Tires gone in 15,000?

[fourtwophd]

I have a 2009 Boxster S. 19 inch Pirelli PZero Tires.

Both rear tires wore through the steel belts within 15,000 miles. Not inside, not outside, but right in the middle of the tire. Outside and inside have lots of tire left.

I was told by the dealer that it was "aggressive driving" or overinflation. I have maybe spun the tires once in 12 months, on wet pavement. I have an auto and it is damn hard to spin them.

I have watched tire pressure religiously during the life of these tires. I have never added pressure to the tires from the day I bought it (dealership new Oct 2010). They have ranged from 28psi to 38psi (when hot in summer).

I have not raced the car. I initially took the dealer's word, but checking Pirelli, these tires were not overinflated.

Any ideas?

Scott