When you think of how long your tires last, treadwear is likely the first thing that comes to mind. Tread depth is necessary for traction, especially in rain or snow, so your tires should be replaced once the treads wear down to a groove depth of 2/32". This is called the minimum tread depth, meaning that your tires are legally considered fully worn and are no longer safe to continue using.
You can measure a tire's tread depth using a tire gauge, or check using the "penny test": Insert a penny in the tire's circumferential grooves, head pointing down. If the tread covers Lincoln's head, then the tire still has some tread life remaining. If his entire head is visible, then the tread is worn down to the minimum depth of 2/32", and the tire needs to be replaced.
Additionally, most tires today come with treadwear indicator bars molded into the bottom of their grooves. These bars come flush with the tread surface when the tire's tread is worn down to 2/32", making it easier to determine when a tire needs to be replaced.
That said, a tire's lifespan not only depends on tread depth, but also the condition of its rubber. The rubber must be flexible enough to adhere to the road and create traction, but also strong enough to endure the constant flexing and rebounding that a tire experiences during driving. Even if the treads aren't fully worn, you'll eventually need to replace your tires before they develop cracks in the rubber.
Like any rubber, tires naturally deteriorate from exposure to the elements. The tire gradually loses its elasticity and strength over the years, becoming stiff, brittle, and prone to cracking. Eventually, the rubber may deterioriate to the point that the tire fails during driving. To counteract this, tire rubber compounds contain anti-ozonant chemicals that slow down rubber deterioration, allowing tires to last longer. If properly cared for, your tires may last as long as 6 to 10 years.
Keep in mind that tires still age even when they aren't in use. In fact, an improperly stored tire deteriorates faster than one driven on frequently, as constant stretching and flexing during driving helps to keep the rubber nice and supple. Sunlight, air, heat, and moisture are all factors that contribute to tire aging, so tires age faster in warmer climates or coastal areas.
Vehicle manufacturers recommend replacing your tires after 6 years, while many tire manufacturers recommend having tires inspected annually after 6 years and replaced after 10. Generally speaking, tires should not be used if they were manufactured more than 10 years ago, regardless of usage or storage conditions.
Tires need to be properly insulated from the elements when not in regular use, such when switching between winter and summer tires. Leaving weight on your tires for long periods of time can damage them, so trailers and RVs that only get used periodically should have their tires removed and put away between uses.
Tires should be stored in a cool, dry place, such as a basement or a climate-controlled garage. This insulates them from heat and moisture. Don't store tires in a regular garage, the attic, a garden shed, or any place affected by changes in temperature and humidity during the day and from season to season.
Make sure your tires are out of direct sunlight, as prolonged exposure to the sun's heat and ultraviolet rays causes rubber to break down quickly. You should also keep your tires away from sources of ozone, such as furnaces, electric motors, or the sump pump.
You should also clean your tires when taking them out of service, as tires accumulate all sorts of dirt and grime over time. Brake dust is especially corrosive to both your tires and your wheels, so be sure to wash and scrub the gunk off your tires. Once your tires are cleaned and dried, place them in black airtight plastic bags, such as lawn and garden bags. The airtight plasic helps prevent oils within the tread compound from evaporating.
All these precautions will help to keep your tires in good condition for the time when you need them again.
The exact lifespan of a tire depends on many variables, including driving habits, vehicle loads, and road conditions. Depending on the situation, you may find yourself needing to replace your tires much sooner than expected. Below are some common causes of tire failure:
Your vehicle and its tires can only carry so much weight before malfunctioning. Loading your vehicle beyond what it can carry puts the tires at risk of heat failure. An overloaded tire collapses under its load weight and squishes against the road, forcing its sidewalls to stretch and flex beyond its limits during driving. This excessive flexing eventually causes the tire to overheat, rapidly degrades the rubber and internal construction, and ultimately results in a blowout.
Keep your vehicle's and tires' specifications in mind when loading up your vehicle. Every vehicle has a Gross Vehicle Weight Rating (GVWR) indicating the maximum weight at which the vehicle is designed to operate (including the vehicle's weight); and each tire has a maximum load rating indicating how much weight it is designed to carry. Exceeding the GVWR or the combined maximum load of all four tires will cause your tires to overload.
Though it sounds counterintuitive, most blowouts are caused by tires not having enough air pressure, rather than having too much. Since a tire's load tolerance is directly linked to its air pressure, tires with inadequate pressure can't carry their full load capacity and are easily overloaded. Unable to support the vehicle's weight, an underinflated tire overflexes and overheats during driving, weakening the tire's structural integrity until its sidewall bursts.
When setting your tires' air pressure, make sure they are inflated to the recommended pressure specified by your vehicle manufacturer. This ensures that the tires can carry your vehicle's weight. Tire blowouts caused by underinflation or overloading will void any warranties on the tires.
Curbing, running over potholes, and other impacts can be fatal to a tire. Even if no external damage is visible right away, the impact may be strong enough to destroy some of the casing plies or separate the plies from the sidewall. This is called an impact break, and forms a bulge or bubble as the sidewall weakens. If ignored, this weak spot eventually ruptures, causing the tire to fail.
The force of impact depends on the hit angle, the size of the obstacle, and how fast you were driving. At lower speeds, a tire may be able to rebound or simply roll over debris unscathed, thanks to the natural flexibility of rubber. At higher speeds, the same debris impacts the tire much harder and is more likely to damage the tire. Think of a speed bump: the faster you drive over it, the stronger the impact.
Sidewall flexibility also affects how well a tire handles impacts. Wide, low-profile tires have shorter sidewalls that can't absorb shocks as well, so they take impacts much harder and are more easily damaged. Overinflated tires are also less flexible overall, making them more vulnerable to impacts.
No one likes getting a nail in their tires. Running over glass, nails, or other sharp road debris can cut or puncture a tire, causing sudden loss of air. Driving on a failed tire is extremely dangerous. Without air pressure, the tire lacks the structural stability to maintain its shape and may be damaged beyond repair. A flat tire also interferes with your car's functionality and can severely damage the brakes and suspensions, eventually causing loss of control, accidents, and even death.
If the damage is small (1/4" or smaller) and limited to the middle of the tread area, you may be able to have your tire repaired instead of needing to replace it. A correct tire repair reseals the inner liner so it can contain air pressure again, and also plugs the hole in the rubber to protect the steel belts from rusting. Large punctures, sidewall or shoulder punctures, long straight cuts, or irregular gashes cannot be safely repaired, so tires with these sorts of damage must be replaced.
Tire blowouts are very common from May to August, when the weather heats up and people tend to drive longer distances at highway speeds. When combined with factors such as underinflation or overloading, these factors can put tires at severe risk of heat failure in the summer heat.
The reason overheating is so detrimental to a tire is that the rubber can only endure so much heat before it starts to weaken and melt. In extreme cases, the rubber weakens to the point that the steel belts and casing plies separate from the tread. Without these reinforcing layers to hold the rubber together, the tire is unable to contain its air pressure and explodes. Older tires with cracks from aging are especially susceptible to tread separations.
You can prevent summer tire blowouts by regularly checking your tires' air pressure, keeping an eye out for road hazards, and taking proper storage precuations when storing your tires away. Tires are more likely to blow out in the summer if they are already weakened from driving while underinflated/overloaded, curb or pothole impacts, bad tire repairs, or regular tire aging. By preventing these types of damage, you can minimize the risk of heat failure and extend the life of your tires.