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Rear end sag and towball height 7P

13K views 167 replies 16 participants last post by  redbarron55 
#1 ·
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I got my 2013 7P 4 weeks ago and had a TAG towbar fitted with Towpro electric brake controller. I also have a Raptor adjustable tow hitch to achieve whatever towball height I need.
Hitching up to my caravan for the first time, I noticed quite a bit of sag on the rear of the Treg and the nose of the caravan pointing down as a result. Is the sag an issue as I have steel springs and no air suspension. Reading other threads most seem to think sag is acceptable and putting in stiffer springs is not recommended as it makes the ride jittery when not towing.

I have the Alex G 2” lift kit on order to get more clearance for sand driving. This will lift the car and I may also raise the Raptor hitch to lift the nose of the caravan. The rear will still be sagging and front pointing skyward but I can get the caravan level. Will this work?
 
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#2 ·
Camper MUST be level. Bring the hitch up another inch and test again. Might need another 2 inches to be level. Single axle trailers suck and this is part of the problem, more tongue weight.

How much does camper weigh and what's the tongue weight
 
#4 ·
Camper is 1400kgs unladen with a massive towball weight of 280kgs which doesn’t change when I get the 220 kgs of dirt bikes in, plus gear, fuel, genset etc. no matter what I have that 280kgs of towball weight. I am looking long term to get a dual axle toy hauler but for now this is it.
 
#8 ·
In the picture it is empty of bikes. Genset 32kgs and fuel can behind the axle inside plus 2 wheel chock stands on top of the axle.
Car will have a Waeco fridge freezer when travelling plus 2 adults including driver. Other than that all the gear is inside the van
 
#9 ·
Part of your problem is the hitch. That height adjustable device is moving the towball what looks like about 150mm further back, and that magnifies the already high ball weight effect on the rear axle and worsens the sag. And then there is the weight of the height adjustable hitch itself. It's also possible the towbar itself has the receiver further back than optimal. Dunno about the 7P, but the CR owners manual specifies how far back the towball should be, and the towbar itself has a placard that shows the max distance the ball can be from the pin. Might be worth seeing if the 7P has similar info.

Is it possible that your 9 year old springs are a bit soft/sagged - maybe new springs at the standard rate would be a start.

If the ball weight is not changing with loading the camper, the scales might be dodgy.

Also, presumably the bikes load over a ramp on the back of the camper and their mass is behind the camper axle? That will help reduce the ball weight and ultimately the sag that's most relevant is when the bikes are loaded ready for travel but Unfortunately any load in the car is only going to make it sag a bit more.

You might want to try it without the adjustable hitch just to see how much effect the extension and its weight has.

Unfortunately through the geometry of your camper with the axle so far back is going to make your life difficult.
 
#10 ·
Good point on hitch length. OEM hitch is like 1.5" long
 
#11 ·
I agree on the hitch length. I queried it with the towbar company as well as it is 140mm further back than a std hitch. By my reckoning that adds 14% to the overall axle to towball distance which increases leverage as me also reduces max towball weight. They said it wouldn’t affect it… but laws of physics says it will. I’ll need to establish the ideal ball height for both the caravan and the boat and then buy 2 std hitches of different heights. When the caravan is level the ball needs to be 51cm off the ground once loaded. For the boat it needs to be 43cm off the ground.

My towball scale works fine. What I’m saying is that no matter how I try I cannot get towball weight below 280kgs. The bike engines are virtually over the axle and has little effect on the towball weight. Packing everything else into the back makes little difference. 50 kgs of fuel cans, genset, camp chairs and tools.

I’ll try a std hitch to see effect on sag but it won’t be high enough for the van.
 
#12 ·
Sucks when the people at the towbar company who should know this stuff well BS you, but hey, a sale is a sale :rolleyes:

Sounds like you already understand this but the biggest impact on towball load with the geometry your hauler has with the axle so far back will be getting weight off the drawbar, most of which will be pretty inconvenient if not impractical, but the sag (and highly likely vehicle rear axle weight) you have at present doesn't look viable. For example moving the BBQ out of the kitchen to the rear of the hauler while you're travelling and switching to a removable jockey wheel you can also put in the hauler. A more extreme option would be to ditch the kitchen altogether and store it all in the hauler. By rough eyeball from your photo, anything from the kitchen forward you move to say right over the axle will reduce ball load by around 2/3 of that item's weight, and if instead you move it to the rear of the hauler, the reduction in ball load will be near 100% of the item weight.

I feel your pain though. Caravan so-called engineers are not my favourite people. My caravan has a bloody stupid compliance plate that specifies a max ball load of 208kg. To get there I have to fill the rear water tank, empty the front and remove one of the gas bottles - so I have no useable water and can put bugger all in the boot, wardrobes or under the bed :mad:
 
#15 ·
Having done some more thinking and talking to towing and suspension specialists there are a few options to think about. Assuming I ditch the Raptor hitch I can

1) use a WDH which VW say don’t. This seems to be the solution the engineers favour as it redistributes weight over the front. I’ve no idea why VW say don’t use one but I’ve read other members here have used them for years with no issues

2) fit stiffer springs which most here recommend against as it ruins the ride when not towing

3) fit coilovers that have adjustable preload and damping. This means I can go with a smaller increase in spring rate to maintain comfort and use preload as the means to reduce sag under load, possibly use ride height adjustment as well to get the car level, like the air suspension does. Doesn’t fix the weight distribution but simulates what air suspension would do without WDH
 
#16 ·
Here’s what I’ve decided on…

The shock absorbers are tuned for the heavier springs so the ride is not compromised like it is if you just put stiffer springs on the std shocks.
They are adjustable for preload and ride height can be raised or lowered. In effect I can have a lowered car one day and a lifted one the next.

The only thing I didn’t think through is whether the AlexG lift kit I’ve also got coming will be compatible… 🤔

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#17 ·
I would stick with bc racing or Ceika personally, if this is the road road you're wanting to take
 
#20 ·
I'm just going to add my 2c here and ask if changing the car over to one with air suspension and stock tow bar might also be an option? A lot of time and expense to go to with new suspension, lift kits, etc etc. Is there something special about this car? Air suspension will fix your problems, and when you upgrade the toy hauler (as you suggest) you won't run into a whole new set of issues. You'll also gain the extra HP as air suspension usually accompanies the 180kw engines. Anyhow, at the very least I'd try a WDH as they will help, but I'm not certain they'll get rid of that much sag.
 
#24 ·
I hear you. I got the car very cheap and willing to put money into it for now. By the time I’m finished it’ll owe me $32k which is still a bargain.
I agree air suspension would be nice but I’d want a much younger car if it had air suspension for reliability.
I have a stage 2 tune on mine which puts it at 200kw and 550Nm so it will pull nicely. The $$$ I save on a car will go towards the new caravan which ain’t gonna be cheap !!! I’m just happy not having to buy a similar year Landcruiser for $85k that people are asking! The Touareg is a bargain in comparison even with the mods.
 
#22 ·
Stiffening up the rear springs, or lifting the car or tow hitch may make it all look better BUT..... that is all cosmetic and may not address the issues.
In Australia even if you use a WDH, the car weights are assessed without the WDH tensioned.
As I discovered a few days ago when I had my whole rig weighed professionally at each wheel it quickly goes pear shaped on rear axle limits when towing with a Touareg.
My setup was 1100kg below the allowed GCM (6415kg) but I had still exceeded the allowed rear axle load limit by 90kg which on my 7P with air is 1530kg
In the car was just me (125kg :rolleyes: ) and a full tank of diesel (100 litres), no luggage or extras in the car, the caravan was heavy on the tongue at 320kg, ok I can shift load off the tongue easy enough to get back to 280kg but I still need to add partner and dogs to the car (another 115kg total)
For towing in Australia where the authorities are now beginning to look closely at axle load limits and overall limits this poses issues as the penalties are tough and insurance may not cover you if overloaded.
 
#25 · (Edited)
Getting the trailer level isn't as important on a single axle trailer. The forces transmitted are nearly the same as a straight trailer, just at a slight angle due to the cant at the trailer ball. The cosine of small angles is nearly 1 so not much difference. e.g. cos(5 deg) = 0.996, so tilted at 5 degrees there's only a 0.4% deviation from a straight trailer. Proper weight distribution fore/aft of the trailer's axle is more important (to prevent sway).

Getting the trailer level is crucial on a dual axle trailer. The angle the trailer sits at determines the weight distribution between the trailer's front and rear axles. If it's flat, it's close to 50/50 (after subtracting the weight supported by the hitch). As you tilt it up or down, you shift the weight towards the rear or front axle respectively. This can lead to you exceeding an individual axle's weight rating just having the trailer hooked up to your car. e.g. If the hitch were high enough, the front wheels would be off the ground (zero weight), and the rear wheels would be bearing all the weight. If you look on the trailer's spec sticker, it should tell you the optimal ball height.

I really wish I had an air suspension for this reason, since hitch height varies with load and each (dual axle) trailer has its own optimal height. But it was no longer an option in the U.S. when I got my Treg. I had to guess how much sag there would be and buy a ball mount with a rise to counteract it.

A WDH compensates for this by more tightly coupling the trailer and tow vehicle in pitch. But does so by transmitting torques through the hitch, which VW never considered when designing the hitch and frame. Hence their recommendation not to use a WDH - they literally don't know what will happen. Based on the numerous user reports of using a WDH and lack of user stories of the rear of their car's unibody construction bending, it seems to work. But just be aware that's all anecdotal evidence, and no engineering calculations have been done to verify it's OK.
 
#27 ·
I don't have a 2013 model. It varies from model to model. I think the value for my 2015 model is about 1530 kg?
 
#31 ·
Thanks for posting those pages. Mine has rear axle limit of 1530kg so next question is what’s the load on the rear axle unladen? That will give me some idea of what payload is possible.

Kerb weight is 2153kg, would it be reasonable to assume 55/45 weight distribution? 968kgs on rear axle? That leaves 562 kgs of payload over rear axle, take away 280kgs towball weight and 80 kgs of fuel, leaves 202kgs for rear passengers or 400kgs in the cabin spread over both axles.
 
#32 · (Edited)
I can tell you that I had mine professionally weighed a week ago
GCM van & car 5300kg
Rear axle came in at 1630 (yes 90kg over)
That includes;
  • 324kg on the ball ( yes too much )
  • 100 litres of diesel
  • 1 driver (125kg)
  • no luggage or passengers
That should give you an idea of how tough it is to manage
 
#33 ·
Unfortunately it doesn't quite work that way. Because of the lever effect of the towball overhang behind the rear axle, more than the towball load is transferred to the rear axle, with a corresponding reduction on load on the front axle. I believe the weight factor is 1+ overhang / wheelbase. For the CR with 2895 mm wheelbase and 1119 overhang, about 1,4 times the ball weight goes onto the rear axle, so 280*1.4 = 392kg. The ONLY way to get an accurate answer is to have your rig weighed with what you carry in the vehicle (fuel, driver and co-driver, anything you'll carry in the car) to establish accurate axle weights, and then repeat it with the van hitched up. There is any number of mobile weighing services that do exactly that. Better to spend a few hundred on that than cop a fine and a defect that would stop you continuing your journey with the van hitched, and worst cased invalidate your insurance if you had a mishap the insurance company could claim was load related.
 
#34 ·
I was so convinced with the GCM figures that the Touareg would be a good tow vehicle and everyone says it is! This rear axle weight limit seems to be a much bigger limitation and you may as well forget GCM, GVM. I’m now wondering if I reconsider my choice of tow vehicle or will it all come good when I upgrade to a twin axle van with lower towball weight? I fear I’ll still be in strife with towball weight as the new van would be close to 3500 GTM. I’d want to be fully laden with 4 passengers…
 
#38 ·
IMO, while Australian van manufacturers and caravanning media remain fixated on 10% ball weights and that 300kg plus ball weights are ok, the Touareg (and most unmodified dual cab utes, Prados and Cruisers) will struggle to tow anywhere near their headline weights while carrying any internal payload without overloading rear axles. For 2t+, the Touareg needs to tow vans designed closer to Euro specs of 5-7% tow ball download. More sensible weight distribution at tare also means that ball load doesn't increase as much from tare to loaded.
 
#37 ·
Achievable if you have 2 passengers each 75kg, no luggage, half a tank of fuel and no more than 280kg on the ball
Then you can tow 3500kg
I LOVE this Touareg, and will manage by shuffling loads to reduce TBM
Already travelling with nothing but 40kg of dogs in the car ( oh and wifey who apparently doesn’t weigh much at all 😀)
 
#39 ·
Yes. I think that if one looked at all the available tow vehicles' the rear axle load would be the limiting factor. It's not just the Toerag that has the problem.
 
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#40 · (Edited)
My van is a 2016 model and heavier on the ball at tare than some,
many of the newer vans are quite light on the ball to the extent that they are sometimes perform poorly on their first trip home from the dealers whilst travelling empty.
I feel the Touareg whilst having and excellent GCM it has the lowest rear axle load of common tow vehicles in Australia
comparison below (There may be some minor variations between models but for discussion this should do)
Tare MassGross
Vehicle
Mass
Gross
Combination
Mass
Towing
Capacity
(braked)
Towing
Capacity
(Unbraked)
Maximum
Towball
Download
Max
Roof Load
Max
Axle Load
- Front
Max
Axle Load
- Rear
2018
Jeep Grand Cherokee
2327 kg2949 kg6099 kg3500 kg750 kg350 kg68kg1452 kg1678 kg
2017
Volkswagen Touareg
2153 kg2860kg6415 kg3500 kg750 kg280 kg100 kg1380 kg1530 kg
2021
Isuzu D-MAX
2035 kg3100 kg5950 kg3500 kg750 kg350 kg1450 kg1650 kg
2021
Isuzu MU-X
2175 kg2800 kg5900 kg3500 kg750 kg350 kg1450 kg1650 kg
2021
Mitsubishi Pajero Sport - Exceed
2110 kg2775 kg5565 kg3100 kg750 kg310 kg80 kg1360 kg1600 kg
1840 kg (Triton)
Toyota LC2002740 kg3350 kg6850 kg3500 kg750 kg350 kg200 kg1630 kg1950 kg
Toyota Prado2240 - 2305 kg2990 kg5990 kg3000 kg750 kg300 kg
2021
Ford Ranger
2099 - 2278 kg3200 kg6000 kg3500 kg1480 kg1850 kg
2021
Ford Everest
2384 kg3100 kg5800 kg3000 kg750 kg1480 kg1750 kg
 
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