Procedure C & Dtire and Wheel Imbalance and Runout

Tire and wheel imbalance is evidenced by a constant low-frequency vibration at speeds from 30 MPH and above.

Tire and wheel balance should be done by using either an off-the-car or on-the-car spin balancer. Static or bubble balancers are not recommended.

Before proceeding with the balance, check air pressure, lug nut torque, front wheel bearing preload and visually inspect the tire for any tread or sidewall irregularities. Also make sure that the tread area of the tire is free of any debris and inspect the wheel for any irregularities.

In order to achieve an accurate balance, it is important that the balancing equipment is in good working condition. Periodic equipment checks and recalibrations are necessary. Stud mounting adaptors are recommended on balance equipment to achieve the most accurate balance.

Non-factory type equipment also must be taken into consideration. After market tire/wheel assemblies, or any suspension or steering modifications can be the cause or contributor to vibration problems.

PROCEDURE D - Tire and Wheel Runout

Though not as common as imbalance, tire and wheel runout also can be a cause of vibration problems. Tire and wheel assemblies must be checked for both radial and lateral runout. This procedure is divided into three sections.

1. Radial runout

2. Lateral runout

3. Tire and wheel phase matching

If a vibration still exists after it is certain that an accurate balance has been achieved and runout and tire to wheel phase match are correct, it may be necessary to phase match the tire/wheel assembly to the hub as follows:

- Raise vehicle.
- Place a mark on the wheel and lug to indicate Position No. 1.
- Remove the tire/wheel and rotate to the next hub stud position. Test drive the vehicle. It may be necessary to perform this step four times, test driving after each repositioning.
SECTION 1.

Radial Runout

Radial runout or "out-of-round" can be identified as a low frequency thumping or tramping vibration that can be felt at speeds of 30 MPH and above. The following diagrams show the procedures for checking radial runout. Make sure that tires are warm and recently driven to ensure that there are no "flat spots".

Radial Runout:

1. Wrap the center tread band with tape to provide a smooth running surface.

2. Position dial indicator pickup against tape to measure radial runout.

3. Rotate tire slowly while reading runout measurement. Note amount and mark maximum and minimum runout points. If runout exceeds specification, phase match tire and wheel assembly. (See Section 3, Phase Matching)

Specification: 1.4 mm (.055 in.)
SECTION 2.

Lateral Runout

Lateral or "side-to-side" runout can be identified as a low frequency side-to-side shake or shimmy at speeds of 45 MPH and above.

Dial Indicator:

1. The dial indicator pickup should be positioned on a smooth running surface as close to the center of the tire sidewall as possible.
2. Rotate tire slowly while reading the runout measurement. Note amount and mark maximum and minimum runout points. If runout exceeds specification, phase match tire and wheel assembly. (See Section 3, Phase Matching)

Specification: 2.0 mm (.080 in.)

If the wheel is suspected to have excessive radial or lateral runout, it should be checked by the following procedure.

Measure Radial Runout:

1. Locate the dial indicator at position "A" and measure radial runout.
2. Locate the dial indicator at position "B" and measure lateral runout.
3. If the wheel exceeds specification for either measurement, replace wheel.

Specification: 1 mm (0.04 in.)
SECTION 3.

Tire and Wheel Phase Matching

Excessive "tire and wheel assembly" radial or lateral runout may be corrected by tire-to-wheel phase matching.

NOTE: The procedures for correcting radial or lateral runout are the same.

Wheel Reassembly:

1. Dismount tire from wheel and reassemble matching minimum tire runout point to the maximum wheel runout point. filled circle - minimum tire runout

X - maximum wheel runout
Tire and Wheel Phase Matching (Cont'd)

2. Recheck assembly runout to confirm improvements.

3. Repair or replace components as necessary. If wheel runout is within specification, replace tire.

4. Install best tire/wheel assemblies to front axle, if possible.