[lunarhighway]

tfirst of all, great that autospeed continues to explore aeromods, and other tweaks with FE in mind, it's on of the reasons it's in my top 3 car sites next to ecomodder and gassavers!

A few points i was wondering about is if perhaps extending the sides of the new wheel fairings beyond the inner sides of the wheels wouldn't have been a good move. they could have ran the entire remaining length of the car preventing air from getting in the rear wheelwells and keeping the rear wheel wake separated from the underbody flow.

yet perhaps the lack of improvement comes from the wrong assumption.

at this point along the length of the car diffusion might be more important that attached flow. that's to say that the design is so that theres a smooth gradual transition from the fast moving air under the car to the slow air behind it even if this is made invisible by the somewhat untidy underside (although most cars look far worse than the insight)... afterall it's a pressure difference.

imagine a car with a perfectly flat underside parallel to the road.
sure the underside will promote smooth airflow but when the air reaches the rear bumper suddenly the pressure will drop in an instance.

where a car with a slightly rougher underside that slopes up near the end would allow for a much smoother transition in pressure.

if the underside of the second car isn't to messy, perhaps it will have a lower Cd than the first while appearing less aerodynamic to the untrained eye

a flat underbody might server to prevent turbulence, but can it restore it if it already exists? as the boundry layer is likely quite think form the uneven surface before this might make the actual surface on the aft portion of the car less critical. and so all your left with is the original diffusing effect of the average shape of the rear. (on the insight, combined with the rear bumper design this is likely to function very well)

what i'd try to do is add some vortex generators to the front of the rear tray, as these might tidy up the uneven flow so it can reattach to the tray, or add finlets as on a racing diffuser to guide the airflow more.

on the other hand given the results, it's quite fair to draw a line and conclude the insights aerodynamics are very good and the undertray is not going to make the difference that would justify the trouble.

still i think a similar setup on less smooth cars (wich are more common than the insight) might illustrate more clearly if a rear undertray has pontential or not...

anyway, regardless of the outcome i'd like to see more like this on autospeed!!!