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.
Wording as it commonly appears on an MOT certificate: “Tyre has a cut, lump, bulge or tear caused by separation or partial failure of its structure”.
What does it mean?
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.
How serious is it?
Usually recorded as: Dangerous. The tester assesses the actual vehicle on the day, so your certificate is what counts.
What normally causes it?
- A hard pothole or kerb strike, which pinches the sidewall against the rim and snaps the cords
- Long-term under-inflation flexing the sidewall
- Kerbing that scrubs the sidewall rubber away
- Impact damage that only shows up as a bulge days or weeks later
What a mechanic would check
Run a hand slowly over both sidewalls with the wheel turning — bulges are easier to feel than see. I'd also check the inner sidewall, which you can't see with the wheel on the car, and look at the wheel rim for a matching flat spot from the same impact.
What might need replacing
- That tyre replaced — structural damage is never repairable
- The wheel checked for buckling from the same impact
Can you still drive it?
This is normally recorded as Dangerous, and it deserves it. A structurally damaged tyre can let go at speed with no warning. Don't drive on it — change to the spare or get it recovered.
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This is general guidance from a UK mechanic, not a substitute for a physical inspection. Only the tester who inspected your vehicle can confirm what was recorded and why.