GarageCalc What 185/55R16 means
185 is the section width in millimeters (7.3 in). 55 is the aspect ratio: the sidewall is 55 percent of the width, so 185 × 0.55 = 102 mm (4.0 in). R is radial construction, and 16 is the wheel diameter in inches (406 mm). Stack two sidewalls on the wheel and you get the overall diameter: 406 + 2 × 102 = 610 mm, or 24.0 in.
A full marking adds a load index and speed rating after the size, for example 185/55R16 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 185/55R16
Going up one wheel size, the closest match is 205/45R17 at +1.0% diameter with a 92 mm sidewall instead of 102 mm. Going down one size, 175/65R15 is -0.2% with a taller 114 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 185/55R16 tire?
24.0 inches (610 mm) in overall diameter: the 16-inch wheel (406 mm) plus two 102 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 185/55R16 in inches?
24.0 x 7.3 R16: 24.0 inches tall, 7.3 inches wide, on a 16-inch wheel. The sidewall is 4.0 inches and the circumference is 75.4 inches, so the tire turns 840 times per mile.
What tire sizes are equivalent to 185/55R16?
Within 3 percent of the same diameter on the same 16-inch wheel: 205/50R16 (+0.2%), 195/50R16 (-1.4%), 195/55R16 (+1.8%); on a 17-inch wheel: 205/45R17 (+1.0%), 205/40R17 (-2.3%); on a 15-inch wheel: 175/65R15 (-0.2%), 205/55R15 (-0.6%). The percentage is the diameter change, which is also your speedometer error.
Can I use 195/50R16 instead of 185/55R16?
Dimensionally yes: 195/50R16 is 1.4% shorter (-9 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 60.8 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 195 mm.