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Informative Article on Radial Force Variation #5342650 02/06/20 11:59 AM
Joined: Jan 2006
Posts: 2,943
SubLGT Offline OP
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Joined: Jan 2006
Posts: 2,943

Some excerpts:

...Radial Force Variation (RFV) is an important measurement in the tire industry that has been around since the 1970s but is often unclear.

...Most tiremakers test tires at the point of manufacture to verify that the RFV is within allowable quality limits. The more uniform the tire, the better the ride. Tires that exceed these limits may be scrapped or sold to markets that do not require stringent quality. Vehicle manufacturers often specify uniformity levels and pay more for tires with less RFV if the vehicle has special needs or is driven at high speeds on very flat surfaces.

...There are two types of OEM Radial Force Variation. The first is a low-speed tire test defined by the Society of Automotive Engineers as SAE Practice J332.

...A second form of OEM measurement is high-speed RFV measurement. The wheel and spindle are locked against a flat track with force sensors. High-speed RFV measurement is the latest technology and gives a better indication of high-speed RFV at the speeds normally encountered by a vehicle at highway speeds when vibration is most prevalent. Besides vertical RFV forces, a tangential (fore-aft) RFV force can also be measured. Many non-speed-rated tires with runout construction characteristics (such as light truck tires) can change shape significantly at highway speeds and exhibit RFV and imbalance that doesn’t show up during low-speed measurement or low-speed garage balancer spin speed.

...RFV pounds force is measured around the tire and the measurements are defined in terms of highest to lowest (peak to peak) measurements and the harmonics (waveforms) that interpret the many measurements taken around the circumference of the tire/wheel.

...Using the harmonic calculation and not the peak-to-peak measurements to find the low and high points of the tire/wheel assembly are critical. As you can see in the accompanying charts (left), the high point, low points and magnitude of the waveform are not the same location or magnitude as shown in the harmonic calculation.

...R1H, Radial First Harmonic RFV, one bump per revolution (like an egg), can be caused by imbalance, runout of the tire and/or wheel, centering error on the balancer and centering error on the vehicle hub. It can be reduced by correct centering on the balancer, match-mounting and on-car hub matching.

...R2H, Radial Second Harmonic RFV, two bumps per revolution (like a football), are most often not displayed on shop RFV balancers and cannot be reduced by match mounting. In some cases, the tire can be loosened and rotated 90° to reduce R2H. The steering column in a vehicle is most sensitive to R2H causing steering wheel “nibble.” If both wheels on the front axle have excessive R1H or imbalance, it can set up a phase-related R2H intermittent vibration that comes and goes as the two wheels turn at slightly different speeds.

...R3H-Radial Third Harmonic RFV, three bumps per revolution (like a triangle), is not often displayed on shop RFV balancers and cannot be reduced by match mounting. R3H vibration in a tire or wheel can add its vibration to driveline-related components with issues. As an example, a final drive axle gear ratio may be approximately 3:1 and if there are components failing and causing vibration, the vibration will add itself to R3H wheel vibration forces.

Re: Informative Article on Radial Force Variation [Re: SubLGT] #5342809 02/06/20 03:08 PM
Joined: Sep 2008
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Boomer Offline
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Yup, Cletus down the tire shop does this here balancing all the time!!

2019 VW Passat 2.0 liter gasoline DI engine, DI, 2,700 miles, Castrol Professional VW 508 0W-20
2017 VW Golf All Track 1.8 liter gas engine DI, 25,500 miles Castrol Professional VW 505 5W-40
Re: Informative Article on Radial Force Variation [Re: SubLGT] #5343448 02/07/20 08:27 AM
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CapriRacer Offline
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Some additional tidbits:

Vehicle suspensions have a natural resonant frequency that generally occurs in the 50 to 70 mph range for balance and R1H (with a few exceptions!). Outside that speed range you generally won't find wheel end (meaning tire and/or wheel related) vibrations. That's because of the damping action of the shock absorber.

The article mentions R2H and R3H. The speed where R2H can become an issue is 25 to 35 mph (notice it is half the speed for R1H), but it generally doesn't because a) R2H levels in tires are generally much smaller than R1H levels and b) there are a lot of other things vibrating at that speed that confuse the human body. Similarly for R3H.

I retired 7 years ago, and at that time, high speed uniformity measurement was a lab test, not an in-line production screening test. I doubt if things have change since then, mainly because the way to reduce high speed RFV issues in tires also resulted in lower low speed RFV issues. (that is, reducing low speed RFV had benefits for high speed RFV)


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