Kerbweight

A big enough tail will always wag the dog.  

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  So I view this as highly outdated advice and will simply follow the legal requirement instead, my car has a max permissable mass of 1960, max towable mass (braked) of 1800, the caravan MIRO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.

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.

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.

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.

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

@ Tinwheeler the NCC, who provide this 85% advice, make clear that it is for stability.  

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.

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.

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.