I'm going to go against the reast of the guys and tell you what someone told me when I asked the same question just a few weeks ago. I had the same trouble and it turned out that if your upper control arm bushings are going bad, the shimmy get amplified when you add larger wheels, dont know why but I changed mine and shimmy is all gone................ OK, i bought a '90 535 about 2 weeks ago all stock (wheels ,suspension) no shimmy at 50mph ,bushings are ok.I bought ac achnitzer wheels 17" ,replaced shocks,springs and i expected to get shimmy at 50-55mph which i did.I finally took a car today to balance the wheels to get rid of vibration.Paid 60$--still shimmy.WHY???I went back to the same place they balanced them all 2nd time---still shimmy.I came back home rotated schnitzers ---still shimmy.When i put the stock tires in the front ---NO shimmy---.What is the problem????Can anyone help me out??? I know it is obviosly something has to do with the wheels , but what can it be??? Thank you Michael '90 535 5 speed(shimmy)