MOT, legal tread and inflation

A UK MOT will fail dangerous tyres: cords showing, lumps, cuts, tread below 1.6 mm in the central three-quarters, or mixing radial and cross-ply on an axle. Inflation itself is not a numbered MOT item in the way headlights are, but a clearly flat tyre is a defect.

Correct pressure still matters between tests. A legal groove can sit on a cooked shoulder if the car ran 0.5 bar low all winter.

Mixing brands or sizes on the same axle can also be an issue. Pressure will not make two different diameters work.

Keep a record of checks if you claim on a mileage warranty. A notebook in the glovebox is enough.

If an MOT tester mentions low pressure, treat it as a warning that the next frost will make worse — then set cold to the placard, not to “a bit more.”