Jayco Jaytech suspension FIX

There is next to no additional weight in the van, it has the Jayco fitted spare on the back bumper, and have just towed it today and it happens mostly going down hill from any speed of about 90kph up, a bump a bend even a change in the camber sets the rock happening and then the sway occurs. I guess we will have to take dehydrated water too.

Isn't that the same for nearly all cars on the road ?? Of course the shocks provide stability and dampening !

No modern passenger car has independent suspension ??

The OP might want to check towball weight 1st, then as said, how it's loaded !

Independant suspension on Ultimate campers is great, I have one.Flawless.
Tvan owners have independant MC2 setups and they find them trouble free with exceptional handling.
In my opinion I think there is a weight distribution problem here.

Gronk ... yet again you miss quote.

Show me one single example of a modern motor vehicle that has a single short arm, trailing link, independent suspension. ..... particularly as crude as pretty much all of those found on caravans.

Pinko mate ..... flawless, I don't thinks so ...... I'll point them out to you later.
Remember what you have is relativly short and has a low centre of gravity ..... so you could put pretty much any crap under it and it will follow quite well. ....... OH that ute in your picture ..... does it have independent rear suspension?

No doubt there is some issue with weight ......... but surely a trailer any trailer should be unconditionally stable unladen ....... OH sorry ..... its a caravan, they all have crappy suspension compared to modern motor vehicles and are not required to perform or be tested to any standards

Sorry but the quality and sofistication of trailer suspensions is an ongoing anoyance to me, particularly when people are being sold very expensive suspensions that will perform no better than a properly designed and constructed leaf and beam axle system.

Oh just as an indicator of the "qulaity" of the jayco suspension in question ....... look at the shock absorbers in the picture ....... notice the over extension straps tied to the shockes with cable ties ........ firstly find me one modern motor vehicle that uses webbing straps to prevent over extension in the suspension ....... and cable ties .... come on.

cheers

Bantam
I didn't realize you were such an expert.
Sorry I added to the conversation ?

ya don't have be any sort of expert to understand basic suspension systems.

One of the problems with the various trailing link suspensions fitted to trailers is that the pivot point of the single trailing link is generally perpendicular to the centre line of the vehice thus the suspension fails to keep the wheels in a good attitude to the road.

At least a beam axle keeps the wheels perpendicular to the road surface and the traction surface of the tyre in good contact with the road.

These suspension systems in question look great in a straight line, but as soon as there is any significant turning or especially when the trailer is getting out of shape ..... the wheel's attitude to the road gets very uggly.

As weight transfers, on most of these systems, the wheels remain perpendicular to the chassis and at times quite dramatic and disadvantageous angles to the road.

In a classic unstable sway situation the tyres roll from inside edge to out side edge at the worst possible times.

This results in munimum traction at maximum sway and thus promotes more sway.

Pretty much all independent motor vehicle suspensions are designed to produce negative camber as the suspension compresses and toward positive canber as the suspension rises ........ this keeps the tyres traction surface in good contact with the road and prevents the tyre from rolling from edge to edge.

This is the single biggest problem of most of the independent suspension systems fitted to trailers and it makes THE most dangerous situation associated with trailers worse.

cheers

Hey Bantam..I can name one car that has that design rear suspension...My 1984 Peugeot 505 STI sedan....and I will defy you to keep up with it on any sort of road surface...be it twisty or straight...in spite of it having nearly 600000 k on it. It still handles great ...and its very supple suspension also has 9 inches of travel which makes it ideal for country roads.
I rest my case...!!!

Cheers Keith

Well Keith,I read your post and I have an immaculate 2003 Peugeot 406 Hdi in the garage and I had to go and have a look, your right.

you do well to mention the 505 sedan ...... but it can be argued that it is semi-trailing and long arm and a hell of a lot better engineereed than what we are finding under caravans and trailers..... but back to that later.

The other major two problems with most of the nasty light trailer independent suspension is the swing arm is too short and the front pivot point is too high .... .... yeh and the springs and shockabsorbers are located at the extreem rear of the arm.

OH and the shock absorbers are tilted in the oposite direction the the suspension travel making them less effective.

In pretty much all unmodified automotive suspensions the swing arms, wishbones or springs are close to horisontal in the at rest position, with the axle centre close to the same horisontal plane as the front pivot or attachment point or in the case of dual wishbones the inner and outer povots are close to horisontal as practicality will allow.

This minimises bump steer, other geometry changes and keeps the spring seats or pivots as close to paralell as possible.

In addition most wishbone or swing arm suspenson have their spring attachment points between the pivot and the axle ...... this means that the spring has to travel considerably less than the axle ..... and because of this springs can be shorter and they are easier to keep in their seats. .... in some dual wishbone designs the axle travels twice or more what the spring seat does.

So back to the Pewgot.
If you google up Peugeot 505 sti rear suspension, you will find some good pictires and comparing them with the jayco video it will show exactly the problems.


On the 505
1/ Most conspicuoulsy, the pivot points are in more or less the same horisontal plane as the axle when at rest.

2/ this can be argued ..... the 505 sti rear suspension looks to me to be semi-trailing.... its not dramatically semi-trailing ...... but it is all the same ......... in that the front pivot points are not perpendicular to the longditudinal axis of the car .......this introduces negative camber as the suspenion compresses ... ... and may I expect to be more intended to correct for bumpsteer.......... some of the traier suspension I have seen are semi-trailing ..... ....the jayco does not appear to be.

3/ the springs and less importantly the shockabsorbers are inbetween the pivot and the axle, this means far greater suspension travel for a given spring compression ..... the longer the spring the less stable it is. ..... the shockies will remain more or less vertical thru the whole suspension travel and will never be disadvantaged.

Per-go have had a very long reputation for soft, long travel suspensions that hold the road very well ..... they have used some strange suspension arrangements over the years .... arrangemenst that other makers have failed with miserably...... it is not the type of suspension ..... it is the attention to detail that gets them results.

look at the differences between these two suspensions and you should be able to see pretty much everything that is wrong with the independent suspensions offered on trailers.

Possibly THE single biggest source of suspension problems on trailers is the pretty much complete failure to deal with the flat straight box section chassis.

pretty much no trailer manufacturer will even attempt lower the front attachment point of a leaf spring to get it in the right attitude and to maximise suspenion travel... hell they are mostly too stingey to fit shackles at the rear unless it is an "off road suspension"

They certainly are not interested in building stepped or curved chassis designs even when a flat floor is not required ......

cheers

Bantam I hate to say but if you call yourself an expert I think that is a drink under pressure. I have a very solid independant camper that weight's in at 2.4 ton with air suspension that has done about 40,000. and on and off road that will tow to 120 ks and handles better than most caravans. and has been on road for 8yrs, Home BUILT.
ps single axle independant

I didn't call myself an expert. ...... besides what I speak of above pretty much any motorsport or car enthusiast that knows their business should understand all too well. ..... this is basic suspension theory.

So ya got a camper ...... yeh far more stable than ya typical caravan ...... and home built..... chances are you put a bit more thaught and care into it than many commercial units.

As I said before, if it is a relativly short and low center of gravity trailer, particularly if it has a long drawbar, it will probably tow respectably with pretty much any sort of crappy suspension under it ...... particularly if it is low, short AND heavy.

After all people have been towing trailers and vans of all types with very badly designed leaf spring suspensions that don't even have shock absorbers for many decades.

Remember THE predominating factors in trailer stability, (and stability of all vehicles) are .... centre of gravity, length, width and weight distribution ..... if those are favorable, no matter what the suspension it should tow respectably

There have been thousands of fundamentally unstable caravans towed all over the country ....... but if they havn't encountered an unfortunate set of circumstances, most people will think they tow perfectly.

Put them in a situation where their faults are exposed and they will show themselves to be the tretcherous items that they are.

AND this is the original posters issue ...... he has a relativly high centre of gravity caravan that has some length to it and maybe some weight distribution issues ....... combine that with a suspension system that does not assist with stability, in fact has traits that promote instability once it occurs..... and there is a problem ........ Good working shock absorbers will go a long way to helping with stability.

cheers

I have to agree with this ...... for many years it simply was not legal in most states to tow a rear hitched trailer that weighed more than the unladen tow vehicle.

Now we are finding many vehicles rated towing capacities 25% higher than the unladen mass of the tow vehicle and other towing specifications require the tow vehicle to be pretty much unladen to achieve maximum towing capacity.

Its madness ....... simple phsyics dictate that one mass has to be significantly higher than another if it is to exert reliable control.

cheers

That is simply not correct ...... it is an old garrage tail ...... many of the new vans and current vehicles are specified with drawbar weights in the 5% range.

Some trailers due to their unstable nature may need far higher than the specified low 5% of some of the modern vans .... indeed up in the 10% and higher .......but it can not be taken as a given ..... somewell designed trailers will tow very well with very low drawbar weights.

cheers

Mick,
Just a thought. Is the caravan absolutely dead level front-to-rear when tug and van are fully loaded while towing? If the van is slightly nose down and there is no load sharing between front and rear axles, it could cause it to become unstable.
It should be towing absolutely dead level to be safe.
Keith

Hi
First swaybars in there simplest design typically restrict suspension movement . [not the best offroad]
BUT if incorperated at the design stage can perform well
I am aware that vehicle components do have a sway bar option on there IS setup
They maybe willing do a retrofit to yours
I cannot remember design but a few pics and it maybe a DIY job also

On a single axle trailer all your heaviest weights should be low down and ontop of the axle with a bias towards front. Towball weight under 10% of van weight .Try and not use load levelling .
These are an unnecessary evil . All vehicles /towbars have a max non leveler use weight .
eg pk pj ranger 1800kgs. Have vehicle fitted with hd leaves in rear if slight sag is present or develops .
The van and vehicle must be within 25mm of level for best handling
Single axles particularly heavy ones are poor to tow and especialy compared to a dual axle .

swampy

A couple of thaughts.

One of the major problems with trailer suspensions is that they are mostly too stiff for the load carried ...... stiffening a suspension does not necessarily improve stability.

Car type stabiliser bars I do not believe will help in most situations because the suspension is already too stiff and increasing roll stifness is not helpfull.

trailer suspensions are made stiff because the suspension designs do not accomodate sufficient suspension travel ....... this comes back to the total failure of most trailer suspensions to deal with the flat beam chassis.

Pretty much all civilised suspensions sit at their mid point with the axle approximately level with the pivot point when at rest ...... with travel up and down from that point.

It is pretty much a legal and a practical design requirement that there should be at least 30% travel either up or down from the rest point at any state of loading with the ideal of 50% travel either way from rest.

Most trailers sit right at the upper point of the suspension travel when unladen .......some even when fully loaded do not have 30% downward travel.

AND most trailers do not have bumps stops at all let alone progressive bump stops.

One dramatic flaw that follows from the above is the suspension spring rate changing dramatically....... when the suspension reaches the top of its travel... the spring rate becommes infinitely soft ...... when the suspension reaces the bottom of its travel and hits the bump stops or bottoms hard on the chassis the spring rate becommes infinitely hard.

It is very very bad to have a suspension reach the end of its travel.

If a suspension particularly an undamped one or a poorly damped one has a too high spring rate it causes instability ....... the period of oscilation becomes short ...... in a sway situation on a trailer it tends to make the trailer hop .......... a softer spring rate lengethens the period of oscilation ....... there are many vehicles out there with relativly soft suspensions that are stable without shock absorbers because of the long periods of oscilation of their suspension.

SO if a trailer (or any other vehicle) has excessivly stiff suspension, all other factors become more critical especially shock absorbers.

A properly designed suspension will consider these factors and the shockabsorbers will be designed specifically to match the springs and the load carried.

cheers

I agree with Bantam that the leaf springs seen on most trailers are too stiff. That's because they are too short in order to save on height because, unlike a ute, the the chassis rails are flat. Look at the leaves on the back of any 4WD ute all of which have upswept chassis rails. They are usually very long and sit almost flat under full load. This gives plenty of wheel travel, a nice progressive spring rate and the axle does not move back so much when the wheel moves upwards, which minimises bump steer.
Kimberley have started fitting air springs to all of their trailers because they have a nice flat spring rate at any load, as opposed to the steep spring rate mentioned by Bantam that you get with short coils and short leaf springs.
Kimberley have also started fitting sway bars to their caravan trailing arm suspensions to overcome the body roll problems caused by the low roll centre that comes with trailing arms. This get worse if the tow has had a suspension lift.
Short of asymetric link suspension, perhaps a solid beam axle with trailing arms and well damped air bags with plenty of room for maybe six inches of suspension travel is the best setup for any RV trailer of more than say 1500 kg. See example below, which unfortunately is very complex and expensive to build.
For dual axles of any configuration it would be easy to make them load sharing by fitting air bags with front and rear interconnected with an air line. Don't know why they don't do that. Must be a money thing.
Good suspension is easy to do, but not so easy to pay for.

Thats what I'm talkin' about... right there.

A properly laid out 5 link suspenion .... about as good as it gets on a rigid axle and very similar to what you will find under the back of a modern truck or trailer with "road friendly suspension"

The only thing missing is ride height regulation like would be found on the rear of most modern prime-movers.

Ride height regulation, adjusts the pressure in the airbags so that the minimum spring rate is used to support the load at the correct height ........ this results in a smoother ride and less damage to roads.

That would be a quite expensive suspenion system and requires some thaught when building the chassis.

As for the leaves ...... I have a 2 tonne flatbed in the front yard waiting for a rebuild ....... I have picked up a set of 70 series rear springs for it ..... that are a fair thing for 2 tonnes ...... those springs are twice the length of the 2 tonne trailer springs currently fitted ....... when I fit them I will have to raise the front attachment point at least 150mm to put the springs in the correct attitude ...... fortunately I have a 200mm drop axle for it ....... AND I will fit a pair of 70 series landcruiser shockes.
that will give me a suspenion already designed and proven by Toyota for approximately that load and springs matched to the shockies ...... I am confident it will tow well.

cheers

I have been in contact with Jayco direct for some time, no apologies required. I am getting the slow and painful runaround. I will let you know how it plays out.

Yeh ... Good luck with that.