Hi Guys
I agree with john h - the relationship between rim width and tyre width is an important safety issue to ensure the tyre operates as designed.
I have 5.5J minilites on my amazon with 195x65x15 Michelins.
I found the following web site gives good advice on comparisons of tyre diameters, percentage changes and effect on speedometer readings.
The site also provides recommended rim sizes for any given tyre size.
http://www.alloywheels.com/tyrecalc.asp
Hope this is of some help.
Cheers