Tires older than six years are the hidden cause behind thousands of highway blowouts, federal research shows

Most drivers judge whether a tire needs replacing by looking at the tread, checking it against a coin or a built-in wear bar and assuming a deep enough groove means the tire is still safe. Federal safety researchers say that habit misses a separate and less visible danger: rubber compounds break down chemically over time, regardless of how many miles a tire has actually driven, and tires that have simply aged past a certain point are disproportionately represented in reports of sudden, catastrophic failure on highways. A tire can look fine and still be a hidden liability.

Unlike a worn tread, which is visible to anyone who bothers to look, chemical aging happens from the inside out. Heat, sunlight, and oxygen gradually degrade the rubber compounds and internal belt structure of a tire, a process that continues whether the tire is mounted on a car driven daily or sitting unused in a garage or on a dealer’s shelf.

Why Age Matters More Than Tread Depth

According to federal guidance on tire safety, tires more than six years old show up disproportionately in tire-related failure claims compared with newer tires, a pattern that holds even when tread depth looks perfectly acceptable to the naked eye. That is because the failure mode driving many of these incidents is not tread wear but internal separation, where the layers of rubber and steel or fabric belting that make up a tire’s structure gradually lose their bond as the compounds holding them together degrade. A tire can pass a casual visual check and still be at meaningfully higher risk of a sudden structural failure once it crosses roughly the six-year mark.

The Silent Failure: Belt and Tread Separation

Aging-related tire failures tend to happen at highway speed, when heat buildup from sustained driving accelerates whatever degradation has already occurred inside an older tire. A separation can develop gradually, sometimes visible as a bulge or an irregular vibration before a full failure, but it can also progress with little external warning until the tread or belt suddenly detaches. Because the failure originates inside the tire’s structure rather than at its surface, it is far harder for an ordinary driver to catch during a routine walk-around inspection than a nail in the tread or a visibly low pressure reading.

Finding a Tire’s True Age, Not Its Purchase Date

Every tire sold in the United States carries a Department of Transportation identification number molded into its sidewall, and the last four digits of that code indicate the week and year of manufacture rather than the date it was purchased or installed. That distinction matters because tires can sit in a warehouse or on a shelf for a year or more before ever being sold, meaning a tire installed as “new” today could already be partway through its safe service life. Checking that sidewall code, rather than relying on memory of when a set of tires was bought, is the only reliable way to know a tire’s actual age.

What Drivers Can Do Between Full Replacements

Beyond simply tracking age, drivers can watch for visible cracking in the sidewall or between tread blocks, a common early sign of the same rubber degradation that eventually leads to structural failure, along with any unusual bulging that suggests internal belt separation has already begun. Spare tires deserve the same scrutiny, since they often sit unused and unchecked for years, aging at the same rate as tires in active service without ever showing the wear that would normally prompt a closer look. For anyone unsure whether a tire’s age has become a safety issue, checking the sidewall date code takes only a minute and requires no special tools, making it one of the simplest habits available for catching a hidden risk before it turns into a highway emergency.

Climate and Storage Conditions Speed Up the Clock

Not every tire ages at the same rate, since heat, humidity, and sun exposure all accelerate the underlying chemical breakdown of rubber compounds. A vehicle parked outdoors in a hot, sun-heavy climate for most of the year will generally see its tires degrade faster than an identical set of tires used in a cooler, more temperate region, even if both sets cover similar mileage. That variability is part of why federal guidance frames six years as a general threshold for closer inspection rather than a strict, universal expiration date, and why drivers in consistently hot climates may want to start checking sidewalls for cracking somewhat earlier than that mark rather than waiting for a fixed anniversary to roll around.

Used Tires Carry an Extra Layer of Risk

The hidden nature of tire aging becomes a particular concern in the used-tire market, where a buyer often has no reliable way to know how a tire was stored or driven before it changed hands, only the manufacture date molded into the sidewall and whatever tread depth remains visible. A used tire with generous tread can still be well past the point where its internal structure is considered reliable, especially if it spent years sitting in outdoor storage rather than mounted on a regularly driven vehicle. Buyers shopping for used tires, or inheriting a vehicle with tires of unknown history, are typically better served checking the manufacture date first and treating tread depth as a secondary consideration, rather than the other way around.

This article was produced with AI assistance and edited by Morning Overview staff.