There’s zero guesswork to finding the manufactured date to determine when to replace your tyres. Or any tyres for that matter. Simply look at the sidewall, and find the tyre identification number. It’ll begin with DOT. The Department of Transportation requires that all tyres bear an alpha-numeric serial number, identifying the tyre’s manufacturing location, plus the week and year of its manufacture.

The last four digits of the tyre identification number, or the date code, tell you all you need to know. The first two digits call out the week in which the tyre was made. The last two are the year. A tyre with the DOT number ending in 4206 was manufactured in the 42nd week of 2006.

Why would it be so important to know this that the Department of Transportation would get involved? Because tyres, despite being made of hardy materials, still succumb to age-even when they aren’t being driven. If you’ve ever looked at an old rubber band, you’ve surely noticed pores and cracks that open up over time. This eventually will happen to even the best-made tyres.

The lawyer keeping his antique Ferrari beneath a blanket in the garage for 20 years will still need new tyres if he wants to take it on the street with any confidence. Environmental factors such as temperature, sunlight, and coastal air accelerate the deterioration process. Even spare tyres resting in the trunk of your car will need to be replaced once they’re past their “expiration date.”

An exact expiration date is impossible to determine, given the range of factors, the greatest of which of course is wear. Most warranties cover a tyre for four years from its date of purchase, or five years from its date of manufacture. So, hold on to your proof of purchase in the event your tyres don’t survive that long.

It’s with great seriousness that this next suggestion is made: never buy used tyres. You simply can’t be certain how they were driven or stored. The risk you run is the tyre failing and causing you to suddenly lose control of your vehicle. However much you might save buying used tyres, it isn’t worth that outcome.