Is yawing or tail wagging normal for Class A mortorhomes? How much?

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TheNewhalls said:
Gregg,
Before going the expensive route did you four corner weigh your rig and adjust the weight to try and even it out at all four corners? Did you adjust  the tire pressures to the mfg tire/psi tables, without adding any extra psi?

Might not work for your mh, but worked for mine and it saved me a lot of moola.  :)
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I had to post this as soon as I got back.  I think the tire pressure was definitely impacting the overall handling.  Based on TheNewHalls suggestion, I dropped the tire pressure down to 85 lbs which is what is posted from the manufacturer.  The tire reseller recommended 100 to 110 which was the max on the tire.  After dropping the pressure, I can not believe it is the same rig.  Just on the way out to the highway I thought it ran over the numerous pot holes and patches that we deal with here in Ohio much better than before.  You expect higher pressure to give a rougher ride, but what a difference.  Jumped on the highway and right off it seemed to handle much better.  Before I white knuckled it at anything above 65.  Took it up to 70 and it drove almost as easy as a car.  It rode and handled like a completely different unit.   

I can not image that the Steering T Plus that was delivered Friday, but not installed yet, is going to improve much but suppose the extra safety with blowouts and ruts may be worth it.  Can not thank everyone enough for taking the time to post suggestions and help me work through getting this corrected.  I will post what my thoughts are on the Steering T Plus after I install and take it out.  Planning on another run in a couple of weeks.  Did not have the opportunity to have a semi pass me, but when smaller trucks and cars passed, I could hardly tell anything.  Big, big improvement.
 
Is that 85 the pressure spec for max load, or based on your actual load?

If that's the max load as posted in the door jamb, you might find even lower pressures are possible based on the tire manufacturer's weight/pressure chart.

I didn't go back an re-read the thread, so apologies if this has already been covered.

Good news on the improvement By The Way!
 
The tire pressure used was based on the GVWR on the sticker.  I have not had an opportunity to take it to the scales to determine the actual weight because still doing some remodeling.  Almost there but waiting until completely done but will check it out when done.  My guess I will be close to the max most of the time but good point.
 
Update:  Just got back and can not thank the Newhalls and others enough for suggesting to drop the tire pressure.  My initial test held true over the last weekend.  Just got back from a 200 mile trip and when a semi passed me it was no longer a white knuckle experience.  There were times I could hardly even tell they were beside me.  I stopped at the tire reseller and told him my experience and he seemed thankful for the feedback.  Kathy even commented how the ride was significantly better. 
 
So on the F53 chassis.. I didn't see (or missed it?) talked about here but it was recommended to me from an RV suspension specialist here in Elk River MN to move the torsion bars to the back two holes on the front and rear torsion bars? He said even that should make a big difference?

Also on our 2007 37Z Four Winds Magellan, the tires that came on it (bought it used), are a 16ply tire but the manufacturer said it should be a 14 ply. This suspension specialist said that would make a big difference, too. Also on ours the tires were mounted incorrectly in that they were mounted oblong (offset...inexperienced tire installer) on the rims to cause a bouncing. Problem is that they are old enough that they cannot be remounted to correct the problem. But they are 5 years old now so they will ALL need to be replaced. Ugh :(  Fronts this year...2 of back two next year and the last 2 year after that...just to offset the cost.
 
BTW..here is the link to the suspension shop in Elk River MN.

http://www.precisionframe.com/

 
Finally installed the Safe-T-Plus steering product.  First impression is that it seems to have helped but nothing close to what I received by setting the tires to the proper pressure.  It does seem to have eliminated the constant tweaking of the steering while going down the road.  Planning on a 2,100 mile trip shortly and will update.   
 
I'm beginning to believe that over inflated tires are the main culprit behind most handling complaints. It's good to have another first hand experience with tire inflation to help convince people to inflate to weight not max pressure on sidewall.
Glad you got your rig stabilized, and realize that even when, perfect they are still weathervanes, on wheels, in crosswinds.

Bill
 
They are like sails with 65 mph winds trying to change your course.  I have gone from wondering if I want to take this thing on a cross country trip, to looking forward to it.  Come on sun and warm weather!  8)
 
I bought a 98 Daybreak on a P30 chassis a few weeks ago, and drove it back home 350 miles, pulling a S10 pickup on a 18ft trailer, running 65 to 70 mph. Even with very old tires set at 80 psi, probably too much but didn't have time to weigh it before we left, it drove wonderful. Even up around Chicago the big trucks were running much faster than I wanted to go, didn't have any handling problems. It is 3.5 ft longer than my Challenger was with a 3 ft + longer wheel base. It actually rode better than my Challenger did and it needs shocks and air bags. My buddy went with me that has the Storm said he couldn't believe the way it handled. We noticed more movement with the cross winds than we did with the trucks. I also went with a 3970 tire instead of a 3640 mainly because of the speed rating. Not going to be pulling with this right away so I wanted to be able to run the speed limit and not worry. Some of the 3640 tires I looked at only had a rating of 71 mph, too close for comfort for me.
 
The tires were the originals when I purchased it and almost 10 years old so the first thing I did was replaced them.  I had no idea how it handled and I was a total newbie owning or driving a MH.  My tire dealer put the max., 110 lbs, in my tires when they installed them.  The manufacturer sticker of my MH stated 85. 

The posters, TheNewHalls and others, saved me a bunch of money and improved overall safety by their recommendation on the air pressure.  This site's help has been priceless to me and that reminds me it is that time of year to hit the Donate button again!
 
My slightly used F53 chassis Vista had been changed to the non factory holes on the bars, which makes the bars effectively stronger. This made it ride very rough on rough pavement, Ford said not to change from factory, I changed back to the factory holes, much improvement. YMMV
 
driftless shifter said:
I'm beginning to believe that over inflated tires are the main culprit behind most handling complaints. It's good to have another first hand experience with tire inflation to help convince people to inflate to weight not max pressure on sidewall.
Glad you got your rig stabilized, and realize that even when, perfect they are still weathervanes, on wheels, in crosswinds.

Bill
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I would think Underinflated.

But design is a witch too..  I found adding track bars to mine helped.. So did the Tru Center.

About the only thing I'm happy with on mine from the factory is the sway bar. Workhorse knows that this chassis is going to have a house built upon it so they oversized the sway bar.
 
Gary RV Roamer said:
That sort of see-saw motion is quite common in gas chassis coaches (except Seilerbird's).
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Put me in the uncommon group along with Tom.  Our 32 foot gasser is not pushed around by passing trucks.  It is however pushed by strong side winds as I believe most light weight sails are.  When I drove our 32 footer the first time, I wanted to return it before we got home.  I was all over the road and it did everything but run down the highway in a straight line.  The only after market device it had was a steer safe.  I haven't added any anti sway devices since buying.  However, I did buy new tires and air them correctly.

IMO, what made a huge difference in handling was the proper air pressure in the tires, rear air bags and weight distribution.  There is no way to load my Aerbus to it's capacity, 18,000 lb GVW, without overloading the rear axle.  At 100% of the GVWR, the front axle is still 750 lbs under max.  This lack of weight on the front axle effects the way the motorhome steers.  In addition to correcting the side to side weight distribution, I moved all the heavy gear as far forward as possible.  The other thing to keep in mind is the location of your fresh water tank.  If it's rear of the back axle, take only the minimum amount of water you need.  Any weight behind the rear axle, is not distributed evenly to both axles.  The majority of the weight goes on the rear axle which acts as a fulcrum.  Think of a teeter totter.   
 
With the bedroom, generator, fuel tank, and fresh water all behind the rear axle there is no doubt the rear axle is carrying a majority of the load.  Not sure if there is anything we can do about that except be aware of the fresh water. 

Dumb question:  How do you determine if you need rear air bags for proper height?  Are the front and rear bumpers supposed to be the same height?
 
Dumb question:  How do you determine if you need rear air bags for proper height?  Are the front and rear bumpers supposed to be the same height?
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A couple of thoughts:
1. The rear suspension ought to have been designed to carry its rated load. If it is sagging too much, chances are the load is greater than the rated capacity. Adding air bags might raise the height somewhat, but may be a band-aid on a more serious issue.

2. The chassis maker intended for the front & rear to be close to the same height in normal operation.  Maybe not at max load, but  probably within a few inches under most conditions.  Whether front and rear will actually be the same height depends mostly on the choices the coach body builder made, and often they don't pay much attention to chassis loading. Even the high end motorhome makers too often produce coaches that are at or near max load on front or rear when they leave the factory. NHTSA records show a history of recalls for overloaded axles & tires.

3. I wouldn't even bother to measure unless there were indications of a suspension or handling problem. Those would be an inability to achieve the front alignment specs, noticeable wandering in the steering, and suspension bottoming out often.

4. Lean to one side or corner is much more significant than a modest difference in front to rear height.
 
Just had it aligned and they supposedly also checked rear tracking and everything seems to be within specs.  Without over thinking things, I am ready to go then.  Will post back the final test of when semis pass me.  Keeping my fingers crossed but optimistic based on short trips.
 
OK finally had the unit out long enough to do some traveling on the highways and thought I would update.  With the steering stabilizer and changes in the air pressure, I could hardly tell if a truck was passing me.  When traveling at 65 MPH, essentially no wagging to speak of so real happy at this point.  No more white knuckling.  I am going to consider this closed and resolved.  Thanks to all that responded.
 
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