325/30R21 tire size

325/30R21 in numbers

325/30R21 works out at 28.68 inches (728 mm) tall and 325 mm (12.8 in) wide, with 97.5 mm of sidewall on each side of a 21 inch rim. One turn covers 2288 mm (90.1 in), so it turns about 437 times per kilometre and 703 times per mile, or 728 times a minute at 100 km/h. Of the 555 passenger sizes listed here, 239 are taller and 315 are shorter. At 30 series this is a low-profile size: only 17 of the other 45 sizes on a 21 inch rim here have a shorter sidewall than its 97.5 mm, and 130 of all 879 sizes in the catalog do. 96 other passenger sizes come within 3 percent of its diameter; the closest is 245/45R20 (+0.01 percent).

What each part of 325/30R21 means

325

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

30

Aspect ratio. The sidewall is 30 percent of the section width: 325 x 30 / 100 = 97.5 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.

21

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 325/30R21 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 325/30R21, any rim

The 10 sizes in this catalog closest to 325/30R21 in overall diameter, of the same type, ranked by how little they change it. The speedometer columns assume the instrument read correctly on 325/30R21 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: 22 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: 20 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 325 mm width, different aspect ratio

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

• 325/25R2026.4 in
• 325/30R1926.7 in
• 325/25R2127.4 in
• 325/30R2027.7 in
• 325/50R1527.8 in
• 325/35R2029 in

Questions this size raises

What does 325/30R21 mean?

325 is the section width in millimetres. 30 is the aspect ratio: the sidewall is 30 percent of the section width, which works out at 97.5 mm. Radial construction. 21 is the rim diameter in inches. The service type is Euro-metric (no prefix).

How tall is a 325/30R21 tire?

28.68 inches (728.4 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 325/30R21?

3.84 inches (97.5 mm) per side.

How many revolutions per mile does a 325/30R21 turn?

703 revolutions per mile, from the nominal circumference of 90.1 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.

What is the plus one size for 325/30R21?

285/30R22 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 325/30R21?

245/45R20 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 325/30R21 against another size - diameter, clearance and speedometer error side by side.