Exactly as dave has stated ,and not to sure why you have these tyres fitted.Yeah, as the width is 285 too! The sidewall is a percentage of the width.
OEM tyres are 265 30 R20, so yours are quite a bit over with width and sidewall. This will over-read on the speedo too.
Use this calculator to get the % difference between OEM and your wheel the same or near enough.
Tyre Size Calculator
A better easy to use tyre size calculator. Use our tyre size calculator to find tyre diameter, width, sidewall, circumference, and revolutions per mile.tiresize.com
You do need a 30 sidewall to get back close to the OEM tyre ratios.
I have thought about upgrading to 20's from the 255/35/19 rotors I have on my S5.
The normal upgrade tyre size would be 265/30/20 ,however the RS5 's have 275 /30/20
So not to sure why you would have 285/35 on the car
