on my green car i have 18x7.5 at 48 offset with 235/40s all round never a rub
on my red car i did a staggered sizing 18x8 with 35 offset front with 235/40 tyres any wider might rub but would be hanging out of the wheel arch is no go.
On the back 18x9 with 265/35 on 40 offset rim..see my other thread on rubbing now fixed...to go wider tyre you would need to go a higher offset 45/48 back closer to the original 55 offset..plus 245/40 on 18s would create a higher speedo error around 3.5% 235/40 for 18s from memory is only 1.8% ..
The only rubbing I've had has been on the outer side of the tire/inside lip of the wheel arch..and only on the back ...and unusually more on the drivers side than the passenger and not on the inside near suspension bits, either.
Oh
and I'm not a fat .rse either at around 73-76kgs depending on eating a salad or Big Mac..but the wheel guys said that they quite regularly have cars where the track width is more to right or to the left..eg. rexs nissans holdens etc and most people wouldn't pick it up until you push the envelope for tyre width/size..everything else underneath is std and no accidents, no bent arms etc..we could see a visisble difference where the wheel sat under the wheel arch...anyway I hope that answers your question ??