GarageCalc What 295/30R18 means
295 is the section width in millimeters (11.6 in). 30 is the aspect ratio: the sidewall is 30 percent of the width, so 295 × 0.30 = 89 mm (3.5 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 × 89 = 634 mm, or 25.0 in.
A full marking adds a load index and speed rating after the size, for example 295/30R18 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 295/30R18
Going up one wheel size, the closest match is 275/30R19 at +2.1% diameter with a 83 mm sidewall instead of 89 mm. Going down one size, 275/40R17 is +2.8% with a taller 110 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 295/30R18 tire?
25.0 inches (634 mm) in overall diameter: the 18-inch wheel (457 mm) plus two 89 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 295/30R18 in inches?
25.0 x 11.6 R18: 25.0 inches tall, 11.6 inches wide, on an 18-inch wheel. The sidewall is 3.5 inches and the circumference is 78.4 inches, so the tire turns 808 times per mile.
What tire sizes are equivalent to 295/30R18?
Within 3 percent of the same diameter on the same 18-inch wheel: 285/30R18 (-0.9%), 275/35R18 (+2.4%); on a 19-inch wheel: 275/30R19 (+2.1%); on a 17-inch wheel: 275/40R17 (+2.8%). The percentage is the diameter change, which is also your speedometer error.