The first letter on a tire indicates the tire’s class. P designates this tire as a passenger car tire, an LT before the tire size would mean the tire is a light truck tire, and a European metric tire would have no letter before the tire size.
What do the numbers on tires mean? There's a massive amount of information branded on the sidewall of every tire ... but it's written in code. The tire size is just one small piece of this code. The tire size "P225/45R17 91V" may not mean much to the average person, but to tire geeks like us it speaks volumes.
The numbers are indicators of the size, type, and performance of the tire. Tire Type The letter "P" at the beginning of the "Tire Size" tells us the tire is a P-Metric tire, referring to tires made to certain standards within the United States, intended for Passenger vehicles.
If your tire size starts with LT rather than a P than it identifies the tire as a Light Truck tire. 225 identifies the tire section width, which is the measurement of the tire from sidewall to sidewall in millimeters.
There’s a lot to learn from the soup of letters and numbers on the sidewall of a tire, but deciphering all of that data takes some explanation. Knowing what the information means, a consumer can decide if a tire is right for their vehicle, driving style, and road conditions.
The two-digit number after the slash mark in a tire size is the aspect ratio. For example, in a size P215/65 R15 tire, the 65 means that the height is equal to 65% of the tire's width. The bigger the aspect ratio, the bigger the tire's sidewall will be.