The life span of a tire can vary greatly depending on how it is used. Contrary to popular belief, infrequently used tires can result in a shorter life than one that is used daily. As such, I frequently speak with people with low-mileage tires that need to be replaced. Of course they are disappointed, as most people relate tire life to number of miles driven. However, rubber needs to be exercised to remain in top condition. Sitting around for extended periods of time, then being asked to go into full service can result in flatspotting (both temporary and permanent), as well as cracking. This is more likely to happen when the tires remain mounted on a vehicle and sitting idle with the vehicle weight on them, as opposed to stored off the vehicle.
Many trailer tires take the worst of it. A typical boat trailer or camper is used a couple times a year. The rest of the time they sit around with the weight of the camper or boat on them. Even worse, is sitting through a tough winter in the backyard or outdoor storage facility. Then you hook it up to the back of the family vehicle and hit the road at highway speeds.
What does the industry say about tire aging? Our experience has been that when properly stored and cared for, most street tires have a useful life in service of between six to ten years. The in-use time starts as soon as the tire is exposed to the elements. For example, your under the truck bed mounted spare is considered in use. Do you have a spare sitting on the back of your Jeep? That's consider in use, too. You can check the production date of your tire very easily to see how old it is. Read "How Old Are the Tires I Buy?" for more details.
Have your tires been in use for longer than they should be? Are you ready for a new set? Shop by vehicle and find a great replacement option for your car.