P-Metric Tire Sizes – P-Metric to Inches Conversion Chart | Offroaders.com
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P-Metric Tire Sizes – P-Metric to Inches Conversion Chart

Offroaders.com Guide to P-Metric Tire Terminology – P-Metric Tire Sizes Conversion Chart – P-Metric to Inches

Rim SizeP-Metric SizeTread WidthActual Tire Height
15 Inch205/70R158.7 inches26.3 inches
215/75R158.45 inches27.7 inches
235/75R159.25 inches28.9 inches
265/70R1510.4 inches29.6 inches
16 Inch225/75R168.8 inches29.3 inches
235/85R169.35 inches31.7 inches
245/75R169.65 inches30.5 inches
265/70R1610.5 inches30.6 inches
265/75R1611.2 inches31.6 inches
285/75R1612.4 inches32.8 inches
305/70R1612.2 inches32.8 inches
315/75R1612.3 inches34.6 inches
345/75R1613.6 inches36.4 inches
17 Inch235/65R179.25 inches29.0 inches
245/70R179.65 inches30.5 inches
255/75R1710.4 inches32.1 inches
255/80R1710.0 inches33.1 inches
265/70R1710.4 inches31.6 inches
275/70R1711.0 inches32.2 inches
285/70R1711.2 inches32.7 inches
285/75R1711.2 inches33.8 inches
305/65R179.8 inches32.6 inches
315/70R1712.4 inches34.4 inches
18 Inch265/60R188.6 inches30.5 inches
275/65R1811.0 inches32.1 inches
275/70R1811.0 inches33.2 inches
285/75R1811.0 inches34.8 inches
295/65R189.4 inches33.1 inches
305/60R1812.2 inches32.4 inches
305/70R189.8 inches34.8 inches
20 Inch275/60R208.9 inches33.0 inches
275/65R2011.0 inches34.3 inches
285/60R2011.2 inches33.0 inches
285/65R2011.5 inches33.5 inches
295/55R2012.4 inches33.0 inches
295/60R2011.7 inches34.5 inches
305/55R2012.4 inches33.5 inches
325/60R2013.0 inches35.6 inches

The values shown are calculated measurements based on the p-metric formula.  Actual advertised tire height and tread width will vary from manufacturer to manufacturer for specific p-metric tire sizes.  Check with the manufacturer’s actual dimensions per individual tire brand before purchasing.

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Reading a Tire:

All tires are required to have certain information molded into the side of the tire in a location known as the sidewall.  Some of the information is self explanatory while other information requires a little knowledge to decipher.  The following will help you understand what this information means.

Tire Type – This Defines the intended proper use of the tire. P indicates this is a passenger car tire while LT indicates the tire would be for a light truck with a heavier load rating.

Tire Width – This is the width of the tire measured in millimeters from sidewall to sidewall.  An example might be 215 representing 215 millimeters.

Aspect Ratio – This is the the ratio of the height of the tire’s cross-section to its width. An example of this might be 65, which means that the height is equal to 65% of the tire’s width.  To calculate the aspect ratio, multiple the first number (e.g. 215) by the second number with a decimal before the number (e.g. .65).  Using the example numbers the tires aspect ratio would calculate as 215x.65=139.75 where 139.75 is the tires height in millimeters.  This is the height of the rubber from rim to tread on one side of the tire. 

To convert the aspect ratio to a full tire height in inches, do this:
Convert the above calculated tire height (aspect ratio) in millimeters to inches by multiplying the millimeters by .03937 (139.75 x .03937 = 5.5 inches).  Then take the inches and multiply by two and add the rim size. Example: 5.5 x 2 + 15 (rim size in inches) = a 26 inch tall tire.

Construction – This indicates how the how the tire was put together and will say much about the tires handling characteristics. R indicates the tire is a radial type tire.  For more information about what a radial is, click hereB indicates the tire is a bias ply type tire.  For more information about bias ply type tires, click here.

Wheel Diameter – This is the width of the opening in the tire where it would be mounted to a wheel.  This is measured from one bead across the opening to the other side of the same bead.  This measurement is in inches and an example would be 15 and indicates that this tire is for a 15 inch rim, or wheel.

Load Index – This is a number corresponds to the maximum load in pounds that a tire can support when properly inflated. You will also find the maximum load in pounds and in kilograms molded elsewhere on the tire sidewall.

Speed Rating – This is a number that corresponds to the maximum service speed for a tire.  See Chart for ratings.  Note: Speed ratings are specific for passenger car tires and not light truck tires.  Light truck tires (LT) are not speed rated. 

Rating

Maximum Speed
Q99 mph
S112 mph
T118 mph
U124 mph
H130 mph
V149 mph
W168 mph
Y186 mph
ZAbove 149 mph