Okay, first of all let me apologize for posting this here. I have gone to the dark side and bought a Dynamax Super C, so I should of course be banned. But with a long history on this forum with guys I know and respect, I'm going to risk the wrath of Johnny T and post anyway. This is a DynaQuest 260ST (27') on an M2 Business Class 106" Freightliner chassis. The rear axle has an air bag suspension, the front suspension is standard M2. It has good tread Toyo 19.5 tires. Now the problem. At highway speeds, if you rock the steering wheel back and forth creating a slalom movement, it over steers to the point of becoming scary. You have the sensation the rear end is going to come around and pass you. The suspension feels like it is seriously overweight, the shocks are gone, and the rear stabilizer bar is missing (not). One the trip I just made bringing it home, the coach was empty except for me and a suitcase, so I'm hardly overloaded. When you enter a curve somewhat aggressively, you have to be careful with the steering input or you will make the hair on your neck stand up. I have experienced this exact feeling before on 2 different diesel pickup trucks upon getting new tires. In both cases I returned to the tire dealer within 10 miles and made them exchange the tires for another brand, and both times it immediately cured the problem. They said the problem was softer rubber, making the tread roll. But these are Toyo's, a brand I have had on other motorhomes without feeling this over steer sensation.The truck steers straight, without pulling, and has no other obvious handling issues I can blame this on. Does anyone have some thoughts for me?

Look up "tire squirm" and see if that is what you are experiencing. It is sometimes a problem with new tires. It usually goes away after several hundred miles. Until then, just hang on.

You most likely have some rear suspension parts worn, such as bushings. Are you sure you have a pan hard bar on the rear? If you have a sway bar, check the end links, and the bushings that attach it to the rear end.I assume you have checked tire pressures. Lets know what you find.

Just to be clear, there is a difference between a sway bar and a panhard/track bar. Do you actually have a panhard bar?

Daveinet wrote:Just to be clear, there is a difference between a sway bar and a panhard/track bar. Do you actually have a panhard bar?Coming from memory here since it is pouring outside, but I remember looking under and seeing a bar mounted from the curbside axle coming across to the street side frame. It is maybe 1.5" in diameter plus/minus. I assumed that to be a sway bar and I may also have the panhard bar (whatever that is) as well. Don't know what to look for actually.Ps. Wildman, I tried several different tire pressures and none of them made any difference.Pss. I am familiar with tire squirm on new tires rgatijnet1. That is what the trucks I mention in the first post were experiencing. These Toyo's probably have 5K on them so not likely (but never sure) the problem. Again, I have had Toyo's before, but then they could have changed the compounding. If other who have them pipe up about recent Toyo problems, then that is new data I can work with and what make forums like this so valuable. .

Okay, just looked it up and that is a panhard bar I am describing. A stabilizer bar must be the one shaped in a 'U' that keep the body from rolling. My bad.Won't know if I have a stabilizer bar until I can get underneath to look.

Tail is Wagging the Dog | Good Sam Community

27 Replies

BigRabbitMan
Explorer
Nov 23, 2013
I run 19.5's as well and am under 15,000 lbs with a rear engine. After reading all of the above and what you have done adjusting tire prissures, I am convinced that it is not the tires and further tire adjustments will be chasing a ghost.

I am also convince, including some experience of my own, that it is worn bushing and/or alignment issues. Loose connection points due to worn bushings will cause all kinds of problems. When you take it in, have them check the entire suspensioin system. It wasn't designed to do that so something is out whack other than tires.
Jarlaxle
Explorer II
Nov 23, 2013
Stupid question: how's the front end alignment? It sounds to me almost like you have caster way off...
randallb
Explorer
Nov 22, 2013
Try running the fronts softer than the rears and see what happens. This pressure change should slow down the steering input. Set the fronts to minimum on the chart, set the rears at the same pressure and drive. Run the rears up in 5# increments and see what happens. Eventually you should be able to get it to push or at least get less rear happy if the over hang isn't excessive. Normally a soft rear tire will allow for more tail wag.
Randy
StuartT
Explorer
Nov 22, 2013
RayChez wrote:
Have you checked the U bolts that secure the axle to the frame?

I am going to let the alignment shop get under there and do the dirty work Ray.

As a side note, I notice that you joined rv.net 4 days before I did back in 2003. Time flies doesn't it?
StuartT
Explorer
Nov 22, 2013
wa8yxm wrote:
Generally I would expect tire squirm to go UP as pressure goes down.

But what I expect and what happens in real life, NOT always the same.

Alignment,,, If there is an issue, they should find it, They check bushings and such during that process.

I agree with you. At some point the sidewalls would seemingly start rolling as you continue to drop pressure. I might get a softer ride and more even tire wear, but I doubt the wagging will be corrected.
RayChez
Explorer
Nov 22, 2013
Have you checked the U bolts that secure the axle to the frame?
wa8yxm
Explorer III
Nov 22, 2013
Generally I would expect tire squirm to go UP as pressure goes down.

But what I expect and what happens in real life, NOT always the same.

Alignment,,, If there is an issue, they should find it, They check bushings and such during that process.
StuartT
Explorer
Nov 22, 2013
Regarding sizes, these are overkill, especially at these load ranges. I am not even on the Toyo load/pressure charts at my individual tire weights.

I am going to lower the pressure more today and try some other combinations. Nothing to loose. I have to wait until next week to get in the alignment shop so I have the time.

I have 95,000 on the odometer.
Ivylog
Explorer III
Nov 22, 2013
What do you have to loose trying 80 all around? For what it's worth, I have 70 all around in my ambulance. Less pressure in a radial tires gives a large/longer footprint. I was surprised that the rear tires are 245 as most rigs this size use 225 on the rear and 245 on the front.
*How many miles on your rig? Mine has 122K and it really handles well.
StuartT
Explorer
Nov 22, 2013
I headed for a truck stop and now have my numbers, and more confusion. From the weigh ticket: 7,500 on the steer axle, 10,740 on the drive axle.

Steers: 265/70-R19.5, L.R. ‘G’, 14 ply, single max = 5070 @ 110psi.
Actual is 7500/2 = 3570. Estimate = 70psi. (chart’s lowest published pressure is 3970 @ 80psi)

Drives: 245/70-R19.5, L.R. ‘H’, 16 ply, dual max = 4540 @ 120psi.
Actual is 10,740/4 = 2685.
The LOWEST the chart goes is 3415 @ 80psi.
760# less could mean - who knows – 50#, 55#?

My thoughts:
*Going from 110 front and rear down to 95 front/85 rear, I felt no difference.
*The tire sizes are correct according to the owner’s manual.
*Load range ‘H’ on the rears is a joke; note that is the only load range available for 245/70-19.5s from Toyo.
*I would expect lowering inflation more would exacerbate the problem due to sidewall flex.
*I don’t want to buy new tires. ?

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Tail is Wagging the Dog

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