Rubber Cracking(Lea en español)
Tires are subjected to one of the harshest environments experienced by any consumer product. In addition to being stretched millions of times as they roll through their life, tires are exposed to acid rain, brake dust, harsh chemicals and direct sunlight, as well as summer's heat and winter's cold. And while a tire's rubber compounds have anti-aging chemicals in their recipes, exposure to the elements will eventually cause rubber to lose some of its elasticity and allow surface cracks to appear.
"The anti-aging chemicals used in the rubber compounds are more effective when the tire is exercised...The repeated stretching of the rubber compound actually helps deter cracks from forming."
The surface cracks that occasionally appear have been called many things: Weather Checking, Weather Cracking or Ozone Cracking. These small cracks typically develop in the sidewalls or at the base of the tread grooves. Depending on their severity, they may be cosmetic in nature if they don't extend past the rubber's outer surface, or may be a reason to replace the tire if they reach deep into the rubber.
Because all tires are made of rubber, all tires will eventually exhibit some type of cracking condition, usually late in their life. However, this cracking can be accelerated by too much exposure to heat, vehicle exhaust, ozone and sunlight, as well as electric generators and motors (that have armature brushes). For example, a vehicle parked outside instead of in a garage will constantly expose its tires to the rays of the sun, increasing the likelihood of cracking. Additionally, some sidewall cracking has been linked to abrasion from parking against a curb, or the excessive use of tire cleaners/dressings that inadvertently remove some of the tire's anti-oxidants and anti-ozone protection during every cleaning procedure. Interestingly enough, when sun exposure or excessive cleaning is the cause of the small cracks, the sidewall of the tire facing outward will show damage, while the sidewall facing inward is rarely affected.
The anti-aging chemicals used in the rubber compounds are more effective when the tire is "exercised" on a frequent basis. The repeated stretching of the rubber compound actually helps resist cracks forming. The tires used on vehicles that are driven infrequently, or accumulate low annual mileage are more likely to experience cracking because long periods of parking or storage interrupt "working" the rubber. In addition to being an annoyance to show car owners, this condition often frustrates motor home and recreational vehicle owners who only take occasional trips and cannot even park their vehicle in a garage or shaded area. Using tire covers at least minimizes direct exposure to sunlight.
Tire manufacturers' warranties typically cover cracking for a period of 4 years from the date the tire was purchased (receipt for the new tires or in-service date of the vehicle required) or four years from the date the tire was manufactured.
There are a few conditions that would possibly void the manufacture's coverage. The same types of cracks can also be caused by poor tire maintenance practices. Driving on a tire that was flat, or one that was underinflated or overloaded causes excessive stretching of the rubber compound, and may result in cracks that appear similar to the surface cracks mentioned above. The manufacturer's warranty might not apply if an interior inspection of the tire clearly indicates that the cracks were due to these conditions.