Suspension Height

[pscars]

Ive just bought a 2002 "02" 1.9 tdi Se Avant Audi A4 as a run around for my dog, im going to fit a set of aftermarket RS4 style 18" wheels to replace the corroded standerd alloys and also im going to lower to compliment the new wheels. I dont want to lower it to an exreme but to the same height as an S4. Can anybody advise on how much lower the S4 is compared to my car so i can order the correct springs ?

THanks in advance.

[nidfix]

Standard S4 chassis is lower by 20mm.