What 215/55R17 means
The inputs are 215 mm nominal section width, a 55-percent aspect ratio, and a 17-inch nominal rim diameter. The R identifies radial construction. The width is not a wheel-width measurement, and the rim number is not the outside diameter of the tire.
Nominal sidewall height is 215 × 55 ÷ 100 = 118.25 mm. Adding two sidewalls to the 431.8 mm rim gives 668.3 mm (26.31 in) of nominal outside diameter.
A calculated reference
This is the original size in TireSpan’s worked reference example against 225/45R18. Its 668.3 mm calculated diameter supplies the denominator for that direction of comparison; swapping the inputs changes the percentage denominator.
Using a perfect-circle model, circumference is 2099.53 mm, equivalent to 476.3 revolutions per kilometer or 766.53 per mile. These are derived from unrounded diameter; actual rolling circumference also depends on the product and operating conditions.
Source and scope
General Tire’s AltiMAX RT45 source includes 215/55R17, article 15576270000. It was checked on October 27, 2026. That record verifies the published marking used here; it does not turn these calculated dimensions into that product’s measured specification or establish availability.
Use the exact product and vehicle requirements for load and speed ratings, permitted rim dimensions, inflation and clearance. Nominal geometry alone cannot verify fitment, braking behavior, handling or safety.
Sources and further reading
- AltiMAX RT45 — General Tire
- Tire Markings Explained — Michelin
- Tire glossary — Michelin