Road Test

DESCRIPTION
A tire vibration diagnostic procedure always begins with a road test. The road test and customer interview (if available) will provide much of the information needed to find the source of a vibration. During the road test, drive the vehicle on a road that is smooth and free of undulations. If vibration is apparent, note and record the following:
^ The speed at which the vibration occurs
^ What type of vibration occurs in each speed range-mechanical or audible
^ How the vibration is affected by changes in engine torque, vehicle speed and engine speed
^ Type of vibration sensitivity-torque sensitive, vehicle speed sensitive, or engine speed sensitive
Use the following explanation of terms to help isolate the source of the vibration.

Torque Sensitive
The condition can be improved or worsened by accelerating, decelerating, coasting, maintaining a steady vehicle speed and application of engine torque.
Vehicle Speed Sensitive
The vibration always occurs at the same vehicle speed and is not affected by engine torque, engine rpm or transmission gear.
Engine Speed Sensitive
The vibration occurs at varying vehicle speeds when a different transmission gear is selected. It can sometimes be isolated by increasing or decreasing engine speed with the transmission in NEUTRAL or by stall testing with the transmission in gear. If the condition is engine-speed sensitive, the condition is not related to tires.
A Thumping Noise
This usually means that the tire is FLAT or has SOFT SPOTS making a noise as they slap the roadway.
Tire Whine/Noise
Tire whine can be distinguished from axle noise. Axle noise diminishes or changes according to load or speed. Tire whine remains the same over a range of speeds. If the road test indicates that there is tire whine but no shake or vibration, the noise originates with the contact between the tire and the road surface.

CAUTION: To prevent damage, deflate tires to their proper pressures after this check is completed.

To verify tire noise is not associated with shake or vibration, inflate the tires one at a time and check for a change in the sound.