Metric Tire Sizes Conversion

by Jarred Potter on December 24, 2012

One of the first things you look into after lifting a truck is upgrading to a larger tire.  When deciding on a larger tire there is many variables to look at. One of these is choosing metric or standard tire sizes?  All suspension lifts listings on the Suspension Connection web site will have a recommended tire size. We want to help you better understand and break down the side wall measurements for each. As well as provide the formula to convert metric to standard and vice versa.

  • Standard tire size:

 A standard tire size will be displayed as 35X1250 R 15 on the side wall of the tire.  The 35 depicts the height of the tire, 35” from top to bottom. The 1250 is the cross section or width of the tire12.5” wide.  The R displayed means it’s a Radial, and the 15 indicates a 15” rim diameter.

  • Metric tire size:

A metric tire size will be displayed as LT 315/70 R16 on the side wall of the tire. Lt Stands for light truck or if there was a P it stands for passenger car. The first three numbers represents the width of the tire (315 millimeters). The second two numbers 70, is Ratio of height to width (aspect ratio). The R shows that the tire is a Radial design. The 16 refers to rim diameter.

Aspect Ratio is the ratio of the height of the tire’s cross-section to its width. The two-digit number after the slash mark in a tire size is the aspect ratio. For example, in a size LT 315/70 R16 tire, the 70 means that the height is equal to 70% of the tire’s width. The bigger the aspect ratio, the bigger the tire’s sidewall will be.

  • The following formulas explain how to convert a metric tire size to inches.

 Tire size sample: LT 315/70 R16 

WIDTH:

                      First Numbers divided by 25.4 = WIDTH

Example: 315 / 25.4 = 12.40” equals Width

HEIGHT:

                   Multiply 2nd Numbers in percentage form by WIDTH, then 

                   Multiply by 2, then add 3rd numbers = Height                                 

                             Example: .70 X 12.40 = 8.68

8.68 X 2 = 17.36

17.36 + 16 = 33.360” equals Height

Solution: LT 315/70 R16 = 33.4” x 12.4” on 16” Rim

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