Noise, Vibration and Harshness (NVH)

second order tire and wheel vibration: 7 Hertz (Hz) (first order tire and wheel frequency) multiplied by 2 (second order) equals 14 Hertz (Hz) (second order tire and wheel frequency).

Relationship of Vibration Frequency to Order of Vibration

After carrying out the road test as described in this section, the vibration was determined to be either vehicle-speed related or electric motor-speed related. That determination will identify the vibration frequency calculations that should be done.

In calculating and using frequency readings it is important to remember the direct relationship between Hertz (Hz) and Revolutions Per Minute (RPM). One Hertz (Hz) is equal to 60 Revolutions Per Minute (RPM). This is easy to remember. Think of Hertz (Hz) as cycles per second. There are 60 seconds in a minute, therefore multiply the Hertz (Hz) reading by 60 to get Revolutions Per Minute (RPM). Conversely, divide Revolutions Per Minute (RPM) by 60 to get Hertz (Hz).

Use the Frequency and Revolutions Per Minute (RPM) Calculations Worksheet to calculate system/component frequencies. The worksheet provides the necessary steps to determine each system/component group frequency.

Frequency Calculations

Calculating Tire and Wheel Frequency

For a vibration concern, use the vehicle speed to determine tire/wheel frequency and Revolutions Per Minute (RPM). Calculate the tire and wheel Revolutions Per Minute (RPM) and frequency by carrying out and following:

Measure the diameter of the tire. Record the speed at which the vibration occurs. Obtain the corresponding tire and wheel Revolutions Per Minute (RPM) and frequency from the Tire Speed and Frequency Chart.

If the vehicle speed is not listed, divide the vehicle speed at which the vibration occurs by 16 km/h (10 mph). Multiply that number by the 16 km/h (10 mph) tire Revolutions Per Minute (RPM) listed for that tire diameter in the chart. Then divide that number by 60. For example: a 40 MPH (Miles Per Hour) vibration with 835 mm (33 in) tires. 40 divided by 10 = 4. Multiply 4 by 105 = 420 Revolutions Per Minute (RPM). Divide 420 Revolutions Per Minute (RPM) by 60 seconds = 7 Hertz (Hz) at 40 MPH (Miles Per Hour).

Tire Speed and Frequency Chart