TJ, I'll try the chalk test, thanks.

When I say one side is worn down, I mean just that one edge, the outside edge. From the middle of the tire inward, the tread is the same depth, but the outside edge is quite a bit thinner. However, this wear pattern is the same on all four tires. I wish I had a digital camera, I'd take pictures.

I'll do the chalk thing and see what happens.