GarageCalc What 255/75R17 means
255 is the section width in millimeters (10.0 in). 75 is the aspect ratio: the sidewall is 75 percent of the width, so 255 × 0.75 = 191 mm (7.5 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 × 191 = 814 mm, or 32.1 in.
A full marking adds a load index and speed rating after the size, for example 255/75R17 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 255/75R17
Going up one wheel size, the closest match is 255/70R18 at -0.0% diameter with a 179 mm sidewall instead of 191 mm. Going down one size, 235/85R16 is -1.0% with a taller 200 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 255/75R17
Typical factory fitments include Jeep Wrangler JK Rubicon (2007-2018). Tire size changes with trim and wheel option, so confirm on the door-jamb placard before buying.
Frequently asked questions
How tall is a 255/75R17 tire?
32.1 inches (814 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 191 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 255/75R17 in inches?
32.1 x 10.0 R17: 32.1 inches tall, 10.0 inches wide, on a 17-inch wheel. The sidewall is 7.5 inches and the circumference is 100.7 inches, so the tire turns 629 times per mile.
What tire sizes are equivalent to 255/75R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 275/70R17 (+0.3%), 235/80R17 (-0.8%), 265/70R17 (-1.4%); on an 18-inch wheel: 255/70R18 (-0.0%), 275/65R18 (+0.0%); on a 16-inch wheel: 235/85R16 (-1.0%), 265/75R16 (-1.3%). The percentage is the diameter change, which is also your speedometer error.
Can I use 265/70R17 instead of 255/75R17?
Dimensionally yes: 265/70R17 is 1.4% shorter (-12 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 60.9 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 265 mm.