GarageCalc What 255/65R17 means
255 is the section width in millimeters (10.0 in). 65 is the aspect ratio: the sidewall is 65 percent of the width, so 255 × 0.65 = 166 mm (6.5 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 × 166 = 763 mm, or 30.1 in.
A full marking adds a load index and speed rating after the size, for example 255/65R17 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 255/65R17
Going up one wheel size, the closest match is 255/60R18 at -0.0% diameter with a 153 mm sidewall instead of 166 mm. Going down one size, 255/70R16 is +0.0% with a taller 179 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.
Frequently asked questions
How tall is a 255/65R17 tire?
30.1 inches (763 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 166 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 255/65R17 in inches?
30.1 x 10.0 R17: 30.1 inches tall, 10.0 inches wide, on a 17-inch wheel. The sidewall is 6.5 inches and the circumference is 94.4 inches, so the tire turns 671 times per mile.
What tire sizes are equivalent to 255/65R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 235/70R17 (-0.3%), 245/70R17 (+1.5%), 245/65R17 (-1.7%); on an 18-inch wheel: 255/60R18 (-0.0%), 235/65R18 (-0.1%); on a 16-inch wheel: 255/70R16 (+0.0%), 235/75R16 (-0.6%). The percentage is the diameter change, which is also your speedometer error.
Can I use 265/65R17 instead of 255/65R17?
Dimensionally yes: 265/65R17 is 1.7% taller (+13 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 59.0 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.