Premier Motors KY — Buying a used car from a | premiermotorsky.com
Tread depth tells you how much grip is left; the DOT code tells you how much time is left — a used set has to pass both.
The legal minimum tread depth is 1.6 mm (2/32 in) in both the US and the UK, and the tire carries its own gauge: tread-wear indicator bars molded across the main grooves sit at exactly 1.6 mm. When the surrounding tread runs flush with those bars, the tire is at the legal floor and done.
For wet roads the working line is higher. Replacement is urged once depth reaches 3 mm (4/32 in), because wet grip falls off well before the legal minimum. A tire at 2 mm is legal and still a bad bet for a rainy season — judge the set by its worst groove, not its best.
On narrow screens, swipe or scroll the plate sideways.
The date lives in the DOT stamp on the sidewall. The last four digits encode the week and year of manufacture: '2521' is the 25th week of 2021. Tires over six years old should be inspected yearly regardless of remaining tread, and ten years is the common retirement limit even if the grooves look deep.
Pressure is the third reading, and it comes from the driver's door-jamb sticker, not the sidewall. Typical figures are 2.2-2.4 bar (32-35 psi), and tires lose roughly 0.1 bar (1-2 psi) per month to natural permeation, so check cold pressure at least every two weeks.
Putting it together for a used car: depth above 3 mm and an age under six years means the set is worth another season; depth between 1.6 and 3 mm, or an age past six years, reprices the deal; tread flush with the bars or a ten-year-old date ends it. The full checklist on this site shows where these lines sit in the wider inspection, and the test-drive guide covers how the tires behave on the road.
Further reading