WHEEL RIM & TYRE SIZES for Z3

[GISPOT]

I am considering creating a little more traction to my rear axle by increasing the rim & tyre sizes to my 1997 Z3 automatic. Can anyone from their own experience or just technical knowhow, advise me what rim sizes & tyres I can increase to without fouling wheel arches or other situations / areas like when suspension goes up & down. So in summary, a wheel + rim size maximum that will be safe & not have any negative issues.
Many thanks in advance,
Simon C.