Tire sidewall deterioration

Vehicles which are parked for extended periods often experience tire sidewall deterioration. Sometimes called tire dry-rot, these sidewalls literally dry, check and eventually crack and split. Each year the loss for RVers, trailer boaters and owners of classic cars adds up to millions of dollars. This article examines this problem.

Is your vehicle susceptible to tire sidewall deterioration?

Tires today commonly contain chemical ingredients which lessen damage from ozone and ultraviolet light, the main environmental enemies of tires. Ozone is an odorless gas, which some people call the electric train smell. Although it is more concentrated in cities and manufacturing centers, ozone is a normal part of the air we breathe everywhere. When combined with ultraviolet (UV) light, ozone causes rubber to dry and become brittle and results in tire sidewall deterioration.

Black Tires

To protect rubber against UV damage is why tires are black. Tire makers use a common type of UV stabilizer called a competitive absorber. Competitive absorbers capture and absorb the UV light instead of the tire's rubber.  Carbon black, a very cheap ingredient, is used as a competitive absorber whereas, all other UV stabilizers are extremely expensive. This is why tires are black and are not made in designer colors.

UV stabilizers are called sacrificial, meaning they are gradually used up and reach a point where they can no longer protect the tire against UV damage. As carbon black loses its ability to do this job, it turns gray, which explains why tires appear gray as the get older.

Ozone Protection

Waxes are used to protect tires against ozone. When tires are being driven they flex. This flexing causes the protective waxes to move to the surface where they form a physical barrier between the air --which contains ozone and oxygen-- and the tire polymer. This is called blooming.

When tires are not regularly used, such as a parked RV, boat trailer, or classic car, this blooming does not happen. Ozone then starts eating away the protective wax and before long reaches the tire polymer. Often by this time, the surface carbon black has lost its ability to protect against UV. With UV light and ozone working together, deterioration starts. The tire dries, checks, and will eventually crack.

Other Degradants

Petrochemicals and silicone oils can also remove protective waxes and increase the rate of decay. Common automotive protectants and tire dressings can contain chemicals and/or silicone oils which dissolve protective waxes and can actually attack the sidewalls.  In the event of failure, one of the first things tire manufacturers look for is evidence of the use of these types of products. If it is found it may be a cause for invalidating a warrant against manufacturing defects.


The most effective solution for this problem is to remove the tires from their rims and store them in a cool dry location which is not exposed to sunlight.

Because this is not always practical or convenient, some specialized products have been developed to deal with this problem and lessen the loss.  One product I've seen is described at :

I have no first-hand experience with this product nor the company which makes it, but if you know of anyone who has, we'd just love you to visit this forum and tell us about it.


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