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Feedback - Choosing & Setting Up a Tow Vehicle

Submitted: Monday, Jul 02, 2007 at 13:00

Member - Welshmun (QLD)

Article Overview - Preparing a Vehicle for Towing
Everyone who intends to tow a caravan, or indeed any sort of trailer, needs to be aware that various tow vehicle and trailer combinations can behave in slightly different ways and certainly different from just driving the tow vehicle itself. View Full Article...
Vehicle/Trailer Load Balancing. Other solutions.
I've not tried load balancing bars, but the effect seems to be that of 'transferring weight from the rear wheels to the front of the tow vehicle, thus ensuring efficient steering and braking' (quoted from the article).
Elsewhere there is a recommendation that tow bar load should be 10% of the trailer weight; so a 2000Kg caravan should have a 200Kg tow bar load (vertically).
For a well balanced rig it would seem important to have 2 parameters about right: the tow bar weight and height (the latter to match the trailer tow hitch height) plus the relative weights of towing vehicle and trailer within regulations.
Air bags on the rear axle of the drive axle also seem to be a common solution but this suggest that tow bar weight might be too much anyway.

However, I've never seen the solution that I've adopted; I don't have an engineering background but chose the following as an alternative solution (suggested by me, fitted by ARB); and it seems to work very well....

I have a 1000Kg offroad dual axle camper trailer (with heavy duty leaf springs and linked for trailer load sharing) , and have fitted airbags to the front axle OF THE TRAILER. By increasing the pressure in these airbags, the balancing point of the trailer moves backwards and adjusts the towbar load, and consequently the height. The trailer is fairly well balanced currently so on the open road I have just 10psi in the bags, but I plan to add weight in the form of a trailbike, and maybe more storage, onto the drawbar (it's a long one), so would just add more air.
The setup has the added advantage that enough air (about 70psi in my case) will lift the rear axle clean off the ground; handy for those tight reverse turns that scrub tyres in a dual axle setup. It makes the tow bar weight too light, but I wouldn't drive far or fast with it anyway. Handy also for decoupling: takes the load off.
I also went one step further and had airlines fitted from my vehicle compressor to the trailer via a control switch & gauge; so the trailer air bag pressure can be adjusted from the cab; even while moving! I'd be interested to know if anyone else has seen such a solution, whether it might work for heavier caravans, and whether anyone has seen a device for measuring actual towbar load.
Camper hitched shows long drawbar with space for trailbike
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AnswerID: 250298   Submitted: Monday, Jul 02, 2007 at 13:25

Notso replied:

There is a device you can buy basically it is a hydraulic jack with a pressure guage calibrated to measure in Kilograms.

You can check the weight on the towbar with it by using it to jack up under the tow hitch. The other way is to use a weighbridge and weigh the trailer only whilst it is hooked to the vehicle, then disconnect the vehicle and weigh the whole van. That way you can then subtract a from b and get c the ball weight. Make sure that the truck and trailer are level when you do the first weight.

Reply 1 of 6
FollowupID: 511566   Submitted: Monday, Jul 02, 2007 at 21:09

Member - Welshmun (QLD) posted:

Thanks Notso; I was convinced there must be something; a jack with a pressure gauge would do the job as I'm looking for a solution that I always have with me, so weighbridge is not so convenient.
Thanks for the fedback
Doug/Welshmun
Camper hitched shows long drawbar with space for trailbike
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AnswerID: 250299   Submitted: Monday, Jul 02, 2007 at 13:27

Member - Doug T (W.A) replied:

Welshmun
I learnt by experience many years ago , during the 1960s my parents had a fruit block at Sunlands near Waikerie, we had a single axle trailer , about 10x5 , Dad sent me off to get 6 bags of fertilizer , i had the trailer on behind my EK Holden, so I loaded 3 on the front and 3 on the back so it was evenly loaded , Not the right way so I found out, it swayed bad as soon as I got to about 30mph so I stopped, shifted 1 bag to the front and the trailer towed perfect, , Now as you might notice these days some of the New Vans have the axles back a little from center , those vans should tow at 100kph with ease , so the idea is not to have the caravan balanced but have some wieght in the tow bar , I used trial and error and have always remembered my early experience,

Doug

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Reply 2 of 6
FollowupID: 511568   Submitted: Monday, Jul 02, 2007 at 21:12

Member - Welshmun (QLD) posted:

Yup. 10% of the trailer weight on the towbar seems to be the norm.
Be nice to have something to measure it with, but, as you say, you can get afeeling for it.
Thanks for the feedback
Welshmun(also Doug)
Camper hitched shows long drawbar with space for trailbike
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AnswerID: 250309   Submitted: Monday, Jul 02, 2007 at 14:50

Member - Barry M (NSW) replied:

I'd apply to get on the Inventors post haste. Seems like a great solution to me.
Probably not a lot of dual axle campers like yours but thousands of caravans that
all could be advantaged at what is a reasonable cost. In fact I think I hear the
noise of many rushing off to procure their airbags right now. Well done....oldbaz.
Morning Tea..Tanami 07
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oldbaz
Reply 3 of 6
FollowupID: 511470   Submitted: Monday, Jul 02, 2007 at 15:43

Member - Kiwi Kia posted:

I agree with Barry, a very elegant solution, great idea.
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FollowupID: 511570   Submitted: Monday, Jul 02, 2007 at 21:14

Member - Welshmun (QLD) posted:

Thanks Barry & Kiwi Kia.
It's posted here to share . I suppose I'll be cross if someone makes a fortune out of it !
Welshmun/Doug
Camper hitched shows long drawbar with space for trailbike
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FollowupID: 511605   Submitted: Monday, Jul 02, 2007 at 23:25

disco1942 posted:

Welshmun

If the front axle is rated to carry that much weight, why do you have 2 axles? I would suggest removing the air bags and letting the load sharing do its work properly. Re arrange the loading if necessary to maintain the 10% on the draw bar.

Throwing the extra weight on the front axle is like Doug T shifting that bag he moved forward back so he had the 3 bags on the front and 3 on the back and restoring the instability he originally tried to correct.

PeterD
FollowUp 3 of 4
FollowupID: 511616   Submitted: Tuesday, Jul 03, 2007 at 00:14

Member - Welshmun (QLD) posted:

PeterD,
Well, there are a number of reasons for having 2 axles: blowouts for one, stability for another.
What is the difference between your suggestion of 'Re arrange the loading if necessary to maintain the 10% on the draw bar' and 'Doug T's shifting that bag he moved forward back so he had the 3 bags on the front and 3 on the back '. (I think he meant shifting them until the tow bar weight felt right)

My solution may put more load on the front axle, but with 10% needed for the towbar weight that would happen anyway. The load sharing shackles still work on rough terrain.
It also gives me finger tip fine tuning.
but I appreciate your comments.
Thank you.
Doug/Welshmun

Camper hitched shows long drawbar with space for trailbike
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AnswerID: 250319   Submitted: Monday, Jul 02, 2007 at 16:00

Member - Oldplodder (QLD) replied:

Great idea.
Congrats on a neat solution.

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John C - aka Oldplodder
In touring mode, the way it should be.
Reply 4 of 6
FollowupID: 511576   Submitted: Monday, Jul 02, 2007 at 21:27

Member - Welshmun (QLD) posted:

Appreciated Oldplodder :)
Camper hitched shows long drawbar with space for trailbike
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AnswerID: 250334   Submitted: Monday, Jul 02, 2007 at 17:19

Crackles replied:

Your setup sounds ideal for allowing for the difference between running the trailer empty & carrying the motor bike & extra gear on the draw bar. The only concern I can see is the axles are no longer load sharing so with 40 psi in the air bags to balance your load, the front axle may be carrying as much as 3/4 of the trailers gross weight. I assume your 1 tonne trailer is the dry weight so after the water, camping gear & bike are loaded there may be as much as 1.5 tonne on that axle, even more when pumped up to 70 psi for those short times when manovering. For others considering retrofitting the system, max loads on the air bags, bearings & axles for some tandems may become an issue.
Cheers Craig..............
Reply 5 of 6
FollowupID: 511574   Submitted: Monday, Jul 02, 2007 at 21:23

Member - Welshmun (QLD) posted:

Quite right, Crackles. With the rear axle relieved of some load, the front takes more.
However, everything about this rig is heavy duty and there doesn't seem to be much of a strain even running on the 1 axle, although towbar weight is almost zilch so it doesn't tow too well. But then, having pulled away, I flick the cab switches to let the air out and the trailer settles nicely on 4 wheels and tracks behind beautifully.
Appreciate your comments.
Doug/Welshmun
PS one thing I didn't mention is that the heavy duty springs don't allow that much movement, which is why I can get the rear trailer wheels off the ground. With softer springs, I think there would need to be a pin or pins to lock the load sharing shackles. Adapted diff lock perhaps !

I guess all of this might not work on caravan engineering unless it's an offroader.
Camper hitched shows long drawbar with space for trailbike
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AnswerID: 250381   Submitted: Monday, Jul 02, 2007 at 20:17

mattie replied:

Hi Welshmun
I may have miss understood this but if u were to unhook your trailer and put the jockey wheel over the weigh bridge this would give u the tow bar weight. Something i don't understand about tow bar weight for a true off road trailer is that the more weight on the tow bar the more traction the tow vehicle has!!!! So the more weight that can be transferred to the tow vehicle without causing damage the better, this will obviously create a need for heavier rear springs or since u have created an elaborate air system why not put a set of rolling sleeve air bags on the rear of your cruiser as u already have an air system on board (and an adjustable one of which i am envious of!!!) and u will be able to pump it up with the ct hooked up and then let it down while travelling empty!!!

MATTIE
Reply 6 of 6
FollowupID: 511563   Submitted: Monday, Jul 02, 2007 at 21:06

Member - Welshmun (QLD) posted:

Mattie
I was looking for a towbar weight mesaurment solution that I always had with me.
Not many weighbridges on the Canning Stock Route !
Airbagging the vehicle too had occurred to me, especially when I get really loaded up. ; as I have 2 airlines running to the 2 airbags in the trailer, separately controlled (another plus, I can level the camper laterally when parked, well a few degrees anyway), so I could use one airline for the rear vehicle axle and 1 for the trailer.)
It's pleasing to hear my solution is getting some degree of approval !
Thanks for the comments
Doug/Welshmun
Camper hitched shows long drawbar with space for trailbike
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