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
Similar diameter does not establish interchangeability. Follow the vehicle manufacturer's approved sizes; see Michelin's tire-size guidance.
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. The 3 percent cutoff is a comparison filter, not a fitment approval. Use vehicle-approved sizes and check rim width, load and speed ratings, and clearances. 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.
For the effect on road speed and distance, see our worked speedometer example. When maintaining this set, use the rotation pattern guide to check whether tire direction or different front and rear sizes restrict rotation.
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. Actual dimensions depend on the tire model, tread depth, pressure and load; check the tire manufacturer specifications.
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%). These are nominal diameter comparisons, not approved replacements. Check vehicle-approved sizes, rim width, load and speed ratings, and clearance before changing size.