Tire Wear Patterns and frequency calculations
Wheel and tire NVH concerns are directly related to vehicle speed and are not generally affected by acceleration, coasting or decelerating. Also, out-of-balance wheel and tires can vibrate at more than one speed. A vibration that is affected by the engine RPM, or is eliminated by placing the transmission in NEUTRAL is not related to the tire and wheel. As a general rule, tire and wheel vibrations felt in the steering wheel are related to the front tire and wheel assemblies. Vibrations felt in the seat or floor are related to the rear tire and wheel assemblies. This can initially isolate a concern to the front or rear.
Careful attention must be paid to the tire and wheels. There are several symptoms that can be caused by damaged or worn tire and wheels. Carry out a careful visual inspection of the tires and wheel assemblies.
Spin the tires slowly and watch for signs of lateral or radial runout. Refer to Fig 1 determine the tire wear conditions and actions.
For a vibration concern, use the vehicle speed to determine tire/wheel frequency and RPM. Calculate tire and wheel 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 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 16 km/h (10 mph) tire RPM listed for that tire diameter in the chart. Then divide that number by 60. For example: a 40 mph vibration with 835 mm (33 in) tires. 40"DIVIDE"10 = 4. Multiply 4 by 105 = 420 RPM. Divide 420 RPM by 60 seconds = 7 Hz at 40 mph.