Readers Letter in April issue of Practical Caravan Magazine

[ProfJohnL]

Hello Colin

" while the legal limit may be considerably higher it is recommended that the trailer weight be as low as possible"

I warm to your suggestion, however I do suggest a change to remove an ambiguity:-

" while the legal towed weight limit may be considerably higher it is recommended that the trailer be as lightweight as possible"

"Low" has positional implications and in the context of the subject and your guideline, could mean a very heavy caravan is ok as long as the position of the weight is low.

 

[Lutz]

In fairness, Prof, Colin did say "that the trailer weight be as low as possible" and not the "centre of mass (or weight) as low as possible", so really there is no ambiguity.

 

[Surfer]

Most people refer to caravans when towing and various guidelines, but many of these so called guidelines go out the window if applied to all trailers including horseboxes and at that stage Lutz has some very valid points. Also have these so called experts on towing actually towed any form of trailer at any point for any length of time?

 

[weejock]

Just a suggestion but since car manufacturers go to quite a bit of trouble to find out what particular models of cars can tow should we not be using that infromation as a starting point. To satisfy most this information is researched and legally binding. This would get around all those issues about one vehicle being better than another in a certain situation and then from that point advice is offered to newbies to lop 10-15% off of the maximum their vehicle is capable off till they build up a bit of experience.

 

[ProfJohnL]

Hello Jock,

Your point has been made many times.

But it is only fair to point out that caravans are probably the biggest physical type of trailer most car will be asked to tow, and consequently they do have different dynamic qualities to garden trailers.

Any caravan towing guidelines needs to take account of the particular difficulties that caravans present, that may need to include de-rating the car when towing a caravan or other large trailers.

 

[colin-yorkshire1]

hi all.
well I have done it sent a letter to the mag so we will see what if anything happens,
I will copy and paste it to see what you think "no hiding for me" I appologise in advance if I have used words or phrases used by others on the subject but in context it is the same issues disscused on this thread.
colin.

To practical caravan mazgazine "letters page"
.In answer to Roger's (aka RogerL) letter in the April issue I would like to clear up a couple of misconseptions he appears to have regarding the 85% recommendation that he so strongly supports. As a caravaner of over 40years experience, I well remember the "85% rule of thumb" and at it's conseption, nearly 50years ago It was a recommendation brought about because the old "rule of thumb" 1ft of caravan per 100cc was deemed unreilable as newer better equipped and now "heavier" caravans were being produced. a better way was needed. I cannot remember which club first made the recommendation I think it was the CC but it was soon taken up by every caravan authority, unforunatly the "of thumb" was soon dropped and it became a "rule" it is this miss use that some forum contributors object to. even though the word recommendation is now used some still refer to it as the "85% rule"

It must also be remembered that at the time all cars had "drum" brakes and turbo's were only used on racing cars, techology and car design has moved on somewhat from those days, not to mention inventions like the ALKO ATC and the advanced design of modern stabilisers. while some recommendations should be made to new caravaners including advice on loading, nose weights ect, surely a better way would be to recommend that the caravan/trailer should be as light as possible, for beginners this would remove any ambigu'ity and make more sense.

The problem is a fixation with the 85% figure like it is some kind of holy grail that must be obtained, it has been known for "newbies" to panic when their outfit is over 85% and go buy a bigger tow car to compensate with all the financial implication of doing so, what would roger advise when after buying a van a new caravanner askes "will my car tow this van" and it turns out to be 90+% . as responsible forum members it is our duty to reassure the poster and give relevent information to them so they can make an informed decision as to "what to do next"

while roger is pefectly entitled to air his views so is everyone else, the 85% recommendation has stood for so very long only because exhaustive tests need to be done to come up with a better recommendation, in these days of austerity that is unlikely to happen has the process would be very expensive and no one would pay for it. futhermore it is suggested that the 85% match (unlaidend weight of tow car/caravan MTPLM) is a safety issue, and it is, but it ignores every other factor involved such as loading. a combination at 85% that is poorly loaded will be far more unstable than one correctly loaded at 90+% and the figure does not take into account the real weights that the combination might be on the road, with a fully loaded towcar and a caravan weighing considerably less than it's MTPLM.

I am afraid the issue is far more complex than roger and people with similar views make out, sticking rigidly to a recommendation that is past it's "sell by date" just because it is there will not be the way to take caravanning forwards into the future. either for the seasoned caravanner or for the beginner we all seek so desperately to help.

colin (aka colin-yorkshire)

I also found this little snippet while on a web search

Professor Jos Darling, senior lecturer in mechanical engineering at the University of Bath, has spearheaded a programme of stability research in collaboration with Bailey Caravans.

"Given the progression in automotive technology" good practice alongside safe loading should mean 90% presents no problem as a new guideline for new or inexperienced caravanners. Simply put, a badly loaded 85% match is dangerous, whereas a safely loaded 90% match is not."

His team’s findings suggest a need to shift our thinking to an understanding that the efficient loading of a caravan can have more impact than weight.

 

[Lutz]

Just to add a comment on Colin's last paragraph, here in Germany which has a reputation for having everything regulated, there are legal limits for weight ratios to allow towing at 100km/h (basically the same speed as the speed limit in the UK):
If the trailer (caravan) is not fitted with hydraulic shock absorbers, the limit is 30% ( !! )
If the caravan has shock absorbers but neither car nor caravan any form of stabiliser, 80%
If the caravan has shock absorbers, the car ABS, and either car or caravan a stabiliser system, 100%
For trailers other than caravans the limits are 30%, 100% and 120%, respectively
If any of the above conditions are not satisfied, the outfit is limited to a maximum speed of 80km/h.
It is highly unlikely that these figures were pulled out of a bag but one would expect that a lot of research went into the issue before such differentiated limits were laid down.
Based on the above, the 85% recommendation should at least have a note that it applies only if the caravan is fitted with shock absorbers. Otherwise the recommendation should be even lower.

 

[xtrailman]

The German system seems reasonable to me.
It at lest looks at stability aids.
But were are the sources of the research?

But sorry Colin your post says little of value, basically all you say is RL is wrong, you are right.
If you have been towing as long as you say then you should remember the recommendation was increased to 85%, from some figure in the 70's.
Your idea of recommending towing a caravan as light as possible, or words to that effect, will only raise the question "what is light".
So that brings us back to recommending a figure, hence 85%.
Also i do think even a beginner is aware that loading is important, along with a good power to weight ratio.

 

[otherclive]

Clearly the German system lays weight on the effectiveness of caravan stabilisers and from experience I know what an improvement they can bring and it is encouraging that more UK vans are being fited with them.

 

[ProfJohnL]

Dr Jos Darling has been mentioned in a couple of posts on this thread.

He was the lead in a study on high speed car and trailer stability in 2009, which was sponsored by Bailey Caravans.

The results of the study are available but you need to search for them but as link on Dr. Darlings listing on the Bath University Web site you can find the following abstract of the report where I have highlighted a very revealing comment:-

Abstract

Previous work on car-trailer stability has been largely limited to theoretical studies with some reference to practical experience or accident statistics. In this study, extensive and systematic experimental investigations were carried out oil a combined car-adjustable-trailer system. The influence of different trailer parameters on the system high-speed stability was examined by changing the mass, dimensions, and inertial characteristics of a fully adjustable trailer. It was found that the dominant factors affecting stability were the trailer yaw inertia, nose mass (mass distribution), and trailer axle position. The tyre pressure also affects the stability, although this effect is less significant. 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. Experimental tests on a friction stabilizer and on car electronic stability programs demonstrate that both of these improve the high-speed stability and help to delay the onset of 'snaking'.
(http://opus.bath.ac.uk/14234/)

Having read the full study report, the other finding the study revealed was that for the given combination of car and trailer, the speed at which the outfit became noticeably more inclined toward instability (with a variety of loading) was remarkably consistent at about 55mph

I suspect that insufficient time or funds prevented this aspect from being explored more fully, but on the face of it limiting speed could be a far more effective safety measure than simply limiting weight ratios. However the critical speed could be very outfit dependant. Further studies including this aspect would be very beneficial.

 

[otherclive]

My comments on the German approach should have refered to shock absorbers not stabilisers although I do support the fitting of the latter.

 

[Lutz]

The German system seems reasonable to me.
It at lest looks at stability aids.
But were are the sources of the research?

Most defined levels specified in German health and safety law, and this includes traffic law, are based on studies carried out by the TÜV and I strongly suspect that this is the case here, too.
It is perhaps also worth noting that the weight ratio limit for outfits fitted with all the specified technical features was raised from 80% to 100% a couple of years ago after analysis of actual accident data had shown that the change did not measurably affect accident rates.

 

[Parksy]

Anecdotal evidence suggests that shock absorbers, electronic caravan stability control and better tyres aid caravan stability and caravan manufacturers now fit these items as standard equipment on some models.
Any blanket recommendation or guideline has to address the lowest common denominator or worst case scenario which is why tyre safety, loading, overall condition of the caravan (service history) towing courses, speed when towing amongst other factors are also mentioned when novices enquire about buying a caravan or towing for the first time. The 85% recommendation forms only part of the overall advice that is available on this website and of that offered by forum members on the message boards.
What most who oppose the 85% recommendation seem to be forgetting is that the guideline is intended for complete novices.
It has to take into account a 'worst case scenario' in terms of driving ability and overall condition of the caravan, it takes no account of present day equipment because not everybody buys a brand new caravan and towing vehicle with the latest stability aids.
The 85% figure, all though by no means backed up by reams of data and aimed at the lowest common denominator has to allow a margin for error.

 

[colin-yorkshire1]

But sorry Colin your post says little of value, basically all you say is RL is wrong, you are right.
If you have been towing as long as you say then you should remember the recommendation was increased to 85%, from some figure in the 70's.
Your idea of recommending towing a caravan as light as possible, or words to that effect, will only raise the question "what is light".
So that brings us back to recommending a figure, hence 85%.
Also i do think even a beginner is aware that loading is important, along with a good power to weight ratio.

hi Ray if that is the impression you got then obviously you have either not understood or my explaination was not good enough.
while it is true that I (as well as others) do not agree with rogers view it appears that david motton and the PC team do.
having read the full letter and reply I got the impression that while they accept there are other factors involved and more research needs to be done the 85% sits nicley in a little box a recommendation to be used as a starting point, allthough it is 50 years old and should be seen in that context it's relevence today is in question. the very fact that it is given so much importance is as I see it missleading can anyone think of any other 50 year old recommendation that has survived.
we all seek to advise newbies so their transision into the hobby is as smooth as possible I believe putting a figure on it is counter productive in many cases it is the first outfit that causes the most anguish as most newbies after their first year have a a dammed good idea what it is all about and after this formulate their own opinion as to the best way forwards
in his letter Roger appears to take the view that discussing the criteria surrounding this first outfit that is the problem and not following preconceived convention that causes the most distress to those who post on the subject however how is the questioner able to get informed opinion without a discussion.

my suggestion that the 85% be dropped in favor of as light as possible is just that a suggestion I changed it from as LOW as possible after comments from John, there is no abiguity in this just a suggestion that the lighter the van the better, it is my fault that I did not explain exactly what I meant an examlpe of this could be. a newbie has a ford focus with a tow limit of say 1300kg and goes looking for a van he finds one that is say 1200 kg MTPLM well within the cars capabilites but exeeds the 85% recomendation by 4% is he then not to buy it as it is 4% over. or by using other critera and go ahead and load it is as light as possible for his first couple of outings. experienced caravanners allready know that shifting weight from the van to the car is helpful no matter what the ratios is.
is it then wrong to advise this to newbies, we all know that towing is a complex issue and anyone new has to get their head round all the reams of legistlation involved, are we to assumed therefore that they are incabable understanding what should or could be unsafe without putting a concrete figure on it.

 

[xtrailman]

Good summation Parksy.

Quote from profs link.

"Having read the full study report, the other finding the study revealed was that for the given combination of car and trailer, the speed at which the outfit became noticeably more inclined toward instability (with a variety of loading) was remarkably consistent at about 55mph"

Interesting point Prof, since towing at 91% with all the latest gadgets fitted, with meticulous attention to loading, nose weight, and tyre pressures, I've found the caravan noticeably more settled at 55mph than 60mph.
And also the towing mpg has risen from 23/25mpg up to 26/29mpg.
The Valencia is the longest and heaviest caravan i have towed to date, and any instability is quicker noticed.
However i am still debating whether to tow at near 100% with my next possible tow car, a 1600kg mazda cx-5.

 

[xtrailman]

But that's the point Colin, 85% gives a margin for error, all this talk about focus man towing at 89%, how can that be established?

Kerb weight will vary car to car, caravan MTPLM will vary, probably well over in practise, proven only by a weigh bridge, which is why i am completely in agreeance with a fixed figure to aim for.
Then if the ratio varies a little over or under (unlikely?), the the newbie is still working within "safe" limits.

You say 85% has been around for 50 years, that's not what I've read, its been lower but increased to allow for the more modern car.

I think Lutz has a point with the German method at lest that looks at what stability aids are fitted.

My previous caravan had no shockers, the wheels were not balanced, and i towed safely at around 85% or less.

 

[Lutz]

Based on the information in my last two replies, the 85% is already inappropriately high if no shock absorbers are fitted to the caravan. That applies even more so for the novice.

 

[Lutz]

..... caravan MTPLM will vary, probably well over in practise, .....

The caravan MTPLM is absolute. It is a plated figure and can never vary.
The car's kerbweight is also a fixed value. It differs from car to car, but is specific to each and every vehicle.

 

[xtrailman]

..... caravan MTPLM will vary, probably well over in practise, .....

The caravan MTPLM is absolute. It is a plated figure and can never vary.
The car's kerbweight is also a fixed value. It differs from car to car, but is specific to each and every vehicle.

In theory, but not practise.

 

[Lutz]

Not only in theory, but also in practice, because that's how the two terms are defined. They both are NOT actual weights, at least not unless they happen to be the same.

 

[ProfAlGoogle]

I have been following this thread with interest over the last few days, refraining from replying, as like many I find it tends to be governed by a few individuals who tend to set themselves up as an authority to any caravan, or non caravan related topic.

It's been a while since I have posted on here but i would like to give my take on the debate.

I started caravanning back in the late 60s, not a great deal of advice was around in those days as to regard van and car matching, like others have quoted it was normally determined by foot of caravan per 100cc of engine size.

My first combination being a late 50s sprite musketeer matched to a 1965 Hilman minx of some 1700 cc. So with the sprite being 14ft in length should have presented no problem towing.
Not quite so, with it's low slung metal chassis, 2" coupling with flip over collar for reversing, solid wood interior complete with double pull down bed at the rear of the caravan, no stability aids, it was a complete nightmare. And as for nose weight, I never heard that mentioned, but with care and consideration and 100% concentration, and a serious approach to what I was doing, all was well, but back then the maximum speed limit was 40 mph on any type of road, perhaps that was my saving grace, plus it was very rare that the Hilman could hit that limit!

85% recommendation can't remember when that came about, certainly not fifty years ago. I remember when they upped the limit to 50mph, and to comply you had to display a 50 sticker to the rear of the caravan with a weight sticker to the front of the caravan, and likewise a weight sticker attached to the towing vehicle, otherwise it was 40mph.

But things since then have changed a lot, for example motor cycle training, back in my day it was anything up to 250cc on L plates, unless you wanted to attach a sidecar then the sky was the limit!
The same applied to driving a lorry, pass your car test on a Monday then jump in to a twenty ton lorry on the Tuesday. Compare that to the amount of training today's lorry driver has to undertake before he is let loose on his own.

So what changes in law have we seen as regards to towing a caravan/trailer? Very little apart from the 1997 licence change, but there is still one heck of a lot of people out there that obtained there licence prior to 97, and it's frightening to know that there is nothing to stop them from taking to the road with a large caravan and no training whatsoever.

You also have to bear in mind that it is a very very small percentage of people that bother to make any enquiries on these types of forums, or subscribe to any type of caravanning magazine, with the only advice most receive is from the salesman eager to make a sale.

One or two colleagues I work with have taken to caravanning and there ignorance on some of the legalities is frightening, so you can have all the recommendations you like.But it is high time the law changed to make it compulsory to undertake training followed by a test for any trailer above 750kg.

Allan.

 

[colin-yorkshire1]

Where's Sproket?? if you see him ask him to send me one of those white flag waving thingies I 've got a headache from banging it against the wall'
for the very last time let's be clear,
1 the, MTPLM is a fixed figure (as Lutz remarked) it is an absolute no caravan can weigh more than it's plated maximum if it is one ounce over it will be deemed overloaded it can however be increasd by obtaining a new plate (if the manufacturer allows it)
2 the kerb weight of the towcar will be the given weight empty and therefore the lightest it can be
3 85% ratio this figure assumes for the pupose of calculation that the van is at it's MTPLM and maximum and the towcar will be at its kerb weight ie the lightest it can be. NO-ONE has an outfit that coresponds to this formula it does not exist
because as soon as the car is loaded is weight increases and as soon as the van is attached its towload decreases by the noseight it puts on the car,
the 85% figure that you started with will now be considerable less. the weight difference could be in the region of 10 to 20%
so the actual towing ratio that started @85% could well be 65% on the road
absolutely none of this takes into account the legal requirments of max trailer weight. gross vehicle weight, or maximum train weight.
any combination that falls within these absolutes is a viable configuration even when the combination falls well short of these absolutes it may fall foul of the magical 85% recommendation.
is someone realistiticaly trying to us that a 2 tonne caravan towed by a 2.5 ton tow vehicle is a safer outfit than a focus with a coachman on the back, because one conforms to the 85% recommendation and the other does not
give us a break

 

[Sproket]

give us a break

 

[colin-yorkshire1]

hi Sproket thats not the one I was thinking of but it will do nicely thanks.

 

[Sproket]

hi Sproket thats not the one I was thinking of but it will do nicely thanks.