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Wheels and Tires:
Tires
 Tires are made from vulcanized rubber and are responsible for both cushioning the impact of driving over road surfaces as well as providing adequate traction.
Today, most vehicles rely on radial tires.
However, that hasn't always been the case. In fact, until the 1970s, bias ply tires enjoyed the dominant market position. Bias-ply tires are constructed of rayon, nylon, or polyester casing plies in a crisscross pattern wrapped around steel bead wires. These bead wires prevent the tire from opening up and separating from the rim at high speeds. The casing plies give the tire its shape. But the superior durability and handling provided by radials led to their gradual market dominance.
Radial Tire Basics
In general, the radial's construction is made of numerous layers of tough, rubberized material called plies. Plies are sheets of rubber with strong fiber cables called cord bonded to the rubber for strength and durability. Within each sheet, cords are arranged side by side so that they all run in the same direction. When the tire is manufactured, the rubber sheets or plies are arranged in alternating layers. Each layer is alternately arranged so that they form a criss-cross pattern of plies for added strength. Collectively, the various layers of plies form the body or carcass of the tire. A radial ply tire runs cooler than a comparable cross-ply tire, and this increases tread life. Also, a radial tire has less rolling resistance as it moves over the road surface.
 Now that we have the basics of tire construction, lets take a closer look at the construction of a generic tire and see how the various parts work together. Starting from the inside layer and working our way out to the tread. The innermost layer is made of an especially thin layer of rubber called the liner. The liner is similar to a thin rubber film or membrane and is responsible for providing a leak-proof seal along the inside of the tire. In many ways, the liner takes the place of an inner tube found in early automobile tires.
The next layer is comprised of piles with the cords running from bead to bead. In other words, the tire “grain” runs 90° to the direction the tire rolls. Additional plies or layers are added so the cords form a criss-cross pattern.
Stabilizer belts are located between the plies and the tire tread. Anymore, stabilizer belts tend to be made out of a rubber base with reinforced strands of steel imbedded. Steel belts add a lot of stability to the tire as it corners. In addition, the steel belts further increase durability from punctures or from damaging potholes or road debris.  These layers keep the tread rigid while the rubber sidewall flexes. This gives the radial its characteristic side-bulge and allows the tread to run flatter on the road. This allows for better grip, handling and fuel economy, but gives the car a somewhat bumpier ride.
The sidewall is not generally exposed to any direct contact or wear and tear. Nor does the sidewall produce much heat. As a result, sidewalls tend to be relatively thin. Nonetheless, pile fibers form a durable mesh. A series of letters, numbers and classifications are printed on every tire's sidewall. This information is critical to understand which tires are appropriate for your automobile. A little later on, we'll address all of the information found on your tire's sidewall in more detail.
The tire beads are the inner and outer edges or lips of the tires that fit along the inside edge of the wheel. Beads are comprised of reinforced steel wire hoops encased in a thick molded rubber wall. When the tire is inflated, the bead is pressed against the wheel and forms an airtight seal.
The outermost layer is bonded to the top layer of piles and is called the tread and its main job is to provide traction. The amount of tread in contact with the road is called the contact patch or footprint. One of the attractive characteristics of radial tires is the amount of tire tread in contact with the road at any one time. In other words, radial tires tend to provide a relatively large footprint or contact patch relative to traditional bias ply tires. Radials tend to maintain greater road contact in a variety of driving conditions. Greater flexibility allows the tire to maintain a wide footprint even while going over obstacles. In addition, because of sidewall flexibility, the tire is able to stretch proportional to the driving force. Traditional bias ply tires tend to loose a portion of their footprint because of the rigid sidewall construction. As a result, radials provide an ideal tire for cornering.
 No matter what type of tire you may be driving, tire treads must be able to withstand tremendous forces, be durable and provide traction in a wide variety of potential driving conditions. Most automobiles are equipped with an all seasons tire. All seasons tires offer a moderate tire tread that is well equipped for a wide variety of potential driving conditions, such as rain, snow or highway driving. Snow tires are one example of a specially designed tread for snowy weather
conditions.
The Aspect Ratio
In general terms, aspect ratio is the ratio between two dimensions of an object. In tire terms, the aspect ratio is the relationship (ratio) between a tire sidewall's height to width. You can use this measurement to determine the height of the sidewall.
The lower the aspect ratio, the more squat the tire becomes. For example, a tire with an aspect ratio of 70 is shorter and fatter than a tire with an aspect ratio of 80. Typically, aspect ratios are usually given as a percentage.
An aspect ratio of 98% means the section height of the tire is slightly less than the section width. This is called a cushion or balloon tire.
An aspect ratio of 88% means the height is 12% less than the width, giving a lower profile. It is called a medium low profile tire.
The profile of cross-ply tires was reduced further to between 78 and 82%, called a super low section. However the stiffness of cross-ply tires makes them unsuitable for further reduction in profile.
Radial ply tires have been manufactured in 78% profile, but are also made with further reductions in profile, from 75%, to 45%.
Tire tread designs
Tire tread patterns can be classified with these general characteristics:
Directional
Directional tread patterns are designed to provide a range of attributes during particular driving conditions. The tire can only be mounted to the wheel so that it revolves in a particular direction to correspond with the tread pattern. An arrow on the tire sidewall indicates the designed direction of forward travel.
Non-directional
Non-directional tread patterns are designed in such a way that the tire can be mounted on the road wheel for any direction of rotation.
Symmetric
Symmetric tread patterns have the same tread pattern on both sides of the tire and are usually non-directional tires.
Asymmetric
Asymmetric tread patterns have a tread pattern that is different from one side of the tire to the other. They are designed to provide good grip when traveling straight and in turns. They are generally directional tires and must be fitted to the road wheel in accordance with the fitting instructions to ensure that they perform as designed under operating conditions.
Performance characteristics
Tread wear
Friction between the tire and the road surface causes the tread rubber to wear away over time. Government legal standards prescribe the minimum allowable tread depth for safe operation.
There are several types of abnormal tread wear. Poor wheel alignment can cause excessive wear of the innermost or outermost ribs. Over inflation can cause excessive wear to the center of the tread. Under inflation can cause excessive wear to the outer ribs. Unbalanced wheels can cause uneven tire wear, as the rotation may not be perfectly circular. Tire manufacturers and car companies have mutually established standards for tread wear testing that include measurement parameters for tread loss profile, lug count, and heel-toe wear. Also can be known as tire wear. See also TKPH below.
Dry traction
Dry traction is measure of the tire’s ability to deliver traction, or grip, under dry conditions. Dry traction increases in proportion to the tread contact area. Dry traction is also a function of the tackiness of the rubber compound.
Wet traction
Wet traction is measure of the tire’s ability to deliver traction, or grip, under wet conditions. Wet traction is improved by the tread design’s ability to channel water out of the tire footprint and reduce hydroplaning.
Force variation
The tire tread and sidewall elements undergo deformation and recovery as they enter and exit the footprint. Since the rubber is elastomeric, it is compressed during this cycle. As the rubber deforms and recovers it imparts cyclical forces into the vehicle. These variations are collectively referred to as Tire Uniformity. Tire Uniformity is characterized by Radial Force Variation (RFV), Lateral Force Variation (LFV), and Tangential Force Variation. Radial and Lateral Force Variation is measured on a Force Variation Machine at the end of the manufacturing process. Tires outside the specified limits for RFV and LFV are rejected. In addition, Tire Uniformity Machines are used to measure geometric parameters including Radial Runout, Lateral Runout, and Sidewall Bulge in the tire factory at the end of the manufacturing process as a quality check.
Balance
When a wheel and tire is rotated, it will exert a centrifugal force characteristic of its center of gravity. This cyclical force is referred to as balance, and a non-uniform force is referred to as imbalance or unbalance. Tires are checked at the point of manufacture for excessive static imbalance and dynamic imbalance using automatic Tire Balance Machines. Tires are checked again in the auto assembly plant or tire retail shop after mounting the tire to the wheel. Assemblies that exhibit excessive imbalance are corrected by applying balance weights to the wheels to counteract the tire/wheel imbalance.
To facilitate proper balancing, most high performance tire manufacturers place red and yellow marks on the sidewalls of its tires to enable the best possible match-mounting of the tire/wheel assembly. There are two methods of match-mounting high performance tire to wheel assemblies using these red (Uniformity) or yellow (Weight) marks[5].
Centrifugal growth
A tire rotating at higher speeds will tend to develop a larger diameter, due to centrifugal forces that force the tread rubber away from the axis of rotation. As the tire diameter grows the tire width decreases. This centrifugal growth can cause rubbing of the tire against the vehicle at high speeds. Motorcycle tires are often designed with reinforcements aimed at minimizing centrifugal growth.
Rolling resistance
Rolling resistance is the resistance to rolling caused by deformation of the tire in contact with the road surface. As the tire rolls, tread enters the contact area and is deformed flat to conform to the roadway. The energy required to make the deformation depends on the inflation pressure, rotating speed, and numerous physical properties of the tire structure, such as spring force and stiffness. Tire makers seek lower rolling resistance tire constructions in order to improve fuel economy in cars and especially trucks, where rolling resistance accounts for a high amount of fuel consumption.
The pneumatic tire also has the more important effect of vastly reducing rolling resistance compared to a solid tire. Because the internal air pressure acts in all directions, a pneumatic tire is able to "absorb" bumps in the road as it rolls over them without experiencing a reaction force opposite to the direction of travel, as is the case with a solid (or foam-filled) tire. The difference between the rolling resistance of a pneumatic and solid tire is easily felt when propelling wheelchairs or baby buggies fitted with either type so long as the terrain has a significant roughness in relation to the wheel diameter.[citation needed]
Stopping distance
The use of performance oriented tires, which have a tread pattern and rubber compounds designed to grip the road surface, usually has slightly shorter stopping distances. However, specific braking tests are necessary for data beyond generalizations.
Tire distortion
During cornering, centrifugal force acts on a vehicle to produce a side force. This side force must be resisted by the interaction of the tire on the road surface. The greater the side force, the greater the opposing force must be.
Without this resistance, the vehicle will continue in a straight line.
The pneumatic tire provides this opposing force by being able to distort while still gripping the road.
Then since the tire’s construction makes it elastic, it exerts a force, called cornering force, which acts between the tread and the road surface. It pulls the distorted rubber back to its normal position.
The tire’s sideways distortion makes the vehicle follow a path at an angle to the direction the road wheel is pointing. This is called the slip angle. As cornering force increases, so does slip angle.
When a vehicle is being driven into a turn with decreasing radius, both slip angle and cornering force increase, until a point is reached where the tire slides, and the only resistance comes from sliding friction across the road surface.
The tire grips again only when the vehicle has slowed, or is making a turn with a larger radius. That is, when the side force is reduced to a level the tire can withstand without skidding.
Since both front and rear tires develop a slip angle in a turn, the vehicle’s path is determined by the steering of the front tires, and the slip angles of both the front and rear tires. These slip angles depend on the location of the major components.
New developments
But what happens to a radial if you run over a nail? New technology gives drivers easier, safer ways to survive a punctured tire. In the past, manufacturers equipped cars with full-size spare tires, which can be heavy and cumbersome to change on the roadside.
 Now, owners can purchase temporary spares. These compact tires retain the outside diameter measurements of the original tire but are lighter and use much higher tire pressures.
However, where full-size spares could be used for long distances, a temporary spare is designed to get the car off the road and to the closest service center. Another solution is to use heavier 'run-flat' tires, which can operate completely flat for about 100 miles at 50 mph. Run-flats are steel-belted radials that use reinforced sidewalls for support and can be mounted to ordinary rims. With run-flats, a driver won't have to spend time changing a flat, but these tires are often an expensive alternative to carrying a spare. |
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Introduction
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 Articles
When Parts Go Bad
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Article Pages
1. An Introduction to Wheels and Tires
3. Learning To Read Your Tires
4. Manipulating The System
5. Valves
6. Tire Pressure Monitoring Systems (TPMS)
7. Tire Inspection
8. Tire Wear Guide
9. Tire Rotation
10. Wheel Assembly
11. Wheel And Rim Construction
Hot Topics
-> 4 Things You Can Start Doing Today To Extend The Life Of Your Tires
-> New Tires Guide
-> Tire Safety Tips
-> What Does It Mean When My Wheels Are Imbalanced?
-> Wheel Balancing
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