Tire age and the DOT date code

The code after “DOT” is the tire identification number, or TIN. Federal rules have required one since 1971, mainly so manufacturers can trace tires in a recall. Since a 2015 rule, new tires carry a 13-symbol TIN in three groups, preceded by the DOT mark. Plants with older two-symbol codes were allowed to keep using them until April 13, 2025, so you will still see shorter TINs on tires made before then.

Older tires are harder to date. Before July 2, 2000, the date code had only three digits: two for the week and one for the year. A code ending in 299 could mean week 29 of 1999, 1989 or even 1979, which is why NHTSA moved to four digits. If you find a three-digit code on a tire still in use, it is at least about 25 years old, and it should come off the vehicle.

One small reading tip: TINs never use the letters G, I, O, Q, S or Z, because they are easily confused with numbers. If you think you see an O, it’s a zero.

For passenger and light-truck radial tires made since September 1, 2009, FMVSS No. 139 requires the full TIN, date included, on the intended outboard sidewall. The other side may carry a partial TIN that leaves the date off. So if you find a short code with no four-digit group at the end, you are looking at the inner side.

“Intended outboard” doesn’t always mean the side facing out. The National Transportation Safety Board notes that tires are sometimes mounted reversed, for example when an owner wants raised white letters facing in. NHTSA tells consumers to look on both sides. Trailer (ST) tires and compact spares may carry the TIN on one side only, and older tires could have it on either side. A flashlight helps, and so does turning the steering wheel to expose the front tires’ inner faces.

There is no U.S. federal age limit for tires in service or for sale. NHTSA studied tire aging for more than a decade and decided in 2014 not to add an aging test to the tire standard, citing tire pressure monitoring, better aging resistance in modern tires and falling tire-related deaths. The NTSB disputed that reasoning in 2015 and noted that 27 of 60 modern tires in NHTSA’s own aging tests were still damaged.

That leaves manufacturers’ recommendations, and they don’t agree. NHTSA’s consumer page simply says some vehicle and tire makers recommend replacing tires at six to ten years regardless of tread. The NTSB called the industry’s guidance “inconsistent and confusing” for consumers. Here is what the main voices say:

Two things reconcile the numbers. First, the six-year figure mostly comes from automakers, and the ten-year figure is an outer limit tire makers set as a precaution. Bridgestone says outright that ten years is not an indicator of any individual tire’s life, and many tires need replacing sooner. Second, Michelin, Bridgestone and Pirelli all pair the ten-year limit with regular inspections from about five years.

A sensible reading: follow your owner’s manual, have tires older than five years inspected each year, and don’t keep any tire past ten years from its manufacture date, however good it looks. For most drivers this never comes up. NHTSA calculated the average tire’s service life at 3.6 years in 2004, so tread usually wears out first. It matters most for spares, low-mileage cars, collector cars, RVs and trailers.

NHTSA describes tire aging as thermo-oxidative degradation: heat and oxygen slowly changing the rubber and the bonds between the tire’s layers, faster at higher temperatures. In its field study of used tires from Phoenix, older tires showed weaker adhesion between the steel belts, harder and less stretchy rubber, and faster crack growth, much of it inside the tire where nobody could see it.

Climate matters. NHTSA chose Phoenix for its research because it has the highest daily maximum temperatures of any large U.S. city in the lower 48, and it says aging is a greater concern in the southern Sun Belt states. Its laboratory test, five weeks in an oven at about 65°C, approximates roughly four years of service there.

Sitting still doesn’t protect a tire either. NHTSA says aging happens whether or not a tire is driven. The British Tyre Manufacturers’ Association explains why parked tires can fare worse: makers add protective chemicals that work their way to the surface as the tire flexes, and in a tire that rarely rolls, that slows down, leaving it more exposed to ozone and sunlight. NHTSA’s research found full-size spares degrade while stored on the vehicle too.

Because aging is mostly internal, the date is the most reliable warning you have. NHTSA says aging can’t be detected just by looking, and Continental says drivers can’t rely on a visual check to find rubber cracking. Still, some signs are worth watching for:

Read the date on all four tires and the spare. Tires on the same vehicle are often replaced at different times, so they may not share a date. Our guide to when to replace tires covers tread depth and wear patterns, the other half of the decision.

No U.S. rule limits how old a new tire can be when it is sold. Tires age slowly when stored well, and Tire Rack reports that tires often arrive from manufacturers six to nine months old, with most of what it ships under a year old. Low-volume sizes and clearance tires from discontinued lines can be several years old, though.

The catch is that different clocks start at different times. Your treadwear warranty starts on the day you buy, while Michelin, Bridgestone, Continental and Pirelli count their ten-year limit from the manufacture date. A tire that sat in a warehouse for three years has three fewer years under that guidance.

The TIN exists so that tire recalls can reach the right owners, and that only works if the manufacturer knows who you are. Registration is easy to skip. Dealers owned by a tire manufacturer must register every sale, but independent dealers only have to offer it: hand you a pre-filled form to send in, or register for you within 30 days. NTSB found registration rates of around 10% for tires sold through independent dealers, and tire recall completion averaging about 44% from 2009 to 2013.

To check your tires, search NHTSA’s recall database by brand and tire line and compare your TIN and date code with the recalled range, or enter the TIN in the U.S. Tire Manufacturers Association’s recall lookup, which covers its member companies. Then register the tires with the manufacturer so a future recall reaches you.