Tires are highly engineered structural composites whose performance can be designed to meet the vehicle manufacturers’ ride, handling, and traction criteria, plus the quality and performance expectations of the customer. The tires of a mid-sized car roll about 800 revolutions for every mile. Hence, in 50,000 miles, every tire component experiences more than 40 million loading-unloading cycles, an impressive endurance requirement.
There are two main functions of passenger car tires. The primary function of passenger car tires is to provide the interface between the vehicle and the highway. The rubber contact area for all four tires for a typical mid-size car is less than that of an 8½ x 11 inch sheet of paper; each tire has a footprint area of about the size of an average man’s hand. Yet we expect those small patches of rubber to guide us safely in a rain storm, or to allow us to turn fast at an exit ramp, or to negotiate potholes without damage.
The secondary function lies on the fact that the Vehicle load causes tires to deflect until the average contact area pressure is balanced by the tires’ internal air pressure. Assuming a typical passenger tire is inflated to 30 psi, then a 300 lb load would need an average of 10 square inches of contact area to support the load. Larger loads require more contact area (more deflection) or higher tire pressures. A larger contact area usually requires a larger tire
It is highly important to maintain the optimal air pressure. When air pressure is below recommended, tires expand and shrink during each cycle and therefore shearing takes place between the layers and heat is being generated. This could tear the tire and cause to an accident.
Another benefit of the pneumatic tire is the ability to absorb road irregularities.
In effect, tires act as a spring and damper system to absorb impacts and road surface irregularities under a wide variety of operating conditions.
Diagonal (bias) tires
Still used today in some applications for trucks, trailers and farm implements, as well as in emerging markets, bias tires have body ply cords that are laid at angles substantially less than 90º to the tread centerline, extending from bead to bead (see Figure 1.1).
Advantages: Simple construction and ease of manufacture.
Disadvantages: As the tire deflects, shear occurs between body plies which generate heat. Tread motion also results in poor wear characteristics
Radial tires have body ply cords that are laid radially from bead to bead, nominally at 90º to the centerline of the tread. Two or more belts are laid diagonally in the tread region to add strength and stability. Variations of this tire construction are used in modern passenger vehicle tire
Advantages: Radial body cords deflect more easily under load, thus they generate less heat, give lower rolling resistance and better high-speed performance. Increased tread stiffness from the belt significantly improves wear and handling.
Disadvantages: Complex construction increases material and manufacturing costs.
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