Some info...written by our very own Mayor!
"....Like the wheels, your tires have several formidable enemies, including water, formaldehyde, petroleum distillates, ultraviolet (UV) light and ozone. Water washes away the natural oils and waxes in rubber that keep it elastic. Formaldehyde and petroleum distillates act as solvents, eating rubber on contact. When ozone is combined with UV light, a reaction occurs that attacks the tire and its polymers.
To protect against ozone and UV damage, a stabilizer molecule called a competitive absorber is blended with the tire polymer. Competitive absorbers work by capturing and absorbing UV radiation and converting it to heat, which is dissipated harmlessly. All tire manufacturers use the same competitive absorber, called carbon black. This is why most tires are black. These absorbers are sacrificial; they expend themselves in performing their function of converting UV light to heat. However, as carbon black loses its ability to perform, it turns gray. This is one reason tires tend to discolor with age.
To protect tires from further ozone damage, tire manufacturers add a wax compound to their formulas. Tires flex when they are in motion, causing the wax molecules to migrate to the surface. This forms a protective barrier between the air (ozone and oxygen) and the tire polymer. In the tire trade this is called blooming. When tires are parked for extended periods, blooming does not occur, and ozone quickly attacks the tire polymer. With UV light and ozone working in concert, the degradation is accelerated, resulting in drying, discoloration and cracking.
To combat the negative effects of water, solvents and UV light on tires, the car care industry makes tire dressings. Tire dressings fall into two groups: oil-based and water-based silicones.
Oil-based silicone dressings are nonpenetrating coatings that seal rubber and vinyl. They are very good at providing a protective surface barrier. Oil-based silicone dressings create a glossy film that never really dries. I'm not a fan of these products, as most contain petroleum distillates as a cleaning agent. Petroleum distillates are harmful to rubber and vinyl, and will cause cracking.
Water-based dressings do not contain oils or petroleum distillates that can harm and dull the surface of rubber and vinyl over time. Most water-based dressings offer a nongreasy, more natural looking satin finish; however, they are not as durable as the oil-based products....."