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Towing Myths


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This is one of those subjects that provides entertainment on forums amongst members and on CMHC sites amongst senior CMHC devotees regularly. Weight ratios are only part of the stable towing equation but form a reasonable foundation to work from, however, the belief that simply using a set of printed figures brings safety is only something the foolish rely on.

 

For years we had single axle caravans at around a 90-95% ratio. These towed fine. We now have a twin axle towing with a Volvo estate at a theoretical 87% ratio. Again, it tows fine, but I have recently upgraded the MTPLM which puts the theoretical ratio at 99%. Nothing has changed. Nothing more is loaded but according to advice it’s only a match for the very experienced. But it’s exactly the same as when it were an 87% match, the only difference is the number on a plate.

 

These discussions will never go away but maybe when the use of trailer caravans becomes so difficult due to the changing of vehicle fuels we’ll look back fondly and laugh?

2018 Volvo V90 and 2018 Swift Sprite Quattro EB

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Well said Gary and I STILL await the emphatic and objective evidence that inappropriate weight ratio alone is the cause of caravan accidents. 

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17 hours ago, Lutz said:

If Continental and UK caravan manufacturers use the same chassis, but UK caravans have a shorter A-frame then this can only be because the body is mounted further forward on UK caravans, presumably to keep the overall length down. 

 

Nope,the chassis's are modular and assembled at the caravan factory to suit the specific model, each chassis rail has multiple holes drilled so the front and rear sections can be shortened or extended dependent on the required length.

image.png

Jaguar E-Pace 180D HSE R Dynamic - 2008 Swift Conqueror 540

 

"Unless otherwise stated, my posts will be my personal thoughts and have the same standing as any other member of Caravan Talk"

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54 minutes ago, Steven said:

the chassis's are modular and assembled at the caravan factory

 

Does the modularity extend to the angle of taper from full width towards the hitch, do we know?

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53 minutes ago, Steven said:

 

Nope,the chassis's are modular and assembled at the caravan factory to suit the specific model, each chassis rail has multiple holes drilled so the front and rear sections can be shortened or extended dependent on the required length.

image.png

 

Sorry Steven but your diagram clearly shows the front steadies mounted on the chassis and we know well that many UK vans have them mounted to the floor which clearly proves my earlier point that UK vans in the main have longer bodies per chassis than their continental counterparts. n'est ce pas?

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Welll said Flatcoat88-just seen a bucanneer towed very stably by a 5 series BMW.

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3 hours ago, Scarab said:

A couple of activations on the motorway wouldn't burn out your brakes. Would they even be felt?

 

But if the van was inherently unstable it is unlikely to be a "couple of activations". There, unless things changed, it would be unstable as soon as the ATC took off the van's braking, going into an ever repeating on off cycle, that would very rapidly overheat the shoes.

 

I have only had it activate at speed when the van jumped in and out of the tyre grooves caused by heavy lorries [A34 north of Newbury, going north], I was left in no doubt it had activated.

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1 minute ago, JTQ said:

 

But if the van was inherently unstable it is unlikely to be a "couple of activations". There, unless things changed, it would be unstable as soon as the ATC took off the van's braking, going into an ever repeating on off cycle, that would very rapidly overheat the shoes.

 

I have only had it activate at speed when the van jumped in and out of the tyre grooves caused by heavy lorries [A34 north of Newbury, going north], I was left in no doubt it had activated.

 

Indeed, but I don't think we were talking about inherent instability.

 

The fact that you have been able to feel it activate at high speed tells me that ours never did, and that it was adding nothing to our everyday towing (which is what I thought, so thank you)

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48 minutes ago, SamD said:

 

Sorry Steven but your diagram clearly shows the front steadies mounted on the chassis and we know well that many UK vans have them mounted to the floor which clearly proves my earlier point that UK vans in the main have longer bodies per chassis than their continental counterparts. n'est ce pas?


Sam, my reply was to Lutz  and proves nothing of what you have posted, the aim of the picture was to show the additional bolt holes to make the chassis longer or shorter.

 

As for mounting the steadies on the chassis, the chassis at its extremes would not be strong enough to support the caravan if they  were attached, and the diagram shows the main supporting plate and bracketing outside of the chassis above the foot, where the inner fixing is is not relevant as that is not where the majority of the load is.

Jaguar E-Pace 180D HSE R Dynamic - 2008 Swift Conqueror 540

 

"Unless otherwise stated, my posts will be my personal thoughts and have the same standing as any other member of Caravan Talk"

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HAve never knowingly had ATC activate on any of our caravans-had one without it which towed equally as well as the ones with it-but it's there just in case and am glad it it! I'd rather it never had to work, just like abs or a seat belt.

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1 hour ago, Scarab said:

 

Does the modularity extend to the angle of taper from full width towards the hitch, do we know?

 

We know the taper angle is fixed, in that it is factory pre- formed in the "A" girders supplied.

 

As the bolting position, main to "A" girders moves over the provided range, so the hitch to axle changes, reflecting where and by how much the bolts are then placed.

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34 minutes ago, JTQ said:

 

We know the taper angle is fixed, in that it is factory pre- formed in the "A" girders supplied.

 

As the bolting position, main to "A" girders moves over the provided range, so the hitch to axle changes, reflecting where and by how much the bolts are then placed.

 

Yes, that's what I thought. I think that means that if you have an apparently shorter A frame, the caravan body must be mounted further forward on the "A girders" section of the chassis.

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35 minutes ago, Scarab said:

 

. I think that means that if you have an apparently shorter A frame, the caravan body must be mounted further forward on the "A girders" section of the chassis.

 

No!   I think AL-KO have at least two lengths of A-frame, just as they have various lengths of chassis section.   I would imagine that when a caravan builder designs a new van, they leave it to AL-KO to design a suitable chassis for the body.   When all is agreed and tested, the specified chassis are delivered - maybe  in 'flat-pack'.

 

Citroen C5-X7 Tourer+Avondale Rialto 480/2
https://jondogoescaravanning.com

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You can never have too much body on a chassis seems to be the British way.
My exposed A frame is @6 foot long on a caravan half the length.

 

A57F860E-9236-4280-8987-62A00CC199F9.jpeg

Edited by Whomer
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17 minutes ago, Jaydug said:

 

No!   I think AL-KO have at least two lengths of A-frame, just as they have various lengths of chassis section.   I would imagine that when a caravan builder designs a new van, they leave it to AL-KO to design a suitable chassis for the body.   When all is agreed and tested, the specified chassis are delivered - maybe  in 'flat-pack'.

 

Which means that there must be at least two taper angle versions of the A frame (for a given chassis width)

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10 minutes ago, Scarab said:

 there must be at least two taper angle versions of the A frame (for a given chassis width)

 

But are there chassis of different widths?   Surely it's axle width which needs to be matched to body width?

Citroen C5-X7 Tourer+Avondale Rialto 480/2
https://jondogoescaravanning.com

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1 hour ago, Jaydug said:

I would imagine that when a caravan builder designs a new van, they leave it to AL-KO to design a suitable chassis for the body.   When all is agreed and tested, the specified chassis are delivered - maybe  in 'flat-pack'.

 

I very much doubt it happens that way round, IMO much more likely a caravan designer works with the product lines AL-KO have available, selectively picking the items that are cross compatible. Then the selection is reviewed by AL-KO engineers to validate that selection and the company to furnish the kit.

Most definitely from where the components are manufactured they will end up in AL-KO UK from their builders as nested flat packs of transportable items, I actually know having seen them there. Most probably they also leave there to the van builder to assemble at or near where  needed. Transportation being what it is and the total lack of torsional stiffness of the assembled chassis, pre meeting its "floor", IMO there simply is no other logical way with these particular chassis.

 

Edit: Sadly, over here in this design loop, the evidence points to no one "designing" where the axle ends up other than to satisfy the "stylists" layout.

Otherwise, the in use noseweights  would be more readily achieved by the end users. So often they end up way over or way under, whereas with just a little bit of initial design input, they would end up somewhere near right. 

Edited by JTQ
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I suspect that AL-KO have a parts list resembling a Meccano set and are able to pick & mix to suit 101 different caravan applications. However, only AL-KO have the answers!

2018 Volvo V90 and 2018 Swift Sprite Quattro EB

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11 minutes ago, GaryB1969 said:

I suspect that AL-KO have a parts list resembling a Meccano set

That's the way I see it.   Even the A-frame isn't a one-piece unit.   It's two separate U-sections - one size for a long A-frame and a shorter one for a 'UK' A-frame.   Both sections are bolted at a suitable place along the lengths of chassis rail, and at the hitch end with a A-shaped plate with elongated holes for adjustment.

Citroen C5-X7 Tourer+Avondale Rialto 480/2
https://jondogoescaravanning.com

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From memory even the rearmost holes of the hitch are slotted to suit different A-frame angles.

2018 Volvo V90 and 2018 Swift Sprite Quattro EB

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5 hours ago, Steven said:


Sam, my reply was to Lutz  and proves nothing of what you have posted, the aim of the picture was to show the additional bolt holes to make the chassis longer or shorter.

 

As for mounting the steadies on the chassis, the chassis at its extremes would not be strong enough to support the caravan if they  were attached, and the diagram shows the main supporting plate and bracketing outside of the chassis above the foot, where the inner fixing is is not relevant as that is not where the majority of the load is.

 

Yes I agree with that but what is clear from your response is that my post was less than clear!

Edited by SamD
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4 hours ago, Jaydug said:

 

But are there chassis of different widths?   Surely it's axle width which needs to be matched to body width?


They only need to fit a 2.2 - 2.4m body width. Changing the Wheel offset will sort most of  that.

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3 hours ago, JTQ said:

 

 

Edit: Sadly, over here in this design loop, the evidence points to no one "designing" where the axle ends up other than to satisfy the "stylists" layout.

Otherwise, the in use noseweights  would be more readily achieved by the end users. So often they end up way over or way under, whereas with just a little bit of initial design input, they would end up somewhere near right. 


 

Thats a very good point. Nowhere in my Hymer user manual is there Talk of loading the van with wheels, awnings etc arranged on the floor to achieve a designed noseweight. All the heavy items, the battery, spare wheel, 50l water tank , the heavy table, main storage locker and wardrobe are all built over or adjacent to the axle. Out of the box, the nose weight is on the money, the lateral balance is also very even, within a few Kgs. Loading it without giving  it much thought always ends up with the nose weight remaining in the right ballpark. 

 

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On 21/07/2021 at 11:55, Flatcoat888 said:

Well said Gary and I STILL await the emphatic and objective evidence that inappropriate weight ratio alone is the cause of caravan accidents. 


 

It will be a very very long wait.

Mention ‘weight ratios’ to  a European caravaner,  and you will be met with blank looks, You can tow up to your cars limit, end of.

Its not a matter in the specialist caravanning press either, you won’t see any test reviews talking about the U.K. caravan markets sacred 85% ratio.

 

 

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Exactly, just go on a site in Eurolandia and see the outfits. 

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