ST155/80R13 tire size

ST155/80R13 in numbers

ST155/80R13 works out at 22.76 inches (578 mm) tall and 155 mm (6.1 in) wide, with 124 mm of sidewall on each side of a 13 inch rim. One turn covers 1816 mm (71.5 in), so it turns about 551 times per kilometre and 886 times per mile, or 918 times a minute at 100 km/h. It is the shortest of the 20 trailer sizes listed here. At 80 series the sidewall is 0.8 times the width, 124 mm: 8 of the other 14 sizes on a 13 inch rim here have a taller one. The ST prefix marks a special trailer tire, for trailer axles only. Same nominal dimensions, different duty: 155/80R13. No other trailer size in this catalog comes within 3 percent of its diameter; the nearest are ST175/80R13 (+5.53 percent) and ST185/80R13 (+8.30 percent).

What each part of ST155/80R13 means

155

Section width in millimetres, sidewall to sidewall at the widest point. Not the tread width, which is narrower.

80

Aspect ratio. The sidewall is 80 percent of the section width: 155 x 80 / 100 = 124 mm. A lower number is a shorter sidewall on the same width.

R

Radial construction. The R here is construction, not the speed symbol R. The speed symbol sits after the size, in the service description.

13

Rim diameter in inches. The bead seat diameter of the wheel this tire mounts on.

ST

ST (special trailer). What the prefixes mean

Dimensions ST155/80R13 implies

These are the nominal dimensions the size code implies. A real tire's measured dimensions depend on its mould, its construction and the rim width it is mounted on, so a manufacturer's specification sheet for a specific tire is the authority for that tire.

The overall diameter formula used here reproduces all 52 radial passenger design diameters published in an Indian vehicle standard to within 1.4 mm, 0.5 mm on average: AIS-044 (Part 2) Amendment 2, Annexure A.

Questions this size raises

What does ST155/80R13 mean?

155 is the section width in millimetres. 80 is the aspect ratio: the sidewall is 80 percent of the section width, which works out at 124 mm. Radial construction. 13 is the rim diameter in inches. The service type is ST (special trailer).

How tall is a ST155/80R13 tire?

22.76 inches (578.2 mm) in nominal overall diameter. That is the diameter the size code implies; a specific tire's measured diameter depends on its mould and the rim width it is mounted on, and the manufacturer's specification sheet is the authority for that tire.

What is the sidewall height of a ST155/80R13?

4.88 inches (124 mm) per side.

How many revolutions per mile does a ST155/80R13 turn?

886 revolutions per mile, from the nominal circumference of 71.5 inches. A loaded tire deflects and turns slightly more often than that, so a manufacturer's published revolutions figure usually runs a few percent higher.

The rest of the sidewall

The size is one line of a sidewall. What follows it decides whether the tire is legal on the vehicle at all.

• Load index table - the number after the size, and the mass it stands for. Must meet or exceed the vehicle placard.
• Speed symbol table - the letter after the load index, including the ZR, W, Y and (Y) cases.
• DOT date code - how old the tire is, and why a three digit code is not the same as a four digit one.
• Every other marking - UTQG grades, load range letters, M+S against the three peak mountain snowflake.
• Compare ST155/80R13 against another size - diameter, clearance and speedometer error side by side.