Specifications

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Preventive Maintenance 30 17730-248

AIRTEK

•

SOFTEK

for Blue Bird Buses

The most common conditions of concern are:

■

Overall Fast Wear (Miles per 32nd)

■

Feather Wear

■

Cupping

■

Diagonal Wear

■

Rapid Shoulder Wear (One Shoulder Only)

■

One-Sided Wear

FIGURE 7-10

Overall Fast Wear — Fast wear can be described as exhibiting a good, but accelerated

wear pattern. It is typically caused by operating conditions, such as mountainous terrain,

frequency and severity of turning, abrasive road surfaces in combination with vehicle con-

figurations and their attributes-such as power steering, heavy axle loads, high wheel cuts,

setback axles, short wheel base tractors, long wheel base straight trucks. To correct this

problem, consult with vehicle and tire manufacturers when specifying equipment or replac-

ing tires. For more information, see TMC RP 219A publication, page 11. For information on

how to accurately measure and record tire rates, see TMC RP 230 publication.

FIGURE 7-11

Feather wear — Tread ribs or blocks worn so that one side is higher than the other result-

ing in step-offs across the tread face. Generally, ribs or blocks exhibit this wear. To spot this

problem, do the following:

With one hand flat on the tread of the tire and a firm down pressure, slide your hand across

the tread of the tire. In one direction, the tire will feel smooth and in the opposite direction

there will be a sharp edge to the tread. Typical causes of feather wear include: excessive

side force scrubbing, resulting from conditions of misalignment such as excessive toe, drive

axle misalignment, worn, missing or damaged suspension components, bent tie rods or

other chassis misalignment.

To correct this problem, tires can be rotated to another axle for maximum utilization of

remaining tread. Additionally, diagnose the vehicle itself and correct misalignment condi-

tion as required. If steer tire feathers are in opposite directions, an improper toe condition is

most likely the cause. For more information, see TMC RP 219A publication, page 5.

If feather wear on both steer tires is in the same direction, drive axle or other chassis

misalignment is indicated. If one steer tire shows feather wear and the other steer tire has

normal wear, a combination of toe and drive axle or chassis misalignment is indicated.

FIGURE 7-12

Cupping — Localized, dished out areas of fast wear creating a scalloped

appearance around the tire. Cupping, which appears around the tire on

the shoulder ribs, may also progress to adjoining ribs, see TMC RP 219A

publication, page 7.

Cupping is usually a result of moderate-to-severe imbalance, improper

rim/wheel mounting, excessive wheel end play or other assembly non-

uniformity. It can also be due to lack of shock absorber control on some

suspension types.

To solve cupping problems:

■

Tires

– Correct mismount or balance problem. If ride complaints arise,

steer tires may be rotated to drive or trailer axle.

■

Vehicle

– Diagnose component imbalance condition, i.e., wheel, rim,

hub, brake, drum. Correct as necessary.

APPENDIX

SERVICE MANUAL