Whenever u buy new tires check the date they were manufactured. Look for the DOT number. The last four should be a number. Let's say 4610. That would mean that the tire was manufactured in week 46 of the year 2010. Even if the tires are new they could be a couple of years old because they were sitting somewhere for a while. Which would explain why the tires are dry rotted. They get really hard if they sit for a couple of years in a warehouse, then they don't last.