What 185/65R15 means
The inputs are 185 mm nominal section width, a 65-percent aspect ratio, and a 15-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 185 × 65 ÷ 100 = 120.25 mm. Adding two sidewalls to the 381 mm rim gives 621.5 mm (24.47 in) of nominal outside diameter.
A calculated reference
The curated comparison with 195/65R15 keeps the 15-inch rim and the aspect ratio unchanged. It shows why a 10 mm width increase also increases each sidewall by 6.5 mm. The unchanged ratio label does not mean unchanged sidewall height.
Using a perfect-circle model, circumference is 1952.5 mm, equivalent to 512.16 revolutions per kilometer or 824.25 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 185/65R15, article 15576070000. 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