GarageCalc What 285/40R22 means
285 is the section width in millimeters (11.2 in). 40 is the aspect ratio: the sidewall is 40 percent of the width, so 285 × 0.40 = 114 mm (4.5 in). R is radial construction, and 22 is the wheel diameter in inches (559 mm). Stack two sidewalls on the wheel and you get the overall diameter: 559 + 2 × 114 = 787 mm, or 31.0 in.
A full marking adds a load index and speed rating after the size, for example 285/40R22 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 285/40R22
No common 23-inch size stays within 3 percent of 31.0 in. Going down one size, 285/45R21 is +0.4% with a taller 128 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 285/40R22 tire?
31.0 inches (787 mm) in overall diameter: the 22-inch wheel (559 mm) plus two 114 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 285/40R22 in inches?
31.0 x 11.2 R22: 31.0 inches tall, 11.2 inches wide, on a 22-inch wheel. The sidewall is 4.5 inches and the circumference is 97.3 inches, so the tire turns 651 times per mile.
What tire sizes are equivalent to 285/40R22?
Within 3 percent of the same diameter on the same 22-inch wheel: 275/40R22 (-1.0%), 265/40R22 (-2.0%), 305/40R22 (+2.0%); on a 21-inch wheel: 285/45R21 (+0.4%), 275/45R21 (-0.7%). The percentage is the diameter change, which is also your speedometer error.
Can I use 305/40R22 instead of 285/40R22?
Dimensionally yes: 305/40R22 is 2.0% taller (+16 mm) and 20 mm wider, and at a true 60 mph the speedometer would read 58.8 mph. The extra width needs about 0.39 in of clearance on each side of the tire and a rim width that suits 305 mm.