When is it Time to Replace your Tyres

December 5, 2006 at 5:39 am 1 comment

When is it time to replace your tyres? Should I wait till they’re bald? When are they bald?

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.

However, the bars serve a useful purpose, and are much more realistic than the old ‘stick a match head in the tread groove, and if you can see the head, it’s bald’ trick.

That leaves commonsense.

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.

If you know that the big wet is due, that you are traveling into a high rainfall area, that it’s getting close to winter in the southern States, it’s time to check your tyres. Who knows, the drought might even break with a ‘big Wet’.

Entry filed under: When to Replace your Tyres. Tags: , , , , , , , .

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1 Comment Add your own

  • 1. Michael  |  January 28, 2007 at 6:08 pm

    I live in NSW, each year when my car rego is due and I have to get a pink slip, my tyres are examined by the authorised inspection station.
    I rely on them to inform me if my tyres need replacing, otherwise I am clueless when it comes to my tyres. By reading your Blog, I have a greater understanding about tyres….

    Reply

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