Caravan rollovers

Colin Penrose · Senior Member

Caravan rollovers

iana · Guru

Hope you are wrong, we tow a 24ft. On the other hand, had a good look at a new Silverline the other week. The salesman mentioned there had been one in a roll over, Seemed to make reasons for not stowing effects under the club lounge, and I notice the front boot has been modified so that only limited gear can be stored, while tool boxes have been fitted behind the wheels.

Aus-Kiwi · Guru

Balance and more importantly., The NUT behind the wheel !!!

Mamil · Senior Member

According to what I've read on the subject, it's a combination of bad loading, ie. too much weight at the extremities which increases the yaw effect, plus speed which exacerbates it exponentially.
A good video here which says much more than I could explaining it in words...

https://youtu.be/PFzrWHTG5e8

Tony Bev · Guru

I would also like to know, why some caravans overturn
As (in my opinion), it would help other travellers in the future

Until people are honest enough to say, what happened to make their caravan overturn, then we can only guess

I was towing an old 17 foot single axle pop top, doing (slightly over the speed limit) downhill, to help get up another hill, when I felt a wobble
Slowing down to below the legal speed limit, stopped the wobbling

I am unsure if the wobble was caused by the speed, road surface, or perhaps a gust of wind
I can only say, that from that point on, by never going over the speed limit, I never had any more wobbles, in about 30,000 kilometres of towing

If as Col has already said, it appears that it is the larger tandem axle vans overturning, then this may be a common factor to look at

Knight · Senior Member

I often observe vehicles towing caravans that are too far front down or front up, tow hitch not at a suitable height for the caravan.

And they sway at highway speeds, of course.

Having experienced a single axle caravan driver's side of vehicle tyre blowout at a real 90 KMH west of the Queensland border last year I recommend the ALKO stability control hitch. The caravan (Jurgens) and vehicle (Isuzu MU-X) remained in a straight line until I could pull off the highway, thankfully with more than enough room to do so.

-- Edited by Knight on Saturday 10th of August 2019 11:31:36 AM

Peter_n_Margaret · Guru

Mamil wrote:
According to what I've read on the subject, it's a combination of bad loading, ie. too much weight at the extremities which increases the yaw effect, plus speed which exacerbates it exponentially.
A good video here which says much more than I could explaining it in words...
https://youtu.be/PFzrWHTG5e8

Correct.

It needs to be understood that all pig trailers (those with an overhung hitch) are inherently unstable unlike dog trailers (like 5th wheelers and semi trailers) where the hitch is over the rear axle which are inherently stable.

The other thing that makes a big difference is the distance of the hitch behind the axle. Further back is a lot worse, especially if the wheel base is relatively short.

The other aspect that makes a difference is the suspension type. Leaf spring suspensions have a low roll centre which is most stable. Trailing arm independent suspensions have a higher roll centre which is less stable.

Lots of reading material here... https://www.rvbooks.com.au/page/technical/

Cheers,

Peter

Aus-Kiwi · Guru

Pete in motorhome . Driving out center . Have you had a gust of wind nearly blow you off the road ? I have about once a week while in outback or WA. There seems to be strong gusts . The bigger, longer the van or vehicle the more it effects . Talked to some whove had accidents . They have said they lost attention for a few seconds looking at something else .. Guess fatigue comes into it ? The weight of tow vehicle V van exaggerates any away . Some are from turning back into lane after passing too sharp ? Maybe combination of wind off semi plus sharp turn ??

-- Edited by Aus-Kiwi on Saturday 10th of August 2019 11:59:11 AM

iana · Guru

There are a couple of areas I have thought about (and acted on), one is the bigger vans carry multiple water tanks, having had a factory fitted grey water tank in ours, I found with both water tanks (forward) filled, the van was untowable, with the ball weight way over the limit. The new vans are coming out just the same, hence about what I said in the above statement.
The other is the off road van, the C of G would be higher, so they would roll easier, but conversely, I have noticed with ours and the high clearance underneath, that there is little or no effect of air pressure when being passed by a semi, sooooooo, my conclusion for that is the vans that have a low ground clearance, the air is trapped between the two vehicles, both negative and positive pressures, sure it can escape, but it is momentarily trapped, where as with the high clearance, the air pressures can easily equalize. So reduced effect, that's my theory anyway.

Mamil · Senior Member

This is one of the best articles I've found on the subject, and includes an answer to that thorny topic of why the Europeans only use 5-6% ball weight whereas we're told here in Oz it should be 10%.

https://www.outbacktravelaustralia.com.au/driving-towing-towing/towball-weight-and-trailer-stability?fbclid=IwAR1VIs6XdO7K5eEsvllazyK2ANfgyq0joQOugFfIBxKsxHR_FMF8HYyQuI0

drtooheys · Senior Member

Colin Penrose wrote:
Hi all. This is just my observation but I thought that I would put it out there. I have been taking an extra close look at all the caravan rollovers over the past year or two. I think all of them look like tandem off road vans of over 20 in length. Which brings me to think that there is either a problem with these huge heavy vans or a problem with the way they are being towed ???? The last one was obviously a very large van and once it started swaying the poor people had no hope stopping it. I dont Know the answer but I am just putting it out there. I pull a 16 pop top and so far I have never had a sway or anything untoward. I do always drive to the conditions but some of these rollovers seam to be on straight roads in good weather.
Just a thought to start, hopefully, a respectful discussion. Any useful suggestions for how to tow these very large vans.
Cheers Col

If my memory serves me correct, the last one I think you refer to mentioned that the 60+ year old driver got into a sway while overtaking confuse not a real fan of that move with a van hitched on the back, surely sit back and take in the surroundings, thus ensuring you get to your destination safely.

yobarr · Guru

iana wrote:
........the high clearance underneath, that there is little or no effect of air pressure when being passed by a semi, sooooooo, my conclusion for that is the vans that have a low ground clearance, the air is trapped between the two vehicles, both negative and positive pressures, sure it can escape, but it is momentarily trapped, where as with the high clearance, the air pressures can easily equalize.

Now THAT is an interesting theory,certainly worthy of further investigation.My van has 700mm clearance under the floor,so I am hoping that your theory proves to be fact! Cheers.

iana · Guru

yobarr, I thought of that all by myself, I would be interested in finding if you experience the same. However we do feel the wind, especially where there are gaps in trees along the road forming wind breaks, however been in quite high winds and have not had reason to be concerned.

yobarr · Guru

iana wrote:
yobarr, I thought of that all by myself, I would be interested in finding if you experience the same. However we do feel the wind, especially where there are gaps in trees along the road forming wind breaks, however been in quite high winds and have not had reason to be concerned.

Ian,how big is your van? Mine is only 6 metres and seems OK,but I will now do some research into the merit of your suggestion.Cheers

Peter_n_Margaret · Guru

iana wrote:
I have noticed with ours and the high clearance underneath, that there is little or no effect of air pressure when being passed by a semi, sooooooo, my conclusion for that is the vans that have a low ground clearance, the air is trapped between the two vehicles, both negative and positive pressures, sure it can escape, but it is momentarily trapped, where as with the high clearance, the air pressures can easily equalize. So reduced effect, that's my theory anyway.

That is totally contrary to every theory and practice of creating good road holding that I have ever heard. confuse

Minimising ground clearance and minimising CofG height is the way to go for maximum stability, not the opposite.

Cheers,

Peter

Eaglemax · Guru

I think most caravanners that are technically minded do worry about out of control issues, its what makes them good drivers. Like others Ive worried about it and I lean towards speed and sway inertia eg excess weight front and rear extremes rather than centre. My home made single axle van omly weighs 998kg atm 730kg tare 16ftx7ft. That means from the axle to the rear bumper about 7ft, the weight of that section of van is only about 400kg loaded. This means very little chance of sway due to weight. Side wind is more likely but to date, touch wood, no sway has been detected more than 50mm, if that. I dont exceed 95kph, usually 90 and get passed on the Hume by rigs doing 110 even more. As seen on youtube at that speed a slight sway and you're gone! My view Tony.

Nevd · Senior Member

I honestly don't think any type of van can be singled out. Think of the rollover videos you have seen - off road, on road, European. I think more attention to weights, loading and driving awareness is more of a factor.

Olive Oil · Senior Member

Inexperience, overloading, too higher speed & many more caravans on the road equates to more accidents. Simple really.

So many theories on forums frequented by retirees. Driver age may be a contributing factor as well.

We've seen people leave campsites towing huge caravans when 75kph winds are forecast, DH's!

What's the hurry, you're retired. biggrin

montie · Guru

In my opinion...rollovers have three main causes:

1) Van/tug weight ratio...tug weight should exceed van weight by at least10%

2) ESC should be mandatory on all vans

3) Driver experience or lack of it when it comes to towing. Tow Ed courses should be mandatory.

Peter_n_Margaret · Guru

I think the big factors are:

1. Yaw inertia. Long, end heavy van are the worst. It is measurable with a machine, but there is currently not one in Australia.

2. Ratio of the hitch overhang to the wheel base. The bigger the overhang, the more likely it is to loose control. No hitch overhang = a stable rig (semi trailer/5th wheeler).

3. Van/tug weight ratio - we agree Montie :)

Collyn Rivers has studied and written much on this subject. I don't agree with 100% of what he says, but mostly I reckon he has it right.

https://www.rvbooks.com.au/page/why-caravans-sway/

Cheers,

Peter

oldbloke · Guru

"Minimising ground clearance and minimising CofG height is the way to go for maximum stability, not the opposite."

Correct. +1

Izabarack · Guru

montie wrote:
In my opinion...rollovers have three main causes:

1) .....

2) .....

3) Driver experience or lack of it when it comes to towing. Tow Ed courses should be mandatory.

What level of driver experience is necessary before rollovers are no longer a concern? How, exactly, does lack of experience cause a rollover? I wonder because I recently spoke to a van owner who had a rollover after 30+ years of doing the yearly trip from Vic to FNQ with a van on the back.

Tow Ed courses will get my support when someone shows me some research derived evidence that a Two Ed course does anything more than make money for the providers of the courses. Again, exactly what content in a generic tow ed course prevents rollover? And has that content ever been shown to prevent rollovers?

Iza

Snippy · Senior Member

montie wrote:
In my opinion...rollovers have three main causes:

1) Van/tug weight ratio...tug weight should exceed van weight by at least10%

2) ESC should be mandatory on all vans

3) Driver experience or lack of it when it comes to towing. Tow Ed courses should be mandatory.

Add speed to that, have often been overtaken by 'vans well exceeding 100km/hr

brickies · Guru

Old saying the speed that Thrills is the speed that Kills .

deverall11 · Guru

montie wrote:
In my opinion...rollovers have three main causes:

1) Van/tug weight ratio...tug weight should exceed van weight by at least10%

2) ESC should be mandatory on all vans

3) Driver experience or lack of it when it comes to towing. Tow Ed courses should be mandatory.

Agree on all of those, especially Tow Ed course. I am guessing in one of those courses they would also

explain how to recover from a sway.

Some people say: Put your foot down', some say go for the brakes.

I say, grab the caravan brakes and nothing else. The sway is coming from the van, makes sense to slow

that part down and get it straight again.

iana · Guru

Just curious, I agree low center of gravity helps stability, but what difference does ground clearance make. For instance are you saying a camper trailer that would have a very low C of G, but a high ground clearance is unstable ?

Olive Oil · Senior Member

Snippy wrote:
montie wrote:
In my opinion...rollovers have three main causes:

1) Van/tug weight ratio...tug weight should exceed van weight by at least10%

2) ESC should be mandatory on all vans

3) Driver experience or lack of it when it comes to towing. Tow Ed courses should be mandatory.
Add speed to that, have often been overtaken by 'vans well exceeding 100km/hr

Some retirees haven't towed anything larger than a 6'x4' trailer to the the local tip before they buy a 23' caravan & bore down the highway at 110kph.

Something's bound to happen.

Colin Penrose · Senior Member

That is what I thought. If you have a lot of clearance underneath the wind can lift the van more easily ???

Knight · Senior Member

Colin Penrose wrote:
That is what I thought. If you have a lot of clearance underneath the wind can lift the van more easily ???

The greater the ground clearance the poorer the road holding worsening the higher the speed.

montie · Guru

Olive Oil wrote:
Snippy wrote:
montie wrote:
In my opinion...rollovers have three main causes:

1) Van/tug weight ratio...tug weight should exceed van weight by at least10%

2) ESC should be mandatory on all vans

3) Driver experience or lack of it when it comes to towing. Tow Ed courses should be mandatory.
Add speed to that, have often been overtaken by 'vans well exceeding 100km/hr
Some retirees haven't towed anything larger than a 6'x4' trailer to the the local tip before they buy a 23' caravan & bore down the highway at 110kph.
Something's bound to happen.

As dealers we see this all the time!