Over loaded axel!

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Nov 11, 2009
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I've just had a quick look at those two findings and my initial response without going into detail of reading over 200 pages would be that the first one concentrated on the effect that dampers may or may not have on overall chassis performance and durability, and the second more on lateral stiffness. That dampers won't affect lateral stiffness is very much to be expected. However, neither of the two reports seem to go into much detail on the effect of dampers on vehicle handling, in particular in something like the "Elk test" and that's where I would have expected results that confirm benefits for fitting dampers, ultimately leading to the significant legal weight ratio restriction in Germany if they are not fitted.
The basis of why I posted that report (2013) related more to the effectiveness of dampers working in conjunction with the suspension inherent in the Alko axle rubber bushes and their effect in damping potentially damaging forces on the axle, chassis or internals. In that respect they do not contribute much benefit.

There are limits on what can be carried out during an Mphil project. It’s a pity that subsequent post graduate studies did not continue the project into handling with or without dampers.

Are there German studies supporting the fitting of dampers in order to run at higher speeds ?
 
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The link suggests that there is something in the design which limits suspension movement, but to prevent wheel arch damage that must be effective before the tyre can contact the wheel arch. I have the impression that in the past that was not always the case.
I agree, but the design concept shown in the cross section appears unchanged over the years. Yet collapsing through overloading remains an issue for some users.

It is not a problem I ever had, and I was far from good about checking my weights.

John
 
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I agree, but the design concept shown in the cross section appears unchanged over the years. Yet collapsing through overloading remains an issue for some users.

It is not a problem I ever had, and I was far from good about checking my weights.

John

I simply cannot believe that the chassis manufacturers design their product with such a small margin of safety that an overload of, say, up to 50kg, is going to result in the suspension collapsing. Either not enough clearance to the wheel arch was provided in the first place or there was a material fault, but even if the suspension did collapse, it would be good practice to provide a bump stop to prevent tyre to wheel arch contact.
 
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I simply cannot believe that the chassis manufacturers design their product with such a small margin of safety that an overload of, say, up to 50kg, is going to result in the suspension collapsing. Either not enough clearance to the wheel arch was provided in the first place or there was a material fault, but even if the suspension did collapse, it would be good practice to provide a bump stop to prevent tyre to wheel arch contact.
Totally agree. But it seems there are failures. And the response from the manufacturers and Alko seems to be it has been overloaded or driven over potholes.

John
 
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I agree, but the design concept shown in the cross section appears unchanged over the years. Yet collapsing through overloading remains an issue for some users.

It is not a problem I ever had, and I was far from good about checking my weights.

John
John
From experience of Bailey owners with new vans there were reported axle issues a few years back. Also one recent post on this Forum described a virtually new Sprite with an MTPLM of 1300 kg had suffered a problem and its axle rating was 1500 kg. I don’t believe all of these can be down to overloading the payload. In my case the van was serviced in a December and no issues reported. Arriving back from Shropshire the following spring the offside had dropped noticeably. My van had an asymmetric load distribution with most of the heavy kit on the offside. I recall reading that Swift can allow up to a 45/55% asymmetry. How is that dealt with in the design of the suspension and dampers?

The van wasn’t overloaded but the potholes in the roads in that route in the Shropshire area were appalling. If potholes can wreck car tyres, wheels or suspension I don’t think the relatively unsophisticated caravan suspension is going to withstand them despite the flexure in the high profile tyres that now run at high pressure on SA caravans.

I didn’t notice any discernible handling improvements after fitting a new axle plus dampers. But the van always behaved itself prior to fitting new kit as the weight ratio was well below 85% and the car was well loaded.

PS In error I once overloaded a 1000kg MTPLM by nearly 25% and asked the Brecon weighbridge to recheck. It towed beautifully and wasn’t in the least bit skittish and my payload weight spreadsheets were remarkably accurate. I must admit the journey back from Brecon was very steady, When I got home everything was stripped out and the caravan weighed again. I had boobed big time 😱
 
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Nov 6, 2005
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Dampers, also known as shock absorbers, come in a wide range of stiffness - at least on cars they do - the range of stiffness for one model varies from soft for low-powered versions sold in North America to very stiff for track-specials sold in Europe - with everything between for the various other versions.

Given that studies seem to question the value of Alko dampers, perhaps they need to be a lot stiffer - this would reduce some of the dynamic forces on the rubber spring elements.
 
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The normal excuse for cracked panels was always trotted out and blame placed on potholes etc until you involve the insurance company and they prove that the issue was due to poor design. Win Win for consumer!
 
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Despite numerous threads seeking the source of the 85% recommendation no one has ever been able to pinpoint where and when it came from. Lost in the depths of time.
Whilst I cannot prove it, I do suspect the someone at the NCC does know exactly how the figures came into being, but I also suspect they know how tenuous the reasons were for it and consequently are embarrassed to admit they have been responsible for such poorly founded advice.
 
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Whilst I cannot prove it, I do suspect the someone at the NCC does know exactly how the figures came into being, but I also suspect they know how tenuous the reasons were for it and consequently are embarrassed to admit they have been responsible for such poorly founded advice.
At one time I thought it might be in a U of B report, but no joy there.
 
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At one time I thought it might be in a U of B report, but no joy there.
The U of B were involved with a research project entitled:

An experimental investigation of car–trailer high-speed stability

Peer reviewed and Published in 2009, This is the research project often cited in caravan forums as being responsible for the Caravan industries towing weight ratio advice. In fact it says this in the abstract-

"It is interesting to see that the trailer mass alone does not dramatically affect the high-speed stability as this runs contrary to current guidelines relating to limits on the relative mass of the car and trailer."

Th research was conducted only using 1 car (1.8 Turbo Diesel Litre Ford Mondeo Estate) and one adapted caravan chassis without body.

U of B's research did produce a small model which was shown in public and demonstrated how Yaw inertia was one of the largest contributors to outfit instability, but it was not proof of weight ratio's.

View: https://www.youtube.com/watch?v=PFzrWHTG5e8


It was a learning model rather than a functional scale model. It was publicly demonstrated at caravan shows .

The real life car and caravan outfit they used exhibited the same overall characteristics at about 55 mph, but it could not be used to inform on the expected point of instability of any other combination of car and caravan.
 
Nov 11, 2009
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The U of B were involved with a research project entitled:

An experimental investigation of car–trailer high-speed stability

Peer reviewed and Published in 2009, This is the research project often cited in caravan forums as being responsible for the Caravan industries towing weight ratio advice. In fact it says this in the abstract-

"It is interesting to see that the trailer mass alone does not dramatically affect the high-speed stability as this runs contrary to current guidelines relating to limits on the relative mass of the car and trailer."

Th research was conducted only using 1 car (1.8 Turbo Diesel Litre Ford Mondeo Estate) and one adapted caravan chassis without body.

U of B's research did produce a small model which was shown in public and demonstrated how Yaw inertia was one of the largest contributors to outfit instability, but it was not proof of weight ratio's.

View: https://www.youtube.com/watch?v=PFzrWHTG5e8


It was a learning model rather than a functional scale model. It was publicly demonstrated at caravan shows .

The real life car and caravan outfit they used exhibited the same overall characteristics at about 55 mph, but it could not be used to inform on the expected point of instability of any other combination of car and caravan.

The wheel has turned full circle in the last seven years and we are still no further forward in the search for the Holy Grail of 85%


 
Nov 6, 2005
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The U of B were involved with a research project entitled:

An experimental investigation of car–trailer high-speed stability

Peer reviewed and Published in 2009, This is the research project often cited in caravan forums as being responsible for the Caravan industries towing weight ratio advice. In fact it says this in the abstract-

"It is interesting to see that the trailer mass alone does not dramatically affect the high-speed stability as this runs contrary to current guidelines relating to limits on the relative mass of the car and trailer."

Th research was conducted only using 1 car (1.8 Turbo Diesel Litre Ford Mondeo Estate) and one adapted caravan chassis without body.

U of B's research did produce a small model which was shown in public and demonstrated how Yaw inertia was one of the largest contributors to outfit instability, but it was not proof of weight ratio's.

View: https://www.youtube.com/watch?v=PFzrWHTG5e8


It was a learning model rather than a functional scale model. It was publicly demonstrated at caravan shows .

The real life car and caravan outfit they used exhibited the same overall characteristics at about 55 mph, but it could not be used to inform on the expected point of instability of any other combination of car and caravan.
That research from 2009 can't be the source of the NCC Towing Ratio recommendation as the Caravan Club published a ratio recommendation back in the early 1980s to my knowledge, possibly earlier - the ratio has varied over time, my earliest recollection is at 75% and in later years the blanket 85% was split to recommend 85% for beginners and up to 100% for experienced caravanners.
 
Mar 14, 2005
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That research from 2009 can't be the source of the NCC Towing Ratio recommendation as the Caravan Club published a ratio recommendation back in the early 1980s to my knowledge, possibly earlier - the ratio has varied over time, my earliest recollection is at 75% and in later years the blanket 85% was split to recommend 85% for beginners and up to 100% for experienced caravanners.
I too remember earlier values, but the question still remains, how were these values derived, based on what evidence and by whom? If the values have been changed who took that decision, and on what evidence. For advice like this there should be a trail to show how and why it was ever introduced, and some one or an organisation (and I suspect it is the NCC) must have ownership of it.
 
Jun 20, 2005
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My first box was 1978 a little 12 footer. I joined the CC and enjoyed their En route magazine and all its tips for a first timer . I vaguely recall it was in that Journal I read aboutb’ balancing weights between car and caravan. Nothing I remember about 85% but certainly back in those days most cars struggled with their own weight never mind a caravan🤪. I can’t say I was aware of the NCC in those days 🤔🤔
 
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My first box was 1978 a little 12 footer. I joined the CC and enjoyed their En route magazine and all its tips for a first timer . I vaguely recall it was in that Journal I read aboutb’ balancing weights between car and caravan. Nothing I remember about 85% but certainly back in those days most cars struggled with their own weight never mind a caravan🤪. I can’t say I was aware of the NCC in those days 🤔🤔
The NCC was founded in 1939
 
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My first box was 1978 a little 12 footer. I joined the CC and enjoyed their En route magazine and all its tips for a first timer . I vaguely recall it was in that Journal I read aboutb’ balancing weights between car and caravan. Nothing I remember about 85% but certainly back in those days most cars struggled with their own weight never mind a caravan🤪. I can’t say I was aware of the NCC in those days 🤔🤔
In 1968 my first car was a 1962 Ford Zephyr so would have no issue pulling any caravan. Next was a Ford Cortina followed by a couple of V8s from the states. I did have as second cars, a Fiat 500 and an Anglia 10E with the side valve engine which was not good in a hot climate. Most of the time they were parked up, but where there for the extra ration of fuel coupons.
 
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They were very quiet
In the 1990s I knew one of the NCC's directors, and despite that point of contact, I was unable to get a straight answer about the towing advice.

Just in case need readers have got this far, I don't have a problem with there being advice about weight ratios for towing caravans, but I could never understand the way so many caravanner's are prepared to go to the trouble of matching the towing advice, yet ignoring other far more relevant even legal issues. It's because the advice is repeated so many times often erroneously, but it's sheer presence in so many places has elevated its perceived importance and it's become a dogma, followed blindly and your frowned on if you don't follow it.

It's only advice, it has no legal authority, and yet in a few cases it's been followed doggedly and the outfit has actually been illegal. Advice that can lead to an illegal situation is bad advice.

As I have already said, I'm not against advice, good advice, and I support the concept that caravans represent difficult trailers, and thus it makes good sense to keep caravans(in fact all trailers) as small (by weight and size) as possible, but at the same time, you must not exceed any of the outfits legal limits. If there needs to be a formula, it must use criteria that can be found or measured easily and have an impeachable source such as the vehicles data and vin plates or part of the registration documents, so there is no ambiguity as to the values to be used.

The advice would not be complete if it didn't also include advice about loading strategies to maximise the natural stability, and to emphasise good driving habits, and especially speed which is under the driver's control and is always a major factor that creates instability.

I cannot see any part of the industry being prepared to fund proper research into developing an effective advice package as to cover all possible combinations of tow vehicles and caravan would be prohibitively expensive, and it's unlikely Govt would fund it, but I wouldn't be surprised if such a research project were undertaken, to find one outcome being an even smaller equivalent towing ratio figure being advised.

The current advice is not fit for purpose, and I am sure there hasn't been a study to verify if the current advice actually has reduced towing incidents.

But in the absence of any better advice what we have is better than nothing, but is not to say we should be complacent about it.
 
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