The 1989 535i has the stock wheels - 15" and stock size tires 225/60. By my calculations this makes for a total diameter of approximately 25.60".
If I want to keep the overall diameter the same for the sake of speedometer accuracy then going to a larger wheel size with the same tire width will get me:
225/55 R16
or
225/50 R17
If I go with a bigger diameter wheel ideally shouldn't I get a wider wheel? Is there an accepted standard for figuring that? About how wide can I go with the 535i without flaring the fenders?
And finally, is there a web site that will calculate all the possibilities?

TIA

Jim