How Old Are Your Tyres, Really? Reading the DOT Date and the 10-Year Rule

Most drivers judge a tyre by its tread. Fair enough: that’s what wears out, and it’s easy to see. But tread depth only tells you half the story. A tyre can carry deep, healthy-looking tread and still be past its safe working life, because rubber doesn’t just wear out. It ages out.

We see it at both depots: a trailer that sits between seasonal runs, a spare that’s never touched the road, a good second-hand buy off a low-kilometre truck. Loads of tread, and an owner surprised to hear the tyre might be the weakest thing on the rig.

Where the age is written on the tyre

Every tyre has its birth date stamped into the sidewall. Look for the letters DOT followed by a string of characters, ending in a four-digit number. That last block is the one that matters.

The four digits read as week and year of manufacture. So 2419 means the 24th week of 2019. 0324 means the third week of 2024. It’s usually inside an oval on one side of the tyre, and sometimes only on the inner sidewall, so you may need to duck under and look.

Once you can read it, you can answer a simple question most operators have never actually checked: how old is the tyre I’m trusting at 100 kilometres an hour?

Why rubber ages even with tread to spare

Tread wear is mechanical. It comes from kilometres. Ageing is chemical, and it happens whether the tyre turns a wheel or not.

Rubber is a flexible compound held together by oils and bonding agents. Over the years those break down through oxidation, reacting with oxygen and heat, and the rubber slowly hardens and loses its elasticity. You’ll sometimes see the result on the surface as fine cracking in the sidewall or between the tread blocks. That’s the visible edge of a process happening all through the carcass.

A hardened, brittle tyre doesn’t grip or flex the way it was designed to. Under sustained load and heat, exactly the conditions on a loaded highway run, an aged carcass is far more likely to let go, even with tread still on it. The tread lied; the rubber underneath had already given up.

The 10-year rule (and why 6 years is the checkpoint)

There’s no single legal expiry date stamped on a tyre, but the industry works to a widely accepted rule of thumb, and it’s a sensible one:

• From around 5–6 years old, a tyre should be inspected regularly by someone who knows what they’re looking at, regardless of tread.
• By around 10 years from the date of manufacture, most tyre and vehicle manufacturers recommend a tyre be replaced, again regardless of how much tread remains.

Treat those as guidance, not a countdown clock. A tyre stored in a hot shed, run underinflated, or left out in the sun will age faster than the numbers suggest. One kept cool, out of the weather and correctly inflated will do better. The date code tells you when to start paying closer attention; the condition tells you the rest.

Where age bites hardest

Some tyres age out long before they wear out. These are the ones worth checking first:

• Spares. A spare can sit for a decade doing nothing, then get fitted in a breakdown and asked to carry a full load home. Check its date now, not on the roadside.
• Trailer tyres. Trailers often cover fewer kilometres than the prime mover and can sit parked for weeks or seasons. Plenty of tread, plenty of years.
• Low-kilometre and second-hand tyres. A tyre off a low-use truck can look almost new and still be years old. When we inspect second-hand and reconditioned stock, the date code and carcass condition matter as much as the tread. That’s part of why we check them properly before they go back on.
• Agricultural and regional units. Trucks and utes that work hard for part of the year and sit the rest, often outdoors, cop the worst of the sun and temperature swings across both our Victorian and Tasmanian patches.

A quick check you can do today

You don’t need tools for this one:

1. Find the DOT code on each tyre, and don’t forget the spare and the inner duals.
2. Read the last four digits: week, then year.
3. Anything over about 6 years, book it in for a proper look.
4. Run your hand over the sidewalls and tread grooves. Fine cracking or a hard, glazed feel is worth a second opinion.

None of this means a tyre with a few years on it is unsafe. Plenty of them are perfectly good. It means age is a factor most people never check, and it’s an easy one to get on top of before it becomes a problem.

Ruband Tyres has been keeping commercial vehicles on the road since 1998. If you’re not sure how old your tyres are, or you’d like an honest inspection of your spares, trailer or second-hand stock, call our Melbourne depot at Bayswater North on (03) 9729 8799, or our Hobart depot at Derwent Park on (03) 6272 7500. You can also request a quote and we’ll get back to you.