I have my 2010 S3 in at AMD Woking at the moment for a few bits including a full turbo-back exhaust and a front and rear ARB upgrade. I ordered the front (24mm) and rear (26mm) H&R.
I have just had a call from the garage to explain that everything has been fitted except for the rear ARB. The reason given was that with the new exhaust the rear ARB wouldn't fit. But apparently this is OK because it they discovered that the rear ARB that is on the car is actually thicker than on the older S3 models.
Now I am a bit confused because I was advised that installing the ARBs (front and rear) would reduce understeer and improve handling. However, my understanding is that a stiffer front ARB will actually increase understeer if the rear ARB is not also uprated! I am picking up the car tomorrow morning!