What do the numbers on my tyre mean?

The size on a sidewall — 205/55 R16 91V — is five separate statements. This reads them from UN/ECE Regulation No 30, which is the regulation that defines them.

For the age, you want the other page. That is a different marking under a different regulation, and the tyre date code page reads it.

The speed symbols, and why the table looks wrong

“Speed category” means the maximum speed which the tyre can sustain, expressed by speed category symbol. The regulation prints them in this order:

That order is LMNPQRSTUHVWY, and it is not alphabetical. H sits at 210 km/h, between U at 200 and V at 240. It looks like a misprint and it is not: H was in use before the rest of the sequence was laid out around it.

Any decoder that sorted these symbols, or assumed a later letter means a faster tyre, would put H in the wrong place — between G and I, where nothing is. This page keeps the regulation’s order and never sorts it, and check-r30.js asserts that H still sits between U and V.

The load-capacity indices

All 121, from 0 to 120, in kilograms per tyre:

It is a reference mass, not a budget. The regulation defines the index as “a number associated to the reference mass a tyre can carry when operated in conformity with requirements governing utilization specified by the manufacturer”. Those conditions — pressure above all — are part of the figure rather than a footnote to it.

The rim number is not always inches

This is the part most decoders get wrong by never considering it. Paragraph 2.17.1.3 says the rim diameter is “expressed either by codes (numbers below 100) or in millimetres (numbers above 100)”.

So R16 is a 16 code, and R400 is four hundred millimetres. Both are legal markings and they are not the same kind of number. The tool above says which it is reading, and never prints the word inches next to a figure above 100.

The space between the size and the rating does real work

A sidewall reads 205/55 R16 91V, with a gap. Take the gap away and R1691V can be split two ways the regulation allows: a 16 code with load index 91, or a 169 mm rim with load index 1.

Both are arithmetically fine, and the second is only possible because of the rule above. So when the space is there, this page uses it and gives one reading. When it is not — which is what happens in the universal lookup box, because that strips spaces before matching — it shows every split that fits and says why.

What this page does not date, and one thing it settles

There is no year in a size designation. But the same regulation, at paragraph 3.1.9, does require a date of manufacture: “The date of manufacture in the form of a group of four digits, the first two showing the week and the last two the year of manufacture” — the same week-then-year form the tyre date code page reads, and that page does the arithmetic rather than this one doing it twice.

What is worth adding here is a footnote that page cannot have. It says of the US regulation that it “does not mention a three-digit code at all, and does not say when the four-digit form began”. That is true of 49 CFR 574. This regulation dates its own change:

“Before 1 January 2000, the date of manufacture may be indicated by a group of three digits, the first two showing the week and the last one the year of manufacture”

So a European three-digit code is from before 1 January 2000, and a DOT three-digit code still is not dated by anything this site can read. They are different regulations for different markets, and one does not settle the other. Note also that a single year digit cannot say which decade it is: a 3 could be 1983, 1993 or 1999’s neighbours, and nothing in the code decides.

What is not covered

The regulation states its own scope: “This Regulation covers new pneumatic tyres designed primarily, but not only, for vehicles in categories M 1 , O 1 and O 2” — passenger cars and light trailers. Commercial vehicle tyres, with load indices above 120 and rim sizes like 22.5, are set by a different regulation and will not read here. The tool says so rather than reporting them as unrecognised.

Which version of the regulation this is

UNECE publish their own regulations, and unece.org returns 403 on robots.txt — so under RFC 9309 the rules are unknown and this site fetches nothing from them. The same text is published in the EU Official Journal, which permits reuse, so that is where it was read.

The consequence is worth stating plainly: the tables above are the text as published in the Official Journal, and UNECE have issued later revisions this site cannot fetch. If a symbol or an index has been added since, it will not be here, and this page would rather say that than imply it is current.

A note on where this came from

EUR-Lex permits reuse of the legal documents it publishes, commercially or otherwise, under Commission Decision 2011/833/EU. So both tables are complete rather than summarised.