What 255/70R17 means
The inputs are 255 mm nominal section width, a 70-percent aspect ratio, and a 17-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 × 70 ÷ 100 = 178.5 mm. Adding two sidewalls to the 431.8 mm rim gives 788.8 mm (31.06 in) of nominal outside diameter.
A calculated reference
At 70 percent, a 10 mm width increase would add 14 mm to full diameter when the rim is fixed. Its curated comparison with 265/70R17 demonstrates that relationship, while the external discussion is used only as evidence that the pair is considered.
Using a perfect-circle model, circumference is 2478.09 mm, equivalent to 403.54 revolutions per kilometer or 649.43 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 Grabber APT source includes 255/70 R 17, article 04507970000. 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
- Grabber APT — Specifications — General Tire
- Tire Markings Explained — Michelin
- Tire glossary — Michelin