Here is the tread at somewhere a little over 20,000 miles. You can see how the middle strip looses it's teeth first, then other sipes and tread elements wear off over time. No big deal if you don't mind grooving them later, but it ticks most people off. The only reason I can guess for this tread design is to increase total tread life to meet the mileage warrantee. Maybe it makes them more stable but I doubt it.
