Metric / Inch Tire Size Converter:Tire Size Converter | Metric to Inch Tire Size Calculator
In-depth Sidewall Markings Definitions & Meanings: http://www.tirerack.com/tires/tirete....jsp?techid=46
Quick Summary ('Borrowed' from the Internet):
We'll first label the parts as follows:
A- 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.
B- 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:
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.
C- 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 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
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