Mobile Puncture Repair in Oxford & Oxfordshire

What BS AU 159 actually allows

BS AU 159, the British Standard every reputable fitter works to, sets out exactly where a car tyre may and may not be repaired. It exists because a badly placed repair can fail at motorway speed, and because an external string plug pushed in without removing the tyre tells you nothing about the state of the inside.

In broad terms, a car tyre may be repaired only when the injury sits within the central three quarters of the tread width — the "minor repair area" — and the hole is no larger than 6 mm in diameter. The tyre must be removed from the wheel and inspected internally, the repair must be made from the inside with a combination plug and patch that fills the injury and seals the liner, and repairs must not overlap each other.

• Injury within the central three quarters of the tread — never the shoulder or sidewall
• Injury diameter no greater than 6 mm on a passenger car tyre
• Tyre demounted and inspected internally, every time
• Repaired from the inside with a combination plug and patch
• No overlapping repairs

When a puncture cannot be repaired

This is the part most people want a straight answer on, so here it is. We will not repair, and no reputable fitter should, in any of the following cases.

It is worth saying plainly: the most common reason a perfectly repairable nail becomes a new tyre is that the car was driven on it while flat. A few hundred metres at low speed is usually survivable. A few miles is not — the sidewall folds over on itself and the internal cords are destroyed even though the outside still looks fine. If you have a puncture, stop somewhere safe and call rather than trying to reach home.

• Damage in the sidewall or shoulder, including kerbing cuts and bulges
• Any bulge, lump or egg — that is a broken cord, not a surface mark
• Evidence the tyre has been run flat or very underinflated (a grey or powdery inner liner, or folded cord lines)
• Exposed, damaged or corroded cords
• Tread already at or below the 1.6 mm legal limit
• A previous repair that was done badly, or that the new injury overlaps
• Perished, crazed or age-hardened rubber, or bead damage
• Most run-flat tyres, where the manufacturer prohibits repair

Slow punctures, and the ones that are not punctures at all

If a tyre loses a few psi a week, it is worth finding out why rather than topping it up forever. A genuinely slow leak is often a small nail that has partly sealed itself, but a surprising share of "slow punctures" turn out to be nothing to do with the tread. Corrosion on the rim where the bead seats is very common on alloy wheels once they are a few years old, and a perished valve or a leaking TPMS sensor seal accounts for many of the rest.

Because we take the tyre off the rim anyway, we find those. A bead leak is cleaned up and resealed; a tired valve is replaced as standard with every repair we do. Driving around persistently underinflated is not a small thing — it wears the shoulders of the tyre, raises fuel consumption, and significantly increases the chance of a blowout on a hot motorway run.

What about the sealant in my boot?

Many cars now ship with a sealant canister and a compressor instead of a spare. They are a genuine get-you-home tool for a small tread puncture, and there is no shame in using one. Be aware of two things, though. Sealant is a temporary fix, usually rated for a limited distance and a reduced speed, and it is not a repair — the tyre still needs to come off and be assessed properly afterwards.

Sealant also coats the inside of the tyre and, in many cars, the TPMS sensor. Tell us if you have used it so we can clean the liner properly before repairing and check the sensor. It does not automatically write the tyre off, but a liner full of gel cannot be patched until it is cleaned back to bare rubber.