Learning Objective: Identify and describe the parts of a tire and the methods of tire construction. Explain tire and wheel sizes. Describe tire ratings and the different types of wheels. Identify the parts of driving and nondriving hubs and wheel-bearing assemblies.
This section introduces the various tire designs used on modern vehicles. It explains how tire and wheels are constructed to give safe and dependable service. This section also covers hub and wheel-bearing construction for both rear-wheel and front-wheel drives.
They must act as a soft CUSHION between the road and the metal wheel.
They must provide adequate TRACTION (friction) with the road surface.
Tires must transmit driving. braking. and cornering forces to the road in all types of weather. At the same time, they should resist puncture and wear. Although there are several tire designs. the six major parts of a tire are as follows:
TIRE BEADS (two steel rings encased in rubber that holds the tire sidewalls against the wheel rim).
BODY PLIES (rubberized fabric and cords wrapped around beads. forming the carcass or body of the tire).
TREAD (outer surface of the tire that contacts the road surface).
SIDEWALL (outer surface of the tire extending bead to tread; it contains tire information).
BELTS (used to stiffen the tread and strengthen the plies; they lie between the tread and the inner plies).
LINER (a thin layer of rubber bonded to the inside of the plies: it provides a leakproof membrane for tubeless tires).
There are many construction and design variations in tires. A different number of plies may be used and ran at different angles. Also, many different materials may be used. The three types of tires, found on late model vehicles, are bias-ply, belted bias. and radial.
A bias-ply tire (fig. 8-29) has the plies running at an angle from bead to bead. The cord angle is also reversed from ply to ply, forming a crisscross pattern. The tread is bonded directly to the top ply.
A major disadvantage of a bias-ply tire is that the weakness of the plies and tread reduce traction at high speeds and increase rolling resistance.
Belted Bias Tire
Radial Ply Tire
Figures 8-29.- Bias-ply tire construction.
A major disadvantage of the radial ply tire is that it produces a harder ride at low speeds. The stiff tread does NOT give or flex as much on rough road surfaces.