A puncture does not automatically mean a replacement tyre. A fitter may be able to make a permanent repair when the injury is within the permitted area and the removed tyre passes inspection. The decision cannot be made from the nail size or remaining tread alone.
What the inspection needs to establish
The fitter checks the injury location and prepared size, then examines the tyre inside and out. Routine minor-repair guidance includes a maximum prepared penetration diameter of 6mm, but diameter is only one condition. The appropriate repair area, the injury's path and the tyre's overall condition matter too.
Structural damage, separation, exposed reinforcement and damage associated with deflated running can rule out repair. Earlier repairs also need inspection. Do not assume a second puncture automatically means rejection, or that a tyre with no earlier repair must be suitable.
Why the tyre must come off
A tyre can lose pressure slowly enough that the driver does not notice the damage caused while it was underinflated. Internal inspection is therefore essential. Simply finding the leak and sealing the outside misses part of the assessment.
Tell the fitter about any flat running, warning lights, temporary sealant or plug. That history helps them interpret what they find.
What a permanent repair involves
The injury needs an appropriate approved repair system addressing the penetration and the inner surface. A suitable combination unit is one method; the repair guidance also recognises appropriate separate components. An external string plug or liquid sealant is not the equivalent of that permanent workshop repair.
A repair does not make an otherwise worn or structurally damaged tyre suitable for continued use. Run-flat and other specialised products may also have manufacturer restrictions.
Repair or replacement: making the decision
Ask the garage to explain the inspection finding and the price before authorising work. If repair is refused, ask whether the reason is the tyre's condition, manufacturer guidance or a service the garage does not offer. Do not drive on a potentially unsafe tyre to shop for a different answer.
For a replacement, confirm the full specification and whether the vehicle requires a matched pair or another arrangement. An isolated puncture should not distract from checking the condition of the remaining tyres.