255/70R18 designates a tire 255 mm (10.0") wide with a sidewall 70% as tall as it is wide — about 179 mm (7.0") — mounted on a 18-inch wheel. That works out to an overall diameter of roughly 32.1", a circumference of about 100.7", and approximately 629 revolutions per mile. Exact figures vary slightly by manufacturer and tread design.
Of the 67 255/70R18 tire models we track, the most common category is all-terrain (39 models), followed by highway all-season truck (21) — a good indicator of the kind of vehicles and driving this size is designed for.