A cut is a type of damage to the sidewall or tread of the tyre. On close inspection, it looks like a gouge or rip in the surface of the rubber. The presence of a cut has a significant impact on tyre safety, and it doesn't occur through ordinary wear and tear.
A cut in the sidewall of the tyre is especially troublesome; the sidewall is the part of the tyre that withstands pressure and keeps your car stable. If you find a tear, nick, or bulge in the sidewall, it's typically a sign of damage to the structural integrity of the tyre, and a blowout may be imminent.
The cause of a cut is usually external influences; potholes in the road, protruding bodywork parts, or sharp, foreign objects like stones or glass. They may not cause a puncture when your car drives over them, but are still long-term consequences for the tyre.
Avoid tyre damage such as this by not driving your car on rough or unpaved roads. And if an unpaved road is unavoidable, then try not to drive too aggressively.
Another tip is to avoid coming into contact with kerbs. A rough scrape against a kerb or pavement when attempting to park, for example, could lead to a cut in the sidewall and long-term damage.
Finally, regularly inspect your car tyres for debris wedged in the tread. If these are left unattended, they will cause lasting tyre damage. The quicker they're spotted and prised out, the fewer chances of permanent problems.
Important to note is that the inside of a tyre contains ply and cords which can become exposed if the tyre has a deep cut in the tread or sidewall.
According to UK road law, if a tyre cut is 25mm or 10% of section width – whichever is greater – then these are grounds for instant MOT (Ministry of Transport) test failure. A cut of this size is considered deep enough to reach the ply and cords.
If you discover a cut on the tyre surface before your MOT test, either on the sidewall or the tread, then it's advisable to replace it with a new tyre. An attempt to have it repaired is not recommended, and for the sake of tyre safety it mustn't be ignored.
When buying the new tyre, ensure that it matches the tread on the same axis; it's also essential that it's the same size as the others and follows manufacturer guidelines.
If in doubt, visit your local tyre dealer and have your tyre condition assessed by an expert.