Air suspension and weight distribution hitch - Club Touareg Forums
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post #1 of 51 Old 04-21-2015 Thread Starter
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Air suspension and weight distribution hitch

I currently drive a 2008 V6 TDI and haul a 23 feet/3 ton caravan using a Reese WDH. The Touareg tows it with ease and the rig is in perfect balance. I am considering moving into a newer model but have been informed that the 7P model introduced in 2011 has had the chassis removed to save weight - the construction now being 'unitary'. Furthermore, the standard OEM self-levelling air suspension does not allow the use of a weight distribution hitch. This would seem to defy logic to me since no matter how good the air suspension was, it could not transfer some towball mass to the front wheels. I really want another Touareg but not at the cost of inability to have the rig in balance. Can anyone confirm the details I have provided above?
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post #2 of 51 Old 04-21-2015
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Well a couple of points

The Touareg does not have a separate chassis, neither 7L or 7P models, so in that regard they are the same - as you called it "unitary". Whoever told you that the chassis was removed from the Touareg in the change from 7L to 7P is err shall we say misinformed. No doubt a salesman. This contrasts with the VW Amarok which does have a ladder chassis.

On the 7L Touareg, if you have read your manual, VW states that WDH is not to be used on any Touareg, steel sprung or air suspension. Well it does on mine. You are currently using a WDH against the specific written direction from VW in the manual (well it does on mine here in Australia where both I and the OP are from). This may be different in other markets, but I doubt it. Most people seem to ignore what the manual says, or have not read it, if it doesn't agree with what they want to hear. Many still use a WDH, your choice but I wonder if it would give an insurance company wriggle room???

With the introduction of the 7P model, the Touareg had a complete redesign and slimed down somewhat, losing a couple of hundred kilos in the process.
As part of that many specs were revised including for towing. While the overall amount that can can be towed remains the same, 3,500kg max braked, the towball limit was reduced to 280kg from 350kg.
However I believe that this may have been associated with the vertical hitch receiver and that with later VW approved horizontal hitches the towball limit may have returned to 350kg. I seem to recall some discussion on here about that. Perhaps some other Aussie owner will know.

Given this is your first post and have just recently joined, you might like to have a look at this thread from the UK Touareg forum
Buying a used Touareg. What to look for. - myTreg forums
Lots of good useful information there if you take the time to look through it (perhaps npt on this particular topic though). Newcomers are often given the link and it has proved valuable to many.

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post #3 of 51 Old 04-21-2015
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You are correct pjod.
I have been towing a 2.3 ton caravan with a 2009 Touareg for 5 years and definitely no WDH. Never a problem and I must say when emergency situations have arisen, the air suspension has always held up well. I now have the 2015 180 and a real attraction to this vehicle are the improvements VW has made to ensure the stability of both Touareg and caravan.
I have met those who say (and use) WDH and they remain unswayed in their opinions (no pun intended) The air suspension is self levelling (as stated in the fact sheets) and is indeed a very safe system on its own tow wise.
Cheers.

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post #4 of 51 Old 04-21-2015 Thread Starter
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Thanks PJOD. You are correct in assuming that I had not picked up on the fact that the user manual in my current T prohibits the use of a WDH. Nevertheless, it still performs brilliantly the way I use it and my wife and I are so impressed that we want a newer one. I can now see that we may have to reconsider our options. It would be interesting to hear the experiences of someone who has done similar to us and used a WDH on a self-leveling air suspension model without reading the user manual.
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post #5 of 51 Old 04-21-2015
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With air suspension the car will actively try to self level - that is the nature of a well designed air suspension system. It actively works on the suspension all the time, unlike a passive steel sprung system which reacts to forces applied to it and then settles.

The WDH is like a double lever, with a common point being the towball which acts as the end of two levers, the other ends of those two levers are towards the front of the car (for simplicity the front axle) and the van (the van axle)

By leverage when mass is applied to the towball, the force (weight) moves the ball downwards (and hence the front of the vehicle upwards - along with the rear of the van). The WDH when connected acts as a lever to transfer this force (weight) to both the front axle and van axle, effectively putting the force (weight) on them and removing some of the force (weight) from the ball and hence rear axle.

The WDH acts to limit the suspension travel when attached, and reduces the travel it would normally have. Given the air suspension is an active system that uses the air pressure and monitors to actively try to level the ride, the WDH can interfere not only with the self levelling but also introduce forces in opposition to the air suspensions normal operation, especially on bumpy or undulating roads. The dynamic forces introduced by the WDH will be increased when going down a dip as the vehicle bottoms out, and reduce or even be negative when cresting a rise, or so it has been described to me if I have understood it correctly.

I understand it is for the reasons of introducing forces that were not designed for is the reason why car manufacturers say not to use a WDH with their OEM air suspension systems. (Quite different approach may be needed where an aftermarket airbag helper system is applied to a conventionally sprung vehicle). As an aside hydraulically suspended vehicles (I refer here to Citroens) also do not have WDH recommended, indeed they recommend against them.

In terms of steel sprung vehicles, especially those where a separate ladder chassis is not included in the vehicle, many manufacturers also recommend against using WDH. This is for the reason that the WDH acting as a lever has a pivot point introduced somewhere under the vehicle (in order to transfer the force forward).

This will introduce stress and forces at a point where the body has not been designed to accommodate this, often leading to cracking and distortion, as the forces also tend to be in an opposite direction to gravity and again dynamic loads can quite quickly multiply the force (weight) applied.

Of course this will also apply to the air suspended versions of those same vehicles.

Another reason for also being wary of WDH's is that they tend to introduce further length behind the rear axle to the towball. The VW OEM towball mount would have the towball about 300-400mm closer to the rear axle than a say Hayman Reese WDH mount.

This can be important in terms of stability. A car and van act like a double pendulum with the ball being the second pivot point. Simply put the further out that second pivot point is from the axle (the primary pivot) the lower the speed at which sudden and uncontrollable instability may be reached. And the relationship is not linear as I understand it either. On my Touareg the ball is a bit under 1.00m from the centreline of the rear axle. By comparison Landcruisers with WDH's have the ball anywhere from 1.3 to 1.5 m or even more from the rear axle.

As all this is quite a bit off the original topic, for more on Caravan stability see some of the articles by Collyn Rivers who has written and researched this topic extensively. Google him but to get you started here is a link:
Caravan Dynamics | Caravan and Motorhome Books

Bottom line is I would not use a WDH with air suspension full stop. It introduces too many forces that are not factored into the design of such an active suspension.

And I don't trust insurance companies not to try to use the manufacturers recomendation to wriggle out of a payout should the worst occur.

I follow Rosco's advice, though our van is quite a bit lighter than yours.

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post #6 of 51 Old 04-22-2015
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Our van puts on a ball weight of about 240kg and the 7P tows perfectly with no hitch and I would not use one anyway. The car looks perfectly level with no saggy looking rear.
The rear goes down when you first put the van on the ball and then is pumped back up to where it was within a few seconds.
I have tried towing in sport position and normal and can't really perceive any difference so I leave it in sport


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Out there Tregin:
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post #7 of 51 Old 04-23-2015
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Quote:
Originally Posted by pjod View Post
Bottom line is I would not use a WDH with air suspension full stop. It introduces too many forces that are not factored into the design of such an active
Agreed.
I still need to figure out how the WDH will interfere (or not) with the anti-sway program.

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post #8 of 51 Old 04-23-2015
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Touareg7L,

We have recently returned from a lap around the block, clocking up 47,000 kms in the last 10 months and at a guess 30,000 of those towing a close to 3.5 ton van. We have not use WDH on this car and I, like hundreds of others we spoke to on the road cant believe how well this tows and how level it is whilst towing. We had to do a full on stop to avoid a Giant Kangaroo with van on and doing about 75Kmph at the time. Pulled up very straight no sway no issues. Only advise I give is to try and keep to the max ball weight of 280 as in the wet the front could get light if your well over 300. Other than that I hope to never need WDH ever again.

I worked out when I pulled up to slip a bit of timber under the Trail mate jack on the jacks lowest setting, then all I do is open tail gate and press button to load and car slowly drops down from hitch.....

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post #9 of 51 Old 04-23-2015
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Quote:
Originally Posted by Packhorse View Post
I worked out when I pulled up to slip a bit of timber under the Trail mate jack on the jacks lowest setting, then all I do is open tail gate and press button to load and car slowly drops down from hitch.....
Yep, Air suspension is a death sentence to a wind up jockey wheel!!

Stu....

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post #10 of 51 Old 04-23-2015
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Interesting discussion.
Mercedes air-suspension works with WDHs by disabling ride height changes when a trailer is connected.

Given the way a WDH works, if the vehicle height is lowered (as many do at speed) weight is transferred to the front axle.
Most SUVs do not have as much reserve capacity on the front axle as on the back, and it is very easy to overload the front (and/or the frame).
I would suspect hat VW did not include ride height limitations in the trailer control module adaptions the vehicle makes when towing.

If I was to use a WDH on a Touareg (and I will have to see how it tows first to decide), A would keep it relatively loose (Minimal weight transfer to front) and set the ride height to a fixed setting (I don't yet know enough to know if this is possible).
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