So to my understanding ET is positive offset, I'm looking at a rear 9" ,33 and a front 8", 37 offset, I'm guessing that's fine because it doesn't change the wheel position too far from stock parameters to affect handling
Running staggered wheels, however, will create understeer but since you'll be running a 21mm rear bar, I don't see you having a problem with understeer.
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1995 318ti Base - Cosmosschwarz/Sandgrau R.I.P. 1997 318ti Active - Alpinweiß III/Sandgrau 2013 328i Coupe - Le Mans Blau
Et offset 
Linear Mode
