GarageCalc What 245/55R17 means
245 is the section width in millimeters (9.6 in). 55 is the aspect ratio: the sidewall is 55 percent of the width, so 245 × 0.55 = 135 mm (5.3 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 × 135 = 701 mm, or 27.6 in.
A full marking adds a load index and speed rating after the size, for example 245/55R17 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 245/55R17
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 245/50R18 at +0.1% diameter with a 123 mm sidewall instead of 135 mm. Going down one size, 225/65R16 is -0.3% with a taller 146 mm sidewall for more comfort and pothole margin. 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.
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 245/55R17 tire?
27.6 inches (701 mm) in overall diameter: the 17-inch wheel (432 mm) plus two 135 mm sidewalls. Actual dimensions depend on the tire model, tread depth, pressure and load; check the tire manufacturer specifications.
What is 245/55R17 in inches?
27.6 x 9.6 R17: 27.6 inches tall, 9.6 inches wide, on a 17-inch wheel. The sidewall is 5.3 inches and the circumference is 86.7 inches, so the tire turns 730 times per mile.
What tire sizes are equivalent to 245/55R17?
Within 3 percent of the same diameter on the same 17-inch wheel: 225/60R17 (+0.1%), 235/55R17 (-1.6%), 235/60R17 (+1.8%); on an 18-inch wheel: 245/50R18 (+0.1%), 225/55R18 (+0.5%); on a 16-inch wheel: 225/65R16 (-0.3%), 235/65R16 (+1.5%). These are nominal diameter comparisons, not approved replacements. Check vehicle-approved sizes, rim width, load and speed ratings, and clearance before changing size.