why not use some basic logic ? just measure what you have at present then see where/how it will be different ??
few calculators here will
help
http://www.seatcupra.net/forums/showthread.php?t=225813
::Original::
Rim diameter :
Rim width:
Rim offset:
Tyre diameter
Tyre width:
Tyre profile:
::Body Dimensions::
Front arch clearance top:
Front arch clearance front:
Front arch clearance rear:
Rear arch clearance top:
Rear arch clearance front:
Rear arch clearance rear:
::New Wheel::
Rim diameter :
Rim width:
Rim offset:
Tyre diameter
Tyre width:
Tyre profile:
:Body Dimensions:
Front arch clearance top:
Front arch clearance front:
Front arch clearance rear:
Rear arch clearance top:
Rear arch clearance front:
Rear arch clearance rear:
Tyre profile is a % of the width so take that calculation into consideration also as it will drastically affect the rolling radius especially if you are already upping the wheel diameter anyway
The reason behind listing arch clearances is to make sure you allow for tyres

as believe me some don't even think about it and it will also give you a measure as to how limited you are for lowering and space available to start.
That list above is by no means exhaustive, just a way I have used many times along with the calculators in the link to get an idea of what sort of difference a certain rim would make
Once you start adding lowering height differences, suspension travel and steering lock limits and size of spacers/adapters for to add into the mix you can end up in all sorts of trouble mind - as they say measure twice cut once
..