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When is it the Right Time to Replace Your Bald Tyres ?
There are two schools of thought. One is based on commonsense, the other the law. The law has to define things clearly, so that it is unambiguous. The law states that tyres are illegal when they are worn down far enough to show the tread wear indicator bars in a band across the tread. How far across the tread (all the way, or merely two ribs of the design) is defined in the State Roadworthiness or Vehicle Inspection regulations. Not every State has an annual vehicle inspection prior to re-registration. The tread wear indicator bars are a raised portion of the tread groove, approx 12 –15 mm wide, which show as a bar around the tyre in about six places when the tread is worn down to 1.5 mm of tread pattern remaining. There is an assumption here that the tread pattern will wear evenly across the tread, which is far from the case, common causes being misalignment, or heavily cambered wear on front or rear independent suspensions which can wear the very edge of a tread pattern prematurely.
Tread patterns are there only to remove water from under the tyre, so that it can grip the road, not a film or sheet of water. So if you live in Innisfail or Tully in North Queensland, your requirements for wet road adhesion are somewhat higher than for Uluru. It isn’t generally realised that the ability of a tyre to clear water away from under it, declines as the tread pattern wears away, simply because the grooves aren’t as deep. This is progressive. It doesn’t suddenly fall away with only 1.5 mm left; it has been falling away all the time since new. So if you have noticed that the tyre performance isn’t what you expect, you slip and slide in the wet, it’s time to have a look at them.
Tyre Tread Wear
You get bald tyres because they grip the road by developing friction. Friction is a study in itself, but without it, you would get nowhere – no acceleration, no braking, and no steering. This all occurs where the tyre meets the road. The less movement of the rubber under the footprint, the less the tyre wears. The less heavy braking, or fast cornering you do, the less the tyre wears. The reason – in order to develop friction, the tyre must slip to develop grip. In order to corner, the tyre surface must distort at the contact patch by slipping. This is happening all the time. When your tyres chirp as you accelerate, or squeal as you brake violently, you are only hearing what goes on all the time. The A.B.S. braking systems on modern cars pick the point of maximum grip, which is just before the tyre starts to skid, to optimise their brake performance. A.B.S. systems are calibrated to pick this point of maximum grip. They ‘let go’ just before the tyre starts to slide, pulsing far more rapidly, on and off, than even a skilled motorist could do, to maintain maximum braking power. So realise that it is not the brakes that stop the car, it’s the tyre grip. If there is no grip available, like on ice, then you have trouble going anywhere at all!
Due to excessive movement of the tread rubber, the bias ply tyre, which was the normal tyre 30 years ago, reached its engineering limit. It couldn’t go much faster, got too hot, wore fast, and distorted at high speed. Michelin invented and marketed the steel belt radial in 1948, patented its method of construction, and the world’s tyre engineers had to wait till the patents expired. An interim radial tyre, called the Pirelli Cinturato, was developed in this period, which didn’t infringe the patents. At one stage, 44 tyre companies around the world were making tyres of that design.
When is it time to replace your tyres?
Tyres have grooves in the tread pattern. In fact, grooves are the tread pattern. But the depth of the grooves varies, either for cosmetic, drainage, pattern stability, but mostly, because the law requires them to. If you look on the sidewall of the bald tyre, up near the tread, at around six places around the buttress you will see tiny letters ‘T.W.I.’, for ‘Tread Wear Indicator’ This marks the spot where the tread groove is 1.5 mm shallower than the rest of the groove around the tyre. All the grooves across the crown of the tyre are shallower at that point. When the tyre wears down to a depth of 1.5 mm of pattern remaining, a bar of solid rubber about 12 mm wide appears right across the tyre tread. The remainder of the groove circumference is still 1.5 mm, this means you have bald tyres .
They can also be misleading. You might be led to think that you do not have bald tyres until the bars appear. Be aware that the ability of the tyre pattern to shift water from under the tyre reduces progressively as the tyre wears down. That is the only purpose of the pattern after all. The deeper the pattern grooves, the better the wet road hold, but there is a practical limit on how deep the pattern can be. 20% deeper pattern would not necessarily give 20% more tread life from the tyre. So, every 60,000 kilometres or so, get onto our web site, and enter the challenge to once again equip your vehicle with these black doughnuts. ‘60000! I’ve never had that much out of a set of tyres’ you say. That’s because you are probably driving a front wheel drive. The front wheels are doing all the work (slip), accelerating, steering and braking, while the rear wheels are trundling along for the ride, holding up one corner each. Easy!
Information found at : http://www.carbonblack.com.au/car-tyres/when-to-replace-your-tyre.aspx#When is it Time
If you have bald tyres and you need to get them replaced but still have questions, our onlinetyre shop includes an online chat. Our online chat allows you to ask any question regarding tyres or wheels. One of our expert staff will get back to you within 24 hours. Alternatively, you can hop onto our Facebook page and all questions will be answered there too. But if you prefer a faster paced conversation, call us on 1300 699 699, and our staff will guide you step by step in making the best purchase for you.
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