Many posts concern tires and their actual sizes. This was located on another site and may be of use here.


METRIC TIRE SIZE CONVERSION CHART


15 inch tires sizes

Width Aspect Wheel Diameter Section Width
205/70 15 = 26.3 8.1
245/70 15 = 28.5 9.6
205/75 15 = 27.1 8.1
215/75 15 = 27.7 8.5
225/75 15 = 28.3 8.9
235/75 15 = 28.9 9.3
245/75 15 = 29.5 9.6
265/75 15 = 30.6 10.4
215/85 15 = 29.4 8.5
245/85 15 = 31.4 9.6
275/85 15 = 33.4 10.8
315/85 15 = 36.1 12.4
325/60 15 = 30.4 12.8




16 inch tires sizes

Width Aspect Wheel Diameter Section Width
305/65 16 = 31.6 12.0
345/65 16 = 33.7 13.6
245/70 16 = 29.5 9.6
305/70 16 = 32.8 12.0
225/75 16 = 29.3 8.9
245/75 16 = 30.5 9.6
265/75 16 = 31.6 10.4
285/75 16 = 32.8 11.2
295/75 16 = 33.3 11.6
215/85 16 = 30.4 8.5
235/85 16 = 31.7 9.3
255/85 16 = 33.1 10.0
265/85 16 = 33.7 10.4
305/85 16 = 36.4 12.0
255/70 16 = 30.1 10.0


The above numbers are computed values and some rounding has been done on the computed values. The actual tire sizes can and will vary depending on the tire manufacturer.

To compute the values in the table above, use the formula of:

HEIGHT = ((width * aspect-ratio * 2) / 2550) + rim size

WIDTH = (width / 25.50 )

For example, a 235/75R15 tire is ((235*75*2)/2550)+15) = 28.8 inches of tire height. The tire width is figured by 235/25.5 = 9.21

Metric tire sizes are stated as three numbers. The way it reads is:

width / aspect ratio R tire rim size
235 / 75 R 15