When putting rear aero/wing on a car - how high is right?
Im currently looking at doing a rev5 spoiler on my MR2, and people make carbon fiber 'riser plates' for the center section to raise it up over half a foot.
Does that do anything?
Obviously the car will determine aero,but, as a rule of thumb, is there a rule of thumb when it comes to wing height?
From what I have seen, as far up and as far back as the rules allow.
This allows the wing to have the best chance to be in clean air and have the highest leverage it can on the vehicle.
Now, when attempting to combine aero effects from various devices, the answer will change. Some people are capable of using a wing and a diffuser to act together to get a higher efficiency for example.
I am not an aero guy. I just have some fluorescent powder paint, some 3 in 1 oil, some string, and a camera. So I wouldn't take what I wrote as gospel.
The complete engineering answer is: It depends.
As mentioned, further aft helps with leverage and balance shift. Height is a function of how far aft, what the rear underbody looks like and how close to the rear window/roof/c-post the wing is.
If there is a "safe" location it is high so that the air approaching the wing is mostly consistent. Lower mounting means the ends will see less angle of attack than the center of the wing (due to the air coming down the rear window and around the C-post.
Unfortunately, there is no standard solution, but any rear wing will generate rearward balance shift, so if that is what you need you can get it.