What 235/60R18 means
The inputs are 235 mm nominal section width, a 60-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 235 × 60 ÷ 100 = 141 mm. Adding two sidewalls to the 457.2 mm rim gives 739.2 mm (29.1 in) of nominal outside diameter.
A calculated reference
The 141 mm sidewall is 11.75 mm taller than the nominal sidewall for 235/55R18. Doubling that difference gives 23.5 mm of diameter change. A comfort question may motivate that comparison, but geometry does not supply a ride-quality score.
Using a perfect-circle model, circumference is 2322.27 mm, equivalent to 430.61 revolutions per kilometer or 693.01 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 235/60R18, article 15576630000. 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