[jime57]

It would probably "advance the art" to have before and after testing on the undertray. From what I've read, I think the undertray is important to the performance of the boat tail. In fact, I think I remember that you found that the case with the Metro tail.

As you know, I don't have much faith in fine grain measurements on the Insight because of lean burn, but I am pretty sure that a full undertray has improved the fuel economy of my experimental unit. I just can't provide a number. Hucho and most of the cutting edge manufacturers, including Honda, seem to think it helps.

If your stock under panels are intact, then you need a fairly small piece of coroplast to complete a full under tray. Because the shape is rather complex, I'd start with a piece of cardboard as template. It is a single plane of about 3-4 degree uptick from the little plastic deflector at front of axel to the bumper cover. Attachments are kinda scarce.