I just got a new set of 18" zen wheels and new tires and i want to change the spacing for the back tires. the front ones sit nice but the back ones are a little more shallow. What is a good size spacer to get, which will safely fit on the stock hub?
Like mentioned, go with a hubcentric spacer, with a 67.1mm center bore. As far as what thickness spacer you'll need, you have to measure that for yourself. In order to clear my larger calipers with OEM wheels, I stacked washers on the lug studs, and placed the wheel up for reference. Once i was happy with the clearance I measured the washers (mm) and found a spacer that would work.