Everything You Need to Know About Wheels and Tires

Regardless of what kind of vehicle you have or the status of the vehicle in question there is one common element that binds every car or truck or van or SUV and that is that thing that has often been called the single most important invention in the entire history of civilization: the wheel. Those four (or more) rubber tires can cause endless frustration and expense and though they are the perhaps the most familiar element involved in the world of driving they are usually also the the most overlooked. Tires are, when it comes down to it, the only thing between you and certain extinction. If the engine goes you’ll probably be okay, but if all four tires suddenly blew you would be facing the decision to walk into the light or not. Only the four brakes that are attached to your tires have as much power over your fate. What do you really know about tires and wheels and what is absolutely vital knowledge for you to possess?

Each and every tired produced has a set of numbers imprinted on them that can be so incredibly confusing that most people never even bother to learn what they stand for. In fact, deciphering this code is far less difficult than decoding those text messaging shortcuts for the average person. These codes can be located on the sidewall of your tire and the information contained within this seemingly foreign language unlocks the mystery to everything you need to know about tires and wheels. The first thing to keep an eye out for is a combination code of letters and numbers.
P is used to designate passenger cars.
LT is used to designate light trucks.
ST is used to designate special trailers.
T is used to designate a temporary status.

Following these letter codes will be a number that indicates the width of the tire in millimeters. The width is measured from sidewall edge to sidewall edge. Following this number be a slash followed by yet another number. Example: LT215/65. The final number gives the tire’s height to width ratio and this number will in turn be followed by another letter:
B stands for a bias belt.
D stands for a diagonal bias.
R indicates it is a radial tire.

Believe it or not, but following B, D or R will be still another number that measures diameter of the rim. A final example will of this combination might look like this: LT215/65D15. Following the last number will be a space and then another code that indicates the load and speed indices. The load index is a number that is assigned to the actual capacity of the tire to support a weight. Obviously, the higher the load index number is the greater amount of weight that it will be capable of handling. A load index of 71 could support 761 pounds, while a tire with a load index of 110 could support well over two tons. Although replacing your original tires with a lower load index is absolutely out of the question, you can usually buy the highest rated load index tire that will fit your vehicle without suffering any serious problems in handling or maneuvering. The speed rating indicates the maximum sustained speed that the tire can handle safely. This code is represented by a letter that follows the load index. A Q speed index would mean that tire handles safely up to 99 mph; a Z means you can get that Ferrari up above 189 mph safely. In theory, at any rate.