Ditto with silversand. Not seeking to flame anyone but tires do age and personally I am suspicious of any tire more than 5 years old. In my real life I oversee a fleet of 14 school buses and I will not under any circumstance run a tire older than 5 years on the steer axle and only because many of these buses are low speed, local use only and dual rears will we stretch that another couple of years on the drive axle. We have a couple "full size" buses and those tires are built to a much higher standard that "E" range so they get more of a time cushion. 10-12 ply commercial tires are a bit different.
I have scaled my own rig and I am under the truck & tire weight rating (OK, not by a huge margin) but between the TC and pulling some heavy trailer I have had a tread separation that I attribute to the combination of high load, heat (Alabama) and extended hours on the road.
Next time anyone starts to quibble about tires, take a measuring tape to their tires. For the sake of discussion, 8" wide tread, total length of contact with the ground, 4" at best. SO...4" x 8" = 32in/sq x 4 = 128in/sq. Now measure your feet with shoes on. Again just an example, 3" x 10" = 30 in/sq x 2 = 60in/sq. Basically you are counting on about the same contact patch as two guy wearing size 10 shoes. All you are asking that 128 square inches of rubber to do is carry you, your TC, and your family at 60mph in summer, AND save your life if some ding-a-ling pulls out in front of you. Pretty amazing what tires are expected to do for 30-50,000 miles.
http://tires.about.com/od/Tire_Safety_Maintenance/a/The-Science-Of-Tire-Aging.htm
