To assist students in understanding the relationship between worn suspension components, tire wear, and increased fuel consumption.

The student will learn how worn front suspension components may:

1. Cause improper front end alignment.

2. Increase tire wear.

3. Reduce fuel economy and increase operational costs.

Tire Conditions:
Gradual tire wear is normal; flat, even tire wear is a sign of correct alignment, tire balance, and proper inflation.

Alignment compensates for slight normal front suspension tolerance and component wear in king pins, bushings, tire rod ends, steering gear, and springs that sag.

Regular lubrication prevents or defers wear to these components. Not only is it important to lubricate the front suspension at correct intervals, but it is also very important to use the correct type of lubricant.

Tires with even the slightest edge wear, cupping, or spotty wear are exhibiting signs of misalignment. This misalignment may be a result of either poor alignment settings or worn parts that create a misaligned front suspension.

Energy Savings:
Tire scrub, a lateral force that pushes the tire sideways, adds to the rolling resistance of the vehicle. As a result, more energy is required to move the vehicle in its intended path of travel. Tires are constructed from petroleum stock; therefore, if tires wear out prematurely, natural resources are wasted.

Tire and wheel balance compensates for static and dynamic unbalance of wheels and tires. Unbalanced tires bounce and lose contact with the road. The "heavy side" of the tire comes in contact with the road and small excessive amounts of the rubber are rubbed off.

Improper Inflation:
Improper inflation, too low or too high, may also result in excessive tire wear. Underinflating wears out the edges of the tire and adds to tire drag. Fuel is wasted due to increased drag. Overinflation wears the tire in the center. The illustrations below portray road contact and wear patterns when tires are:
Illustrations courtesy of Moog Automotive.

Tire Wear:
Heavy, spotty, cupped or irregular tire wear are signs of components of king pins, bushings, tire rod ends, steering gear, pitman arms, idler arm, spring sag, shock leakage, or wheel bearings that are out of specification. Figures 1, 2, 3, and 4, identify each type tire wear problem.
Figure 1
Imprper Toe causes this tire wear

Figure 2
An improperly set camber caused this tire wear.

Combination of factors caused these tires to wear:
Figure 3
Worn / loose king pins plus an incorrect camber could cause this tire wear pattern.

Figure 4
Worn / loose king pins plus a toe-out condition would cause this tire wear pattern.
Tire Illustrations Figure 1, 2, 3, and 4 courtesy of Moog Automotive.

1. Use the data chart on the next page to determine a medium or heavy truck's front suspension condition.

2. Using an appropriate manufacturer's shop manual, inspect each front suspension component for excessive wear.

3. Have your instructor check your findings. Make recommendations for any needed correction. If authorized, repair the component(s) and after the work is completed, have the instructor repeat his inspection of the work.

4. Complete the summary report.

5. Calculate the cost per mile for two tires of the size inspected. Assume that the ideal useable tire life is 80,000 miles. If there was two feet per mile side scrub, how much faster would these tires wear out? Now, what would the tire cost per mile for two front tires?


Model:____________________________Front Tire Size:___________________

Tube Type or Tubeless:_________________________________________________

Local retail cost per tire: $______________________________________________

Inspect both front tires for the following:
1. Inflation:
Recommended ___________ Actual__________
Check One
______ High
______ Low
______ OK

2. Visually inspect the tread. Is it (check one):
_____ flat and evenly worn
_____ cupped
_____ uneven and jagged
more worn on one edge
other - describe: ________________________________________________

3. Using the correct shop manual, inspect each front suspension component. What is the condition of each (check one)?

a. Wheel bearings:
______ too tight
______ too loose
______ rough
______ correct pre load and smooth rolling

b. Tie-rod ends:
______ worn, out of tolerance
______ worn, but in tolerance
______ too tight
______ very little perceptible wear
______ rubber boots need replacing

c. Steering gear:
______ worn, out of tolerance
______ worn, but in tolerance
______ too tight
______ very little perceptible wear
______ other condition. Describe: __________________________________________

d. Pitman Arm:
______ worn, out-of-tolerance
______ worn, but in tolerance
______ too tight
______ very little perceptible wear

e. Springs:
______ sagging to one side
______ correct ride height and in tolerance.

f. Other components:
List abnormal conditions found:





C. Recommended repairs (if any)


Instructor's inspection and approval:____________________________________

D. Authorized repairs made:


E. Summary Report:


Determine the replacement cost of the tire for this vehicle:


F. What is the cost per mile for this tire if it lasts 80,000 miles?

What is the cost per mile for this tire if it side scrubbed two feet per mile and wore out prematurely?

Formula for side scrub:
1/8" toe/tire = 12 feet/mile scrub (5,280 ft/mile)
1/4" toe/tire = 24 feet/mile scrub (63,360 inch/mile)

2 ft/mile = 1/48" toe
Then each tire scrubs 1/48" for 80,000 miles =
(5,280 ft/mile)Then 80,000 ÷ 24 = 3,333.33 inches scrubbed in 80,000
(63,360 in/mile)Then 63,360 ÷ 3,333.33 = 19 miles sideways scrub!

(Show work)

Many heavy truck operators and technicians ignore minor suspension and tire wear problems. Traditionally, tire cost has been insignificant to the overall cost of operation. Since the trucking industry has become increasingly more competitive, small incremental costs can begin to reduce an operator's profit margin. Tire scrub results not only in worn tires, but also in decreased fuel economy. Technicians must demonstrate to customers superior knowledge of methods that can lower operating costs.

Signs of Tire Wear. The Effects of Misalignment and Worn Parts on Tire Life. Moog Automotive. St. Louis. 1988.

Brady, Robert N. On-Highway Trucks. Reston Publishing Co. Inc., Reston, VA. 1982.

Schulz, Erich J. Diesel Equipment I. Gregg Division of McGraw Hill, New York. 1982.

Comments or questions to: TechAsmt@LA.GOV

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