Uneven tire wear is an expensive problem for car owners. This is the number one reason people will have to prematurely replace a tire on their car or truck. Uneven tire wear can be caused by a number of factors. Some of these include incorrect inflation (outer edge wear equals low tire pressure), alignment issues, vehicle over-loading and worn out shocks or struts. Tire wear just on an inner or outer edge shows a problem with vehicle camber. Feathering, or patchy tread wear indicates tire scrubbing, which indicates problems with toe adjustment. Cupping, or unevenness in the tread indicates the shocks or struts are worn out.
For more info, see 3 Causes of Tire Wear and Tear