A cut becomes serious the moment it reaches the layers that hold the tyre together. While the rubber is thick, a shallow nick may be harmless, but once a cut exposes the internal cords or ply, the tyre is both unsafe and illegal.
When a cut matters
Tyres take knocks from sharp stones, glass, kerbs and road debris, and most leave only surface marks. The concern is depth. A gouge deep enough to reach the fabric or steel cords beneath the rubber has breached the tyre's safety layers, and from that point the tyre can fail under load.
If any wire or fabric is visible poking through the rubber, the tyre is legally unroadworthy and dangerous to drive on. That applies anywhere on the tyre, tread or sidewall.
How the MOT judges a cut
The MOT inspection manual sets out clear criteria for a cut, and they are stricter than many drivers expect:
- Any ply or cord that can be seen without touching the tyre is a fail
- Exposed ply or cord seen when folding back the rubber or gently opening a cut with a blunt instrument is a fail, whatever the size of the cut
- A cut larger than 25mm, or more than 10% of the tyre's width (whichever is greater), where cords can be felt with a probe, is a fail
In short, it is not the length of a cut that fails a tyre but whether it has reached the cords. A short cut that exposes cord fails; a longer, shallow scuff that has not may pass, sometimes with an advisory.
One safeguard exists in the rules: before failing a cut, the tester must be sure it is genuinely the cords they can see or feel, and not a stone or other foreign object lodged in the rubber. If there is doubt, the guidance is to pass and advise.
Repair or replace?
A small cut or puncture confined to the central tread area, that has not exposed the cords, can sometimes be repaired under the proper standard. Anything else cannot. A cut in the sidewall or shoulder, or any cut that has reached the cords, means the tyre must be replaced; there is no safe way to patch it. The detail of the damage that can be repaired is its own subject, covered separately.
When cords are showing, there is no judgement call to make: the tyre comes off and a new one goes on, ordered online from Tyres.co.uk and fitted at a local garage.
From the workshop: people often ask if a cut "looks bad enough" to worry about. My answer is always the same: it is not about how it looks, but about whether it has reached the cords. If I can see the weave, the tyre is finished, however small the cut.
Sources and accuracy. The MOT cut criteria and the exposed-cord rules here reflect the MOT testing requirements at the time of writing, which can change. Anything safety-critical should be confirmed against the current official DVSA guidance. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
Is a tyre illegal if the cords are showing?+
Yes. Any exposed cord or ply makes a tyre unroadworthy and a dangerous MOT failure. It means the protective rubber has been worn or cut through to the structure beneath, and the tyre must be replaced immediately.
How does the MOT judge a cut in a tyre?+
Any ply or cord visible without touching the tyre is a fail. So is exposed cord seen when folding back the rubber or opening a cut, whatever its size. A cut over 25mm or 10% of the tyre's width with cords detectable by probe also fails.
Can a cut tyre be repaired?+
Sometimes, but only a small cut or puncture in the central tread area that has not exposed the cords. Cuts in the sidewall or shoulder, and anything reaching the cords, cannot be repaired and mean replacement.
What is the difference between a cut and an embedded object?+
A cut exposes the tyre's own cords, whereas a nail or stone is a foreign object lodged in the rubber. An MOT tester must confirm it is genuinely the cords showing before failing a tyre, as the two can look similar.