Thanks for the response. I haven't noticed any unusual tire wear. The tires have been on since December. Car tracks straight and returns to straight after a turn. About the same time that the shimmy started and I also noticed a noise when turning at slow speeds--noise comes from driver's front. It's particularly noticeable when pulling into a parking space or backing out. Took it to a shop and they put it on a lift--couldn't find anything wrong with tie rods, etc. They examined it with both weight on the tires and off. I'll get them to check the ball joints again because I understand that problems are hard to see.