Verifying Loaded Weight

[TheTravellingRooster]

..................
Edit - the cost of the weighing was £6 with a single printout showing 3 weight readings (a) train weight (car + van), (b) van on its own after moving the car off, and (c) the calculated nett difference (ie car weight). Good value for money.

Hello WC.
When you said "van on its own after moving the car off" was the caravan still coupled to the car?

If it was still coupled, the caravans weight will be its towed weight, i.e. the load carried by its wheels. It will not include the nose weight which was still coupled to the car.

To work out its total weight you need to add the caravans nose weight to the 'caravan' reading and then compare to the caravan's MTPLM to workout if you are within the MTPLM limit.

Hi PJL. The last time that I had my total outfit weighed it was carried out on a VOSA spec Dynamic Axle Weighbridge/Beam. This was done at the premises of the company that make,install and service the VOSA ones.
I had previously been and had the outfit weighed as :-
1) Kerbweight & MiRO by pushing the caravan across the beam on the jockey wheel and the four wheels.
2) As an outfit hitched and ready to load and go.

Generally speaking VOSA and the police - when called are primarily interested in axle weights and for that reason I did my first pass with the outfit loaded and ready to go. This of course can only be reasonably accurately arrived at by knowing exactly what both the MiRO of the caravan is and what the kerbweight of the car is. From then on in,everything is weighed and an inventory is retained with the outfit.

By weighing the outfit hitched and then as individual subjects I got the axle weighs of both and the with just the car only - it confirmed that my hitch-head weight was correct at that point because the car rear axle weight was 75kgs lighter.

Having established the hitch-head weight I was then able to maintain that when loading by the placement of the various items and boxes that all was packed into. Boxes do not roll about in transit. Loading was always carried out on flat & level ground and the Milenco Nose-weight gauge was always to-hand.

My kerbweight check was ever so simple because I am that 68kgs driver as per the driver allowance.
For the ease and convenience I simply filled my car to the brim - the difference between Full and 90% full is give or take;the luggage allowance of 7kgs.

I really cannot abide the senseless/brain-dead thinking of those that never bother to carry out what is such a fundamental and vital part of safe and responsible caravanning practice. Bragging about it is doubly criminal.

 

[WoodlandsCamper]

Were you using a 50 tonne weighbridge? If so the readings are only about +/- 20 kg, so calculating a noseweight of 75 kg from the readings could also be 75 +/- 20 kg.

 

[TheTravellingRooster]

Were you using a 50 tonne weighbridge? If so the readings are only about +/- 20 kg, so calculating a noseweight of 75 kg from the readings could also be 75 +/- 20 kg.

Hi WC. have a ring-around for a bridge with 5kg or 10kg cells. Better still check with VOSA for a local Check/Weigh Station and consult with them.

My very first full outfit check was after a phone call to the M6 Southbound site at Sandbach,Cheshire. A very obliging chap invited me down for a slot the next afternoon ( subject to a possible wait if they had a truck/trucks in the yard).

 

[ProfJohnL]

Hello TR

From your description I gather you have a twin axle caravan. TA's can actually present a real problem to weigh properly unless provision is made to cover these eventualities.

"You should remember for I have often told you so, Oh best beloved" (Kipling) that nose load must be be measured at the actual towing height. This is because the position of the caravan centre of mass will move fore and aft if the caravan is tipped up or down. The horizontal change in its position relative to the caravans axles changes the turning moment that produces the nose load. This change in load vs hitch height is far more dramatic and complicated for TA's compared to SA's. that is why NONE of the available noseweight gauges are really fit for purpose - even the Milenco because it does not offer height adjustment and when it is loaded it changes its length!!!

The reasons for nose load changes on TA's can also compromise weighbridge analysis of axle loads on TA's

Because the suspension units used on most TA caravans is fully independent, when one axle has to rise to ride over something none of the increased load change is shared with the second axle. If the leading axle has to rise to get onto the weighbridge it has to compress the suspension unit to do so, That means the suspension unit is pushing down harder because it is compressed. By doing so it unloads the trailing axle, and the weight is transferred to the leading axle. If the weighbridge has a step of only 5mm this could easily see an extra 30 to 40kg added to the axle load. The same thing will happen to the trailing axle when it reaches the weigh bridge beam, so another 40kg could be added thus giving the appearance the caravan is 80kg heavier than it really is.

The converse is also true, if the weighbridge beam is lower than the surrounding ground as the wheel s drop onto it, the bean will under read the caravans weight.

I am also concerned at the way you describe calculating your nose load figure. Because the hitch on the car is behind the rear axle, any load applied to the hitch will indeed compress the rear suspension, but at the same time it will unload the front axle by a smaller amount. You need to take both of these changes in axle loads into account to establish the applied nose load.

There is nothing wrong in keeping a spreadsheet of loaded items, but the methodology is far from perfect for establishing the total load. The problem lies with inaccuracies of measuring small masses, each of which will have an error. By adding all the small readings together you can get a compounding error which can have a large standard deviation. Its not uncommon to find tabulated results are quite different to the actual weight of the caravan.

These types of errors are particularly important for caravan owners, as we so often work very close to several upper load limits. By not measuring our loads correctly, it is so easy for a caravan to slip over one of the legal limits, with possible consequences that can bring.

 

[Dustydog]

Prof
We have done the TA axle weights to death recently.
I am really beginning to wonder if Bailey and Swift have got it right?
Again you are inferring an axle plated by Al-ko at 1000kgs will at various times be carrying a full MTPLM of 1800 kgs.
This theory introduces another complication regarding the chassis itself which is now having all 1800kgs loaded on the front or rear axle and having the additional weight of the airborne axle.
If the axle and chassis were strong enough to support what you say then it must be Al-ko got it wrong ??
In reality I have never once felt any instability with weight changes between the two axles.
There is then the question that if one axle is weightless will the Al-ko ATC brake stabiliser system work correctly?

Maybe someone from Bailey, Swift or Al-ko could give us a professional technical explanation please or even PCv mag?

 

[TheTravellingRooster]

Hello TR

From your description I gather you have a twin axle caravan. TA's can actually present a real problem to weigh properly unless provision is made to cover these eventualities.

"You should remember for I have often told you so, Oh best beloved" (Kipling) that nose load must be be measured at the actual towing height. This is because the position of the caravan centre of mass will move fore and aft if the caravan is tipped up or down. The horizontal change in its position relative to the caravans axles changes the turning moment that produces the nose load. This change in load vs hitch height is far more dramatic and complicated for TA's compared to SA's. that is why NONE of the available noseweight gauges are really fit for purpose - even the Milenco because it does not offer height adjustment and when it is loaded it changes its length!!!

The reasons for nose load changes on TA's can also compromise weighbridge analysis of axle loads on TA's

Because the suspension units used on most TA caravans is fully independent, when one axle has to rise to ride over something none of the increased load change is shared with the second axle. If the leading axle has to rise to get onto the weighbridge it has to compress the suspension unit to do so, That means the suspension unit is pushing down harder because it is compressed. By doing so it unloads the trailing axle, and the weight is transferred to the leading axle. If the weighbridge has a step of only 5mm this could easily see an extra 30 to 40kg added to the axle load. The same thing will happen to the trailing axle when it reaches the weigh bridge beam, so another 40kg could be added thus giving the appearance the caravan is 80kg heavier than it really is.

The converse is also true, if the weighbridge beam is lower than the surrounding ground as the wheel s drop onto it, the bean will under read the caravans weight.

I am also concerned at the way you describe calculating your nose load figure. Because the hitch on the car is behind the rear axle, any load applied to the hitch will indeed compress the rear suspension, but at the same time it will unload the front axle by a smaller amount. You need to take both of these changes in axle loads into account to establish the applied nose load.

There is nothing wrong in keeping a spreadsheet of loaded items, but the methodology is far from perfect for establishing the total load. The problem lies with inaccuracies of measuring small masses, each of which will have an error. By adding all the small readings together you can get a compounding error which can have a large standard deviation. Its not uncommon to find tabulated results are quite different to the actual weight of the caravan.

These types of errors are particularly important for caravan owners, as we so often work very close to several upper load limits. By not measuring our loads correctly, it is so easy for a caravan to slip over one of the legal limits, with possible consequences that can bring.

Hi PJL. I can see why you have the "handle" Prof !!!!!!!!!!!!!!!!! You are actually telling me everything that I have ever advocated and in the eyes of many BANGED ON ABOUT for a very very long time - indeed long before I ever subscribed to this and or any other caravan related forum.

As far as towing height is concerned I have even gone into great detail as to how I achieved this critical factor/consideration prior to hooking the twin-axle caravan on the back of the car. Always carried out on level and flat ground.

I fully understand your point/points about the complexity of towing twin-axle caravans and or 8x4 and larger twin axle boxed trailers. The Dynamics of Towing are considerably more complex and constantly variable with twin axle than with single axle caravan/trailers.

When ever I took out the caravan and indeed upon the return journey the routines were the same initially the caravan would be loaded and adjustments made on the basis of using my Milenco Nose-weight Gauge and setting the hitch-head at the towball centre height relevant to that of the car after ensuring that it was at the optimum height when the 75kgs maximum hitch-head load was applied to the ball - this 75kgs was coincidentally the same for both the car and the hitch-head.

I found that with the twin axle caravans that I had owned over the years - finding the fulcrum point with an empty caravan on the gauge and chocked front and rear of the axles was relatively easy. Then the loaded and all in stout cardboard boxes was easily position and secured from movement.

I do not use Plate Bridges because of the known issues/potential discrepancies,a number of operators will not allow the removal of the caravan/trailer whilst the total load is on the plate.- the Dynamic Axle Weighbridge is actually a fine beam set into a concrete bed and all on perfectly level/flat ground. They give variable and recorded readings as one passes across at a slow roll pace.. The individual axle weights are all perfectly visible on a large digital read-out at the head of the weigh area.

When loads/loading is being carried out the smaller items are weighed as box loads and not individual items because of the potential for compounding errors. Larger items are weighed and rounded-up NOT down.

At the end of the day all is carried out on flat and level ground and in that respect the optimum is then as neutral a result as can be reasonably expected - from there-on in the towing dynamics are not already influenced by inaccuracies created by gradient and or uneven ground.

Yes - the tow-ball is behind the axle but that is the case with every vehicle fitted with a tow- and on can only hope and trust that the vehicle manufacturers that homologate their vehicles and deem them fit for towing are fully in the knowledge of that very detail - as are the various manufacturers of towing equipment.

That is essentially why the home-made/DIY/Bodged tow-bars are outlawed and all now have to be approved and accepted/approved by the vehicle manufacturers as fit for purpose.

In conclusion - In my 50yrs of towing al-sorts with al-sorts I have only ever had one serious snake which was caused by a holiday coach from National Express Coaches travelling far to fast and damned near taking my towing mirrors off of the car and a tow-bar frame on a previous employers vehicle suffering a very serious weld failure whilst on-route to Yorkshire via Scout Head in the late 60's with a very large trailer loaded with contract furniture.

 

[ProfJohnL]

Hello DD,

You have got your threads mixed up, and I'm sorry if it is causing you some distress. Let me assure you the chassis manufacturers will have been fully aware of the issues we have discussed, and taken them into account when they recommend chassis components to the caravan manufacturers.

I am confident Alko would refuse to supply parts that were clearly not capable of safely carrying what the trailer manufacture has designed.

What I have been describing is nothing new, its been normal for years so ask yourself, how many caravan you have seen or read about that have suffered damage as a result of under specified chassis? Not many if any at all! so that should give you confidence.

I cannot quite recall how all this started, but it all ties into the reason that I've been extolling taking care with nose load, and other caravan weight measurements especially with TA's.

It is important because so many caravanners are loading caravans to a few kg of their legal limits, and being aware of incorrect measurement techniques could make the difference between being legal or collecting points on your licence.

Let me specifically assure you that the weight of the axles is already included in the MTPLM so if one is totally unloaded it doesn't add anything new to the weight of the caravan, and yes, it will have been taken into account by the manufacturer.

In respect of the ATC systems, they are designed for use when the caravan is on the move. Under normal towing the wheels are not likely to completely leave the road The wheel is only likely to unload completely when moving slowly such as when negotiating a kerb at which time ATC won't be required any way, so your concern is unfounded.

I hope this helps.

 

[ProfJohnL]

As far as towing height is concerned I have even gone into great detail as to how I achieved this critical factor/consideration prior to hooking the twin-axle caravan on the back of the car. Always carried out on level and flat ground.

............................

When ever I took out the caravan and indeed upon the return journey the routines were the same initially the caravan would be loaded and adjustments made on the basis of using my Milenco Nose-weight Gauge and setting the hitch-head at the towball centre height relevant to that of the car after ensuring that it was at the optimum height when the 75kgs maximum hitch-head load was applied to the ball - this 75kgs was coincidentally the same for both the car and the hitch-head ..................................................

Hello TR.

I have read, reread and read again your description above and the previous post of how you carry out your nose weight measurement. You do not explain how you establish the working height of your loaded tow ball.

There is no such thing as the "optimum height" for the towball. The regulations call for the loaded tow ball on cars to settle between 350 to 420mm floor to centre of ball. The actual value will change as the applied loads change.

The regulations also stipulate the applied nose load must be measured with the trailer hitch at exactly the same vertical height from the floor as when it is coupled to the tow vehicle in its ready to tow condition with all passengers and luggage. If the nose load measurement is taken at any other height it will be wrong!

So until you have coupled the caravan to the car, and measured the height of the hitch, uncoupled and then measured the nose load AT THE SAME HEIGHT, you don't know what you nose load is.

The Milenco in common with most off the shelf gauges has a uncompressed length, and will change its length as apply a load. As I won't own one,I do not know what the scale length is, but from the photographs it would appear to be at least 100mm which means the gauge will dip as you apply the load. This dipping unless you are very luck and it happens to settle at the correct height, will therefore give you a false reading on nose load. This is the fundamental flaw with gauges of this type.

With TA'a I guestimate that you could see as 0.5kg change in applied nose load for every mm of change in hitch height, which is why correct measurement technique is so critical.

It is perfectly possible to calculate your nose load using a weigh bridge, but in your description you only consider the change of load on the cars rear axle. You do not seem to have considered the effect of the nose load on the cars front axle. Application of nose load to the tow ball will predominantly compress the rear suspension. But it will also reduce the load on the front axle. How much is dependant on the ratio of the cars wheelbase to the rear axle to ball distance. Most towing cars will have a ratio of about 3:1 which means a change of 75kg on the rear axle could translate to reduction on the front axle of -25kg that actually gives a nose load of only 75-25 = 50kg!

Historically caravaneers have rarely taken much care in checking weights and loads, as there was little enforcement. But with general increase in the weight of caravans lighter cars and increasing legislation, we can no longer be as complacent about getting it right. For anybody contemplating using all their MTPLM or the nose load allowance being able to ensure they are legal means they must adopt the correct and accurate methods of weight measurements.

 

[WoodlandsCamper]

Have heard from Lunar, they can re-plate my van from 1,210 kg to 1,295 kg, so I will take them up on the offer but it will cost me £50.

Have received the new weight plate today. The plate now shows the MRO (sic) as 1,210 kg, which I assume now notionally includes the weight of the dealer-special additions plus gas, battery, spare wheel and motor mover. The MTPLM is shown as 1,295 kg, giving a 'true' user payload of 85 kg. Unfortunately the VIN on the new plate is incorrect so I have requested another one.

 

[Surfer]

We took our twin axle caravan to the weigh bridge in February 2015. We were told that the bridge had been calibrated the day before. The caravan weighed exactly 1780kg, 20kg below its MTPLM but we needed to lose a minimum of another 15kgs. Nose weight was just under 100kg We removed some stuff from the caravan and weighed it again in April. This time the reading was 1800kg although we had removed some stuff and noseweight increased as the spare tyre had been removed from the rear.
The caravan should have weighed about 1764kg using my calculations on what had been removed and what had gone back into the caravan. This indicated to us that weigh bridges were not that accurate.

 

[WoodlandsCamper]

Are you sure the OH hadn't sneaked items back into the van without your knowledge? hair drier, hair tongs, etc

 

[Sproket]

We took our twin axle caravan to the weigh bridge in February 2015. We were told that the bridge had been calibrated the day before. The caravan weighed exactly 1780kg, 20kg below its MTPLM but we needed to lose a minimum of another 15kgs. Nose weight was just under 100kg We removed some stuff from the caravan and weighed it again in April. This time the reading was 1800kg although we had removed some stuff and noseweight increased as the spare tyre had been removed from the rear.
The caravan should have weighed about 1764kg using my calculations on what had been removed and what had gone back into the caravan. This indicated to us that weigh bridges were not that accurate.

Read this

 

[ProfJohnL]

Hello Sprocket,
That's an interesting document. It confirms some of the problems of weighing multi axle trailers. The fact that e document mentions the sites levels, and where certain types of weighly devices are used the need to use additional any dummies or levelling mats (3.5.3b) to support un weighed wheels, shows the issues of load shifting on independant articulated axles is significant.

On the down side though, it also shows that most commercial weighbridges whilst calibrated to +/- 10kg can only legitimately give results with an accepted error of +/- 20kg. This is only a small proportion of the weights normally found on commercial vehicles, but for caravanners it represents approximately 10% of main axle loads and about 60% of nose loads.

Basically this suggests that using such a commercial weighbridge for a caravan outfit is not going to give particularly accurate results. However this is the type of equipment enforcement officers will use, so in theory we have to consider making allowances for the wide tolerance range of the measurement systems. This makes it even more imperative that caravanners are careful with their loading, for fear the system may be erring on the high side of its permitted tolerance band.

 

[Sproket]

Hi Prof

Technology is only getting better

 

[ProfJohnL]

Yes indeed!!!

 

[Surfer]

Hello Sprocket,
That's an interesting document. It confirms some of the problems of weighing multi axle trailers. The fact that e document mentions the sites levels, and where certain types of weighly devices are used the need to use additional any dummies or levelling mats (3.5.3b) to support un weighed wheels, shows the issues of load shifting on independant articulated axles is significant.

On the down side though, it also shows that most commercial weighbridges whilst calibrated to +/- 10kg can only legitimately give results with an accepted error of +/- 20kg. This is only a small proportion of the weights normally found on commercial vehicles, but for caravanners it represents approximately 10% of main axle loads and about 60% of nose loads.

Basically this suggests that using such a commercial weighbridge for a caravan outfit is not going to give particularly accurate results. However this is the type of equipment enforcement officers will use, so in theory we have to consider making allowances for the wide tolerance range of the measurement systems. This makes it even more imperative that caravanners are careful with their loading, for fear the system may be erring on the high side of its permitted tolerance band.

It would be interesting to know how accurate a portable DVSA weigh bridge is like they appreantly use in a services area and how often it is calibrated. On a commercial vehicle 20kg or even 100kg overload probably would be ignored by DVSA, but on a caravan outfit that is a serious overload as the load rating on the tyres will probably be exceeded. However how would the police go about having a succesful prosecution without a calibration certificate? Probbaly why they find it easier to get people to put excess stuff from the trailer into their cars. Our MTPLM is 1800kg, but the total load rating of the tyres is 1900kg.

 

[ProfJohnL]

It would be interesting to know how accurate a portable DVSA weigh bridge is like they appreantly use in a services area and how often it is calibrated. On a commercial vehicle 20kg or even 100kg overload probably would be ignored by DVSA, but on a caravan outfit that is a serious overload as the load rating on the tyres will probably be exceeded. However how would the police go about having a succesful prosecution without a calibration certificate? Probbaly why they find it easier to get people to put excess stuff from the trailer into their cars. Our MTPLM is 1800kg, but the total load rating of the tyres is 1900kg.

All public weigh bridges and those used by the authorities to check weights have to be calibrated by trading standards Check the document that Sprocket has found, Granted it's not the legal frame work but it does appear to be the accepted code of practice. A defence lawyer would have a field day is the authorities could not produce a calibration certificate to support a prosecution.

 

[Sproket]

The frequency of testing is every six months, when in service. They are tested under the “Enforcement Weighing of Vehicles – Consolidated Code of Practice” published in 2002, which is a voluntary non-statutory Code of Practice, a copy of which is available via the following link

Read this....

You may also want to read this Freedom of Information response about VOSA weighbridges

 

[Surfer]

As public weighbridges can be out by 20kg or more, where does that leave a caravan owner wanting to stay within the MTPLM of their caravan? Can I assume that if the caravan is hooked up to the vehicle and the vehicle is not on the weigh bridge, the difference will be the nose weight of the caravan carried by the car?
We want to take the caravan again to a public weigh bridge, but how will we know when last it has been calibrated etc unless we ask the operator? Seems pointless if there is a 20kg descrepancy on a 1800kg caravan.
We have had an air conditioner fitted on top of the caravan and the weight of it is 32kg however we have removed the mattress topper weighing 10kg and exchanged the caravan mattress for a lighter Duvalay mattress weighing about 13kgs so another saving there of about 10kg. Hopefully we are within the MTPLM of the caravan. My sums tell me that we should be about 8kg under the MTPLM of 1800kg, but .........

 

[WoodlandsCamper]

Can I assume that if the caravan is hooked up to the vehicle and the vehicle is not on the weigh bridge, the difference will be the nose weight of the caravan carried by the car?

Only if the surface of the weighbridge is at the same height as the surface of the road on which the car sits.

 

[Surfer]

Can I assume that if the caravan is hooked up to the vehicle and the vehicle is not on the weigh bridge, the difference will be the nose weight of the caravan carried by the car?

Only if the surface of the weighbridge is at the same height as the surface of the road on which the car sits.

Our nose weight is about 100kg, so are talking about 100kg off the weight of the caravan or only part of the 100kg? I have been told that DVSA would weigh the unit connected to the vehicle. We are well within the train weight of the towing vehicle.

 

[WoodlandsCamper]

All 100 kg if car and van on the same level. See other threads about reading the nose weight if hitch is not at the normal height when attached to the car.

Edit - yes, add the 100 kg nose weight of the van to that measured at the main wheels to get the loaded weight (which must be less than the MTPLM). But remember there is [strike]about[/strike] +/- 20 kg tolerance in the measuring equipment.

 

[ProfJohnL]

As public weighbridges can be out by 20kg or more,..................

If you read the code of practice, it tells you that Trading Standards will use calibrated loads with an accuracy of +/-10kg. The weighbridges must conform to the Trad Stds loads within +/-20kg to passed suitable for vehicle weighing. Your results will therefore never be more than 20kg out.

 

[Surfer]

As public weighbridges can be out by 20kg or more,..................

If you read the code of practice, it tells you that Trading Standards will use calibrated loads with an accuracy of +/-10kg. The weighbridges must conform to the Trad Stds loads within +/-20kg to passed suitable for vehicle weighing. Your results will therefore never be more than 20kg out.

That may be just after calibration but 5 - 6 months down the line it may be more than w20kg hence the need to re-calibrate on a public weigh bridge, but I take your point.

 

[ProfJohnL]

That may be just after calibration but 5 - 6 months down the line it may be more than w20kg hence the need to re-calibrate on a public weigh bridge, but I take your point.

The idea of calibration is to confirm the correct operation of an instrument and if the instrument is outside its calibration range to flag it up.

However if proper calibration procedures are followed, any instrument that repeatedly fails to meet its specification, will flagged up as unserviceable, and will need to be able to show that corrective actions have been taken to prevent it drifting outside its prescribed limits within it normal calibration period.

A good instrument should not need to be adjusted at every calibration.

You can also be pretty sure that Trad Stnd reference weights and loads will be significantly better than the +/-10kg allowed which means the actual weighbridges should be well within the +/-20kg.

So if a weighbridge repeated drifted beyond the allowed +/-20kg Trad Stnds would not certify it to be used until it had been repaired and proven to be more consistent.