When I put 1400 lbs, .008 Crr, 21.5 sq ft, .15 Cd, and .9 drivetrain efficiency into the calculator it says 93 mpg @ 55 mph. Achieving that would be great!
Since there's still ambiguity about it, 23 sq ft w/all else the same nets 88 mpg. Still great.
On that note, .15 Cd is mighty optimistic; assume .20 w/23 sq ft and 72 mpg pops out.
Assume .25 and 60 mpg pops out.
The calc says my car should get 40 mpg @ 55 mph. Without a scangauge I can't tell, but it just might be doing that-
at a steady state 55. In the real world of starts and stops and cold starts it loses about 10-15%, to end up at 34-36 mpg. Apply that correction and 93 becomes 79-84; 88 become 75-79; 72 becomes 61-65; 60 becomes 51-54.
There is little to go on at this point besides these vague assumptions but at least we can guess a likely range.
How are you going to do tuft tests? Are you going to make it drive after all?
The Cyclone steamer looks promising but it may be a while before you can get one...