Feature
NVH issues and answers Start your investigation with the tires and wheels By Mike Mavrigian
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Courtesy Hunter
n this article, we’ll address a variety of noise, vibration and harshness (NVH) issues. We’ll also offer tips on how to avoid and/or cure these ills. When trying to solve NVH problems, a good place to start is with the tire and wheel assemblies.
point of maximum RFV with the wheel’s point of minimal radial runout (high point of tire to low point of wheel). Radial force variation is a term that relates to a tire-sourced out-of-round/vibration that occurs, and masks itself as an imbalance vibration, only under dynamic conditions... when the wheel and tire package rolls in
Examples of tire and wheel vibrational issues. The illustration at the top depicts an imbalance condition wherein dynamic imbalance results in the tire’s contact patch deviating from the axle center as the wheel rotates. The center row is an example of radial runout, where the wheel is not properly centered on the hub. The bottom row depicts radial force variation where a high spot on the tire (or an area of the tire that is more dense/stiffer than the rest of the tire) is present.
Tire radial force variation In addition to dynamic balance of a tire/wheel assembly, we need to consider tire radial force variation (RFV) when diagnosing tire-related vibrations that occur at varying speeds and conditions. Ideally, the wheel should be phase matched to align the tire’s 6
a loaded state. It must be noted that the term “radial” refers to forces applied at the radius of the tire, not to the type of tire construction. Radial force vibration could potentially occur with any type of tire, regardless of its construction (radial, bias ply, etc.). In other words, a radial force variation may prove
to be the cause of a vibration that won’t reveal itself during a static or dynamic balance job, or by checking the mounted tire for runout in an unloaded state. Radial force is determined by measuring loaded radial runout. According to Hunter Engineering’s research, on an average passenger car tire/wheel assembly, one thousandth of an inch (0.001 inch) of loaded radial runout is equivalent to approximately one pound of road force. For example, a measured 0.030 inch of loaded radial runout (about 30 pounds of road force) will cause the same amount of vibration as 1.5 ounces of wheel imbalance at 50 mph, which is fve times greater than the .30 ounce imbalance limit. Tire makers usually supply a red dot on the tire sidewall, which indicates the tire’s maximum RFV, or the highest point of radial runout. When mounting the tire, this red dot should be aligned to a white dot on the wheel (if the wheel is so marked). The white dot on the wheel indicates the wheel rim’s minimum radial runout point (on a steel wheel, a dimple may be featured that indicates the wheel’s low point). When using alloy wheels that don’t feature a white dot, the tire’s red dot should be aligned with the valve stem, as this should be the minimum radial runout point. A yellow dot may be found on the tire sidewall which indicates the lightest point of the tire (in terms of weight from a balance consideration). If a yellow dot is found, this should be aligned to the wheel’s valve stem, which should be
