How old are your tyres?

Every tyre sold in the United States carries four digits that give the week and year it was made. Not the year it was sold, not the year it was fitted — the week it came out of the mould.

It matters more than tread depth for a tyre that has sat still. Rubber ages whether or not it turns, and a tyre with perfect tread and a date ten years back is a different proposition from the same tread on a tyre made last spring.

Where to find it

On the sidewall, in an oval, after the letters DOT. The date is the last group of the number — the groups before it are the plant, the size and the manufacturer’s own code.

Often only one sidewall carries the full number. The regulation allows the other side to carry a shortened version without the date, so if the tyre you are looking at has no date on it, look at the other side before concluding anything.

This one comes from the law, not from a manufacturer

Almost every scheme on this site belongs to a company. This one is 49 CFR 574.5 — a federal regulation, public law, which can be quoted in full here without asking anybody. It is worth knowing how much difference that makes: of the sources behind the rest of this site, most reserve their content and several forbid reproducing it outright.

“The date code, consisting of four numerical symbols, is the final group. The date code must identify the week and year of manufacture. The first and second symbols of the date code must identify the week of the year by using ‘01’ for the first full calendar week in each year, ‘02’ for the second full calendar week, and so on. The calendar week runs from Sunday through the following Saturday. The final week of each year may include no more than six days of the following year.”

The law’s week is a third week, and it agrees with neither of the others

Two other pages here decode a week number and have to show you two answers, because the maker never said which week numbering they meant. Milwaukee give a week. Trane give a week. Neither says whether it is the ISO 8601 week, which starts on Monday and puts week 1 where the first Thursday falls, or the US broadcast week, which starts on Sunday and puts week 1 where 1 January falls.

49 CFR 574.5 answers the question, and its answer is neither of them. Weeks start on Sunday, like the broadcast week — but week 1 is the first full week, so a year that opens mid-week has its first few days in no numbered week at all.

Over the 41 years from 1995 to 2035, the first day of week 1 under the regulation differs from ISO 8601 in 41 of them, and from the US broadcast week in 35. It is not a relabelling of either.

The regulation checks its own homework, so this page checks against it

574.5 does the best thing a specification can do: it works an example.

“For example, 0109 means the tire was manufactured in the first full calendar week of 2009, or the week beginning on Sunday, January 4, 2009, and ending on Saturday, January 10, 2009.”

The decoder above is tested against that sentence rather than against anybody’s reading of the rule that precedes it, including mine. tools-parse-cfr574.py pulls the example out of the regulation, runs the decoder on 0109, and fails if the dates come back different. A rule and a worked example are two chances to be wrong in different directions, and agreeing with both is worth more than agreeing with one.

Two digits of year, and no ambiguity — which is unusual here

A two-digit year normally leaves the century open, and half the pages on this site have to show both. Not this one.

Part 574 was made by 36 FR 1197 on 26 January 1971, which the regulation prints as its own citation. So a 19yy reading has to be 1971 or later, and a 20yy reading has to have happened already. No two-digit number satisfies both, so exactly one reading always fits.

And forty-four of the hundred possible years fit neither. Everything from 27 to 70 is in the future as 20yy and before the rule as 19yy. If your four digits land there, they are almost certainly not the last four of the DOT number — which is a useful thing for a decoder to be able to tell you.

Older tyres, and what this page will not guess

Tyres made before about 2000 are widely said to carry a three-digit date code rather than four. The regulation as it stands today does not mention a three-digit code at all, and does not say when the four-digit form began.

So this page does not decode three digits, and does not date the change. That is the same position the boat page takes about hull numbers before 1984: the current text does not describe the earlier scheme, and filling the gap from memory is how a wrong year gets written down as a fact. If you have a three-digit code, what you know is that the tyre is old enough to be worth replacing on that basis alone.