Are you sure that the tread is actually separating from the tires? If a tread was separating, it is highly unlikely that it would occur to all four tires at the same time. Especially since it would have involved defects on tires made in different batches/times (different size, etc.). There would probably be lots of others complaining of the same issue. Plus, if the tread were separating from the inner plys, at least one of those tires would probably have suddenly failed already. Are you sure you weren't seeing more of an issue with dry rot - where the outer tread and/or sidewall start to develop cracks along the circumference of the tire? That's a common issue with just about any tire in just a few years, though it is largely cosmetic. I'm still driving around on original PS2s that were manufactured in July 2004, LOL. They have so much dry rot that they look out of place on my nearly new-looking 04 (non-srt). I figure I'll replace them next spring.