I have Y rated (Michelin 4S) 275 30 20" and at 36/32 the car is too sticky & steering feels heavy, whereas at 42/39 it feels too jumpy and light on tight bends at speed, so I have found that 39/36 is ideal (without passengers or luggage) for my B8 3.0 Tdi Cab which is 45 kg lighter than the B8 RS5.
Racks- I wouldn't recommend those ZZ's either as they have inner tubes..
Racks- I wouldn't recommend those ZZ's either as they have inner tubes..