Insurance and liability: the fine print that turns on your tyres
Modification is the second trap. Changing wheel and tyre sizes away from the manufacturer's approved fitments, fitting different sizes front to rear where the maker does not specify it, or deleting run-flats on a car designed around them are all changes an insurer can treat as undeclared modifications. None of this means you can never change anything; it means changes should stay within the approved fitment list in your handbook, and anything beyond it should be declared to the insurer in writing before renewal rather than discovered by a surveyor afterwards.
Liability also runs the other direction, toward the fitter. If a wheel detaches or a repaired tyre fails and the cause is workmanship, the workshop's insurance responds, but only if you can prove who did the work. Keep the invoice, keep the booking record, and photograph the DOT dates of newly fitted tyres. It takes ninety seconds and it converts a hopeless argument into a documented claim. The same records help in the ordinary case too: manufacturer warranties on tyres cover defects, not damage, and the distinction is argued with paperwork, so a dated invoice showing where and when the tyre was fitted is the difference between a goodwill replacement and a shrug.