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 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.