Car Advice

Why tyre tread depth is so important

Most Australians don’t know when to replace their car tyres or why tyre tread depth is so important. Here’s everything you need to know.

MOST PEOPLE NEVER CHECK their tyres. Do you? Most rely on their mechanic to tell them when their tyres need replacing, but getting into a habit of checking your tyres weekly, fortnightly or monthly is something everyone should be doing.

Whether you drive a sports car or SUV, the condition of your tyres is more influential in the way your car grips the road than almost anything else. We’ve all seen those Bridgestone Ads on TV talking about how there’s only a hand-heel-amount of rubber (otherwise known as ‘contact patch’) on the road per tyre, so it pays to make sure you’ve got as much ‘meat’ on your tyres as possible.

See, while cars these days are loaded down with sophisticated traction and stability controls, autonomous emergency braking, lane keeping assist and more, none of it matters a jot if you don’t have any grip left on your tyres.

Comprehensive Car Insurance

Legal Minimum Tread Depth

The average tyre has around 8mm of tread depth when brand new. At 3mm it’s recommended you replace your tyres and at the minimum tread depth of 1.5mm (across around three-quarters of the tyre’s surface) you’re tyres are worn out. Continuing to drive on tyres with only 1.6mm of tread or less can lead to a hefty fine of more than $200 and several demerit points, depending on the State or Territory you live in. More than this, you’re endangering your own life and the lives of those around you.

With each loss of tread depth your tyre’s functionality is being reduced, meaning its ability to shed water is reduced, its grip is reduced and thus braking distances increase. Travelling at around 80km/h on brand new tyres on a wet road will see most cars pull up in around 100m, halve the tread and this stopping distance blows out to around 120m, wear your tyres down to 1.5mm and your stopping distance will be nudging closer to 140m.

What’s the point of tyre tread?

Beyond helping your tyre grip the road, the grooves on your tyre are designed to help shed water, from a wet road obviously, as effectively as possible or if it’s a four-wheel drive tyre the tread might even have grooves designed to flick mud out of the tread or grip on the tyres shoulder to help give grip when driving in mud ruts. But back to wet roads.

A new-ish tyre will displace around 15L of water every second…by comparison a ‘wet tyre’ on a Formula One car will shed around 60L or more of water every second.

the importance of tyre tread depth

As the tread wears down the tyre’s ability to shed water is reduced, increasing the chance of aquaplaning on the road, this is when your tyre hits a patch of water on the road and skims across the surface of the water, potentially losing control.

Someone said tyres have tread depth indicators?

That’s true but relying on them rather than checking your tyres regularly will mean you’ll know when your tyres are worn out. The tread depth indicator is a little moulding in the tyre that, will, as the tyre wears down eventually sit flush with the surface. When this happens, your tyre is stuffed and ready for immediate replacement.

Tread Depth Indicator on a car tyre

Keeping an eye on your tyres

Some recommend using coins, but it’s cheaper and easier just go to your local automotive retail store and buy a tyre tread depth gauge. A basic gauge will cost you less than $10. If you do use a gauge, don’t just check one of your tyres, check them all, and don’t just check the tyres in one spot, check them in several areas.

If you own a trailer and use it regularly, then it pays to regularly check the tyres on your trailer. More than just the depth of the tread you should also keep an eye on the age of your trailer’s tyres. These things get a lot less use or attention than the tyres on your car and age is not a tyre’s friend. So, look for signs of splitting, etc as the tyre becomes harder. And, remember, if in doubt, get it checked out.

What causes tyre wear?

Beyond just general use, there are a couple of things that can lead to premature tyre wear, like improper inflation of your vehicle’s tyres. If the tyre is under- or overinflated than it’s not able to do, properly, the job it was designed to do and so can end wearing unevenly due to improper stress, causing it to wear unevenly or too quickly. Check the air pressure in your car’s tyres at least once a month and preferably with an air pressure gauge, check the spare too. The manufacturer’s air pressure specifications are usually on a placard on the inside edge of the driver’s door or along a door jamb. Improper wheel alignment can also cause your tyres to wear unevenly and prematurely. You should be able to feel a slight tugging through the steering wheel if your car’s wheels are out of alignment.

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Isaac Bober

Isaac Bober

Isaac Bober was born in the shadow of Mount Panorama in Bathurst and, so, it was inevitable he’d fall into work as a motoring writer. He began his motoring career in 2000 reviewing commercial vehicles, before becoming editor of Caravan & Motorhome magazine. He then moved to MOTOR Magazine before going freelance and contributing to Overlander 4WD, 4×4 Australia, TopGear Australia, Men’s Health, Men’s Fitness, The Australian, CARSguide, and many more.