185/70R15 tire size

185/70R15 in numbers

185/70R15 works out at 25.2 inches (640 mm) tall and 185 mm (7.28 in) wide, with 129.5 mm of sidewall on each side of a 15 inch rim. One turn covers 2011 mm (79.2 in), so it turns about 497 times per kilometre and 800 times per mile, or 829 times a minute at 100 km/h. Of the 555 passenger sizes listed here, 464 are taller and 90 are shorter. 79 other passenger sizes come within 3 percent of its diameter; the closest is 225/35R19 (+0.02 percent).

What each part of 185/70R15 means

185

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

70

Aspect ratio. The sidewall is 70 percent of the section width: 185 x 70 / 100 = 129.5 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.

15

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 185/70R15 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 185/70R15, any rim

The 10 sizes in this catalog closest to 185/70R15 in overall diameter, of the same type, ranked by how little they change it. The speedometer columns assume the instrument read correctly on 185/70R15 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.

Plus one: 16 inch rim, same rolling diameter

A bigger wheel with a shorter sidewall, holding the overall diameter within 3 percent. Only sizes inside that window are listed - a "plus size" that changes the diameter by six percent is a different tire, not an alternative.

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.

Minus one: 14 inch rim, same rolling diameter

A smaller wheel with a taller sidewall. Common for winter fitments, where sidewall is wanted and wheel diameter is not.

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.

Same 185 mm width, different aspect ratio

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

• 185/60R1321.7 in
• 185/55R1422 in
• 185/60R1422.7 in
• 185/55R1523 in
• 185/70R1323.2 in
• 185/50R1623.3 in

Questions this size raises

What does 185/70R15 mean?

185 is the section width in millimetres. 70 is the aspect ratio: the sidewall is 70 percent of the section width, which works out at 129.5 mm. Radial construction. 15 is the rim diameter in inches. The service type is Euro-metric (no prefix).

How tall is a 185/70R15 tire?

25.2 inches (640 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 185/70R15?

5.1 inches (129.5 mm) per side.

How many revolutions per mile does a 185/70R15 turn?

800 revolutions per mile, from the nominal circumference of 79.2 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.

What is the plus one size for 185/70R15?

195/60R16 keeps the overall diameter closest on a rim one inch larger, of the sizes in this catalog. Plus sizing trades sidewall for wheel while holding the rolling diameter, so the speedometer stays close to correct. Whether the wheel and tire clear the vehicle is a separate question this site cannot answer.

What is the minus one size for 185/70R15?

235/60R14 keeps the overall diameter closest on a rim one inch smaller, of the sizes in this catalog. Minus sizing is common for winter fitments, where a taller sidewall and a narrower tread are wanted.

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 185/70R15 against another size - diameter, clearance and speedometer error side by side.