Can Your Punctured Tyre Be Repaired, or Does It Need Replacing?

Not every puncture means a new tyre

A puncture does not automatically mean you need a new tyre. Many are safely repairable, and a proper repair is a permanent, legal fix — not a temporary bodge. But there are strict limits on what can be repaired, and those limits exist for good safety reasons. A tyre is the only thing connecting your car to the road, so it is worth understanding the rules before deciding.

In the UK, permanent tyre repairs are carried out to a recognised standard, BS AU 159. A repair that meets this standard involves removing the tyre from the wheel, inspecting it inside and out, and fitting a combined plug-and-patch from the inside — not simply pushing a string plug in from the outside. Anything less is not a compliant repair.

The minor repair area: where a puncture can be fixed

Whether a puncture is repairable depends largely on where it is. A tyre has a defined minor repair area, which is the central three-quarters of the tread. A puncture within this central band, in the part of the tyre that meets the road, can usually be repaired. A puncture in the shoulder or the sidewall — the outer edges and the flexing side wall of the tyre — cannot be repaired and means the tyre must be replaced.

The reason is that the sidewall and shoulder flex constantly as the tyre rolls and carries load. A repair there would be under continuous stress and could fail suddenly. That is why even a small, neat nail hole in the sidewall is an automatic replacement.

Size and condition limits

Location is not the only factor. For a puncture to be repairable it must also meet size and condition limits:

• The puncture must be no more than 6mm in diameter. Larger holes, splits or tears are not repairable.
• The tyre must not have been run flat or badly underinflated. Driving on a flat or very soft tyre, even a short distance, generates heat and flexing that causes hidden internal damage to the sidewall lining — often invisible from the outside, but enough to make the tyre unsafe to repair.
• The tyre must be otherwise sound, with no existing damage, perishing, cracking, bulges or previous poor repairs.

This is why a fitter always inspects the inside of the tyre. A tyre can look fine externally but show tell-tale internal damage that rules out a repair.

When a tyre must be replaced

Some findings mean the tyre has to be replaced, with no repair possible. Replace the tyre if there is:

• A sidewall or shoulder puncture of any size.
• A bulge, blister or egg-shaped lump in the sidewall — a sign the internal structure has been damaged, often after hitting a kerb or pothole.
• Cracking or perishing of the rubber, common on older tyres.
• A tyre that has been driven on while flat or run-flat, including a genuine run-flat tyre that has been used beyond its designed limited distance and speed.
• A puncture larger than 6mm, or multiple punctures close together.

In these cases replacing the tyre is not being cautious for the sake of it — it is the only safe and legal option.

The tread depth law

Even a healthy, unpunctured tyre becomes illegal once it is too worn. The UK legal minimum tread depth for cars is 1.6mm, and that must be met across the central three-quarters of the tread and around the entire circumference of the tyre. It is not enough for one patch to have tread; the whole central band has to be above the limit all the way round.

Driving on tyres below 1.6mm is an offence that can carry a fine and penalty points for each illegal tyre, and it will fail an MOT. Many manufacturers and safety bodies recommend replacing well before the legal limit — around 3mm — because wet grip and stopping distances deteriorate noticeably as tread wears down.

The 20p test

You do not need special tools to get a rough idea of your tread. The 20p test is a quick check anyone can do. Take a 20 pence coin and insert it into the main grooves of the tyre. If the outer band of the coin is hidden by the tread, your tread is likely above the legal minimum. If you can see the outer band of the coin, your tread may be below 1.6mm and the tyre should be checked properly and probably replaced.

Do the 20p test at several points around the tyre and across its width, because tyres often wear unevenly. Uneven wear on one edge can also point to a tracking, alignment or pressure problem worth investigating.

Getting it checked or replaced

If you have picked up a puncture, the honest answer to "can it be repaired?" is: it depends on where the puncture is, how big it is, and whether the tyre has been run flat. A proper inspection is the only way to know for certain, and a good fitter will tell you plainly whether a compliant BS AU 159 repair is possible or whether replacement is the safe course.

We can come to you, assess the tyre against these rules, and either carry out a compliant repair or fit a replacement at the roadside or on your driveway. To arrange a mobile tyre check or replacement, call 07737477003.