You opened a thread for the very same topic towards the end of Februrary so I'll just paste what I replied with there.
The spacer size is heavily dependent on your wheel offset, tire size, and suspension setup. If you're trying to figure out what spacer will give you a flush look without rubbing we'll need to know what wheels you're currently running as well as if you're at stock ride height or how much lower than stock the car is.
Mine is low and I was able to run 8mm spacers with the OE 18x7.5 51et wheels and 225/40-18 tires...but it also has H&R front & rear swaybars which reduce body-roll when cornering. Your best steps to take are mount the wheel & tire combo you plan on running. Use a straight edge placed vertically against the wheels or tires. Measure the amount of space you have for clearing the inner fender surface. In the front there is a wheel arch liner screw to contend with. You may even try jacking one side up to replicate body-roll before measuring.
When I swapped to 18x8 45et wheels with the same tires and spacers...it rubbed when pushing it while cornering. So I removed the spacers and sold them along with the longer wheel bolts.
This is the 18x8 45 et wheels with 225/40-18 tires and the FTG(fender-to-ground) of 24"...