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285/30R21 in inches

A 285/30R21 tire is 27.7″ tall and 11.2″ wide, and fits a 21″ wheel. In inches it is written 27.7×11.2R21.

Diameter27.73″
Width11.22″
Sidewall3.37″
285/30R21 drawn to scale: 27.73 inch diameter, 3.37 inch sidewall, 21 inch wheel, 11.22 inch tread width21″ wheel3.37″27.73″ overall11.22″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 285/30R21 tires really are

Heights published by Michelin for all 2 tires in this size. Their published revolutions per mile work out to 26.9″ under load (below).

Real 285/30R21 tires measure 27.76–27.80″, against 27.73″ from the size code. Every one runs taller than the size code.

Height under load26.9″

Published revs per mile (749) mean the tire rolls like a 26.9″ tire on the vehicle. Use this for speedometer calibration.

Weight spread28.0–29.3 lb

The lightest (Michelin Pilot Alpin PA4, XL) is 1.3 lb lighter per corner than the heaviest (Michelin Pilot Sport 4 S, XL).

2 tires in 285/30R21

Sort by the spec you care about.

LoadRevs/miSource
Michelin Pilot Alpin PA4WinterXL · 100W27.7628.010.51,764749Spec page
Michelin Pilot Sport 4 SPerformanceXL · 100(Y)27.8029.39.51,764749Spec page

Is 285/30R21 a 28-inch tire?

≈28″

Yes. The size code works out to 27.73″, and the 2 tires here publish 27.76–27.80″, so people call it a 28.

All 28-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 285/30R21Difference
265/30R2127.26-0.47″-1.7%
325/25R2127.40-0.33″-1.2%
275/30R2127.50-0.24″-0.9%
245/35R2127.75+0.02″+0.1%
345/25R2127.79+0.06″+0.2%
295/30R2127.97+0.24″+0.9%
355/25R2127.99+0.26″+0.9%
255/35R2128.03+0.30″+1.1%
305/30R2128.20+0.47″+1.7%
265/35R2128.30+0.57″+2.1%

How to read 285/30R21

How to read any tire size

285/30R21 100W as printed on the tire sidewall, with each part numbered285/30R21 100W123456
How 285/30R21 100W is printed on the sidewall. It's the most common code among the 2 tires here (1 of them); tires in this size come in other load and speed ratings too.
1285Section width

285 mm across the widest point, or 11.22 inches. Every 285 size

230Aspect ratio

A percentage, not a measurement: the sidewall is 30% as tall as the tire is wide, which is 85.5 mm or 3.37 inches.

3RConstruction

Radial construction.

421Wheel diameter

Mounts on a 21-inch wheel. Approved wheel widths run 9.5″ to 10.5″.

5100Load index

Each tire carries up to 1,764 lb (800 kg) at its maximum pressure.

6WSpeed rating

Rated for up to 168 mph sustained.

XLExtra load

Printed after the size.

SpecificationInchesMetric
Overall diameter27.73704 mm
Section width11.22285 mm
Sidewall height3.3785.5 mm
Circumference87.12,213 mm
Revolutions per mile (calculated, unloaded)727.2452 per km
Revolutions per mile (published by manufacturers)749465 per km
Approved wheel width9.5–10.5241–267 mm

Speedometer error after switching to 285/30R21

Your actual speed– mph

Questions about 285/30R21

What is 285/30R21 in inches?

27.73 inches tall, 11.22 inches wide, on a 21-inch wheel. Written in inches, that is roughly 27.7×11.2R21.

How much does a 285/30R21 tire weigh?

Between 28.0 lb and 29.3 lb for the 2 tires listed here. The lightest is the Michelin Pilot Alpin PA4 (XL); the heaviest is the Michelin Pilot Sport 4 S (XL).

What wheel width do I need for 285/30R21?

Manufacturers approve 9.5–10.5″ wide wheels for this size.

How many revolutions per mile does a 285/30R21 make?

Published figures run 749 revolutions per mile. The calculated figure is 727.2, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 285/30R21 than 275/30R21?

0.24 inches taller on paper (27.73″ vs 27.50″), which raises the axle about 0.12″. Your speedometer will read about 0.9% slow.