EI07266 - Tire Vibration, P275/55R20 or LT265/70R17 (Engineering Information)

Some customers may comment on a vehicle/tire vibration.

GM Engineering is attempting to determine the root cause of reported tire vibrations on vehicles equipped with P275/55R20 or LT265/70R17 tires. GM has a need to obtain information during diagnosis and BEFORE repair. This information will be used by engineering to "root cause" the customer's concern and develop/validate a field fix.

If the customer's concern can not be duplicated -- disregard this bulletin. If the customer's concern can be duplicated, complete the following steps. Be sure to note the following information on the repair order:

1. Verify that the VIN and mileage listed on the repair order is accurate.
2. Describe the customer's concern (i.e. shake, buzz, roughness, tingling). Note when (mph, idle, accel, decel, etc) and where (steering column, seat, etc) the vibration is felt.
3. Document the tire size and manufacturer of the tires currently on the vehicle.
4. Inspect the following components to verify that they are in good working condition. Note any "faults" on the repair order:

•	tire/wheel assemblies

•	steering components

•	suspension components

5. Install the J 38792-A (Electronic Vibration Analyzer -- EVA) sensor to the component identified by the customer as the most respondent to the vibration. If no component was identified, install the J38792-A sensor to the steering column.
6. Select a smooth, level road and slowly accelerate the vehicle up to highway speed.
7. Observe the vehicle for disturbances that match the customer's description and note the following conditions:

•	Vehicle speed

•	Engine RPM

•	Transmission gear range and specific gear

•	Vibration frequency reading, detected by the J 38792-A

8. If the sensor was originally placed on the steering column, and the vibration seems to excite a particular component of the vehicle more than the steering column, move the J 38792-A sensor to that component and repeat steps 6 and 7.
9. Does the frequency data clearly fall within the tire/wheel parameters? (Refer to Symptoms -- Vibration Diagnosis and Correction, found in SI).

•	NO -- continue to diagnose and repair the vibration not related to the tire and wheel assembly. Fax the completed repair order (front and back) to: 248-685-6140 -- Attn: Kevin Kelly

•	YES -- proceed with Step 10.

10. Using the HUNTER GSP9700 Roadforce/Balancer, measure the roadforce variation of each tire/wheel assembly. Also, with the original balance weights still installed, measure the inboard and outboard imbalance. Record the findings on the RO.
11. PRIOR to making any repairs, contact the engineer listed below with information from your diagnosis. The engineer will provide direction to repair the customer's concern. For vehicles located in SE Michigan, the engineer may need to physically inspect the vehicle.

If necessary, leave a message with the following information:

Important: If the engineer is unable to return your call within one (1) hour, proceed with diagnosis and repair according to SI. Fax the complete repair order (front and back) to 248-685-6140.

Important:  For vehicles in which the customers concern was due to a tire vibration, submit the warranty claim using the following labor operation. For all other causes of vibration, submit the warranty claim using the appropriate labor operation found in the Labor Time Guide (LTG).