The 20p Coin Test
The quickest and most widely used method for a basic tyre tread check is the 20p coin test. Insert a 20p coin into the main tread groove of your tyre. If the outer band of the coin — the raised rim around its edge — is obscured by the tyre tread, your depth is above 3mm and likely fine. If the outer band is visible, your tread is at or approaching the level at which replacement should be seriously considered.
Repeat this test at multiple points around each tyre and across the full width of the tread. Uneven readings can indicate alignment or pressure problems that are causing localised wear.
Using a Digital Tread Depth Gauge
For an accurate measurement rather than a quick approximation, a digital tread depth gauge is the right tool. These are widely available online and at motor factors for under £10 and provide a precise reading in millimetres. Insert the probe into the tread groove and press down until the gauge base sits flat on the tread surface, then read the depth from the display.
Take readings at a minimum of three points around the circumference of the tyre and at three positions across the width — near each edge and in the centre — to build a complete picture of wear across the whole tyre.
Reading the Wear Indicators Built Into Your Tyre
All modern tyres include tread wear indicators — small raised rubber bars positioned at the base of the main tread grooves. These bars sit at exactly 1.6mm — the UK legal minimum. When the tread surface wears down to be flush with these indicators, the tyre has reached the point at which it must legally be replaced.
These wear indicators are useful as a final warning, but by the time they become visible the tyre has already entered the zone of reduced performance on wet roads. Use the 20p test or a gauge regularly so you are never in the position of relying solely on this last-resort indicator.
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