GarageCalc What 225/55R17 means
225 is the section width in millimeters (8.9 in). 55 is the aspect ratio: the sidewall is 55 percent of the width, so 225 × 0.55 = 124 mm (4.9 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 × 124 = 679 mm, or 26.7 in.
A full marking adds a load index and speed rating after the size, for example 225/55R17 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 225/55R17
Going up one wheel size, the closest match is 245/45R18 at -0.2% diameter with a 110 mm sidewall instead of 124 mm. Going down one size, 225/60R16 is -0.4% with a taller 135 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 225/55R17 tire?
26.7 inches (679 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 124 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 225/55R17 in inches?
26.7 x 8.9 R17: 26.7 inches tall, 8.9 inches wide, on a 17-inch wheel. The sidewall is 4.9 inches and the circumference is 84.0 inches, so the tire turns 754 times per mile.
What tire sizes are equivalent to 225/55R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 215/60R17 (+1.5%), 215/55R17 (-1.6%), 235/55R17 (+1.6%); on an 18-inch wheel: 245/45R18 (-0.2%), 225/50R18 (+0.4%); on a 16-inch wheel: 225/60R16 (-0.4%), 205/65R16 (-0.9%). The percentage is the diameter change, which is also your speedometer error.
Can I use 235/55R17 instead of 225/55R17?
Dimensionally yes: 235/55R17 is 1.6% taller (+11 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 235 mm.