The 19" wheels that are coming with my S85 are 8.5 inches wide. The aftermarket wheels I am looking at are 9" wide. I'm staying with the same tires (Michelin Primacy). Is this 1/2" difference a no no? I've been told that this will work fine but I would like to hear from actual owners their opinion. Thanks.
A 245/45-19 will fit properly (albeit, the max) on a 9" wide wheel according to the Tire Rack. btw, I would not stray too far from the factory 40mm offset (I had my 20's cut on a factory spec 40mm ET to completely eliminate any tire to wheel house interference)
you'll be fine with the exception of more grip! I am running 9" in the front and 10" in the rear and it grips and looks so much nicer.