So turns out someone has run 255 in the front before.
Got this email from the Apex guys:
"There was a customer that used the EC-7's on their car in the 18x9" ET31 fitment all around with 255/35/18 Hankook RS-3's with maxxed out front negative camber. They told us that there was no rubbing unless going over a very large dip, which is rare, and they believe it's due to the Hankook RS3 running much wider than an average street tire. This would be a great fitment for your car, providing a Profile 2 in the front and the rear. "
http://europeanautosource.com/blog/a...on-e89-z4.html
He had rubbing because he was 13mm closer to the fender. He should have run ET35 instead of ET31.
Another guy ran 245 tires on BBS LM wheels that are 22mm closer to the fender and said he only rubbed on the first day.
http://e89.zpost.com/forums/showpost...6&postcount=17
Really good point about measuring the actual tire width. Some tires are much wider than others.
I do feel comfortable that we have at least 15mm of fender clearance with wide tires and the right offset wheels based on the BBS LM guy. (22mm - 2mm to avoid rubbing on first day - 10mm/2 assuming he was using an extra-wide tire = 15mm fender clearance). 9mm should be safe.