How to Check Tyre Tread Properly

To check tyre tread properly, use the 20p coin test (or a penny if you’re in the US): insert the coin into the main tread groove; if the outer band is visible, the tread is below the 1.6mm legal limit and needs replacing, but if it’s hidden, it’s generally safe. For more accuracy, use a tread depth gauge or check the tread wear indicators (small bars in the grooves), ensuring the tread is level with them, as this also signifies the legal minimum. Always check multiple spots across the tyre for even wear. 

Methods to check tyre tread

1. 20p Coin Test (Quick Check):
   • Take a 20p coin (use a penny in the US) and place the outer edge into the main tread groove of the tyre.
   • If you can see the outer band (rim) of the coin, your tread is below the 1.6mm legal limit and unsafe.
   • If the outer band is completely covered, your tread is above the legal minimum.
   • Note: Experts recommend replacing tyres when they reach 3mm for better grip, especially in wet conditions, as the 20p test checks against the 1.6mm limit.
2. Tread Wear Indicators (Visual Guide):
   • Look for small, raised bars built into the tyre’s grooves.
   • If the tyre tread is worn down to the same level as these bars, it has reached the 1.6mm legal limit and must be replaced.
3. Tread Depth Gauge (Most Accurate):
   • This is the most precise method, using a calibrated gauge (digital or analogue).
   • Insert the gauge’s probe into the deepest groove, press the base flat, and read the measurement in millimetres.
   • Measure in several spots (inner, middle, outer) to check for uneven wear. 

What tread depth really tells you

Tread depth is the usable groove depth that clears water, grips loose surfaces, and gives the tyre edges that can bite under braking and cornering.

Why tread depth matters on real roads

Tread’s main safety job is water evacuation. The grooves act like channels that move water away from the contact patch so rubber can touch tarmac, which reduces the chance of a loss of grip in standing water. When grooves get shallow, the tyre has less capacity to clear water and the margin drops fast. 

Tread depth is not just a wet-weather issue. Shallow tread struggles on slush and compacted snow, and it becomes easier for the tyre to slide on polished winter roads. Legal limits exist as a minimum, yet they do not represent peak safety in poor conditions.

Tread depth is a wear story and a setup story at the same time. A tyre can have acceptable depth in the centre and still be unsafe if the shoulders are worn, the inner edge is bald, or the tread blocks are tearing.

The legal minimums

In the UK, the legal minimum for car tyres is 1.6 mm across a continuous band covering the central three-quarters of the tread width, around the full circumference. 

In the US, 2/32 inch, about 1.6 mm, is widely used as the minimum wear threshold for passenger tyres, and it aligns with the built-in treadwear indicator height used on tyres. 

Treat those figures as a hard stop, not a target. A tyre at the legal limit has already given away a large chunk of wet grip and water clearance potential. 

The real goal: spotting uneven wear early

A proper tread check is less about one number and more about pattern recognition. Inner edge wear can flag alignment or suspension issues. Centre wear can point to chronic overinflation. Shoulder wear can suggest persistent underinflation or aggressive cornering on a soft carcass.

Catching uneven wear early saves tyres and improves braking and stability, since the tyre can only grip consistently when the contact patch stays consistent.

A tread gauge and a five-minute routine will spot these patterns long before the tyre looks obviously bald.

The tools that give accurate answers

You can check tread with a gauge, with built-in wear bars, or with coin tests. Each method has a place, yet only one gives a precise measurement.

Use a tread depth gauge for a real measurement

A tread depth gauge measures the groove depth directly, which removes guesswork. Insert the probe into the main grooves and read the value in millimetres or 32nds of an inch, then repeat across several points. The number you want is the lowest repeatable reading in the main grooves, not the best one you can find.

Gauge checks work best when tyres are clean. Stones and compacted debris can make a groove look shallower than it is, so clear the groove with a fingernail or a small plastic pick before measuring.

A good routine uses the same gauge every time. Cheap gauges can vary slightly, yet consistency across readings is what reveals change over time.

Know what the treadwear indicators are telling you

Most tyres have raised wear bars built into the grooves. When the surrounding tread wears down to the same level as those bars, the tyre is at the 2/32 inch wear point and replacement is due. 

Wear bars are useful as a fast visual check, yet they have limits. They do not show you whether the tyre is wearing unevenly across the width, and they do not tell you how close you are to the bar until you are near the end.

Use wear bars as the first glance, then confirm with a gauge when any section looks close.

Coin tests: good for a quick check, not a full inspection

In the UK, the 20p test is a common quick check, using the 20p coin edge in the tread groove, then looking for how much of the outer rim remains visible, which gives a fast sense of whether the tyre is near the legal limit. 

In the US, the penny test is widely used. If you can see the top of Lincoln’s head, tread is at a worn level and replacement is due. 

Coin tests are fast, yet they can miss uneven wear. A tyre can pass a coin check in one groove and still be unsafe on an inner edge, so coins belong in the glovebox routine, not as the final word.

The step by step method that catches the real problems

A correct check measures across the tyre, around the tyre, and compares left to right, since tyres rarely wear evenly.

Step 1: pick the right grooves, then check multiple points

Measure the main longitudinal grooves, the ones designed to clear water. Ignore shallow secondary grooves that are not meant to last the full tyre life. 

Take readings across the width: inner, centre, outer. Then take readings around the circumference, at least four points per tyre. This matters since a tyre can wear more on one sector from alignment, suspension movement, or repeated corner loads.

Write down the lowest reading you find on that tyre, then repeat for all four tyres. The lowest reading sets the real condition.

Step 2: compare the inner and outer edges

Inner edge wear is one of the most missed issues, since it can hide under the car. Turn the steering to full lock, or crawl behind the tyre and look at the inner shoulder with a torch.

If the inner edge is wearing faster than the centre and outer, treat it as a setup or geometry clue rather than a tyre problem. A gauge will show that difference clearly.

Outer shoulder wear can come from repeated hard cornering, yet it can also reflect underinflation that rolls the tyre onto its shoulders.

Step 3: look for wear patterns that signal faults

Tread depth tells you what is happening, and the pattern often tells you why.

Common patterns worth flagging:

• Inner edge bald, centre acceptable: alignment or suspension geometry issue likely
• Centre worn, shoulders acceptable: chronic overinflation likely
• Both shoulders worn, centre acceptable: chronic underinflation likely
• Cupping or scalloping: worn dampers, balance issues, or suspension play possible
• One tyre wearing far faster than the others: alignment, corner weight, or a dragging brake check

If a pattern appears on one axle only, that points toward axle specific issues. If it appears across all tyres, pressure management and driving style become more likely culprits.

How to interpret the numbers

A number only helps if you know what it means for legality and real world grip.

Converting mm and 32nds without guessing

Useful reference points:

• 1.6 mm is about 2/32 inch
• 3.2 mm is about 4/32 inch

The UK legal limit is expressed in millimetres. The US system often uses 32nds. Knowing those anchor points helps you translate advice instantly.

When your gauge reads close to 2/32 inch or 1.6 mm, the tyre is at end of life territory under both systems. 

Legal minimum versus sensible replacement depth

The UK legal minimum is 1.6 mm across the central three-quarters for the full circumference. 

At 2/32 inch, the tread is effectively finished for safe wet-weather use, which is why the built-in wear bars and the penny test line up with that replacement threshold.

Many tyre professionals replace earlier for wet performance, often around 4/32 inch, which is about 3.2 mm, since water clearance and wet grip drop before the legal limit. 

What matters most for winter and heavy rain

For winter driving and heavy rain, tread depth is about drainage headroom. A tyre with shallow grooves can look fine in dry conditions, then lose confidence fast when roads shine with standing water, slush, or salted wet film.

If you see frequent heavy rain, rural standing water, or motorway spray, aim to keep tyres above the legal minimum by a meaningful margin. That gives more consistent wet braking and a more predictable steering response.

Tread depth is only one factor in winter grip, yet it is the one you can measure in your driveway in minutes.

Extra checks that belong in a proper tread inspection

A tread check done properly includes tyre condition, not just depth.

Inspect sidewalls, shoulders, and the contact patch

Look for cuts, bulges, cracking, and exposed cords. A tyre can have acceptable tread depth and still be unsafe due to sidewall damage or impact bubbles.

Scan the shoulder blocks for tearing or feathering, which can signal alignment or pressure issues. Shoulder damage often shows up before depth reaches the legal limit.

Run your hand lightly across the tread blocks. If one direction feels smooth and the other feels sharp, that feathering often points toward alignment drift.

Check age and heat damage signs

Tread depth does not tell you the tyre’s age or compound health. If a tyre is old, hardened, or cracked, it can lose grip even with plenty of tread.

Look for small cracks between tread blocks and around the sidewall lettering. If you see widespread cracking, replacement is usually the sensible call.

Heat damage can show as chunking or missing pieces on the tread blocks, often from hard driving on underinflated tyres.

Document your readings like a mechanic would

Write down tread depth by tyre position: front left, front right, rear left, rear right. Record inner, centre, outer readings.

Repeat monthly, or more often if you do high mileage, winter driving, or carry heavy loads. Trends matter more than one snapshot, since the trend shows whether the car is chewing tyres unevenly.

A simple log makes it easier to decide when alignment work is due and helps avoid buying tyres early while a hidden geometry issue destroys them.

Checking tread properly, then replacing tyres before they fall below safe wet weather depth, is one of the simplest ways to protect your family because it directly improves braking, steering control, and stability when the road surface turns cold and slick.

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