I've used 23 mm in the rear to get a flush look. That would go with 18 mm in front. However, I am compromised due to the Tarett Cup LCA's with their own spaces to kick up the camber, but at the same time also changes the track width. You just do not want your tire shoulders hitting the upper fender lips under compression. My camber is -2.9 f and -2.5 r so I'm not a stock OEM suspension platform. I can use the 987.1 OEM 8 " 57 offset f and 9" 43 offset rear with Michelin PS4Ss in 245/35/18 f and 275/35/18 r. This setup will be going on my car in a couple of weeks.