Kerbweight
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A big enough tail will always wag the dog.
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From what I can see in the NCC towing guide, the whole 85% concept is badly defined. Kerbweight, whatever that means, should refer to the weight of the laden car when towing. The NCC definition of it being the car and driver only is very conservative, I guess they are just trying to keep things as simple as possible and whilst you can be sure a car will have a driver then all other variables such as number of passengers, weight of luggage, etc will be different for each journey so to make things easy (and probably to protect themsevles legally) they say that kerbweight is the car and driver only. So if you load the car to within its Max permissable Mass with luggage, people, tanks of water, whatever, that gets ignored in their calculation which makes no logical sense. Twin axle, ALKO ATC, all is ignored. So I view this as highly outdated advice and will simply follow the legal requirement instead, my car has a max permissable mass of 1960, max towable mass (braked) of 1800, the caravan MIRO plus mover weight is 1545 so I am well within limit and if I want to be safe I can add ballast to the car, but on the other hand I have a twin axle and ALKO ATC so I should also get credit for that.
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Also, I note that the NCC 85% guidance is supposed to concern stability, whereas the legal regulations concerning technical permissable towable mass are determined based on hill gradients. So we are talking about two different things. The empty car (with a driver of course) can haul a braked trailer of technical permissable towable mass from a standing start up a 1 in 10 gradient. So in my case my car can pull a 1800kg braked trailer up a 1 in 10. As to the "stability" mentioned by the NCC, this seems to be a very vague concept, but to completely ignore the difference in stability between single and twin axles seems a major omission that undermines the usefulness of the advice.
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You were talking of the 85% recommendation, not stability.
Of course it makes a difference how the trailer is loaded but nothing on earth will alter the fact that too heavy a trailer will potentially overwhelm the towing vehicle and be dangerous. I repeat, weight is weight.
As for stability, some people say a TA is more stable, others say not. My own experience says not. Tbh, the manoeuvring issues of a TA outweigh all else to my mind and I'd stick with the lighter and easier SA.
If I may say so, you seem to have become unduly bogged down with the 85% figure. It's not hard and fast and as long as you're within range of it, you should be OK as long as you know what you're doing. Don’t forget the kerbweight of the car cannot be altered by loading it and it is the loaded MTPLM weight of the caravan you need to consider, not it’s unladen weight.
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Hi, I am not sure which part of 'guide' or advice' is not clear but that's exactly what you are dealing with.
One suggestion from me would be to see what Lutz says and take that as your benchmark.
Many people appear uncomfortable making decisions around weights but, as pointed out earlier, if you need more clarity it is there in the figures stated on your vehicle.
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Whatever way you calculate things we must be doing something correct as the vast majority of us will get to the end of caravan ownership without a major mishap.
Colin
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@ Tinwheeler the NCC, who provide this 85% advice, make clear that it is for stability.
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While the regulations only specify technically permissible towable mass based on hill gradients, any self-respecting car manufacturer will also take into account other parameters, such as braking performance and handling characteristics, in his towload limits.
If the NCC interpretation of kerbweight includes the driver then this is not in line with the legal definition.
Using actual vehicle weight figures when establishing weight ratios may sound more to the point, but it does make comparisons between outfits based on published data difficult when actual figures are not available. One has therefore chosen to rely on a worst case scenario, with the heaviest possible caravan in conjunction with the towing vehicle in its lightest possible condition. The actual weight ratio will always be more favourable. As any recommendation, be it 85% or any other figure, is purely arbitrary anyway. It's only meant as a rough guide or starting point, not to be taken too meticulously. After all, it's not a legal limit, at least not in the UK.
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Stability as in the heavy tail not wagging the lighter dog.
All I can suggest is that, as you have asked questions on a Caravanning forum where members have hundreds of years experience between them, you could consider the replies have some credence.
Good luck with your venture.
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ISTM that our erstwhile trailertenter is endeavouring to massage the figures to attain something close to 85% to justify using his existing, possibly light, vehicle to tow a heavy caravan upon which he has set his heart. Lies, damn lies and statistics spring to mind.
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@cyberyacht Yes, there is an element of that, but in doing so I am trying to dig down into what these numbers really mean and how they are calculated. My conclusion is that this NCC towing guidance is not fit for purpose and I will follow the legal requirements but ignore this 85% suggestion, which is kind of superstition at worst and rule of thumb at best, marauding as fact. We should not be misled into buying bigger cars than we need. Rather than upgrading to a more polluting car I can continue using the lighter one. Its also annoying to me that other "safe matching" tools use this 85% suggestion in their analysis of how safe your outfit is. "Kerbweight" is useless as a definition, the forces of physics do not care if the mass of the vehicle pulling is composed of cast iron engines, human beings or tanks of water. Weight is weight as someone else said, the only issue is to make sure it is properly distributed, but it should not be ignored. To say kerbweight is only ever calculated as the car and driver, when it could be 300kg heavier with passengers, luggage and whatever else, is ridiculous. This is why there is such a big gap between the legal limits and the limits imposed by the 85% suggestion. My legal towing limit is 1800kg, but as its mass in service is only 1,548 then using this 85% rule would give only allow a MTPLM of 1,315. That's an enormous difference. The key is to know how much weight is in your car, how much in the caravan, and stay within legal limits. I would have hoped that over a 30 year period the NCC advice could have kept up with advances in technology (cars are delivering more power for less weight) and innovations like twin axle, etc instead of remaining unchanged as it is becoming irrelevant. It doesn't say a lot about the industry that they can't sort this out and at least use the same definitions as are used in the V5 and VIN plate instead of vagaries like 'kerbweight'.
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"...then using this 85% rule would give only allow a MTPLM of 1,315."
which sounds sensible to me for the car in question.
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Superstition. The car has been tested to within an inch of its life dragging 1,800kg around the french alps for 3 weeks. that's how it got a legal braked towing limit of 1,800kg. so how can 1315kg possibly be reasonable?
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You just don’t get it, do you?
I hope your exaggeration never comes back to bite you.
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Does any of this really matter. Each vehicle has a max towing limit as designated by the manufacturer. This might be anything from about 40% in the case of electric vehicles to 150%+ for some 4wd.
It does not matter a hoot how you define kerb weight, if you exceed the manufactures maximum then you are towing illegally.
Colin
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Bear in mind that the picture can also be the other way round. Some cars have a maximum permissible towload that is less than 85% of their kerbweight.
Whether an outfit is safe or not depends more on the ability, due care and attention of the driver than a weight ratio.
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Regarding stability and weights I always consider the difference in safety between carrying a 25 kg bag of sand and a 25kg sheet of ply in heavy wind. Weight might be weight but only one of them is likely send you to your death over a cliff.
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With due respect if you are happy to bat away & argue against every attempt to help why not just do your thing the way you see it & enjoy👍🏻
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Lutz, to give an extreme example, do you think an empty low loader car transporter at 1200kg would not be a safer tow than a 1200kg 2.5m high empty box trailer.
The shape/profile has to enter into the equation.
Colin
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I had a dozen happy years towing a small Eriba all over Europe with a Freelander- the caravan was exactly half the weight of the car. That ratio works a treat - especially with a 2.2 litre engine under the car lid.
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As I said, one has to drive to suit the conditions. This may mean that to tow a 2.5m high empty box trailer safely you would have have to reduce your speed to 40mph whereas the low loader can be towed safely at over 60mph, but if that is taken into account, one is as safe as the other.
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superstition? I think that is really not the appropriate word here.
The thing is you use whatever towing rule/guidance/percentage you want. Within the law no one, NCC, club... is forcing you to use any figure in your towing. Do what you think best.
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The whole conversation is highly unscientific and that is the problem with this 85% guidance, it also lacks any scientific basis. For example, if you look in the ALKO caravan chassis brochure, there is a section on the weight reduction you can legally get from a stabiliser device like the AKS. ALKO calculates that having a chassis with an AKS stabiliser allows you to tow an additional 20% of weight from the same tow vehicle. The example they give is a tow car weighing 1,600kg can tow a caravan maximum laden 1,600kg with a stabiliser but only 1,280 without, i.e. the stabiliser allows an additional 320kg. ALKO know a thing or two about trailers. None of this information is taken into account in the 85% rule. Its a dinosaur. See page 44-45
https://www.alko-tech.com/sites/default/files/uploaded_files/EN/499668_htk-caravan_12-2018_en.pdf
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The trailertenter with no name seems determined to operate on the "what can I get away with" rather than approaching from" what is safe". We are a year into Covid with numerous restrictions and lockdowns because people have taken a similar stance regarding prudent rules. When you are on the road just stay away from me!
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I think that you have completely misunderstood AlKo's publication, which is, admittedly, misleading. The regulation referred to in their publication applies only to Germany and fitment of a stabiliser is only to one of several requirements that must be fulfilled in order to allow towing at 100km/h instead of the regular 80km/h speed limit that applies in that country. A towing vehicle fitted with an electronic Trailer Stability Assist feature is equally acceptable as an alternative to an AKS unit.
If one is prepared not to exceed 80km/h there is no weight ratio restriction.
It does not, in any way, allow higher towloads than what the manufacturer of the towing vehicle specifies. It certainly does not allow you to tow an additional 20% of weight with the same towing vehicle, as you suggest.
Note that an 85% weight ratio recommendation is unheard of on the Continent. Other than in Germany one is limited only by the vehicle manufacturers' specifications.
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In my view Trailertenter, you are hopelessly over complicating this by mixing what is legal with the 85/100% ‘guidelines’, single/twin axle, ATC etc etc. I do agree with you the 85/100% guidelines are out of date insofar as not reflecting safety improvements, AND they are too often mis-understood as having a legal standing. I would add that sur le continent there are no such guidelines (as Lutz also refers). The starting point is simple legality, is the car/towed unit (caravan) combination legal and that is straightforward to establish. Second, is the driver qualified to drive it (B + E license). Following that is checking your insurance (some insurers limit the cover to 100% max ratio) and are you, the driver, confident with the resulting set up? The issue of whether ATC adds 5% is eroneous and i defy anyone to tell me they can tell the difference that 5% makes when towing, that 5% could simply be the difference between the car having a full/empty fuel tank. I have towed both single and t/a and there are benefits of both however i am not aware of any accident data to indicate one is safer than the other. There is no gaurantee of safe anything in life including towing. Many who tow are firmly in the camp that regard 86% as reckless and get the smelling salts out when anyone suggests towing over 85%. Others make their own minds up (me). The old adage used to be buy the biggest heaviest most powerful car you can afford to tow the smallest lightest caravan you can manage.
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My point is that surely the NCC guidance should be scientifically assessed and updated for the advances in vehicle and trailer technology. It should not remain unchanged for 30 years. If I have a new twin axle trailer with a modern stabiliser and ATC system then it is absolutely not the same as pulling a 20 year old single axle with no stablisier or ATC, but the NCC guidance takes none of this into account. Of course I realise the ALKO data are not UK law but the point is they express the benefit of having a stabiliser in terms of additional load that can be towed, i.e. they put it into numbers. How is there no such attempt to do this by the NCC? They should test these devices and make the calculations, as buyers we need to know are these products actually delivering the extra stability they promise. It seems the whole world is moving in the opposite direction to the caravan industry approach of 'bigger car is always better'. Rather, the NCC should be doing scientific tests of what is the SMALLEST car that can safely tow to reduce the environmental impact of the industry.
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NCC is merely a Trade Body. They are there to run a profitable business representing the interests of members and we, the retail buying public are not members of NCC. The 85% thing goes back donkey's years and has never had any scientific basis. We should all forget it as no more than an old wives tale.
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