Kerbweight

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.

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. 

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.

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.

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.

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?! 

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..

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.

Yes, same here now. I hope the penny drops with he/she/they and they can get on with enjoying their nee caravan. 

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.