How Much Road Force Measurement (Radial Force Variation) Can Cause A Vibration In My Vehicle?
Subject: Relating Wheel Imbalance Vibration to Radial Force Variation
In the past, most tire/wheel assembly vibration was considered balance related. Because of this, tire service professionals tend to relate tire/wheel vibration in terms of balance weight. Road Force will be best understood when related to the amount of balance weight required to cause a similar vibration in a wheel that rolls round under a load. In other words, "How much Road Force creates a similar vibration caused by tire imbalance?"
Most tire service professionals and factory service manuals agree that residual static imbalance should not exceed .30 oz. on average size wheels and .60 oz. on larger light duty truck wheels.
Radial Force is determined by measuring loaded radial runout. On an average passenger car tire/wheel assembly, one thousandth of an inch (0.001î) of loaded radial runout is equivalent to approximately one pound of Road Force.
Tests on a Chevrolet Lumina were performed using a chassis dynamometer in a Detroit test lab. The purpose of the test was to determine how much balance weight would be required to produce the same magnitude of force as a measured amount of loaded radial runout.
The tests were performed with the vehicle running at different speeds. The first test was at 50 miles per hour and the second test at 70 miles per hour.
At 50 MPH:
A measured .030" (about 30 pounds) of loaded radial runout caused the same amount of vibration as 1.5 ounces (42 grams) of wheel imbalance at 50 mph. This is 5 times greater than the .30 (1/4) ounce imbalance limit.
At 70 MPH:
A measured .030" (about 30 pounds) of loaded radial runout caused the same amount of vibration as .75 ounces (21 grams) of wheel imbalance at 70 mph. This is 1 1/2 times greater than the .30 (1/4) ounce imbalance limit.