Hi, Pascal: test route is straight, level and 1.6 km/1 mile "at speed" (not counting the distance used to get up to speed & level off, coast down and turn around etc). You can see the section of road I use here:
along the shore of the mighty and lovely St Lawrence River, immediately to the southwest of where that map link is centered.
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I plan to tuft test the bottom of the tail. The car needs a full belly pan for the bottom of the tail to work well. I'm sure it's in very turbulent flow now, but a full undertray will feed it some cleaner flow to work with. It's on the list!