What 185/55R16 means
The inputs are 185 mm nominal section width, a 55-percent aspect ratio, and a 16-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 × 55 ÷ 100 = 101.75 mm. Adding two sidewalls to the 406.4 mm rim gives 609.9 mm (24.01 in) of nominal outside diameter.
A calculated reference
The 16-inch rim adds 25.4 mm compared with 185/55R15 while the nominal sidewall remains 101.75 mm. This is a clear example of a rim-only input change: the outside-diameter calculation changes, but its sidewall term does not.
Using a perfect-circle model, circumference is 1916.06 mm, equivalent to 521.91 revolutions per kilometer or 839.92 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 185/55R16, article 15576010000. 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