What is a Tyre?
Simply put, a tire is a flexible container of compressed air. In reality, a tire’s duties are many. It supports a vehicle’s load, it propels a vehicle: forward, backward, and side-to-side. It stops a vehicle. Finally, it also cushions the load from road imperfections. Today’s tires comprise between 19-25 different components. Contrary to popular opinion, tires are built from the inside out rather than the outside in. The heart of every tire is an inner liner. Its job is to give the tire shape and hold in the air. Wrapped around the inner liner are fabric belts. Fastened to the bottom of the fabric belts is the bead, which holds the tire to the wheel.
On top of the fabric belts are steel belts. These belts have two jobs. One is to give the tire stability, and the other is to make the tread pattern as flat as possible. (A flatter tread means more contact with the road.) On top of the belts is the tread of the tire. There are different tread patterns for different types of tires. Finally, on the side of the tire, appropriately enough, is the sidewall. This is what gives a tire its stiffness or ride characteristics. A taller/softer sidewall will absorb more bumps, while a shorter/stiffer sidewall will provide better cornering ability and sharper steering response
Why are Tyres Important?
Many consumers don’t know enough about tires to make an educated purchase. For some, the choice comes down to price and/or availability. Others buy tires based on appearance or reputation. Educated consumers know to purchase tires based on safety, quietness, road-holding ability, and wear.
Regardless of tire choice, it is necessary that consumers understand why tires are so important. Tires are a vehicle’s only contact with the road. Even the brawniest engine, strongest brakes, or most advanced antiskid system, is at the mercy of the tire’s grip on the road. Every move a driver makes with the steering wheel or brake or gas pedal is transmitted to the road through the four notepad-sized contact patches of the tires.
Since a vehicle doesn’t have the ability to change tires like a person changes shoes, consumers must select a tire that will work year ’round and in every conceivable driving situation. You wouldn’t wear high heels to go hiking, and you wouldn’t wear ski boots to dance a ballet. However, consumers often ask their cars’ tires to do many things, and many times a vehicle’s tires aren’t suited to the task.
Selecting the right tires for your driving needs is as important as selecting the right vehicle. Tires that are worn won’t be able to displace enough water to prevent hydroplaning. Performance tires won’t be able to get much grip in snow. All-season tires can’t manage the heat creased in high-speed driving. Passenger-car tires might not be able to carry the heavy load found in a contractor’s pickup.
One Size Does Not Fit All
Perhaps the biggest mistake a consumer can make when replacing tires is not using the correct size. On the sidewall of your original-equipment tire (and all tires) is a code that tells the tire’s size and capabilities. Here’s a sample tire-size code and a description of what that code means: P195/60R16 63H M+S
- P = Type of tire
- 195 = width of the tire across the tread in millimeters
- 60 = Aspect ratio of the sidewall compared to the width
- R = Radial construction
- 16 = Diameter of the rim in inches
- 63 = Tire’s load rating
- H = Tire’s speed rating
- M+S = Tire is suitable for all-season driving
If the tire-size code starts with LT instead of P, that means the tire is a light-truck tire. Light-truck tires are designed to have higher-load carrying capacities and are usually found on pickups and SUVs. These vehicles are not required to have LT tires, and in many cases, the original-equipment specification calls for passenger-car tires.
A tire’s speed rating is most important if you do a lot of highway driving. Tires are speed rated from 99 to 186 MPH. The most common speed ratings are T (118 MPH) and H (130 MPH). Both of those ratings clearly exceed the nationally posted speed limits and would make excellent long-distance highway tires. If a consumer were to drive only in urban situations at low speeds, a tire with an S (112 MPH) speed rating might be completely acceptable.
You see, the speed rating translates into the the tire’s ability to dissipate heat, or better yet, to prevent heat build-up. Heat is a tire’s enemy. The more heat, the faster the tire wears, and the faster a tire might break down and fail. So a tire with a higher speed rating can dissipate more heat on long highway trips. If a consumer were to spend little time on the highway, the speed rating might not be an important factor in choosing a replacement tire.
Another important factor in choosing a replacement tire is the load rating. The load capacity number on the tire-size code indicates the load-carrying capacity of that single tire. When selecting replacement tires, consumers have to be careful not to select a tire with a lower load-carrying capacity.
Tires need to rotate in more than one direction
Rotating a vehicle’s tires is essential to prevent uneven tire wear. If left unchecked, unrotated tires will cause increased road noise, lower fuel economy, and decreased wet-weather traction. Additionally, badly neglected tires will have to be replaced sooner.
It is generally accepted that on front-drive vehicles, where all tires are the same size, you rotate the front tires to the rear in a straight line and cross the back tires to the front. In a rear-drive vehicle, you rotate the backs in a straight line to the front and cross the front tires to the back.
On all- or four-wheel-drive vehicles, the rotation pattern most often suggested is a simple “X.” The left front and right rear swap and the right front and left rear swap.
Many sports cars and some luxury and sport-utility vehicles have unidirectional tires. Unidirectional tires have tread patterns that are designed to perform in the direction denoted on the tire sidewall only. They should always be rotated front to rear (assuming they are the same size). This ensures that the direction of revolution does not change.