Walk around your car and look at the tires. Decent tread. No cracks you can spot. They look fine.
That tells you a lot less than you think.
According to the National Highway Traffic Safety Administration, there’s no way to see tire aging just by eyeballing the rubber. A tire can have plenty of tread left and still be breaking down inside, where you’ll never see it.
The stakes are real. The NHTSA says 511 people were killed in tire-related crashes on U.S. roads in 2024.
We’ve all been trained to check tread. Shops push it, ads push it, and the penny trick has been around forever. Almost nobody tells you to check the date — even though it’s molded right into the sidewall.
Here are five things to know, starting with the four digits that tell you how old your tires really are.
1. Find the four-digit date code
Look on the sidewall for a string of letters and numbers that begins with “DOT.” That’s the tire identification number, or TIN.
The final four digits are the date code. The first two are the week the tire was made, and the second two are the year. The NHTSA’s example: 0308 means the tire was built in week 3 of 2008. That tire would be more than 18 years old today.
Can’t find it? Check the other side.
Under federal rules for car and light-truck tires, one sidewall gets the full TIN, while the opposite side can carry a shortened version that drops the date code entirely. On a mounted tire, the side with the date may be the one facing under the car, so bring a flashlight.
And if the code ends in three digits instead of four? A 2020 Mississippi State University safety newsletter explains that means the tire was made before 2000. Replace it as soon as you can.
2. The 6-to-10-year rule, even with good tread
Here’s a guideline you may never hear at the service counter. The NHTSA says some vehicle and tire makers advise replacing tires somewhere between six and 10 years after they were made, no matter how much tread is left.
Why a range instead of a hard deadline? Because, as the Mississippi State newsletter puts it, there’s no way to stamp an exact expiration date on a tire. How fast one ages depends on climate, driving and storage.
Now do the math on your own tires.
A date code ending in 20 means the tire was built in 2020, so it’s about six years old — the start of that window. One ending in 16 is about a decade old. Anything ending in 15 or earlier is past the outer edge.
The reason this matters: The NHTSA says that tires become more likely to fail as they age. If it were my car, I’d start watching closely at six years and stop debating at 10.
3. Heat, sun and parked cars age tires faster
Tires don’t age at the same speed. The NHTSA singles out the southern Sun Belt as a region where aging is a bigger worry. Sunshine, hot weather, poor storage and neglect all speed it up, the agency says, and so can long drives on hot days.
The chemistry isn’t complicated. In a 2014 report, the NHTSA explained that tire rubber degrades from heat and from reacting with oxygen, and that higher temperatures make it happen faster.
Much of that oxygen comes from the air you pump into the tire. In other words, a tire on your car is aging every day, whether you drive it or not.
When agency researchers wanted tires that had aged in the real world, they gathered them from cars driven around Phoenix. Their reasoning: The hotter Southern states should produce the worst-case tires in the country.
Here’s the counterintuitive part: Driving less doesn’t save your tires. The NHTSA specifically flags collector cars, RVs, 15-passenger vans and any vehicle you don’t drive regularly.
That motorhome parked beside the house most of the year can be sitting on deep tread and very old rubber at the same time.
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4. Your spare is probably your oldest tire
Quick question: When did you last replace your spare? For a lot of drivers, the honest answer is never.
That’s exactly the problem. The NHTSA notes that spares on every kind of vehicle tend to get old because they so rarely get swapped out. Consumer Reports warned back in 2012 that even a spare that’s never touched pavement can become unsafe after enough years.
Picture it. You’ve owned your car for eight years and bought one new set of tires along the way. The four on the ground might be three years old. The spare is at least eight.
So check its date code the same way, and don’t let it become a regular tire. The NHTSA says not to use the spare as a stand-in for a worn tire.
Winter is the worst time to find out your spare is past its prime. While you’re getting ready for cold weather, it’s also worth running these five car insurance checks before the first snow.
5. Check the date before you buy ‘new’ tires
Here’s the one that catches people. “New” means never mounted. It doesn’t necessarily mean recently made.
Consumer Reports pointed out in 2012 that tires can spend a long time in a warehouse before they ever reach your local shop. Its advice: Even with brand-new tires, read the date code and make sure they were built within the last couple of years.
The Mississippi State newsletter gave the same warning in 2020. It added that a tire sitting unmounted on a shelf ages more slowly than one rolling down the highway — but it still ages.
So before the installer bolts anything on, ask to see the sidewall and read the last four digits. If the tires were made more than two years ago, ask for fresher stock.
You’re paying for the whole life of the tire. You should get all of it.
The bottom line
Age is the check almost nobody does. Tread is the one everybody’s heard of, and it still matters.
The NHTSA says a tire is no longer safe once its tread wears to 2/32 inch. The easy test: Slip a penny into a groove with Lincoln upside down and his face toward you. If the top of his head is visible, it’s time for new tires.
AAA thinks that bar is too low. It recommends replacing tires at 4/32 inch because performance falls off significantly at that point.
While you’re down there, check the air pressure, too. The right number is on your door jamb, not the tire. I explain why in “Stop Changing Your Oil Every 3,000 Miles. 7 Car Myths Costing You Money.”
It’s the same lesson as the date on the back of your smoke alarm: Some of the most important safety information you own is printed right on the product, in small numbers nobody tells you to read.
Go read four of them tonight. It’ll take you two minutes.
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