At first I had 15mm spacers. But I didn't like how deep the wheels seemed. I tried 25mm and the tire scraped, so I ended up getting 20mm. They make the car look much better than stock. It has a nice and flush look. Also I don't want to roll my fenders so 20mm is the best.
Place of Install
I had the cut the factory studs about a third of an inch to clear the inside of the rim. Also the studs on the spacers were a bit long and my lug nuts wouldn't go on them, so I cut those as well.