Tyre Tread Depth The fast guide to stopping safely

Tyres: the essential bond between your vehicle and the road. Millimetres of tread can mean miles of difference

Your tyre tread grips the road as you drive but if it's not deep enough then your vehicle loses traction and braking distances will be extended. Shallow tread grooves make it harder to control the vehicle in wet weather and the chance of aquaplaning increases, as does the risk of a serious accident. To ensure your safety, measure the tread depth and the tyre pressure as part of your regular vehicle maintenance.

Tyre Tread Depth:

Why does it matter?

Tyre tread is what connects with the road and provides traction.  As you drive, tyre tread wears and the tread depth will decrease.  The legal minimum tread depth in New Zealand is 1.5mm but we recommend replacing tyres when the tread depth reaches 3mm.  Below this level, traction is vastly reduced and braking distances begin to increase to potentially dangerous levels.  

As the tread depth decreases so does a tyres ability to channel water away.  This increases the potential for aquaplaning and makes wet surfaces hazardous.  With a reduced biting edge to the tyre, handling is compromised and the tyre may not have enough traction to safely navigate corners or deal with higher speeds.  

On the Test Track at different tread depths

Three quick ways to check your Tyre Tread Depth

  1. Tread wear indicators are spaced evenly through the main grooves in the tyre tread. If they are flush with the level of the tread, then the tyre must be replaced.
  2. If you have a tyre tread depth gauge, insert the probe bar into the groove and push the shoulders flush with the tread. Check the top of the gauge to see the measurement.
  3. Place a 20 cent coin in the groove of the tyre. If you can see the whole of the ‘20’ then you’ve got 2mm or less of tread left and it’s time to get them replaced.
If you can see the whole of the ‘20’ then you’ve got 2mm or less of tread left.

How to use a tread depth gauge

A quick and easy tyre check

There are several different types of tyre tread depth gauges, widely available from auto stores.  All are simple and quick to use.  Insert the probe bar into the wide groove in the centre of the tread.  Next, push the shoulders flush with the tread then check the top of the gauge to see the measurement.  

Be sure to check the tread depth in various locations.  A misaligned wheel may result in uneven tyre wear and if any part of the tread is below the legal minimum, the tyre will fail a Warrant of Fitness.

How to check your tread depth using tread wear indicators

All tyres have tread wear indicators or wear bars.  These are spaced evenly through the main longitudinal grooves in the tyre tread and indicate how worn the tyre is.  Look for a small arrow on the sidewall of the tyre and the letters ‘TWI’.  If the tread wear indicators are flush with the level of the tread then the tyre needs replacing.

Don't forget to check your tyre for Damage

It’s a good idea to look for tyre damage when checking the tread depth.  If there are any small scoops or divots carved from the tread then the tyre might be misaligned, or there may be an issue with your vehicle.  

Also be on the lookout for any bulges in the tread or sidewall.  They can indicate internal tyre damage and tyres with bulges may not be safe to drive.  If in doubt, always consult a professional and exercise caution.

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