The Owner's manual states that 225/40VR18 M+S Winter Tires must be used with snow chains in order to provide clearance to the body. It also recommends RUD-Matic dics chains. Here is the web site:

http://www.rud.de/en/01_schneeketten/index.php

I have driven with these type of chains in the past and they are very low profile and work very well. Thanks.