Horizontal shock absorbers for sway control.

Submitted: Saturday, Jul 16, 2016 at 21:44
ThreadID: 133021 Views:2598 Replies:4 FollowUps:6
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Just been thinking. We have a new caravan on order. I suspect the towball weight will be under 200kg, it will have ESC fitted...so we may or may not need a WDH.
I've looked at after market friction sway control device and got to thinking "why not use a pair of horizontally mounted shock absorbers (dampers) between the towball mount and the draw bar of the van". They could be mounted as a pair one either side both acting in the same direction....or opposed so one was compressing as the other extended. I cant see the mounts for these being hard to fabricate..... am I onto a brilliant idea or is there something major I am missing?
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Reply By: eaglefree - Sunday, Jul 17, 2016 at 00:35

Sunday, Jul 17, 2016 at 00:35
I'm like you, forever inventive. But at times we fall into trying to re-invent the wheel.

I installed a single friction sway bar prior to this round oz trip. Our 11ft homebuilt van had a tare of 450kgm say 650 on the road maybe 700. My worry was if a road train would blow it off the road as it is a full height van and solo light.

I've never seen the van sway more than 25mm at the rear with any trucks passing either way. With 45-50 kph side winds yesterday from Norseman eastbound about 50mm sway only. Truly amazingly stable.

So my view is, buy one or two of these friction units.

PS. I had to fabricate a plate that bolted down with the towball for the mini ball for one end of the bar. Such ball is located around 160mm from the towball.

Tony.
AnswerID: 602485

Reply By: Notso - Sunday, Jul 17, 2016 at 09:00

Sunday, Jul 17, 2016 at 09:00
I've never used sway bars, never had a problem with sway! I was chatting to a truck driver coming up behind me a year or so back and asked him how my van was travelling.

He said it's amazing how much better vans are now, a few years back I called them waggy tails bu now they all seem to be sitting nicely on the road.
AnswerID: 602489

Follow Up By: disco driver - Sunday, Jul 17, 2016 at 20:11

Sunday, Jul 17, 2016 at 20:11
That wouldn't be because the caravans wheels have been generally moved rearward? I reckon that may have more than a little bit to do with the improved stability.
Cheers
Disco
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Follow Up By: Notso - Sunday, Jul 17, 2016 at 21:54

Sunday, Jul 17, 2016 at 21:54
Probably, along with a few other improvements in suspensions I guess.
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Reply By: TomH - Monday, Jul 18, 2016 at 09:40

Monday, Jul 18, 2016 at 09:40
The logical thing to do is wait and see how the van tows. If you need that sort of thing from new you have bought the wrong van. A well engineered van should not need sway controls straight out of the factory.

They do sometimes because of unwise modifications, poor loading and other owner induced things.

I would have thought you would have been told the proposed loaded ball weight before ordering.

ESC and a WDH do two totally different things and one does not replace or really complement the other . In my experience I would use some form of WDH in anything with a ball weight over about 125 kg.

Our van was 300kg on the ball and I wouldnt leave the driveway without one.
Did once and never again.
AnswerID: 602512

Follow Up By: Member - Witi Repartee - Monday, Jul 18, 2016 at 11:30

Monday, Jul 18, 2016 at 11:30
Thanks for your comments Tom...I was after thoughts on the engineering side of a simple anti sway device. I am a professional truck driver and have considerable towing experience..both at work and with my previous vans.
I do know the estimated unladen TB weight of my reputable new van...and expect it to be around 200kg max when near the vans ATM.
Have you any thoughts on my idea for a simple easy mounted anti sway device which I think will not need to be disconnected when off road etc as it will not impose large forces on the draw bar/tow hitch etc..nor will it hang low and be an obstruction when negotiating spoon drains, kerbs etc. I do wonder if the shockies would have sufficient travel particularly when backing/maneuvering.
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Follow Up By: Batt's - Monday, Jul 18, 2016 at 13:28

Monday, Jul 18, 2016 at 13:28
To many people's horror or utter disbelief the simplest anti sway device you can use is to have the correct tow vehicle in the first place and don't tow up to the max of the vehicle give yourself a reasonable safety margin which brings the load closer to the weight of the tow vehicle, load your van correctly use the correct suspension to support any additional weight that is added to the van and tow vehicle making sure the whole setup "sits level" when loaded ready for a trip. Then you will not need to use these band aid type of towing aids wdh etc. It's your choice though but as far as towing aids go a semi can hitch up a loaded trailer which may weigh for arguments sake say 20 or 30 tons without any extra towing aids and using one pivot point just like your car, van does and drive safely down the hwy just something to think about especially if like myself you are a professional truck driver and that has been happening for probably longer than vans have been around for.
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Follow Up By: Member - Witi Repartee - Monday, Jul 18, 2016 at 13:53

Monday, Jul 18, 2016 at 13:53
Totally agree with what you're saying Batt's.
What got me thinking about WDH's and anti sway devices was when I looked at the Andersen WDH which uses chains and a compressible nolathene? collar. It is also claimed to have anti sway properties and I have no reason to doubt that.
It then occurred to me that a couple of shockies acting in tandem or opposed, mounted in parallel to the drawbar could do the same anti sway job and would have simple mounts. I appreciate the comments on towing aids etc etc....but it's not really the core of my conjectures . I'm just floating an idea and hoping someone will come up with an obvious or arcane reason why what I think is a simple system wouldn't work.
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Reply By: Member - J&A&KK - Monday, Jul 18, 2016 at 20:43

Monday, Jul 18, 2016 at 20:43
Hi. My suggestion is to do nothing until you tow the van. If the van does sway too much for your comfort then investigate and remove the causes of the sway. This of course assumes that the van is well designed.

When a van sways it pivots around the towing device and the van suspension and design determines how rapidly it returns to equilibrium assuming it has been loaded correctly. Not knowing what you have in mind for the shock absorber attachments doesn't help. However I assume they would be attached to the draw bar and the car. If this is the case the sway forces will need to be absorbed by the tug.

I would much prefer to remove any caravan sway by judicious loading, assuming the original van design is good, than add a compensating device that changes the tug dynamics.

Your idea may have merit but it really shouldn't be necessary.

Regards John
AnswerID: 602532

Follow Up By: Bobjl - Monday, Jul 18, 2016 at 21:31

Monday, Jul 18, 2016 at 21:31
Agree Johns advice.

You said you will have ESC fitted to your van, ESC is from my personal experience a sensible inclusion to most larger vans, I have experienced the rapid deployment of the ALKO ESC braking system when the sensors detect certain movement. However, ESC must not be relied upon to control yaw/sway, the critical bit is similar to trucking, ensure fully laden Van has load/weight in correct proportion/location and establish tow ball mass. Then where neccesary transfer required amount of weight back to front wheels so as to maintain steeering etc.

Whilst WDH are a pain at times, they are a tried and proven method of maintaining a safe handling rig, provided van is designed right and loaded correctly and vehicle is not overly weighed down at rear, then probability of sway/yaw significantly reduced.

For clarity, my personal experience with the ALKO ESC rapid deployment was not from usual sway, rather it was when right hand tandem wheels rode over an object at 70 plus kph and kicked my 3.4tonne 22 footer around.
Good vanning
Bob

See also http://www.withoutahitch.com.au/caravan/top-five-caravan-myths-busted/
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