GarageCalc What 315/70R17 means
315 is the section width in millimeters (12.4 in). 70 is the aspect ratio: the sidewall is 70 percent of the width, so 315 × 0.70 = 221 mm (8.7 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 × 221 = 873 mm, or 34.4 in.
A full marking adds a load index and speed rating after the size, for example 315/70R17 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 315/70R17
Going up one wheel size, the closest match is 295/70R18 at -0.3% diameter with a 207 mm sidewall instead of 221 mm. No common 16-inch size stays within 3 percent either. 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 315/70R17
Typical factory fitments include Ford F-150 Raptor (2017 on, 35-inch tire). Tire size changes with trim and wheel option, so confirm on the door-jamb placard before buying.
Frequently asked questions
How tall is a 315/70R17 tire?
34.4 inches (873 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 221 mm sidewalls. Real tires land within about 1 to 2 percent of that depending on brand, tread depth and pressure.
What is 315/70R17 in inches?
34.4 x 12.4 R17: 34.4 inches tall, 12.4 inches wide, on a 17-inch wheel. The sidewall is 8.7 inches and the circumference is 108.0 inches, so the tire turns 587 times per mile.
What tire sizes are equivalent to 315/70R17?
Within 3 percent of the same diameter; on an 18-inch wheel: 295/70R18 (-0.3%), 325/65R18 (+0.8%). The percentage is the diameter change, which is also your speedometer error.