I washed my truck today and noticed that my tailgate was the dirtiest part of my vehicle. I think this is a bad sign for aerodynamics, and indicates that my airflow is not detaching cleanly at the rear. I have a tonneau cover and want to try extending it about 6" either straight back or with a small angle.
Any advice for the angle of such a spoiler?
This is a rough idea of what I have in mind.
Not my truck but the same cover I have.