tireheight.com

285/40R18 in inches

A 285/40R18 tire is 27.0″ tall and 11.2″ wide, and fits a 18″ wheel. In inches it is written 27.0×11.2R18.

Diameter26.98″
Width11.22″
Sidewall4.49″
285/40R18 drawn to scale: 26.98 inch diameter, 4.49 inch sidewall, 18 inch wheel, 11.22 inch tread width18″ wheel4.49″26.98″ overall11.22″ wideSide view
Drawn to scale. Nominal dimensions calculated from the size code.
Manufacturer data

How tall 285/40R18 tires really are

Heights published by General and Michelin for all 2 tires in this size. Their published revolutions per mile work out to 26.2″ under load (below).

Real 285/40R18 tires measure 27.00″, against 26.98″ from the size code. Every one runs taller than the size code.

Height under load26.2″

Published revs per mile (770–771) mean the tire rolls like a 26.2″ tire on the vehicle. Use this for speedometer calibration.

Weight spread27.8–27.9 lb

The lightest (General G-MAX RS, SL) is 0.1 lb lighter per corner than the heaviest (Michelin Pilot Sport 4 S, XL).

2 tires in 285/40R18

Sort by the spec you care about.

LoadRevs/miSource
General G-MAX RSPerformanceSL · 101Y27.0027.810.01,819770Spec page
Michelin Pilot Sport 4 SPerformanceXL · 105(Y)27.0027.99.52,039771Spec page

Is 285/40R18 a 27-inch tire?

≈27″

Yes. The size code works out to 26.98″, and the 2 tires here publish 27.00″, so people call it a 27.

All 27-inch tire sizes, on every wheel size.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

SizeDiameter ″vs 285/40R18Difference
215/50R1826.46-0.51″-1.9%
275/40R1826.66-0.31″-1.2%
245/45R1826.68-0.30″-1.1%
315/35R1826.68-0.30″-1.1%
225/50R1826.86-0.12″-0.4%
255/45R1827.04+0.06″+0.2%
235/50R1827.25+0.28″+1.0%
215/55R1827.31+0.33″+1.2%
265/45R1827.39+0.41″+1.5%
345/35R1827.51+0.53″+2.0%

How to read 285/40R18

How to read any tire size

285/40R18 101Y as printed on the tire sidewall, with each part numbered285/40R18 101Y123456
How 285/40R18 101Y 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

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.

418Wheel diameter

Mounts on a 18-inch wheel. Approved wheel widths run 9.5″ to 11.0″.

5101Load index

Each tire carries up to 1,819 lb (825 kg) at its maximum pressure.

6YSpeed rating

Rated for up to 186 mph sustained.

SpecificationInchesMetric
Overall diameter26.98685 mm
Section width11.22285 mm
Sidewall height4.49114.0 mm
Circumference84.72,153 mm
Revolutions per mile (calculated, unloaded)747.6465 per km
Revolutions per mile (published by manufacturers)770–771478–479 per km
Approved wheel width9.5–11.0241–279 mm

Speedometer error after switching to 285/40R18

Your actual speed– mph

Questions about 285/40R18

What is 285/40R18 in inches?

26.98 inches tall, 11.22 inches wide, on a 18-inch wheel. Written in inches, that is roughly 27.0×11.2R18.

How much does a 285/40R18 tire weigh?

Between 27.8 lb and 27.9 lb for the 2 tires listed here. The lightest is the General G-MAX RS (SL); the heaviest is the Michelin Pilot Sport 4 S (XL).

What wheel width do I need for 285/40R18?

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

How many revolutions per mile does a 285/40R18 make?

Published figures run 770–771 revolutions per mile. The calculated figure is 747.6, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 285/40R18 than 225/50R18?

0.12 inches taller on paper (26.98″ vs 26.86″), which raises the axle about 0.06″. Your speedometer will read about 0.4% slow.