GarageCalc What 255/30R22 means
255 is the section width in millimeters (10.0 in). 30 is the aspect ratio: the sidewall is 30 percent of the width, so 255 × 0.30 = 77 mm (3.0 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 × 77 = 712 mm, or 28.0 in.
A full marking adds a load index and speed rating after the size, for example 255/30R22 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 255/30R22
No common 23-inch size stays within 3 percent of 28.0 in. Going down one size, 255/35R21 is +0.0% with a taller 89 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 255/30R22 tire?
28.0 inches (712 mm) in overall diameter: the 22-inch wheel (559 mm) plus two 77 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 255/30R22 in inches?
28.0 x 10.0 R22: 28.0 inches tall, 10.0 inches wide, on a 22-inch wheel. The sidewall is 3.0 inches and the circumference is 88.0 inches, so the tire turns 720 times per mile.
What tire sizes are equivalent to 255/30R22?
Within 3 percent of the same diameter on the same 22-inch wheel: 245/30R22 (-0.8%); on a 21-inch wheel: 255/35R21 (+0.0%), 265/35R21 (+1.0%). The percentage is the diameter change, which is also your speedometer error.