Nose weight - a caution for Unicorn Cabrera owners

[ProfJohnL]

The caravan would be unfit for purpose if the amount of weight needed to trim the caravan for its nose weight limit exceeded the legal payload limit for the caravan.

Technically not, it would only be illegal of the weight of the caravan exceeded its MTPLM. For example a caravan fresh from the dealer may not have battery or gas bottles, which are part of its essential habitation load, under the latest (crazy) definitions, which would allow a greater load than the caravan stated payload margin. It's not likely to occur, but that is how it would go.

 

[Raywood]

I think we are going round in circles a bit but I would still say that a caravan with a 135 kg nose weight would be unfit for purpose if it was designed for towing by a normal car. The exact level it becomes unfit for purpose is arguable though but that 100 kg hitch limit would make towing it empty illegal and that cannot be right.

 

[ProfJohnL]

I think we are going round in circles a bit but I would still say that a caravan with a 135 kg nose weight would be unfit for purpose if it was designed for towing by a normal car. The exact level it becomes unfit for purpose is arguable though but that 100 kg hitch limit would make towing it empty illegal and that cannot be right.

Admittedly I am playing devils advocate here.

The problem is you cannot define a "normal" car the fact is there some vehicles that have 150kg tow bar limit, and these are available to "normal" people so how else do you do it?

I totally agree the ex works nose load should not exceed the couplings nose load limit (SValue) but anything up to that limit is fair game, especially where it will be reduced when the caravan is loaded.

 

[Guzzilazz]

I think we are going round in circles a bit but I would still say that a caravan with a 135 kg nose weight would be unfit for purpose if it was designed for towing by a normal car. The exact level it becomes unfit for purpose is arguable though but that 100 kg hitch limit would make towing it empty illegal and that cannot be right.

Admittedly I am playing devils advocate here.

The problem is you cannot define a "normal" car the fact is there some vehicles that have 150kg tow bar limit, and these are available to "normal" people so how else do you do it?

I totally agree the ex works nose load should not exceed the couplings nose load limit (SValue) but anything up to that limit is fair game, especially where it will be reduced when the caravan is loaded.

The Cabrera SValue is 100kg...

 

[Gafferbill]

As is apparent from my sig, we're new to caravanning, and I've been careful to ensure we stay within the various limits weight wise. However, I hadn't checked nose weight, so lashed out on the Milenco scale, and was astounded to find that empty the nose weight was 130kg!!! I'm flabbergasted that manufacturers don't even "design" the nose weight to be about right with the van empty...

We don't know what your definition of empty is ........any weight added in front of your caravan's axle will increase the noseweight as will any weight removed from behind it's axle.
It would appear you towed the caravan home from the dealers and at a later stage bought a Milenco gauge.

Did you add or remove anything from the caravan before the measurement ?

 

[Raywood]

I think we are going round in circles a bit but I would still say that a caravan with a 135 kg nose weight would be unfit for purpose if it was designed for towing by a normal car. The exact level it becomes unfit for purpose is arguable though but that 100 kg hitch limit would make towing it empty illegal and that cannot be right.

Admittedly I am playing devils advocate here.

The problem is you cannot define a "normal" car the fact is there some vehicles that have 150kg tow bar limit, and these are available to "normal" people so how else do you do it?

I totally agree the ex works nose load should not exceed the couplings nose load limit (SValue) but anything up to that limit is fair game, especially where it will be reduced when the caravan is loaded.

I think a normal car would be the average in the range the caravan is aimed at. 150 kg is exceptional and is still no good if the hitch has a 100kg limit. The caravan has to be suitable for the market it is aimed at and this clearly is not, but where you draw the line is far more difficult.

 

[Thingy]

Thinking about the logistics and effects of counterbalancing to achieve the nose weight, its always been said that putting too much weight at the rear of the caravan can be disastrous if the caravan enters a snake (yaw), and also could cause the effect of a bouncing trailer (pitch). Its not rocket science to know the effect that severe yaw can have, and its lethal consequences, but when discussing the forces on the hitch and drawbar assembly, surely pitch would have the same detrimental effect as being nose heavy. Its not just a matter of adjusting the load to get the weights right, you have to seriously consider what other forces you are adding to the equation.

For me, I am watching this thread keenly as we had originally ordered a Cadiz, but having now seen a 2021 version in the flesh, we are thinking the Cabrera may be a better layout for us. Bearing in mind the gas locker is on the side, removing a fair weight from the nose, you have to wonder how on earth this caravan is so nose heavy.

 

[ProfJohnL]

Thinking about the logistics and effects of counterbalancing to achieve the nose weight, its always been said that putting too much weight at the rear of the caravan can be disastrous if the caravan enters a snake (yaw), and also could cause the effect of a bouncing trailer (pitch). Its not rocket science to know the effect that severe yaw can have, and its lethal consequences, but when discussing the forces on the hitch and drawbar assembly, surely pitch would have the same detrimental effect as being nose heavy. Its not just a matter of adjusting the load to get the weights right, you have to seriously consider what other forces you are adding to the equation.

For me, I am watching this thread keenly as we had originally ordered a Cadiz, but having now seen a 2021 version in the flesh, we are thinking the Cabrera may be a better layout for us. Bearing in mind the gas locker is on the side, removing a fair weight from the nose, you have to wonder how on earth this caravan is so nose heavy.

There isn't a black and white answer to this. Suffice to say that too much end loading is detrimental to handling becasue it increases Yaw Inertia. But no one can categorically say when there is too much end load without trying it.

There are some who will say point blank you must not end load, but they seem to be forgetting that there is already quite a significant of end load simply from the construction of the caravan, and indeed the same range of caravans might have a choice of end bathroom or kitchen or bedroom. Each will have different amounts of end load due to the variety of appliances or fittings in each model yet alone what the owner might store there.

I personally advice to avoid end loading, but on occasions it may be necessary to achieve the desired nose load. - Let's assume you need to reduce your nose load by 10kg. All you need to do is to remove enough weight from the front of the caravan to reduce the nose load by half the excess, because when you reposition those items to the rear of the caravan they will cause a further nose load reduction. Allowing for the lever lengths of the hitch and body you might need to move 6 to 8kg from front to back.

If by moving just 8kg or so to the rear of a caravan is enough raise the yaw inertia to a critical level, it suggests the caravan was already at a critical level before the adjustment, and in reality the whole loading needs t be reconsidered.

 

[Thingy]

The big thing about end loading is that regardless of whether its sorted your noseweight out, you wont know the possible adverse effect until its too late.

 

[ProfJohnL]

The big thing about end loading is that regardless of whether its sorted your noseweight out, you wont know the possible adverse effect until its too late.

I'd disagree - except for idiots who don't feel the way their caravan is towing.

An increase in speed also increases the possibility of instability. Instability doesn't switch on with a "bang", there is a progressive trend towards it as speed and conditions worsen, and a sensitive driver will begin to feel the movement of the caravan well before it becomes unmanageable.

The forces that cause instability extract their energy from the motion of the outfit when being towed, and generally most of those forces will change with the square of the speed, so slowing down slowly makes the best difference and will improve control.

That is one reason why the old caravanners tale of accelerating out of snake to pull it straight is so potentially dangerous, by going faster you are adding energy to the system. The risks far outweigh the possible success.

 

[Thingy]

Unusually brutal there from you Prof.

Lets be charitable and not call them idiots, but rather inexperienced towers.

I have spent a lot of my life on the road with both HGVs and Superheavies, and I would say I have an almost surgeon like feel for the way a vehicle handles, but that is a skill learned over time. We have just seen a huge boom in caravan owners, many of whom will be towing this summer for the first time in their lives, and unfortunately will have no idea how towing a properly laden caravan should feel. So, on they go. bobbing and weaving along the M5 thinking this is a bit unsettled, then it happens. And with all the physics theory in the world assumed, weight at the back end is only going to exacerbate the situation.

I accept a lot of what you say, but its not always an increase of speed that can cause issues. A person could be towing along almost at the point of no return, but another force suddenly applied, like the bow wave from panel van, or artic can tip it over the edge in a split second.

Physics is all very well, but the laws thereof cannot be applied in the same way to every situation.

I know you are a massive advocate of getting the noseweight right, but a specific noseweight can give an unsettled tow, whereas an extra kilo or two either way can make for a very different towing experience.

 

[ProfJohnL]

I stand by my words.

Most people who decide to go caravanning will have been driving cars for several years, and should have developed an understanding or feel for when things are not quite right and thus should also be reading the conditions ahead and adjusting their driving accordingly. For them towing may be a new experience but the basics of feeling how the vehicle is behaving should already be there. As with any new experience one should ease into the process incrementally adjusting things rather than going full blast on the first attempt, and hoping everything will be alright. Unfortunately there are some who who idiotically choose to ignore this vital feedback.

And I still disagree with the notion that instability has no forewarning. If as you say someone was driving "almost at the point of no return" I would be very very surprised if there were no prior indications the outfit was on the edge and should be ********.

Semantically the laws of physics by their very nature have to be applied in the same way each time. otherwise they are disproven and can no longer be used. I should add that as a technically minded person I do not assume the "laws of physics etc" are complete yet, there will continually be new favourite theories which will gain preference until yet another new theory arises to augment or supplant it. However the Newtonian laws of motion have served us very well for many centuries at realistic speeds for cars and caravans, and revisions to the laws to have tended to be concerning near light speeds, something that I don't think caravans are likely to achieve in our lifetimes. - I wonder what the static noseload should be?

I hope every caravanner indeed trailer tower wants to get the noseload right, as we all know how what part it plays in achieving a secure tow. However I have never suggested a specific nodeload value, I have always suggested finding the best value within the available range.

What I have majored on is the correct way to measure the noseload, and how unsuitable compressed length spring gauges are when trying to measure noseloads.

 

[Thingy]

Let me give you a different persepctive on this. On British roads every day, there are hundreds of loads in three classes that are notoriously unstable, and even the most experienced and skilled HGV driver hates them. They are loaded correctly, but I will qualify that by saying loaded as far as the design of the vehicle allows. I personally have driven all three and never had a problem, but I know of many instances that those same loads have bitten drivers, seldomly fatally but it has happened. The loads travel safely every day until an unexpected force is applied. It could be an adverse camber in the road, ruts in the slow lane, though this isnt usually a culprit, a sudden side wind or the driver being suddenly forced to swerve. I doubt you or any non HGV driver would be able to tell me what those loads are, and it isnt a quiz, so here they are. They may surprise you.

Hanging meat. It is loaded from hooks and rails, the slightest lateral force sets this stuff swinging, and when you are talking many tons of the stuff, well, you know the rest.

Some, milk, beer and other foodgrade tankers. Some of these tankers do not (god knows why), have baffles in them. When the driver drops a half load and travels onwards, the load begins to slosh about, the same effect as when you move back and forth in the bath. Forwards and backwards is uncomfortable, side to side potentially lethal.

CemSave. This is an extremely fine powdered iron, added to cement to produce a harder surface for example factory floors. It is so fine it is almost liquid. If you drop a coin in the stuff, you see ripples, and it is truly awful stuff. You can drown in it. It is more active for want of a better word than most fluids, and again, this stuff usually travels in tankers without baffles. It is usually pumped into silos from tipper tanks, but nowadays, there are of course tankers that empty from the belly rather than tip, though both are pressurised

That last category is probably responsible for most tanker accidents. However, as I said, to the best of the design these are all correctly loaded, yet can be upset in a heartbeat by an unexpected lateral force. I still maintain this can and does happen to a lesser degree in caravans.

 

[Thingy]

And Im not arguing, just discussing.

 

[ProfJohnL]

And Im not arguing, just discussing.

Thank you for pointing out the issues with the transport of of unrestrained hgv loads. But there is a significant difference between the load margin of a load carrying HGV and a caravan, so the moveable mass within and HGV tanker without baffles is usually a large percentage of the trailers MAMand thsu the forces involved will also be proportionally bigger. Where as in a caravan the biggest load margins are only about 20% of the MAM,with very little opportunity of the entire load to be unrestrained, so the likelihood of that type of incident in a caravan is minutely small.

It's not impossible if drivers do silly things.

 

[Thingy]

It's not impossible if drivers do silly things.

Now that we do agree on.