What 245/40R18 means
The inputs are 245 mm nominal section width, a 40-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 × 40 ÷ 100 = 98 mm. Adding two sidewalls to the 457.2 mm rim gives 653.2 mm (25.72 in) of nominal outside diameter.
A calculated reference
The verified manufacturer entry uses ZR in its source marking. TireSpan extracts width, ratio and rim diameter for geometry while retaining the original notation in the evidence record. It makes no conclusion about speed capability from the normalized R form.
Using a perfect-circle model, circumference is 2052.09 mm, equivalent to 487.31 revolutions per kilometer or 784.25 per mile. These are derived from unrounded diameter; actual rolling circumference also depends on the product and operating conditions.
Source and scope
Continental’s ExtremeContact DWS06 Plus source includes 245/40 ZR 18, article 15573000000. 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. The source’s ZR notation is retained for traceability; the normalized page notation is used only to identify geometric inputs.
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
- ExtremeContact DWS06 Plus — Specifications — Continental Tire
- Tire Markings Explained — Michelin
- Tire glossary — Michelin