wheel / tire balance thoughts

[Invent1]

My new 30B Itasca/Winnie (Ford F35 V10 chassis) had pretty bad vibration problems when we picked it up from our Itasca dealer (Harberson, Port Richey FL). Before the sale, we told them our previous new RV had a severe vibration that was not corrected even after 6 trips back to the dealer. They assured us that their mechanics were good at fixing tire and wheel problems. However, when we informed them of the vibrations, Harberson said we had to take it to a Ford truck dealership. Lesson learned: never pay for a RV, especially a new one, until after you drive it and everything is fixed.

I wanted this fixed the first time so I carefully analyzed the vibrations. One was at 35-45 and another was at 65 mph. I calculated that at 40 mph, a 19.4"� tire/wheel issue would manifest at about 7 times/second and that seemed about what I felt. (A driveshaft issue would be about 4 times as fast a frequency.) A little research showed most tire weight imbalances don't show until after 55 mph or so when the rotation is fast enough to make the imbalance effect pronounced. However, the resonant frequency of suspensions is in the 7-10 Hz range, so the rule of thumb is that most vibrations under 50 are caused by wheels or tires that are out of round, and over 50 it is caused by tires that are out of balance.

I then called around to find a Ford truck dealer that used EVA (electronic vibration analysis) equipment and that used a tire balancer that measured road force. Road force is measured by a roller that is pressed into the tire with a force of as much as 1500 pounds as it is spun. This attempts to simulated the way the tire is compressed as it rolls down the road and therefore detects variations in sidewall stiffness that can make the wheel hop. The Hunter GSP 9700 is perhaps the most common such machine.

I was happy to hear that Gator Ford, Seffner FL, would perform an EVA analysis before doing anything, and that they use the GSP 9700. When I arrived, I made sure the service writer understood and wrote down that there were two different vibrations. The tech found excessive vibration at several corners and pulled all 6 wheels. He put each wheel on the balancer and the indexed the ones that were over-spec (indexed means he marked the highs and lows on the tire and wheel, dismounted them and remounted them so the highs and lows cancelled as much as possible). When two tires (Goodyear 19.5"� 70 series) still were out of spec, he replaced them, checked to make sure the new ones were within spec. and then balanced all 6 tires.

On the drive home I was pleased to see that both vibrations were significantly reduced. Later, I called asked what else they'd recommend to fully eliminate the vibration. They checked with Goodyear and Ford and were given the answer that I should put down the coach jacks when at rest to reduce flat-spotting, and that the tires will flat-spot less as they age. I've written articles on both tires and balancing so I'm suspicious of the latter answer, but I appreciate that the service writer, Manny, and tech, Travis, took the time to further consult with Goodyear and Ford.

Other sources have told me there has been some issues with the Goodyear 19.5"� 70 series tires. All the tires now have a lot of weight on them and a few have 10 ounces of weight.

My recommendation to Ford is to implement a much higher quality control standard for tires and wheels when they are first mounted and balanced. My recommendation to Winnebago is to insist that Ford does this and monitor their compliance. It is absurd to have a customer pay 6 figures for a new RV and then have to personally spend days calling and driving around to get it repaired properly. It hurts profits too because it costs more to repair things in the field than on the assembly floor.

I wrote this in hopes there is something useful here for others who suffer with vibration issues. For now, I'll drive the RV a while and see if the vibrations decrease, but I doubt they will. The people at Gator Ford did all the right things with the best available equipment and brought the tires/wheels under that specs allowed by Ford/Goodyear. If anyone has further suggestions, I'd appreciate hearing them.

[Invent1]

My new 30B Itasca/Winnie (Ford F35 V10 chassis) had pretty bad vibration problems when we picked it up from our Itasca dealer (Harberson, Port Richey FL). Before the sale, we told them our previous new RV had a severe vibration that was not corrected even after 6 trips back to the dealer. They assured us that their mechanics were good at fixing tire and wheel problems. However, when we informed them of the vibrations, Harberson said we had to take it to a Ford truck dealership. Lesson learned: never pay for a RV, especially a new one, until after you drive it and everything is fixed.

I wanted this fixed the first time so I carefully analyzed the vibrations. One was at 35-45 and another was at 65 mph. I calculated that at 40 mph, a 19.4"� tire/wheel issue would manifest at about 7 times/second and that seemed about what I felt. (A driveshaft issue would be about 4 times as fast a frequency.) A little research showed most tire weight imbalances don't show until after 55 mph or so when the rotation is fast enough to make the imbalance effect pronounced. However, the resonant frequency of suspensions is in the 7-10 Hz range, so the rule of thumb is that most vibrations under 50 are caused by wheels or tires that are out of round, and over 50 it is caused by tires that are out of balance.

I then called around to find a Ford truck dealer that used EVA (electronic vibration analysis) equipment and that used a tire balancer that measured road force. Road force is measured by a roller that is pressed into the tire with a force of as much as 1500 pounds as it is spun. This attempts to simulated the way the tire is compressed as it rolls down the road and therefore detects variations in sidewall stiffness that can make the wheel hop. The Hunter GSP 9700 is perhaps the most common such machine.

I was happy to hear that Gator Ford, Seffner FL, would perform an EVA analysis before doing anything, and that they use the GSP 9700. When I arrived, I made sure the service writer understood and wrote down that there were two different vibrations. The tech found excessive vibration at several corners and pulled all 6 wheels. He put each wheel on the balancer and the indexed the ones that were over-spec (indexed means he marked the highs and lows on the tire and wheel, dismounted them and remounted them so the highs and lows cancelled as much as possible). When two tires (Goodyear 19.5"� 70 series) still were out of spec, he replaced them, checked to make sure the new ones were within spec. and then balanced all 6 tires.

On the drive home I was pleased to see that both vibrations were significantly reduced. Later, I called asked what else they'd recommend to fully eliminate the vibration. They checked with Goodyear and Ford and were given the answer that I should put down the coach jacks when at rest to reduce flat-spotting, and that the tires will flat-spot less as they age. I've written articles on both tires and balancing so I'm suspicious of the latter answer, but I appreciate that the service writer, Manny, and tech, Travis, took the time to further consult with Goodyear and Ford.

Other sources have told me there has been some issues with the Goodyear 19.5"� 70 series tires. All the tires now have a lot of weight on them and a few have 10 ounces of weight.

My recommendation to Ford is to implement a much higher quality control standard for tires and wheels when they are first mounted and balanced. My recommendation to Winnebago is to insist that Ford does this and monitor their compliance. It is absurd to have a customer pay 6 figures for a new RV and then have to personally spend days calling and driving around to get it repaired properly. It hurts profits too because it costs more to repair things in the field than on the assembly floor.

I wrote this in hopes there is something useful here for others who suffer with vibration issues. For now, I'll drive the RV a while and see if the vibrations decrease, but I doubt they will. The people at Gator Ford did all the right things with the best available equipment and brought the tires/wheels under that specs allowed by Ford/Goodyear. If anyone has further suggestions, I'd appreciate hearing them.

[targaboat]

I am a retired engineer so really appreciate your description of the steps in analysis a vibration problem. Also noted the comments on quality control at the coach manufacturer. However, that will probably never happen since from Winnie's view point they expect to get a good product from the supplier which in this case is Ford. Therefore, all of our efforts should be focused on Ford.

Sorry for the above rant. I need to add an experience that I had a few years back on a vibration problem. It appears that the lug nuts had become loose during the delivery process and I had an resulting vibration from the loss of the pilot between wheel and axle hub. It was not until I took the unit to a small low tech balance place and I stood there and saw the wobble in the wheel as they spun it on the vehicle. I immediately took it to the dealer and they diagnosed the problem as a hub quality problem and never noticed the wheel pilot diameter wear. I noticed it later. The resulting fix was easy, but never would have occurred with the conventional wheel balance process.

Lesson learned, keep the lug nuts tight. Also visually inspect ALL of the components involved in the axle, hub, wheel, and tire system before proceeding with the actual spin testing. This must be accomplish by someone with the ability to detect the unexpected problems.