Quote:
Originally Posted by jime57
Yep, but you might still miss the true value even on the big ones. That is one reason that I "copy" the results of trend lines of multiple other testers when it comes to the Insight. (The Insight itself being practically impossible to test.) We know from many tests here that removing both mirrors is worth about 3%. It is sort of a Oracle of Delphi method of seeking the truth 
The low fruit on the Insight is the boattail. How do I know? Several folks have built and tested boattails and gotten 12-15% improvement on Insights and other cars. The "trend" is to the 13.5% =/- range  |
Jim,
I think that simply stating that a tapered tail yields an aero improvement of 12 to 15% is over-simplifying the situation.
Why?
Yes, it's true that the Insight benefits from a tail by about 10% from a gas mileage standpoint, and about 18% from an aero standpoint.
However, we need to keep in mind that on the Insight, the hatchback of the car is already closing down in shape, and that the addition of the tail does not add that much aerodynamically than it would on a car body that does not close at all.
In that case the addition of a tail might be 20% gas and 35% aero, and even higher gains at highway speeds.
Jim.