GarageCalc What 255/80R17 means
255 is the section width in millimeters (10.0 in). 80 is the aspect ratio: the sidewall is 80 percent of the width, so 255 × 0.80 = 204 mm (8.0 in). R is radial construction, and 17 is the wheel diameter in inches (432 mm). Stack two sidewalls on the wheel and you get the overall diameter: 432 + 2 × 204 = 840 mm, or 33.1 in.
A full marking adds a load index and speed rating after the size, for example 255/80R17 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 255/80R17
Going up one wheel size, the closest match is 275/70R18 at +0.3% diameter with a 193 mm sidewall instead of 204 mm. No common 16-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.
Frequently asked questions
How tall is a 255/80R17 tire?
33.1 inches (840 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 204 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 255/80R17 in inches?
33.1 x 10.0 R17: 33.1 inches tall, 10.0 inches wide, on a 17-inch wheel. The sidewall is 8.0 inches and the circumference is 103.9 inches, so the tire turns 610 times per mile.
What tire sizes are equivalent to 255/80R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 275/70R17 (-2.7%); on an 18-inch wheel: 275/70R18 (+0.3%), 265/70R18 (-1.4%). The percentage is the diameter change, which is also your speedometer error.
Can I use 275/70R17 instead of 255/80R17?
Dimensionally yes: 275/70R17 is 2.7% shorter (-23 mm) and 20 mm wider, and at a true 60 mph the speedometer would read 61.7 mph. The extra width needs about 0.39 in of clearance on each side of the tire and a rim width that suits 275 mm.