Tyre size (205/55 R16)
205/55 R16 is the tyre-size designation: 205 mm nominal section width, a sidewall height 55 % of that width, radial (R) construction, for a 16-inch rim.
What to do with it
Fit only sizes the vehicle maker lists for your car; the vehicle’s tyre placard or handbook gives them. When buying, match all of it — width, aspect ratio, construction and rim — then the load index and speed symbol that follow it. Type yours into the decoder above to see each part.
Read the size on your tyre: the tyre size decoder →
- What it looks like
- Three numbers and a letter, the largest text near the rim after the brand: 205/55 R16, sometimes 205/55R16 or 205/55 ZR16.
- Set by
- UN Regulation No. 30, paragraphs 2.17 (tyre-size designation), 3.1.2 and 3.1.3 (structure letters), 6.1.2 (outer diameter D = d + 2H), Annex III; 49 CFR 571.139, S5.5(b) and (h)
In detail
- Worked example: 205/55 R16. The width is 205 mm. The sidewall is 55 % of 205 = about 113 mm tall. The rim is 16 inches = 406 mm (UN R30 has codes below 100 multiplied by 25.4 to give millimetres). So the whole tyre is about 406 + 2 × 113 = 632 mm across, before tolerances — the regulation’s own outer-diameter formula is D = d + 2H.
- The letter before the rim size is the construction: R for radial, D (or nothing) for diagonal/bias-ply, B for bias-belted, and ZR may replace R on tyres rated above 240 km/h. A run flat or self-supporting tyre carries F in front of the rim diameter.
- Where the rim number is above 100 it is in millimetres, not inches: UN R30 Annex III shows 185-560 R 400A, a tyre for a 400 mm rim with the A rim-fitment configuration.
- A T in front of the width (T125/80 R17) is a temporary use spare; a C or LT after the rim size is a commercial or light-truck tyre. Each has its own page.
What it does not mean
The size does not say how much the tyre can carry or how fast it can go: the load index and speed symbol after it do. Two tyres of the same size are not interchangeable if those differ.
Markings that go with it
Sources
Each document was fetched and read on the date shown; the clause is the one that sets this marking.
- UNECE, as published in the Official Journal of the EU: UN Regulation No. 30 — Uniform provisions concerning the approval of pneumatic tyres for motor vehicles and their trailers, Revision 3 (OJ L 201, 30.7.2008) — paragraphs 2.17 (tyre-size designation), 3.1.2 and 3.1.3 (structure letters), 6.1.2 (outer diameter D = d + 2H), Annex III: The size designation shows “the nominal section width … in mm”, “the nominal aspect ratio” and “a conventional number denoting the nominal rim diameter … by codes (numbers below 100) or in millimetres (numbers above 100)”; radial tyres carry “the letter ‘R’ placed in front of the rim-diameter marking”. Checked 2026-09-28.
- US National Highway Traffic Safety Administration, on eCFR: 49 CFR 571.139 — Standard No. 139, New pneumatic radial tires for light vehicles — S5.5(b) and (h): Each tyre must be marked with “the tire size designation” and “the word ‘radial,’ if the tire is a radial ply tire”. Checked 2026-09-28.
- Michelin (UK): Tyre markings explained: How to read a tyre? — “How to read a tyre size”: Michelin reads the size as width in mm, height as a percentage of width, R for radial, and rim diameter in inches. Checked 2026-09-28.