Have you ever had to move a car that’s been sitting awhile, and found the tires were flat from dry rot? What causes tires dry rot in the first place?

If you have any experience with older vehicles, or just need to get a car that’s been sitting awhile moving, you know how quickly dry rot can happen. It can be a pain dealing with rotted tires because their condition is unsafe and means they will need replacing. That means a more considerable expense than many people anticipate, but it is less expensive than a severe accident.

Tires experience dry rot because the rubber compound of tires has oxidized over time and hardened, forcing the material to crack and become brittle. The chemical compounds of the rubber and resins of a tire break down as the tires lose their flexibility and become unsafe to perform on the road.

Tires are a vital component to the health and safety of any vehicle. Poorly conditioned tires can lead to accidents and costly repairs. Every vehicle owner should know what causes dry rot and how to spot the signs of this condition. Like you would change your oil or air filter regularly, checking the condition of your tires can keep you rolling down the road with confidence.

The National Traffic Safety Administration estimates that in 2019, there were 612 deaths related to tire failure. Since maintaining your tires is so important, we have consulted with the experts from Consumer Reports, the government, and tire manufacturers to find the answers to the questions of dry rot. The information they provide could be invaluable to your family’s safety as they travel and help you prepare for the busy summer season.

How Do Tires Dry Rot?

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What Exactly Causes Tires to Dry Rot?

Tires can experience dry rot for various reasons, but primarily the condition occurs due to the disintegration of the binding molecules found in the chemical compounds of a tire. These molecules are very cohesive at first, but they begin to separate after a while, losing their cohesion and producing what is called oxidation. As the rubber compound is exposed to other environmental conditions, like heat or cold temperatures, UV rays from sunlight, or even inactivity, the process of any molecular breakdown is accelerated.

Think of a tire as you might think about the human body. Our bodies suffer when exposed to extreme elements like sunlight or frost as humans. The natural process of aging advances at a more rapid rate under adverse conditions, increasing the failure of the integrity of our bodies.

Tires also age, which means that certain conditions can speed up the natural progression of a tire’s usefulness. Let’s explore how these various factors contribute to the breakdown of a tire’s molecular structure.

Extreme Temperatures

Both heat and cold can affect the molecular structure of a tire. In the annual testing of tires for Consumer Reports, scientists expose tires to extreme conditions to test the material’s viability. As a tire rolls down the highway, the molecules in the rubber heat up in response to friction with the road surface. The hotter the pavement is, the more heat from the friction is produced and the weaker the rubber compound becomes. Eventually, the excess temperatures caused by this scenario are more than the chemical compounds of the tire can absorb. The only result is a catastrophic weakening of the molecular structure, leading to a disintegration of any inferior points of the tire’s tread.

Bitter cold temperatures can cause problems, as the rigidness of the pavement reduces the elasticity of the rubber and can cause cracks and brittleness. Many drivers have experienced a low tire pressure light in colder weather because the air inside the tire is compressing. Rubber molecules react in much the same way. They harden in colder temperatures and molecules move more slowly.

Exposure to UV Light and Ozone

The sun’s ultraviolet rays in the atmosphere are constantly bombarding the tire’s sidewalls. Every time sunlight hits the tire (which is almost constantly), the synthetic polymers of the tire absorb the UV light and a chemical war occurs. Slowly, the sun’s rays change the polymer’s structure and the strength of the compound is weakened, wearing down a tire’s defenses.

Most of the ozone our tires encounter comes from artificial sources. Industrial pollutants are made of a ton of different volatile chemicals and nitrogen oxide. When UV light hits these irritants, the result is a disintegration of air quality and, when exposed to rubber, tends to break down the molecules similar to the sun’s rays.

Age of the Tire

As tires get older, they begin to slowly lose their cohesion and flexibility. While tires are designed to last (the rubber in a tire can take almost 80 years to decompose). This longevity does not mean that the tire is useful for being attached to a motor vehicle. Most commercial tires are built to last about 3-5 years, depending on driving habits and the conditions of the environment. Any tire older than this, should be inspected for dry rot and signs of degradation. Any tire older than ten years will likely have experienced significant compromise in its chemical compounds.

Inactivity

The biggest culprit in the dry rot of tires is a lack of movement. The longer a tire sets, the less time it has to move and retain its elasticity. (Special resins cover the tire to help it maintain flexibility, and when a tire isn’t moving, the wax dries up). Every time a tire rolls over the road, the rubber compound (resin) in a tire is forced to move, flex and breathe. The molecules expand and stretch and absorb energy just as they were designed to do. Just as exercise keeps the human body limber, the molecules in a tire’s materials need their regular workout routine. Essentially, a lack of movement dries out the tire and allows a fungus to begin to break down the compound, similar to the way wood rots over time.

Inner Air Pressure

Dry rot is not just a condition that happens on the outside of the tire but can also occur inside. Incorrect tire pressures can expose too much or too little of the rubber tread to the road’s surface, increasing the tire’s wear and degradation. A recent study by the government found that 12% of vehicles on the road have inadequate tire pressures. A regular check of the tire’s air pressure can ensure the longevity and correct wear of the tread. Many car owners are inflating tires with nitrogen as a substitute for air. The molecules of nitrogen are larger than those of oxygen and do not condense as easily as air.

Tires are filled with air (or, in some cases, nitrogen). Because the inner portion of a tire is constantly exposed to air (just like the outside), this exposure can slowly break down the molecules of rubber. Tires with bulges or bubbles on the sidewall are clear signs that the rubber is breaking down on the inside of the tire. It also means that the rubber is in danger of imminent failure. Any tire in this condition should be replaced as soon as possible.

How To Spot Dry Rot on Your Tires

The condition of dry rot is fairly easy to spot if you will do a simple inspection of your tires. If a tire’s tread shows signs of cracking or feathering, then chances are you have a serious case. Smaller fissures and veins in the rubber can also be a sign of deterioration. A faded or discolored patch of rubber is a definite signal that your tire is rotting. (Be sure to inspect the sidewalls of the tire for bulges or bubbles that are signaling that there is a weakness developing from the inside of the tire. A reliable mechanic can help you spot dry rot should you suspect that your vehicle might have experienced it.

Should I Drive on Tires I Think Are Dry Rotted?

The simple answer is probably not unless you want to risk the life of yourself and others on the road with you. Dry rotted tires are not to be trusted and should be replaced as soon as possible. The chances are if you spot this condition of deterioration on one tire, you probably should change all of the remaining tires just to be safe. And while purchasing a new set of tires can be fairly expensive, it is nothing compared to an expensive automobile accident or a funeral.

What Should I Do if My Tires are Dry-Rotted?

The affected tire needs to be replaced with a newly purchased tire. Due to the fact that one dry rotted tire may be an indicator of all of the tires being bad, the vehicle should be towed to a trusted repair shop in your area. New tires should be installed with appropriate mounting and balancing. A mechanic or tire warehouse can advise you as to the kind of tire that is best for your budget, vehicle, and driving needs.

About THE AUTHOR

Charles Redding

Charles Redding

I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.

Read More About Charles Redding