Why the Instability?

[KNMIB]

There is a million different opinions on tire pressure, so far this is working for me and my tire wear seems to be good but I also have the alignment correct.

[muleshoeracer]

Looking for actual castor number recommendations:

I have a 2016 Axis 25.2. I have all of the handling problems mentioned here. I have done the following: CW alignment under warranty - the front toe has slight toe in, minimal camber and 4 degrees of castor. I still am dissapointed with the handling in a 15mph side wind. Actually blown into the lane of oncoming traffic.

I believe it will benefit by running it up over 5 degrees and have ordered the Ingalls bushings to try it.

Thoughts on the actual number that has worked for others?

[TyCreek]

If you're starting at 4 degrees without sleeves you should be able to get pretty near 6 degrees with sleeves (that would be great). I'd shoot for at least 5.5 and doubt you'll be able to achieve too much caster (over mid 7). However, also consider getting nearest 0 camber that you can (error to slight negative vs. positive). If you drive secondary roads often (crowned) consider cross camber/caster tuning e.g. slightly negative camber and more positive caster on the right side.

Also, ... toe in is good for stability and I'd error on the higher side of specification for toe-in.

[Metalman]

Do you pull a trailer or a toad with your RV? I tow a 7 x 12 foot dual axel enclosed trailer and haven't had serious problems with cross winds.

[Harvard]

If you are starting at 4 degrees without the Ingalls 594 sleeves then I am guessing your RV sits for and aft level which is giving you about 4 degrees as opposed to the typical 3 to 3.5 degrees (without Ingalls sleeves) with a slightly nose down attitude.


You want to use the Ingalls sleeves set to give you the maximum available additional 2 degrees. If you are starting at 4 then that will result in about +6 degrees which is good.

[muleshoeracer]

Actually it started at 5.8 degrees on the left and 4 on the right. What I would have thought would be raise the right side but instead they lowered the left down to 4.

Does Thor actually issue a recomendation for the alignment settings - anyone have a link to the specs?

I race cars and plan on installing the ingalls bushings myself in the next few days. I will double check the alignment vs the $1200 that CW had done - at least they or Thor paid for it - I was amazed at the cost - $600 for the alignment and another $600 for installing a bushing on one side.

Thanks,

[Harvard]

These pictures show Ingalls 594 installed for +2 degrees of caster
and 0.0 Degrees Camber for both sides.

Drivers side M over G




Passengers side M over S

[petef]

I am not sure adjusting castor 1 degree will affect side to side movement, in fact it really does not play into the picture. Caster deals with 2 things, the amount of time the steering wheel realigns to straight, and pulling to one side or the other. At best you want a little positive on the right side, the total numbers don't really mean much unless you don't have power steering. Think of the wheels being a little forward or a little behind your front wheel axis point. A little forward would be harder to steer. In degree terms 3-5 degree is nothing. The problem always was if the right side was negative, ie, behind the axis point of the left side, then a pull to the right was common, and with road crown it had to be fixed.
Your issue of blow by or wind is not a castor issue, some sort or rear trac bar and /or/ stiffen the front suspension will cure it. You have a box on top of a pick up truck chassis, they were made to sleep in not drive!

[PEHetzer]

I had the same problem and I did the following to get the steering under control.

1. Check all tire pressures and assure that they are pressured to the value located on the tag located just below the operator's window. Assure that the pressures are all the same. Tire pressure differences, of only a few pounds of pressure, can make a big difference on how your coach handles. I check my tire pressure often and before each trip.

2. Check the wheel alignment and wheel balance. You'll discover that this usually requires a trip to a good tire shop like Goodyear. Bad wheel balance can make the wheel "hop" at different speeds and the toe-in can make handling erratic. I cannot stress the importance of the first two steps. I discovered that my RV's toe-in alignment was out by 3/4 of an inch and that my RV's tire pressures were all different with differences exceeding 20 psi. What a surprise I got!

3. Have the mechanic increase the loading on the existing front sway-bar. This does not affect your coaches warrantee and really helps with handling.

4. I installed a Steering control module manufactured by Safe-T-Plus. Their website is Safe-T-Plus - The Steering Control Specialists | Helping motorists' vehicles steer safer, less, and with peace of mind.. Installing the steering control module really helped with preventing the wind from blowing me all over the road.

Since I have completed the above steps I can honestly say that the RV has become (almost) fun to drive. We have taken some long trips and the coach will still rattle badly when I encounter rough road surfaces.

I plan to add air bags to lessen the rattle. Then I plan to add a sway bar to the rear axial to stop the rear of the coach from swinging badly when traversing from one surface which is not level to another surface which is level such as from a parking area to the road.

[Metalman]

I might be under thinking the handling situation, but I have done nothing to the coach other than inflate the tires to about 100 psi (as listed on the tire), though they are down to about 90 psi after several months. The coach is subject to wandering when large vehicles pass and in cross winds, and it sways when pavement of different elevations is encountered.

I keep in mind that the RV is a large, slightly top heavy vehicle, with a relatively short wheelbase and it will never handle like a pickup truck. One indication of proper alignment and proper tire balance is tire wear, particularly front tire wear.

I wonder if PEHetzer discussed the caster angle with his front-end alignment specialist? Insufficient caster angle can result in wandering and instability. Caster angle can change on a loaded vs. unloaded coach.

[John & Diane]

PEHetzer,

I'm curious about your plan to add a sway bar to your rear axle. Our 2015 Windsport 27K built on an 18000# chassis has a factory installed sway bar that is pretty substantial. If your unit doesn't have a rear sway bar, add one, if it does have the factory bar I would try the CHF before spending lots of $$.

John

[petef]

Caster angle really won't cause instability. It will cause a pull to one side. It would be possible the wheels don't return to "center" quickly after making a turn if it is to positive.. Toe in/out is the biggest things that cause bad steering/handling.

Originally Posted by Metalman

I might be under thinking the handling situation, but I have done nothing to the coach other than inflate the tires to about 100 psi (as listed on the tire), though they are down to about 90 psi after several months. The coach is subject to wandering when large vehicles pass and in cross winds, and it sways when pavement of different elevations is encountered.

I keep in mind that the RV is a large, slightly top heavy vehicle, with a relatively short wheelbase and it will never handle like a pickup truck. One indication of proper alignment and proper tire balance is tire wear, particularly front tire wear.

I wonder if PEHetzer discussed the caster angle with his front-end alignment specialist? Insufficient caster angle can result in wandering and instability. Caster angle can change on a loaded vs. unloaded coach.

[petef]

I had a rear trac bar put on my 27K, made a big difference in tail wag. I also did the CHF front and rear.

[vkb]

Originally Posted by John & Diane

PEHetzer,

I'm curious about your plan to add a sway bar to your rear axle. Our 2015 Windsport 27K built on an 18000# chassis has a factory installed sway bar that is pretty substantial. If your unit doesn't have a rear sway bar, add one, if it does have the factory bar I would try the CHF before spending lots of $$.

John

John ... our F E450 Chassis has the Ford sway bar in the rear..and Ron is thinking about something stouter. You refer to CHF ... what is that? Ha ! just googled it...reading it next !!

Thanks Kay

[Phil Saran]

I just picked up my MH 34E Class A from Rush Ford in Commerce CO
they are a medium duty truck dealer and the only one in my area that
will work on MH's. It's too tall for all the normal car dealers to get into
their shops.

Earlier this year I had a Super-T-Steering stabilizer installed on the front
suspension while it was at Camping World for some warranty work.
I bought the stabilizer on line from PPL Motorhomes in Houston Texas
while they were having a internet sale. It helped some.

But I finally purchased a rear track bar setup from Brazels RV in Wash
State and had it installed this week at the Ford dealer.

Just from driving it the 30 ought miles home on the freeway I noticed
a improvement over not having the track bar.

I had asked about them doing the Cheap Repair deal to the sway bars
and their response was no not possible. What they said was there have
been reports of the sway bar links breaking in half after such a adjustment.

Anybody that has done the Cheap repair have any problems???

Also note that my MH weights in at about 17K, but it has the 22K rear
differential in it. With 19.5 tires.

[winder1]

I recently put a Safe T Plus on the steering, and 4 Sumo Shocks at each corner. WOW!

I had been wrestling with idea of the Blue Ox rear tracker, but I thought, lets try the Sumo's first. They are attached at both the top and bottom on the rear, and thats feels like its limiting excessive spring movement from side to side.

The ride is MUCH smoother and quieter as well. Right now, I don't see how adding a rear tracbar could further improve things. Might feel differently after a few thousand miles, but so far, this had made the ride and handling feel secure.

[Scintor]

I took my skittish 2014 Thor Palazzo to Henderson's Line-Up to apply a couple of solutions (I couldn't afford ALL of their suggestions). The tech there explained that instability in big DP RVs is complex as others in this thread have pointed out already. One important factor is front to rear weight distribution. It should be close to 50/50, and I'll bet yours, like mine, is not, especially for DPs (diesel pushers). I had the safety steering components installed, and that made a HUGE improvement. I can actually correct my steering for crosswinds and changing road crown as those conditions vary while I am driving. I plan to have Henderson install Koni shocks and replace the standard 1.5" sway bars with 1.75" sway bars. Those two additions PLUS having some weight added to the front end to achieve 50/50 weight distribution will round out the whole solution. In the meantime, I really slow down when I encounter heavy winds from any direction!

[petef]

I called Ford Tech RV number and asked about changing the sway bar bolt holes. They told me the reason 2 holes are there is because motorhomes became bigger and taller and some manufacturers wanted the hole. They said using it is no problem. The thread of the CHF is 300 pages long or more, the only event I have read is someone had a swaybar link break on an older rig, it is not readily attributed to the CHF fix.

Originally Posted by Phil Saran

I just picked up my MH 34E Class A from Rush Ford in Commerce CO
they are a medium duty truck dealer and the only one in my area that
will work on MH's. It's too tall for all the normal car dealers to get into
their shops.

Earlier this year I had a Super-T-Steering stabilizer installed on the front
suspension while it was at Camping World for some warranty work.
I bought the stabilizer on line from PPL Motorhomes in Houston Texas
while they were having a internet sale. It helped some.

But I finally purchased a rear track bar setup from Brazels RV in Wash
State and had it installed this week at the Ford dealer.

Just from driving it the 30 ought miles home on the freeway I noticed
a improvement over not having the track bar.

I had asked about them doing the Cheap Repair deal to the sway bars
and their response was no not possible. What they said was there have
been reports of the sway bar links breaking in half after such a adjustment.

Anybody that has done the Cheap repair have any problems???

Also note that my MH weights in at about 17K, but it has the 22K rear
differential in it. With 19.5 tires.

[Chance]

Originally Posted by Scintor

I took my skittish 2014 Thor Palazzo to Henderson's Line-Up to apply a couple of solutions (I couldn't afford ALL of their suggestions). The tech there explained that instability in big DP RVs is complex as others in this thread have pointed out already. One important factor is front to rear weight distribution. It should be close to 50/50, and I'll bet yours, like mine, is not, especially for DPs (diesel pushers). I had the safety steering components installed, and that made a HUGE improvement. I can actually correct my steering for crosswinds and changing road crown as those conditions vary while I am driving. I plan to have Henderson install Koni shocks and replace the standard 1.5" sway bars with 1.75" sway bars. Those two additions PLUS having some weight added to the front end to achieve 50/50 weight distribution will round out the whole solution. In the meantime, I really slow down when I encounter heavy winds from any direction!

Motorhomes with Dual Rear Wheels (DRW) are designed to carry much more weight over rear axle than over front axle. You'll never get close to 50/50 weight distribution with your motorhome, not that you'd want to. If you tried shifting enough load forward you'd quickly overload the front suspension.

While it's possible to design a motorhome with close to 50/50 weight distribution, if you did, wouldn't you only have four wheels of equal size -- one at each corner? That's what Europeans do on smaller motorhomes, but in US manufacturers normally start out with DRW truck chassis that are designed to carry much more load over rear axle. And diesel pushers, with their overhanging heavy rear engines and transmissions, can't possibly get close to 50/50 front-to-back weight distribution.

[Metalman]

Originally Posted by Chance

Motorhomes with Dual Rear Wheels (DRW) are designed to carry much more weight over rear axle than over front axle. You'll never get close to 50/50 weight distribution with your motorhome, not that you'd want to. If you tried shifting enough load forward you'd quickly overload the front suspension.

While it's possible to design a motorhome with close to 50/50 weight distribution, if you did, wouldn't you only have four wheels of equal size -- one at each corner? That's what Europeans do on smaller motorhomes, but in US manufacturers normally start out with DRW truck chassis that are designed to carry much more load over rear axle. And diesel pushers, with their overhanging heavy rear engines and transmissions, can't possibly get close to 50/50 front-to-back weight distribution.

The front/rear weight bias can be a serious problem on some motor homes. I had a 24 foot class C RV that was so light on the front end that firmly applying the brakes would cause the front tires to slide. The first and only time that happened was a wakeup call for me to allow long following distances and look way ahead.