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Old 11-11-2016, 06:34 PM   #1
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Suspension and Steering Issues

I'd like to hear ideas, opinions, information, etc. on this subject from a broader perspective than usual. Most people know that suspension and steering tuning almost-always involves compromise, but those compromises rarely seem to get much discussion.

Perhaps it's often assumed that most RV owners know about these compromises and/or hidden issues, but if newbies don't already know (or have less mechanical experience, expertise, or aptitude than assumed), they may not fully understand the total impact of available "fixes".


I'll kick it off with one of the simpler topics: Anti-sway or anti-roll bars.

These bars are primarily designed to reduce body lean in fast or sharp turns. But that added roll stiffness comes at the price of adversely affecting ride quality when vehicle encounters bumps on only one side.

Quote:
Originally Posted by Wikipedia
Because an anti-roll bar connects wheels on opposite sides of the vehicle, the bar transmits the force of a bump on one-wheel to the opposite wheel. On rough or broken pavement, anti-roll bars can produce jarring, side-to-side body motions (a "waddling" sensation), which increase in severity with the diameter and stiffness of the sway bars.

Any thoughts on balancing handling versus ride quality? I assume Ford tries to strike a happy medium with standard sway bar sizes, but if some have added roll stiffness with larger sway bars, can you comment to what degree it degraded ride quality on rough or broken pavement?

How about noise? Higher forces transmitted through heavier sway bars also causes more flex in chassis, and thus body, which should be expected to cause more interior noise. Has anyone noticed more noise after making suspension stiffer?
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Old 11-11-2016, 08:32 PM   #2
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Originally Posted by Chance View Post
I'd like to hear ideas, opinions, information, etc. on this subject from a broader perspective than usual. Most people know that suspension and steering tuning almost-always involves compromise, but those compromises rarely seem to get much discussion.

Perhaps it's often assumed that most RV owners know about these compromises and/or hidden issues, but if newbies don't already know (or have less mechanical experience, expertise, or aptitude than assumed), they may not fully understand the total impact of available "fixes".


I'll kick it off with one of the simpler topics: Anti-sway or anti-roll bars.

These bars are primarily designed to reduce body lean in fast or sharp turns. But that added roll stiffness comes at the price of adversely affecting ride quality when vehicle encounters bumps on only one side.




Any thoughts on balancing handling versus ride quality? I assume Ford tries to strike a happy medium with standard sway bar sizes, but if some have added roll stiffness with larger sway bars, can you comment to what degree it degraded ride quality on rough or broken pavement?

How about noise? Higher forces transmitted through heavier sway bars also causes more flex in chassis, and thus body, which should be expected to cause more interior noise. Has anyone noticed more noise after making suspension stiffer?
Anti sway and anti roll are the same thing. They are designed to reduce the sway of the chassis whether it be in turns or from wind forces. Adding anti sway bars will never affect the chassis running in a straight line. So they will not affect ride stiffness or cause additional noise.
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Old 11-11-2016, 08:53 PM   #3
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In relation to the balance between handling and ride quality. If tightening up the sway bars improves sway but makes it a rougher ride, does anyone think something like the Sumo Springs would allow for a better ride with tighter sway bars?

I ask because I am thinking about adding some now that I have completed the CHF.
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Old 11-11-2016, 08:58 PM   #4
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I read often folks moding their sway bars (or other mods) for handling issues....
Often the sway bars for example will be modded for things such as wander or lack of center, tracking problems, as an example.... and not the lean they are "meant" to deal with..... but they will report positive benefit from it.

It seems to me that there is a lot off cross-benefit or overlap in these things....
but I think your point is good, with the good overlap, their is likely a lot of bad overlap form them too....
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Old 11-11-2016, 09:00 PM   #5
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I installed Hellwig sway bars front and rear a year or so ago. Haven't really noticed any rougher riding characteristics though it may have, had I thought to compare. Did make for a more stable feel on the hwy and less roll on driveways etc.
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Old 11-11-2016, 09:17 PM   #6
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After doing the CHF my wife and I both think our coach rides better, less sway of course, but smoother over the bumps too!
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Old 11-12-2016, 06:33 AM   #7
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I think the writer of the Wiki did not really understand what sway bars do. yes, if one hits a bump with a single wheel, the response might be a little stiffer, but that force does not really transmit to the other side because of reaction delays caused by the heavy body and structure of a motorhome.
Concerning Sumo springs, I installed them early this summer prior to a 4000 plus miles trip and am of the opinion that they improve the handling of my unit. Now that I have the CHF applied, a rear track bar and Sumos installed, I am not concerned about passing semis anymore. Most of the time I do not even realize that a semi is passing me.

The Sumos did nothing to make the ride more comfortable. I still have the very harsh spring reaction when driving over bridge expansion slots and similar bad road conditions,
I am currently experimenting with different methods for improving the ride comfort.
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Old 11-12-2016, 11:11 AM   #8
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In my opinion you can only go so far in smoothing out the ride of gas coaches. The gas coach is essentially a truck platform designed to carry cargo, it's not built for comfort. You can improve the ride with shocks, air bags, and other items, but in the end you are still left with a truck! Doing the CHF, adding a track bar, and making other suspension modifications will definitely improve handling, but you are still driving a truck!

I guess my point is you won't find a pot of gold at the end of the rainbow, if there was one it would have been discovered a long time ago. This forum is filled with some extremely smart and inventive individuals and if they can't find the gold then I don't think anyone can!!!
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Old 11-12-2016, 03:43 PM   #9
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For highway travel in an RV, there's not much downside to higher spring rate transfer in my view. The sway bar compromise is when traversing uneven surfaces just as the wiki quote states. For traveling uneven dirt roads a disconnect would yield the best ride and eliminate spring rate transfer induced sway or "waddling" as in that wiki quote.

Why does a stiffer sway bar help highway handling? Here's a shot at trying to explain my observations for independent front suspensions: Wheels change their steering geometry as they travel up or down from center alignment |-| (both toe and camber). If you observe full droop or extension causing wheels to point like this /-\ toe (top down view) and camber \-/ (horizontal view). Full compressed goes the opposite for each toe and camber. With sway, one side is compress and the other is extended so consider the front wheels slightly shifting \-\ or/and /-/ as sway finally settles back to center |-|. Adding spring rate transfer reduces sway and in doing so it also reduces uneven suspension travel so there's less apposing steering geometry changes (win win for highway travel).
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Old 11-12-2016, 03:43 PM   #10
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!

I guess my point is you won't find a pot of gold at the end of the rainbow, if there was one it would have been discovered a long time ago. This forum is filled with some extremely smart and inventive individuals and if they can't find the gold then I don't think anyone can!!!
I might not be able to find a pot of gold, but I might find a pot of silver.

I made my living as a researcher (biomedical stuff) and I apply the skills that I gained in my job to the problem with the ride comfort. I am also in the pretty lucky position to have a son who is a master mechanic with the largest Ford dealer in the state.
He as the tools and the knowledge to do things to this truck that most others can't.
I don't know if you recall the days that cars were riding on leaf springs, and they had a pretty comfortable ride on those platforms.
Ford designed those leaf springs of the F53F550 to handle heavy weights. Kelderman went with their knowledge about that and exchanged the leaf springs in the front to softer springs and helped them with air bags.
Kelderman suspension modifications are almost as good as the air ride systems of buses or big diesel pushers. There is no reason in the world that I cannot get a similar ride quality as Kelderman achieves with their system. Knowing what Kelderman does, and also knowing that any spring of a 4 x 4 F series pickup fits physically into any F series truck allows me to find the proper springs for my motorhome. F series springs can be found at any junk yard. Once you know what you are looking for, it should be easy to find the right springs for your application.
The Ford spring ratings are:
S codes = 4000lbs capacity, 370 inch/lbs, 4.34" travel.
B codes = 4100lbs capacity, 330 inch/lbs, 5.02" travel.
C codes = 4300lbs capacity, 350 inch/lbs, 5.01" travel.
T codes = 4400lbs capacity, 390 inch/lbs, 4.63" travel.
D codes = 4700lbs capacity, 380 inch/lbs, 5.14" travel.
U codes = 4800lbs capacity, 410 inch/lbs, 4.89" travel.
V codes = 5200lbs capacity, 430 inch/lbs, 5.13" travel.
W codes = 5600lbs capacity, 450 inch/lbs, 5.34" travel.
X codes = 6000lbs capacity, 470 inch/lbs, 5.54" travel.
Capacity is per set.
As one can see, the weight rating increases by 400 lb from spring to spring. If your motorhome has a very harsh ride means that your spring rating is to high for the weight. This means that the spring never really will function as such.

I know that my unit is about 350 lb to light in the front (I have 6000 lbs springs installed), and I should go with W code springs and some kind of helper system,
To proof my theory, I will add about 350 lb of steel to the front of my rig (In front of the wheels) and see how the ride is when I go south in the winter. I have Sumo maxim springs installed, and they would be the helper springs like the air bags in the Kelderman systems.
If this theory proves it self to be correct, I will install
W code springs next year, and I should get a ride that is pretty close to that of vehicles with air suspension.
Not exactly a pot of god, but pretty close to it!
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Old 11-12-2016, 04:34 PM   #11
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Please, no offense to anyone, but you are still driving a truck! Without spending a ginormous amount of money and time you will never achieve a car like ride, at most all you can hope to achieve is a compromise.
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Old 11-12-2016, 06:13 PM   #12
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Please, no offense to anyone, but you are still driving a truck! Without spending a ginormous amount of money and time you will never achieve a car like ride, at most all you can hope to achieve is a compromise.
As i said, I am not searching for the pot of gold, one filled with silver is pretty good for me!

And you are right, a truck chassis will always be a truck chassis. Not only we owners with F53 chassis complain about the ride quality, you can find similar complains of owners of shorter and rather light weight diesel pushers that have an air suspension. A big factor in ride quality is the length of the wheelbase and the weight of the coach. The longer the wheelbase, the better the ride, and the heavier the coach, the better is the ride>

I can't do much about the wheelbase, I am stuck with 190", but I can find the proper spring load of my coach, and once I know that, I can select springs and auxiliary suspension systems that help to get a way better ride.
My motorhome is heavy enough over the rear axle. I have everything really heavy behind or above the rear wheels (generator, propane tank, waste water tanks, water tank, and the gigantic storage area). The only heavy stuff in the front are my three house batteries, engine and transmission, the chassis battery, and I. There is no real chance that I can put any substantial weight into the front. And that makes me close to 400 lbs short of the spring rating! That is what I am working on now!
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Old 11-13-2016, 10:27 PM   #13
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Thanks for all comments -- they are very much appreciated.


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Originally Posted by penguin View Post
Anti sway and anti roll are the same thing. They are designed to reduce the sway of the chassis whether it be in turns or from wind forces. Adding anti sway bars will never affect the chassis running in a straight line. So they will not affect ride stiffness or cause additional noise.
Yes, of course they are the same thing. Two commonly used names for the same thing. I personally prefer the name "anti-roll bar", but it doesn't make a difference as long as we are all in agreement on what we are discussing.

Regarding your comments on what they do, anti-roll bars increase suspension roll stiffness; between axle and vehicle frame (or the body in a unitized vehicle). Roll stiffness is added whether vehicle is going straight or turning.

The situation described in Wikipedia means that if you're driving straight ahead and run over a bump (or an object) with the front passenger tire, the anti-roll bar will make it harder for that front passenger wheel to lift up over the object. As the tire is forced to go over the bump or object, it transmits greater upward force at the front passenger corner of the vehicle.

Manufacturers over the years switched to independent suspension in cars to improve ride quality because individual wheels can handle bumps more independent of each other. While a heavy-duty anti-roll bar will undoubtedly add resistance to roll, it also adds resistance to each wheel on same axle going over bumps independently.

It's important to note that when "both" front wheels go over the same size bump, the anti-roll bar doesn't affect suspension stiffness. It's only when the right or left hit a bump that the suspension will react stiffer. That's the underlying message behind the Wikipedia statement.
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Old 11-14-2016, 02:38 AM   #14
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Hudson, I had an opposite front spring condition, though still related to your spring thoughts...

Mid to late 90's I had a 24' C where I tried most handling related items like; both the external and internal center biased stabilizers, sway bars, shocks, timbrens similar to sumo, tires, wheels, etc ... While way better and pretty darn nice to drive it still just wasn't quite "right". I figured the only possibility left to try was an air ride conversion.

I ended up taking the RV to an old truck spring guru for a chat and a look see. ... Under-sprung on the front and apposing corner sag ... best I recall his response. The weight on the front made sense because it had a high WB to length ratio and the front was slightly over its maximum rating. Also the measured weights left and right sides of the axels had considerably different numbers e.g. if the OEM springs were a matched pair they did not match the individual load they carried.

He was more than willing to install an air ride system but said he could fix the springs for a lot less. After the spring rates were position matched, there was a certain driving feel when everything is "right". Certainly any RV is a heavy loaded truck no matter what you do to it and common sense should tell us that. However, when things are right, you know it and everything else was a compromise that I tried living with.

The point for me was that I chased solutions to a slight problem plaguing that particular RV. Each change seemed to make some aspect of handling better. However, it would have been considerably less cost and so much faster to have the spring work done first. Another comment: Springs were never mentioned when I looked or asked for solutions, sadly expected I guess for most every place that also sells handling add-ons.
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Old 11-14-2016, 03:25 AM   #15
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TyCreek, great point; that's an interesting problem that is rarely discussed.

I asked a while back if anyone had weighed their motorhome with full-wall slide to see whether that affected the center of gravity towards the slide (or possibly away from slide?), wondering that if slides add weight to motorhomes, whether that added weight would end up mostly on one side. Obviously, manufacturers can offset slide weight by moving heavy things around to different locations, but given the lack of attention to some details, I still wonder if side-to-side weight distribution is well balanced in most floorplans.
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Old 11-14-2016, 05:21 AM   #16
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I've yet to find a local place that offers corner weights after that spring shop guy retired. I would like to get individual weights and have spring rates tested for the Axis but have yet to find a place with scales where that's easy or even possible. Might be a business opportunity?

Anyway, that former E chassis class C didn't have slides and was 96" wide vs. wide body so you'd think more likely to be better balanced. Something else to mention is that after the spring work was completed the rig sat a good 2" higher (about double the upward travel before hitting bump stops in the front). We went off-road a lot so extra clearance was very appreciated in the rough spots and highway surface transitions had to be much more extreme to cause bump stop contact.
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Old 11-14-2016, 12:06 PM   #17
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On related subject ....

Do taller motorhomes generally have more handling issues?

Unlike springs, anti-roll bars, shocks, etc., this issue is more difficult to compare because owners can't, for the most part, change the height of a motorhome. Before and after comparisons are therefore not possible.

We know that over the years motorhomes have generally gotten taller, which presumably increases the center of gravity on most of them; and also increases side area to winds. Additionally, the center of pressure to side gusts sits higher, which compounds effect of crosswinds. It's a bad recipe all around.

Lower-height motorhomes (thinking typical Class A gasser on F53 chassis as example) could handle and ride better, but the general design would require other types of compromises. First things that come to mind are present elevated floors that allow pass-through storage, and added interior headroom to make them feel more residential. The general adoption of slides also forced manufacturers to increase ceiling height. Unless manufacturers could start with a lower chassis, these design features would have to be limited somewhat in order to make motorhomes of lower overall height.

What do you guys think about this general trend that now has some motorhomes built in excess of 13-feet in height (some toy haulers are nearing the legal limit)? Are most buyers aware of the impact height has on handling and stability? Is the added space worth it? Should there be a legal limit as to what manufacturers can sell?

There are reasons race cars sit close to pavement in order to improve handling. Should designers and engineers try harder to make motorhomes handle better, or should they design what people want regardless of issues that may follow?
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Old 11-14-2016, 08:31 PM   #18
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I've yet to find a local place that offers corner weights after that spring shop guy retired. I would like to get individual weights and have spring rates tested for the Axis but have yet to find a place with scales where that's easy or even possible. Might be a business opportunity?

Anyway, that former E chassis class C didn't have slides and was 96" wide vs. wide body so you'd think more likely to be better balanced. Something else to mention is that after the spring work was completed the rig sat a good 2" higher (about double the upward travel before hitting bump stops in the front). We went off-road a lot so extra clearance was very appreciated in the rough spots and highway surface transitions had to be much more extreme to cause bump stop contact.
Check around for a Truck Center. I have mine weighed at Pete's Road Service but they are only located in So Cal. They weighed all four corners and an alignment for something like $175.
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Old 11-14-2016, 08:36 PM   #19
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TyCreek, great point; that's an interesting problem that is rarely discussed.

I asked a while back if anyone had weighed their motorhome with full-wall slide to see whether that affected the center of gravity towards the slide (or possibly away from slide?), wondering that if slides add weight to motorhomes, whether that added weight would end up mostly on one side. Obviously, manufacturers can offset slide weight by moving heavy things around to different locations, but given the lack of attention to some details, I still wonder if side-to-side weight distribution is well balanced in most floorplans.
My Hurricane is a couple hundred pounds heavier on the slide side, both front and rear.
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Old 11-14-2016, 09:24 PM   #20
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Thanks brucev, that's good to know. I'm trying to avoid slides altogether, but if forced into it by lack of other choices, I expect the smaller ones like on Axis will have minor impact on side-to-side weight distribution.
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