There are basically two reasons tires fail. Let’s examine them.
1. Over-load / under-inflation
(which are closely related since it is the inflation air that carries the load, not the tire)
Under-inflation. A tire operating at less than 80% of the inflation needed to carry the load is considered to have been run flat and there is a good chance that there has been permanent internal structural damage done to the tire. Related to this is having the tire inflated to a level that just barely is rated for the actual load on the tire. Obviously you can be under-inflated because of cut or puncture or a valve leak or if you use an inaccurate gauge. If you run sufficiently low in pressure at highway speeds for a couple miles you can have a Run Low Flex Failure or more commonly a “Blowout“.
Over-loaded Few people realize that by design most passenger vehicles have 13% to 20% or more “Reserve Load”. That means that they are actually underloaded by that much for a vast majority of the time. Most TT on the other hand have tires selected that are at the tire max load and can just barely carry the actual load.
Data on actual loads measured on TT shows that over half of RVs measured (out of many thousands) have one or more tires overloaded based on actual inspection.
Heat damage occurs at the molecular level, compromising the ability of rubber to flex and stretch without breaking the chemical bonds. Once broken, these bonds do not repair themselves, they just continue to grow. If they grow enough you can see the cracks and eventually you may have components come apart.
Heat can be generated by the flexing of the tire with the hottest region being at the belt edges (edge of the tread) in radials. Increased speed generates more heat, sometimes faster than the heat can be transferred to the surrounding air. Over-loading generates more heat. Under-inflation generates more heat. Having 0% reserve load generates more heat than having even 10% reserve load.
Heat also comes from being in the sun. This heat can soak into the structure of the tire and actually accelerate the aging of the rubber in the tire. As rubber ages, it loses it’s flexibility, so this contributes to the breakdown of the rubber at the molecular level mentioned above. For every 18ºF increase in temperature the rate of aging doubles. So if the RV is parked with tires in direct sunlight you can see the tire achieve 36F increase or more which means it is aging at four times the rate it would have if in full shade. Many times the cumulative damage from excess heat can result in a separation of the belts and tread from the rest of the tire.
I have a blog post showing the results of a test of white tire covers to protect tires almost completely from this heat damage.
I hope this helps others understand the primary causes of tire failures.
What can you do to lessen the likelihood of having a tire failure?
1. Install a Tire Pressure Monitor System or TPMS. These units can provide warning if you get a puncture or have a leaking valve.
2. Be sure you have enough inflation in your tires to carry the actual load
Run Low Flex Failure photo taken by author.
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