Passenger Tire Sizes
Most passenger vehicles come equipped with P-Metric and Euro-Metric tire sizes. It is important to understand these sizing systems in selecting the proper tire for your vehicles. Here is a brief review of the tire sizing systems with a breakdown of their individual elements.

P Metric
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%) and is commonly referred to as the tire series (75, 70, 60 series). Lower aspect ratio tires tend to look shorter and wider.




Choose from any section below to enlarge the graphic.



From the examples below, you can determine each tire's Section Width (7.28/8.07") and Section Height (5.10/4.84").

P18570R14

P

Passenger Car Tire

185

Section Width (in millimeters)
(Conversion: 185 mm ÷25.4 = 7.28")

70

Aspect Ratio (Conversion: 7.28" X .70 = 5.10" Section Height)

R

Radial Construction
(D-diagonal)

14

Rim diameter in inches


205/60R15

205

Section Width in millimeters
(Conversion: 205 mm ÷25.4 = 8.07")

60

Aspect Ratio
(Conversion: 8.07" X .60 = 4.84" Section Height)

R

Radial Construction

15

Rim diameter in inches




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.


As the example below illustrates, Overall Diameter can now be determined by adding the sidewall heights (Section Height) and the rim diameter.

P185/70R14
Conversion
(5.10" + 5.10") + 14" = 24.2"

205/60R15
Conversion
(4.84" +4.84") + 15" = 24.68"

Euro-Metric
This system originated in Europe and is also referred to as the European Metric System. Most European tire manufacturers build tires that conform to this system. The Metric System is very similar to the P-Metric System, except in terms of load carrying capacity. Load carrying capacities of Metric and P-Metric tires are sometimes not the same, even for two tires of the same size designation.

Load Limits at Inflation

Size

Load Index

26 psi

 29 psi

32 psi

35 psi

36 psi

44 psi

P195/70R14

90

1135lbs
(515kg)

1201lbs
(545kg)

1257lbs
(570kg)

1312lbs
(595kg)

 

1312lbs
(595kg)

195/70R14

91

1047lbs
(475kg)

1135lbs
(515kg)

1224lbs
(555kg)

1312lbs
(595kg)

1356lbs
(615kg)

 

P205/60R15

90

1124lbs
(510kg)

1190lbs
(540kg)

1246lbs
(565kg)

1301lbs
(590kg)

 

1301lbs
(590kg)

205/60R15

91

1047lbs
(475kg)

1135lbs
(515kg)

1224lbs
(555kg)

1312lbs
(595kg)

1356lbs
(615kg)

 


As the previous examples illustrate, another load related difference between P-Metric and Metric sizes is the maximum inflation pressure. P-Metric standard load tires have a maximum inflation of 35psi (pounds per square inch) while Metric are 36psi. Some speed rated tires have a maximum inflation of 44psi, this capability has been added to enhance handling and high speed capability in some vehicles. Size dimensions of P-Metric and Metric tires are basically the same. It is important to note, however, that actual size dimensions can vary slightly from one manufacturer to another.