How to Check Tyre Tread Depth: A Complete UK Guide

28 July 2026

Table of Contents

• Why Checking Tyre Tread Depth Matters for Road Safety
• Understanding the Legal Tyre Tread Depth Limit in the UK
  • What the Law Says About Minimum Tread Depth
  • How the MOT Test Checks Tyre Tread Depth
• How to Check Tyre Tread Depth Using the 20p Test
  • Step-by-Step Guide to the 20p Coin Test
  • Accuracy and Limitations of the Coin Method
• Using a Tyre Tread Depth Gauge for Precise Measurement
  • Digital Gauge vs. Mechanical Gauge Accuracy
  • How to Use a Tread Depth Gauge Correctly
• Visual Inspection: Spotting Tyre Wear and Damage
  • Locating the Tread Wear Indicator (TWI)
  • Identifying Uneven Wear Patterns and Sidewall Damage
• Consequences of Driving with Illegal Tyre Tread in the UK
• When to Replace Your Tyres: Beyond the Legal Minimum
  • Weather Conditions and Tyre Safety
  • Professional Tyre Replacement at Kettering Motorist Centre
• Common Mistakes When Checking Tyre Tread Depth

Last Updated: July 28, 2026

Why Checking Tyre Tread Depth Matters for Road Safety

Learning how to check tyre tread depth is one of the simplest yet most critical vehicle maintenance tasks you can perform. Your tyres are literally where your car meets the road, and their condition directly determines your grip, braking distance, and ability to handle wet or slippery conditions.

Tyre tread depth matters because it channels water away from the contact patch. When tread wears down, your tyres lose their ability to displace water, increasing the risk of aquaplaning on wet roads. Shallow tread means longer stopping distances, reduced traction in poor weather, and significantly higher accident risk.

The law in the UK is unambiguous: your tyres must meet the legal minimum. Below, we'll show you exactly how to check tyre tread depth using multiple methods, from the simple 20p coin test to digital gauges, and explain what the numbers mean for your driving.

Understanding the Legal Tyre Tread Depth Limit in the UK

What the Law Says About Minimum Tread Depth

The legal minimum tyre tread depth in the United Kingdom is 1.6mm across the central three-quarters of the tyre's width. This requirement applies to all vehicle types and is enforced through MOT testing and roadside police checks. The measurement must be taken in the main tread grooves, not at the edges or sidewalls.

However, many safety organisations and tyre manufacturers recommend replacing tyres at 3mm of tread depth, particularly if you drive regularly in wet conditions. At 3mm, your braking distance on wet roads increases noticeably compared to a new tyre at 8mm.

How the MOT Test Checks Tyre Tread Depth

During an MOT test, an examiner uses a tread depth gauge to measure your tyres at multiple points across the width of each tyre. If any measurement falls below 1.6mm, your vehicle fails the MOT and cannot be driven on public roads until the tyres are replaced.

When you book an MOT with Kettering Motorist Centre in Kettering or the surrounding Northamptonshire area, our technicians check your tyres thoroughly as part of the standard test. If we spot potential issues before they become critical, we'll discuss your options with complete transparency.

How to Check Tyre Tread Depth Using the 20p Test

Step-by-Step Guide to the 20p Coin Test

The 20p coin test is the most accessible way to check tyre tread depth at home. Here's exactly how to do it:

Step 1: Get a 20p coin A standard UK 20p coin is 24mm in diameter, making it a useful reference tool. Keep one in your glove box specifically for this purpose.

Step 2: Locate the tread grooves Find the main tread grooves running around your tyre. These are the deep channels in the rubber, not the smaller sipes between the grooves. Test the central band of the tyre, not the edges.

Step 3: Insert the coin into the groove Push the 20p coin into the tread groove at an angle, with the outer edge of the coin going in first.

Step 4: Check the result If the outer ring of the 20p coin disappears into the tread groove, your tyre tread depth is above 1.6mm and you're legal. If the outer ring remains visible above the tread surface, your tyre is at or below 1.6mm and needs replacing immediately.

Repeat this test at multiple points around each tyre, at least three locations per tyre. Uneven wear across the tyre can indicate alignment or suspension problems that need professional attention.

Step 5: Check all four tyres Don't assume all four tyres wear at the same rate. Front tyres often wear faster than rear tyres. If one tyre is significantly more worn than the others, have your alignment and suspension checked.

Accuracy and Limitations of the Coin Method

The 20p test is reasonably accurate for determining whether you're above or below the 1.6mm legal limit, but it's a binary check, legal or not, without telling you exactly how much tread you have left. If your tyre is at 2.5mm, the coin test will pass, but you're still in a danger zone for wet weather driving.

For more precise measurement, many drivers prefer using a digital tread depth gauge.

Using a Tyre Tread Depth Gauge for Precise Measurement

Digital Gauge vs. Mechanical Gauge Accuracy

A digital tread depth gauge gives you a precise numerical reading in millimetres, far more informative than the pass/fail result of the 20p test. Digital gauges typically measure from 0mm to 25mm with accuracy to within 0.1mm, allowing you to track your tyre wear over time and plan replacement before reaching the legal limit.

Mechanical (analogue) gauges work on a similar principle but use a dial or scale instead of a digital readout. They're often cheaper and require no batteries, but they're slightly less precise and harder to read in poor light.

Digital gauges are generally more user-friendly. You simply press the gauge firmly into the tread groove until it seats properly, and the reading appears on the screen.

How to Use a Tread Depth Gauge Correctly

Step 1: Locate the main tread grooves Identify the deepest grooves running around the tyre, not the smaller sipes.

Step 2: Press the gauge firmly into the groove Insert the probe straight down into the tread groove, perpendicular to the tyre surface. Push it in firmly until the gauge's base plate sits flat on the tread surface.

Step 3: Read the measurement For digital gauges, the reading appears on the screen. For mechanical gauges, read the needle position on the dial.

Step 4: Test multiple locations Check at least three locations around the circumference of each tyre and at least two locations across the width. This reveals wear patterns.

Step 5: Document your readings Write down the measurements for each tyre. This gives you a baseline so you can track wear rate over time.

Visual Inspection: Spotting Tyre Wear and Damage

Locating the Tread Wear Indicator (TWI)

The Tread Wear Indicator is a built-in safety feature on modern tyres that you can use to check tread depth visually without any tools. It's a small raised bar of rubber positioned at the bottom of the main tread grooves, typically placed at intervals around the tyre. When your tyre tread wears down to the same level as the TWI, you've reached 1.6mm, the legal minimum.

To find the TWI on your tyre, look for small markings or symbols on the sidewall that indicate where the indicators are located. Common symbols include a triangle, a dot, or the letters "TWI". If the tread surface is level with the TWI bar, your tyre is at the legal limit.

The TWI is more reliable than the 20p coin test because it's engineered to align precisely with 1.6mm depth. However, it only tells you when you've reached the legal minimum, not when you've reached the 3mm safety threshold that many experts recommend.

Identifying Uneven Wear Patterns and Sidewall Damage

Beyond tread depth, visual inspection can reveal problems that indicate deeper issues with your vehicle. Uneven wear patterns are particularly important because they often signal suspension, alignment, or tyre pressure problems.

Centre wear: If the centre of the tyre is noticeably more worn than the edges, your tyres are overinflated. Check your tyre pressure and adjust to the vehicle manufacturer's recommended level.

Edge wear: If both edges of the tyre are more worn than the centre, your tyres are underinflated. This also reduces fuel efficiency and increases heat buildup.

One-sided wear: If one edge of the tyre is significantly more worn than the rest, your vehicle's wheel alignment is likely out. At Kettering Motorist Centre, we can check your alignment and make adjustments to extend tyre life and improve your vehicle's handling.

Patchy or cupped wear: If the tread surface has a wavy appearance with dips and peaks, your suspension may be worn.

Sidewall damage is also critical. Look for cuts, bulges, or cracks in the rubber on the sides of the tyre. Any damage to the sidewall compromises the tyre's structural integrity and can lead to sudden failure. Sidewall damage cannot be repaired; the tyre must be replaced.

Consequences of Driving with Illegal Tyre Tread in the UK

Driving on tyres below the legal 1.6mm minimum tread depth carries serious consequences. You face a fixed penalty notice of £1,000 per tyre, up to a maximum of £10,000 if all four tyres are illegal. You'll also receive three penalty points on your driving licence for each illegal tyre (up to 12 points total, which would result in disqualification).

Beyond the legal consequences, the safety risks are severe. At 1.6mm tread depth, your braking distance on wet roads is significantly longer than on a tyre with adequate tread. In an emergency stop situation, that extra distance could be the difference between avoiding a collision and hitting another vehicle or pedestrian.

Aquaplaning risk increases dramatically with shallow tread. When water cannot be channelled away from the tyre's contact patch, the tyre loses grip and essentially floats on the water surface. This can happen suddenly and without warning, leaving you with no steering or braking control.

Your insurance may also be affected. If you're involved in an accident and your tyres are found to be below the legal minimum, your insurer may refuse to pay out, arguing that you were driving an unroadworthy vehicle.

When to Replace Your Tyres: Beyond the Legal Minimum

Weather Conditions and Tyre Safety

While 1.6mm is the legal minimum, it's not the safety minimum for most driving conditions. The UK's wet climate means that most drivers encounter wet roads regularly, and tyre performance deteriorates significantly as tread depth decreases.

At 3mm tread depth, your braking distance on wet roads increases noticeably compared to a new tyre at 8mm. Many safety experts recommend replacing tyres when they reach 3mm, particularly if you drive frequently in wet conditions, on motorways, or in winter months. Winter tyres should be replaced even earlier, at around 4mm, because winter performance drops off sharply below that level.

If you regularly drive long distances on motorways, consider replacing tyres at 4mm. Motorway driving at high speeds puts more stress on tyres, and the margin for error is smaller. If you're approaching winter (November through March in the UK), check your tyre tread now. If you're at 3mm or below, replace them before winter arrives.

Professional Tyre Replacement at Kettering Motorist Centre

When it's time to replace your tyres, Kettering Motorist Centre in Kettering, Northamptonshire, handles tyre replacement with attention to detail. Our team can advise you on the right tyre type for your vehicle and driving needs, whether that's all-season tyres, winter tyres, or performance tyres.

We offer hassle-free online booking for tyre appointments with no upfront payment required. You can check availability and book at a time that suits you, and we'll confirm the work and final cost before we start. Beyond just replacing tyres, we also check your wheel alignment and suspension during the process. Uneven wear patterns often indicate alignment issues, and fixing these at the same time as tyre replacement prevents your new tyres from wearing prematurely.

For drivers in Kettering and the surrounding Northamptonshire area, including Corby, Wellingborough, and Market Harborough, we provide expert tyre services backed by our family-run business's reputation for reliability and transparent pricing. If you have a hybrid or electric vehicle, our sister site KMC Electric provides specialist expertise for electric and hybrid tyre and suspension work.

Common Mistakes When Checking Tyre Tread Depth

Many drivers make avoidable mistakes when checking their tyres. Understanding these mistakes helps you get accurate readings and make informed decisions.

Mistake 1: Only checking one spot per tyre. Tyres wear unevenly. Always check at least three locations around the circumference and two locations across the width.

Mistake 2: Confusing the TWI with actual tread depth. The TWI aligns with 1.6mm but doesn't indicate when you've reached the 3mm safety threshold. Use the TWI as a last-resort warning, not as your target replacement point.

Mistake 3: Ignoring sidewall damage while focusing on tread depth. A tyre can have adequate tread depth but be unsafe due to sidewall cracks, bulges, or cuts. Always visually inspect the entire tyre.

Mistake 4: Assuming all tyres wear at the same rate. Front tyres typically wear faster than rear tyres. Check all four tyres separately.

Mistake 5: Using the 20p test as your only check. The coin test is a quick pass/fail check, but it doesn't tell you how much tread you actually have. Use it as a quick check, but follow up with a gauge if you want precise information.

Mistake 6: Ignoring tyre pressure. Tyre pressure affects wear rate directly. Underinflated tyres wear faster and reduce fuel efficiency. Check your tyre pressure monthly and adjust to the manufacturer's recommended level.

Mistake 7: Delaying replacement until you reach the legal minimum. By the time you hit 1.6mm, you're already in a danger zone for wet weather driving. Plan replacement at 3mm.

Checking your tyre tread depth is one of the simplest yet most important vehicle maintenance tasks you can do. Whether you use the 20p coin test, a digital gauge, or the Tread Wear Indicator, the key is to check regularly and replace tyres before they become unsafe. At Kettering Motorist Centre, we understand that vehicle maintenance can feel overwhelming, which is why we've made tyre replacement straightforward and transparent. Our expert team can assess your tyres, advise on the best replacement options for your vehicle and driving needs, and handle the work with complete professionalism. Book your tyre appointment online today, no upfront payment, no pressure, just honest advice and expert service.