Originally posted by westcoaststyle
Wheel or you need hubcentric rings to better balance the wheels on the hub. Do a search on vibrates or shakes and you'll get some returns on this subject. It's been covered before and there are more details regarding the possible problems and solutions. 
if you do a good job of centering the wheels with the lugs, you might not need the rings sometimes. but i highly reccomend them on your front wheels to eliminate any possibility of vibration.