Tyres are the one MOT category where the rules are genuinely black and white. The minimum legal tread depth for a car in the UK is 1.6mm across the central three-quarters of the tread and around the whole circumference, and there's no arguing with a tread gauge.
Tyres are the one MOT category where the rules are genuinely black and white. The minimum legal tread depth for a car in the UK is 1.6mm across the central three-quarters of the tread and around the whole circumference, and there's no arguing with a tread gauge.
Where it gets less obvious is damage wording: bulges, cuts, exposed cords and 'tyre worn close to the legal limit' as an advisory. Those range from an early warning to a genuinely dangerous defect, and the difference matters.
This section covers the tyre and wheel entries I see most, plus how to work out how long an advisory realistically gives you before it becomes a failure.
Tyre tread depth below the legal limit of 1.6mm
The tread is below the UK legal minimum of 1.6mm, measured across the central three-quarters of the tread width and around the entire circumference. It's a measured, black-and-white item — there's no interpretation involved.
Full explanation of Tyre tread depth below the legal limit of 1.6mm
Tyre has a cut, lump, bulge or tear caused by separation or partial failure of its structure
The structure of the tyre has been damaged. A bulge means the internal cords have broken and only the rubber is holding the air in at that point; exposed cord means the outer rubber has worn or been cut through to the carcass.
Tyre pressure monitoring system inoperative or warning indicating a system malfunction
The TPMS warning is indicating a system fault rather than a low tyre. On cars first used from 2012 onwards this is a testable item, so a permanently lit TPMS light is a failure even when all four tyres are correctly inflated.
Tyres of different sizes, types or structures fitted to the same axle
The two tyres on one axle don't match in a way that matters — different sizes, different construction, or in some cases a significant mismatch in type. The two ends of an axle need to behave the same way under braking and cornering.
Full explanation of Tyres of different sizes, types or structures fitted to the same axle
Tyre worn close to the legal limit on the inner edge
The tyre still has legal tread across most of its width, but one shoulder is worn down. It's usually recorded as an advisory until the worn band drops below 1.6mm across the central three quarters of the tread — at which point it becomes a straight failure. More importantly, it's a symptom: tyres don't wear on one edge for no reason.
Full explanation of Tyre worn close to the legal limit on the inner edge
Wheel nut or stud missing or insecure
A wheel is being held on by fewer fixings than it should be, or one of them isn't doing its job. It sounds trivial next to a corroded subframe, but a wheel coming off at speed is one of the worst failures there is, so it's marked hard.
Full explanation of Wheel nut or stud missing or insecure
Decode your exact MOT wording or browse all MOT failure categories.