GarageCalc What 205/55R15 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 15 is the wheel diameter in inches (381 mm). Stack two sidewalls on the wheel and you get the overall diameter: 381 + 2 × 113 = 607 mm, or 23.9 in.
A full marking adds a load index and speed rating after the size, for example 205/55R15 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 205/55R15
Going up one wheel size, the closest match is 185/55R16 at +0.6% diameter with a 102 mm sidewall instead of 113 mm. Going down one size, 195/65R14 is +0.4% with a taller 127 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 205/55R15 tire?
23.9 inches (607 mm) in overall diameter: the 15-inch wheel (381 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 205/55R15 in inches?
23.9 x 8.1 R15: 23.9 inches tall, 8.1 inches wide, on a 15-inch wheel. The sidewall is 4.4 inches and the circumference is 75.0 inches, so the tire turns 845 times per mile.
What tire sizes are equivalent to 205/55R15?
Within 3 percent of the same diameter on the same 15-inch wheel: 185/60R15 (-0.6%), 195/60R15 (+1.4%), 195/55R15 (-1.8%); on a 16-inch wheel: 185/55R16 (+0.6%), 205/50R16 (+0.8%); on a 14-inch wheel: 195/65R14 (+0.4%), 185/70R14 (+1.3%). The percentage is the diameter change, which is also your speedometer error.