Sidewall damage needs to be assessed separately from tread wear. A tyre can have deep tread and still be unsafe because of a cut, outward bulge or damaged reinforcement. A light surface scuff is not the same as a structural injury, but photographs and remaining pressure cannot establish that distinction reliably in every case.
What the sidewall does
The sidewall is part of the tyre's load-supporting structure and includes reinforcement. It is not simply an unreinforced rubber cover. It flexes during use, so the position and depth of an injury matter.
Kerb contact, impacts, rubbing and driving while deflated can damage this area. The visible mark may not show the full extent of the injury inside the tyre.
Scuffs, cuts and bulges
A superficial scrape may affect only the surface rubber. A deeper cut, exposed cords or a new outward swelling needs prompt professional attention. Do not cut away rubber or probe the injury to decide its depth yourself.
A shallow inward indentation can be associated with radial tyre construction. It should not be confused with an outward bulge, especially one that appeared after an impact. If unsure, have the tyre inspected rather than deciding from the shape alone.
Can the sidewall be repaired?
A routine passenger-car puncture repair is confined to the permitted minor-repair area. It is not an appropriate way to repair a structural sidewall injury. A tyre with such damage normally needs replacement following assessment.
The reason is not that the sidewall contains no reinforcement. It is that the injury affects a demanding part of the structure and falls outside the routine repair criteria. A plug or sealant cannot restore damaged reinforcement.
What to do next
If there is a bulge, exposed reinforcement, serious damage or a flat tyre, stop safely and arrange assistance. Do not drive to test whether it still feels normal. If the vehicle is exposed to traffic, follow the breakdown procedure for that road instead of inspecting it in a dangerous position.
After an impact, ask for the wheel and associated components to be checked as well. Replacing the tyre without identifying a damaged wheel or rubbing problem can leave the cause unresolved.