Quote:
Originally Posted by skyking
I read about that, and what happens is you get to a point where the increased frontal area of the dam starts to hurt you. That point seems to move around  |
Both will help - you still want to reduce the air going underneath the vehicle.
But there's indeed a point where lowering the airdam and increased frontal area starts to hurt your fuel economy.
Where exactly the turn-over point is, is hard to say.
With a square rear end, it's not beneficial to add a shallow diffusor aft of the wheels.
But if you do a full belly pan + boattail (i.e. sorting out the squarish rear end), you can gently (about 4° max) angle up the rear end belly pan, from about the rear wheels aft if the structure permits that.
(Well, that's how it would be on smaller vehicles.)