Myths or Facts

[Val & Frank]

85% ratio is about right for stability ???

Length of Van affects stability even at the 85% Ratio???

Length of Van is less important if you are well below the 85% ratio ???

Units are more stable if you fit a second stabiliser ???

How long does it take to become an experienced caravanner, when towing at 100 % will be OK ??. 3 bad snakes or 3 twitches or 1 accident???

A heavy caravan and a heavy tow car make for a more stable unit,within the 85 % guidelines ???

These are not meant to be flippant questions, I have just read so much, and don't know the answers to these.

Frank

 

[DavidW1]

Frank,

It's not that complicated the rules are simple and easy to understand - go to WWW.caravanclub.co.uk and download New to caravaning. I'm not being patronising and nor is the download - it spells out the art of towing in detail even with diagrams.

It won't tell you when you have become experienced but I think most people would aggree that after a few different vans and a number of towcars over a few years, the qualification naturally attaches. Go on a towing course if you still feel confused or buy one of the excellent DVD's on towing tht the clubs offer.

Also beware of "experts"

No particular remit for the CC either, the C&CC probably have just as good advice.

 

[Val & Frank]

Thanks Dave,

Another one is Are twin axels more stable than single when towing.

Val & Frank

 

[DavidW1]

Never towed a twin axle van but a 2006 Wyoming is my dream if I win the lottery - towed twin axle trailers and horseboxes a lot and they are noticably more stable in pitch, ie. they don't cause the back of the towcar to bounch up and down over bumpy bits but they are not the same as vans in respect of side winds and truck bow waves so I really can't say for sure.

Lots of people out there who have towed both types I'm sure, so await responses!

 

[Gary_5039903]

There are so many factors influencing stable towing that it is almost impossible to give straight answers! Basically, the heavier the tow car, the more chance you have of controlling the outfit in the event of any instablilty. Instability can be caused by many things and the ability to re-gain control of a snake is determined by many more things than the weight of the caravan alone. Tyre pressures, loading inside the 'van and nose weight are all key factors. Yes, twin axles do tend to be more stable due to the increased footprint on the road, but by their nature they tend to be heavier. Using two stabilisers will put far too much stress on the vehicles towbar when cornering so is not recommended.

A caravan by its very design is an unstable trailer and the recommendation to keep the towing vehicle heavier is sound. However, to categorically state that an experienced person could tow at 100%, but the world will end if they tow at 101% isn't necessarily true. BUT, to give "blanket guidelines" as the CC and others have done, they need to give general recommendations, hence the 85% and 100% figures and in most cases they are sensible figures to aim for. But, as I said earlier, people should pay equal attention to noseweight, loading and tyre pressures.

I regularly tow a loaded twin axle trailer at about 135% of my cars kerbweight (right up to the max. tow limit) and it is a much more relaxed smoother tow than with my caravan which is at 90% of my cars kerbweight....

 

[354]

Basically if you keep within the 85% rule it will mean a more stable outfit in most cases, because if the van does sway the car has enough weight to control the sway. However loading the caravan correctly is very important as is nose weight. You could have a 65% match but if the heavy items were all stowed to the rear it would make an unstable outfit.

Length of a van also has an effect, the longer the van the more slab side is there to catch side winds. If you imagine a horse box with a horse in it weighs more than a caravan but is less suseptible to side winds as there is less of an area for the wind to catch.

Experience comes with time. I find when I am towing I read the road well ahead and try and anticipate things well in advance, I also keep a constant watch in my mirrors for overtaking coaches etc. The important thing is load the van carefully, have a good match for a tow car and drive well within yours and the outfits capability.

When I get on the motorway I set the cruise control to 55mph and enjoy the drive.

 

[cris_408518]

Off we go again. I recently towed a two ton van on my flatbed trailer with a new Shogun, with no problem at all. It has to be down to loading and balance. The trailer is rated for 3500KG, the mostscary thing was that was that rig felt as though it would have raced away if I wanted to risk that sort of thing.

That said 85% is a caravan guide line I've alays kept well within.

You can ofcourse have a single axle stable tow set-up, I've had both and there is no way I will ever go back to single axle.

Yes it can be a little more difficult to manouvre when unhitched but just look at the set-up, it is not rocket science to work out that twin axles just have to be the safer bet.

Taking the wheels as a front to back of van mid way pivot point alone, a twin axle just has to be more stable apart from anti pitching benefits and less percentage chance of losing all the tyre air on one side of the van!

 

[CliveV]

Similar to you cris I towed a Range Rover back from Southend to Salisbury for a mate with my Range Rover. with spares etc I was well over the 100%.

No problem tho'

I would suggest that much of the problem is down to the "sail" effect of out big white sheds on wheels.

The weight of the RR on the Ifor Williams twin axle trailer meant it was stable and not affected by cross winds or buffeting.

Towing a caravan is totally diferent and needs a lot of care in comparison

 

[ProfJohnL]

Hello Frank.

There is no simple magic formula that guarantees a stable towing combination. There are some mechanical legal limits that you must obey, for example the trailer must not exceed the tugs towing limit., maximum size etc

The are some academic legal limits, such as what your licence permits you to drive and tow.

None of these provide any guarantee that your outfit will be easy to control.

In my view the biggest variable effect is the driver, the driver is responsible for ensuring the outfit is road legal and that also means controllable, but eventually even the best combination can be driven in such a way as to make it loose its composure and become unstable.

The driver is also responsible for loading the trailer, A badly loaded trailer will be far more likely to become uncontrollable at lower speeds than a well loaded one

All the aspects you mention can and will affect the towing performance of an outfit. And whilst some super mathematicians may be able to derive a definitive formula for ensuring towing safety, I am confident that there are so many variables as to make it impractical for general use.

In the mean time I have no doubt that a sensible driving using a heavy tug coupled to a light trailer is more likely to tow well, and the 85% figure is a sensible starting point.

The 85% figure is not a holy grail. It is not a rule and there is no law that requires it use. It was derived by some people who decided that it might help inexperienced caravanner's to maintain a improved level of safety. but it is not unassailable, and as before compliance with it does not gurantee a good tow.

 

[Steve L]

John is quite right, the 85% figure was suggested as a safer starting point for the novice tower. BUT and it's a big BUT you can get into just as much trouble with a 3 by 4 foot camping trailer if that is loaded wrong.

I once saw a Volvo 850 estate towing a camping trailer go past me doing a good 70mph on the motorway, then without warning it started to sway. It swayed so violently from side to side that the trailer smashed both rear quarters on the volvo.

Both he and I stopped on the hard shoulder as I'd got a split windscreen to sort out and I wasn't going to be paying the excess.

On looking at the trailer, he'd only put the heavey stuff all at the back.

Loading the trailer (caravan) with the heavey items as close to the axle and on the floor is a good start, and also getting the nose weight is another.

A stabiliser is there as an aid and not a cure. Infact a correctly loaded unit could tow as happy with or without a stabiliser.

As for experience, I've been driving for over thirty years and still learn today. Practice gives knowledge and there is no definative end to obtaining that. As I've said to many so called trainers "the person who knows it all has not been invented".

The only tow limits you have to stick to are:-

Your own confidence level, what you are comfortable with.

The legally stated max gross vehicle weight of your car (what it can carry on it's own).

The gross train weight of the vehicle and trailer.

Both of the weights above can be found on the VIN plate on the vehicle.

Finally the hitch weight which is the lower figure of the ones specified by the car/trailer manufacturer or towbar manufacturer.

Those three are the ones the man from the ministry will be interested in should you get pulled over.

As for twin axle vans. Having towed both twin and single axle vans, I do find twin axle vans less prone to swaying but more suseptable to cross winds. This is mainly due to their inheraht desire to go straight due to the aditional axle and the longer length of body, in that order. You still need to load correctly and often a twin axle has more carrying capacity so people tend to use that.

 

[Lutz]

I think the others before me have covered the 85% issue quite well. Nothing magical happens at 85% and a badly laden outfit at 85% can be less safe than another at 100% where everything else is set up correctly, so 85% is just a good starting point. Like I wrote in the deleted thread, the ratio limit for towing at 100kph here in Germany was recently lifted from 80% to 100% because accident statics involving caravans showed that other causes were generally to blame and no direct correlation between weight ratio and accident rates could be proved.

What I would like to add, however, is don't add a second stabiliser in an attempt to improve the safety margin unless it is a stabiliser that doesn't transmit any additional forces through the towbar (such as an electronic stabiliser). Towbars are designed to take the torques of normal frictional stabilisers, as specified in ISO Standard 11555-1, for example, and durability could be adversely affected with any higher loads. The only type of stabiliser that may be combined safely with, say, an AlKo, Winterhoff, or blade-type is an active (i.e. electronic) system.

The length of the caravan alone has no direct affect on stability. It's the combination of length and weight that affects the polar moment of inertia and this only determines the frequency of the snake, i.e. how quickly the caravans swings from side to side, not whether it happens at all.

 

[WatsonJohnG]

Hi Lutz

The old chestnut of two stabilisers again !!

While I agree with what you say the ISO figure for loading is a max and we don't know what is the actual loading and what is left over so to speak.

Straightliner stabilisers and the Scott type don't rely on friction at the towball itself (I realise the strain is on the towbar fittings etc butI say this in view of Alko's reply ).

Straightliner told me that I could use both as I already had the Straightliner when I aquired a caravan with the Alko.

Alko said that the forces on the tow ball would be too great but they then produced a more powerfull hitch type one themselves but retained the same ball.

It would be very interesting to see some proper tests with actual data rather than being told that there is a limit that we have no idea how close we are to reaching.

I towed for over a year using the Straightline and Alko but after Alko said that it was against their advice I now only use the Alko and also it less hassle setting up.

 

[Lutz]

In order to get the best possible performance out of a stabiliser, I would not think that the manufacturers, whether it be AlKo, Winterhoff, or anyone else, would design their products to be much below the stated maximum. It is not likely that the towball is the weakest link in the structural chain as all towballs that I have seen appear to be of quite a solid construction. Results from development tests show that it is far more the attachment of the towbar to the vehicle underbody where potential durability problems occur, bearing in mind that the sheet metal to which the towbars are attached is relatively thin (in the order of 1 to 1.5mm) and requires measures to spread the load. As towbar design is specific to the respective manufacturer (despite EU Directives for common attachment points, they still have some leeway here), I cannot see how Straightliner can make a blanket statement that it is safe to use their product together with an AlKo or Winterhoff. Some towbars and their attachments may take it, others not.