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Tire and Wheel Rotational Speed Calculation

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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 TWO 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 Fig 1 . For example: According to the Tire Rotational Speed table, a P215/60R15 tire makes 1.14 revolutions per second (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's rotation increases by 1.14 revolutions per second (Hz).
    2. Fig 1: Tire Rotational Speed At 8 km/h (5 mph) Tire Size
    G02570246Courtesy of GENERAL MOTORS CORP.
  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 (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 (Hz) for one increment: 12 (increments) X 1.14 Hz = 13.68 Hz (rounded to 14 Hz).
  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: 14 Hz X 2 (for second order) = 28 Hz second-order tire/wheel assembly rotation related 14 Hz X 3 (for third order) = 42 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.
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