Signs of tyre wear and what it means
3 September 2019
Mark Oastler has been a prominent motoring journalist in print and electronic media for more than three decades. His diverse roles have included more than a decade of motor sport TV commentary for both the Seven and Ten networks, editor of Street Machine magazine, founding editor of Australian Muscle Car magazine and freelance contributor to Wheels, Motor, Auto Action, Unique Cars, V8X, AMC and more. He also provides road test reviews for Carsguide.com.au and is a feature writer and TV host for the popular Shannons Club website.
Keeping your tyres in good condition is crucial to your driving safety because tyres provide the only contact point between your car and the road. Think about that. A tyre’s contact patch on the road is typically only about the size of your handprint, so you’re relying on just four rubber handprints to keep your car travelling safely.
Therefore, it makes good sense to pay attention to your tyres. In fact, you should get into the habit of thinking about your tyres every time you refuel your car. When did I last look at the treads for signs of unusual wear? When did I last check the tyre pressures? Could that unusual noise or change in steering behaviour be caused by the tyres?
You also need to understand what your tyres are telling you about their condition and that of your car. And most of those answers can be found by learning how to check the tyre tread.
Tread depth is deeply important
The sobering facts are that most car owners do not know the minimum legal tyre tread depth in Australia and one in three are driving cars with tread depths dangerously below that limit.
Sufficient tyre tread depth is crucial in allowing your tyres to maintain a firm grip on the road surface, particularly on wet roads as the deep grooves channel water away from those contact patches mentioned earlier. Sufficiently deep tyre tracks also provide the cut-through needed in mud or snow. Worn tyres can also greatly increase stopping distances.
Australia’s minimum legal tread depth is 1.5mm, but we stress - that is a bare minimum. Tread depth can be easily monitored by looking at the tread depth indicators (or tyre wear indicators), which are small protrusions found in the tread grooves at equal points around the tyre. When the tread wears down to the same height as these indicators, it’s time to replace your tyres asap.
However, you should replace your tyres before they wear down to this bare minimum tread depth (no less than the depth of a match head is a good guide), to maintain the largest safety margin you can.
Uneven wear: what to look for and what it means
The two main causes of uneven tyre wear are incorrect inflation pressures and incorrect wheel alignment. Fortunately, both of these problems can also be identified easily.
Most cars have a small placard located on the driver’s door jam, which shows recommended tyre pressures. This information can also be found in your car owner’s manual. You should check your tyre pressures (including the spare, if you have one) at least once a month, but ideally every two weeks. This can be done yourself if you have a small air compressor at home, or at a nearby petrol station or local tyre retailer. A quality tyre gauge is also a good investment.
Keep in mind that recommended pressures are based on cold tyres. Pressures increase as tyres rotate and start to heat up, so it’s best to check them first thing in the morning or later in the evening when your tyres have cooled.
Incorrect wheel alignment
Wheel alignment is just as important as pressures in maintaining good tyre performance and long service life. That’s why car manufacturers provide recommended settings for steering and suspension to ensure the wheels - and therefore tyres - are positioned correctly.
When a new car rolls off the assembly line these settings are spot-on, but over time they can be thrown out due to glancing off kerbs when parking, hitting large bumps or potholes, steering or suspension damage and general wear and tear. The steering might start to feel different, or the car might pull to one side or the other. Again, alignment problems will soon appear as uneven wear on the tread face, with the usual culprits being toe and camber.
Camber is the vertical angle a tyre makes with the road. When viewed from the front of the car, negative camber means the top of the tyre leans inwards, but too much can result in excessive wear on the inside edge of the tread. Positive camber means the top of the tyre leans outwards and too much will increase wear on the outside edge of the tread.
Caster controls the self-centering effect of the steering but is usually not a major factor in tyre wear if the correct factory settings are maintained.
Replacing your tyres
Healthy habits for healthy tyres
A good tyre maintenance schedule should include regularly checking the treads for any signs of uneven wear or damage and also checking their pressures at least once a month. For convenience you can do both of these checks at the same time.
You should also ‘rotate’ your tyres (generally swap them diagonally front to rear however, check your owner’s manual regarding recommendations for your vehicle) once a year to share the wear, which is also a good time to get an annual wheel alignment done. Your local tyre retailer can assist with any of these tasks, to ensure you get the best performance, safety and longest life from your tyres.
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