145R12 tire size

145R12 in numbers

145R12 prints no aspect ratio, so its height depends on which convention is assumed. At 82 series it works out at 21.36 inches (543 mm); at 80 series it would be 21.13 inches (537 mm), 5.8 mm shorter. One turn covers 1705 mm (67.1 in), so it turns about 587 times per kilometre and 944 times per mile, or 978 times a minute at 100 km/h. Of the 17 no-aspect sizes listed here, 15 are taller and 1 is shorter. Only 2 sizes in this catalog sit on a 12 inch rim. No other no-aspect size in this catalog comes within 3 percent of its diameter; the nearest are 145R13 (+4.68 percent) and 125R12 (-6.04 percent).

What each part of 145R12 means

145

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

no aspect ratio

This size prints no aspect ratio. Published references treat these older European sizes as either 82 series or 80 series, so the diameter below is an assumption, not a reading off the tire. Both are shown. Measure the tire or check the manufacturer's data sheet before relying on either.

R

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

12

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

no prefix

Euro-metric (no prefix). An unprefixed size is Euro-metric, not P-metric with the P left off. The prefix decides which standards body's load table rates the tire. What the prefixes mean

Dimensions 145R12 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.

Same 145 mm width, different aspect ratio

What changing only the aspect ratio does, holding the width and the rim.

• 145R1322.4 in
• 145R1524.4 in

Questions this size raises

What does 145R12 mean?

145 is the section width in millimetres, R means radial construction and 12 is the rim diameter in inches. No aspect ratio is printed on this size at all, so its sidewall height is not stated on the tire and every diameter below rests on an assumed aspect ratio.

How tall is a 145R12 tire?

21.36 inches (542.6 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 145R12?

4.68 inches (118.9 mm) per side. This size prints no aspect ratio, so that figure follows from an assumption rather than from the tire.

How many revolutions per mile does a 145R12 turn?

944 revolutions per mile, from the nominal circumference of 67.1 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 145R12 against another size - diameter, clearance and speedometer error side by side.