good explanation UkNuck.
OP, you need to be more specific as to what your reasons are for changing wheel size.
example: I went from stock 17x7.5 +52 offset (stock) to 17x8 +48 offset
I wanted: wider wheels so I can mount wider tires, slightly wider track and didn't want to worry about rubbing either the struts or the lip of the fender.
I got all that and am now just waiting for summer/my stock tires to wear out so I can fully justify putting on 235/40 summer tires