Unfortunately, tread depth is not a reliable way to determine the age and potential longevity of a tyre. For that, you should be looking at the tyre’s date of manufacture.
You’ll find this information stamped on the tyre’s sidewall, just after the DOT number. These days, the manufacturing date is depicted as a four-digit code, where the first two digits represent the week the tyre was manufactured, while the last two digits represent the year.
For example: If the tyre’s sidewall is stamped 4920, it means the tyre was manufactured in the 49th week, of the year 2020.
HOW OLD IS TOO OLD
But what about an expiry date? Is this information also displayed on the sidewall?
In most cases: No it isn’t.
However, in terms of industry standards, it’s widely considered that most tyres should be replaced once the manufacturer’s warranty has lapsed. Typically speaking, this period is limited to 5- or 6-years depending on the brand and/or quality of the tyre.
That said, it’s important to remember that even if the tyre’s tread depth appears deep enough to keep using, it could be that the tyre is too old to safely use.
Because tyres are made from naturally occurring materials (i.e. rubber), overtime, these materials may oxidise and “dry out”. This oxidation effect can impact the tyre’s flexibility making the compound harder, more brittle, and poorer performing.
If left long enough, the tyre may start to break apart under stressful conditions, such as: hard braking, acceleration and cornering.
What’s more, because the oxidation process starts – albeit very slowly – from the day the tyre is made, it’s important to note the date of manufacture on any set of tyres, especially on a used vehicle.
CARAVANS & TRAILERS
This last point is particularly important for caravan or trailer owners. This is because, in most cases, caravan tyres seldom need replacing due to mileage and tread wear, but instead, because of oxidation and/or UV damage over time.