The MOT Files

MOT defect file

Tyre ply or cord exposed, or the casing separating

Last updated

Quick answer

The tyre's internal structure has failed — cords or ply are showing through the rubber, or the casing has begun to come apart. This is graded dangerous outright, and the tyre cannot be repaired.

Typical cost
£70–£160 per tyre
DIY viability
Garage job
Tyre wall cut through to the reinforcing cordA straightened section through a tyre wall shows tread blocks joined continuously to the outer rubber, a distinct reinforcing ply band containing closely spaced parallel cords, and the inner liner below. A deep V-shaped cut passes through a tread block and all of the covering rubber until it reaches and exposes the cord band. The remaining tread blocks do not alter the result: visible or damaged ply or cord is a major MOT defect.Remaining tread blocksCord exposed by cutReinforcing ply and cordInner linerExposed cord = major defect, whatever the tread depth
If any tyre ply or cord is exposed or damaged, the tyre has a major defect regardless of its remaining tread depth. The curved tyre wall is straightened and the layers and cut are enlarged here for clarity, not shown to scale.

What you might notice

  • Woven strands of steel or fabric visible in the base of a cut, or through a worn patch on the shoulder
  • A soft, uneven lump in the sidewall or tread that you can feel by running a hand around the tyre
  • Rhythmic thumping or vibration at low speed that smooths out as you go faster, then returns worse
  • Nothing at all from the driver's seat until the tyre is looked at — inner shoulders are the usual hiding place

What causes it

  • A kerb strike or pothole snapping the casing cords, so the belt separates and the rubber over it wears through
  • Long-term under-inflation flexing the sidewall until the internal structure breaks up
  • A misaligned wheel or a worn suspension arm scrubbing the inner shoulder bare while the visible tread still looks fine
  • A puncture driven on flat, even briefly, which grinds the bead area and the inner liner apart

Advisory or failure?

There is no advisory or minor version of this. A tyre with ply or cord exposed, or with a lump, bulge or tear caused by the casing separating, is a dangerous defect — the most serious grading the test carries — and the vehicle should not be driven away until it is replaced. The same grading applies to a cut longer than 25mm or 10% of the tyre's section width, whichever is greater, that is deep enough to reach the cords. It is worth knowing what sits below that line: tread down to but not below 1.6mm across the central three-quarters of the tread, around the entire circumference, is legal, and superficial crazing of the rubber that does not reach the casing is normally only an advisory. The spare is not inspected, so a spare in this condition will not appear on the certificate at all.

Can you fix it yourself?

Garage job

Nothing about this is repairable, so the only decision is where the tyre gets fitted. A structural repair to a sidewall does not exist, and only a puncture inside the central three-quarters of the tread can be plugged, to BS AU 159. Inspection is genuinely worth doing yourself: turn the wheels to full lock and look at the inner shoulders, which is where scrubbing hides, and run a hand over the whole sidewall rather than trusting your eyes. If you have to move the car at all, put the spare on and drive it to the fitter rather than driving on the damaged tyre.

What it costs

A budget tyre in a common 15 or 16 inch size is £55 to £75 fitted, balanced and with a new valve; mid-range and premium in the same size run £85 to £130. Larger diameters, low-profile fitments and run-flats sit at the top of the band, as does any wheel where a pressure sensor has to be serviced at the same time. Replace across the axle in pairs if the surviving tyre is also part-worn, and where the damage came from scrubbing rather than an impact, pay for an alignment check as well or the new tyre will wear out exactly the same way.

What happens if you ignore it

A tyre in this condition does not go down gradually, it lets go, and a front tyre bursting at speed takes the steering with it. The legal exposure is the same as for a bald tyre: up to £2,500 and three penalty points, applied per tyre, so a car with two like this can lose a licence in one stop. Because a dangerous defect is recorded on the public MOT history, an insurer looking at a claim afterwards has a documented fault the owner was told about in writing.

Common questions

Is exposed ply or cord on a tyre an MOT failure?
Yes, and it carries the most serious grading the test has. A tyre with ply or cord exposed, or with a lump or tear caused by the casing separating, is a dangerous defect, so there is no advisory or minor version of it. The vehicle should not be driven away from the test centre until the tyre has been replaced.
Can a tyre with exposed cord or a sidewall bulge be repaired?
No. There is no such thing as a structural repair to a tyre sidewall, and only a puncture inside the central three-quarters of the tread can legitimately be plugged, to BS AU 159. Once the cords are damaged or the casing has begun to separate, the tyre is scrap and replacement is the only option.
What is the penalty for driving on a dangerous tyre?
Up to £2,500 and three penalty points, and both apply per tyre rather than per vehicle. A car with two tyres in this condition can therefore cost a driver their licence in a single roadside stop. A dangerous defect is also recorded on the vehicle's public MOT history, where an insurer can see it later.
How much does it cost to replace a tyre with exposed cord?
A budget tyre in a common 15 or 16 inch size is £55 to £75 fitted, balanced and with a new valve, while mid-range and premium tyres in the same size run £85 to £130. Larger diameters, low-profile fitments and run-flats sit at the top of the band, and servicing a pressure sensor adds to it.
Why is only the inner edge of my tyre worn down?
Inner shoulder wear usually means a wheel alignment fault or a worn suspension arm scrubbing the tyre away while the tread you can actually see still looks healthy. It is the commonest hiding place for exposed cord. Turn the steering to full lock and look at the inside face of each front tyre, and have the alignment checked as well as the tyre replaced.

Cars this happens to most

Of every model with at least 2,000 tests in the DVSA data, these record tyre ply or cord exposed, or the casing separating on the largest share of their MOTs. Across all of them the typical rate is 1.7% of tests.

  1. Tesla Model X9.3%

    578 times in 6,213 tests

  2. Mercedes-Benz Eqc8.3%

    1,036 times in 12,524 tests

  3. BMW I48.0%

    560 times in 6,958 tests

  4. Mercedes-Benz Eqb7.5%

    239 times in 3,194 tests

  5. Tesla Model Y7.0%

    2,445 times in 34,928 tests

  6. Dacia Jogger5.5%

    182 times in 3,338 tests

  7. Volvo V505.1%

    1,332 times in 26,141 tests

  8. BMW X75.0%

    131 times in 2,595 tests

A high rate here is a property of the fleet as much as the car: these models skew old, and almost everything fails more with age. It is a reason to check the item on a used example, not proof the model is badly built. Models with fewer than 2,000 tests are left out because a rate drawn from a few hundred cars moves too much to rank.

Pass rates for every make and model

The warning light behind this

This defect is what a tester writes down. What you see from the driver’s seat is a symbol, and it is worth checking which one, because manufacturers reuse the same shape for more than one system.

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.

Spaces are optional

Other common defects