General comment on the topic.
I think that most can understand that the numerous variables involved such as Ambient temperature, operating temperature, load, and operating speed all can affect the "life" of a tire. Also there is the obvious variation in the numerous components and assembly practice of each tire itself.
All of this adds up to an impossibly complex equation if trying to predict the life of a tire.
While many may understand that if a tire spends it's life in Arizona, Texas, Alabama, Louisianian and Florida it will have a definitely different life span than one that spends its life in new England, even if the load, inflation and speed were magically identical. I do wonder how many have even a passing understanding of the complex nature of manufacturing a tire as seen in THIS
animated video. Actual shots of the process here
. Here is an alternate view
of Truck tire process which would be essentially identical to what is seen in both LT and 22.5" size tires.
Unlike materials like steel or Aluminum, rubber is not a homogeneous material so even minor variations in the raw materials can affect tire life.
Here is a video
showing the basic process of preparing rubber before it is applied to steel or polyester cords. Note these are videos of very low tech methods. Modern equipment is much larger and the process is harder to see as there is much more automation behind closed chamber shields.
The estimates of maximum tire life is based on assumptions of the variability of the tire and the variability of the use of the tire. The estimate must also consider the probability of the variables stacking up and the potential for the severity of the tire failure.
Some companies may feel that no greater than 0.5% probability of failure at 7 years is acceptable IF
the tire is always operated in North America, never exceeds its max speed rating or is overloaded for the inflation in the tire. Another company may feel that less than 5% at 12 years is the goal.
It is also important to remember that only after thousands of tires have completed years of service can a company know if it made the correct calculations. I do not know of any company that is not constantly working to lower
the failure rate or extend the usage time while at the same time trying to meet customer demands for better wear, fuel economy, traction, ride and lower cost.