What 255/40R19 means
The inputs are 255 mm nominal section width, a 40-percent aspect ratio, and a 19-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 255 × 40 ÷ 100 = 102 mm. Adding two sidewalls to the 482.6 mm rim gives 686.6 mm (27.03 in) of nominal outside diameter.
A calculated reference
The source lists a ZR marking, which is preserved in the provenance record. The geometry uses 255 mm, 40 percent and 19 inches, producing a 102 mm sidewall. The normalized page heading is not a complete service description.
Using a perfect-circle model, circumference is 2157.02 mm, equivalent to 463.6 revolutions per kilometer or 746.1 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 255/40 ZR 19, article 15573170000. 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