Tire Size? How To Read a Tire Sidewall and What it All Means

The side of your tire, known as the tire sidewall, contains all of the information you need to know about your tire size.

Regardless of the manufacturer, all tires are required to show this information.

Tire Size and Rating

Tire Load Index

When the engineers designed and built your car, they crunched some numbers and determined exactly how much weight it could carry safely based on the right tire size and pressure. This is what is called the “tire load index.”

The tires that come on your vehicle will have the proper load index, so stick to that number or higher when you purchase new tires. You can also check the vehicle’s manual to find the recommended tire size and load rating.

Why Is Tire Load Index Important?

The tire load index tells you how much weight your tire can carry, and overloading your tires is never a good idea! When you put too much weight on your tires, you can cause damage and wear them down prematurely. Even worse, you run the risk of experiencing a tire blowout. Imagine trying to carry a box full of cement blocks. Just like your legs would buckle under the weight, your tires can completely give out if they’re overloaded.

Speed Rating Chart

A tire’s speed rating indicates the optimal speed that the tire can safely maintain over time. In short, it’s the fastest speed a tire can handle before it no longer performs as designed. The higher the speed rating, the better control and handling you’ll have at higher speeds.

The speed rating system was developed to help control the safe performance of tires at standardized speeds. A tire’s certified speed rating is given a letter from A to Z, ranging from 5km/h (3mph) to above 300 km/h (186 mph).

This rating system (see below) shows the top speed for which a tire is certified. It does not indicate the total performance capability of a tire.

“ZR” Designation

Tires having a maximum speed capability over 149 MPH may have “ZR” in the size designation. Tires with a maximum speed capability over 186 MPH are required to include “ZR” in the designation. Below are examples of tire sizes with a “ZR” speed rating.

DOT Tire Serial Numbering System

“DOT” indicates the tire meets or exceeds the Department of Transportation’s safety standards.

“XX” is the code number assigned by DOT to the manufacturing plant. See complete list of tire manufacturer plant codes below.

“5Y” is the tire size code.

“XX00” is a group of up to four symbols, optional by the manufacturer, to identify the brand or other significant characteristics of the tire.

“2613” means the tire was made during the 26^th week of 2013.

For 3 digit date codes (indicates a tire manufactured pre-2000):

Example: DOT MDU4 DMA 032
Manufactured during the 03^rd week of the year
Manufactured during the 2^nd year of the decade

• How To Determine The Age Of Your Tires

Tire Manufacturing Plant Codes