The clearance from strut housing to the inside of the wheel will be 4mm LESS
The outside edge of the wheel will RETRACT in towards the body by 4mm
This is what the offset calculator says, so it is debatable if you would neeed spacers, unless you just want to push the wheels out further. I'm not a lover of spacers, if you are not already commited to these wheels I would suggest looking at something bigger like a 18" x 81/2 they fill the wheel arch better and look the part. You may need to fit shorter studs instead of spacers so they don't foul the disc.