New tyres start with roughly 8 mm of tread. Wear bars moulded into the grooves show when you reach the legal limit. Many drivers plan to replace at around 3 mm.
What the law says
Australian rules require at least 1.5 mm of tread in the main grooves, anywhere the tyre touches the road. Below that the tyre is unroadworthy.
Penalties vary by state, a defect notice can take the car off the road, and bald tyres may complicate an insurance claim. The rule covers every tyre in use, including a spare once it's fitted.
How to check tread depth
- Tread wear indicators. Small raised bars across the grooves at the legal limit. Tread level with the bars means the tyre is done.
- A tread depth gauge. Cheap and accurate. Measure the inner, centre and outer grooves of each tyre.
- The 20-cent test. Put a 20-cent coin in the groove. If the tread doesn't reach the platypus's bill, about 3 mm in, start planning new tyres even if you're still legal.
Why 1.5 mm is a floor, not a target
Tread clears water from under the tyre. As it wears down, the tyre clears less water, stopping distances in the wet grow and the tyre is more likely to aquaplane.
Low tread can feel fine in the dry. The first heavy downpour is where it shows.
What uneven wear tells you
- Worn shoulders, healthy centre: running too low for too long. Live pressure monitoring helps you spot it early.
- Worn centre, healthy shoulders: running too high.
- One edge worn: wheel alignment is out.
- Flat spots or scalloping: suspension or wheel balance.
Tread tells you how a tyre has lived. So does its age: a tyre can pass on tread and still be too old. Our guide to tyre age and the date code covers that half.
Want to keep an eye on pressure between checks? See every TPMS kit, or print our pre-trip tyre check.
Questions
How often should I check tread depth?
Monthly, and before any long trip. It takes a minute, and you can do it while you check your pressures.
Is the legal tread limit different for 4WDs or caravans?
No. The 1.5 mm minimum applies to light vehicles across Australia, caravans included. A heavy van in the wet is exactly where extra tread earns its keep.
Do I have to replace tyres in pairs?
It's good practice to replace at least both tyres on an axle, so grip stays even side to side. Your tyre shop can advise for your vehicle.
Not sure what your rig needs? Email us your rig: info@flatmate-tpms.com
