Can a puncture be repaired, or do you need a new tyre?

The short answer: a car tyre puncture can normally be repaired if the damage is in the central three-quarters of the tread, is no more than about 6mm across, and the tyre has not been driven on while flat. Sidewall and shoulder damage is never repairable.

The repairable area

Picture the tread split across its width into four strips. The outer strip on each side — the shoulders — is off limits. Only the middle section can take a repair, because that is the part of the tyre that stays flat against the road and is backed by the full casing structure.

Move outwards into the shoulder and the rubber is flexing constantly as the tyre rolls and corners. A plug there works loose. That is why a reputable fitter will refuse a repair that a tyre-sealant advert implies is fine.

Damage that can never be repaired

• Sidewall damage of any kind. Cuts, splits or a nail through the side. The sidewall does the flexing, and there is no way to patch it that survives.
• A bulge or egg. This means the internal cords have already snapped, usually from a pothole or kerb. The tyre is structurally finished even though it is holding air.
• Anything driven on while flat. Running a deflated tyre grinds the inner liner to dust within a few hundred yards. It may look fine from outside and be scrap inside.
• A tyre already at or near the legal limit. Repairing a tyre with 2mm left is money you will spend again in a month.
• Multiple repairs close together, or a second repair overlapping an existing one.

What a proper repair involves

A correct repair is done from the inside. The tyre comes off the rim so the fitter can inspect the inner liner — which is the only way to see whether the casing has been damaged. The hole is prepared and sealed with a combined plug and patch, then the wheel is rebalanced.

An external plug pushed in without removing the tyre is a roadside get-you-home measure, not a repair. If someone offers that as a permanent fix, be sceptical.

Why we will sometimes tell you it is repairable

It is worth saying plainly: a repair is cheaper for you and less profitable for us. If we say a tyre needs replacing, it is because of where the damage is, not because we would rather sell you a tyre. Ask us to show you — the position of the damage is visible and you can judge it yourself.

What about sealant kits?

The aerosol kits supplied in place of a spare will get a small tread puncture holding air long enough to reach somewhere safe. They are a mobility aid. The tyre still has to be inspected and usually replaced afterwards, and the sealant has to be cleaned out of the rim and the valve.

Not sure which you have?

Send us a photo of the damage before we come out and we will usually be able to tell you over the phone. Call 07989 606060, or read more about our mobile puncture repair service.