Can my puncture be repaired, or does the tyre have to be replaced?
Where on a tyre a repair is legally permitted, the size limit, why sidewalls and shoulders can never be repaired, and what a run-flat or a sealant kit changes.
- Difficulty
- beginner
- Time
- 12 min
- Read
- 5 min
- Safety
- warning
Short answer
A puncture can be repaired only if the damage is inside the central portion of the tread — the minor repair area defined by British Standard BS AU 159 — and no larger than the standard's limit, 6 mm across for a car tyre. Anything in the shoulder or sidewall, anything larger, a tyre driven on flat, and in almost all cases a run-flat, must be replaced. A proper repair is done from inside with the tyre off the wheel; an external plug is not a legal repair.
This is one of the few areas of car ownership with a genuine published standard behind it, and knowing it protects you in both directions. It stops you being talked into a new tyre when a repair is legitimate, and it stops you pressing a fitter to do something they are not allowed to do. The standard exists because a tyre is a pressure vessel whose sidewall flexes on every rotation. A patch in the tread sits in an area that barely moves and is backed by steel belts. The same patch in a sidewall is on a surface that bends thousands of times a minute, and it peels.
Safety
Step by step
- Find where the damage actually is.The repairable zone is the central band of the tread. British Standard BS AU 159 defines it as the middle three-quarters of the tread width for a car tyre — the shoulders, where the tread curves over towards the sidewall, are outside it, as is every part of the sidewall.
- Measure the size of the injury.The standard sets a maximum damage diameter for passenger car tyres of 6 mm. A nail hole is comfortably inside that; a screw that has been driven over repeatedly, a cut, or a tear is often not. A fitter measures it after removing the object.
- Be honest about whether it was driven on flat.This is the question people answer optimistically and it matters more than anything else here. Running a tyre at very low pressure destroys the inner liner and the sidewall structure invisibly. A tyre that has been driven on flat should be scrapped, and any competent fitter will look for the tell-tale rubber dust inside.
- Check whether it is a run-flat.Run-flats have reinforced sidewalls designed to support the car with no pressure at all, and they are marked with codes such as RSC, RFT, ZP, SSR or DSST on the sidewall. Most manufacturers and most of the industry say run-flats should not be repaired after deflation, because there is no way to tell how far the reinforced sidewall has been compressed.
- Understand what a proper repair involves.The tyre comes off the wheel, the inside is inspected for hidden damage, the injury is cleaned and reamed, and a combination plug-and-patch unit is fitted from the inside, sealing both the hole and the inner liner. It is a workshop job of fifteen or twenty minutes and it is cheap.
- Treat external plug kits as temporary only.The sticky rope plugs sold for pushing into a tyre from outside do not seal the inner liner and do not allow the inside to be inspected. They will get you home. They are not a repair, they are not legal as a permanent fix, and any fitter will remove one before doing the job properly.
- Tell the fitter if you have used a sealant kit.Aerosol sealant coats the inside of the tyre and the pressure sensor. Fitters need to know before they break the bead, and some sealants make a permanent repair impossible. Not mentioning it wastes their time and sometimes ruins a repairable tyre.
- Ask how many repairs the tyre already has.The standard also limits how many repairs a tyre may carry and how close together they may be. A tyre with existing repairs may not be repairable again, which is a legitimate reason for a refusal that sounds like an upsell.
Common mistakes
- Driving on a flat tyre to reach a garage — It destroys a tyre that might have been repairable, wrecks the inner liner, and can damage the wheel. It also risks the tyre coming off the rim. A few hundred metres at walking pace to get off a carriageway is a safety decision; anything more is not.
- Leaving an external plug in place indefinitely — It has not sealed the inner liner and nobody has inspected the inside of the tyre. Air is still slowly permeating and any internal damage is undiscovered.
If it doesn't work
Nail in the tread, tyre still holding most of its pressure
Cause: A classic repairable puncture, if it is in the minor repair area — Fix: Leave the nail in place — it is partly sealing the hole — inflate to the correct pressure and drive gently straight to a tyre bay. Pulling it out on the driveway turns a slow leak into a flat.
Bulge or egg-shaped swelling on the sidewall
Cause: Internal structural damage, usually from a pothole or kerb impact — Fix: Not repairable under any circumstances, and genuinely dangerous — the carcass cords have snapped and only the rubber is holding the pressure. Replace it, and have the other side and the alignment checked.
Cut or gouge in the sidewall
Cause: Kerbing, or debris — Fix: Not repairable. Any cut deep enough to show cords means replacement. A superficial scuff on the sidewall lettering is different and usually fine.
Tyre fitter says the repair is too close to the shoulder
Cause: The damage is outside the minor repair area — Fix: This is a standards judgement, not a sales pitch. If you want a second opinion, ask them to show you where the boundary falls on that tyre — a reputable fitter will.
Repair done, tyre goes down again over a week
Cause: A second puncture, a corroded rim, or a faulty valve — Fix: Take it back. A properly done repair does not leak. The catalogue's guide on a tyre that keeps losing pressure covers the alternatives.
Questions people ask
Is a tyre repair legal in the UK?
Yes, when it complies with British Standard BS AU 159, which sets out the minor repair area, the maximum damage size, and how the repair must be carried out. A repair outside those limits makes the tyre non-compliant, which affects roadworthiness and can affect an insurance claim.
Can a run-flat tyre be repaired?
Almost always no. Most tyre manufacturers and the run-flat industry position is that once the tyre has been driven on deflated there is no reliable way to assess whether the reinforced sidewall has been damaged, so it should be replaced. A few manufacturers permit repair under narrow conditions; check the specific tyre.
How much does a puncture repair cost compared with a new tyre?
A repair is a small fraction of the cost of a tyre, which is exactly why it is worth knowing when one is permitted. It is also why an unnecessary refusal is worth questioning politely — ask them to show you where the damage sits relative to the repair area.