The COMPLETE Tire Buying Guide: Size, Ratings And More

Buying tires for the first time can be a fairly difficult task. While you will always be able to depend on the assistance of a tire salesperson to help you find a tire that can be safely mounted to your vehicle, your lack of knowledge can lead you to paying more than you actually need to.

If you are about to purchase your first set of tires for your vehicle, use this tire buying guide to help you make the appropriate selection that fits well into your budget.

Tire Size Guide

Finding the right size tire for your vehicle is the first step to buying a tire. You can find your vehicle’s factory tire size in the owner’s manual. If you do not have access to the owner’s manual, you can read the markings on the sidewall of your tire, which should be facing outward and is clearly visible when standing in front of the tire. The tire size is actually measured through a tire code.

Here is an example of a tire code: P215/65/R15

The “P” indicates that the tire is for a passenger vehicle. Other letters that might start a tire code include “LT” for light truck, “ST” for special trailer and “T” for temporary or spare tires.
The first number, “215,” specifies the width of the tire in millimeters.
The second number, “65,” specifies the height to width ratio.
The “R” stands for radial, which is the type of construction.
The “15” represents the diameter of the wheel or rim, which is 15 inches.

When finding the appropriate size, it is best to stick with the factory specified tire size. If you are looking to increase the size of the wheel or rim, the tire size would be affected. Choosing a different tire size can affect the vehicle height, handling, suspension and can leave you with an inaccurate speedometer reading.

Speed Rating and Load Index

Another code you will need to know for selecting the right tire for your vehicle is the service description code. The service description code will indicate the speed rating of the tire and the tire’s load index. The service description code can also be seen on the sidewall of most tires.

Here is an example of a service description code: 91S

The “91” indicates the vehicles load carrying capabilities, which calculates to 1,356 pounds. Check online sources for a complete list of load index and the correlating weight in pounds or kilograms.
The “S” indicates the tires speed rating. An “S” speed rating is a maximum speed of 112 miles per hour. Exceeding the maximum speed can lead to unsafe driving conditions. Check online sources for a complete list of speed ratings and the correlating maximum speed in miles or kilometers per hour.

Treadwear

A tire’s treadwear grade indicates how long the tire will last under certain driving conditions. The higher the treadwear grade, the longer the tire should last. While an estimate of how many miles a tire will last is included with a treadwear grade, one must understand that the grading system can vary for individual tire brands.

Driving conditions, driving habits, climate and maintaining an appropriate tire service schedule can also affect a tire’s treadwear and should always be factored into your car’s overall maintenance schedule.

Tires for Special Driving Conditions

The local climate and driving conditions can affect your decision when determining the appropriate tire for your vehicle. The most common types of tires are:

Summer tires: meant for driving under both dry and wet conditions with the appropriate levels of traction and handling.
All-season tires: meant for driving through virtually any type of weather conditions, including snow. Like summer tires, these are capable of driving through dry and wet conditions.
Winter or snow tires: these tires were specifically made to handle road conditions with snow and ice, and provide the necessary traction.
All terrain: these tires are specifically meant for off-road vehicles that need to traverse roads with gravel, stones, dirt and snow along with regular pavement.

Final Tips

When purchasing new tires for your vehicle, it helps a great deal if you know the factory specifications for your tire size and type. Make sure you inform the tire salesperson assisting you what the car is used for, road conditions you plan on driving in, if the vehicle is for commuting or for leisure and whether or not you are deciding on increasing the wheel or rim size. This information must be factored in when buying new tires.