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is 90% the new 85%?


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It never was a rule of course, just a guideline and generally aimed at inexperienced caravanners. I see nothing wrong with having a guideline to help newcomers. However what is not helpful is at the same times as promoting 85/90% the actual law never seems to be mentioned. Obviously as people get more experience they are in a better position to judge for themselves. I suppose upping the ration might help more cars fit into those you could use for towing so might be helpful that way as caravans seem to be getting heavier.

 

David

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Having towed caravans for the past 30 years, I must say that today's vehicles are easily and safely capable of towing a caravan with a ratio of 90%.

Our outfit is Freelander V6 and an Adria Adiva. It is listed as all green very safe on the towsure match list and yet the caravan weighs 93% (loaded) of the car's weight. Towing our caravan is a stress free pleasure and we have never experienced a problem of any sort. Careful loading does of course help and must be carried out.

 

I believe that the two big clubs ( we are members of both) have the best interests of caravanners at heart, however I do believe that progress needs to come a little more quickly than it does with the clubs.

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  • 1 month later...

My take is that for an inexperienced towcar driver any weight ratio can be dangerous, and for that reason I think it is dangerous to imply that 84% (or even 89%) is "safe" whereas 86% (or 91%) is "dangerous." The two main clubs are in error in my opinion since they state 85% as if it were law whereas in reality there are a lot more factors to take into account.

 

My own towcar (Discovery TD5) has a maximum towing weight of 3,500kg. on a kerb weight of about 2,200 kg., i.e. 85% ratio. I have towed big trailers for nearly 40 years, 20 of them in Disco's, from ground exploration borehole rigs through heavy plant trailers and boat trailers to caravans. In all of the former categories trailer weights have been up to or probably in some cases over the max. towing weight for whatever vehicle I had at the time.

 

At present we tow a Coachman 650/5 with an MTPLM of 1870kg. That is fine but I am not sure I would want to be towing a caravan that was much heavier. The handling difference between a caravan and a boat, plant trailer or whatever is the sheer windage from the long flat sides. We lost our last Coachman (and Disco) in dramatic fashion after the driver (not me I would add) lost control after being overtaken at massive speed by a white panel van. The weight of the caravan, once sent into oscillation by the pressure wave from the van, simply took over.

 

In contrast much heavier trailers do not have the same windage so are much more stable in overtaking conditions, provided of course that they are properly loaded.

 

Other factors include the presence or not of a towhitch damper and how well it is maintained, the overhang from tow vehicle rear axle to towball, the type of vehicle of course and whether or not Alko ATC is fitted.

 

There is also the question of power and reasonabe progress. My Disco TD5 is O.K. but could do with a bit more oomph on steep Cornish inclines, which must be due to a combination of weight and wind resistance since performance is much better with my 3 tonne plant trailer. Speed, more particularly lack of it, is a factor when considering other motorists, as of course we all do.

 

In summary therefore I would not support a blanket increase in the max. tow weight percentage since this could be dangerous for some. I would strongly support more use of the phrase "recommended max. tow weight, subject to towing experience / type of rig etc." and whilst anything like this will be more cumbersome to express it would open the door to better consideration and allow experienced drivers to perhaps buy a slightly heavier caravan if they are happy they can handle it. Also as said elsewhere there is the implication to a novice that 85% or whatever is OK without reference to loading, nose weight etc.

 

p.s. I sent a similar letter to this to the Caravan Club a year or so ago. That and other correspondence has never been published, leading me to think that the Club is rather selective in what it prints, preferring praise to debate! Given that both "clubs" are of course commercial concerns they will not like any implication of criticism for their policies.

 

 

 

 

 

 

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Really good analysis from Balliol. Pretty much agree with everything said. Having towed most things all I would add is that a twin axle is far more stable - even when towing a small trailer.

 

Towing horse trailers, with horses in! - where they move about so the "loading" varies is interesting - So my two penneth worth on any set "limit" "rule" "guideline" whatever is that the main factor is care and attention.

 

The most frightening words I hear? - "I don't know I am towing it" - if this were really true then it is a recipe for disaster.

 

Only thing I would add is that whatever the "rule" is - do inform your towcar insurance policy company that you tow and set out the relative weights, ratios etc. Because if you are some way over - your insurance cover can be compromised.

 

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Balliol - 2010-04-12 11:49 AM

My own towcar (Discovery TD5) has a maximum towing weight of 3,500kg. on a kerb weight of about 2,200 kg., i.e. 85% ratio.

 

Hi Balliol,

 

There's a slight error in your calculations here I'm afraid.

The figure should be the fully laden weight of the caravan as a percentage of the kerb weight of the car so in your case this works at a maximum possible 159%.

 

Keith.

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There is one other often forgotten rule of thumb, which is that the noseweight should be about 7% of the ALW of the caravan.  This is also relevant to stability, and because many modern cars have hitch weight limits of 50Kg, should logically restrict the ALW of a caravan towable by such vehicles to a little above than 700Kg.  In Europe, where higher towing speeds are common, the recommended noseweight is 10% of ALW.

My final point, is what is an "experienced" caravaner?  The driver of Balliol's car + van at the time he wrote both off would presumably qualify, but would a driver who had towed many thousands of miles without any incident also qualify, or is he really, just one of life's spectators.  It is surely the experience of incidents that teaches (though hopefully in less dramatic fashion than the above driver) the valuable lessons. 85% is a "rule of thumb" based on accumulated experience of many caravaners over many years, with a bit of assistance from, I think, Bristol university.

Some caravaners would like it increased to 90%, or 100%, to suit their convenience.  The problem with this is that convenience doesn't make good physics, and empirical physics is, loosely, what governs the behaviour of caravans under varying road, and wind, conditions.

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Does this have more to do with the type of towcar used, I wonder?

Also the sheer physical size of a caravan must have some bearing on safety regardless of weight?

I gave up towing a caravan umpteen years ago but I have over the years towed boats, some of 'em big 'uns, with a number of vehicles the best of which for purpose was a swb Land Rover Defender.

The best boat trailers were those with the wheels as far back as possible as these are more inherently stable - but at the expense of increased noseweight.

I would imagine that a Land Rover Dicso would be considerably more capable of towing a caravan of 90% of its own weight than, say, a large estate car which although it may well have enough bhp on tap would also have a longer wheelbase and longer overhang behind the rear wheels - both of which have a huge impact on stability, handling and manoeverability.

I have seen too many cars and caravans on their side in a ditch over the years but cannot recall seeing a big 4x4 and caravan in such a predicament?

I thought that all cars came with a maximum towing weight allowance these days as well as a maximum nosewight and if these two figures are incompatible with the chosen caravan it can only be a disaster waiting to happen?

Towing is not really within my area of knowledge these days - but common sense is?

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Keithl - 2010-04-12 1:03 PM
Balliol - 2010-04-12 11:49 AM My own towcar (Discovery TD5) has a maximum towing weight of 3,500kg. on a kerb weight of about 2,200 kg., i.e. 85% ratio.
Hi Balliol, There's a slight error in your calculations here I'm afraid. The figure should be the fully laden weight of the caravan as a percentage of the kerb weight of the car so in your case this works at a maximum possible 159%. Keith.

A slip of the finger, I think.  I believe Balliol is referring to "maximum train weight" (i.e. the combined actual laden weights of towcar and trailer), not the weight of the trailer alone.

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  • 3 months later...
Brian Kirby - 2010-04-12 1:05 PM

There is one other often forgotten rule of thumb, which is that the noseweight should be about 7% of the ALW of the caravan.  This is also relevant to stability, and because many modern cars have hitch weight limits of 50Kg, should logically restrict the ALW of a caravan towable by such vehicles to a little above than 700Kg.  In Europe, where higher towing speeds are common, the recommended noseweight is 10% of ALW.

Although technically correct Brian it is often impossible to achive these figurers due to the design of the caravan.The Lunar we had when loaded had a nose weight of 220lbs (a few years ago) Lunar's max recommended was 160lbs I carefully reloaded the van taking spare wheel etc., out of the gas locker and putting it in the van over the axle. First trip on a French Autoroute I had the most almighty sway, stopped threw everything back in the locker & it towed fine for the next 10 years.The last caravan we had was a Hobby, Gross weight 1350kg with full gas bottles spare wheel & loads of junk including cast iron bar-b-cue in the gas locker nose weight was a max of 35kg sounds light but it towed like a dream.
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  • 2 months later...
  • 1 month later...

Hi to you all out there.To some of you,Yes,it's Me Again.

It is my personal opinion that the 85% should not be messed with,unless is is a reduction. In real terms whilst caravan & tow vehicle technology has come on in leaps & bounds,the human element hasn't. Beginners to caravanning haven't & won't always have the benefit of technology,nor the money to afford all of the "Essential Toys" to get them out of scrapes. That only comes with experience & bigger pay packets. As good as technology is,it won't tell you that it is about to fail,it just does it. You will only see the light (on the dashpanel ) if the bulb hasn't died. A novice with a caravan on the back that exceeds 85% and is pushing it "because he/she now feels confident" after all of of the first 100miles or so of his/her maiden outing with the outfit. Then suddenly,something goes wrong,a sudden tyre deflation or a truck gets to close,the driver was using his lap-top on the steering wheel or having his Fast-Food Breakfast(FAST, yes,on the move) or both whilst aiming the truck with his knees. Then BANG,the outfit becomes a contender for Strictly, but with a load of F-in & G-effin. The only musical input is then at the Cremation or if there is enough left,a funeral.

Oh,while I am at it. Towing above 100% of kerbweight,no matter how clever you think you are,on the Queens Highway (don't be smart & say it may soon be Charlies)is NUTS.

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  • 7 months later...

A friend of mine is a Police Traffic Officer and often takes part in roadside or motorway service areas exercises, checking on max weights of loaded vehicles. When confronted with a poorly matched or incorectly loaded towing rig or even overloaded rig ,he can at present "advise " the owner of their ways and lighten the load there and then till safe ....but should he encounter an incident caused by the above circumstances..then he will proscecute. Also be advised that your vehicle and caravan insurance is more likeley than ever be declared null and void through you disregarding "reccomended" advice and overloading your rig. All the info. you need is in your car and van tech. manuals.

So is 90% worth it ?. I believe that my hobby is to get away from the restraints of home and as my van has the kitchen sink already in it ...why do I need to carry the rest of my world with me with my Vauxhall Vectra 2.2 and Vanroyce EK 450.

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I also think the guideline of 85% is reasonable for newcomers, I believe it helps with the tail waging the dog principle,

once they have gained towing experience then its up to them on what % they feel comfortable with

 

Paul

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  • 3 weeks later...
Brian Kirby - 2010-04-12 1:05 PM

 

  In Europe, where higher towing speeds are common, the recommended noseweight is 10% of ALW.

 

That does not stack up with my experience of German Caravans. Both my previous 1700 kg and present 1900 kg Hymers have a 100 kg upper limit and a sticker quoting [my translation from German] that the noseweight "should not be under 4% or 25 kgs whichever is the higher".

 

If it were anyway near 10% then the standard 50mm Dia hitch that are limited to an "S" value of 150kgs could not be used; precluding normal cars.

 

Returning to the original question, what is "safe" or not is wholly dependent on the dynamics of the unit.

In the physics of that are many factors that control the core issue, the natural frequencies of the unit, of these the yaw frequency being the prime one that worries us.

They are going to be unstable and thus not "safe" at some point, the art being to limit the variables so as not to encounter and excite the natural frequency.

Weight match is but one factor but I suggest one given totally disproportionate importance, probably as its one of the few tangible ones. The dynamic lateral stiffness of the tow vehicles rear end is far more critical factor but never mentioned in the public press. However most modern normal domestic [and well maintained ] cars have a much higher rear-end lateral stiffness than was the case even 10 years ago. Technically this makes the 85% ratio vehicle of today a much safer tow car than one of yesteryear and gives sound argument to a relaxing of the guidelines. In this lateral rear stiffness area many true off-road 4X4s are worse than normal domestic cars, simply to get the requisite off-roading height clearance. These luckily are also heavy so offsetting their inherent stiffness weakness as tow vehicles.

Mega powerful short tailed, "sports" suspension, cars are good as being sporting they need high levels of lateral stiffness; add to that a sporting estate using its high mass capability over the rear axle and things get better still.

The introduction of intelligent dynamic stability systems both for towing and the caravan itself bring very powerful tools into play. A newcomer or even the experienced tow driver would be much [very much] better served by paying attention to getting those systems on board than ignorantly playing with a few % changes in mass ratio.

 

NO it is silly if expedient to stick so focused on an 85% mass ratio, where the real issues are not mentioned.

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