Tire Construction (Auto Repair)

Every tire has several major parts (see Figure 19-1):
The tread is the rubber part of the tire that gets most of the wear and tear. The tread patterns help the tire grip the road and resist puncturing. These patterns are also excellent indicators of tire wear. I get into reading these clues later in this chapter, in in the section called “Checking your tires for wear.”
The sidewall is the part of the tire between the tread and the bead. The section called “The Secrets on Your Sidewalls, Revealed!” later in this chapter decodes all the useful data molded into the sidewall of a tire.
The bead is a hoop of steel wire that’s shaped to help hold the tire onto the rim of the wheel.
The casing (or carcass) is the body of the tire, located beneath the tread and the sidewalls. It helps the tire keep its shape when inflated, instead of letting it blow up like a balloon. The casing is made up of various materials, called cords.
The belts are also made up of cords, which are coated with rubber and located between the body and the tread. The type of material used for the belts, and the way it’s wrapped around the bead, determine the kind of tire and its price. Originally, cotton was used for the cords, but it soon gave way to better materials, such as steel, aramid (which is harder than steel)7fiberglass, polyester, rayon, and nylon. Steel-belted radials are the most popular type of tires today.
The tire valve lets air into and out of a tire. The valve core prevents air from escaping. Each valve should have a valve cap to keep dirt and moisture from getting into the tire.
Until recently, tires came in a variety of constructions. There were bias-ply tires, which featured cords wrapped around the beads at overlapping angles. These were superseded by bias-belted tires, which were constructed in the same manner as bias-ply tires but featured belts of another material that wrapped around the tires’ circumference, providing longer wear, puncture resistance, and more directional stability. Today, all vehicles come fitted with radial tires and, because all but the oldest vehicles run well with them, bias-ply and bias-belted tires are no longer readily available.
tmpDA7_thumb2Anatomy of a tire.
Figure 19-1:
Anatomy of a tire.
tmpDA9_thumb2
If you have an antique or classic vehicle that requires old-style tires, you can find companies that manufacture reproductions of the original tires for your vehicle’s make, model, and year.
Radial tires have become the standard because they provide better handling, especially at high speeds; they tend to grip the road more efficiently, especially when cornering; and they can deliver twice the mileage that bias-ply and belted tires did. Radial tires run cooler because they have less internal friction. (Bias and bias-belted tires had overlapping cords that translated into more internal friction and more heat when in motion.) Wear varies from 25,000 miles and up, depending on the belt material used. Top-of-the-line steel-belted radials can last from 40,000 to as many as 100,000 miles under average conditions.
To decide what type of tire is right for your vehicle, see “Tips for Buying Tires,” later in this chapter.


Next post:

Previous post: