We are all told that the tow vehicle should be at least 10% heavier than the van we are towing and I don't doubt that for one moment.
What I would like to know is the scientific reason a semi trailer prime mover can be less in weight that its trailer let alone with a B-Double or a Road Train. Just curious.
Peter_n_Margaret said
11:40 AM Oct 5, 2021
The position of the hitch makes the difference between being inherently stable and inherently unstable.
A semi has the hitch over (or slightly in front) of the axle.
A caravan has the hitch a metre or more behind the axle. It is inherently unstable.
The further it is behind the axle, the more likely the trailer will overpower the towing vehicle.
Cheers,
Peter
KevinJ said
12:49 PM Oct 5, 2021
Peter_n_Margaret wrote:
The position of the hitch makes the difference between being inherently stable and inherently unstable. A semi has the hitch over (or slightly in front) of the axle. A caravan has the hitch a metre or more behind the axle. It is inherently unstable. The further it is behind the axle, the more likely the trailer will overpower the towing vehicle. Cheers, Peter
Thanks Peter. That makes sense.
Peter_n_Margaret said
01:04 PM Oct 5, 2021
A bit more...
When a van pushes the tow hitch sideways, the overhang causes that force to push the front wheels sideways.
From there it is a small step to loosing total control.
If the hitch is directly over the rear axle, there is zero force transferred to the front (steering) axle.
Cheers,
Peter
KevinJ said
01:24 PM Oct 5, 2021
Peter_n_Margaret wrote:
A bit more... When a van pushes the tow hitch sideways, the overhang causes that force to push the front wheels sideways. From there it is a small step to loosing total control. If the hitch is directly over the rear axle, there is zero force transferred to the front (steering) axle. Cheers, Peter
Yes, makes sense. Just a matter of moments and force.
Gundog said
01:58 PM Oct 5, 2021
There is no requirement for the towing vehicle to be heavier than the towed trailer, precedents that come first are GVM, GCM, TBW, Axle weights and Max towing load must not be exceeded.
The single biggest issue is poorly setup combinations, just drive along the Bruce Hwy in Qld on any given day you will observe many vans being towed have the front low and the rear high, and conversly there are also many with the front high and the rear low. However if your combination is setup correctly its irrevelent if your towing vehicle is lighter than your caravan, the 10% heavier is a furphy just like the tow ball weight 10% non rule.
Peter_n_Margaret said
02:14 PM Oct 5, 2021
Being "legal" does not make it safe.
Gundog, please explain (in physics/engineering terms) why having the van NOT level is a problem.
Cheers,
Peter
yobarr said
05:00 PM Oct 5, 2021
Gundog wrote:
There is no requirement for the towing vehicle to be heavier than the towed trailer, precedents that come first are GVM, GCM, TBW, Axle weights and Max towing load must not be exceeded.
The single biggest issue is poorly setup combinations, just drive along the Bruce Hwy in Qld on any given day you will observe many vans being towed have the front low and the rear high, and conversly there are also many with the front high and the rear low. However if your combination is setup correctly its irrevelent if your towing vehicle is lighter than your caravan, the 10% heavier is a furphy just like the tow ball weight 10% non rule.
Graham,I have covered this many times before,but I will again ask you to explain why it is law that if a vehicle has a GVM above 4500kg,any PIG trailer it tows MUST have less weight on its wheels than is on the tow unit's wheels.This is why you have people like earthmoving contractors often having to drop a couple of ton of dirt onto the back of their tow unit if it is towing an excavator,for example,on a PIG Trailer.At some stage,it is likely to become law that ALL tow vehicles must have more weight on their wheels than is on the wheels of any PIG trailer they're towing.And the sooner the better,in my opinion.Simple physics at work here.As for your "front up,rear down" or "front down,rear up" question,either situation MAY be acceptable if the van has load-sharing suspension.If not,and the front of the van is down,you're playing with fire,as the whole caravan will tend to "pivot" on the front axle,thus dramatically increasing what is effectively your rear overhang,and hugely increasing the chances of YAW sending it all R Sup.Again,simple physics and not negotiable.I could go on and explain why the generally accepted 10% TBW is important,and why the tow unit should ALWAYS have at LEAST 10% more weight on its wheels than is on the wheels of the van,but again it is simple physics that I already have explained,many times,in great detail.Cheers
P.S You no doubt find this acceptable? Or where do you draw the line?
-- Edited by yobarr on Wednesday 6th of October 2021 04:27:40 AM
Also, a semi trailer has the wheels almost on the corners whereas a caravan has the wheels in the centre. The latter allows the caravan to yaw, or something like that, thus being able to throw the towing car around whereas having the wheels on the corners provides a lot more stability.
-- Edited by Buzz Lightbulb on Tuesday 5th of October 2021 11:50:45 PM
montie said
07:50 AM Oct 6, 2021
There is currently no regulation that covers van/tug weight ratio, however, in the interest of safe towing it is recommended that the tug should exceed the van weight by at least 10%.
It is also recommended that the measured loaded ball weight should be 10% of the van's ATM. Again, this is purely a recommendation.
oldbloke said
08:39 AM Oct 6, 2021
montie wrote:
There is currently no regulation that covers van/tug weight ratio, however, in the interest of safe towing it is recommended that the tug should exceed the van weight by at least 10%. It is also recommended that the measured loaded ball weight should be 10% of the van's ATM. Again, this is purely a recommendation.
This makes the most sense to me.
KevinJ said
08:52 AM Oct 6, 2021
Thank you all for the scientific answers to my question. I will ignore the obviously incorrect reply.
Jaahn said
09:09 AM Oct 6, 2021
Hi ,
In times past, in NSW at least, possibly elsewhere, there was a requirement to have the trailer less weight than the tug. I forget the exact details now. But over time it was stretched and a big push was made by horse trailer owners. Lots of clout there ! When the federal gov encouraged the states to harmonise the road rules and regs there was a lot of discussion on the trailer rules. But the lowest common denominator was decided on, no rules !
I might also say with regards to semi trailers and their safety. It is required that all heavy vehicles are required to have trained and appropriately licenced operators. This also includes loading and checking the rig as well as driving. As the size of the rig goes up the experience and licences required go up also. You can not just retire and then buy a 'big rig', more than you ever drove, and go driving around Australia in a heavy vehicle, but you can with a big caravan ?? Hmmm
Jaahn
PS It has been my limited experience that the attitude of the caravan, front up or down, has some effect on the aerodynamics of the van and the stability towing.
-- Edited by Jaahn on Wednesday 6th of October 2021 09:14:38 AM
yobarr said
10:00 AM Oct 6, 2021
You can not just retire and then buy a 'big rig', more than you ever drove, and go driving around Australia in a heavy vehicle, but you can with a big caravan ?? Hmmm
Exactly! If a person wishes to drive a furniture truck with a 4 metre tray,for example,if said 'truck' has a GVM over 4500kg,a special licence is required. (MR?).Total length of vehicle would be under 6 metres,and it is a rigid vehicle,so naturally stable.However,if Ma and Pa Kettle realise that the ubiquitous LC200 cannot safely tow more than 3000kg,and choose,for example,a Y62 Nissan Patrol,to tow their 8 metre van,3500kg ATM van, they can run legally at 6520kg GCM,and set sail. Not only does this unit weigh 6520kg,it also is an articulated vehicle,more than 15 metres long. Because the trailer being towed is a PIG trailer,it is inherently unstable.And these people are allowed to roam our highways,perhaps incompetent,certainly inexperienced,as a mobile accident looking for a place to happen.Spare me!
P.S The car is neither an LC200,nor a Y62,but this an "accident" that occurred on the Kuranda range.
There is currently no regulation that covers van/tug weight ratio, however, in the interest of safe towing it is recommended that the tug should exceed the van weight by at least 10%. It is also recommended that the measured loaded ball weight should be 10% of the van's ATM. Again, this is purely a recommendation.
This is getting harder and harder to achieve as more vans become heavier, most new offroaders being ATM 3500kg.
This would mean the tug would have to have a GVM of 3750kg, the mighty LC200 is only 3350kg and others below that. Not to mention the combined weight of both.
To be safe, they need to make lighter vans.
KJB said
10:26 AM Oct 6, 2021
Bobdown wrote:
montie wrote:
There is currently no regulation that covers van/tug weight ratio, however, in the interest of safe towing it is recommended that the tug should exceed the van weight by at least 10%. It is also recommended that the measured loaded ball weight should be 10% of the van's ATM. Again, this is purely a recommendation.
This is getting harder and harder to achieve as more vans become heavier, most new offroaders being ATM 3500kg.
This would mean the tug would have to have a GVM of 3750kg, the mighty LC200 is only 3350kg and others below that. Not to mention the combined weight of both.
To be safe, they need to make lighter vans.
Buy a smaller, lighter caravan - there are plenty to choose from. - KB
Peter_n_Margaret said
10:26 AM Oct 6, 2021
They MAKE what people BUY.
Besides, there are lighter vans (including "off road" vans) available, but there is a mistaken view that they need to be heavy to be strong.
Cheers,
Peter
-- Edited by Peter_n_Margaret on Wednesday 6th of October 2021 10:28:51 AM
montie said
11:24 AM Oct 6, 2021
Manufacturers build what the market demands and untill such time as some regulation regarding Van/tug weight ratio is introduced, this situation is unlikely to change.
Tug manufacturers are already making dubious claims about the towing ability of their vehicles.
yobarr said
12:05 PM Oct 6, 2021
montie wrote:
Manufacturers build what the market demands and untill such time as some regulation regarding Van/tug weight ratio is introduced, this situation is unlikely to change.
Tug manufacturers are already making dubious claims about the towing ability of their vehicles.
And their "out",when challenged,is that these lightweights can indeed tow 3500kg (or whatever),but only as a DOG trailer.Heavy vehicles have a totally different set of rules,and the sooner a law is enacted that requires ALL tow vehicles to be heavier than the trailer they're towing as a PIG trailer,the safer we all will be.Common sense,and simple physics.Cheers
Jaahn said
01:57 PM Oct 6, 2021
Hi
There is another alternative and that is to get a more stable rig that has the van just as big but stable like a semi ! Not popular here so I guess the punters think they must be not as good. 5th wheel caravans they are called and instead of the caravan being an unstable pig design they are an inherently stable wheels at the back and hitch over the tug rear axle similar to a heavy semi layout. If I did not drive a modest MH then I would get a 5th wheeler and tow comfortably and happily and quite possibly more cheaply.
Jaahn
oldbloke said
02:12 PM Oct 6, 2021
For those who may not understand the truckie jargon.
The caravan is a "pig" trailer. Note axles location.
The large SS one is a "dog" trailer. Again note axles position.
" another.Shows that even Tritons can tow a decent sized van! Cheers"
Now, now. Control yourself.
.
watsea said
09:45 PM Oct 6, 2021
I like the dog trailer arrangement. Of course, I have not seen any caravan ones in Australia. Plenty of truck dog trailers though. So, how hard is a dog trailer to reverse in the direction required? I haven't been given the opportunity to try.
yobarr said
10:03 PM Oct 6, 2021
watsea wrote:
I like the dog trailer arrangement. Of course, I have not seen any caravan ones in Australia. Plenty of truck dog trailers though. So, how hard is a dog trailer to reverse in the direction required? I haven't been given the opportunity to try.
Like riding a bicycle,perhaps,reversing a dog trailer is an absolute nightmare to learn,but becomes second-nature once it has been mastered.The longer the dog trailer,the easier it is to reverse,but towbar length also affects things! Given that many caravanners have an apparent inability to reverse even a simple pig trailer,I doubt that caravans built in a dog trailer configuration ever will become popular.BUT,if they ever did become popular,at least the current crop of twin-cab utes,and LC200s,might be able to safely reach their rated towing capacity.Won't ever happen though! Even an AWD Territory could tow 2700kg! Cheers
We are all told that the tow vehicle should be at least 10% heavier than the van we are towing and I don't doubt that for one moment.
What I would like to know is the scientific reason a semi trailer prime mover can be less in weight that its trailer let alone with a B-Double or a Road Train. Just curious.
A semi has the hitch over (or slightly in front) of the axle.
A caravan has the hitch a metre or more behind the axle. It is inherently unstable.
The further it is behind the axle, the more likely the trailer will overpower the towing vehicle.
Cheers,
Peter
Thanks Peter. That makes sense.
When a van pushes the tow hitch sideways, the overhang causes that force to push the front wheels sideways.
From there it is a small step to loosing total control.
If the hitch is directly over the rear axle, there is zero force transferred to the front (steering) axle.
Cheers,
Peter
Yes, makes sense. Just a matter of moments and force.
There is no requirement for the towing vehicle to be heavier than the towed trailer, precedents that come first are GVM, GCM, TBW, Axle weights and Max towing load must not be exceeded.
The single biggest issue is poorly setup combinations, just drive along the Bruce Hwy in Qld on any given day you will observe many vans being towed have the front low and the rear high, and conversly there are also many with the front high and the rear low. However if your combination is setup correctly its irrevelent if your towing vehicle is lighter than your caravan, the 10% heavier is a furphy just like the tow ball weight 10% non rule.
Gundog, please explain (in physics/engineering terms) why having the van NOT level is a problem.
Cheers,
Peter
Graham,I have covered this many times before,but I will again ask you to explain why it is law that if a vehicle has a GVM above 4500kg,any PIG trailer it tows MUST have less weight on its wheels than is on the tow unit's wheels.This is why you have people like earthmoving contractors often having to drop a couple of ton of dirt onto the back of their tow unit if it is towing an excavator,for example,on a PIG Trailer.At some stage,it is likely to become law that ALL tow vehicles must have more weight on their wheels than is on the wheels of any PIG trailer they're towing.And the sooner the better,in my opinion.Simple physics at work here.As for your "front up,rear down" or "front down,rear up" question,either situation MAY be acceptable if the van has load-sharing suspension.If not,and the front of the van is down,you're playing with fire,as the whole caravan will tend to "pivot" on the front axle,thus dramatically increasing what is effectively your rear overhang,and hugely increasing the chances of YAW sending it all R Sup.Again,simple physics and not negotiable.I could go on and explain why the generally accepted 10% TBW is important,and why the tow unit should ALWAYS have at LEAST 10% more weight on its wheels than is on the wheels of the van,but again it is simple physics that I already have explained,many times,in great detail.Cheers
P.S You no doubt find this acceptable? Or where do you draw the line?
-- Edited by yobarr on Wednesday 6th of October 2021 04:27:40 AM
Also, a semi trailer has the wheels almost on the corners whereas a caravan has the wheels in the centre. The latter allows the caravan to yaw, or something like that, thus being able to throw the towing car around whereas having the wheels on the corners provides a lot more stability.
This is a useful video to watch:
https://youtu.be/gGzMajuCYgk
-- Edited by Buzz Lightbulb on Tuesday 5th of October 2021 11:50:45 PM
It is also recommended that the measured loaded ball weight should be 10% of the van's ATM. Again, this is purely a recommendation.
This makes the most sense to me.
Thank you all for the scientific answers to my question. I will ignore the obviously incorrect reply.
Hi
,
In times past, in NSW at least, possibly elsewhere, there was a requirement to have the trailer less weight than the tug. I forget the exact details now. But over time it was stretched and a big push was made by horse trailer owners. Lots of clout there ! When the federal gov encouraged the states to harmonise the road rules and regs there was a lot of discussion on the trailer rules. But the lowest common denominator was decided on, no rules !
I might also say with regards to semi trailers and their safety. It is required that all heavy vehicles are required to have trained and appropriately licenced operators. This also includes loading and checking the rig as well as driving. As the size of the rig goes up the experience and licences required go up also. You can not just retire and then buy a 'big rig', more than you ever drove, and go driving around Australia in a heavy vehicle, but you can with a big caravan ?? Hmmm
Jaahn
PS It has been my limited experience that the attitude of the caravan, front up or down, has some effect on the aerodynamics of the van and the stability towing.
-- Edited by Jaahn on Wednesday 6th of October 2021 09:14:38 AM
Exactly! If a person wishes to drive a furniture truck with a 4 metre tray,for example,if said 'truck' has a GVM over 4500kg,a special licence is required. (MR?).Total length of vehicle would be under 6 metres,and it is a rigid vehicle,so naturally stable.However,if Ma and Pa Kettle realise that the ubiquitous LC200 cannot safely tow more than 3000kg,and choose,for example,a Y62 Nissan Patrol,to tow their 8 metre van,3500kg ATM van, they can run legally at 6520kg GCM,and set sail. Not only does this unit weigh 6520kg,it also is an articulated vehicle,more than 15 metres long. Because the trailer being towed is a PIG trailer,it is inherently unstable.And these people are allowed to roam our highways,perhaps incompetent,certainly inexperienced,as a mobile accident looking for a place to happen.Spare me!
P.S The car is neither an LC200,nor a Y62,but this an "accident" that occurred on the Kuranda range.
This is getting harder and harder to achieve as more vans become heavier, most new offroaders being ATM 3500kg.
This would mean the tug would have to have a GVM of 3750kg, the mighty LC200 is only 3350kg and others below that. Not to mention the combined weight of both.
To be safe, they need to make lighter vans.
Buy a smaller, lighter caravan - there are plenty to choose from. - KB
They MAKE what people BUY.
Besides, there are lighter vans (including "off road" vans) available, but there is a mistaken view that they need to be heavy to be strong.
Cheers,
Peter
-- Edited by Peter_n_Margaret on Wednesday 6th of October 2021 10:28:51 AM
Tug manufacturers are already making dubious claims about the towing ability of their vehicles.
And their "out",when challenged,is that these lightweights can indeed tow 3500kg (or whatever),but only as a DOG trailer.Heavy vehicles have a totally different set of rules,and the sooner a law is enacted that requires ALL tow vehicles to be heavier than the trailer they're towing as a PIG trailer,the safer we all will be.Common sense,and simple physics.Cheers
Hi
There is another alternative and that is to get a more stable rig that has the van just as big but stable like a semi ! Not popular here so I guess the punters think they must be not as good.
5th wheel caravans they are called and instead of the caravan being an unstable pig design they are an inherently stable wheels at the back and hitch over the tug rear axle similar to a heavy semi layout. If I did not drive a modest MH then I would get a 5th wheeler and tow comfortably and happily and quite possibly more cheaply.
Jaahn
For those who may not understand the truckie jargon.
The caravan is a "pig" trailer. Note axles location.
The large SS one is a "dog" trailer. Again note axles position.
This caravan is a "dog" trailer. The ball weight is close to zero.
The front wheels are steerable by the "A " frame.
Cheers,
Peter
And another.Shows that even Tritons can tow a decent sized van! Cheers
Now, now. Control yourself.
.
Like riding a bicycle,perhaps,reversing a dog trailer is an absolute nightmare to learn,but becomes second-nature once it has been mastered.The longer the dog trailer,the easier it is to reverse,but towbar length also affects things! Given that many caravanners have an apparent inability to reverse even a simple pig trailer,I doubt that caravans built in a dog trailer configuration ever will become popular.BUT,if they ever did become popular,at least the current crop of twin-cab utes,and LC200s,might be able to safely reach their rated towing capacity.Won't ever happen though! Even an AWD Territory could tow 2700kg! Cheers