Reviving this old thread for a question. I read the image below to mean that the most advantageous angle for my rear diffuser is about 4* or slightly less, since I am starting at about the rear axle. My question is how do I judge measure the angle I accomplish reasonably precisely? EDIT: maybe go to my favorite flat spot, park, and use a level to judge the ground and a "quick square," such as
this one, to judge the angle? (I have never laid my hands on a "quick square" but a neighbor friend might have one I can borrow). I really have no idea, so maybe I'll just give it my best guess.
