The 20p Test: Quickest Way to Check If Your Tyres Are Road Legal
Keeping your tyres road legal doesn’t need special tools — just a 20-pence coin.
The 20p test is the simplest way for UK drivers to check tyre tread depth at home and avoid fines, penalty points, or MOT failures.
Here’s how it works, why it matters, and what to do if your tyres don’t pass.
Why Tyre Tread Depth Matters
Tyre tread channels water away from the road, maintaining grip and preventing aquaplaning.
When the tread wears below the legal limit, your stopping distance increases dramatically — especially in wet weather.
The law is clear:
Tyres must have a minimum tread depth of 1.6 mm across the central three-quarters of the tread and around the entire circumference.
Driving below this legal tyre tread depth limit is illegal and can lead to a £2,500 fine and three penalty points per tyre.
What Is the 20p Test?
The 20p test is a quick visual check using a regular 20-pence coin to measure tyre tread.
The outer rim of a 20p coin is 2.7 mm deep — slightly more than the legal limit — making it a reliable guide for everyday drivers.
How to Perform the 20p Test
- Take a clean 20-pence coin.
- Insert it into the main tread groove of your tyre.
- Look at the coin from the side:
- If the coin’s outer rim is hidden by the tread, your tyres are above the legal limit.
- If you can see the rim, your tread is at or below 1.6 mm — and your tyres are no longer road legal.
- Repeat the test across several points and on all four tyres, including the inner and outer edges.
If in doubt, measure with a tread-depth gauge or visit a local fitter for confirmation.
Alternative Ways to Check Tyre Tread Depth
- Tread-Depth Gauge: A digital or manual gauge gives a precise millimetre reading.
- Built-in Wear Indicators: Most modern tyres have raised rubber bars inside the grooves. When these sit flush with the tread, it’s time for replacement.
- Professional Free Checks: Many UK garages and Tyre Savings partner fitters offer complimentary tread-depth inspections.
How Often Should You Check Tyre Treads?
The DVSA recommends checking your tyres at least once a month and before any long journey.
Regular checks help prevent MOT failures and extend tyre life.
When to Replace Your Tyres
Even though 1.6 mm is the legal minimum, tyre experts and safety organisations recommend replacing tyres once tread reaches around 3 mm for optimal braking performance.
New tyres start with roughly 8 mm of tread.
Curious what affects tyre lifespan overall? Read our guide on how long tyres last and what speeds up wear
Final Word
The 20p test is one of the quickest safety checks you can do.
It takes less than a minute per tyre, costs nothing, and could save you from fines, accidents, or MOT failure.
If your tyres don’t pass, book a free tyre safety check near you or order new tyres online with Tyre Savings today.
FAQs: The 20p Tyre Test
Q1: Is the 20p test accurate?
Yes. The 20p rim is 2.7 mm deep — giving a clear indication of whether your tyres are near or below the 1.6 mm legal limit.
Q2: Should I test all four tyres?
Absolutely. Tyre wear can vary between front and rear wheels. Check each tyre in multiple spots.
Q3: Can my car fail an MOT if I pass the 20p test?
If tread depth is above 1.6 mm, you’ll pass — but tyres near that limit may receive an advisory note.
Q4: What should I do if my tyres fail the 20p test?
Order replacements immediately. Tyre Savings offers affordable tyres with local fitting at trusted UK centres.