GarageCalc What 245/55R17 means
245 is the section width in millimeters (9.6 in). 55 is the aspect ratio: the sidewall is 55 percent of the width, so 245 × 0.55 = 135 mm (5.3 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 × 135 = 701 mm, or 27.6 in.
A full marking adds a load index and speed rating after the size, for example 245/55R17 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 245/55R17
Going up one wheel size, the closest match is 245/50R18 at +0.1% diameter with a 123 mm sidewall instead of 135 mm. Going down one size, 225/65R16 is -0.3% with a taller 146 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 245/55R17 tire?
27.6 inches (701 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 135 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 245/55R17 in inches?
27.6 x 9.6 R17: 27.6 inches tall, 9.6 inches wide, on a 17-inch wheel. The sidewall is 5.3 inches and the circumference is 86.7 inches, so the tire turns 730 times per mile.
What tire sizes are equivalent to 245/55R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 225/60R17 (+0.1%), 235/55R17 (-1.6%), 235/60R17 (+1.8%); on an 18-inch wheel: 245/50R18 (+0.1%), 225/55R18 (+0.5%); on a 16-inch wheel: 225/65R16 (-0.3%), 235/65R16 (+1.5%). The percentage is the diameter change, which is also your speedometer error.