hy mikvest
this is my car:
http://img148.imageshack.us/img148/2710/tiefcs6.jpg
not as low as the car you posted, but low. at he front i got 8.5x18 et 30 with 225/35 continental sportcontact 2 on my car.
my kw suspension still got 2 cm space to make the car lower, but, hmmm, now i got 5cm from the lowest part of the underbody to the street, and that´s the limit in my opinion.
EDIT:
My Rims usually got ET 35, and 5mm Spacers on each Site are enough that rim and tyre do not touch the suspenison.