Originally Posted by Joe@ApexRaceParts
A square set up on your 128i would be preferred. This will create a much more neutral driving car on the track that is prone to much less understeer. Considering that you do not have the power to warrant a staggered wheel set up the wider rear tire would not be necessary. A square fitment of 18x8.5" ET45 with 235/40/18 tires would work great and not need any spacers or fender rolling.
235 would be borderline. 245 on my stock 130i isn't enough.