How To Know Tire Tread

Knowing your tire tread depth is essential for safe driving and ensuring your vehicle meets legal requirements in Great Britain. This guide provides clear, step-by-step instructions on how to accurately measure tire tread using simple tools like a 20p coin or a dedicated depth gauge. By following these steps, you can identify when your tires are nearing their legal limit or showing signs of uneven wear, helping you make informed decisions about tire maintenance and replacement before issues arise.

Fast Answer

Minimum legal tread depth (GB): 1.6 mm
Tool for quick check: 20p coin

10-15 minutes Time needed

Easy Difficulty

Uneven wear across the tire Watch out for

Before You Start

A safe, flat area to park your car, away from traffic.
Good lighting (daylight is best, or a bright torch if checking at night).
A reliable tire tread depth gauge (digital or manual).
Alternatively, a 20p coin for a quick, approximate check.
A pen and paper to note down your findings (optional but recommended).
A clean rag to wipe away any dirt from the tire grooves.

Check first: Always ensure your car is parked safely on level ground with the engine switched off and the parking brake firmly applied before you begin any inspection. This prevents unexpected movement and ensures your safety. Remember to check all four road tyres, and the spare tyre if your vehicle has one.

Step-by-Step Instructions

1. Park Safely and Prepare the Tires

Before you start, make sure your car is in a safe location. Park on a flat, solid surface like a driveway or a parking bay. Turn off the engine, engage the parking brake, and put the car in park (for automatics) or in gear (for manuals). This prevents your vehicle from rolling unexpectedly during the inspection. Ensure there is enough light to clearly see the tire tread. If any of your tire grooves are packed with mud, small stones, or debris, carefully remove it with a stick or the clean rag so you can get an accurate measurement.

Tip: Checking your tire tread is easiest when the tires are clean. A quick wipe down with a damp cloth can help remove surface dirt, making the tread patterns and wear indicators easier to spot.

2. Locate the Tread Wear Indicators (TWIs)

Your tires have built-in safety features called Tread Wear Indicators (TWIs). These are small, raised bars of rubber located at the bottom of the main tread grooves. You can often find them in six to eight locations around the circumference of the tire. They are usually spaced roughly every 30cm or so. When the tire tread wears down to the same level as these indicator bars, it means your tire has reached the minimum legal tread depth of 1.6 mm in Great Britain. This is a visual warning that your tires need replacing.

Tip: Look for a small arrow or the letters "TWI" on the sidewall of the tire. These markers point directly to where the tread wear indicators are located in the main grooves, making them much easier to find.

3. Perform the 20p Coin Test for a Quick Check

The 20p coin test is a simple and common method for a quick, rough check of your tire tread depth. Take a 20 pence coin and insert it into one of the main grooves of your tire, making sure the outer band (the raised border) of the coin faces into the tread. The legal minimum tread depth of 1.6 mm is roughly equivalent to the distance from the edge of the 20p coin to the start of the raised outer border. If you can see the entire outer band of the 20p coin when it's inserted into the tread, your tires might be below the legal limit and should be checked more accurately with a gauge.

Warning: The 20p test is a quick indicator, not a precise measurement. It's useful for a 'traffic light' check (green = clearly above, amber = close, red = definitely below), but for accurate assessment, especially if the 20p test suggests low tread, always use a proper depth gauge.

4. Use a Tread Depth Gauge for Accurate Measurement

For the most accurate assessment, you should use a dedicated tire tread depth gauge. These can be manual or digital. To use one, push the probe of the gauge into the deepest part of a main tread groove, ensuring it's not on a TWI. Push the base of the gauge firmly against the top surface of the tread block. The gauge will then display the depth. If using a digital gauge, it will show the reading on a screen. With a manual gauge, you'll read the measurement from the scale. Always measure in millimetres (mm) as this is the standard unit for tire tread in the UK.

Tip: Ensure the gauge is inserted straight down into the groove, not at an angle. If it's tilted, your reading will be inaccurate and could make your tire seem to have more tread than it actually does.

5. Check Multiple Grooves and Around the Tire

It's crucial not to just take one measurement per tire. Tread wear can be uneven across the tire's surface and around its circumference. Take at least three or four measurements in different main grooves across the width of the tire – one near the inner edge, one in the middle, and one near the outer edge. Then, repeat this process at several different points around the entire circumference of the tire, such as at 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock positions. Always use the lowest reading as your reference point for compliance with the legal limit.

Tip: To check different points around the tire, you might need to slowly move your car a short distance. If doing so, remember to follow all safety procedures (engine off, parking brake on) each time you stop to take new measurements.

6. Record Your Readings and Understand the Legal Limit

After measuring each tire, it's a good idea to write down the lowest tread depth you found for each one. This allows you to track wear over time and compare the condition of your front and rear tires, or left and right tires. In Great Britain, the legal minimum tread depth for cars is 1.6 mm across the central three-quarters of the tread width and around the entire circumference of the tire. If any of your measurements fall at or below 1.6 mm, your tire is legally worn and needs to be replaced immediately. Driving with illegal tires can result in a hefty fine and penalty points on your license, per tyre.

Warning: Driving with tires below 1.6 mm tread depth is not only illegal but also extremely dangerous. It significantly reduces your car's grip on the road, especially in wet conditions, increasing stopping distances and the risk of skidding or aquaplaning.

7. Inspect for Uneven Wear and Damage

While checking the tread depth, also take the opportunity to visually inspect the tires for any signs of uneven wear or damage. Look for:

Wear on the shoulders (edges): This often indicates under-inflation.
Wear in the centre: This can suggest over-inflation.
Uneven wear in patches or on one side: This could point to wheel alignment issues, unbalanced wheels, or problems with your vehicle's suspension.
Cracks, bulges, or cuts: Even if tread depth is fine, these can compromise tire integrity.
Embedded objects: Small stones, nails, or glass that could cause a slow puncture.

Tip: If you spot any severe cracks, bulges, or cuts on the tire's sidewall, do not drive on that tire. It indicates a structural failure and could lead to a sudden blowout. Seek professional assistance immediately.

8. Decide on Next Steps

Based on your findings, decide on the appropriate action. If your tire tread is consistently above 3 mm, your tires are in good condition. If it's between 1.6 mm and 3 mm, your tires are nearing their legal limit and you should start thinking about replacement soon, especially before winter or long journeys. If any measurement is at or below 1.6 mm, the tire must be replaced immediately. If you notice significant uneven wear or damage, even if the overall tread depth is still legal, it's best to have your car checked by a professional to identify and fix the underlying cause, preventing further tire wear or potential safety hazards.

Tip: Many tire shops offer free tire checks. If you're unsure about your findings or suspect underlying issues, taking advantage of a professional opinion is a smart and safe choice.

Quick Reference

Situation	Use this	Why
Quick, casual check	20p Coin Test	Fast visual indicator if tread is getting low.
Accurate measurement	Tread Depth Gauge	Provides precise numerical depth for legal compliance.
Checking for overall wear	Tread Wear Indicators (TWIs)	Factory-set markers indicating when tread reaches 1.6 mm.
Suspect uneven wear	Measure at multiple points (inner, middle, outer grooves & around tire)	Helps identify underlying issues like alignment or inflation problems.
Tread depth below 1.6 mm	Replace tire immediately	Illegal and dangerously reduces grip, especially in wet conditions.
Tread depth between 1.6mm and 3mm	Plan for replacement soon	Performance degrades significantly as tread approaches legal limit.

Common Problems When You Know Tire Tread

Even with clear instructions, you might run into a few common issues when checking your tire tread. Knowing what to look for and how to fix it can save you time and ensure accurate results.

Difficulty Finding Tread Wear Indicators (TWIs): Sometimes, if a tire is very worn, the TWIs can be hard to see because the surrounding tread has worn down almost completely to their level. In other cases, they might just be obscured by dirt or simply blend in.

Solution: Look for the small arrow or "TWI" marking on the tire's sidewall, which points directly to their location. If still hard to see, assume the tread is low and use a depth gauge for certainty.

Inconsistent Readings with a Depth Gauge: You might get different numbers each time you measure, even in the same groove, leading to confusion about the actual depth. This can be frustrating.

Solution: Ensure you are inserting the gauge perpendicular (straight down) into the groove, not at an angle. Make sure the base of the gauge is pressed firmly against the tread block. Take multiple readings in the same spot and use the average, or simply the lowest, if you want to be extra safe.

Realising You Have Significant Uneven Wear: You might find one part of the tire is much more worn than another (e.g., edges worn more than the centre, or one side of the car’s tires worn more than the other).

Solution: While replacing the worn tire is the immediate solution for safety and legality, uneven wear usually points to a deeper mechanical issue such as incorrect tire pressure, wheel misalignment, or a problem with your vehicle's suspension. Get your car inspected by a professional mechanic to diagnose and fix the root cause. Otherwise, new tires will quickly wear down in the same way.

Forgetting to Check All Tires: It's easy to check one or two tires and forget the others, especially the rear ones or the spare.

Solution: Make it a habit to check all four road tires thoroughly. If your vehicle has a spare tire, give it a quick check too, especially if it's a full-size spare, as it might be needed in an emergency and must also be roadworthy. Keep a simple checklist if it helps.

Advanced Tips for How To Know Tire Tread

Beyond the basics, there are several advanced practices that can help you maintain your tires better and get more insights into your vehicle's health.

Track Tread Wear Over Time: Don't just check once. If you make a habit of checking your tires monthly, or before long journeys, and record the readings, you can identify patterns. A sudden drop in tread depth between checks, or one tire wearing much faster than others, can be an early warning sign of a problem before it becomes severe. This data can be invaluable for your mechanic.
Understand the Impact of Tyre Pressure: Incorrect tire pressure is a leading cause of uneven tread wear. Under-inflated tires tend to wear more on the outer shoulders, while over-inflated tires wear more in the centre. Regularly checking and correcting your tire pressure according to your car's manufacturer specifications (found in the owner's manual or on a sticker inside the driver's door jamb or fuel flap) is critical for even tread wear and extending tire life.
Consider Tire Rotation: Having your tires rotated periodically (typically every 5,000 to 8,000 miles or 6-12 months) can help ensure they wear more evenly. Since front tires and rear tires experience different stresses (e.g., steering, braking, power delivery), rotating them helps balance out the wear patterns, often extending the overall life of the set.
Recognise the Importance of Wheel Alignment and Balancing: If your wheels are out of alignment or unbalanced, it can cause rapid and uneven tire wear. Misalignment might lead to feathering (tread blocks worn more on one side than the other) or shoulder wear on one specific side of the car. Unbalanced wheels can cause cupping or scalloping (uneven dips in the tread pattern). If you notice these patterns, even if tread depth is still legal, a professional alignment or balancing service is advisable to prevent premature tire replacement.
Factor in Driving Style: Aggressive driving, such as hard braking, rapid acceleration, and fast cornering, can significantly accelerate tire wear. Smooth, consistent driving helps to preserve your tire tread for longer. While it's not a direct 'check', being mindful of your driving style can dramatically influence how quickly your tread disappears.
Know Your Replacement Threshold: While 1.6 mm is the legal minimum, many experts and tire manufacturers recommend replacing tires when they reach 3 mm of tread depth. This is because performance, especially in wet conditions and for emergency braking, starts to diminish significantly below 3 mm, even if they are still technically legal. Consider 3 mm as a safety recommendation rather than a strict legal requirement.

How To Know Tire Tread FAQ

Here are answers to some frequently asked questions about checking tire tread.

How often should I check my tire tread?

It's recommended to check your tire tread depth at least once a month and always before any long journey. This regular check allows you to catch any significant wear or damage early, ensuring your safety and compliance with the law.

What is the legal minimum tread depth in the UK?

In Great Britain, the legal minimum tread depth for cars is 1.6 mm. This measurement must be across the central three-quarters of the tread width and around the entire circumference of the tire. Driving with less than this can lead to a fine of up to £2,500 and three penalty points per tire.

Can I mix tires with different tread depths?

While generally not recommended, it is legally permissible to have tires with different tread depths on the same vehicle, as long as each individual tire meets the 1.6 mm legal minimum. However, for optimal handling, safety, and even wear, it's best to have tires with similar tread depths across an axle, or even better, on all four wheels. When replacing only two tires, new ones should typically go on the rear axle for better stability, regardless of whether your car is front or rear-wheel drive.

What causes uneven tire wear?

Uneven tire wear can be caused by several factors: incorrect tire pressure (under-inflation causes outer edge wear, over-inflation causes centre wear), improper wheel alignment, unbalanced wheels, worn-out suspension components (like shock absorbers), or even aggressive driving habits. If you notice uneven wear, it's crucial to have your vehicle inspected by a professional to identify and correct the underlying issue.

Is it really dangerous to drive with low tread?

Yes, driving with low tire tread is extremely dangerous. As tread depth decreases, a tire's ability to grip the road, especially in wet conditions, significantly reduces. This leads to much longer stopping distances, a higher risk of aquaplaning (losing control on wet roads), and reduced overall handling and stability. Low tread depth compromises your ability to safely control your vehicle, putting yourself and other road users at risk.

Final Checklist for How To Know Tire Tread

Before you consider your tire tread check complete, use this checklist to ensure you've covered all the important points:

Car is parked safely on level ground with the engine off and parking brake on.
You have adequate lighting to clearly see the tire tread.
All four road tires have been inspected.
You've located the Tread Wear Indicators (TWIs) on each tire.
A 20p coin test has been performed for a quick check.
An accurate tread depth gauge has been used for precise measurements.
Measurements were taken in at least three main grooves (inner, middle, outer) on each tire.
Measurements were taken at multiple points around the circumference of each tire.
The lowest tread depth for each tire has been identified and noted.
All tires meet the 1.6 mm legal minimum in GB.
You've visually inspected each tire for uneven wear, cracks, bulges, or embedded objects.
You have a clear plan for replacement if any tire is below the legal limit or severely damaged.
If uneven wear or damage was noted, you plan to consult a professional mechanic.