Metric Tire Conversion Applet
This application takes a metric tire size and returns the
size in inches. The purpose is to answer questions like, "I have
LT235/75R15s on my truck, how much clearance will 31s buy me?" and
"I know 30s will fit my Jeep with out a lift, but will a LT235/75R15?".
All this can be done with out breaking out the tape measure! You must
have a Java compatible browser to run this Applet.
How to Convert Metric Tire Sizes
Metric tire sizes are made up of four components: prefix, width, aspect
ratio, and wheel size. It takes three of these components to calculate
the diameter of the tire. It sure is not a very straight forward sizing
The prefix is used to indicate general use of the tire. The
tire input field trys to ignore the prefix and if your prefix causes an
error, just don't input it. The Gear and Tire Applet currently will
successfully ignore 'P' for passenger car and 'LT' for light truck. When
in doubt, drop the prefix.
The width simply the width of the tire in mm. For example the tire size
P215/75R15 has a width of 215mm.
The next component is the aspect ratio. The aspect ratio is the percentage
of the width that makes up the sidewall of the tire. In the above example
the aspect ratio is 75 or 75%, so the sidewall height is 75% of 215 or
161.25mm. If you want the diameter of the tire, you need to take into
acount that the diameter of the tire passes two sections of the side wall.
This means the sidewall takes up 161.25*2 or 322.5mm of the diameter.
The next component is the wheel size. In the above example the wheel size
is 15". If you convert the total sidewall into inches you get
322.5mm*0.03937in/mm or about 12.6". Add that to wheel size and you get the
diameter 15"+12.6" is 27.6". So a P215/75R15 tire has a diameter of about
Last modified Wednesday, 01-Dec-2010 09:20:06 MST
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