GarageCalc What 235/70R17 means
235 is the section width in millimeters (9.3 in). 70 is the aspect ratio: the sidewall is 70 percent of the width, so 235 × 0.70 = 165 mm (6.5 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 × 165 = 761 mm, or 30.0 in.
A full marking adds a load index and speed rating after the size, for example 235/70R17 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 235/70R17
Going up one wheel size, the closest match is 235/65R18 at +0.2% diameter with a 153 mm sidewall instead of 165 mm. Going down one size, 235/75R16 is -0.2% with a taller 176 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 235/70R17 tire?
30.0 inches (761 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 165 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 235/70R17 in inches?
30.0 x 9.3 R17: 30.0 inches tall, 9.3 inches wide, on a 17-inch wheel. The sidewall is 6.5 inches and the circumference is 94.1 inches, so the tire turns 673 times per mile.
What tire sizes are equivalent to 235/70R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 255/65R17 (+0.3%), 245/65R17 (-1.4%), 245/70R17 (+1.8%); on an 18-inch wheel: 235/65R18 (+0.2%), 255/60R18 (+0.3%); on a 16-inch wheel: 235/75R16 (-0.2%), 255/70R16 (+0.3%). The percentage is the diameter change, which is also your speedometer error.
Can I use 245/65R17 instead of 235/70R17?
Dimensionally yes: 245/65R17 is 1.4% shorter (-11 mm) and 10 mm wider, and at a true 60 mph the speedometer would read 60.8 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.