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General UniversityTire TalkSidewalls and Ozone
Sidewalls and Ozone

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Sooner or later, everyone in the trucking industry comes across a tire that has been attacked by ozone. Some call it ozone cracking, some call it weather checking, everybody calls it a nuisance.

But what exactly is ozone cracking?

Ozone (O3) is a naturally occurring gas that can become concentrated around urban and manufacturing areas. Ozone attacks a tire at the molecular level, and with rubber, bonding at the molecular level is the key to a tire's longevity. Rubber compounds are comprised of polymer chains. These chains form a very complex and interconnected series of "webs" within the rubber. This network of polymer chains is what provides the rubber compound with strength and integrity. Ozone contact the outside surface of a tire and literally "cuts" the chains exposed at the surface of the rubber compound. This is the start of the cracking. As the sidewall of the tire flexes the cracks grow and expose more surface are to the ozone attack. Without preventative measures, the persistent attack by ozone and dynamic stresses will utlimately cause the rubber compound to become inadequate. To slow this process down, rubber manufacturers add anti-ozonants to the rubber. Thses chemical additives continously migrate to the surface of the rubber and intercept ozone before it reaches the polymer chains. Ozone is not only captured by the anit-ozonant, but the two react, leaving behind reaction products that can form a protective film that physically shields the rubber from further ozone attack. Weather checking starts on the outside of the tire and will work its way into the face of the sidewall.


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Now, how can you measure the degree of weather checking?

Visually, a person can make an educated judgment as to the severity of the cracking, with the help of a visual reference guide. As an example, Bandage Inc., a leader in tire retreading technology, has such a tool. It is a visual template that is held up to the sidewall of a tire being prepared for retread. On the template are graphic example of the varying degrees of weather checking. By placing the template against the sidewall on an un-mounted, un-inflated tire with beads in a natural state, a person only has to make sure that the condition of the sidwall is not visually worse that the desired displays three difference degrees of ozone cracking: acceptable, suspect, and reject (see illustrations). Bandag, with more than 40 years experience, and a process used in more than 100 countries has established itself as an industry leader. By using a visual reference, a person can make an educated decision as to the degree of weather checking on a tire.


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