GarageCalc What 235/55R18 means
235 is the section width in millimeters (9.3 in). 55 is the aspect ratio: the sidewall is 55 percent of the width, so 235 × 0.55 = 129 mm (5.1 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 × 129 = 716 mm, or 28.2 in.
A full marking adds a load index and speed rating after the size, for example 235/55R18 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 235/55R18
Going up one wheel size, the closest match is 235/50R19 at +0.3% diameter with a 118 mm sidewall instead of 129 mm. Going down one size, 235/60R17 is -0.3% with a taller 141 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.
Which cars come with 235/55R18
Typical factory fitments include Toyota RAV4 XLE (2013-2018). Tire size changes with trim and wheel option, so confirm on the door-jamb placard before buying.
Frequently asked questions
How tall is a 235/55R18 tire?
28.2 inches (716 mm) in overall diameter: the 18-inch wheel (457 mm) plus two 129 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 235/55R18 in inches?
28.2 x 9.3 R18: 28.2 inches tall, 9.3 inches wide, on an 18-inch wheel. The sidewall is 5.1 inches and the circumference is 88.5 inches, so the tire turns 716 times per mile.
What tire sizes are equivalent to 235/55R18?
Within 3 percent of the same diameter on the same 18-inch wheel: 225/55R18 (-1.5%), 245/55R18 (+1.5%), 225/60R18 (+1.6%); on a 19-inch wheel: 235/50R19 (+0.3%), 255/45R19 (-0.5%); on a 17-inch wheel: 235/60R17 (-0.3%), 215/65R17 (-0.6%). The percentage is the diameter change, which is also your speedometer error.
Can I use 245/55R18 instead of 235/55R18?
Dimensionally yes: 245/55R18 is 1.5% taller (+11 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 245 mm.