Methodology

Where every number on TreadFacts comes from.

Tire date codes

The tire identification number is set by federal regulation, 49 CFR 574.5. Under section 574.5(b)(3) the date code is the final group of four numerals: the first two give the week of the year, the last two give the last two digits of the year of manufacture.

Before a 1999 rule (64 FR 36807, July 8, 1999) the date code had three numerals: two for the week and one for the year, with no decade. In interpretation letter 12375.wkm (1996) NHTSA explained that the single digit is generally read as the most recent year ending in that number. Because every three-digit tire predates the four-digit code, we report it as made before 2000 and give its minimum age.

Age is counted in whole years from the middle of the printed week to today, rounded down.

Recalls

Recall records are the National Highway Traffic Safety Administration's tire recall campaigns, published by the U.S. Department of Transportation and collected by recallsapi.com, PrimeZen LLC's recall data service. TreadFacts uses 314 campaigns dated 2000 or later, copied 2026-10-12 (2026-10-12_tire-recalls_from-recallsapi_v1.json). Brand names are merged into the name printed on the tire (for example B F GOODRICH and BFGOODRICH become BFGoodrich); model names keep the agency's capitals, with the slash restored in tread codes such as A/S.

Tire sizes

Sidewall height = width x aspect ratio / 100. Overall diameter = wheel diameter + 2 x sidewall height (25.4 mm to the inch). Circumference = pi x diameter. Revolutions per mile = 1,609,344 mm / circumference. The speedometer reading assumes the original size, so with a new size the true speed is the reading x new diameter / original diameter. These are design dimensions; a mounted tire under load measures slightly less.