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gsp9700Over the past few years, I've had a handful of vehicles that all at one point vibrated my teeth out. Whether it be bad luck, bent wheels, or poor balancing jobs - I've seen it all and then some. Maybe I drive too fast (unlikely), or maybe I shouldn't have taken my car to certain tire shops that just don't care. In any case, I've learned a bit about wheel balancing throughout these scenarios and thought it might be useful to share my story.

Smooth Vibrations

In theory, a true wheel with a new tire should not need a road force balance. 99% of people get a normal balancing job done on their daily driver and it does not vibrate. I, on the other hand, have had very poor luck when it comes to getting new tires on my Volvo.

A few years ago I got a new set of wheels for my Volvo, with a new set of Yokohama tires. Got them mounted at my favorite local tire guy and hit the highway. No problem at 50, 60, or 70mph. Once 80+ came on, the bad vibrations started to settle in. I went back for a rebalance, and we verified that the assembly was balanced properly.

I decided that I would take my Volvo to the local Toyota dealership, who had a brand new Hunter GSP9700 Road Force Touch machine. Upon spinning the wheels up, we found that three out of the four wheel/tire assemblies had RFV (Radial Force Variation) values way above 15lbs, some up to 20lbs.

What's RFV?

Radial Force VariationRadial Force Variation can be described as a hard or soft spot on the rotating axis of a tire, aka the tread. It is typically depicted using imaginary springs. A defective tire will exhibit the symptoms of having harder or softer springs inside of it, whereas a quality tire should have uniform springs throughout its circumference.

Vibratesoftware.com explains RFV by stating:

"Think of the tire's sidewall as a series of springs that should all be of equal tension. Stiffness variation occurs when the tension of one or more of those imaginary springs is greater than or less than the rest of the springs. This will cause a tire with no runout, which is also balanced, to push the vehicle's suspension system up and down while driving resulting in a vibration."

The Hunter GSP9700 has software that can correct these variances in the tire, by telling the technician where to place the tire on the wheel so the RFV is lessened. If you mount a tire's high-RFV area on the heaviest section of a wheel, the rotating assembly's RFV value will be very high. Conversely, if you mount a high-RFV area on a wheels' "low-spot," the RFV can be reduced to an acceptable value in most cases.

In my case, the tires were so defective that the RFV value could not be brought down to an optimal single digit number, and they needed to be returned for a refund.

When to Road Force Balance

When a proper wheel and tire assembly is out of balance, it typically vibrates around 50mph. This is a telltale sign that the assembly needs to be run on a spin balancer again - a common, easy, and easy to find service. My wheel and tire assemblies were indeed "balanced," however the defective nature of my tires caused a vibration at higher speeds. If I never exceeded 50mph, I would still own those tires. However, I buy European vehicles for their tolerance to high speed highway runs, so that could never happen.

When using bent wheels, it is possible to reduce vibration using a road force balancer. However, in my experience the vibration can only be eliminated so much. As an example, if you're experiencing vibrations at 75mph on a bent-but-balanced assembly, a road force balance may extend the smoothness up to 80-85mph, but a bent wheel will always vibrate eventually, perhaps at 90mph, perhaps at 100mph.

If you are experiencing vibrations that just can't be solved at your regular tire shop, consider finding a shop with a road force balancer in your area. Hunter provides a useful locator tool on their website.

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About the Author: Alex FiehlAF Headshot

Alex is FCP's Blog Editor and an IT technician from Endwell, NY. He has over 8 years of experience working on a wide array of import makes, but lately is partial to Volvo . For some reason he just purchased a Volkswagen, and is excited to see what breaks first.


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Written by :
Alex Fiehl


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