255/40R18 Tire Size in Inches

26.0" tall, 10.0" wide, 4.0" sidewall

Diameter26.0"661 mm
Overall diameter26.0"661 mm
Section width10.0"255 mm
Sidewall height4.0"102 mm
Circumference81.8"2077 mm
Revolutions per mile775481 per km
Wheel diameter18"≈ 26.0x10.0R18 in inches

A 255/40R18 tire is 26.0 inches (661 mm) tall and 10.0 inches wide. The sidewall is 40% of the width, 4.0 inches, on a 18-inch wheel, and the tire turns about 775 times per mile.

In flotation terms that is about 26.0x10.0R18. People often call it a 26-inch tire.

The size most often compared with it is 265/35R18, which is 0.7" shorter (−2.8%). At an indicated 60 mph you would be doing 58.3 mph on it.

255/40R18
265/35R18
Diameter difference−2.80%diameter 26.03" → 25.30"
CurrentNew
CurrentNewDifference

Speedometer

ShowsActual speed

Gear ratio to match

–enter your current axle ratio

Sizes near 255/40R18

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

SizeDiameterWidthSidewallvs 255/40R18
265/40R1826.3"10.4"4.2"+1.2%
275/35R1825.6"10.8"3.8"−1.7%
275/40R1826.7"10.8"4.3"+2.4%
265/35R1825.3"10.4"3.7"−2.8%compare
255/35R1825.0"10.0"3.5"−3.9%compare
255/45R1827.0"10.0"4.5"+3.9%
275/30R1824.5"10.8"3.2"−5.9%
275/45R1827.7"10.8"4.9"+6.6%
255/50R1828.0"10.0"5.0"+7.7%
265/50R1828.4"10.4"5.2"+9.2%

Same height on a different wheel

Sizes within 2% of 26.0" on 17" or 19" wheels.

SizeDiameterWidthSidewallvs 255/40R18
255/45R1726.0"10.0"4.5"+0.0%
285/40R1726.0"11.2"4.5"−0.2%
305/30R1926.2"12.0"3.6"+0.7%
295/40R1726.3"11.6"4.6"+1.0%
315/35R1725.7"12.4"4.3"−1.3%
275/40R1725.7"10.8"4.3"−1.4%

Speedometer with a different size

Actual speed when the speedometer is calibrated for 255/40R18.

Speedometer showson 265/35R18on 255/35R18on 265/40R18
30 mph29.2 mph28.8 mph30.4 mph
45 mph43.7 mph43.3 mph45.5 mph
60 mph58.3 mph57.7 mph60.7 mph
70 mph68.0 mph67.3 mph70.8 mph

255/40R18 comparisons

255/40R18 FAQ

How tall is a 255/40R18 tire?

26.0 inches (661 mm). The sidewall is 4.0 inches.

How wide is a 255/40R18 tire?

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

What is 255/40R18 in flotation size?

About 26.0x10.0R18.

Can I use 265/35R18 instead of 255/40R18?

265/35R18 is −2.8% in diameter, within the common 3% guideline. It is 0.4" wider.