285/40R20 designates a tire 285 mm (11.2") wide with a sidewall 40% as tall as it is wide — about 114 mm (4.5") — mounted on a 20-inch wheel. That works out to an overall diameter of roughly 29.0", a circumference of about 91.0", and approximately 696 revolutions per mile. Exact figures vary slightly by manufacturer and tread design.
Of the 32 285/40R20 tire models we track, the most common category is winter (10 models), followed by ultra high performance summer (9) — a good indicator of the kind of vehicles and driving this size is designed for.