Interesting assertion, would you like to detail why that particular unit should be inherently unstable?
Interesting assertion, would you like to detail why that particular unit should be inherently unstable?
The very thought of towing at 100%+ , in the wet , emergency stop required,aaaarghhh. Will I stop in time. Will the tail be wagging the dog? Brown trousers! Heart in mouth!
Sorry Jezzer your methodology doesn’t suit me, in fact it scares me. Your choice. But this is a public Forum and imo we must think carefully what implications our suggestions may have for those new to our game.
Sorry Jezzer your methodology doesn’t suit me, in fact it scares me. Your choice. But this is a public Forum and imo we must think carefully what implications our suggestions may have for those new to our game.
We indeed must think carefully what the implications are, so one misleading inference needs addressing.
"Will I stop in time", that if the unit is properly maintained, should have near zilch to do with the weight ratios involved, both the car's and van's brakes should look after themselves.
There is only that small force via the overrun device to set the brakes, additionally placed on the tow car.
A wet stop will be longer, but then it occurs solo as well.
"Will I stop in time", that if the unit is properly maintained, should have near zilch to do with the weight ratios involved, both the car's and van's brakes should look after themselves.
There is only that small force via the overrun device to set the brakes, additionally placed on the tow car.
A wet stop will be longer, but then it occurs solo as well.
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You obviously haven't read what I have written-in this post-rain follows us-we drove up to Ben Nevis in hurricane Brian-we had no choice and other than slowing to 50 on motorways that had gaps in hedgerows in the hurricane I should add, and even then we had never a wobble or worrying moment-but am cautious and sensible. The awning-well that was a different matter. We stupidly put it up thinking the worst was over and had to take it down at 2 in the morning before it took itself down. The car had no issues stopping-the caravan has brakes that work in conjunction with the car slowing as is stated above, and stopping distances didn't feel much worse than unladen; while I tried to avoid it you always get some muppet who requires you to take avoiding action/emergency stop etc. The car and caravan as a unit handled brilliantly and I never experienced a waver and I use my mirrors a lot! Never had a brown trouser moment. These are facts from experience and not based on rumour or false information and I am not exaggerating in any way-in fact the opposite perhaps. The lighter Avondale was ok but it never felt quite so planted and nor did it pull so well -the car always felt like it was working harder somehow which is odd. Maybe the aerodynamics of the caravan are more important than I first thought? We always had the Duster in 4wd mode and the diff lock came in very handy on some wet sites!
There was no methodology-it was suck it and see as we'd bought the car first then caravan. We were happy to change the car if we had to but found the reverse was true. We were happier. Just goes to show it's not just a pencil and paper exercise. And if a beginner reads this I hope they would major on the fact that we checked our outfit was legal and took it very steadily to begin with. I should add we load very carefully-and mostly in the car, and I am fastidious with tyre pressures!
Sadly swmbo wanted a twin axle so the time came to sell the Duster-after 5 years we lost 5k on it-from new-and never had a fault-. The only costs were the yearly service at a fixed £149 and the petrol; it did 22mpg towing and 32 the rest of the time so a bit thirsty, but never cost a penny even the tyres showed 5mm after 36000miles!Best car we've ever had-very probably! (I have no affiliation with any car company-our other cars are Minis! and our new tow car a Navara-proving to be another good choice-SWMBO has great taste in cars!
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I fully understand what Parksy has to say about the word in question. However the subject is relevant to the topic, and I was offering my opinion on how the 85% advice/ suggestion/ recommendation has been misused and consequently has become an "end rather than a means", in too many peoples minds. I was offering an alternative approach which would reduce its misinterpretation.
It clearly is still an issue, becasue we continue to see new and old posters who seem to be placing adherence to the advice as their highest priority.
It seems necessary for me to restate my position again, that whilst I cannot accept the advice as being scientifically derived, and we know it does have its flaws, it is the only advice presently available, However it needs to be presented in a fuller form which includes references to other important factors, rather than isolation as so often happens at the present.
The advice is better than nothing! But it's naivety is showing and it needs to reviewed and to take into account the legal status of weight limits, and the amount of technical information that is now available from both car and caravan manufacturers.
To follow on from some subsequent comments:
No one can look at just a weight ratio calculation and categorically say the outfit will be stable or unstable when being driven. To do so ignores all the other factors, some of which are variables such as speed, road conditions and driver habits.
It is however well proven that as the speed of an outfit increases the forces the trailer produces on the tow vehicle also increase. In fact the forces will be proportional to the mass and moments of inertia of the trailer, but they go up by the square of the difference in speed, so at 60mph the trailer is trying 4 times more difficult to control than at 30MPH.
This is why when you might first detect instability, it only takes a fraction more speed or for the road conditions to change, to rapidly reach the point where you loose control. It is also why it is so effective to reduce your speed gently to bring things back under control.
The point is that there is far more to maintaining stability than just adhering to a arbitrary non scientifically derived weight ratio.
It clearly is still an issue, becasue we continue to see new and old posters who seem to be placing adherence to the advice as their highest priority.
It seems necessary for me to restate my position again, that whilst I cannot accept the advice as being scientifically derived, and we know it does have its flaws, it is the only advice presently available, However it needs to be presented in a fuller form which includes references to other important factors, rather than isolation as so often happens at the present.
The advice is better than nothing! But it's naivety is showing and it needs to reviewed and to take into account the legal status of weight limits, and the amount of technical information that is now available from both car and caravan manufacturers.
To follow on from some subsequent comments:
No one can look at just a weight ratio calculation and categorically say the outfit will be stable or unstable when being driven. To do so ignores all the other factors, some of which are variables such as speed, road conditions and driver habits.
It is however well proven that as the speed of an outfit increases the forces the trailer produces on the tow vehicle also increase. In fact the forces will be proportional to the mass and moments of inertia of the trailer, but they go up by the square of the difference in speed, so at 60mph the trailer is trying 4 times more difficult to control than at 30MPH.
This is why when you might first detect instability, it only takes a fraction more speed or for the road conditions to change, to rapidly reach the point where you loose control. It is also why it is so effective to reduce your speed gently to bring things back under control.
The point is that there is far more to maintaining stability than just adhering to a arbitrary non scientifically derived weight ratio.
Jezzer B, I do have to say that that you did get away with it. The ratio is simply far too high to take a risk on. As the prof says a stable towing outfit relies on a number of variables as well as the weight ratio, and what looks on paper as a good combination can be flawed, and a bad looking combination can work. There can be no doubt your ratio s were far too high and the outfit should have been unstable.
In its favour your tow car is regarded as excellent within its limits and the design is good. What you have is the rear wheels very close to the rear of the car so that the distance from the back axle to the towball is very short. This is excellent for stability which would certainly have helped.
I cannot now remember what you were towing, but I accept it was small and seems to be quite heavy for its length. Caravan weight is a bit of a double edged sword. Higher weights do mean that the caravan is less affected by side winds, but against this if it is caught there is more weight for the car to control, and I do wonder if the car would have struggled had you had a real problem.
Shorter caravan do also have a smaller flat side than larger ones, and again catch the wind less, with near 6 meters of body length ours possibly needs more weight to control it as it is far more susceptible to side winds.
I can accept that your outfit might have towed well, but it has to have been the exception to the rule, and is not any basis for advising others to ignore the weight ratio. Give that caravan to most cars of the weight of yours and you would have a seriously unstable outfit, which could be extremely dangerous. The problem is that you cannot be sure of the stability before you buy an outfit so you need to be careful.
In its favour your tow car is regarded as excellent within its limits and the design is good. What you have is the rear wheels very close to the rear of the car so that the distance from the back axle to the towball is very short. This is excellent for stability which would certainly have helped.
I cannot now remember what you were towing, but I accept it was small and seems to be quite heavy for its length. Caravan weight is a bit of a double edged sword. Higher weights do mean that the caravan is less affected by side winds, but against this if it is caught there is more weight for the car to control, and I do wonder if the car would have struggled had you had a real problem.
Shorter caravan do also have a smaller flat side than larger ones, and again catch the wind less, with near 6 meters of body length ours possibly needs more weight to control it as it is far more susceptible to side winds.
I can accept that your outfit might have towed well, but it has to have been the exception to the rule, and is not any basis for advising others to ignore the weight ratio. Give that caravan to most cars of the weight of yours and you would have a seriously unstable outfit, which could be extremely dangerous. The problem is that you cannot be sure of the stability before you buy an outfit so you need to be careful.
If I thought there was going to be a 'how to load yourcaravan'. display at a woosie fest I would turn up myself to be educated there's bound to be an expert there,
At the Woosie fest, at Pickering, the New king was presented with a set of bathroom scales, for his use to check his caravans nose weight, they were promptly broken, after a session of Buckfast wine, and crackers.
And thereby lies the contradiction that are the kerbweight fraternity. As I have already posted our Bailey Pegasus VErona at 7.17m shipping length, was a long caravan . We most definitely had emergencies-swerving to miss clowns at high ish speeds and emergency stops. 30000miles of trouble free caravanning in every weather and wind-we don't take notice of forecasts any more, as rain follows us means we have had to have had a few and in all cases the outfit behaved impeccably. Without ATC i should hasten to add. Hurricane Brian was similar to what we have today and we did Ben Nevis in that!
You clearly state the Duster has a short distance between rear wheels and towbar so therefore we have the beginnings of a scientific way of working out what might tow better/worse.
I wonder how many of the kerbweight doomsayers actually have experience of unstable outfits in the modern car world? Hopefully not many. Here on the forums and reviews our Navara was also slated as being potentially 'unstable' with a 2000kg caravan in tow. Everyone says trucks are unstable because of their lack of rear weight. Wrong again! It is rock solid and in fact I am hard pushed to remember the caravan is on the back and very glad it has a speed limiter and cruise control!
I also clearly stated that if we had felt the outfit unstable in any way on our exploratory runs out, we were in a lucky position to swap the towing car. We quickly realised that would be a huge waste of money and could have been worse-cannot imagine how it could have towed any better other than the engine had to be kept in peak power range for long hills.
Sorry folks-rant over. I don't mean to decry kerbweight as sound advice for beginners but want to make it quite clear that it must only be a sensible starting point and there must be better ways.
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As you say weight is only the starting point but it is a very important one. It is vital that newcomers understand this and all other relevant factors and is does help if they understand what makes a good tow car in terms of design. This very complex but a short overhang at the rear does help, although we have a far longer one and that car works, although others do not work as well. At that point you are looking at the suspension as well and the harder ones again should be more stable and I think the Daihatsu fits that criteria as well.
My point is that some cars perform well beyond their on paper spec would suggest and others do not. On that basis some caution is needed and keeping the weight ratio down is vital if you are not in a position to change the car.
My point is that some cars perform well beyond their on paper spec would suggest and others do not. On that basis some caution is needed and keeping the weight ratio down is vital if you are not in a position to change the car.
Yes agree, out of interest the Dacia Duster has supremely comfy suspension and has been criticised for being a bit wallowy-so that doesn't fit either! Hey ho.
I do however object to the phrase 'got away with it' in the strongest terms and find it a bit offensive. Am sure it wasn't meant like that but it implies we were acting in a manner that might leave us open to causing an issue. That wasn't the case as we were and always will be cautious with any new outfit -it is a learning curve with every caravan and car change and should be approached accordingly.
I do however object to the phrase 'got away with it' in the strongest terms and find it a bit offensive. Am sure it wasn't meant like that but it implies we were acting in a manner that might leave us open to causing an issue. That wasn't the case as we were and always will be cautious with any new outfit -it is a learning curve with every caravan and car change and should be approached accordingly.
My point is that that outfit should not have worked and I am still not convinced that if you had the start of a serious problem then that car was heavy enough to get you out of it.
I have seen someone lose it ahead of me, and believe me it was frightening for us, never mind the driver, he did have a very heavy estate which helped, but I suspect he stopped at the next services to change his trousers. Basically we were traveling at about 60 and he came past at what must have been 70 plus. He was passing two lorries ahead of us when he must have been caught by a cross wind or the bow wave of the lorry. He was swerving across all three lanes of the motorway and how he got it under control I will never know but it showed me the dangers of getting it wrong.
I have seen someone lose it ahead of me, and believe me it was frightening for us, never mind the driver, he did have a very heavy estate which helped, but I suspect he stopped at the next services to change his trousers. Basically we were traveling at about 60 and he came past at what must have been 70 plus. He was passing two lorries ahead of us when he must have been caught by a cross wind or the bow wave of the lorry. He was swerving across all three lanes of the motorway and how he got it under control I will never know but it showed me the dangers of getting it wrong.
But there’s getting it wrong and there’s getting it wrong. Your example is stupidity in the extreme. Not so long ago there was a video of a Shogun loosing it doing similar high speed antics.
From what the OP has said he had experience with the Duster and a lighter caravan before moving to a heavier van. Which whilst legal didn’t conform to the norms for outfit matching. He was prepared to upgrade the car if he didn’t feel okay with the outfit. But his experience over many miles has satisfied him that the outfit was fine. What none of us know is how far below the calamitous threshold we are. Not being test pilots we don’t explore the complete performance envelope. Which for a caravan outfit probably has far more variables than an aircraft.
Very very true; I absolutely cannot vouch for the caravan Duster outfit being stable at over 70 (officer) . I do prefer to stick to legal limits but as shown by satnav ie accurate, not speedo, at all times. Passing lorries was no issue and strong cross winds likewise-however I have always erred on the side of caution when towing and given strong cross winds and open roads with hedge gaps etc my motorcycling psyche kicks in and most definitely then would be doing lorry speeds rather than overtaking them. Just common sense really. I am sensible and it was a very stable unit even in emergency situations-ie quick braking lane change due to muppetry!
Huge assumption with its logic buried in just a mass ratio, blind of the powerful influence the overhang has, and I suspect despite the Dacia's soft vertical suspension a vehicle with a high lateral stiffness.
Choosing a long overhang vehicle which inherently is very poor in respect to optimising towing stability, then weights will be far more critical to help mitigate that.
That highlights why the mass ratio is so defended, it mitigates an otherwise unsound choice, easily made even by experienced towers.
It is obvious from the replies to this thread that the influence of weight ratios is very specific to each and every combination. While 85% is a starting point, it is entirely arbitrary. Why 85% and not 80% or 90%? It is only intended as a rough guide.
I started my caravanning career with a 100% weight ratio outfit and never came into a situation where I felt unsafe, either to myself or to other road users except. From personal experience, load distribution, speed and wind conditions had a far greater effect on stability than anything else.
I started my caravanning career with a 100% weight ratio outfit and never came into a situation where I felt unsafe, either to myself or to other road users except. From personal experience, load distribution, speed and wind conditions had a far greater effect on stability than anything else.
I would like to see people who have felt their outfit unstable, post their combos-be interesting to hear from anyone and we could look at why-weight, aerodynamics overhangs etc?
We saw a 'toilet block' being towed by a disco-should have been rock solid on twin axles-and it was all over the place-wonder if it was the totally box type shape-absolutely no curves at all. And the tyres didn't look flat.
We saw a 'toilet block' being towed by a disco-should have been rock solid on twin axles-and it was all over the place-wonder if it was the totally box type shape-absolutely no curves at all. And the tyres didn't look flat.
The reason the twin axle toilet block was all over the place was the tyres would not be inflated to the correct pressure in other words flat, my mate was on that kind of work delivering toilet blocks and work cabi ns to building sites and festivals he never check a. tyre in his life he just went in a compound picked up what he wanted and off he went I doubt if they had been emptied from the last job,
I appreciate the points made but the simple point is that if you do need to have the car control a swaying caravan then a heavy enough tow car is vital. Unless you get into that situation then you will never know if your car is up to this.
I appreciate that my example was extreme, it was more to illustrate how frightening the situation is than a comment on the vehicles or driver. Perhaps I did not make this clear but having seen it I know just what the dangers are. Frankly we were expecting the outfit to turn over in front of us, but the driver was lucky in that all three lanes were clear alongside him and the car was heavy enough to just hold the caravan.
I appreciate that my example was extreme, it was more to illustrate how frightening the situation is than a comment on the vehicles or driver. Perhaps I did not make this clear but having seen it I know just what the dangers are. Frankly we were expecting the outfit to turn over in front of us, but the driver was lucky in that all three lanes were clear alongside him and the car was heavy enough to just hold the caravan.
The Industry advice is that even experienced caravanners should not exceed a towing ratio of 100%. Poorly informed commentators have added the idea that at 100% ratio the mass of the caravan now matches the car therefore the forces the caravan can produce will overwhelm the cars control of the outfit, commonly referred to as "The tail wagging the dog"
The implication is that at under 100% the tail cannot wag the dog becasue it is lighter so you will be safer. This is an unsound connection of ideas.
There will be plenty of readers who will attest to having had early signs of instability whilst their outfits are well below 100 and even below 85% industry ratio.
Weight ratios are only one factor that influences an outfits characteristics, it is empirically known that higher ratios are generally less good, but they have to be considered within a context of other factors, many of which are uncontrolled variables, and arguably have a greater influence on stability than just weight ratios.
Large weight ratios may not be ideal, and it may be counter to advice, but as the advice is only advice it should not be used on its own to condemn an outfit.
The implication is that at under 100% the tail cannot wag the dog becasue it is lighter so you will be safer. This is an unsound connection of ideas.
There will be plenty of readers who will attest to having had early signs of instability whilst their outfits are well below 100 and even below 85% industry ratio.
Weight ratios are only one factor that influences an outfits characteristics, it is empirically known that higher ratios are generally less good, but they have to be considered within a context of other factors, many of which are uncontrolled variables, and arguably have a greater influence on stability than just weight ratios.
Large weight ratios may not be ideal, and it may be counter to advice, but as the advice is only advice it should not be used on its own to condemn an outfit.
Talking about the tail wagging the dog and this is nothing to do with Caravaning but still of interest regarding weight ratios, my first job back in the 60,'s was working for a heavy haulage company and an example would be of braking weights would be for every twenty ton of load we would have add five ton of ballast to the ballast tractor( that's the front bit that pulls the load so for a 150 ton pressure vessel we would add about 35 ton of ballast to the tractor so the gross weight of the tractor would be 55 ton still a lot lighter than the load and bogies additional braking would be provided by an extra tractor coupled to the rear of the load, also combined braking would be 76 wheels all braked, a little bit different than trying to work out you 85% caravan matching,
Nope - There are some "Show me/Tell Me" questions during the test, but these are banal questions like "Where is the washer fluid filler?". The test purely shows that you are competent to tow a large trailer.
Just the once in 2 years of 'big' caravan ownership: Crosswind on an elevated/exposed section of dual carriageway (50mph limit) instigated some 'instability'. I have a 76% (I think) ratio, caravan was light due it being towed to the dealers. and car was not packed with gear. The car started to get "wagged" by the caravan but it immediately stopped once power was removed. (No ATC but Alko AKS + shocks fitted.) It was so minor that I had time to ask my passenger if they felt the movement and dashcam had no visual record.
I think Camel has made a point with quite a lot of relevance
Whilst it's fairly obvious a car and a caravan is very different to a double tractor pressure vessel trailer, there are perhaps more similarities than might seem apparent.
In both cases the towing vehicles need to have enough power to move the load, and to have enough grip to start and stop the outfit.
With such heavy loads the tractor unit need the enough weight to force the tyres into better contact with the road to increase the grip without skidding.
There has to be concern given to taking corners, where the mass of the load will try to continue in a straight line, the tractor unit needs enough authority to be able to pull the load round securely.
Incidentally a quick calculation based on the figures you gave; You pressure vessel with a weight of 150 Ton's needed two tractor units of 55 Ton's each that gives a towing ratio of 150/110 which is 136% That is not massively differnt to the caravan industry advice of 100%
One of the reasons why the pressure vessel was considered safe enough to travel, would be its limited speed. By keeping the speed quite low (I'd guess you were told to keep it below 15mph) the disruptive kinetic energy that builds up due to motion and the forces it creates are also kept low. If you doubled your speed to 30mph those same forces will grow by the mathematical square of the speed difference and would stand a better chance of disrupting the safe tow.
Caravan outfits are just the same, at low speeds the disruptive forces are small. For example if an outfit were travelling at 15mph and one caravan wheel rides over a bump, it will momentarily lift that side of the caravan. That motion will be translated to a sideways nudge at the coupling hitch which will try to move the car sideways. At low speed the nudge force generated it will small and the car will easily accommodate it. Let us suppose the nudge is 250N (or about 25kgf) If the same bump is traversed at twice the speed 30mph the force produced will follow the squared law and teh nudge will be 250 x (30/15)squared = 1000N. A bigger nudge. If the same bump was traversed at 60mph the nudge will increase to 4000N which could well be enough to cause the cars wheels to skid sideways and loose control
This illustrates why speed is so paramount to stability issues. and weight ratio's less so.
Does anybody feel his pressure vessel at 136% towing ratio was unsafe?
Whilst it's fairly obvious a car and a caravan is very different to a double tractor pressure vessel trailer, there are perhaps more similarities than might seem apparent.
In both cases the towing vehicles need to have enough power to move the load, and to have enough grip to start and stop the outfit.
With such heavy loads the tractor unit need the enough weight to force the tyres into better contact with the road to increase the grip without skidding.
There has to be concern given to taking corners, where the mass of the load will try to continue in a straight line, the tractor unit needs enough authority to be able to pull the load round securely.
Incidentally a quick calculation based on the figures you gave; You pressure vessel with a weight of 150 Ton's needed two tractor units of 55 Ton's each that gives a towing ratio of 150/110 which is 136% That is not massively differnt to the caravan industry advice of 100%
One of the reasons why the pressure vessel was considered safe enough to travel, would be its limited speed. By keeping the speed quite low (I'd guess you were told to keep it below 15mph) the disruptive kinetic energy that builds up due to motion and the forces it creates are also kept low. If you doubled your speed to 30mph those same forces will grow by the mathematical square of the speed difference and would stand a better chance of disrupting the safe tow.
Caravan outfits are just the same, at low speeds the disruptive forces are small. For example if an outfit were travelling at 15mph and one caravan wheel rides over a bump, it will momentarily lift that side of the caravan. That motion will be translated to a sideways nudge at the coupling hitch which will try to move the car sideways. At low speed the nudge force generated it will small and the car will easily accommodate it. Let us suppose the nudge is 250N (or about 25kgf) If the same bump is traversed at twice the speed 30mph the force produced will follow the squared law and teh nudge will be 250 x (30/15)squared = 1000N. A bigger nudge. If the same bump was traversed at 60mph the nudge will increase to 4000N which could well be enough to cause the cars wheels to skid sideways and loose control
This illustrates why speed is so paramount to stability issues. and weight ratio's less so.
Does anybody feel his pressure vessel at 136% towing ratio was unsafe?
Ignoring weight ratios , yes I have had a snake, decades ago. Why? I can only conclude the caravan was a short 12 footer , on a Peak Chassis. Over the years my caravans have got longer and longer. Like a pendulum , the longer imo , the less severe swing movements.
Contrary to what some may say my current TA at 7.98 mtrs is one of the most stable caravans I have ever towed. In fairness the SA before was very long . Only once did I feel a twitch when I was overtaken by a National Express Coach.
It goes without saying correct loading is crucial to a safe tow. I make no comment about ratios in this post.
In fairness to all the previous posters on this thread the Dr Jos Darling at the University of Bath has carried out extensive research into “ trailer” caravan stability. From what I have read , I’m not the only one on here, amongst the numerous factors , length of trailer is important. But so is correct loading. I have towed at near on 100% but maybe I did think about all the other factors each one being relevant.
So maybe , on reflection Jezzers views may just be tenable from where he sits.👍👍
Contrary to what some may say my current TA at 7.98 mtrs is one of the most stable caravans I have ever towed. In fairness the SA before was very long . Only once did I feel a twitch when I was overtaken by a National Express Coach.
It goes without saying correct loading is crucial to a safe tow. I make no comment about ratios in this post.
In fairness to all the previous posters on this thread the Dr Jos Darling at the University of Bath has carried out extensive research into “ trailer” caravan stability. From what I have read , I’m not the only one on here, amongst the numerous factors , length of trailer is important. But so is correct loading. I have towed at near on 100% but maybe I did think about all the other factors each one being relevant.
So maybe , on reflection Jezzers views may just be tenable from where he sits.👍👍
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