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Understanding Metric Tire Measurements

A chart to convert Metric tire measurements to Imperial while explaining what the numbers mean.
Metric to Imperial Tire Conversion Chart
Metric Imperial   Metric Imperial   Metric Imperial
215/75/15 27.7"x 8.5"   245/75/16 30.5"x 9.6"   315/70/17 34.4"x 12.4"
225/70/15 27.4"x 8.9"   255/70/16 30.0"x 10.0"   275/65/18 32.1"x 11.0"
225/75/15 28.3"x 8.9"   265/70/16 30.6"x 10.4"   375/50/18 33.0"x 15.4"
235/75/15 29.0"x 9.3"   265/75/16 31.6"x 10.4"   325/60/18 33.2"x 13.3"
245/75/15 29.5"x 9.6"   275/70/16 31.2"x 10.8"   325/65/18 34.8"x 13.5"
255/75/15 30.0"x 10.0"   285/75/16 32.8"x 11.2"   305/70/18 35.0"x 12.2"
265/75/15 30.6"x 10.4"   295/75/16 33.4"x 11.6"   375/60/18 35.7"x 15.5"
205/85/16 29.7"x 8.1"   305/70/16 33.0"x 12.2"   395/65/18 37.8"x 15.7"
215/75/16 28.7"x 8.5"   315/75/16 34.8"x 12.4"
  325/50/20 33.0"x 13.2"
225/70/16 28.4"x 8.9"   375/55/16 32.8"x 15.5"    
225/75/16 29.2"x 8.9"   395/70/16 37.9"x 16.0"      
235/70/16 29.0"x 9.3"   245/70/17 30.6"x 9.8"      
235/85/16 31.7"x 9.3"   265/70/17 31.6"x 10.7"      
245/70/16 29.5"x 9.6"   285/70/17 33.0"x 11.5"
     



Example: 225/70R15

225 = Section width in millimeters
70 = Aspect ratio (ratio of section height to section width)
R15 = Rim diameter
  R = Radial Construction, B = Bias Construction, D = Bias Belted Construction

 






 

Calculations for Measurements

Tire Width: Section width divided by 25.4 (Ex: 225 / 25.4 = 8.86")
Section Height: Tire width times aspect ratio (Ex: 8.86" x 70% = 6.20")
Overall Diameter: Section height times 2 plus rim diameter (Ex: (6.20" x 2) + 15 = 27.40")

Article Type: 
How It Works