Hayman Reese now make towbars for Tiguan's.

[jcubed]

Hi All,

I do not think the ball down weight limit is determined by the strength of the hitch or tow bar. On the side of the trailer/caravan end of the fitting that attaches to the ball, it has 750 kg embossed in the casting on the light-weight one I have on my (unbraked) trailer.

The hitch will be able to take at least as much.

The problem lies with what your suspension can take prior to bottoming out, with the major factor not determined by the static weight caused by whatever is attached to it, but by the road surface and downward moment exerted on it during braking.

For example, consider 80kg on the ball, with the axle of the trailer 1.5 m back from this point. During braking, the moment exerted by the trailer, is the mass x g (almost 10) x arm length (1.5m), which comes to 1176Nm. If the trailer wheels were further back (large caravan), lets say at 3m, the moment would be double that. Vehicle manufacturers have to outguess owners and state a mass that covers worst case, so they provide quite a low value to avoid complaints.

If you want to lift the front wheel of your motorbike off the ground and hang it on the hitch - like owners of off-road bikes often do locally - you would be able to exceed the stated value considerably as the moment arm is so short - distance of rear wheel to hitch.

I have done some measurements in order to check full rear suspension articulation as part of an off-road mod I was contemplating. Without going into the math, the results were obtained as follows (adapted from a year-old mytiguan post):

During the evaluation process the limits of the rear suspension at the travel extremes had to be determined. To be able to remove external influences, the rear torsion bar was disconnected to get the side being worked on independent of the other and allow the absolute mechanical extremes to be reached. The suspension would not easily go there with the torsion bar connected as long as one rear wheel is still on the ground.

The spring was removed to prevent the car from "getting away" as the suspension was raised with a trolley jack. At the upper extreme (suspension bottomed out) some measurements were taken.

Under load-bearing conditions, 12mm of tread will be inside the wheel arch at maximum compression, with sufficient room to not cause any rubbing of the tyre.

The suspension is solid at this point, although the spring would not be fully compressed yet and no drive train or suspension components run out of range: the drive shaft, the transverse link, both upper and lower track control arms and the longitudinal (forward) link still has ample clearance.

Considered in the light of the figure which VW provides as the maximum permissible load for this axle, the following: This info can be obtained by opening the front passenger door and reading it off the label applied at the bottom of the B-pillar. The last figure relates to the rear axle, and on my T&F Tip 2.0TDi it specifies 1130 kg. However, 1300 kg (calculated using spring parameters) would be required for the rear suspension to bottom out as above. If it was now possible to relate this load margin to the clearance between the top of the tyre and the wheel arch, a caravanner would know to move some stuff from the car boot to the back of the caravan to ease the load on the axle.

The VW-specified axle limit (assuming the load is equally distributed left-right) is reached when the gap between the top of the tyre and the wheel arch is 20 mm. This still allows 32mm of further suspension travel before hitting the bump stops - unfortunately provided by the damper - aided somewhat by the top and bottom coils of the spring being wound tighter than the middle 6, providing some degree of progression as the spring is loaded. This 32mm of travel is what remains to provide damping as the car goes over bumps

The mass is distributed 54/46% front/rear, if I recall correctly. So of the 1604 kg empty weight (also from memory), 738 kg is on the rear axle. Using arbitrary numbers, adding 2 rear passengers (150kg), luggage in the boot (80 kg) and a tank of fuel (60kg), the total mass is now 738 kg + 290kg = 1028 kg. 102 kg is therefor left to place over the rear axle before you reach the limit VW regards as safe. Only you are not placing it over the rear axle when you hitch, but behind it. As you may know from jumping on the towbar of any car, the suspension movement due to this is much more than by e.g. jumping on the back seat.

So I reckon, if you are sensible, the stated ball weight can be exceeded. It's not as if the whole lot is going to drop off the car.

It should be interesting feedback if someone knows of a case where a ball neck has snapped off due to overloading.

[Arctra]

WOW!
It's not half obvious that you are an engineer by trade J!

Thanks very much for that though. I actually thought the limit would be to protect the chassis from bearing weight (and therefore being stressed) in places it is not meant to be. If it's just a question of the suspension, then I should easily be able to carry my bike using one of these suckers:

[NZTiguan]

Just a thought... what if the trailer is NOT a braked trailer? Does it do much then?

It does NOTHING to the trailer brakes etc, it does it to the Tiguan's !! Doesn't matter if the trailer is braked or not but the "effect" it has on the Tiguan's stability and braking.

Cheers

[T&M]

It does NOTHING to the trailer brakes etc, it does it to the Tiguan's !! Doesn't matter if the trailer is braked or not but the "effect" it has on the Tiguan's stability and braking.

Cheers

Hmmm I'm still confused... This magic box has the ability to keep both the car and trailer stable, without braking the trailer's brakes (in the case of an unbraked trailer of course). What page of the manual should I read about all this? I'm sorry I'm very very bad with manuals. Sounds like it was invented by Kevin Rudd!

[jcubed]

Hi T&M,

To understand this, one has to split the Tiguan and trailer braking systems, as they are completely independent of each other.

The trailer brake referred to, is known as an overrun brake. If the car decelerates, the trailer momentum will try to maintain the speed. This force is used to compress a damper - could be a spring in there as well - on the trailer hitching mechanism, which will then tighten the trailer handbrake cable, as far as I know. The damper is there so that the trailer does not brake for every little slow down of the car, but only operates when the trailer's "push" exceeds a certain level. Emergency conditions, therefor.

The Tiguan has no idea of whether the trailer is braking, neither can it be controlled. But it can sense sway via an accelerometer. This is an electronic device which works like a pendulum. If it sees no sideways acceleration, the pendulum hangs down vertically. As soon as a sideways acceleration is detected - it may be smaller than you can feel inside the car - the pendulum swings left or right, and the direction and magnitude is known. It provides a sinusoidal output, e.g. when vertical, the reading is 1, and as it deviates, it becomes smaller negative or positive, i.e. - 0.95 or + 0.95, etc.

Depending on the polarity and magnitude of this signal, the Tiguan knows which way the trailer is going and by how much. So it knows which wheel to retard - and by how much - to control the sway. As it is a closed loop control system, i.e. the accelorometer output is continuously measured as the correction takes place, the whole process is executed proportionally, i.e. smoothly, so the occupants would not experience a sudden jerk as the car is pulled straight.

To me the logic seems that if the rear of the trailer goes right, it will push the hitch, and therefor the car, to the left. To correct for this, the left rear wheel should be braked so the nose of the car can swing round, pulling the rig straight.

[T&M]

Thanks jcubed,

First up, as you can see I am very interested in this topic, so am willing to understand a little more about the Tig's in built genius vs getting a Hayman Reece "aftermarket" tow package that will allow me to tow a box trailer (unbraked) or a small camper trailer (braked) to our favourite camp spot.

The braking system you mentioned above is a hydraulic overrun system, but what if I had an electric brake controller eg. one of the Tekonsha models that work completely different to an overrun system. Tekonsha Website - Electric Trailer Brake Controllers and Trailer Breakaway Brake Systems

As long as it's 1. legal and 2. safe, I would be more than happy with the outcome.

VW Tow package - $1600++
Other options such as the Hayman Reece $900+ (I already have a controller) Hmmm so I don't get the fancy wheel braking. I'm OK with that.

Cheers.

PS I still can't find any reference to accelorometer or sinusoidal output in the damn manual!! Gee I'm hopeless at reading them!

[Sanman]

The Tiguan braking and stability control is tuned for a vehicle about 1600kg and 50/50 front/rear weight distribution. Once it is told there is a trailer connected, it would use a second map that is tuned for maybe 2500kg and 30/70 weight. It knows nothing of the detail of the trailer weight, braking type etc. Its Audi sibling also has the same setup for when a roof box is installed. Not rocket science, but a nice addition that can be done for almost free by the manufacturer.

[jcubed]

Hi T&M,

Regarding your PS, you won't find anything about accelerometers or sinusoidal in the VW manual. They only tell you the "need to know" stuff.

My background knowledge of these systems come mainly from inertial navigation sensors as applied in airborne observation systems. As useless information - I do not know if they still have/use them - but years ago I demonstrated and then installed and trained the operators in the use of these observation systems on the Victoria Police Airwing Dauphine helicopters - still the tail-draggers - at Essendon Airport, off the Tullamarine Freeway, I think. They were known as the LEO Airborne Observation systems, but these were pre-INS days. Here's what it looked liked in 1998.



It is also the technology around which active suspension systems are built. Funny thing is, as recently as last week, I was actually doing measurements on exactly such a device, this time used on a gun turret providing tilt orientation of the armoured infantry vehicle so that this can be corrected for when firing.

[T&M]

Thanks Sanman,
So please correct me if I am wrong... if I have a genuine VW towbar, the only extra "smarts" I get is a slight remapping that tells the car there is more weight on the back and splits it approx 30/70. There is no alteration to anything else?
For the sort of towing that I will be doing, I can live without the remapping.
Regardless of trailer type or setup, if the trailer has electric brakes, you will still need a brake controller anyway.
If I'm taking the box trailer to the tip, it won't matter at all.
Cheers.

[Sanman]

Thanks Sanman,
So please correct me if I am wrong... if I have a genuine VW towbar, the only extra "smarts" I get is a slight remapping that tells the car there is more weight on the back and splits it approx 30/70. There is no alteration to anything else?
For the sort of towing that I will be doing, I can live without the remapping.
Regardless of trailer type or setup, if the trailer has electric brakes, you will still need a brake controller anyway.
If I'm taking the box trailer to the tip, it won't matter at all.
Cheers.

My thoughts too - I confirmed with Hayman Reece:
Our wiring solution does not have any interaction with the ABS or stability control system, it is simply a way of correctly controlling the lights on the trailer without affecting or causing damage to the sensitive electronics on the vehicle.