width/tyre issues?

i have very recently fitted a set of Rondell "58" on to my E39 (which i do really like the look of  )
the tyres came with the wheels & on the rear are a pair of 10" rim's fitted with near new pirelli pzero "275/35/18" i'm getting a very slight bit of wheel arch buff on the O/S rear.

basicly my question is: if any one has these wheels/size fitted to there E39 saloon do you have any issues?

i think i'll either be downsizing the tyres or i have a weak rear spring on the N/S which TBH changing 2 rear springs would be cheaper than 2 new rear tyres  

pis of my car, looking at the clearance from tyre to wheel arch i'd say my rear spring is the culprit? (to much flex & sagging under pressure).. that said, it's the other side that's buffing at the rear 

Edited by 523 iAN - 08-September-2012 at 08:34

yeah i had the same issue on my last E39 running 18" wheels (proper off set, just phat tyres, lol) i just popped spring assister's in between the rear coil's and all was good, drove it for over 2yrs with them in place with no prob's ... there's a good chance they might still be in place on that car??