275/55R18 Tire Size in Inches

29.9" tall, 10.8" wide, 6.0" sidewall

Diameter29.9"760 mm
Overall diameter29.9"760 mm
Section width10.8"275 mm
Sidewall height6.0"151 mm
Circumference94.0"2387 mm
Revolutions per mile674419 per km
Wheel diameter18"≈ 29.9x10.8R18 in inches

A 275/55R18 tire is 29.9 inches (760 mm) tall and 10.8 inches wide. The sidewall is 55% of the width, 6.0 inches, on a 18-inch wheel, and the tire turns about 674 times per mile.

In flotation terms that is about 29.9x10.8R18. People often call it a 30-inch tire.

The size most often compared with it is 265/55R18, which is 0.4" shorter (−1.4%). At an indicated 60 mph you would be doing 59.1 mph on it.

275/55R18
265/55R18
Diameter difference−1.45%diameter 29.91" → 29.48"
CurrentNew
CurrentNewDifference

Speedometer

ShowsActual speed

Gear ratio to match

–enter your current axle ratio

Sizes near 275/55R18

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

SizeDiameterWidthSidewallvs 275/55R18
265/55R1829.5"10.4"5.7"−1.4%
285/55R1830.3"11.2"6.2"+1.4%
285/50R1829.2"11.2"5.6"−2.3%
295/55R1830.8"11.6"6.4"+2.9%
275/50R1828.8"10.8"5.4"−3.6%
275/60R1831.0"10.8"6.5"+3.6%
295/45R1828.5"11.6"5.2"−4.9%
265/50R1828.4"10.4"5.2"−4.9%
285/60R1831.5"11.2"6.7"+5.2%
265/65R1831.6"10.4"6.8"+5.5%

Same height on a different wheel

Sizes within 2% of 29.9" on 20" or 16" or 17" wheels.

SizeDiameterWidthSidewallvs 275/55R18
315/40R2029.9"12.4"5.0"+0.0%
235/75R1629.9"9.3"6.9"−0.1%
235/70R1730.0"9.3"6.5"+0.1%
275/60R1730.0"10.8"6.5"+0.3%
255/65R1730.1"10.0"6.5"+0.5%
255/70R1630.1"10.0"7.0"+0.5%

Speedometer with a different size

Actual speed when the speedometer is calibrated for 275/55R18.

Speedometer showson 265/55R18on 285/55R18on 285/50R18
30 mph29.6 mph30.4 mph29.3 mph
45 mph44.3 mph45.7 mph44.0 mph
60 mph59.1 mph60.9 mph58.6 mph
70 mph69.0 mph71.0 mph68.4 mph

275/55R18 FAQ

How tall is a 275/55R18 tire?

29.9 inches (760 mm). The sidewall is 6.0 inches.

How wide is a 275/55R18 tire?

10.8 inches (275 mm) section width, measured sidewall to sidewall.

What is 275/55R18 in flotation size?

About 29.9x10.8R18.

Can I use 265/55R18 instead of 275/55R18?

265/55R18 is −1.4% in diameter, within the common 3% guideline. It is 0.4" narrower.