Does bigger mean wider?

[JMI]

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

[winfred]

heres one of the best calculator i've found http://www.bncoffroad.com/tire_gear_cal.html

[JMI]

heres one of the best calculator i've found http://www.bncoffroad.com/tire_gear_cal.html

Nice

Thanks

[Alexlind123]

http://www.miata.net/garage/tirecalc.html

[BillionPa]

you want to maintain the contact patch aspect ratio, so you would need to go to wider tires due to the way the tires deform, not much though, think 1" per 1".