When shopping for tires, it's important to know the meaning of all those mysterious embossed letters on the sidewall of the tires. It's not as complicated as you may think. Here's how to decipher them. 1) The first letter in the series is the tire's class designation -- for example, "P" for passenger, "LT" for light truck or "T" for temporary. 2) That letter is followed by the tread width. In this case, "235" means this tire's tread is 235 millimeters in width. So larger tread-width numbers mean wider tires (figure A). Read the rest of this article.