MOT defect file
Tyre damaged or deteriorated
Last updated
Quick answer
The tyre has a cut, bulge or perishing sidewall. This cannot be repaired — the tyre needs replacing.
- Typical cost
- £70–£160 per tyre
- DIY viability
- Garage job
What you might notice
- A bulge or egg-shaped swelling in the sidewall, usually appearing after a pothole or a kerb strike
- Fine cracking across the sidewall or between the tread blocks on a tyre that has aged rather than worn
- A slow puncture that keeps returning, or a tyre needing topping up every couple of weeks
- Nothing visible from the kerb — inner sidewall damage only shows itself on full lock or from underneath
What causes it
- Kerbing or a pothole impact snapping some of the casing cords, so air pressure pushes the sidewall outwards
- Age: rubber hardens and crazes after roughly six to ten years regardless of mileage, which is why low-mileage cars fail on tyres
- Persistent under-inflation flexing the sidewall until the structure breaks down internally
- Contact with oil or fuel, or rubbing against a displaced arch liner or a worn suspension component
Advisory or failure?
Superficial crazing of the rubber that does not reach the casing is generally recorded as an advisory. Damage becomes a major defect once the tyre is cut, torn or perished more seriously than that. It is a dangerous defect — and one of the most common reasons a car is failed as dangerous — where ply or cord is exposed or damaged, where there is a lump, bulge or tear caused by the casing separating, or where a cut is longer than 25mm or 10% of the tyre's section width, whichever is greater, and deep enough to reach the cords.
Can you fix it yourself?
Garage job
Fitting requires a tyre machine and the wheel must be rebalanced afterwards, so the replacement itself is never a home job. Inspecting is, and it is worth doing: turn the wheels to full lock and look at the inner sidewalls, where kerb damage and rubbing hide, and check the four-digit date code moulded into the sidewall — 3419 means the thirty-fourth week of 2019. Know what cannot be fixed: a sidewall cut or bulge is never repairable, and only a puncture within the central three-quarters of the tread can be plugged, to BS AU 159.
What it costs
A budget tyre in a common 15 or 16 inch size is around £55 to £75 fitted, balanced and with a new valve; mid-range and premium in the same size run £85 to £130. You reach the top of the band with larger diameters, low-profile and run-flat fitments, and where a tyre pressure sensor has to be serviced or replaced at the same time. Replace in pairs across an axle if the surviving tyre is also part-worn, and where the damage came from rubbing rather than an impact, have the alignment and suspension checked or the new tyre will go the same way.
What happens if you ignore it
A damaged carcass tends to fail suddenly rather than deflate gradually, and a front tyre letting go at speed takes the steering with it. The legal position matches that for a bald tyre: up to £2,500 and three penalty points, applied per tyre, so a full set can put a licence past the twelve-point threshold in a single stop. An insurer presented with a claim involving a tyre the owner knew was damaged has firm ground to argue from.
This is general guidance, not a diagnosis. The severity DVSA records depends on the specific fault found, so the same item can appear as an advisory on one test and a failure on another. Ask a qualified tester or mechanic to inspect the vehicle.
Has this been recorded on your car?
Check the full MOT history for any UK registration.