How+Tyres+Work


 * How Tyres Work**

[|How Tyres Support a Car] There is a flat spot on the bottom where the tire meets the road. This flat spot is called the **contact patch.** Since there is a certain amount of pressure per square inch in the tire, say 30 psi, then you need quite a few square inches of contact patch to carry the weight of the car. If you add more weight or decrease the pressure, then you need even more square inches of contact patch, so the flat spot gets bigger. When the tire is spinning, the contact patch must move around the tire to stay in contact with the road. At the spot where the tire meets the road, the rubber is bent out. It takes force to bend that tire, and the more it has to bend, the more force it takes.

The tire is not perfectly elastic, so when it returns to its original shape, it does not return all of the force that it took to bend it. Some of that force is converted to heat in the tire by the friction and work of bending all of the rubber and steel in the tire. Since an underinflated or overloaded tire needs to bend more, it takes more force to push it down the road, so it generates more heat. This suggests that the rubber in the tyre will burn faster than if it were properly inflated. So if a tyre is not properly inflated, then the tyre will burn out.

[|How Tyres are Made]
 * The **bead** is a loop of high-strength steel cable coated with rubber. It gives the tire the strength it needs to stay seated on the wheel rim and to handle the forces applied by tire mounting machines when the tires are installed on rims.


 * The **body** is made up of several layers of different fabrics, called **plies**. The most common ply fabric is **polyester cord**. The cords in a radial tire run perpendicular to the tread. Some older tires used **diagonal bias tires**, tires in which the fabric ran at an angle to the tread. The plies are coated with rubber to help them bond with the other components and to seal in the air.


 * In steel-belted radial tires, **belts** made from steel are used to reinforce the area under the tread. These belts provide puncture resistance and help the tire stay flat so that it makes the best contact with the road.


 * Some tires have **cap plies**, an extra layer or two of polyester fabric to help hold everything in place. These cap plies are not found on all tires; they are mostly used on tires with higher speed ratings to help all the components stay in place at high speeds.


 * The **sidewall** provides lateral stability for the tire, protects the body plies and helps keep the air from escaping. It may contain additional components to help increase the lateral stability.


 * The **tread** is made from a mixture of many different kinds of natural and synthetic rubbers. The tread and the sidewalls are extruded and cut to length. The tread is just smooth rubber at this point; it does not have the tread patterns that give the tire traction.

At this point the tire has all of its pieces, but it's not held together very tightly, and it doesn't have any markings or tread patterns. This is called a **green tire**. The next step is to run the tire into a **curing machine**, which functions something like a waffle iron, molding in all of the markings and traction patterns. The heat also bonds all of the tire's components together. This is called **vulcanising**. After a few finishing and inspection procedures, the tire is finished.

[|What all the numbers mean] The **P** designates that the tire is a passenger vehicle tire. Some other designations are **LT** for light truck, and **T** for temporary, or spare tires.
 * Typre of Tyre**

The 235 is the width of the tire in millimeters (mm), measured from sidewall to sidewall and is measured when the rim is placed inside the tyre.
 * Tyre Width**

This number tells you the height of the tire, from the bead to the top of the tread. This is described as a percentage of the tire width. The lower the aspect ratio, the wider the tire in relation to its height.
 * Aspect Ratio**

The **R** designates that the tire was made using radial construction. This is the most common type of tire construction. Older tires were made using diagonal bias (**D**) or bias belted (**B**) construction. A separate note indicates how many plies make up the sidewall of the tire and the tread.
 * Tire Construction**

This number specifies, in inches, the wheel rim diameter the tire is designed for.
 * Rim Diameter**

Passenger car tires also have a grade on them as part of the **uniform tire quality grading** (UTQG) system.
 * Uniform Tire Quality Grading**
 * **Tread Wear**: This number comes from testing the tire in controlled conditions on a government test track. The higher the number, the longer you can expect the tread to last. Since no one will drive his or her car on exactly the same surfaces and at the same speeds as the government test track, the number is not an accurate indicator of how long your tread will actually last. It's a good relative measure, however: You can expect a tire with a larger number to last longer than one with a smaller number.
 * **Traction**: Tire traction is rated **AA**, **A**, **B** or **C**, with AA at the top of the scale. This rating is based on the tire's ability to stop a car on wet concrete and asphalt. It does not indicate the tire's cornering ability.
 * **Temperature**: The tire temperature ratings are **A**, **B** or **C**. The rating is a measure of how well the tire dissipates heat and how well it handles the buildup of heat. The temperature grade applies to a properly inflated tire that is not overloaded. Underinflation, overloading or excessive speed can lead to more heat buildup. Excessive heat buildup can cause tires to wear out faster, or could even lead to tire failure.

The service description consists of two things:
 * Service Description**
 * **Load Ratings**: The load rating is a number that correlates to the maximum rated load for that tire. A higher number indicates that the tire has a higher load capacity. The rating "105," for example, corresponds to a load capacity of 2039 pounds (924.87 kg). A separate note on the tire indicates the load rating at a given inflation pressure.
 * **Speed Rating**: The letter that follows the load rating indicates the maximum speed allowable for this tire (as long as the weight is at or below the rated load). For instance, **S** indicates that the tire can handle speeds up to 112 mph (180.246 kph).

- Now that we know what these numbers mean, we can calculate the overall diameter of a tire. We multiply the tire width by the aspect ratio to get the height of the tire.
 * Calculating the Tire Diameter**

- Then we add twice the tire height to the rim diameter. - This is the unloaded diameter; as soon as any weight is put on the tire, the diameter will decrease.

[|Problems with Tyres]
 * Underinflation** can cause tires to wear more on the outside than the inside. It also causes reduced fuel efficiency and increased heat buildup in the tires. It is important to check the tire pressure with a gauge at least once a month.


 * Overinflation** causes tires to wear more in the center of the tread. The tire pressure should never exceed the maximum that is listed on the side of the tire. Car manufacturers often suggest a lower pressure than the maximum because the tires will give a softer ride. But running the tires at a higher pressure will improve mileage.


 * Misalignment** of the wheels causes either the inside or the outside to wear unevenly, or to have a rough, slightly torn appearance.