treadwear issues help

[ssmoked]

I have stock 18' rims on my 2011 Z. I bought a set of Michelin Pilot Sport A/S plus replacing my OEM at 10k miles. The tires are rated at 500AA with 45,000 mile warranty. After driving 10000 miles, the center is almost worn to the wear bar and the sides are only slightly worn. I tried to drop the psi down to 31 from 34 around 8000 mile mark on the rears (thinking it was over inflated) with no luck. any ideas and suggestions? Anyone else using these tires and care to share how many miles you get out of them, psi, and any premature wear (i know our cars comes factory with -1 camber)?

I do spirited runs, but that shouldnt cause premature center wear.

Thanks for your input