heat during operation. The center of the tread flexes upward and does NOT touch the surface of the road. Underinflation will cause rapid tread wear, loss of fuel economy, and possibly ply separation (plies tear away from each other).

Uneven tire inflation pressure can cause steering wheel pull. For example, when a vehicle that has the left front tire underinflated and the right front tire properly inflated, the vehicle has a tendency to pull to the left. The low air pressure in the left tire has more rolling resistance. This action tends to pull the steering wheel away from the normally inflated tire.

Tire Vibration Problems

When one of the front tires is vibrating, it can be felt in the steering wheel. When one of the rear tires is vibrating, the vibration can be felt in the center and rear of the vehicle. Tire vibration can be attributed to several problems, such as out-of-balance condition, ply separation, tire runout, a bent wheel, or tie cupping.

Tire and Wheel-Bearing Noise

Tire noise usually shows up as a whine due to abnormal tread wear or a thumping sound caused by ply separation. Tire replacement is required to correct these problems.

Wheel-bearing noise is produced by dry, worn wheel bearings. The bearing will make a steady humming type sound. This is due to the rollers or balls being damaged from lack of lubrication and are no longer smooth. To check for a worn wheel bearing, raise and secure the vehicle, and rotate the tire by hand. Feel and listen carefully for bearing roughness. Also, wiggle the tire back and forth to check for bearing looseness. It may be necessary to disassemble the wheel bearing to verify the problem.

REVIEW 4 QUESTIONS

Q1. What are the two basic functions of a tire?

Q2. List the six major parts of a tire.

Q3. What is the major disadvantage of a radial tire?

Q4. What information is commonly given on the tire sidewall?

Q5. What is the most commonly used wheel used on passenger vehicles?

Q6. What are the two basic wheel-bearing configurations?

Q7. For a tire to be in dynamic balance, the weight must be evenly distributed around the axis of rotation. (T/F)

WHEEL ALIGNMENT

Learning Objective: State the purpose and describe each wheel alignment setting. Describe the different types of equipment used during wheel alignment service.

The term alignment means to position in a straight line. Relating to vehicles, alignment means to position the tires so they roll freely and evenly over the road surface. The main purpose of wheel alignment is to make the tires roll without scuffing, slipping, or dragging under all operating conditions. Correct wheel alignment is essential to vehicle safety, handling, extending tire life, and achieving maximum fuel economy.

The different types of wheel alignments are front end alignment, thrust angle alignment, and four-wheel alignment.

1. In a front end alignment, the front only is checked. This is fine in some cases, but are the front tires properly positioned in front of the rear tires?

2. With the thrust angle alignment, the wheels are squared to each other. This action will eliminate "dog tracking" that you may have seen on a vehicle that appears to be going down the road with the rear end a foot over from the front.

3. The best way to align a vehicle is a four-wheel alignment. This alignment will not only do what the thrust angle alignment does but also includes adjusting the settings on the rearofthe vehicle as well as the front.

Not all vehicles are fully adjustable, so before any alignment always consult the manufacture's service manual. Regular wheel alignments will save you as much in tire wear as they cost. It should be considered routine, preventive maintenance.

STEERING GEOMETRY

Steering geometry is the term manufacturers use to describe steering and wheel alignment. The six fundamental angles or specifications that are required for a proper wheel alignment are as follows:

Caster

Camber

Toe