51.1, 49.8 =50.45
B2: 50.6, 50.4 =50.5
B3: 50.7, 50.5 =50.6
B total AVG: 50.51mpg
2A1: 51.6, 52.7 =52.15
2A2: 51.3, 53.0 =52.15
2A3: 51.4. 52.6 =52
2A total AVG: 52.1mpg
ABA @ 60mph, WITH: 51.925mpg, WITHOUT 50.51mpg
= 2.8% increase
70mph:
A1: 47.4, 49.2 =48.3
B1: 46.9, 47.2 =47.05
2A1: 47.6, 48.9 =48.25
ABA @ 70mph, WITH: 48.275mpg, WITHOUT 47.05mpg
= 2.6% increase
Not much of a change, but every little bit helps!