Tread depth tells you how much of a tyre has been used. It tells you nothing about how long the rubber has been alive. Those are separate clocks, and the second one runs whether or not the car is driven.
That is why the most likely place to find a genuinely unsafe tyre is not on a high-kilometre commuter car. It is on the low-kilometre weekend car with plenty of tread left, on the caravan that has sat under a carport for six years, and on the spare wheel nobody has looked at since the car was new.
A tyre can be sold to you as new years after it was manufactured, and nothing about it will look different. Check the date code before the tyre is fitted, not after — once it is on the car and paid for, your options narrow considerably.
Reading the date code
Every road tyre carries a DOT marking on the sidewall followed by a string of characters. The last four digits are the date of manufacture:
- The first two digits are the week of the year, 01 to 53.
- The last two are the year.
So 2224 means the tyre was built in the twenty-second week of 2024. A tyre marked 0819 was built in February 2019, whatever its tread looks like today.
Two practical notes. The full code is sometimes moulded on one side only, so check both sidewalls before concluding it is missing. And on a car, the inner sidewall may be the one carrying it, which can mean lying down with a torch or turning the steering to full lock.
What ageing actually does
Rubber is not chemically stable. It degrades through a process usually described as thermo-oxidative degradation: oxygen attacks the polymer chains and the compounds bound into them, progressively hardening the rubber and reducing its flexibility. Ultraviolet light, ozone and repeated heating and cooling all accelerate it.
Two consequences matter to a driver.
Grip falls. A tyre grips partly by conforming to the microscopic texture of the road surface. Hardened rubber conforms less well, so an aged tyre has less grip than its tread depth suggests, and the shortfall is worst when it is cold or wet.
The structure weakens. Ageing also affects the bond between the rubber and the internal steel and textile reinforcement. That is the mechanism behind tread and belt separation, which tends to happen at speed under load, and is a far more serious failure than a puncture.
The visible signs come late. Fine cracking or crazing in the sidewall or at the base of the tread grooves, sometimes called perishing, indicates rubber that is well advanced in the process. A tyre can be significantly degraded before any of it shows.
How old is too old
There is no single Australian legal age limit for a tyre on a passenger car, and it is worth being straight about that. What exists is manufacturer and industry guidance, which is reasonably consistent:
- Have tyres inspected by a professional from about five or six years after manufacture, regardless of appearance and regardless of tread.
- Treat ten years from manufacture as an outer limit, after which replacement is recommended whatever the tread depth and however little the tyre has been used.
Those figures are guidance rather than law, but they come from the people who make the product and they align across brands. Storage conditions matter within them: a tyre kept cool, dry and out of direct sunlight ages more slowly than one that has spent years on a trailer in the Australian sun.
The spare is the one everyone forgets
A full-size spare bolted under a ute tray or slung beneath a wagon lives a hard life — heat, road grime, and often direct sun — and gets checked roughly never. It ages on the same clock as the others while nobody watches.
The uncomfortable version of this: the spare is used precisely when something has already gone wrong, often on a roadside, often in a hurry. A tyre that has been degrading for eleven years is a poor thing to discover at that moment. Check its date code and its pressure when you check the others.
Space-saver spares have the same ageing issue plus their own speed and distance restrictions moulded into the sidewall, which are worth reading before you need them.
Buying tyres
- Ask for the date code before purchase, and treat it as a normal question rather than an awkward one. A reasonable retailer will not mind.
- Anything more than about a year or two old is worth a conversation about price, particularly if it has been discounted as old stock.
- Be careful with unusual sizes. Slow-selling sizes sit in warehouses longest, so the rarer your size, the more the date matters.
- Be very careful with second-hand tyres. You cannot see internal damage from a previous impact or from having been run flat, and you have no history of how the tyre was stored. The saving is small relative to the unknown.
Buying a car
Take the date codes on all five tyres, not just the tread depths. The combination tells you a story: deep tread with old date codes on a low-kilometre car means the tyres will need replacing on age long before they wear out, which is a real cost to factor into the price.
Mismatched date codes across an axle, or four different brands, tell you something about how the car has been maintained more generally.
For the rest of what the sidewall reveals, see how to read a tyre sidewall; for what the tread is telling you, see tread depth and what you lose as a tyre wears.
Related
- Tread depth: what you lose as a tyre wears down
- How to read a tyre sidewall: size, load, speed and age
- What makes one tyre cost three times as much as another
- Used car inspection and test drive: your questions answered
FAQs
How do I check the age of a tyre?
Find the DOT marking on the sidewall and read the final four digits. The first two give the week of manufacture and the last two the year, so 3523 means week 35 of 2023. The full code is sometimes moulded on one sidewall only, and on a fitted tyre it may be on the inner face, so check both sides before deciding it is absent.
When should tyres be replaced because of age?
There is no single legal age limit for a passenger car tyre in Australia, but manufacturer guidance is fairly consistent: have tyres professionally inspected from around five or six years after manufacture, and treat ten years as an outer limit for replacement regardless of remaining tread. Storage conditions affect how quickly a tyre ages within that window.
Can a tyre be unsafe even with plenty of tread left?
Yes, and this is the main reason age matters. Rubber hardens as it oxidises, which reduces grip on cold and wet roads, and ageing also weakens the bond between the rubber and the internal steel and textile reinforcement, which is the mechanism behind tread separation. Neither shows up in a tread depth measurement.
Is it safe to buy second-hand tyres?
It carries risk that is difficult to assess. You cannot see internal damage from a previous impact or from the tyre having been run while flat, and you have no record of how it was stored or how old it is beyond the date code. Given the small saving relative to the unknown, second-hand tyres are difficult to recommend.
Does my spare tyre need replacing on age too?
Yes, and it is the tyre most often overlooked. A spare ages on the same clock as the others while typically living in harsher conditions — heat, road grime and often direct sunlight under a tray or beneath a wagon. Since it is used only when something has already gone wrong, an aged spare fails at the least convenient possible moment.