For context, i worked in a speed shop specializing in wheels from 02-08 so i'm speaking from experience on a large array of vehicles. i'm not a fan of them. I think if you're not happy how your wheel fits you need different wheels. if you must use them make sure they're hubcentric like Litespeed said or at least use a hubcentric ring adapter. a few mm isn't going to hurt anything, but i saw a lot of trashed wheel bearings when guys would use the 1" thick ones that bolt on to the existing studs and give you new studs. They were never balanced well either, so you would get vibrations in the steering wheel, especially under hard braking. I recall once we had a long time customer using them on a 350Z with lots of vibrations, darting off to the side under braking, and steering wheel shake on the highway. We tried mounting the adapter to the wheel then balancing the whole wheel/tire/spacer assembly and it improved things but still had vibrations and was unpredictable under hard braking. If you're going to use them, look for something from a reputable company. If memory serves Eibach makes spacers, and they're one of my most trusted companies. Not sure how common it is to find balanced spacers, but i would consider it essential.
