In the illustrative tire marking P225/60R16 97T, P identifies a passenger-tire designation, 225 is the nominal width in millimeters, 60 is the sidewall-height percentage, R means radial construction, and 16 is the rim diameter in inches. The final 97T contains two separate rating codes. Those characters describe different properties, so the whole string cannot be read as one measurement.
This reference decodes the printed notation only. The example is not a size recommendation for any vehicle. Vehicle specifications belong to the vehicle’s owner’s manual or Tire and Loading Information Label, as identified by NHTSA’s tire information.
The example, one part at a time
The spaces below separate the fields for reading: P | 225 | /60 | R | 16 | 97 | T. The slash marks the transition from width to aspect ratio. It is not an instruction to divide 225 by 60. Cooper’s tire-size reference uses this same passenger-tire example.
| Marking | Field | Meaning in this example |
|---|---|---|
| P | Passenger-tire prefix | A tire-type designation |
| 225 | Nominal section width | 225 millimeters |
| 60 | Aspect ratio | Sidewall height is 60% of section width |
| R | Construction | Radial |
| 16 | Rim diameter | 16 inches |
| 97 | Load index | A coded load-capacity value |
| T | Speed rating | A letter identifying a speed-rating category |
P and 225: type comes before width
The P prefix places this example in passenger P-metric notation. Other prefixes identify other categories: LT refers to light-truck tires, ST to special-trailer tires, and T at the beginning to a temporary spare. Some passenger tires use Euro-metric notation without a leading P. An absent prefix therefore does not, by itself, mean that a code is incomplete.
The next field, 225, is the nominal section width. Section width describes the tire from sidewall to sidewall, rather than just the patterned tread surface. Its unit is millimeters even though no “mm” appears in the string. Bridgestone’s size guide explains both the prefix distinction and this sidewall-to-sidewall measurement.
Nominal means the stated size designation. The number is not a promise that every photograph or physical example will show an exactly 225 mm span. It also does not describe rim width. Keeping the name of the field beside the number prevents those two different widths from being confused.
60: a percentage, not a height in millimeters
The aspect ratio expresses sidewall height relative to section width. In this example, 60 means 60 percent of 225 mm. A percentage needs a base quantity: “60” alone is not enough to calculate a height. That is why the width and aspect-ratio fields belong together when interpreting the proportions.
Nominal sidewall height = nominal section width × aspect ratio ÷ 100
For this example: 225 mm × 60 ÷ 100 = 225 mm × 0.60 = 135 mm. An independent arithmetic check gives the same result: 10% of 225 is 22.5, and six lots of 22.5 equal 135. Dividing 135 by 225 returns 0.60, confirming the ratio.
The result describes one nominal sidewall height. It is neither the full outside tire diameter nor the rim diameter. It is also not a measurement taken from the accompanying photographs, which are illustrative scenes rather than dimensioned technical images.
R and 16: construction followed by rim diameter
R identifies radial construction. It is a letter describing the tire’s internal structure, not an abbreviation for radius. Although R and 16 sit together visually, they remain separate fields: radial construction followed by a 16-inch rim-diameter designation.
The change of units is easy to miss. The width field used millimeters; the rim-diameter field uses inches. The number 16 does not describe the entire tire from one outside tread edge to the opposite edge. Rubber sidewalls and tread extend beyond the rim. Michelin’s marking guide separates construction and wheel diameter in the same way.
97T: two rating codes after the size
The number-and-letter pair after the dimensional fields is often called the service description. Here, 97 is the load index, a number associated with a load-capacity entry in a rating table. It does not mean 97 kilograms or 97 pounds, and it is not another width or diameter.
The final T is a speed-rating symbol. Its meaning comes from its position after the load index. A T at the beginning of a different size string would instead be a temporary-spare prefix. Reading by position resolves that apparent contradiction without treating every occurrence of a letter as the same thing.
Load and speed ratings describe capabilities under specified conditions. They are not a vehicle payload calculation, a road-speed recommendation, or proof that a tire suits a particular vehicle. This reference identifies the fields without turning their rating-table entries into operating advice.
Keep the complete string in your reference notes
A useful written transcription preserves the prefix, slash, construction letter and final rating pair. Recording only “225” loses the proportions; recording only “16” loses everything except the rim-diameter field. Separating the complete example into labeled columns makes each number’s unit and purpose visible.
If small print is difficult to read, you can browse reading magnifiers on Amazon. Keep the full code in your notes and compare each part with the table above.
The compact reading is: passenger prefix, width, percentage, construction, rim diameter, then load and speed codes. That order explains this P-metric example; other tire notation systems require their own definitions.
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