Tyre tread channels water away from the contact patch and gives you grip on wet, loose and uneven surfaces. As tread wears, stopping distances increase and the risk of aquaplaning rises. Checking tread depth takes less than five minutes and is one of the simplest safety checks you can do on any vehicle.
This guide covers how to measure tyre tread depth properly, what the legal minimums are in Australia and the US, and how to spot wear patterns that signal alignment or inflation problems.
Before you start
You need a tyre tread depth gauge. These are inexpensive and available from auto parts stores. If you do not have a gauge, a 20-cent coin works for a quick approximate check (see the coin test section below). Have a pen and your tyre and rim inspection form ready to record your readings.
Park the vehicle on a flat, level surface. Turn the front wheels to full lock so you can access the full tread face. Engage the park brake.
Step-by-step tread depth check
1. Park on level ground and turn the wheels
A flat surface ensures you are not measuring tread depth on a tyre that is deformed by a slope. Turning the wheels to full lock exposes the inner and outer edges of the front tyres so you can measure across the full width of the tread.
2. Locate the tread wear indicators
All modern tyres have tread wear indicator (TWI) bars moulded into the base of the main tread grooves. Look for small raised bridges running across the groove, usually marked by a triangle or "TWI" stamp on the sidewall. When the tread surface wears flush with these bars, the tyre has reached the legal minimum.
3. Measure depth at multiple points
Insert the gauge probe into a main tread groove and press the base flat against the tread surface. Read the measurement in millimetres. Take three readings across the tread: inner edge, centre and outer edge. The lowest reading is the one that counts for legal compliance.
4. Check all tyres including the spare
Repeat the process on every tyre, including duals on heavy vehicles and the spare. Each tyre wears at a different rate depending on its position, the vehicle's alignment, inflation pressure and load distribution. A spare with no tread is useless in an emergency.
5. Compare readings to legal minimums
Check each reading against the legal minimum for your jurisdiction:
- Australia: 1.5 mm across the full width of the tread that contacts the road (varies by state, but 1.5 mm is the national standard)
- United States: 2/32 of an inch (approximately 1.6 mm) for passenger vehicles; 4/32 inch for steering axle tyres on commercial vehicles
Many safety organisations recommend replacing tyres at 3 mm, not waiting for the legal minimum, because wet-weather braking performance degrades significantly below this point.
6. Record findings
Log each tyre position (e.g. front left, rear right inner), the tread depth reading and any observations such as uneven wear, sidewall cracks, bulges or embedded objects. File the record in your vehicle maintenance history. A vehicle pre-start checklist usually includes a tyre condition field for this purpose.
Legal minimum tread depths
| Jurisdiction | Vehicle type | Minimum depth |
|---|---|---|
| Australia (national) | All vehicles | 1.5 mm |
| United States (federal) | Passenger vehicles | 2/32 in (1.6 mm) |
| United States (federal) | CMV steering axle | 4/32 in (3.2 mm) |
| United Kingdom | Cars | 1.6 mm |
Driving on tyres below the legal minimum is an offence that can result in fines, demerit points and, in the case of commercial vehicles, defect notices and grounding orders.
The coin test (without a gauge)
If you do not have a gauge handy, an Australian 20-cent coin provides a rough check. Insert the coin into the tread groove with the platypus bill facing down. If the tread does not reach the bill, the tyre is approaching the legal minimum and should be measured with a proper gauge as soon as possible.
In the US, the penny test works similarly. Insert a US penny with Lincoln's head pointing into the groove. If the top of Lincoln's head is visible, the tread is at or below 2/32 inch and the tyre needs replacing.
The coin test is an approximation. Always confirm with a calibrated gauge before making replacement decisions.
Wear patterns and what they mean
| Wear pattern | Likely cause | Action |
|---|---|---|
| Centre wear only | Over-inflation | Reduce pressure to OEM spec |
| Both edges worn, centre OK | Under-inflation | Increase pressure to OEM spec |
| One edge worn more than the other | Wheel misalignment | Book a wheel alignment |
| Cupping or scalloping | Worn suspension or shock absorbers | Inspect suspension components |
| Flat spots | Heavy braking or locked wheels | Check ABS system, replace tyre if severe |
Uneven wear patterns mean the tyre is not making full contact with the road. Fixing the root cause (inflation, alignment or suspension) before fitting new tyres prevents the same wear pattern recurring on the replacements.
Going digital with MapTrack
Tracking tyre condition across a fleet on paper makes it difficult to spot trends or schedule replacements proactively. With MapTrack, each vehicle carries a QR code label that links to its full inspection history. Tyre readings entered via digital forms are stored against the vehicle record, making it easy to trend wear rates over time.
When a tyre approaches the replacement threshold, the system can trigger an automated alert to the fleet manager, ensuring tyres are replaced before they become a safety or compliance issue.
