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The Mystery Of Tire Size
Calculation And How Its Done
For some people calculating tire size is black magic or a
mathematical nightmare. Its really quite simple thought.
Tire Size Calculation Basics
Width x Aspect Ratio = Section Height x 2
= Combined Section Height + Wheel Diameter = Tire Diameter
Example...185/60R14 85H or 185/60HR14
185mm x .60=111mm x 2=222mm + 355.6mm(14")= 577.6mm or
22.74"
The first number is the width of the tire in millimeters,
measured from sidewall to sidewall. To convert to inches,
divide by 25.4 In the example above, the width is 185mm or
7.28".
The second number is the aspect ratio. This is a ratio of
sidewall height to width. In the example above, the tire is
7.28" wide, multiply that by the aspect ratio to find the
height of one sidewall. In this case, 185x0.60=111mm or
7.28"x0.60=4.36".
The last number is the diameter of the wheel in inches.
Tire calculation for the outside diameter of a tire:
- take the sidewall
height and multiply by 2,(remember that the diameter is made
up of 2 sidewalls, the one above the wheel, and the one
below the wheel)
- and add the diameter of the wheel to get
your answer.
article courteousy
The Tire Rack
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