Kerbweight
Comments
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But fitment of a stabiliser in any form does not affect the load that may be towed. It only affects the speed at which the load may be towed, and that only in Germany. Just as an example, even if a caravan is fitted with AKS (or ATC) it still wouldn't be permissible to be towed in Germany at 100km/h if it's not fitted with shock absorbers (dampers) as well.
Stability of an outfit is dependent on a lot more than weight ratio, fitment of stabilisers, etc. The thousands of possible combinations and permutations of towcar and caravan outfits would result in an almost infinite number of tests that would have to be carried out to establish what you are asking for - a task that would be completely outside the resources of the NCC, or for that matter, any testing facility.
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Trailertenter, The NCC are not responsible for setting towing legislation and legal towing limits so however much testing they do or don’t do, will make no difference to the legal position with an outfit. You really are way off on a tangent with this issue and in the spirit of helping i suggest you buy a beginners guide to caravanning that will hopefully explain what is LEGAL and what is recommended in ways the various responses to your query have thus far clearly failed to do.
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I agree with that, but even as a trade body they don't seem to be doing a good job as they throw up barriers to people purchasing caravans for no good reason. This rule, and the difficulty in reconciling it to the legal requirements and the numbers on the V5 and VIN, actually increases the cost of buying a caravan and therefore reduces demand. E.g. in my case I have now decided I don't need to upgrade my car and can therefore go ahead and buy the caravan, because I can afford the caravan but not an upgraded car and caravan. But all the outfit matching tools refer to this 85% rule and were telling me I needed a bigger car, in which case I would not be able to afford the caravan. I really have no idea what they think they are doing.
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But the NCC didn't dream up the 85% weight ratio recommendation. That was done by its members. Nobody says that you need a bigger car if your current one doesn't fall within the 85%. The decision is wholly up to you. It should be obvious to anyone that the stability of an outfit depends on more than just weight ratio. Therefore, a blanket figure can only be arbitrary. It is only meant as a starting point for anyone who is new to the field of caravanning and unsure of himself. I started my caravanning career with a 100% weight ratio outfit because that was the only way to go with the car I had at the time and a caravan that was large enough to accommodate the family. I never regretted the move although I do admit that a heavier car later made the towing experience more relaxing.
I think you are attaching too much importance to the recommendation. A recommendation can only be just that. If you've had lifelong experience of towing at 100% and you have always felt comfortable with it under all road conditions, so be it, but that's no reason to raise the figure from 85% to 100%. One is perfectly at liberty to ignore the recommendation so long as one is satisfied, by one's own experience, that a higher figure is appropriate under all conditions that one encounters. It may mean, for instance, that one needs to break off a journey due to high winds or other inclement weather or road conditions before those outfits with lower weight ratios.
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You keep talking about rules but remember it is not a rule or a barrier but a safety guideline, and I think if I recall correctly is that the 85% guideline is aimed at novice caravaners and it does say as you become more experienced one can tow at 100%.
I think most do believe that the car should be heavier than the caravan and as a starting point for people new to towing it can certainly do no harm. Towing does take some learning and erring on the side of caution for novices until they get more experience is probably a good idea. Of course there is nothing to stop a complete novice ignoring it.
As I said you can totally ignore it too as long as you keep within the law so why get so upset on here, write to the NCC.
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The CAMC outfit tool is rubbish and i would use the Towcar website tool, far better. However you really need to read slowly and carefully what Lutz, myself and others are pointing out about the NCC GUIDELINES - THEY ARE NOT RULES!!!!! The only ‘rule’ is being legal. I really struggle to understand why you make this so difficult, it is not the NCC’s fault or problem if you want to buy a caravan above the 85% ratio. If it is legal and you are confident with towing what is your problem?!
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What a shame that, in attempting to help, posters have been drawn into this ridiculous series of posts from Trailertenter.
I think his thread "Twin axle stability and 85%" shows that all he is after is for someone to say its OK to do what he proposes but clearly has doubts about..
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Yep, I realised that way back. I'm only prepared to have my advice rebuffed and argued about for so long and then I leave them to it.
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I can speak from experience of towing single and twin axle UK and European vans with and without ATC at 70 - 100% of kerbweight with full fat 4x4s, 4wd SUVs and normal cars. Not a scientific study but towed a bit.
My observations are that each combination of car and van has a different stability dynamic, the cars mass is an important part of that dynamic along with the cars suspension set up, ability to take nose weight, tyre pressure and the distance from the rear axle centre to the tow hitch, daresay there are many others. The most dominant factors I have found are speed and steering input. Regards the van, obviously loading has a large effect along with drawbar length and aerodynamics. I have found that my outfits stability since 2010 better than from say 1990-2005.
I found towing at 100% of kerbweight with ATC on modern single and twin axle to have similar stability however the twin does bounce and jiggle the car more whereas the single axle provoked more wallowy ride. I did find ATC intervened frequently mostly on single carriageway A/B roads where cornering steering input and poor roads induced some lateral force and perceived transient instability. This did not happen when towing at 80% load irrespective of single or twin. In the end for the feeling real or not of better stability and the safety of my family I settled for a more capable heavier tow car. Why? ATC can fail, it also relies on well maintained and adjusted drum brakes. Like ABS it's there for emergency not as a regular aid. Personally I would not exceed 100% of declared kerbweight as instability is not a pleasant experience.
Yes cars are capable of towing to their max rating but that's just it's hill start ability not the capability to control it's trailer in a high speed emergency downhill manoeuvre where the laws of physics will inevitably win. Consider that the larger the towed mass for a given car and speed the closer to the threshold of instability you are.
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Under normal conditions, ATC should never deploy. It is only intended to provide assistance in case of necessary sudden and unexpected evasive action. If it does more than that you weren't driving to suit the conditions. One should always be driving as though ATC weren't fitted, without having to rely on such a feature.
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I had the ATC trigger towing a t/a through some French village chicanes a few years ago, the road geometry and layout seemed to create the effect of a snake. Otherwise only twice had it perform, both in horrendous cross winds, once caught by a completely out of the blue gust on the M62 on a very hot day in mid summer and the second time we were ‘overtaken’ by a gathering winter storm and had a very hairy, very slow drive from Berwick upto Edinburgh.
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Some may not even notice ATC deploying. I guess it will deploy more frequently as the threshold of instability is approached from whatever cause, weight ratios, loading, speed/steering input or indeed external winds or road conditions. I have noticed uneven road surfaces causing deployment even at relatively low and certainly safe speeds.
I think the caravan ATC systems are fairly crude compare to cars
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AD, bit puzzled by your comment, which van do you have? I know of at least 2 people who had ATC retro-fitted to existing vans (with Alko chassis) they owned.
Viatorem, agree re crudeness but its better than nothing and in my view such systems should be mandatory on new vans with perhaps an allowance of 2 years for owners to retrofit systems onto vans upto 10 years old (although i agree in the absence of caravan MOT’s am not sure how that could be enforced). And for the avoidance of doubt i am not advocating caravan MOT’s!
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I have had two c/vans with ATC fitted and know of a couple of times it has activated once on our previous van coming out of a left turn a bit fast into a gap in traffic, and on out current van when getting caught in the "wash" when overtaking loaded car transporter
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Thank you, along with Lutz and one or two others this is useful, although what you are saying is that single/twin and ATC/no ATC does not make a big difference in practice. Overall I believe the more useful definition is to say the actual weight of the vehicle including passengers and luggage excluding the fuel tank as that varies compared to the actual weight of the caravan and whatever load it carries. However, on the other hand my legal towing limit is much higher than "kerbweight" and I have seen the explanation given by Nissan of how they calculate the legal towing limit which seemed to me to be a more rational and tested way of doing it than this very general rule of thumb. So I will start off with my existing car whose towing limit is 1,800kg versus MPTLM of caravan of 1,700, although I do not intend to load it so the actual weight is more like 1,550. I'll then drive it home from dealer, then drive it out to storage and see how it goes.
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ATC cannot make any difference to any weight! I still do not think you understand. Weight is weight. ATC is there purely to help lessen the onset of a snake or instability, it is not a pre-emptive or dynamic device, far too crude for that. However good luck with your new van.
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Weight ratio has only theoretical significance anyway, so it really doesn't matter that kerbweight is used. At least it enables worse case scenario comparison between outfits. Above all, it is important that there is a common understanding on which value to use. Using actual weights has the disadvantage that they are variable, thus preventing any possible comparison.
The towing limit, by the way, is not calculated, but determined by test.
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Re the towing limit being determined by test, yes that is what I also understand after having watched a video by Nissan explaining how they test their cars for maximum towing limit. I understand the point about "kerbweight" being a worst possible scenario (although it isn't as it also includes 50kg for fuel which gets depleted en route) but that should not detract from the actual physics which means the total actual weight of the tow car that will remain unchanged through the trip (i.e. excluding fuel but including everything else) should be compared to the total actual weight of the caravan, with some caveats around how the load is distributed in the vehicles. I see the law refers to actual weights not plate weights when it talks about gross train weight, which is a rare bit of logic creeping through.
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I don't know where you got the information from that kerbweight includes 50kg for fuel. It actually includes a full fuel tank. However, kerbweight doesn't include the driver so any weight ratio calculated on that basis Is not really representative of actual conditions, but at least such values are comparable between different outfits, even if they not, strictly speaking, realistic. But nothing more is expected of the weight ratio recommendation. It has no scientific basis and makes no claim to that effect. It is not intended as anything more than a quick rough guide for a novice without making things too complicated for him or her. It only contributes to stability to a limited extent anyway. That's why it has no legal substance - at least not in the UK.
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Just for my own sanity, I wanted to check kerbweight definition, becuse I was sure that I had seen [on a Tow check website, IIRC] a 'definition' that it included 75kg for the weight of a driver. I can't find that particular definition [only made a quick scan] BUT I found another variation of 'kerbweight includes 75kg for driver AND luggage' and claims to be the EU weight used for emissions testing!
For such a 'simple matter', as I believe it was referred to very early in the thread, it's caused a lot of discussion and a fair few definitions. I have towed a folding caravan for 2 years and a small touring caravan for 18 months [plus trailer tents and trailers for many years], so use the 85% 'Rule' as a guiding principle for my novice status. Current set up is just over 77% of kerbweight so my peace of mind is boosted by a 10% margin. In practical terms, it reduced the weight to belugged over the Pyrenees on the ascent; and gave less weight shoving me on the descent [although the folding caravan was worse on the descent because the 'aerodynamics of a loaf' feature was absent!
Steve
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There can only be one definition of a term such as kerbweight. Anything else makes nonsense of the word 'definition'. If there were more than one definition then no-one would know which one is talking about. I therefore think one should leave kerbweight as defined in UK legislation and that is what I quoted in my original post. It does NOT include the driver.
The so-called EU weight that you refer to is not kerbweight. In fact, the word 'kerbweight' is nowhere to be found in any EU regulations. They only talk about 'mass in running order' and 'actual mass of the vehicle'.
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I used the term' definition' in a semi- ironic way to highlight the point made in one of the early posts that described kerbweight as [sic] 'something that is not difficult to understand' but which has generated almost 9 pages of comments and debate.
The 'definition' to which I referred came from evo.co.uk and refers to numerous definitions, including dry weight, kerbweight, DIN kerbweight [Car weight including all fluids and 90% fuel level] and EU kerbweight where the reference to the driver + luggage allowance of 75kg is used for emissions testing.
I know we are no longer EU Members and I acknowledge that therecan only be one definition of a term for strict legal and/or academic purposes; although you can argue that in a differnt context, an expanded or reduced 'definition' is appropriate.
But, in the real world, the newcomer to towing will search for what [s]he needs for a 'definition' of kerbweight and will be bombarded with internet search results, forum comments, car salespersons' [heaven forfend] advice, plus that of their mate down the pub who has 'towed a caravan for 45 years and never had an accident, don't bother with noseweight, and just kick the tyres when we go on holiday'. None of which is clear, all of which is fine; until the accident happens and the Traffic Police close the road for investigation ...
I am happy to use the kerbweight guide as the basis for safe towing limits and cannot see myself exceeding the 85% figure, preferring my current safety margin of some 10% beneath that level, happy that more experienced towers will tug up to 100% without a qualm.
I shall withdraw from this Thread now.
Steve
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This discussion once again highlights the dangers of treating the Club’s weight ratio guidelines as either ‘law’ or some sort of magical safety net without equal emphasis on and due regard to all the other factors which contribute to safe (or dangerous) towing. To assume that 85% is magically safe and 86% is suddenly dangerous is naive. Too little emphasis is placed on nose weight, weight distribution and balance, tyre pressures to name just a few. There is no point in towing at 85% if all the other factors are ignored. Who is taking risks, the person towing a well balanced and legal outfit at 100% or the person towing an outfit at 85% but with total ignorance of nose weight, balance, car tyre pressures etc? Personally i think the Club are negligent in not emphasising ALL the factors involved and hiding behind 35 year old data.
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