How to convert your metric tire size to inches

[hobbybob]

Hello!

To get the tire size in inches we need to use this formula.

Width x Aspect Ratio = Section Height

Section Height x 2 = Combined Section Height

Combined Section Height + Wheel Diameter = Tire Diameter

for my example I will use the following tire size.

235/75R 15

The first number (235) is the width of the tire in millimeters.

235 divided by 25.4 = 9.25 inches

The second number (75) is the aspect ratio or the difference in the rubber height compared to tire width.

The R stands for radial tire.

235 x .75 = 176.25 millimeters

This number needs multiplied by 2 to add the top and bottom rubber section together.

176.25 x 2 = 352.5 millimeters

352.5 divided by 25.4 = 13.877 inches .

The last number (15) is the wheel size, add this to the last number we got

13.877 + 15 = 28.877 inches

A 235/75R 15 tire = 9.25 inches x 28.77 inches with a 15 inch rim

I have a couple really cool links.

The first one is a Tire comparison calculator furnished by Americas tire co. You list your current tire size and a wanted tire size and It will calculate the difference in size, road speed, revolutions per mile.

http://www.americastire.com/dtcs/infoTireMath.dos

This next site is the best metric conversion site I have ever seen.

http://www.worldwidemetric.com/metcal.htm

I hope this helps someone I tried to make it as clear as I could.

Please let me know what you think!