ST175/80R13 tire size

ST175/80R13 in numbers

ST175/80R13 works out at 24.02 inches (610 mm) tall and 175 mm (6.89 in) wide, with 140 mm of sidewall on each side of a 13 inch rim. One turn covers 1917 mm (75.5 in), so it turns about 522 times per kilometre and 840 times per mile, or 869 times a minute at 100 km/h. Of the 20 trailer sizes listed here, 18 are taller and 1 is shorter. At 80 series the sidewall is 0.8 times the width, 140 mm: 3 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: 175/80R13. 1 other trailer size comes within 3 percent of its diameter; the closest is ST185/80R13 (+2.62 percent). The next closest, outside that window, is ST195/70R14 (+3.02 percent).

What each part of ST175/80R13 means

175

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: 175 x 80 / 100 = 140 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 ST175/80R13 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.

Sizes within 3 percent of ST175/80R13, any rim

The one size in this catalog closest to ST175/80R13 in overall diameter, of the same type, ranked by how little they change it. The speedometer columns assume the instrument read correctly on ST175/80R13 and that nothing was recalibrated.

A positive difference means the replacement is taller, so the vehicle travels further per revolution and the speedometer reads LOW. Many vehicles leave the factory reading slightly high on purpose, so treat this as a change from whatever the instrument did before, not as an absolute claim about it.

Questions this size raises

What does ST175/80R13 mean?

175 is the section width in millimetres. 80 is the aspect ratio: the sidewall is 80 percent of the section width, which works out at 140 mm. Radial construction. 13 is the rim diameter in inches. The service type is ST (special trailer).

How tall is a ST175/80R13 tire?

24.02 inches (610.2 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 ST175/80R13?

5.51 inches (140 mm) per side.

How many revolutions per mile does a ST175/80R13 turn?

840 revolutions per mile, from the nominal circumference of 75.5 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 ST175/80R13 against another size - diameter, clearance and speedometer error side by side.