Hatchback 4WD F4-1781cc 1.8L (1983)
Wheels: Customer Interest
Wheels/Tires - Highway Speed Vibration/Harshness/Noise
NUMBER: 05-50-10R
DATE: 02/03/11
APPLICABILITY:
All Subaru Vehicles
SUBJECT:
Noise, Vibration and Harshness (NVH) at Highway Speeds Caused by a Tire Imbalance or Excessive Radial Force
INTRODUCTION
This bulletin is to serve as information only and is intended to help minimize steering wheel vibrations at highway speed.
DESCRIPTION
Some customers may describe a concern of a steering wheel vibration, oscillation or a "shimmy" condition at highway speeds that may be caused by
improper tire and wheel balance or excessive radial force variation (RFV).
Subaru of America Inc. (SOA) recommends the use of the Hunter GSP 9700 Wheel Balance and Road Force Measurement System to properly balance
the wheel and tire assemblies "dynamically" and to measure the radial force variation of the wheel and tire assembly. While the majority of these
conditions can be greatly reduced with proper wheel balancing, some road feel may be considered characteristic and can be compared to like model
vehicles with similar mileage.
Wheel Imbalance
The two most common types of wheel imbalances are static (single weight plane) and dynamic (dual weight plane). A static imbalance is best described
as a vertical imbalance when the assembly is mounted on the vehicle. A dynamic imbalance is defined as a vertical and inner/outer imbalance while the
assembly is mounted on the vehicle.
Wheel and tire assembly imbalance should be addressed first as this is the most common source of tire and wheel vibrations. A well maintained dual
weight plane balancer (commonly known as a Dynamic Balancer) such as a Hunter G5P9700 should be used to achieve the best possible results.
Balancer settings and proper maintenance are critical to obtaining the best results. Refer to the operating instructions as provided by the balancer
manufacturer for setup and maintenance instructions.
Radial Force Variation (RFV)
Radial force variation is an industrial measurement describing the tire uniformity under load. These variations, or harmonics, are measured in kilograms,
pounds or newtons. SOA asks that all weight measurements be reported using the metric system (grams, kilograms, etc.) The Hunter GSP 9700 Road
Force Measurement System is capable of measuring these harmonics and displaying them as R1H (radial first harmonic), R2H (radial second harmonic)
and R3H (radial third harmonic.) These different harmonic levels indicate the number of bad occurrences per revolution.
Most commonly, radial first (R1H) harmonics are the cause of steering wheel or body related vibrations that can be felt at highway speeds. Radial force
variation can be greatly affected if the vehicle has been parked for an extended period of time causing flat spots or by improper tire inflation. Before
performing any diagnosis~ be sure to drive the vehicle at least 10 miles and adjust tire pressures as indicated on the door label.
Machine Setup
SOA recommends the use of the Hunter GSP 9700 Road Force Measurement System to properly balance and measure radial force on tire and wheel
assemblies. To ensure the most accurate results, the following guidelines should be used:
^
Refer to the operating instructions to set the machine to measure in grams (for balancing) and kilograms (for radial force measurements)
^
Refer to the operating instructions to enable the dynamic balancing mode
^
Refer to the operating instructions to disable the Quickmatch(TM) function, if available.
^
Select the "Mixed Weights Balance" mode and measure the weight location carefully.
^
Calibration should be checked at least once per week
^
Ensure the arbor threads and base plate are clean and in good condition
^
Measure the wheel center bore and select the proper cone for mounting the wheel to the balancer
