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Tire Pressure Numbering System
The numbers used to identify passenger tires contain a lot of information
buried in that long string of codes that appear on every tire rim. Here is a
brief explanation. These codes apply to passenger car tires, but not to snow
tires.
The traction index can be AA, A, B or C. This gives a relative indication of
the tire's stopping ability on wet pavement.
The temperature index follows and can be A, B, or C. This is a relative
indication of how well the tire stands up under various temperature
conditions.
The tread wear index rates how well the tire resists to wear under
"normal" conditions. A reference value is 100. Thus with in the same
manufacturer's lot of tires, a rating of 300 suggests the tire should last
three times as on rated 100.
The size code follows and shows several aspects of the tire size.
- The first letter or letters shows the vehicle type the car is intended for.
- P denotes passenger car.
- LT denotes light truck.
- Unfortunately this letter code is not always used.
The next several digits show the width of the tire in millimeters.
Following the slash are (usually) two digits that are a comparison of tire
height to width.
A maximum speed rating sometimes appears here.
Q denotes a maximum of 100 mph.
U denotes a maximum of 124 mph.
Z denotes a maximum of 149 or more mph.
The next field is construction type.
The next field - which is optional - identifies the factory where the tire
was made.
The last four digits denote the week and year the tire was made.
- The first two digits show show the week, with the first week of the year
being a one.
- The last two digits show the last digits of the year.
For example -
- P205/70R15 95S
This has the following interpretation -
- No traction index.
- No temperature index.
- No tread wear index.
- P - for a passenger car
- No maximum speed index.
- The width of the tires is 205 millimeters. (25.4 millimeters = one inch).
- R - The tire is of radial construction.
- No factory identification is supplied.
- The tire was made during the 15th week of 1995.
- S - ?
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