The difference between a 235/40 and a 245/40 is only 10mm in width and and 8mm in diameter. If the 245/40's are say half worn there going to be close in size to a new 235/40 so I doubt rubbing will be an issue. Also if the wheels are 18's and from an A8 there 5x112 with an et45 exactly the same stud pattern and offset as S4 Avus wheels which fit on my A4 with no problems at all no need of spacers etc. The only difference to the S4 wheels are the Fat fives are 8.5 width and the S4 Avus wheels are 8 width. To be honest easiest way to find out if they will rub or not is to fit them up and try them.