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285/40R21 in inches

A 285/40R21 tire is 30.0″ tall and 11.2″ wide, and fits a 21″ wheel. In inches it is written 30.0×11.2R21.

Diameter29.98″
Width11.22″
Sidewall4.49″
285/40R21 drawn to scale: 29.98 inch diameter, 4.49 inch sidewall, 21 inch wheel, 11.22 inch tread width21″ wheel4.49″29.98″ overall11.22″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 285/40R21 tires really are

Heights published by Michelin and Toyo for all 5 tires in this size. Their published revolutions per mile work out to 29.1–29.3″ under load (below).

Real 285/40R21 tires measure 29.96–30.20″, against 29.98″ from the size code. They run both taller and shorter than the size code.

  1. Michelin Pilot Sport All-Season 430.20″ +0.22″
  2. Michelin Pilot Sport 4 SUV30.00″ +0.02″
  3. Toyo Celsius Sport29.96″ −0.02″
  4. Michelin Pilot Alpin 529.96″ −0.02″
  5. Michelin X-Ice Snow29.96″ −0.02″
Each bar runs from the size code's 29.98″ (the orange line) to the model's published height. The track spans 1.0″. Where a model comes in several load ranges, the darker part shows its range of heights; the number after the name is how many versions it comes in.
Height under load29.1–29.3″

Published revs per mile (689–694) mean the tire rolls like a 29.1–29.3″ tire on the vehicle. Use this for speedometer calibration.

Weight spread33.0–36.6 lb

The lightest (Michelin Pilot Sport All-Season 4, XL) is 3.6 lb lighter per corner than the heaviest (Michelin X-Ice Snow, XL).

5 tires in 285/40R21

Sort by the spec you care about.

LoadRevs/miSource
Michelin Pilot Sport All-Season 4PerformanceXL · 109Y30.2033.010.02,271689Spec page
Michelin Pilot Sport 4 SUVPerformanceXL · 109Y30.0034.19.52,271694Spec page
Michelin Pilot Alpin 5WinterXL · 109V29.9635.310.52,271694Spec page
Toyo Celsius SportPerformanceXL · 109Y29.9635.89.72,271693Spec page
Michelin X-Ice SnowWinterXL · 109H29.9636.610.52,271694Spec page

Is 285/40R21 a 30-inch tire?

≈30″

Yes. The size code works out to 29.98″, and the 5 tires here publish 29.96–30.20″, so people call it a 30.

All 30-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 285/40R21Difference
265/40R2129.35-0.63″-2.1%
305/35R2129.41-0.57″-1.9%
275/40R2129.66-0.31″-1.1%
245/45R2129.68-0.30″-1.0%
315/35R2129.68-0.30″-1.0%
255/45R2130.04+0.06″+0.2%
235/50R2130.25+0.28″+0.9%
295/40R2130.29+0.31″+1.1%
265/45R2130.39+0.41″+1.4%
305/40R2130.61+0.63″+2.1%

How to read 285/40R21

How to read any tire size

285/40R21 109Y as printed on the tire sidewall, with each part numbered285/40R21 109Y123456
How 285/40R21 109Y is printed on the sidewall. It's the most common code among the 5 tires here (3 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

240Aspect ratio

A percentage, not a measurement: the sidewall is 40% as tall as the tire is wide, which is 114.0 mm or 4.49 inches.

3RConstruction

Radial construction.

421Wheel diameter

Mounts on a 21-inch wheel. Approved wheel widths run 9.5″ to 11.0″.

5109Load index

Each tire carries up to 2,271 lb (1,030 kg) at its maximum pressure.

6YSpeed rating

Rated for up to 186 mph sustained.

XLExtra load

Printed after the size.

SpecificationInchesMetric
Overall diameter29.98761 mm
Section width11.22285 mm
Sidewall height4.49114.0 mm
Circumference94.22,392 mm
Revolutions per mile (calculated, unloaded)672.8418 per km
Revolutions per mile (published by manufacturers)689–694428–431 per km
Approved wheel width9.5–11.0241–279 mm

Speedometer error after switching to 285/40R21

Your actual speed– mph

Questions about 285/40R21

What is 285/40R21 in inches?

29.98 inches tall, 11.22 inches wide, on a 21-inch wheel. Written in inches, that is roughly 30.0×11.2R21.

How much does a 285/40R21 tire weigh?

Between 33.0 lb and 36.6 lb for the 5 tires listed here. The lightest is the Michelin Pilot Sport All-Season 4 (XL); the heaviest is the Michelin X-Ice Snow (XL).

What wheel width do I need for 285/40R21?

Manufacturers approve 9.5–11.0″ wide wheels for this size.

How many revolutions per mile does a 285/40R21 make?

Published figures run 689–694 revolutions per mile. The calculated figure is 672.8, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 285/40R21 than 315/35R21?

0.30 inches taller on paper (29.98″ vs 29.68″), which raises the axle about 0.15″. Your speedometer will read about 1.0% slow.