GarageCalc What 265/35R18 means
265 is the section width in millimeters (10.4 in). 35 is the aspect ratio: the sidewall is 35 percent of the width, so 265 × 0.35 = 93 mm (3.7 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 × 93 = 643 mm, or 25.3 in.
A full marking adds a load index and speed rating after the size, for example 265/35R18 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 265/35R18
Going up one wheel size, the closest match is 265/30R19 at -0.2% diameter with a 80 mm sidewall instead of 93 mm. Going down one size, 255/40R17 is -1.1% with a taller 102 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 265/35R18 tire?
25.3 inches (643 mm) in overall diameter: the 18-inch wheel (457 mm) plus two 93 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 265/35R18 in inches?
25.3 x 10.4 R18: 25.3 inches tall, 10.4 inches wide, on an 18-inch wheel. The sidewall is 3.7 inches and the circumference is 79.5 inches, so the tire turns 797 times per mile.
What tire sizes are equivalent to 265/35R18?
Within 3 percent of the same diameter on the same 18-inch wheel: 255/35R18 (-1.1%), 275/35R18 (+1.1%), 245/40R18 (+1.6%); on a 19-inch wheel: 265/30R19 (-0.2%), 275/30R19 (+0.8%); on a 17-inch wheel: 255/40R17 (-1.1%), 275/40R17 (+1.4%). The percentage is the diameter change, which is also your speedometer error.
Can I use 275/35R18 instead of 265/35R18?
Dimensionally yes: 275/35R18 is 1.1% taller (+7 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 59.4 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 275 mm.