When people argue the physics of a subject and at the same time ignore mass when discussing how two linked masses behave I begin to wonder. Another thing is that I would imagine that caravans with an ATM of 3000kg and up would have double axles rather than single. The lowball weight of my double axle 3000kg ATM caravan is 164kg according to the manafacturer. Today I drove down the hill from Toowoomba to Ipswich. When I stopped at the bottom to fill up at the Freedom service station I checked all the wheel temperatures. The car front pair were the hottest( touchable for about 5 secs or so) then the car back wheels, nowhere near as hot and the van wheels not even warm. This is what I expected.
I would be doing some adjustments to rectify the situation while you and your Rig are all still in one piece ......
yobarr said
11:35 AM Sep 17, 2022
jegog wrote:
yobarr wrote:
Hmmm. You do, of course, realise that the towball weight listed by the van manufacturer means nothing ... absolutely nothing? Assuming the generally accepted 10% towball weight, with a loaded 3000kg ATM caravan your towball weight would be around 300kg. As an aside, your brakes are incorrectly set up if the front wheels are "hot" and the van wheels "not even warm". Cheers
Well that says it all, you know better than the manufacturer. What arrogance?
For your information Jobarr, my caravan is a dual axle torsion bar suspension system.
Increasing tow-ball weight moves the van centre of gravity towards the front of the van.
Weight is moved off the back wheels and onto the front wheels when the tow-ball weight is increased.
Increase the tow-ball weight too much and the load on the front tyres could exceed the tyres rating.
Which is not something we want to do.
So I will be ignoring your erroneous advice and heeding the caravan manufacturer.
There are a couple of dual axle torsion bar systems suspension systems. On the load-sharing type it does not matter where the weight is placed, it always will be shared equally between the axles. If it is not a load-sharing arrangement, provided the chassis level, it does not matter where the weight is placed either, as the weight will still be shared equally between the two axles. If the van is slightly nose-down a small decrease in front axle tyre pressures fixes the perceived "problem". On non-load sharing suspension systems it is important that the chassis of the van be as close as possible to level, with slightly lower pressures in the lead axle. This helps to prevent the van from pivotting on that lead axle, and minimises the effects of tyres scrubbing when turning corners, as well as reducing the effects of yaw. Cheers.
P.S In Canada it is legal for trucks to have no front brakes when weather conditions make doing so essential to safety. Snow, ice etc.. Front axles do next to no braking on Roadtrains that have 86 wheels, sometimes more, like this one with its 110 wheels. Never should you have your car doing all the braking when you're towing, and coming down the Toowoomba range you should also be using your gears to maximise engine braking. Just saying! Cheers
P.P.S You should realise by now, after excellent advice from Greg, Stephen and Kerry, that the manufacturer's stamped towball weight means zilch . nothing nil, nada and that for Australian vans a towball weight of 10% of ATM is the generally accepted figure if safety is of any concern. Cheers
This is a typical Roadtrain in North West WA, but please note that it is NOT the actual Roadtrain that I drive.
-- Edited by yobarr on Saturday 17th of September 2022 01:15:37 PM
Pray tell me how you think that removing weight from the rear axle reduces the effects of yaw. And how do you think a WDH reduces risks of yaw? As you suggest, the rear axle is a pivot point, so it needs to have as firm a grip on the road as possible. Appropriate tyre pressure is critical. Cheers.
-- Edited by yobarr on Sunday 21st of August 2022 10:12:29 PM
The way I understand it yaw is started by the van moving off track and exerting a sideways force on the tow-ball. This force on the tow-ball will distort the sidewall of the tyres, the pivot point being the front wheels. Radial tyres are renown for distortion when a lateral force is applied.
Then the van swings back into line and aided by the back tyres un-distorting tend to overcorrect. This is a form of feedback and at low speeds it is negative feedback but there is a critical speed where it becomes positive feedback, with disastrous results.
I don't know what effect weight distribution has but increasing the distance between the back axle and the tow-ball will result in increased likelihood of yaw.
Are We Lost said
06:47 PM Sep 24, 2022
jegog, the pivot point is the rear wheels, not the front. One of those times I agree with Yobarr.
While the distortion of the tyres might play a part I don't think it is significant. The fact that the wheel is able to move sideways with very little resistance (but only a few centimetres) may help to start the yawing motion, and then the kinetic energy tends to continue the motion in that direction. Maybe it is a contributing factor.
However the quote you pasted was Yobarr's response to a comment of mine from 5 weeks ago. As the thread had moved on I did not address that. But rather than get too involved again I will just link to my earlier comment which I think explains it well enough.
jegog, the pivot point is the rear wheels, not the front. One of those times I agree with Yobarr.
While the distortion of the tyres might play a part I don't think it is significant. The fact that the wheel is able to move sideways with very little resistance (but only a few centimetres) may help to start the yawing motion, and then the kinetic energy tends to continue the motion in that direction. Maybe it is a contributing factor.
However the quote you pasted was Yobarr's response to a comment of mine from 5 weeks ago. As the thread had moved on I did not address that. But rather than get too involved again I will just link to my earlier comment which I think explains it well enough.
Unfortunately your explanation is at odds with these videos.
Are We Lost said
11:05 AM Sep 25, 2022
If you watch the video of the model you will see it does exactly as I was saying .... the leverage on the rear end rotates the vehicle with the axis being the rear wheels. And that is despite a very short towball overhang on the model.
This image is from the 1:00 mark and it very clearly shows the front pointing in a different direction while the rear end has hardly moved. The same applies earlier in the video where the weight placement was considered correct.
The videos of actual caravan rollovers are a bit harder to see for sure. It is the initial movements that are important. Once movement becomes siginficant there are multiple forces at play. Perhaps that few centimetres of tyre distortion you raised is enough to allow the yawing motion to begin. A well set up rig should overcome this with ease, but maybe it becomes the trigger in some cases.
Have a 2020 Wildtrack towing a large Crusader van. Not using a WDH. Actually the van frame bars Prevent having them. We are just careful in the van load and distribution. So far all has been good and no problems.
Roy E said
10:14 AM Nov 6, 2022
All in all, a very interesting discussion.
My old-style HR WDH fitted deeply into my previous car receiver HR towbar receiver giving minimum overhang.
The same hitch fitted to my later car (Pajero Sport with HR towbar) gave 70mm additional overhang because hitch-pin hole in receiver drilled so far rearward and receiver very short. This gave total overhang over and above that of original MM hitch-tongue of 115mm.
I cut 50mm off HR WDH shank end and had new pin hole drilled in shank 70mm rearward. This allowed HR WDH to go all the way into HR tow bar receiver on the Paj Sport.
Overhang now on HR WDH is 45mm where it was 115mm before modification.
Cheers,
Roy.
I would be doing some adjustments to rectify the situation while you and your Rig are all still in one piece ......
There are a couple of dual axle torsion bar systems suspension systems. On the load-sharing type it does not matter where the weight is placed, it always will be shared equally between the axles. If it is not a load-sharing arrangement, provided the chassis level, it does not matter where the weight is placed either, as the weight will still be shared equally between the two axles. If the van is slightly nose-down a small decrease in front axle tyre pressures fixes the perceived "problem". On non-load sharing suspension systems it is important that the chassis of the van be as close as possible to level, with slightly lower pressures in the lead axle. This helps to prevent the van from pivotting on that lead axle, and minimises the effects of tyres scrubbing when turning corners, as well as reducing the effects of yaw. Cheers.
P.S In Canada it is legal for trucks to have no front brakes when weather conditions make doing so essential to safety. Snow, ice etc.. Front axles do next to no braking on Roadtrains that have 86 wheels, sometimes more, like this one with its 110 wheels. Never should you have your car doing all the braking when you're towing, and coming down the Toowoomba range you should also be using your gears to maximise engine braking. Just saying! Cheers
P.P.S You should realise by now, after excellent advice from Greg, Stephen and Kerry, that the manufacturer's stamped towball weight means zilch . nothing nil, nada and that for Australian vans a towball weight of 10% of ATM is the generally accepted figure if safety is of any concern. Cheers
This is a typical Roadtrain in North West WA, but please note that it is NOT the actual Roadtrain that I drive.
-- Edited by yobarr on Saturday 17th of September 2022 01:15:37 PM
The way I understand it yaw is started by the van moving off track and exerting a sideways force on the tow-ball. This force on the tow-ball will distort the sidewall of the tyres, the pivot point being the front wheels. Radial tyres are renown for distortion when a lateral force is applied.
Then the van swings back into line and aided by the back tyres un-distorting tend to overcorrect. This is a form of feedback and at low speeds it is negative feedback but there is a critical speed where it becomes positive feedback, with disastrous results.
I don't know what effect weight distribution has but increasing the distance between the back axle and the tow-ball will result in increased likelihood of yaw.
jegog, the pivot point is the rear wheels, not the front. One of those times I agree with Yobarr.
While the distortion of the tyres might play a part I don't think it is significant. The fact that the wheel is able to move sideways with very little resistance (but only a few centimetres) may help to start the yawing motion, and then the kinetic energy tends to continue the motion in that direction. Maybe it is a contributing factor.
However the quote you pasted was Yobarr's response to a comment of mine from 5 weeks ago. As the thread had moved on I did not address that. But rather than get too involved again I will just link to my earlier comment which I think explains it well enough.
Previous explanation
This video shows a yaw incident, if you look closely you will see that it is the back of the tug which moves literarily first
https://www.youtube.com/watch?v=nd-hUX8memY
and this is a video of a simulation of induced yawing
Notice how when the load is deflected sideways the tug's back wheels move in the opposite direction first
This video is of yaw dynamics
https://www.exploroz.com/Vehicle/Caravans/Caravan_Dynamics.aspx
Unfortunately your explanation is at odds with these videos.
If you watch the video of the model you will see it does exactly as I was saying .... the leverage on the rear end rotates the vehicle with the axis being the rear wheels. And that is despite a very short towball overhang on the model.
This image is from the 1:00 mark and it very clearly shows the front pointing in a different direction while the rear end has hardly moved. The same applies earlier in the video where the weight placement was considered correct.
The videos of actual caravan rollovers are a bit harder to see for sure. It is the initial movements that are important. Once movement becomes siginficant there are multiple forces at play. Perhaps that few centimetres of tyre distortion you raised is enough to allow the yawing motion to begin. A well set up rig should overcome this with ease, but maybe it becomes the trigger in some cases.
G'day
Have a 2020 Wildtrack towing a large Crusader van. Not using a WDH. Actually the van frame bars Prevent having them. We are just careful in the van load and distribution. So far all has been good and no problems.
My old-style HR WDH fitted deeply into my previous car receiver HR towbar receiver giving minimum overhang.
The same hitch fitted to my later car (Pajero Sport with HR towbar) gave 70mm additional overhang because hitch-pin hole in receiver drilled so far rearward and receiver very short. This gave total overhang over and above that of original MM hitch-tongue of 115mm.
I cut 50mm off HR WDH shank end and had new pin hole drilled in shank 70mm rearward. This allowed HR WDH to go all the way into HR tow bar receiver on the Paj Sport.
Overhang now on HR WDH is 45mm where it was 115mm before modification.
Cheers,
Roy.