Rear tire wear on 1997 Mazda Protege DX?

My back tires are wearing unusually. When you look at the rear tires, the top half has decent tread, where the bottom is nearly bald. It is worse on the driver's side than the passenger side. I don't think it is worn shocks, because I have had most of the suspension on this car replaced within the last 30k miles. My tires are Altimax R/T's so they aren't cheap. Any ideas? Thanks :)
 
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