How to Check Your Tyre Tread Depth (and When It's Too Low)

Your tyres are the only part of your car that actually touches the road, and the tread on them does a huge amount of work, especially in the wet. As tread wears down, your car takes longer to stop and is far more likely to slide in heavy rain. The good news is that checking your tread depth takes about two minutes and you don't need any special tools.

In this guide we'll walk through how to check your tyre tread at home, what the numbers mean, and how to tell when it's time for a fresh set. If you'd rather have a professional eye on it, the team at Speed Service in Salisbury is happy to do a free tread check while you wait.

What is tread depth and why does it matter?

Tread is the pattern of grooves moulded into the rubber of your tyre. Those grooves channel water out from under the tyre so the rubber can grip the road. When tread gets too shallow, water has nowhere to go and your tyres can 'aquaplane' — effectively floating on a film of water with almost no grip. Brand new tyres usually start with around 8mm of tread.

The legal minimum in Australia

In Australia, the legal minimum tyre tread depth is 1.5mm across the entire tread that normally contacts the road. Drive on tyres below that and you risk a fine, demerit points, and an insurance claim being knocked back after an accident. But 1.5mm is a bare legal minimum, not a safety target — braking distances in the wet increase dramatically well before you reach it.

How to check your tread at home

There are three easy ways to check, from quickest to most accurate:

1. The tread wear indicators

Every modern tyre has small raised bars moulded into the bottom of the grooves, usually marked by a small triangle on the tyre's sidewall. These wear bars sit at exactly 1.5mm. If the surface of your tread is level with these bars, your tyre is at the legal limit and needs replacing now.

2. The 20-cent coin trick

Pop an Australian 20-cent coin into the main tread groove. The distance from the edge of the coin to the tip of the platypus's bill is about 3mm. If the tread doesn't reach the bill, you're getting low and should plan for new tyres soon.

3. A tread depth gauge

A cheap tread depth gauge from any auto store gives you an exact reading in millimetres. Check several spots across each tyre — inner edge, centre and outer edge — because uneven wear tells its own story.

What uneven wear is telling you

Where a tyre wears can point to other problems worth fixing before you buy new rubber:

• Worn on both edges but fine in the middle: usually under-inflation.
• Worn in the centre only: often over-inflation.
• Worn on one edge: commonly a wheel alignment issue.
• Patchy or scalloped wear: can indicate worn suspension or unbalanced wheels.

If you spot uneven wear, it's worth having the cause looked at — alignment, pressures or worn suspension — before fitting a new set, otherwise it'll wear out the same way. Pop into Speed Service at 99 Cross Keys Rd, Salisbury and we can check it over and point you the right way.

When should you take action?

Check your tread roughly once a month and before any long trip. If any tyre is at or near 1.5mm, showing the wear bars, or wearing unevenly, book it in. Give us a call on 0481 309 775 and we'll get you sorted.