Puncture: can it be repaired, or does it need replacing?
Five questions. Where the damage is matters more than how big it is — and one of these answers rules out a repair on its own, no matter how small the hole.
Where the damage sits decides almost everything
A tyre is not a uniform object. The central tread is thick, backed by steel belts and relatively rigid. The sidewall is thin and flexes through its whole shape thousands of times a minute. That difference is why a repair works in one place and can never work in the other.
British Standard practice limits repairs to a defined central area of the tread, with a maximum damage size of around 6 mm. Outside that area — on the shoulder or anywhere on the sidewall — no repair is permitted, however small and tidy the hole looks. A plug in a flexing sidewall will work loose, and the failure when it does tends to be sudden rather than gradual.
Driving on a flat destroys the tyre from the inside
This is the answer that surprises people most, because the outside of the tyre can look untouched.
When a tyre runs deflated, the sidewall folds over on itself and the inner liner is ground against the casing. That shreds the internal structure and leaves a fine black dust inside. A fitter finds it the moment the tyre comes off the rim, and at that point no repair is permissible — the tyre has already been structurally compromised even though the tread looks perfect.
If you pick up a puncture, that is the argument for not driving to a garage on it. Getting off a live carriageway to somewhere safe is right; carrying on for miles is what converts a repairable puncture into a new tyre.
Two special cases
Run-flat tyres. Marked RFT, ROF, ZP, SSR, DSST, EMT or RSC depending on the manufacturer, these have reinforced sidewalls that let you keep driving for a limited distance after losing pressure. Most manufacturers do not permit them to be repaired, precisely because the tyre may already have run deflated without the driver noticing much.
Sealant kits. Many cars now carry a bottle of sealant instead of a spare wheel. It will usually get you home, but it is a temporary measure rather than a repair, and it does not change whether the tyre can be properly repaired afterwards. Tell whoever removes the tyre that sealant has been used.
Whatever the outcome, check the tread while you are there — our guide to tread depth and the UK legal limit covers the 20p test, and the tyre size decoder tells you what to order if it needs replacing.
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Do not drive on it if you can avoid it. Our mobile tyre fitting service comes to your home, work or the roadside across North Wales, and we will tell you honestly whether it needs a repair or a replacement once we can see it.
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Questions, answered
Can a tyre with a nail in it be repaired?
Often yes, if the nail is in the central tread area, the damage is around 6 mm or less, the tyre has not been driven on while flat and it is not a run-flat. Punctures in the shoulder or sidewall cannot be repaired at all.
Why can't a sidewall puncture be repaired?
The sidewall flexes constantly as the tyre rotates, so a patch or plug there cannot hold. Repairs are only permitted within a defined central area of the tread, where the tyre is thicker and supported by steel belts.
Can I repair a tyre I drove on while flat?
No. Running a tyre deflated grinds the inner liner against the casing and destroys the internal structure, leaving fine black dust inside. The outside can look perfect while the tyre is structurally ruined, which is why a fitter checks the inside once it is off the rim.
Can run-flat tyres be repaired?
Most manufacturers say no. Because a run-flat can be driven on while deflated without the driver noticing, the reinforced sidewall may already have been damaged. Check the sidewall for RFT, ROF, ZP, SSR, DSST, EMT or RSC markings.
How big a puncture can be repaired?
Around 6 mm across is the usual maximum within the repairable central tread area. Anything larger, or any cut, slash or tear, means the tyre must be replaced.
Does tyre sealant count as a repair?
No. Sealant from a puncture kit is a temporary measure to get you home, not a permanent repair. Tell whoever removes the tyre that sealant has been used, and have the tyre properly inspected and repaired or replaced.
Is it cheaper to repair than replace?
Usually, yes, and a proper repair is perfectly safe when the damage qualifies. If the tread is already close to the replacement point, though, paying to repair can be false economy since the tyre will need changing soon anyway.