Yeah they're the same size. 265 millimeters is section width, the widest part of the tire halfway up the sidewall. 75 means that the sidewall is 75% as tall as the section width. So the sidewall is 75% of 265, or 199 millimeters tall. Two sidewall heights plus the rim height will give you the height of the tire, or 2*199 millimeters + 15 inches. 398 millimeters divided by 25.4 millimeters per inch = 15.65 inches, + 15 inches = 30.65 inches. And 265 / 25.4 = 10.43 inches of section width. So it's a 30.65 x 10.43R15, although due to the undersizing involved in tire sizes it usually ends up identically to a 31x10.50. The wierd part is, since rim size comes into account in the height of a metric sized tire, flotation sizes like 31x10.5R15 and a 31x10.5R16 would be the same height, but a 265/75R16 is an inch taller than a 265/75R15.