GarageCalc What 275/65R18 means
275 is the section width in millimeters (10.8 in). 65 is the aspect ratio: the sidewall is 65 percent of the width, so 275 × 0.65 = 179 mm (7.0 in). R is radial construction, and 18 is the wheel diameter in inches (457 mm). Stack two sidewalls on the wheel and you get the overall diameter: 457 + 2 × 179 = 815 mm, or 32.1 in.
A full marking adds a load index and speed rating after the size, for example 275/65R18 91V. Those two codes set how much weight and speed the tire is certified for; look them up in the load index chart and the speed rating chart.
Plus and minus sizing from 275/65R18
No common 19-inch size stays within 3 percent of 32.1 in. Going down one size, 255/75R17 is -0.0% with a taller 191 mm sidewall for more comfort and pothole margin. Anything inside 3 percent keeps the speedometer, ABS and gearing effectively stock; the comparison calculator shows the full speedometer table for any pair.
Which cars come with 275/65R18
Typical factory fitments include Ram 1500 (2019 on), Ford F-150 18-inch trims (2015 on) and Toyota Sequoia (2008-2022). Tire size changes with trim and wheel option, so confirm on the door-jamb placard before buying.
Frequently asked questions
How tall is a 275/65R18 tire?
32.1 inches (815 mm) in overall diameter: the 18-inch wheel (457 mm) plus two 179 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 275/65R18 in inches?
32.1 x 10.8 R18: 32.1 inches tall, 10.8 inches wide, on an 18-inch wheel. The sidewall is 7.0 inches and the circumference is 100.8 inches, so the tire turns 629 times per mile.
What tire sizes are equivalent to 275/65R18?
Within 3 percent of the same diameter on the same 18-inch wheel: 255/70R18 (-0.1%), 265/65R18 (-1.6%), 285/65R18 (+1.6%); on a 17-inch wheel: 255/75R17 (-0.0%), 275/70R17 (+0.3%). The percentage is the diameter change, which is also your speedometer error.
Can I use 285/65R18 instead of 275/65R18?
Dimensionally yes: 285/65R18 is 1.6% taller (+13 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 59.1 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 285 mm.