GarageCalc What 285/75R17 means
285 is the section width in millimeters (11.2 in). 75 is the aspect ratio: the sidewall is 75 percent of the width, so 285 × 0.75 = 214 mm (8.4 in). R is radial construction, and 17 is the wheel diameter in inches (432 mm). Stack two sidewalls on the wheel and you get the overall diameter: 432 + 2 × 214 = 859 mm, or 33.8 in.
A full marking adds a load index and speed rating after the size, for example 285/75R17 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 285/75R17
Going up one wheel size, the closest match is 285/70R18 at -0.4% diameter with a 200 mm sidewall instead of 214 mm. Going down one size, 285/75R16 is -3.0% with a taller 214 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 285/75R17 tire?
33.8 inches (859 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 214 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 285/75R17 in inches?
33.8 x 11.2 R17: 33.8 inches tall, 11.2 inches wide, on a 17-inch wheel. The sidewall is 8.4 inches and the circumference is 106.3 inches, so the tire turns 596 times per mile.
What tire sizes are equivalent to 285/75R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 295/70R17 (-1.7%); on an 18-inch wheel: 285/70R18 (-0.4%), 295/70R18 (+1.3%); on a 16-inch wheel: 285/75R16 (-3.0%). The percentage is the diameter change, which is also your speedometer error.
Can I use 295/70R17 instead of 285/75R17?
Dimensionally yes: 295/70R17 is 1.7% shorter (-15 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 61.0 mph. The extra width needs about 0.20 in of clearance on each side of the tire and a rim width that suits 295 mm.