By Roger Marble
I’ve 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, i.e., tire life. Some are told, “Replace at 5 years.” They may hear that as, “You will die if you drive on a 6-year-old tire.”
Discount tire has presented this diagram:
You will note that they do not show some cliff that you fall off. I responded to a question on tire life where the person thought that the tire companies were simply pushing tire sales.
Tire “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. In addition, 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
In addition to the rate of aging doubling for every 18F increase in operating temperature, heat also comes from being in the sun when parked. So if the RV is parked with tires in direct sunlight, you can see the tire achieve 36F increase or more. That means it is aging at more than four times the rate it would have if in full shade.
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:
Wikipedia: Reaction rate
ThoughtCo.: Factors that Affect the Chemical Reaction Rate
Here is an article 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.
Have a tire question? Sign up for Roger Marble’s new Facebook Group: RV tire news, information and discussion, hosted by RVtravel.com and moderated by Roger. He’ll be happy to help you.