The 20p test is the easiest way to check if your tyres are legal and safe. Here's how to do it correctly — and what to do if they fail.
The UK legal minimum tyre tread depth is 1.6mm — and driving with tyres below this limit can result in a £2,500 fine and 3 penalty points per tyre. The simplest way to check is the 20p test, which takes under a minute and could save your life.
How to Do the 20p Tread Depth Test
- Take a 20p coin from your pocket
- Insert the coin into the main tread groove of your tyre
- If the outer band of the coin is hidden, your tread is above 1.6mm
- If the outer band is visible, your tyres are potentially illegal — replace immediately
- Check multiple points around each tyre, including the centre and edges
What Does 1.6mm Actually Look Like?
The outer border of a 20p coin is approximately 2mm wide. If you can see the entire outer border, your tread depth is below 2mm — dangerously close to the legal limit. Most tyre manufacturers recommend replacing tyres at 3mm for optimal safety, particularly in wet conditions.
Why Tread Depth Matters in Wet Weather
At 3mm tread depth, stopping distances in wet conditions are significantly longer than at 8mm (new tyre). The grooves in your tyres are designed to channel water away from the contact patch — as they wear down, the risk of aquaplaning increases dramatically.
Failed the 20p test? Book a same-day tyre replacement with Local Mobile Tyre Guys. We come to you — no garage needed.
Tyre Wear Indicators
Most modern tyres have built-in tread wear indicators — small raised sections moulded into the tread grooves. When the tread has worn level with these indicators, it's at exactly 1.6mm. These are a useful visual check but don't wait until you reach them — replace at 3mm.
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