I've lived in the greater phoenix area most of my life, and never really thought about how long tires last... until I spent a year in Seattle commuting. Using a conti contact II up front, tour ride out back I was getting 2500-3000 miles out of the rear tire... (estimate, it was about 50% tread when I left) put a new tire on the back when I moved back to phoenix and barely got 1500 out of it before it was bald in the center and needed replacing.

Front tire hasn't needed replaced but I'm noticing accelerated wear.

Hence replacing the set with the schwalbes