Decoding the numbers on your car's tire sidewall

Do those combination of number and letters written on the sidewall of your car's tires puzzle you?

Aside from the model name of the tire, not far from it there's that curious code. This code specifies what size and kind of tire your car needs. Let's decipher this tire sidewall code. 

Example of numbers on tire sidewall

Let's use the code P225/50/R17 98H as an example. Each letter and number corresponds to the tire's specifications and purpose. The letters and numbers differ from one type of tire to another, but the pattern of the tire sidewall code is the same. 

Tire size

In tire sidewall code P225/50/R17 98H, the letter "P" (or PMetric) means the tire is a Passenger Tire. If the tire size starts with "LT" rather than "P," the tire is classified as a Light Truck tire.

The number 225 identifies the tire section width, which is the measurement of the tire from sidewall to sidewall in millimeters. There are 25.4 millimeters per one inch. 

The digit 50 is the two-figure aspect ratio. Meaning, this number compares the tire's section height with the tire's section width. Given this, the aspect ratio of 50 shows that the tire's section height is 50% of the tire's section width.

Meanwhile, R indicates the construction used within the tires casing, and in this case, R stands for radial construction. B means belted bias and D stands for diagonal bias construction.

The number 17 is the last dimension listed in the size is the diameter of the wheel rim, which is most often measured in inches.

Load index and speed rating 

In the given tire sidewall code, the "98H" refers to  load index and speed rating or service description.

The load index determines how much weight the tire can support when properly inflated. Load indices range from 75 to 105 for passenger tires, with each numeric value corresponding to a specific carrying capacity. The carrying capacity for each value can be found on a load index chart.

On US passenger car tires, the load limit is listed in pounds.  On the other hand, European tires have the load limit listed in kilograms and sometimes pounds.

The "H" is a speed rating that are represented by letters ranging from A to Z. Each letter coincides to the maximum speed a tire can sustain under its recommended load capacity. For instance, S is equivalent to a maximum speed of 180kph. 

Below is the speed rating chart for the tire sidewall code. 

• Q - 160kph
• S  - 180kph
• T - 190kph
• U - 200kph
• H - 210kph
• V - 240kph
• W - 270kph
• Y - 300kph
• Z - over 300kph

Tire expiration date  

Another code that you will see in the tire sidewall is the tire's expiration date. Like many car parts, tires experience wear and tear and need regular replacing.

To know when tires expire, read our helpful guide here.  

Photos from Goodyear and Dylan Afuang