The legal minimum tread depth for car tyres in New Zealand is 1.5mm, measured in the principal grooves right around the tyre. It has been 1.5mm since 2007. A lot of tyre advice online is written for the UK and Europe, where the figure is 1.6mm, so it's worth knowing which rule applies here.

Where it's measured

The principal grooves are the main channels that run around the tyre. The 1.5mm has to be there right around the circumference, not just at one point. Tyres often wear unevenly, so the worst spot is what counts. That is frequently the inside edge, which you can't see without turning the steering or getting down on the ground.

How to check it yourself

  • Use a tread depth gauge. They're inexpensive and far more reliable than eyeballing it.
  • Look for the wear indicators — small raised bars across the bottom of the main grooves. Once the tread is level with them, the tyre is at or very near the limit.
  • Check at several points around each tyre and across its full width, inside edge included.
  • Don't forget the spare.

Legal is not the same as safe in the wet

Tread clears water from under the tyre so the rubber stays in contact with the road. As the tread wears down, that ability drops away steadily, well before the legal limit. Tyre makers' own testing shows wet braking distances growing noticeably as tread drops, which is why many recommend replacing at around 3mm rather than waiting for 1.5mm. With the amount of rain the Bay of Plenty gets, that margin matters.

Uneven wear is a warning

  • Worn on one edge — usually wheel alignment.
  • Worn on both edges — usually running underinflated.
  • Worn down the centre — usually overinflated.
  • Worn in patches or scallops — balance, or worn suspension.

Replacing the tyre without fixing the cause just means wearing out the next one the same way. That's why we check alignment when new tyres go on.

Tread depth and your WOF

Tread depth and tyre condition are part of every WOF inspection, and worn tyres are one of the most common reasons for a fail. If you're not sure, call in to 151 Totara Street, Mount Maunganui, and we'll measure them. If they need replacing, we can fit new or used tyres and do the WOF in the same visit. Call +64 29 777 7122.