285/40R18 Tire Size in Inches

27.0" tall, 11.2" wide, 4.5" sidewall

Diameter27.0"685 mm
Overall diameter27.0"685 mm
Section width11.2"285 mm
Sidewall height4.5"114 mm
Circumference84.7"2153 mm
Revolutions per mile748465 per km
Wheel diameter18"≈ 27.0x11.2R18 in inches

A 285/40R18 tire is 27.0 inches (685 mm) tall and 11.2 inches wide. The sidewall is 40% of the width, 4.5 inches, on a 18-inch wheel, and the tire turns about 748 times per mile.

In flotation terms that is about 27.0x11.2R18. People often call it a 27-inch tire.

The size most often compared with it is 275/40R18, which is 0.3" shorter (−1.2%). At an indicated 60 mph you would be doing 59.3 mph on it.

285/40R18
275/40R18
Diameter difference−1.17%diameter 26.98" → 26.66"
CurrentNew
CurrentNewDifference

Speedometer

ShowsActual speed

Gear ratio to match

–enter your current axle ratio

Sizes near 285/40R18

Same 18" wheel, within 20 mm of width and 10 points of aspect ratio.

SizeDiameterWidthSidewallvs 285/40R18
275/40R1826.7"10.8"4.3"−1.2%
295/40R1827.3"11.6"4.6"+1.2%
305/35R1826.4"12.0"4.2"−2.1%
265/40R1826.3"10.4"4.2"−2.3%
275/45R1827.7"10.8"4.9"+2.8%
295/35R1826.1"11.6"4.1"−3.1%
285/45R1828.1"11.2"5.0"+4.2%
285/35R1825.9"11.2"3.9"−4.2%
275/35R1825.6"10.8"3.8"−5.2%
265/50R1828.4"10.4"5.2"+5.4%

Same height on a different wheel

Sizes within 2% of 27.0" on 20" or 17" or 19" wheels.

SizeDiameterWidthSidewallvs 285/40R18
295/30R2027.0"11.6"3.5"−0.0%
255/35R2027.0"10.0"3.5"+0.2%
285/45R1727.1"11.2"5.0"+0.5%
285/35R1926.9"11.2"3.9"−0.5%
305/30R2027.2"12.0"3.6"+0.8%
205/60R1726.7"8.1"4.8"−1.1%

Speedometer with a different size

Actual speed when the speedometer is calibrated for 285/40R18.

Speedometer showson 275/40R18on 295/40R18on 305/35R18
30 mph29.6 mph30.4 mph29.4 mph
45 mph44.5 mph45.5 mph44.0 mph
60 mph59.3 mph60.7 mph58.7 mph
70 mph69.2 mph70.8 mph68.5 mph

285/40R18 FAQ

How tall is a 285/40R18 tire?

27.0 inches (685 mm). The sidewall is 4.5 inches.

How wide is a 285/40R18 tire?

11.2 inches (285 mm) section width, measured sidewall to sidewall.

What is 285/40R18 in flotation size?

About 27.0x11.2R18.

Can I use 275/40R18 instead of 285/40R18?

275/40R18 is −1.2% in diameter, within the common 3% guideline. It is 0.4" narrower.