245/35/19. It's basically 4 front tires from the 550i Sport. You could also go 255/35/19 and make it look fatter. Best bet is to call Tire Rack and discuss with them.
Make sure to add TPMS, else you will get error warnings in iDrive.
Audio: Jehnert Flatline speakers, Mobridge M1000 DA2 prepro, Helix P-DSP, Zapco Z-150.6 amp, CIC iDrive upgrade
Performance: Cobb Pro Tune, AR Downpipes, ER FMIC/CP, DCI, RB turbos and inlets, KW V2 coilovers, Fuel-It Stage 2 pump w Ported fuel rail, Mfactory LSD