Suzuki XL7 2007 Service Manual page 1068

2D-4 Wheels and Tires:
Component Rotational Speed Calculation
Special tool
J 38792-A Electronic Vibration Analyzer (EVA) 2
Tire Rotational Speed
Determining Tire Revolutions Per Second at 8 km/h
(5 mph) — Using EVA
Tire and wheel assembly rotational speed can be
obtained through using the J 38792-A. Perform the
following steps using the J 38792-A to obtain the
rotational speed at 8 km/h (5 mph). Use the Enter key to
advance and the Exit key to backup.
1. On the Main Menu screen, select Auto Mode.
2. On the Suspected Source screen, select Vehicle
Speed.
3. On the Tire Info Source screen, select Manual Entry.
4. On the Tire Width screen, enter the specific width of
the tires.
For example: For a P275/55R20 tire, enter 275.
5. On the Aspect Ratio screen, enter the specific
aspect ratio of the tires.
For example: For a P275/55R20 tire, enter 0.55.
6. On the Rim Diameter screen, enter the specific rim
diameter size.
For example: For a P275/55R20 tire, enter 20.0.
7. On the Driveshaft Configuration screen, enter FWD,
even if the vehicle is a rear wheel drive.
8. The next screen will display the tire size just entered
for confirmation.
For example: 275 0.55 20.0 - Front Wheel Drive. If
the tire size displayed is correct, press Enter.
9. On the Vehicle Speed Units screen, press Enter,
disregard mph or km/h.
10. Press the Exit key several times slowly while
watching the backwards progression of the screens.
Stop at the Tire Info Source screen.
11. On the Tire Info Source screen, select RPS at 5
mph.
12. The next screen will display the revolutions per
second (RPS) at 8 km/h (5 mph) for that specific tire
size.
For example: The P275/55R20 will display 0.90
RPS.
Calculating Tire Revolutions Per Second at 8 km/h (5
mph) — Without EVA
If the J 38792-A is not available, the tire and wheel
assembly rotational speed can be calculated
approximately by performing the following steps.
Diagnostic Information and Procedures
1. Convert the rim diameter size from inches to
centimeters.
For example: For a P275/55R20 tire, the rim
diameter of 20 in X 2.54 converts to 50.80 cm.
2. Calculate the radius of the rim by dividing the rim
diameter by 2.
For example: For a P275/55R20 tire, the rim
diameter of 20 in converted to 50.80 cm divided by 2
= rim radius 25.40 cm.
3. Calculate the approximate tire sidewall height by
multiplying the specific tire tread width by the aspect
ratio, then reduce 7 percent from the amount by
multiplying by 93 percent to approximate load on the
tire reducing the sidewall height.
For example: For a P275/55R20 tire, tread width 275
mm X aspect ratio as a decimal 0.55 = 151 mm X
0.93 = approximate sidewall height 140.43 mm.
4. Convert the calculated approximate tire sidewall
height from millimeters to centimeters.
For example: For a P275/55R20 tire, approximate
sidewall height 140.43 mm converts to 14.04 cm.
5. Calculate the approximate tire and wheel assembly
radius by adding the rim radius and approximate
sidewall height, both in cm.
For example: For a P275/55R20 tire, rim radius
25.40 cm + 14.04 cm = approximate tire and wheel
assembly radius 39.44 cm.
6. Calculate the approximate circumference of the tire
and wheel assembly by multiplying 2 X pi, or
6.283185 X the approximate tire and wheel
assembly radius.
For example: For a P275/55R20 tire, 6.283185 X
approximate tire and wheel assembly radius 39.44
cm = approximate tire and wheel assembly
circumference 247.809 cm.
7. Calculate the approximate revolutions per kilometer
by dividing the number of cm in 1 km, 100,000 cm by
the approximate tire and wheel assembly
circumference.
For example: For a P275/55R20 tire, 100,000 cm
divided by approximate tire and wheel assembly
circumference 247.809 cm = approximate
revolutions per kilometer 403.537.
8. Calculate the approximate revolutions per second
(RPS), or Hz, by dividing the approximate
revolutions per kilometer by the number of seconds
to travel 1 km at a speed of 8 km per hour, 450
seconds.
For example: For a P275/55R20 tire, approximate
revolutions per kilometer 403.537 divided by the
number of seconds to travel 1 km at a speed of 8 km
per hour, 450 seconds = approximate RPS, or Hz
0.897 rounded to 0.90.