What 245/50R18 means
The inputs are 245 mm nominal section width, a 50-percent aspect ratio, and an 18-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 245 × 50 ÷ 100 = 122.5 mm. Adding two sidewalls to the 457.2 mm rim gives 702.2 mm (27.65 in) of nominal outside diameter.
A calculated reference
The 50-percent ratio makes two sidewalls equal 245 mm. Adding the 457.2 mm rim term yields 702.2 mm. A different product with the same marking can have a different measured shape; this page supplies a consistent nominal reference.
Using a perfect-circle model, circumference is 2206.03 mm, equivalent to 453.3 revolutions per kilometer or 729.52 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 245/50R18, article 15577800000. 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