I don't know if this is relevant to the thread, as you're talking about four wheel vehicles and airplanes I assume, but it seems to me they're two different animals. Why is it that when in an airplane in a diving spin, pilots are quite often unable to stop the spin using all of the principles suggested by people in this thread, and one guy in particular. Are you saying a fin is a cure all to keep high speed vehicles on all four, with the shiny side up?
I can only go with people "who have been there and done that". A few years back when talking to Don Vesco, we discussed stablizer fins. I asked, "Should I or shouldn't I put a stablizer fin on the motorcycle streamliner I'm planning to build?" He said, "Not necessary. IT'S NOT AN AIRPLANE. If the bike is built right, it'll go straight. The only thing a fin on a motorcycle does is increase sail area, which ain't good for cross winds, and the only thing it'll do is increase drag and slow you down."
Then I asked, "Why so has the Turbinator got a fin on it?" He answered, "Mostly for looks, it makes it look faster in a picture".
He went on to say, "If you still feel you need a
stablizer fin on the bike, hang a couple of fins on either side of the tail, but make them so they don't increase sail area. Nothing sticking up or below."
The Easy Rider had a little four inch fin on it. I asked Dave Campos about it. Dave said, "It was Joe Teresi who wanted the fin, and changed Bob George's original design. Teresi liked it better. That fin was put on there just for looks." I did the same in 2005, on the Vincent streamliner, just for looks.
Max