I have owned trucks since 1964 and up until about a year ago I had about 500 radial tires on the ground. I never let them get over 4 years old because that is when they start blowing out. And when they blow out, they usually do damage to the vehicle. We routinely check the date codes. Age is much more important than tread on a radial. Give these guys a call. A company in Lincoln NE builds trailers for us and I have bought from them before. http://www.nebraskatire.com/