Sorry for reviving an old thread. I was looking at willem toet's blog post here:
http://www.racetechmag.com/2017/08/will ... diffusers/
I put those values into excel and did some combinations with angle of attack and ride height. I sort of get the idea that the diffuser loses very little downforce on braking and corner entry. This is because of my understanding of the combined effect of ride height and angle of attack. When braking the nose goes down and the rear comes up. This lifts up the rear diffuser away from the ground. But as the nose goes down and the rear goes up the angle of attack also increases.
Looking at the second plot image on the blog it shows that diffusers with bigger angles peak at higher ride heights. So if you take the 15deg diffuser and simulate it under braking. Let's pick 28mm as our base ride height value. Let's say our wheelbase is 2.4meters and rear goes up 3cm and front goes down 3cm. This results in an increase of about 2 degrees of angle and increase of 30mm ride height for the diffuser.
Could it be totally wrong to interpret it now as 17deg diffuser? Kinda? So we can see that a 15deg diffuser peaks at 28mm ride height and produces 1.5Cl at 58mm (28+30mm). But because of the angle of attack has now changed we are looking at the 17deg diffuser which gives you 1.73Cl at 58mm. I'd imagine it is not that straightforward and maybe the truth is somewhere between the 15 and 17deg angles but that basic idea is correct? Diffuser loses less downforce if the angle also changes? Assuming the stuff happening in front of the diffuser is ignored (front wings, splitters etc..)? 30mm ride height change also doesn't sound too massive for me considering it is the combined effect of tire and suspension.
