GarageCalc What 285/60R18 means
285 is the section width in millimeters (11.2 in). 60 is the aspect ratio: the sidewall is 60 percent of the width, so 285 × 0.60 = 171 mm (6.7 in). R is radial construction, and 18 is the wheel diameter in inches (457 mm). Stack two sidewalls on the wheel and you get the overall diameter: 457 + 2 × 171 = 799 mm, or 31.5 in.
A full marking adds a load index and speed rating after the size, for example 285/60R18 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 285/60R18
Going up one wheel size, the closest match is 275/55R19 at -1.8% diameter with a 151 mm sidewall instead of 171 mm. Going down one size, 265/70R17 is +0.5% with a taller 186 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 285/60R18 tire?
31.5 inches (799 mm) in overall diameter: the 18-inch wheel (457 mm) plus two 171 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 285/60R18 in inches?
31.5 x 11.2 R18: 31.5 inches tall, 11.2 inches wide, on an 18-inch wheel. The sidewall is 6.7 inches and the circumference is 98.8 inches, so the tire turns 641 times per mile.
What tire sizes are equivalent to 285/60R18?
Within 3 percent of the same diameter on the same 18-inch wheel: 265/65R18 (+0.3%), 275/65R18 (+1.9%); on a 19-inch wheel: 275/55R19 (-1.8%); on a 17-inch wheel: 265/70R17 (+0.5%), 275/65R17 (-1.2%). The percentage is the diameter change, which is also your speedometer error.