GarageCalc What 285/65R20 means
285 is the section width in millimeters (11.2 in). 65 is the aspect ratio: the sidewall is 65 percent of the width, so 285 × 0.65 = 185 mm (7.3 in). R is radial construction, and 20 is the wheel diameter in inches (508 mm). Stack two sidewalls on the wheel and you get the overall diameter: 508 + 2 × 185 = 879 mm, or 34.6 in.
A full marking adds a load index and speed rating after the size, for example 285/65R20 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 285/65R20
No common size on a 19 or 21-inch wheel stays within 3 percent of 34.6 in, so 285/65R20 is best replaced like for like. The comparison calculator checks any candidate against the 3 percent guideline.
Frequently asked questions
How tall is a 285/65R20 tire?
34.6 inches (879 mm) in overall diameter: the 20-inch wheel (508 mm) plus two 185 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 285/65R20 in inches?
34.6 x 11.2 R20: 34.6 inches tall, 11.2 inches wide, on a 20-inch wheel. The sidewall is 7.3 inches and the circumference is 108.7 inches, so the tire turns 583 times per mile.
What tire sizes are equivalent to 285/65R20?
Within 3 percent of the same diameter on the same 20-inch wheel: 305/60R20 (-0.5%), 275/65R20 (-1.5%), 295/65R20 (+1.5%). The percentage is the diameter change, which is also your speedometer error.
Can I use 295/65R20 instead of 285/65R20?
Dimensionally yes: 295/65R20 is 1.5% taller (+13 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 295 mm.