Largest size of shim spacers?

[Jakg]

Thinking of adding some spacers at the rear of my car, but don't really want to spend £100 on the proper hubcentric ones - you can get the shims on eBay for ~£10 - obviously it's not a good idea for anything large, but whats a suggestable size to go for doing it this way? 5mm, 10mm?

[TheEnd]

Certain thin ones will just get in the way of the original spigot, and the car will be resting on the wheel bolt shafts.

Hubcentric will avoid the wheels shaking from being misaligned.