Aside from sunlight, the next leading tire deteriorator is oxygen. While some things in storage require airflow to breathe and stay in good condition, tires, on the other hand, do better when sealed tight. An airtight space prevents oxygen from reaching the tires, slows the oxidation process, and prevents the oil from evaporating and drying out the tires. Remember to wrap each tire individually for the best results.
To find the perfect cool and dry environment to keep your tires, you want to locate a place where the temperature and humidity remain consistent. Dips or hikes in either of these can result in premature tire aging. Storing tires in a consistently warm environment is not good for the rubber, but keeping tires in freezing temperatures is also not good. Ironically, the place you keep your car is one of the worst places to store tires. Constant sunlight, weather exposure, and fluctuating temperatures—all things a garage is known for—damage tires over time.
Some argue that UV rays are the biggest factor in tire aging since direct sunlight can heat the rubber, dry it out, and cause premature deterioration. The best way to keep tires from dry rotting is to limit sun exposure whenever possible.