How to Check Tyre Tread Depth: UK Legal Limits and Safety Guide

Summary

• Legal minimum: 1.6mm of tread across the central 3/4 of the tyre, around the full circumference.
• Safety recommendation: Replace tyres at 3mm - braking distance increases significantly below this.
• Quick check: Use a 20p coin. If you can see the outer band, your tread is too low.
• Penalties: £2,500 fine and 3 penalty points per illegal tyre.

Tyres are the only part of your car that touches the road. Yet many drivers never check their tread depth until they fail an MOT.

This guide shows you how to check tyre tread depth and explains why it matters.

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UK Legal Requirements

The law states that tyres must have:

• At least 1.6mm of tread depth
• Across the central three-quarters of the tyre
• Around the entire circumference

This applies to cars, light vans, and trailers.

Penalties for Illegal Tyres

• Fine up to £2,500 per tyre
• 3 penalty points per tyre
• Four illegal tyres = 12 points = driving ban
• Instant MOT failure

Your insurance may also be invalidated if you're driving on illegal tyres.

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The 20p Coin Test

This is the quickest way to check your tread:

1. Take a 20p coin
2. Insert it into the main tread grooves of your tyre
3. If you can see the outer band of the coin, your tread is below 3mm
4. Check in at least three places around the tyre
5. Check all four tyres

The outer band of a 20p is about 3mm from the edge. If it's visible, your tyres are getting close to the legal limit and should be replaced soon.

Note: The 20p test shows when you're approaching the limit, not exactly at 1.6mm. Use a proper gauge for precise measurement.

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Using a Tread Depth Gauge

For accurate measurement, use a tread depth gauge:

1. Place the gauge into the main groove
2. Push down until the base sits flat on the tread
3. Read the measurement
4. Check several points around the tyre
5. The lowest reading is what counts

Tread depth gauges cost just £2-5 from car accessory shops or online.

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Tread Wear Indicators

Most tyres have built-in wear indicators:

• Small raised bars in the tread grooves
• Located at 1.6mm height
• Look for small arrows or "TWI" on the sidewall to find them
• When the tread is level with these bars, you're at the legal limit

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Why Tread Depth Matters

Tyre tread disperses water from under the tyre. Without adequate tread, you lose grip - especially in wet conditions.

Braking Distance Comparison (at 50mph in wet)

Tread Depth	Stopping Distance
8mm (new)	~25 metres
3mm	~35 metres
1.6mm (legal limit)	~43 metres

That's 18 metres more stopping distance - about 4 car lengths. In an emergency, that's the difference between stopping safely and crashing.

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When to Replace Your Tyres

Although 1.6mm is the legal minimum, safety organisations recommend replacing at 3mm:

• Significant grip loss below 3mm
• Much longer braking distances in wet
• Increased aquaplaning risk

Many tyre manufacturers and motoring organisations advise 3mm as the safe minimum for UK driving conditions.

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Checking for Uneven Wear

Don't just check the centre - check across the width of the tyre:

Wear Pattern	Possible Cause
Centre worn more	Over-inflation
Edges worn more	Under-inflation
One edge worn	Wheel alignment problem
Patchy wear	Suspension or balance issue

Uneven wear means part of your tyre may be illegal even if other parts look fine. Address the underlying cause to prevent future problems.

For more on this, see our wheel alignment vs balancing guide.

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Making Tread Checks a Habit

Check your tyre tread:

• At least once a month
• Before long journeys
• After hitting kerbs or potholes
• When you check tyre pressures

While checking tread, also look for:

• Cuts or bulges in the sidewall
• Objects embedded in the tread
• Signs of cracking (age-related)

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Tyres and the MOT

Tyres are checked as part of every MOT. Your car will fail for:

• Tread depth below 1.6mm
• Cuts longer than 25mm or 10% of tyre width
• Lumps, bulges, or tears
• Exposed ply or cord
• Incorrectly seated on the rim

For more, see our MOT guide.

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Common Questions

How long do tyres last?

Typically 20,000-40,000 miles depending on driving style, tyre quality, and road conditions. Check tread monthly regardless of mileage.

Is 2mm tread legal?

Yes, technically. But it's approaching the limit fast. At 2mm, wet weather grip is significantly reduced. Replace soon.

Do I need to replace all four tyres at once?

Not necessarily. But ideally replace in pairs (front or rear axle) and ensure the best tyres are on the rear for stability.

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Final Thoughts

Checking tyre tread takes 2 minutes and could save your life. Use the 20p test regularly, invest in a cheap gauge for accuracy, and replace tyres at 3mm for safety.

Your tyres are your only contact with the road. Don't neglect them.

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