285/30R18 in inches

A 285/30R18 tire is 24.7″ tall and 11.2″ wide, and fits a 18″ wheel. In inches it is written 24.7×11.2R18.

Diameter24.73″

Width11.22″

Sidewall3.37″

Drawn to scale. Nominal dimensions calculated from the size code.

Manufacturer data

How tall 285/30R18 tires really are

Heights published by Michelin and Toyo for all 5 tires in this size. Their published revolutions per mile work out to 24.0″ under load (below).

Real 285/30R18 tires measure 24.76–24.80″, against 24.73″ from the size code. Every one runs taller than the size code.

Height under load24.0″

Published revs per mile (839–840) mean the tire rolls like a 24.0″ tire on the vehicle. Use this for speedometer calibration.

Weight spread24.8–26.4 lb

The lightest (Toyo Proxes R, SL) is 1.6 lb lighter per corner than the heaviest (Michelin Pilot Sport PS2, SL).

5 tires in 285/30R18

Sort by the spec you care about.

	Load					Revs/mi	Source
Toyo Proxes RPerformance	SL · 93W	24.80	24.8	3.7	1,433	839	Spec page
Michelin Pilot Sport Cup 2 ConnectPerformance	XL · 97(Y)	24.80	25.2	7.2	1,609	840	Spec page
Michelin Pilot Sport 4 SPerformance	XL · 97(Y)	24.80	25.9	9.5	1,609	840	Spec page
Toyo Proxes RRPerformance	SL	24.76	26.0	3.6	1,433	839	Spec page
Michelin Pilot Sport PS2Performance	SL · 93(Y)	24.80	26.4	8.5	1,430	840	Spec page

Is 285/30R18 a 25-inch tire?

≈25″

Yes. The size code works out to 24.73″, and the 5 tires here publish 24.76–24.80″, so people call it a 25.

Compare with nearby sizes

Differences in overall diameter, calculated from each size code.

Size	Diameter ″	vs 285/30R18	Difference
205/40R18	24.46	-0.28″	-1.1%
245/40R17	24.72	-0.02″	-0.1%
245/35R18	24.75	+0.02″	+0.1%
215/40R18	24.77	+0.04″	+0.2%
295/30R18	24.97	+0.24″	+1.0%
255/35R18	25.03	+0.30″	+1.2%
225/40R18	25.09	+0.35″	+1.4%
265/35R18	25.30	+0.57″	+2.3%
235/40R18	25.40	+0.67″	+2.7%
315/30R18	25.44	+0.71″	+2.9%

How to read 285/30R18

How to read any tire size

How 285/30R18 97Y is printed on the sidewall. It's the most common code among the 5 tires here (2 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.

418Wheel diameter

Mounts on a 18-inch wheel. Approved wheel widths run 9.5″ to 10.5″.

597Load index

Each tire carries up to 1,609 lb (730 kg) at its maximum pressure.

6YSpeed rating

Rated for up to 186 mph sustained.

XLExtra load

Printed after the size. In this size the XL tires carry up to 1,609 lb each and the standard-load tires up to 1,433 lb, as published.

Specification	Inches	Metric
Overall diameter	24.73	628 mm
Section width	11.22	285 mm
Sidewall height	3.37	85.5 mm
Circumference	77.7	1,974 mm
Revolutions per mile (calculated, unloaded)	815.5	507 per km
Revolutions per mile (published by manufacturers)	839–840	521–522 per km
Approved wheel width	9.5–10.5	241–267 mm

Speedometer error after switching to 285/30R18

Your actual speed– mph

Questions about 285/30R18

What is 285/30R18 in inches?

24.73 inches tall, 11.22 inches wide, on a 18-inch wheel. Written in inches, that is roughly 24.7×11.2R18.

How much does a 285/30R18 tire weigh?

Between 24.8 lb and 26.4 lb for the 5 tires listed here. The lightest is the Toyo Proxes R (SL); the heaviest is the Michelin Pilot Sport PS2 (SL).

What wheel width do I need for 285/30R18?

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

How many revolutions per mile does a 285/30R18 make?

Published figures run 839–840 revolutions per mile. The calculated figure is 815.5, but manufacturers measure the tire under load, where it rolls on a smaller radius.

How much taller is 285/30R18 than 205/40R18?

0.28 inches taller on paper (24.73″ vs 24.46″), which raises the axle about 0.14″. Your speedometer will read about 1.1% slow.