So I tried some rear Edgarwits to see if I could reduce wake size. These were additional to the front ones, and taller. GOE222 true aerofoil profile.
I did some throttle stop testing with the following results (km/h at 30 per cent throttle, low-moderate gusty headwind):
- No rear Edgarwits: 95
- 1 finger rear gap: 93
- 2 finger rear gap: 95
- 3 finder rear gap (ie about parallel): 96
- 4 finger rear gap (ie diverging): 96.5
That would make 4 finger vs std about 3 per cent improved in drag.
4 finger gap:
For people interested, but having other cars, don't forget Insight boat-tails a lot with its narrower rear track.
Interesting to see the better performance at the rear with the diverging duct - opposite to what occurred at the front.
I'll do some more testing on a still day, but to me this result is borderline. I'd need to see a big jump in drag reduction on a still day to go in this direction.