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Dusty Dog, its a short story, Went to the NEC to buy a pair of Suspension dampers, for our Coachman 545, came away happy, Next day went to our local dealer and bought a new Cochman 560 that had dampers fitted, so took them back to AlKo for a refund.
I have been following the Bailey relaxed axle debate on a few different sites, it would appear that on inspection and weighing of the caravan in most instances the finger has been pointed at the owner for overloading.
Can I ask when the weighing procedures are carried out is it with the caravan static or attached to a towing vehicle as both methods will produce a different axle weight. In its hitched condition I would expect the caravan axle to be minus its nose weight and vice versa, so an overloaded axle of say 80kg static could be 20kg within its limits with a given nose weight of 100kg in its hitched and ready for the road position. Your thoughts on this matter?
Can I ask when the weighing procedures are carried out is it with the caravan static or attached to a towing vehicle as both methods will produce a different axle weight. In its hitched condition I would expect the caravan axle to be minus its nose weight and vice versa, so an overloaded axle of say 80kg static could be 20kg within its limits with a given nose weight of 100kg in its hitched and ready for the road position. Your thoughts on this matter?
Volly said:
No point in asking me about Bailey mines a Swift. Also at five years old when the problem was found there’s not any point in taking it up with Swift as it’s not possible to prove it has or it has not been overloaded. But you are correct that noseweight does reduce the axle load by a commensurate amount. Who knows even a big pothole could have caused the damage. But the previous owner did have kids!!! Just one of life’s pleasures in owning a caravan. If they had the suspension with trailing arm as of yesteryear we wouldn’t be having this discussion.
Volly said:
It is very difficult to weigh a caravan in anything other than its "static" condition, If it isn't static it's moving! Static means stationary. All vehicle weights and loads for legal and compliance purposes are measured when the vehicle is stationary. Not only is it very difficult to physically measure loads when vehicle is motion, but the dynamic effect of the motion will affect the values during measurement.
But the question you have actually asked is should the axle be weighed hitched or unhitched, becasue you suspect the load on the axle will change when the caravan is unhitched.
The simple answers it should be hitched, as that is the condition it will be in when on the road. And the weight will be different, but not to the degree or reason you have suggested.
This all can be explained by turning moments (forces x distances) and also bearing in mind that the weight of an object when its stationary will be matched exactly by the sum of the thrust each of its support points bears.
For simplicity if we consider a single axle caravan, the axle load to be the sum of the load on both road wheels, and the total caravan weight will be the axle load and the nose load.
When the caravan is unhitched, the road wheels still take the bulk of the total weight but the nose is usually supported by the jockey wheel. But becasue the distance between the hitch and the axle is greater than the jockey wheel stem to the axle, due to turning moments the load on the jockey wheel will be greater.
But the total weight has not changed, so if the jockey wheel is carrying more load than the hitch did, the load on the main axle must have been reduced by exactly the same amount. It all to do with the geometry of the caravan, and some simple maths will show that a jockey wheel stem will carry something like 25 to 30% more load then the hitch, and by the same token it means the main axle load would reduce by exactly the same amount.
Its all further complicated by the the fact that nose load is not a fixed value, not only is it dependant on how the caravan is loaded, but also the height of the when its attached to the tow vehicle. This is why its important to ensure nose load is measured when the hitch is supported by the measurement device at exactly the same height as when its couple to the tow vehicle.
Some people suggest its not necessary to measure accurately. I disagree.
Thanks for the reply John.
If you can cast your mind back a few years ago there was quite a lengthily debate on the effect that nose weight has on the weight transfer from caravan to car, you agreed with Lutz that the nose weight could not be in two places at the same time, ie. if you loaded the caravan to its maximum MTPLM @ 1500KG with a nose weight set at 100kg then you would have a towed load of 1400kg as the nose weight had now been transferred to the towing vehicle, The axle weight when weighed whilst coupled to the towing vehicle must therefor be 1400kg.
To my way of thinking with the relaxed axle weight issue the only correct way when investigated would be to weigh the caravan whilst coupled to the towing vehicle with the appropriate nose value set, to weigh the caravan in an un hitched condition would surely produce a higher axle weight.
If I was to find myself in this predicament I would be insistent that the axle weight be measured whilst coupled and the correct nose weight set.
It seems to convenient in the majority of cases that a guilty verdict is returned for overloading, and not forgetting that in a lot of cases a weight upgrade plate would have covered the difference in the weight discrepancy.
As previously stated John this issue does not effect me, I am trying to give those in the unfortunate position a different angle to approach the supplying dealers with.
If you can cast your mind back a few years ago there was quite a lengthily debate on the effect that nose weight has on the weight transfer from caravan to car, you agreed with Lutz that the nose weight could not be in two places at the same time, ie. if you loaded the caravan to its maximum MTPLM @ 1500KG with a nose weight set at 100kg then you would have a towed load of 1400kg as the nose weight had now been transferred to the towing vehicle, The axle weight when weighed whilst coupled to the towing vehicle must therefor be 1400kg.
To my way of thinking with the relaxed axle weight issue the only correct way when investigated would be to weigh the caravan whilst coupled to the towing vehicle with the appropriate nose value set, to weigh the caravan in an un hitched condition would surely produce a higher axle weight.
If I was to find myself in this predicament I would be insistent that the axle weight be measured whilst coupled and the correct nose weight set.
It seems to convenient in the majority of cases that a guilty verdict is returned for overloading, and not forgetting that in a lot of cases a weight upgrade plate would have covered the difference in the weight discrepancy.
As previously stated John this issue does not effect me, I am trying to give those in the unfortunate position a different angle to approach the supplying dealers with.
Volly said:
Hello again Volly.
Yes I do remember the debate, and the subject has been brought up on several occasions since. For some it has been a good news, but for others the reasoning is still a mystery, and I have to point out that this thread still shows that you have not grasped the principles and logic behind it.
The nose load produced by a trailer is a force, which is applied to the hitch of the tow vehicle, so the tow vehicle must accommodate that applied load within its own axle loads. So for example I hope you would agree you could not load up a solo tow vehicle to its limits and the expect it to cope with the additional applied load from the trailer. This means as you point out a 1500kg MTPLM caravan might have a 100kg nose load leaving only 1400kg as its towed or axle load.
In simplistic terms unhitching the caravan does not radically change the balance of the caravan, it will still have only roughly 1400kg on its main axle, and about 100kg nose load is now carried by jockey wheel. This assumes the jockey wheel is used to keep the hitch at the same height as when its coupled to the tow car.Though in practice there will be a slight increase in the load on the jockey wheel, and an equal reduction in the load on the main axle becasue the jockey wheel is closer to the axle than the hitch and this affects the mechanical advantages .
So the answer is still the caravan axle load should be measured whilst the caravan is coupled to the tow vehicle for absolute accuracy, but if it is measured with the caravan using the jockey wheel the axle load will reduce slightly - only up to about 20Kg less. it depends on the geometry of the chassis and the position and height of the jockey wheel. The axle load will not increase as you have suggested and certainly not by the amount of the nose load..
ProfJohnL said:
When I was "invited" for a VOSA weight check near to Ringwood, the coupled outfit was weighed, axle loads, weighed, and the caravan on its own supported on its nose wheel and with nose wheel off of the weighbridge. Also the van's tyre Load Index was checked.Everything came out okay, and I wasn't given any paperwork; not that I needed it.
Hello John, it would appear that you have not fully remembered the archive post from a few years back as you now appear to be contradicting yourself.
“and I have to point out that this thread still shows that you have not grasped the principles and logic behind it.”
I fully understand the principles and logic behind nose weight, as I have pointed out in my previous post you quoted that the nose weight could not be in two places at the same time, and at no point did you mention the part that the jockey wheel plays in the configuration.
You also quoted that full use of the payload was not beng used, ie a caravan with a MTPLM of 15000kg and running with a nose weight of 100kg would have a towed load of 1400kg, with the nose weight now being carried by the tow vehicle,(remember your quote it can’t be in two places at the same time) thus allowing a further 100kg to be added to the payload of the caravan as the MTPLM would still be within it’s limits at 1500kg.
I argued this point with you at great length that if the caravan was weight checked un hitched it would be overloaded by 100kg.
The reason for my post is quite simple, if your formula was correct then the axle weight would be reduced and could shed a light of hope for those unfortunate to have a relaxed axle.
“and I have to point out that this thread still shows that you have not grasped the principles and logic behind it.”
I fully understand the principles and logic behind nose weight, as I have pointed out in my previous post you quoted that the nose weight could not be in two places at the same time, and at no point did you mention the part that the jockey wheel plays in the configuration.
You also quoted that full use of the payload was not beng used, ie a caravan with a MTPLM of 15000kg and running with a nose weight of 100kg would have a towed load of 1400kg, with the nose weight now being carried by the tow vehicle,(remember your quote it can’t be in two places at the same time) thus allowing a further 100kg to be added to the payload of the caravan as the MTPLM would still be within it’s limits at 1500kg.
I argued this point with you at great length that if the caravan was weight checked un hitched it would be overloaded by 100kg.
The reason for my post is quite simple, if your formula was correct then the axle weight would be reduced and could shed a light of hope for those unfortunate to have a relaxed axle.
Volly said:
This thread is reopening several previous similar ones. The logic is sound but MTPLM as specified by the maker is the total all up weight of the caravan including that which is taken by the nose wheel. As the Design Authority for the caravan the maker has ultimate responsibility for its specification. What we never get information on are caravans which are weighed by DVSA and are above MTPLM but have an axle load within the axles specification. As most overweight caravans seem to be sent on their way perhaps with some rearrangement of load between the car and caravan I suspect DVSA take a pragmatic approach. But you wont find anything "legal" written down. So that why most try and stay within MTPLM.
The advantage of so doing is that you will be relieving the rubbish Alko axle of around 75-100kg if load, and saving the hassle and significant cost of installing a new axle.
Volly said:
Hello Volly
I confess I have not reread the old thread, nor will I becasue, such time has passed and we mat a be a little wiser now than then. BUT I have always understood the all up weight of a caravan (i.e the sum of axle load and nose load) must never exceed the MTPLM, so I cannot conceive that I would suggest a strategy that could lead to overloading.
Perhaps if you wish to pursue this discussion further, rather than over complicate this thread you might like to start another thread.
As you have apparently already found the old thread you might like to post relevant quotes or link the thread in your post.
Check the height of the axle both sides, if it is like mine the fault is in the chassis weakening not the suspension
Mel
Moderator
This is an old thread that has been reopened before. I am locking it. If further discussion is needed feel free to start a new thread.
Mel
Mel
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