Ozone Cracking

Though exceedingly rare, tire examiners and experts today occasionally see tire failures resulting from ozone cracking (also known as “ozonolysis”). Ozone cracking is characterized by the formation of small cracks or fissures on the surface of the rubber which run perpendicular to the direction of strain.

Atmospheric ozone is a natural enemy of natural rubber compounds. It creates such marked changes in the properties of natural rubber that oxidation itself is considered a chemical modification of the polymer. At ambient temperatures, oxidation in air is a slow process. At higher temperatures, the process is speeded up. At any rate, the effects of the chemical changes are cumulative over time, and since the cracks are perpendicular to the direction of strain, ozone cracking can cause rapid deterioration of tire sidewalls in some areas.

Most rubber compound from which most tires on the market today are made include an antiozonant which protects the polymer against the harmful effects of atmospheric ozone. Furthermore, the best UV absorber, carbon black, is used in substantial quantities in most high quality rubber articles, and some compounders nowadays actually double the quantity of antioxidants in high-quality black carcass compounds used in tire construction to increase resistance to UV-induced oxidation. Therefore, any ozone cracking in a tire of today's manufacture is almost always the result of negligence in the manufacturing process - specifically the failure to include antiozonants in the rubber compound.