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Techniques Winching - Recoveries - Chainsaw Safety - Proper aproach to 4wding etc

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Old 02-12-15
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Default Tow Ball Weight

Whats the correct towball weight when towing? The Pajero is limited to 180 kg if the trailer is 3000Kg Ie 6% not the usual "recommended" 10% which would be 300Kg.
Personally I have trouble understanding how hanging 300 kg off the end of the towbar would make a car more stable! IMO 300 Kg would be taking so much weight off the front wheels of the car it would be dangerous, perhaps the Mitsubishi Engineers have done their home work.
The following article makes for interesting reading to bust an old myth.
http://www.outbacktravelaustralia.co...iler-stability
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Old 02-12-15
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I've heard the same about ball weights - we are looking at a new van that will have a ball weight of around 6% of trailer mass and I'm looking forward to the ball weight reduction from the current van, despite the new van being overall heavier.

For my money, I think the 10% rule came about before we had access to scales and when caravan/trailer designs (and suspensions) were much less advanced than they are now.
I have fond memories of my father towing an early Franklin van behind our Nissan Cedric and the thing getting a sway up whenever you looked at it. Increasing the tow ball weight always solved the problem and I think this approach led to the 10% rule.

But, more recent stuff I have read suggests that it's not the actual towball weight that's critical - it's how the weight is distributed with regards to the van axles.
If heavy weights (eg water tanks, stoves, etc) are a long way forward or behind the axles, they can develop significant angular momentum (ie sway) around the axles. Moving weight forward in the van and onto the towball tended to negate this sway action as the weight was being restrained by the towball and vehicle - again, this led to the 10% rule without a real understanding of why the rule worked.

Modern van designs tend to place heavy weights close to the axles in order to control the build up of angular momentum around the axles.
And this is why the 10% rule is really no longer valid - we have a much better understanding of why vans sway now.

As far as America goes, they most probably won't work out what this all means for another twenty years or so.
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Old 02-12-15
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Oh, and I should have said - the theory of 10% towball weight wasn't about making the vehicle stable - it was supposed to improve caravan/trailer stability.
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Old 02-12-15
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With caravans costing more than cars nowadays I do not think it is an unrealistic expectation to have them designed so that they are safe to tow. If caravan designers designed cars or aeroplanes then there would be an outcry at designing, building and selling "death traps", it is about time the caravan industry employees some engineers that understand not any static centre of gravity calculations but also dynamic centre of gravity calculations.
Maybe caravan design should have to go through some approval process or meet an Australian Standard in regards to stability.

Best laymans article I have read on the subject, thanks to the OP's link.

cheers, OJ.
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Old 02-12-15
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Quote:
Originally Posted by old Jack View Post
With caravans costing more than cars nowadays I do not think it is an unrealistic expectation to have them designed so that they are safe to tow. If caravan designers designed cars or aeroplanes then there would be an outcry at designing, building and selling "death traps", it is about time the caravan industry employees some engineers that understand not any static centre of gravity calculations but also dynamic centre of gravity calculations.
Maybe caravan design should have to go through some approval process or meet an Australian Standard in regards to stability.


cheers, OJ.
Which will all change once people load it up. No two people will pack the same and that will change the dynamics considerably.
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Originally Posted by sharkcaver View Post
Which will all change once people load it up. No two people will pack the same and that will change the dynamics considerably.
Yes true, that said I would rater start with something that was designed well and risk messing it up than something designed badly and trying to fix it.

I believe the biggest threat to the Australian caravan industry is the European manufactures which are coming in with engineered vans that are 500kg lighter, stronger, better finished and properly set up for towing.
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Not being an engineer and generally detesting towing anything thats not shaped like a boat im not really qualified to offer anything other than opinion.

My take is that the stepped tow ball weight is mitsubishi's subtle suggestion that anything greater than 2500 should have a weight distribution hitch. Which you should tweek to a lower ball weight so the thing isnt constantly trying to bunny hop the car and overtake it from time to time.

Now that the cold war is over it appears to have been replaced by a caravan arms race. Were the bloke who cant drive into the most areas, has the most difficulty finding a spot in the places they can g and has the biggest portable toilet cassete to carry to the dumper wins.
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Old 02-12-15
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https://youtu.be/PFzrWHTG5e8

great simulation on caravan / trailer stability
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Quote:
Originally Posted by MSF View Post
https://youtu.be/PFzrWHTG5e8

great simulation on caravan / trailer stability
Good find, very clear demo of importance of loading
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Quote:
Originally Posted by MSF View Post
https://youtu.be/PFzrWHTG5e8

great simulation on caravan / trailer stability


A great visual demonstration that reinforces the linked article from the OP.
Great in theory but most caravans have most of the storage at either end and not in the middle over the axle, weight forward of the axle is better than weight rear of the axle in regards to stability but the downside is excessive tow ball loads.

Exactly the same dynamic yaw forces are amplified and applied to the rear suspension of the tow vehicle. A LWB NW Pajero has a 2780mm wheel base with a 1355mm rear overhang to the rear side of the spare wheel, add 200mm tow tongue extension and you have a leverage factor of 156%. This means for ever 1 kg of tow ball download hitched up there is 1.56kgs of weight that must be carried and controlled by the rear suspension (if WDH is not used), so 200kgs of ball download is effectively 312kgs on the rear suspension and this a static load that must be counted as payload in the GVM calculations. The dynamic loads that these static loads create can easily be 2x to 5x greater. If the caravan has been loaded or constructed incorrectly so that the weight distribution is incorrect the problem multiples again. Hit a pot hole or puncture a tyre at any speed over 60kph and you are in trouble.

The PB/PC Challenger is slightly better due to the longer wheel base and shorter rear overhang, so with a 200mm tow tongue extension the leverage factor is 141%.

If you do not think this matters, remember in your youth, 3 guys sitting in the back of a small Japanese hatchback and they start to sway from left to right and how this effected the handling of the car and that is 210kgs over the back axle and not leverage!

cheers, OJ.
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