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P Metric Tires
With the P-Metric system, Section Width is measured in
millimeters. To convert millimeters into inches, divide by 25.4. The Aspect
Ratio (Section Height divided by Section Width) helps to provide more
dimensional information about the tire size.
Aspect ratio is expressed as a percentage (75%, 70%, 60%) & is commonly
referred to as the tire series (75, 70, 60 series). Lower aspect ratio tires
tend to look shorter & wider. |
From the examples below, you can determine each tire's
Section Width (7.28/8.07") & Section Height (5.46/4.84").
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P18570R14
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P
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Passenger Car Tire |
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185
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Section Width (in millimeters)
(Conversion: 185 mm ÷25.4 = 7.28") |
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70
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Aspect Ratio (Conversion: 7.28" X .70
= 5.10" Section Height) |
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R
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Radial Construction
(B-bias, D-diagonal) |
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14
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Rim diameter in inches
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205/60R15
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205
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Section Width in millimeters
(Conversion: 205 mm ÷25.4 = 8.07") |
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60
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Aspect Ratio
(Conversion: 8.07" X .60 = 4.84" Section Height) |
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R
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Radial Construction |
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15
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Rim diameter in inches
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NOTE: The dimensions in the
sizes noted are nominal. This means they are figured from the number for
that size. Actual dimensions may vary by manufacturer from the actual
dimensions in the size because of tolerances allowed. |
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As the example below
illustrates, Overall Diameter can now be determined by adding the sidewall
heights (Section Height) & the rim diameter.
P185/70R14
Conversion
(5.10" + 5.10") + 14" = 24.2" |
205/60R15
Conversion
(4.84" +4.84") + 15" = 24.68" |
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