GarageCalc What 205/45R17 means
205 is the section width in millimeters (8.1 in). 45 is the aspect ratio: the sidewall is 45 percent of the width, so 205 × 0.45 = 92 mm (3.6 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 × 92 = 616 mm, or 24.3 in.
A full marking adds a load index and speed rating after the size, for example 205/45R17 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 205/45R17
Going up one wheel size, the closest match is 225/35R18 at -0.3% diameter with a 79 mm sidewall instead of 92 mm. Going down one size, 195/55R16 is +0.7% with a taller 107 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.
Which cars come with 205/45R17
Typical factory fitments include Mazda MX-5 (ND) and Mini Cooper 17-inch trims. Tire size changes with trim and wheel option, so confirm on the door-jamb placard before buying.
Frequently asked questions
How tall is a 205/45R17 tire?
24.3 inches (616 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 92 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 205/45R17 in inches?
24.3 x 8.1 R17: 24.3 inches tall, 8.1 inches wide, on a 17-inch wheel. The sidewall is 3.6 inches and the circumference is 76.2 inches, so the tire turns 831 times per mile.
What tire sizes are equivalent to 205/45R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 225/40R17 (-0.7%), 215/45R17 (+1.5%), 215/40R17 (-2.0%); on an 18-inch wheel: 225/35R18 (-0.3%), 215/35R18 (-1.4%); on a 16-inch wheel: 195/55R16 (+0.7%), 205/50R16 (-0.8%). The percentage is the diameter change, which is also your speedometer error.
Can I use 215/45R17 instead of 205/45R17?
Dimensionally yes: 215/45R17 is 1.5% taller (+9 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 59.1 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.