As Cain pointed out the fitting of one of his valances made a big difference to the stability on my 4/4.
Less problems with sidewinds..also I disliked the showing of the undercarriage without the valance..the car looked somehow unfinished without one.
I also used the 2 air inlets to pipe cold air up to the air box.
Luckily my +4 Supersport has a similar valance fitted as standard.