You dont *need* the studs, but it makes it a lot easier to put the wheel on should you take them off frequently. Rather then holding the wheel and trying to thread the bolt, you put the wheel on and the studs hold them in place. With spacers you need longer bolts either way, so most just upgrade to the studs out of convience. My 18"s weigh 45lbs each, so i cant imagine trying to lift a 20" in place and holding it while I thread in the lug nuts. http://store.bimmerworld.com/standar...tud-p1352.aspx
The spacers come in mm widths so just convert the it over to find the one you need. Spacers are cheaper then coilovers so start with those.
From the Turner website:
A wheel spacer helps by moving the wheel away from the caliper, wheel spokes, or suspension that is causing the clearance issue. If your wheels have the wrong offset (too high an offset, causing the wheels to be too far inward) a set of wheel spacers can correct this by pushing the wheel out to the correct offset.