Most people think tyre replacement is necessary only when the tyre tread depth is below the minimum legal tread depth (1.6mm). However, tyre replacement is required when the tyres get too old. Even if they've never been driven on, tyres older than six years should be replaced. The reason is that the rubber hardens and could fail catastrophically when in use - it's that simple. After six years of age, tyre replacement should be a no-brainer - but it isn't.
Tyre replacement regulations
Unfortunately, no regulations in Australia require tyre replacement on a use-by date basis.
Tyre replacement practicalities
This tyre replacement situation affects you if, for example, you have a 10-year-old car with the original spare tyre. Tyre replacement on an age basis also affects plenty of classic car owners (since classic cars generally do very few annual kilometres and their tyres are unlikely to wear out in under six years). Tyre replacement by age also affects the owners of thousands of trailers too - box trailers, camping trailers, boat trailers and car trailers. Trailer tyres tend not to wear very much because they neither drive nor steer. However, all tyres just don’t last more than six years even if they’ve never been used. And the ones baking in the sun on the tailgate of some 4WD won’t even go that long before fading badly.
Tyre replacement and conventional tyres
Most tyres actually in contact with bitumen don’t get to their use-by date because tread wear usually intervenes and makes them candidates for tyre replacement on a tread-wear basis. The average car - and therefore the average tyres - travels about 15,000km annually. At this rate a set of decent tyres lasts about three years before replacement is required because the tread is too worn.
For the tyres that do very little work, however, getting to six years or beyond is likely to herald the tyre equivalent of osteoporosis - the rubber will start to harden and, potentially, crack. There could still be plenty of tread remaining.
It begs an obvious question: how old are your tyres right now, and how can you tell?
Tyre replacement and cracking the code on tyre age
Want to know how old your tyres are? Thankfully, among the hieroglyphics on a tyre’s sidewall is a more or less 'secret' 12-digit manufacturer’s alphanumeric code. It's the only 12-digit code on the sidewall, so if you find just one, you're at the right place.
The last four digits are what you're after. If they say:
You can rest assured the tyre was manufactured in the 16th week of 2006. So it's a candidate for tyre replacement in about autumn 2012.
For the 27th week of 2007 you’ll see it ends in:
Here's another important point: How old are the tyres when you buy them? They could have been in various warehouses for some time. Tyres older than three years when they'repurchased should sound warning bells. Over the next three years your tyres might get to their use-by date with some useful tread remaining. It really all depends how long those tyres have been lying around before you buy them.
Smarter tyre replacement
Consumer empowerment time: ask to see the new tyres you’re about to buy – before they’re fitted. That's the actual tyres, not a photograph or a tyre brochure. Check the 12-digit codes on each, and don’t buy any tyres older than three years. Retailers who won’t facilitate this request, or argue the toss over the tyre’s age? Time to exercise the 'golden' rule: you've got the gold; you make the rule. If your request can't be accommodated, walk out and shop elsewhere.
Confused about tyre sized? Here's how to crack the tyre sidewall code and figure out the size.