Im thinking they are designed to only last 4-5 years max. Remember back in the day on a trip to a "Junk yard" you could find tires that where 10-20 years old and would last till worn out. The down side is those tires lasting a long time in the dumps, in fact never going anywhere. So now they crumble and come apart in 6 years, brake down faster. Once all the tire manufacturers came on line making these, they make more money with the quicker turnover. Why would they want to make a tire that last 10 years when they can sell 2-3 sets in the same time. Make the EPA happy and get richer, no brainier.