The 31/10.5 tire size is an older size that gives the nominal tire measurement in inches. The size is commonly written 31x10.50R15; the tires fit on a 15-inch-diameter rim measuring 7 to 9 inches wide.
The 31x10.50R15 tire size is a light truck size, and the tires---most commonly used on older four-wheel-drive vehicles---have a wide cross section. Tread patterns range from mud and snow radials to extremely aggressive lugs not suitable for on-road driving.
The closest metric size to 31x10.50R15 is 265/75R15. This metric size indicates a tire diameter of 30.7 inches and width of 10.5 inches. The standard size of the 31x10.50 is 30.5 inches in diameter and 10.5 inches wide.
For replacement tires, the 265/75R15 size will provide more choices for tires with highway or all-season tread patterns. The original 31x10.50R15 size is the choice for finding aggressive off-road tires.
