Suzuki XL7 2007 Service Manual page 1190

3D-3 Propeller Shafts:
Calculating Tire Revolutions Per Second, or Hz
at Concern Speed
A size P235/75R15 tire rotates ONE complete revolution
per second (RPS), or 1 Hz, at a vehicle speed of 8 km/h
(5 mph). This means that at 16 km/h (10 mph), the same
tire will make 2 complete revolutions in one second, 2
Hz, and so on.
1. Determine the rotational speed of the tires in
revolutions per second (RPS), or Hertz (Hz), at 8 km/
h (5 mph), based on the size of the tires. Refer to the
preceding Tire Rotational Speed information.
For example: According to the Tire Rotational Speed
information, a P275/55R20 tire makes 0.90
revolutions per second, or Hz 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 rotation
increases by 0.90 revolutions per second, or Hz.
2. Determine the number of increments of 8 km/h (5
mph) that are present, based on the vehicle speed
km/h (mph) at which the disturbance occurs.
For example: Assume that a disturbance 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
3. Determine the rotational speed of the tires in
revolutions per second, or Hz, at the specific vehicle
speed km/h (mph) at which the disturbance occurs.
For example: To determine the tire rotational speed
at 96 km/h (60 mph), multiply the number of
increments of 8 km/h (5 mph) by the revolutions per
second, or Hz, for one increment:
12 (increments) X 0.90 Hz = 10.80 Hz, rounded to 11
Hz
NOTE
If the J 38792-A is not available, compare the
calculated rotational speed to the frequency
range associated with the symptoms of the
vibration concern. Refer to "Symptoms -
Vibration Diagnosis and Correction: ".
4. Compare the rotational speed of the tires at the
specific vehicle speed at which the disturbance
occurs, to the dominant frequency recorded on the J
38792-A during testing. If the frequencies match,
then a first-order disturbance related to the rotation
of the tire/wheel assemblies is present.
If the frequencies do not match, then the disturbance
may be related to a higher order of tire/wheel
assembly rotation.
5. To compute higher order tire/wheel assembly
rotation related disturbances, multiply the rotational
speed of the tires at the specific vehicle speed at
which the disturbance occurs, by the order number:
11 Hz X 2, for second order = 22 Hz second-order
tire/wheel assembly rotation related
11 Hz X 3, for third order = 33 Hz third-order tire/
wheel assembly rotation related
If any of these computations match the frequency of
the disturbance, a disturbance of that particular
order, relating to the rotation of the tire/wheel
assemblies and/or driveline components, also
rotating at the same speed, is present.
Calculating Propeller Shaft Revolutions Per
Second, or Hz at Concern Speed
1. Determine the first order rotational speed of the
propeller shaft system in revolutions per second, or
Hz, based on the first-order rotational speed of the
tire/wheel assemblies and the drive axle, or axles
final drive ratio or ratios.
11 Hz X 3.42 drive axle final drive ratio = 37.62 Hz,
rounded to 38 Hz, first-order propeller shaft rotation
related
2. Compare the rotational speed of the propeller shafts
at the specific vehicle speed at which the
disturbance occurs, to the dominant frequency
recorded on the J 38792-A during testing. If the
frequencies match, then a first-order disturbance
related to the rotation of the propeller shaft is
present.
If the frequencies do not match, then the disturbance
may be related to the second-order of propeller shaft
rotation.
3. To compute a second order propeller shaft rotation
related disturbance, multiply the first order rotational
speed of the propeller shaft at the specific vehicle
speed at which the disturbance occurs, by the order
number of 2:
38 Hz X 2, for second order = 76 Hz second-order
propeller shaft rotation related
If the computation matches the frequency of the
disturbance, a disturbance relating to the second-
order rotation of the propeller shaft is present.