Nose Weight (again)

[Torort]

Hi,

Sorry for the question, I'm sure these have all been asked before but I'm a bit of a newbie.

So, we've just bought a Sterling Eccles Elite Trekker for weekends away and holidays with the kids.
I read a researched a lot before we bought it as I know it's quite a big twin axle caravan.
We tow with a Vauxhall Antara and the max ratio between kerb weight and MTPLM is 92%. I have towed boats a lot in the past so I'm comfortable with the ratio and take it steady and will be sensible with weight when loading.

So on to nose weight.
Making sure everything was fine to tow before I bought the caravan, I checked the nose weight at the dealer. It read 60kg empty. The Antara can take 80kg so all seemed fine and we bought the caravan.

We picked the caravan up and towed it home. Only items added were a 6kg propane bottle and the 110a battery for the mover.

Weve just been away for the weekend and I've just checked the nose weight again and it's 113kg (empty apart from cadac and porch awning at rear and aqua roll and waste at front)

Clearly I can't of checked it correctly before I purchased the van.

I'm looking for advice on how to best reduce the nose weight by 30kg without loading too much heavy stuff to the rear of the caravan.

The caravan towed great with the higher nose weight but I'm conscious of the legalalities.

Thanks for your help.

Mike

 

[Jaydug]

How much forward of the axles are the gas bottle and the battery? And where is the spare wheel stored?

 

[Torort]

The gas bottle is in the front locker, battery is quite far forward. The spare wheel is slung under just behind the rear axle.

I had considered removing the gas and storing at the rear under the seats.

 

[WoodlandsCamper]

I had considered removing the gas and storing at the rear under the seats.

NO, NO, NO. The bottle should travel upright in its designated storage location.

 

[Dustydog]

Hi Mike.
Measuring the nose load on a TA is more complex than one a SA.
It is essential the caravan is absolutely level and on level ground.

Whilst I use a Reich TA gauge I suggest you use the bathroom scales.
You will he amazed that as you load the caravan how the nose load changes. Once you have all your kit on board move stuff towards the rear of the axles keeping them low down. You will then find the correct reading. Good luck

 

[Torort]

Ok, thanks for all your help.

So to make sure I sleep tonight I've just been out to the caravan and took everything out of the front locker (left the gas in situe) and front side locker. Also left the battery in place.

I moved the a aqua roll and wastemaster to the rear of the van and measured it all again.
Down to 85kg.

I don't feel like there is a lot to the rear of the caravan - in total, aqua roll , wastemaster cadac and a 7kg porch awning.

I can redistribute when we load the rest of the gear so the weight of everything else is balanced or is over the axle.

So I think I've nearly cracked it. We will want another gas bottle at some point so I suspect I'll need to get 2 light weight ones.

 

[Martin24]

As far as a second bottle of gas goes, we always have a spare as the gas always runs out when you're cooking. Calor are phasing out their current lite bottles but will probably be replaced with another product reasonably soon.

 

[ProfJohnL]

...It is essential the caravan is absolutely level and on level ground.

Sorry Dusty but NO.

Hello Torort

A big twin axle eh!

This replay may become long winded and you will almost certainly get some contributors who will try to dismiss the points I make.

Lets get the legalities out of teh way first. I am a strong believer that you do need to try to keep within the law, but nose loads are an area that many seem happy to ignore. In their defence they say there has never been a prosecution for too much nose load. Well none that's made it to internet anyway.

The underlying fact is they admit they may be overloaded.

So how important is nose load? Basically the most common limiting factor is the cars tow bar rating. The car manufacture has designed the tow bar to accept a certain maximum static vertical load, in full knowledge that under towing conditions the actual dynamic loads will exceed this value by quite a margin. Under test, the impact loads that can arise on a tow bar are in the regions of 5 to 8g which means for every kg of static nose load you have the dynamic loading can be 5 to 8 times bigger. So what a 10 to 15kg extra kg on static figure means you could be over stressing the tow bar by 50 to 120kg quite easily. To be fair these loads are generally imposes as a vibration and will be of short duration and often fully reversed several times a second. but never the less a small static over load can translate into a much bigger dynamic overload.

I've jumped on Dusty's comment becasue it is wrong. The legal way of measuring nose load requires the trailer nose to assume the exact same height from the ground as when it is coupled and ready to tow. That does not mean the caravan has to be level. In fact with the available range of tow ball heights, a caravan may be nose down level or even slightly nose up.

The reason why this is so important may not be obvious, but if you load a trailer, then measure the nose load with the hitch on the ground and then in the air, you will get two different readings. This is all to do with the location of trailers centre of gravity, and how it will describe an ark over the trailers main wheels when the trailer is tipped up or down.

With single axle caravans the geometry is pretty straight forward and the nose load change with height is is always bigger the lower the hitch. The problem with Twin axle units is far more complicated. Some TA's will sit unhitched with the nose wheel up with the hitch floating above the ground. That means it has ZERO nose load at that height but lift it just a bit a few centimetres and it can need a really tug to lift it. As a consequence the measurement technique for TA nose loads is super critical.

Dusty is correct in so far you need flat (horizontal) ground. Load you car and caravan just as if you are about set of on holiday (that is all luggage and people' Pull up straight on the level ground and measure the height of the hitch from the ground.

Chock the caravan main wheels (don't apply the brakes! Its on level ground so it shouldn't run away)and uncouple the caravan. Adjust the height of your gauge (a caravan step with magazines to support a pair of bathroom scales) so that when the nose load is applied to the gauge it settles at the same height as when coupled to the car. Then read your nose load. Simples!

 

[Dustydog]

Yes Prof I have to agree and apologise for any confusion.
Rightly or wrongly and we have been here before my concern relates to one axle being more loaded than the other. We know the individual axles are rated at 1000kgs. My view has always been to try and be absolutely level thus ensuring as near an equal load as possible on each axle.
I am sure you will agree that if you lift the hitch higher the weight will increase dramatically, if you check it when lower the weight will decrease dramatically.
It's very different to a single axle.
On the move things are different and change by the milli second. I have also been lucky , some may say , that my vehicle's self levelling suspension affords me the luxury of getting everything level at the start. But I do take your observations fully on board. Thanks

 

[Torort]

Thanks for the sound advise.
Our car also has self levelling suspension so I'm currently using the block of wood on the bathroom scales method.
My main worry was that I would have to put a significant amount of weight to the rear of the caravan to get down to the 80kg I needed but its looking like that shouldn't be the case. I just need to not load the front.

The hardest part is finding flat level ground to measure it accurately.

Couple of other questions then:

If the Reich guages sit on the tow ball between the hitch and the ball then aren't they artificially reducing the nose weight by having the hitch that bit too high? (Albeit a small amount)

If level ground and hitch height are so critical then how do the police accurately check nose weight when doing spot checks? And if they can't accurately check then how can they prosecute?

 

[Martin24]

There's always my method but if I suggested it the Prof and his henchmen would be paying me a visit

 

[ProfJohnL]

Hello Torort

Lets address your questions in a different order:

If level ground and hitch height are so critical then how do the police accurately check nose weight when doing spot checks? And if they can't accurately check then how can they prosecute?

There are a number of different ways of assessing nose load most of which includes a weighbridge. As this is not a method generally available to caravanners its not really a domestic method, but by checking the axle loads of the coupled outfit, and the solo car the difference on the cars axles must equate the nose load.

If the authorities were to try a nose load measurement on non horizontal ground, any barrister worth their salt would wipe the court room floor with it.

If the Reich guages sit on the tow ball between the hitch and the ball then aren't they artificially reducing the nose weight by having the hitch that bit too high? (Albeit a small amount)

Any measurement device that does not measure the hitch at its coupled height does not produce a nose load measurement. So the on hitch systems raise the hitch do not measure the true nose load. Some claim to compensate but as they do not allow the input of critical dimensions the compensation they apply cannot be guaranteed to apply the correct offset. (Some contributors do claim they have done comparisons with fair correlation) I must point out that the complexity of the nose load height effect of a TA makes it even more likely that the applied compensation may be out.

It also follows that any nose load gauge that changes its length almost certainly will not support the hitch at its working height. - even those that claim they are calibrated!

My main worry was that I would have to put a significant amount of weight to the rear of the caravan to get down to the 80kg I needed but its looking like that shouldn't be the case. I just need to not load the front.

In general the advice to avoid rear loading is good, but it isn't an absolute no no. Your caravan will already have a load at the rear becasue of its own body work and of course the internal furniture. Unless you caravan is already on the edge of instability, a modest additional rear load is unlikely to be a major problem.

In practice if you have a 10Kg overload at the nose, all you need to move to the rear of the caravan will be about 6 or 7kg (its not exact becasue its all down to relative distances If a 7kg extra rear load is enough to cause problems then I'm sorry but you have much bigger issues than just the nose load.

 

[pensioner]

I've read many topics on Nose Weight since we joined and it's only now that I've found the one I've always thought to be logical but have never read it until now.

That made by ProfJohnL ( reply 35053 ) hope that's the right way to identify it.

It's always made total sense to me to measure the weight at the towing height, but as I say it's the first time I've seen it in print. Thanks ProfJohnL.

 

[GD485]

Hi Prof John
Am I right in thinking that the theory of nose weight is to indicate the approximate position of the centre of mass, ideally in in front of the axle.
I sure you've mentioned it before even if the nose weight is correct it doesn't necessarily mean the caravan is loaded correctly.
With a heavy gas locker and a counter balanced weight at the rear of the van provides a large radius polar moment and a very unstable vehicle.
The same goes for a mass that is near to the axle but not at floor level. Again the polar moment radius can exaggerate pitching.
I think aerodynamic loading has an effect. The centre of pressure moves rearwards as the speed increases.
Which in effect moves the centre of mass rewards.
The centre of pressure location is caused drag pressing on the front of the van whilst the back of the van is low pressure zone tries to pull on the back.
The centre of pressure should be on the longitudinal axis but this could easily be disturbed by a cross wind.
As the airflow acting on the caravan is partially screened by the towcar the force on the front panel will be well above the floor level of the caravan.
This may cause the caravan to lift slightly at the front and maybe have the effect of moving the centre of mass slightly rewards.

One thing for certain, the nose weight is dynamic and can't be consider a fixed point.
I consider this to be a contributing factor in high speed stability.

 

[ProfJohnL]

Hello GD485

You have posed quite a number of points in you comment.

The purpose of nose load is to ensure the trailers hitch provides a downward vertical thrust on the tow vehicle when its stationary and coupled. Its not to locate the position of the trailer Centre of Gravity (CoG), though it can help in that regard. Under towing conditions the nose load is anything but constant, and the dynamic effects of vibrations can make the actual value vary dramatically, even turning to a lifting force on occasions. Because towing conditions are so variable, it would be nigh on impossible to produce a standard safe method for ordinary caravan users to manage to take dynamic nose load readings.

Car and trailer manufacturers have to engineer int their designs enough safety margin to withstand most towing conditions.

A correctly loaded caravan will exhibit a correct nose load. However, you cannot reverse the logic and assume that if you have a compliant nose load, you will have correctly or even safely loaded caravan.

You write
"With a heavy gas locker and a counter balanced weight at the rear of the van provides a large radius polar moment and a very unstable vehicle."

Your statement is not necessarily true. However It is noted that with some outfits having more mass distributed towards the extremities of the trailer can have a greater tendency towards early speed related instability. I know this as Yaw Moments.

But in practice you should look at what is being carried in the gas locker, and rather that counter balancing it by end loading, look to see what weight can be removed from the gas locker, and perhaps relocating that material to the rear of the caravan. Gas bottle must be carried upright and secured in their designated and ventilated locker.

I agree that aerodynamic effects do impart additional loads to the outfit.
It is difficult to generalise how those forces will interact with the body of the car and the caravan, becasue of the detail differences of every possible combination.

But just considering the frontal area of the caravan; gone are the days of almost vertical front panels. If you were to consider the front of an older caravan without a tow car, I would agree the faster the windage on the front as the centre of pressure would be nominally half way up the front as the wind impinges on the panel it would be like applying a air brake. In doing so it will tend to try and lift the hitch.

But more modern caravans have a marked rake to their frontages. especially the upper part will receive wind, but as the front is angled the wing will tend to bend and move up the front. This may start to impart a downward push on the front countering some or all of the air brake effect.

The windage around the car throws the concept of steady state wind testing of caravans to the gods.

I recall our company looking for a new solid body 7500kg goods van. The seller pointed out about a 10 to 15% fuel saving for going for one with a moulded hemi tube device stuck to the leading edge of the body: a small difference for a significant gain.