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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
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
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 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
The last four digits denote the week and year the tire was made.
- 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 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 -
This has the following interpretation -
- P205/70R15 95S
- 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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