Winter tyre tread depth is a simple question with a legal answer. In the UK the minimum is 1.6mm across the central three-quarters of the tyre, around the whole circumference. Many drivers want more margin than that before the first frost, so this guide explains where the legal line sits, how to check your tyres with a 20p coin, and what an MOT tester looks for.
It is written for owners of cars and small vans in England, Scotland and Wales, where November and December bring wet leaves, morning frost and dark commutes. The aim is a clear decision: keep the tyres, measure again in a few weeks, or book new tyres before the weather turns.
What is the legal tyre tread limit for winter tyres in the UK?
The rule comes from the Road Vehicles (Construction and Use) Regulations and is summarised in the Highway Code on GOV.UK. The tread must be at least 1.6mm deep across the central three-quarters of the tyre's width and around the whole circumference. The outer eighth on each side is excluded from the measurement, so a shoulder worn smooth can still be legal if the central grooves are deep enough.
Winter tyres follow the same legal limit as summer tyres. There is no separate UK minimum for winter rubber, and the 1.6mm figure applies whatever the tyre is labelled.
Below the limit the penalty is serious. GOV.UK guidance describes a fine of up to £2,500 for each illegal tyre, with three penalty points per tyre. A 2016 Volkswagen Golf with two rear tyres at 1.2mm therefore faces the possibility of two separate offences, even though only the back axle is affected.
Tread wear indicators are a useful prompt. Modern tyres have small bars moulded into the main grooves, and when the tread is level with them the tyre is at about 1.6mm. This is a visual sign rather than a measurement, so when the bars look close, measure the tyre properly before the next long drive.
How do I check winter tyre tread depth with a 20p coin?
A 20p coin is a quick check that most drivers can do in a car park in under two minutes. The usual version of the test uses the outer rim of the coin, which is commonly described as about 3mm. It tells you whether the tread is above or below the level at which many tyre makers and road safety groups suggest planning a replacement. It does not prove legality, so treat a borderline result as a reason to measure properly.
- Park on level ground and look at the main grooves in the centre of each tyre, not the outer shoulder.
- Insert the 20p into a groove with its outer rim pointing down into the tread.
- If the rim is hidden by rubber, the tread is at or above about 3mm.
- If you can see the outer rim all the way round, the tread is at or below about 3mm, so book a tyre check soon.
- Repeat at three points around each tyre, and check both the inner and outer grooves.
A depth gauge gives a more reliable reading than a coin. Many tyre centres and motor factors sell one for a few pounds, and some fitters will measure tread when you visit. Write each reading down with the date, because two or three readings over a month show the wear rate more clearly than a single figure.
Take a worked example. A driver with a 2019 Skoda Octavia measures 3.4mm on the front tyres in early November but only 2.2mm on the rears. The rear reading is close to the legal line with several weeks of wet roads ahead, so the owner books a winter fit for all four wheels before the first hard frost, rather than waiting for an MOT advisory.
Should I replace winter tyres before they reach the legal limit?
There is no UK law that requires winter tyres on cars, and the Highway Code does not set a winter tyre standard. The decision is about grip, which depends on tread depth and rubber compound. Tyre makers commonly say that summer rubber stiffens below about 7°C, a temperature many parts of the UK reach from late October onwards.
Tread depth matters because the grooves move water away from the contact patch. When tread is shallow, that water has nowhere to go, and a car is more likely to aquaplane on standing water at motorway speed. Winter tyres use a softer compound and more sipes, the small slots cut into the tread blocks, so their margin also shrinks as the tread wears.
A practical rule many drivers use is to replace tyres at about 3mm rather than waiting for the legal 1.6mm. That leaves a margin for wet roads, road salt and grit, and it avoids a rushed purchase in January when fitting slots are fewer.
Consider a Ford Focus driven mostly on rural A-roads with tyres at 2.6mm in mid-November. The owner has three weeks of wet, dark commutes ahead. Booking a fitting on a quiet weekday in late November gives time to compare prices and choose the correct speed and load rating, instead of accepting whatever stock is available during the first cold snap.
What do MOT testers check on tyres?
Tyres are part of the standard MOT inspection. A tester checks tread depth, the condition of the sidewalls and whether each tyre is the correct type and size for the vehicle. A tyre with tread below the legal limit is a fail, and a tyre with cuts, bulges or exposed cord also fails.
Tyres close to the limit are commonly recorded as advisories. An advisory is not a fail, but it appears on the certificate and is a sign that replacement is coming. The MOT is a check on the day, so it does not replace regular checks at home.
Plan the test around your deadline. The CarDiary MOT due date calculator at https://www.car-diary.net/en-gb/mot-due-date-calculator helps you find the date and book a slot before the current certificate runs out. For the official rules, read the MOT guidance on GOV.UK.
Logging each tyre fitting in a service log, with the date, the tread reading and the fitter's invoice, keeps the replacement and MOT dates in one place; CarDiary is a digital cost and deadline log and does not replace the MOT certificate or any official record.
What mistakes do drivers make with winter tyre tread checks?
The most common mistake is measuring one groove on one tyre and assuming the rest match. Uneven wear tells a story. A worn inner edge often points to alignment, and a worn centre often points to over-inflation. Check every tyre, including a full-size spare if the car carries one.
- Checking only the front tyres, because they are easier to see.
- Treating 1.6mm as a safe target rather than the legal minimum.
- Fitting winter tyres to the front axle only, which upsets handling on a wet bend.
- Ignoring tyre age. The four-digit date code on the sidewall shows the week and year of manufacture, so an older tyre with plenty of tread may still need inspecting.
- Running low pressure, which speeds up shoulder wear and hides the true depth of the centre grooves.
Mixing tyre brands or patterns on the same axle can also make the car behave unpredictably in the wet. Where a pair needs replacing, fit a matching pair on that axle.
Frequently asked questions about winter tyre tread depth
What is the legal winter tyre tread depth in the UK?
The UK minimum is 1.6mm across the central three-quarters of the tyre and around the whole circumference. Winter tyres follow the same legal limit as summer tyres.
Can I check tread depth with a 20p coin?
Yes, the 20p test is a quick guide to whether tread is around 3mm. A depth gauge is more accurate, so measure properly if the reading is borderline.
Will a car fail its MOT for worn tyres?
Yes, if any tyre has tread below 1.6mm or has cuts, bulges or exposed cord. Tyres close to the limit may be noted as advisories.
Do I need winter tyres by law in the UK?
No. There is no UK law requiring winter tyres on cars, although the grip difference in cold, wet weather is a practical reason to consider them.
