What Is Tire Dry Rot?

Tire dry rot is common on classic cars because they're rarely used. According to an Angie's List poll, only about 40 percent of classic car owners drive their classic or vintage vehicle more than once a month. (Photo by Katie Jacewicz)

Tire dry rot is common on classic cars because they're rarely used. According to an Angie's List poll, only about 40 percent of classic car owners drive their classic or vintage vehicle more than once a month. (Photo by Katie Jacewicz)

If you notice little cracks running spider-like along the sidewalls of the tires and running all the way to the tread, you may be experiencing a common phenomenon that occurs in stagnant cars – tire dry rot.

One of the most common reasons for tire dry rot is improper storage or infrequent use. According to an Angie's List Classic Car member poll, only about 40 percent of classic car owners drive their classic or vintage vehicle more than once each month.

What are signs of tire dry rot?

Rubber and plastic materials naturally degrade over a period of five to six years depending on the climate, temperature and humidity, the use and storage of the vehicle, and the air pressure levels of the tires. Dry rot is indicated by hard and brittle surfaces on the tires. As the oils in the rubber begin to evaporate, the chemical bonds break down, leaving a dry tire behind.

What causes dry rot?

The most common causes of dry rot include low inflation of the tires, storage near excessive heat and a lack of use.  Constant exposure to sun can speed up the effects of dry rot upon the tires, so if your car sits for long periods of time in balmy Florida, for example, chances are your tires will deteriorate quicker.

Causes of tire dry rot.
Checking your tire's pressure can prevent tire dry rot. (Photo by Eldon Lindsay)

Finally, if your tires were manufactured several years ago, they could be unwrapping, whether they’ve been on your car the whole time or not.

How can I prevent tire dry rot?

If you have to store your vehicle for long periods of time, ideally store it in a climate-controlled garage, keep the tires inflated to the manufacturer’s recommendations, store it with boards under the tires and check the air pressure at least once a month.

Can you repair tire dry rot?

Dry rot can be fixed only in the early stages. Try using a water-based tire product to help seal cracks and avoid products using petrochemicals or silicone. If dry rot is advanced, the only real solution is to replace the tires.

Is it safe to drive rotted tires?

In most cases, tires with dry rot are probably not safe to drive on. Around town, you may have a little time before you need to replace the tires. Once the cracks reach the cords of the tires, the heat of long distance driving will cause the rubber to expand and the tires to actually break apart while driving.


Editor's note: This is an update of a story that was originally published November 7, 2011.


Comments

I have foam rubber parts on my Kayak carrier which is mounted on top my X-Terra, what can I use to rub on the rubber to prevent damage from sitting in sun all the time. I live in south west Florida.

Some of what appears in the "How to prevent tire dry rot" article are simply inaccurate. It is true that dry rot is the result of exposure to the sun and high temperatures over time. The exposure results in the evaporation of the petroleum products that are necessary to bind rubber molecules together. These petroleum products evaporate over time and result in a break in the bond of the rubber molecules which presents itself as cracks in the surface of the rubber. It can be simply thought of as the result of mud being exposed continuously to the sun. Water is the bonding agent for the particles of dirt that produce mud. When the water evaporates the bond between the particles of dirt in the mud breaks down, the dirt shrinks, and cracks are formed in the drying mud. Low tire inflation does not directly result in dry rot. However, low tire inflation does result in excessive heat and tire sidewall and tread de-formation which exacerbates the dry rot condition by excessively stretching of the rubber in undesirable ways thus contributing to the cracking. As far as repairing dry rot is concerned, I can tell you as an aviation maintenance technician with more than 20 years of experience on large commercial jets, that dry rot is not routinely re-parable and no professional in the automotive or aviation industries attempts to effect such a repair. In addition, in many jurisdictions dry rot is cause for tire rejection during a vehicle inspection since dry rot has the potential to cause a catastrophic tire failure. With respect to storage it is much the same as putting meat in your freezer; the cold temperature, unless it is extremely low, only delays the rotting process and does not prevent it. As for tire inflation the inflation stretches the tire rubber which as previously indicated exacerbates dry rot. If tires are mounted on rims it is better to deflate to minimum pressure them and store them by suspending them off the ground so that the weight of the rim and the tire itself does not de-form the tire and the uniformity of the low-pressure helps keep the tire' s shape.

Well thought out comment, thanks.

Who is more liable for extremely dry rotted car tires on a brand new 2010 model excluding customer negligence ? the manufacturer who supplies the dealership with their stock or the dearships themselves is the a way to determine ?

I have the same question. My car just failed inspection because of this.

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