You can run 18 x 9 front and rear and 265/35-18 would be almost identicle to the over ratio of the stock setup (That is Dinan's and Alpina's recomended setup). 235 is way too small for that car and handling will suffer greatlty do to the weight of the car. Currently I am running 245/40-18 front and 295/35-18 rear on 18 x 8 and 18 x 9.5 MParrallel wheels. BMW spec for the euro 850CSi is those wheels with 245/40-18 and 285/35-18. Stay away from those low end Bridgestones. As you have read all over this forum the handling ability is absurd. If you are going to do it right you should consider: Bridgestone S-02 PP's, Michelin Pilot Sports or Pirelli P-Zero's (my current tire).