Are there any magic numbers?

[justpassntime]

I saw a little rice rocket the other day that had an aero kit on it. I noticed the defuser under the rear of the car looked very functional. It had four large fins, probably three inches or more high.

I think it was a Mitsubishi but not sure it was traveling pretty fast and I was looking at the aero kit not the car. I am sure the guy driving just put it on there for looks anyway not fully understanding the function of the parts.

[justpassntime]

Well here's an update on the roof extension. Although it looks great it has no effect from what I can tell. The angle of it is right on judging from the rain that sit on the rear window and mpgs (no significant change). The rain doesn't care whether or not the extension is installed on the car or not, just sits there happily on the rear window going for the ride. I think that it is probably too short, just being a seven inch extension.

[Concrete]

well that may be a good thing

I am on version two and I have lost at least 2 mpg @ 65mph on both
I finally adjusted the second to get to a point where I don't loose any @65
at 40 it may be an advantage, hard to tell
so I have entered the realm of flow separation at about 55?!?
I've tuffed and video-ed and am still unclear as to the issue (poor video)

at this point I would settle for looking cool
because driving in traffic with blue foam on the truck & tuffs & a camera taped on the back

...well it ain't exactly pretty