To help you understand tire sizes a little better here's a quick lesson.

For an example we'll use a fairly common tire size for trucks with a 3" lift, a 285/70/R17.

We'll first label the parts as follows:

285/70/R17

_^__^__^

_A__B___C

**- This is the width of the tire in millimeters. The conversion is 1"= 25.4mm so for our example: 285/25.4= 11.22" width.**

A

A

**- This part is the "aspect ratio" of the tire and is a relation of the tire's width to the sidewall height of the tire. In our example it's '70'. This means the sidewall height is 70% (.70 in calculation) of the width of the tire. That means the sidewall height is:**

B

B

11.22 x .70= 7.85"

BUT there is a 'sidewall' both above and below your wheel when measuring height, so you must multiply this by 2 when calculating the tire's overall height.

**- This third piece is simply your rim size. So, for a final calculation of a tire's size, you add this to the total from part**

C

C

**B**.

In conclusion, a 285/70/R17 equates to 11.22" wide and is (7.85x2)+17"= 32.71" tall, or basically equivalent to a 33x11.50R17 if we called it a standard size.

How about one more example, 265/75/R16:

Width: 265/25.4= 10.43"

Sidewall: 10.43 x .75= 7.82"

overall height: (7.82" x 2)+ 16"= 31.64" tall. Basically, a 32x10.50R16

This method of finding a tire size will work for every metric tire size out there!

NOTE:

It should also be mentioned that different manufacturers' tire sizes will slightly vary from these calculations. Its usually a very minor amount but it's still there none the less. For this reason I recommend everyone looking at tires to go to the respective Manufacturers web site and look up the exact specifications they list for the tire before buying a set, or to compare tires between different manufacturers.

Hope this helps someone and that you can calculate tire sizes without having to be reliant on a program.