GarageCalc What 275/55R20 means
275 is the section width in millimeters (10.8 in). 55 is the aspect ratio: the sidewall is 55 percent of the width, so 275 × 0.55 = 151 mm (6.0 in). R is radial construction, and 20 is the wheel diameter in inches (508 mm). Stack two sidewalls on the wheel and you get the overall diameter: 508 + 2 × 151 = 811 mm, or 31.9 in.
A full marking adds a load index and speed rating after the size, for example 275/55R20 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 275/55R20
Going up one wheel size, the closest match is 275/50R21 at -0.3% diameter with a 138 mm sidewall instead of 151 mm. No common 19-inch size stays within 3 percent either. 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 275/55R20
Typical factory fitments include Ford F-150 Lariat and King Ranch 20-inch, Ram 1500 20-inch, Toyota Tundra 20-inch (2014-2021) and Chevrolet Tahoe and GMC Yukon 20-inch (2015-2020). Tire size changes with trim and wheel option, so confirm on the door-jamb placard before buying.
Frequently asked questions
How tall is a 275/55R20 tire?
31.9 inches (811 mm) in overall diameter: the 20-inch wheel (508 mm) plus two 151 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 275/55R20 in inches?
31.9 x 10.8 R20: 31.9 inches tall, 10.8 inches wide, on a 20-inch wheel. The sidewall is 6.0 inches and the circumference is 100.2 inches, so the tire turns 632 times per mile.
What tire sizes are equivalent to 275/55R20?
Within 3 percent of the same diameter on the same 20-inch wheel: 285/55R20 (+1.4%), 265/60R20 (+1.9%), 285/50R20 (-2.2%); on a 21-inch wheel: 275/50R21 (-0.3%), 285/45R21 (-2.5%). The percentage is the diameter change, which is also your speedometer error.
Can I use 285/55R20 instead of 275/55R20?
Dimensionally yes: 285/55R20 is 1.4% taller (+11 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 59.2 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.