Your tyres are the only part of your car in contact with the road. At motorway speeds on a wet A1 or M62, four tyre contact patches — each about the size of a hand — are all that stands between you and a serious incident. Tread depth directly determines how quickly those patches can push water out of the way and maintain grip. It is, bluntly, one of the most important safety checks you can do.
The 20p Test
The quickest way to check. Take a 20 pence coin and push it into the main tread grooves of your tyre. If the outer band of the coin — the thin rim around the edge — is hidden by the tread, you're above the legal minimum. If you can see the outer band clearly, your tread is below 1.6mm and the tyre is illegal.
Check at least three points across the width of the tyre, and do it in multiple locations around the circumference. Tyres wear unevenly — particularly if your tracking or tyre pressure has been off — and a tyre can be legal in one spot while illegal at another.
The problem with 1.6mm: At 1.6mm on a wet road at 70mph, stopping distances are nearly double those of a new tyre at 8mm depth. The AA and most tyre manufacturers recommend replacing at 3mm for this reason. It's not the law — but it is the sensible threshold.
Tread Wear Indicators (TWIs)
Every modern tyre has built-in tread wear indicators — small raised bars moulded into the base of the main tread grooves. They're set at exactly 1.6mm. When your tread is level with these bars, the tyre is at the legal limit and needs replacing immediately.
Look for the TWI marker on the tyre sidewall — it's usually indicated by an arrow, a triangle, or the letters "TWI". Follow it around to find the indicator in the groove. Easy to check, impossible to argue with.
Uneven Wear Patterns: What They Mean
How your tyre wears tells a story. Centre wear — where the middle of the tread wears faster than the edges — typically means overinflation. Edge wear — both shoulders wearing faster than the centre — points to chronic underinflation. One-sided wear usually means poor wheel alignment or camber issues. Patchy, flat-spotted wear can indicate a locking brake or a suspension problem.
Don't just check depth. Look at the wear pattern. Uneven wear often means a mechanical problem that will eat your new tyres just as fast as your old ones if it isn't fixed before the replacement.
How Often Should You Check?
Once a month is the right cadence. It takes ninety seconds and a 20p coin. You should also check:
- Before any long motorway journey
- After a significant pothole impact
- If you notice any change in handling, braking, or road noise
- When the seasons change — tread becomes more critical as temperatures drop and roads get wetter
Do You Need a Tread Depth Gauge?
A proper tread depth gauge costs about £3 from any motor factor and gives you an accurate reading in millimetres. The 20p test is good enough for a pass/fail check, but a gauge gives you visibility of where you are in the safe zone. If you're at 4mm, you know you've got some life left. If you're at 2.1mm, you know you're close to the legal limit and should budget for replacements soon.
We check tread depth on every tyre as part of every job — whether you've called us for a puncture repair, a new fitting, or wheel balancing. If we see a tyre that's borderline, we'll tell you and give you an honest assessment rather than a hard sell.
If your tyres are at 3mm or below, or if you're not sure what you're looking at, book a free check or call us on 07814 095 395. We cover all of Leeds, West Yorkshire and North Yorkshire and can usually be with you the same day.
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