Once the vibration can be readily duplicated and is thought to be abnormal, the next step is to identify the frequency of the vibration. (If the vibration has not yet been duplicated, refer to Road Test .) Use the electronic vibration analyzer (EVA) in order to measure the vibration frequency. If the EVA is NOT available, the vibration frequency can be categorized into different groups according to how the vibration feels or sounds. The majority of vibrations will fit into one of the following categories; depending upon whether the vibration can be felt or heard.

Refer to the following list of vibration category definitions:

Shake

A low frequency vibration, 5 to 20 Hz. Sometimes SHAKE is visible in the steering wheel, the seat, or the console. The best way to describe shake is to compare it to the way an out-of-round or imbalanced tire feels.

Customers may refer to shake using one of the following terms:

shake usually relates to one of the following two groups.

Roughness

A vibration with a slightly higher frequency than the shake, 20 to 50 Hz. Roughness is similar to the feeling of holding a jigsaw.

This type of vibration is usually related to driveline components.

Buzz

A vibration with a slightly higher frequency then roughness, 50 to 100 Hz. Buzz is similar to the feel of an electric razor. Buzz may be felt in the hands through the steering wheel, in the feet through the floor, or in the seat of the pants.

This type of vibration is often related one of the following:

Tingling

The highest frequency vibration that can still be felt. Tingling may sometimes produce a pins-and-needles sensation. Customers may say the vibration puts their hands or feet to-sleep.

Boom

A low frequency interior noise, 20 to 60 Hz. Sometimes the customer complains of a pressure in their ears. Examples of noises that are similar to boom include; a bowling ball rolling down an alley, deep thunder, or a bass drum.

Words commonly used to describe boom:

Boom may or may not be accompanied by a perceptible vibration (roughness).

Boom is usually related to driveline components.

Moan or Drone

A sustained tone at low frequency, 60 to 120 Hz, somewhat higher than boom.

Examples of noises that are similar to moan or drone include; a bumblebee, or blowing air across the top of a soda bottle.

Words commonly used to describe moan or drone:

Moan or drone may be accompanied by a perceptible buzzing vibration.

Many times moan or drone is related to one of the following:

Howl

A noise at mid-range frequency, 120 to 300 Hz. Howl sounds like the wind howling.

Whine

A prolonged, high-pitched sound; frequency, 300 to 500 Hz. Sounds that are similar to whine include; mosquitoes, turbine engines, and vacuum cleaners.

Whine is usually related to the meshing gears or gear noise.

At this point in the diagnosis the vibration has been:

Automotive vibrations are almost always related to the rotating speed of a component. The speed of these components can be calculated using either an engine speed or vehicle speed method.

Cycles per second or Hertz, and cycles per minute, are the units being used. These two units are interchangeable by either multiplying or dividing by 60.

Engine-Speed Related Calculation

For the calculation to convert the engine speed (RPM) readings taken during road testing, and for continued diagnosis of an engine-speed related vibration, refer to Engine Related Vibration .

Vehicle-Speed Related Calculation

If the vibration is vehicle-speed related, the rotational speed of the tires needs to be determined. As long as the vehicle is operated at a constant speed (km/h, mph), the tires will operate at their own constant speed. The speed of the tires can be measured in how many times the component (the tires) cycles or rotates in one second. This component rotational speed can then be compared to the frequency of the vibration, which is also measured in cycles per second.

For the calculation to determine the rotational speed of the tires, and for continued diagnosis of a vehicle-speed related vibration, refer to the following:

A P235/75R15 tire rotates ONE complete revolution per second (RPS) at a vehicle speed of 8 km/h (5 mph). This means that at 16 km/h (10 mph), the same tire will make TWO complete revolutions in one second, and so on.

FIRST, determine the rotational speed of the tires in revolutions per second (RPS), or Hertz (Hz), based on the size of the tires and vehicle speed (km/h, mph) at which the vibration occurs.

According to the Tire Rotational Speed Table, a P245/45ZR17 tire makes 1.13 revolutions per second at a vehicle speed of 8 km/h (5 mph). This means that for every increment of 8 km/h (5 mph) in vehicle speed, the tire's rotation increases by 1.13 revolutions.

Assume that a vibration occurs at a vehicle speed of 96 km/h (60 mph). A speed of 96 km/h (60 mph) has 12 INCREMENTS of 8 km/h (5 mph):

96 km/h (60 mph) divided by 8 km/h (5 mph) = 12 increments

To determine the tire rotational speed at 96 km/h (60 mph), multiply the number of increments (12) by the revolutions per second (RPS, Hz) for one increment:

12 increments X 1.13 Hz (RPS) = 13.56 Hz (14 Hz)

If this matches the frequency of the vibration, a first-order vibration is present in the tire/wheel assembly. However, if the frequency of the vibration does not match, the vibration may be of a higher order.

To compute possible higher-order vibrations that can be caused by the tire/wheel assembly, multiply the tire rotational speed by the order number:

14 Hz X 2 (for second order) = 28 Hz second-order vibration

14 Hz X 3 (for third order) = 42 Hz third-order vibration

If any of these computations match the frequency of the vibration, a vibration of that particular order is present in the tire/wheel assembly.

Utilize the following worksheet as an aid in calculating tire rotational speed and the possible vibration-order present in the vehicle.

If after completing the Tire/Wheel Rotation Worksheet, none of the frequencies match the frequency of the vibration, either recheck the data, or attempt to rematch the figures allowing for 1½ to 8 km/h (1 to 5 mph) of speedometer error.

If the possible tire and wheel related frequencies still do not match the frequency of the vibration, the vibration is most likely driveline component related and/or torque sensitive. Refer to Driveline Vibration Analysis .

If after completing the Tire/Wheel Rotation Worksheet, the frequencies match the frequency of the vibration, the vibration is most likely tire and wheel component related. Refer to Tire and Wheel Vibration .