GarageCalc What 205/55R17 means
205 is the section width in millimeters (8.1 in). 55 is the aspect ratio: the sidewall is 55 percent of the width, so 205 × 0.55 = 113 mm (4.4 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 × 113 = 657 mm, or 25.9 in.
A full marking adds a load index and speed rating after the size, for example 205/55R17 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 205/55R17
Going up one wheel size, the closest match is 225/45R18 at +0.4% diameter with a 101 mm sidewall instead of 113 mm. Going down one size, 225/55R16 is -0.5% with a taller 124 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 205/55R17 tire?
25.9 inches (657 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 113 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 205/55R17 in inches?
25.9 x 8.1 R17: 25.9 inches tall, 8.1 inches wide, on a 17-inch wheel. The sidewall is 4.4 inches and the circumference is 81.3 inches, so the tire turns 779 times per mile.
What tire sizes are equivalent to 205/55R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 225/50R17 (-0.1%), 215/50R17 (-1.6%), 215/55R17 (+1.7%); on an 18-inch wheel: 225/45R18 (+0.4%), 215/45R18 (-1.0%); on a 16-inch wheel: 225/55R16 (-0.5%), 205/60R16 (-0.7%). The percentage is the diameter change, which is also your speedometer error.
Can I use 215/50R17 instead of 205/55R17?
Dimensionally yes: 215/50R17 is 1.6% shorter (-11 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 61.0 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 215 mm.