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Calculating Tire Revolutions Per Second at 8 km/h (5 mph) - Without EVA

WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.

If the J 38792-A  is not available, the tire and wheel assembly rotational speed can be calculated approximately by performing the following steps. See Special Tools .

  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.

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