Have seen a number of posts on RV forums and Facebook asking why there are different answers to the question of when to replace tires in RV application. Some are told "Replace at 5 years" and hear " you will die if you drive on a 6year old tire.
Discount tire has presented this diagram.
"Life" is not an on-off switch. Rubber begins to lose its strength and
flexibility the day it is put in the tire warehouse. Temperature and
time are the primary drivers of the loss of strength and flexibility.
Tires can fail for a variety of reasons. Hitting potholes creates cracks
in the internal tire structure. Most are microscopic but all cracks
grow and none repair themselves so the number and size of cracks simply
grow till one day the rubber will not be strong enough to tolerate
hitting a pothole or piece of road debris and the heat generated with a long run at high speed on a hot day simply lowers the remaining strength of a tire.
The more a tire is driven the more flexing it experiences. Older tires, having lost some of their flexibility, will experience more actual tearing rather than stretching. Driving faster increases the rubber temperature. The higher the rubber temperature the faster the rubber loses its ability to stretch and recover.
My post on tire covers pointed out the "aging rate' of tires doubles with each increase in operating temperature of 18 degrees F.
Part of Organic Chemistry is chemical reaction rate.
If you want to understand the technology behind this accelerated aging due to heat I suggest you can read some of these sources if you have a few hours.
Here are some specific references on tires
The idea that tires be replaced after 5 years of use is based on probability. Some tires fail at 3 years of use and some are still running after 9 but it's the odds that can get you. If you have an RV trailer I can assure you that the science shows that backing into an RV site is much harder on the tires than pulling through. This is because the Interply Shear is much higher backing in because the side forces are much higher. I wrote about that force in this blog post. https://www.rvtiresafety.net/2018/09/warning-super-technical-post-tire.