255/45R18 Tire Size in Inches

27.0" tall, 10.0" wide, 4.5" sidewall

Diameter27.0"687 mm
Overall diameter27.0"687 mm
Section width10.0"255 mm
Sidewall height4.5"115 mm
Circumference84.9"2157 mm
Revolutions per mile746464 per km
Wheel diameter18"≈ 27.0x10.0R18 in inches

A 255/45R18 tire is 27.0 inches (687 mm) tall and 10.0 inches wide. The sidewall is 45% of the width, 4.5 inches, on a 18-inch wheel, and the tire turns about 746 times per mile.

In flotation terms that is about 27.0x10.0R18. People often call it a 27-inch tire.

The size most often compared with it is 275/40R18, which is 0.4" shorter (−1.4%). At an indicated 60 mph you would be doing 59.2 mph on it.

255/45R18
275/40R18
Diameter difference−1.38%diameter 27.04" → 26.66"
CurrentNew
CurrentNewDifference

Speedometer

ShowsActual speed

Gear ratio to match

–enter your current axle ratio

Sizes near 255/45R18

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

SizeDiameterWidthSidewallvs 255/45R18
275/40R1826.7"10.8"4.3"−1.4%
265/40R1826.3"10.4"4.2"−2.5%
275/45R1827.7"10.8"4.9"+2.6%
255/40R1826.0"10.0"4.0"−3.7%
255/50R1828.0"10.0"5.0"+3.7%
265/50R1828.4"10.4"5.2"+5.2%
275/35R1825.6"10.8"3.8"−5.4%
265/35R1825.3"10.4"3.7"−6.4%
275/50R1828.8"10.8"5.4"+6.6%
255/35R1825.0"10.0"3.5"−7.4%

Same height on a different wheel

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

SizeDiameterWidthSidewallvs 255/45R18
255/35R2027.0"10.0"3.5"−0.0%
285/45R1727.1"11.2"5.0"+0.2%
295/30R2027.0"11.6"3.5"−0.2%
305/30R2027.2"12.0"3.6"+0.6%
285/35R1926.9"11.2"3.9"−0.7%
265/35R2027.3"10.4"3.7"+1.0%

Speedometer with a different size

Actual speed when the speedometer is calibrated for 255/45R18.

Speedometer showson 275/40R18on 265/40R18on 275/45R18
30 mph29.6 mph29.2 mph30.8 mph
45 mph44.4 mph43.9 mph46.2 mph
60 mph59.2 mph58.5 mph61.6 mph
70 mph69.0 mph68.2 mph71.8 mph

255/45R18 FAQ

How tall is a 255/45R18 tire?

27.0 inches (687 mm). The sidewall is 4.5 inches.

How wide is a 255/45R18 tire?

10.0 inches (255 mm) section width, measured sidewall to sidewall.

What is 255/45R18 in flotation size?

About 27.0x10.0R18.

Can I use 275/40R18 instead of 255/45R18?

275/40R18 is −1.4% in diameter, within the common 3% guideline. It is 0.8" wider.