DSC on or off when towing a van

[Gypsy_Pete]

I have a D3 and I've just started towing a 20' caravan (about 2,000 kg all up). I noticed that directional control was unnerving, particularly in side winds when compared with towing my previous, lighter, pop-top caravan. The new van is higher and therefore more susceptable to side winds.

It seemed that the car was being pushed around and not in unison with the forces from the van. I was wondering if the DSC was trying to compensate with what it considered to be directional instability. So I turned it off and I felt (emphisis on 'felt') like I had more control.

Has anyone had similar experiences? Should DSC be on or off when towing?

[stig0000]

this is new, il be watching the out come of this, plz tell me you dont have load levelers on do you, they fite with the air sus and play big time with the handling

[rmp]

DSC definitely on. If the car is being moved about by the trailer to the extent that DSC activates then you need to reorganise your tow setup asap as the trailer is exerting forces it should not be on your vehicle.

If the trailer lacks directional stability that is usually indicative of too low a towball mass, or possibly a correct towball mass with significant weights a long way from the CoG. I would also be checking tyre pressures all round and increase for towing on the towcar.

You must get this fixed asap because the conditions you describe mean the rig will be very prone to trailer sway and that could be deadly. I would fix the base setup issue rather than mask it with kit like anti-sway bars.

Also need to make a general allowance for the 2000kg 20" which is not a trivial tow, it will feel different to the lower, lighter poptop.

Best of luck and let us know how you get on.

[Disco4SE]

Hi Pete,
I agree with Robert. You need to have a look at your tow setup.
My boat is around two tonnne and have noticed that when we go away with the boat fully loaded with our gear, the vehicle handles better with most of the gear towards the rear of the boat, not the bow.
Normally, you would think that more weight on the ball would work better, but that isn't the case with my setup.
Cheers, Craig

[rmp]

D4SE, don't doubt your point but I'm concerned someone may read your post and then load towards the rear which is more dangerous than loading the front.

Trailer setup with the larger rigs can be tricky and it is definitely (literally and metaphorically) a balance. A lower towball mass (TBM) will improve responsiveness and make the rig easier to turn, it'll feel nimble. However, you lose directional stability and start to run the risk of trailer sway at speed. Not nice at all.

Loading up the TBM makes the thing feel heavier and less nimble, but is more stable and less chance of sway. However, it can be too stable and difficult to change direction. Also, once the trailer is knocked out of balance it requires more force to bring it back into line.

One mistake is to get the TBM right but by using heavy weights at either end. This gives an effect similar to high TBM - difficult to overcome the interia to turn the trailer, but if it is overcome it doesn't want to stop. Weights should ideally be as close to the CoG as possible.

The correct TBM should be supplied by the trailer manufacturer and should be less than the lower of the vehicle's TBM and the towbar's TBM. The latter two are not necessarily identical. Also if your towcar is at or close to GVM then the TBM will be reduced so as not to exceed the rear axle load limit.

Common misconceptions:

- my car can tow 3500kg, therefore anything like 2000-2500 is no drama at all just hook up and go
- it all feels fine so far, so good (wait till you hit a big gust at 110 or hit an off-camber windy patch on wet bitumen)
- if the car has the grunt to move it, all good (excess power and torque is about the least important criteria for a safe towcar)
- don't notice the trailer on the back so all good (wait till you need to brake hard or similar...then anything other than a good setup will bite, and bite hard)

that's enough, train about to arrive ;-)

[Disco4SE]

Hi Robert,
Totally agree with the theory not to load the rear of the boat / caravan etc. Been towing all my life and know this for a fact.
I am forever telling my guys not to load the back of the rubbish trailer too much as it causes sway.
However, for some reason it worked with my boat scenario???
Cheers, Craig

[Gypsy_Pete]

Thanks all for your comments. Firstly, my D3 is an'S' with all coil suspension. Rear wheels are up to 42 psi as per LR tyre guide. The caravan is dual axle with the wheels set well back making for a long "A" frame. The bed is at the front with very little weight in the underneath storage. About all that is behind the wheels is the fridge and the ensuite. But their is much greater weight on the rear of the car with this van, since the rear still sits down a bit despite the Hayman Reese WDH which I believe is able to be used on an all coil suspension D3. I am loath to add anymore weight to the front of the van because the car will just sit down further. I am considering fitting Polyair adjustable air bag inserts on the rear of the car to bring the rear up to level.

Thanks again, Peter

[Bushwanderer]

Hi GP,
Our setups are different, but I can only give you my experience.

Like you, I have a coiler, but the coils are King Springs, giving a 50-60mm lift (& 30% stiffer than original). As I didn't tow the caravan with the D3 before the spring change, I don't know what effect this mod has had.

My 'van is a 1500(?)kg single axle pop-top, so again, different to you.

I have a Hayman Reece adjustable hitch. With this, I have set the 'van to be perfectly horizontal when everything is loaded.

I keep the 'van tyre pressures high.

My Hayman Reece hitch has provision for WDHs (that I used to use on my D1), however, I have never felt the need for them with my D3.

So some questions:;)
1. Is your 'van chassis horizontal when connected to the D3? If not, this may placing more load on one of the axles.
2. What is the 'van towball mass as against manufacturer's recommendation?
3. What are the 'van tyre pressures set to as against manufacturer's recommendation?
4. Are you considering going off-road with your D3? If yes, then may I suggest the King Spring lift (or similar) as the D3 LR coils are set to about the same height as the air sprung on-road setting. If not, the Polyair's may help.

I'm sure that there are some things that I've forgotten, but your responses to the above would be a useful start.

HTH,
Peter
PS: If you lived nearby, you could try my D3 with your 'van.

[Disco4SE]

Hi Pete,
The Polyair bags are a good idea. Had them on several vehicles.
Mind you, the ride is as rough as hessian undies once you unhook the van.

Craig

[Gypsy_Pete]

Thanks Bushwanderer.

In answer to your questions,

1. The van sits horizontal but only because the rear of the D3 is sitting low. Once I get the D3 to sit horizontal, I'll have to look at setting the tow ball one hole lower than it currently is.

2. I don’t know what the ball weight is because I haven’t been able to check it yet. I think the van’s ID plate says that it should be 150KG (tare is 1750kg on this unit) but it is certainly heavier than my previous pop-top.

3. Windsor recommends 310 Kilopascals which I think equates to 45 PSI. For this first trip, I ran all 4 at 42 PSI.

4. I don't go off road so I don't want to have extra height and/or stiffer suspension on a permanent basis. That’s why I'm considering the Polyair bags since I can let them down while we tour without the van.

Thanks for your most generous offer of checking against your D3 but I live in Ballarat.
Regards, Peter

[Gypsy_Pete]

Thanks Craig. The way we tour is to put the van in a central spot for a week at a time and then go exploring. So I would let down the air bags when the van is not attached, to restore the normal ride comfort. I'm told they only need about 15 psi so a small pump could get them up again.

Regards, Peter

[Duck's Guts]

I've still got my 2006 Pathfinder & it's got Polyair springs on the rear.
Bought direct from the USA, about 2.5hrs to fit, and made towing the c/van level & safe without need for weight distribution hitches.
Also, easy to adjust using an El'cheapO air compressor or visit the servo to air up. When airing down a simple tyre gauge did the job.
Requires little air to adjust between 5 & 35psi. At 5psi there is no difference in ride quality. At 35psi it's ridiculously rock hard. Depending on the load, I found that 10-20psi was all I required for a 17" offroad pop top.
Highly recommend these air springs.

[Bushwanderer]

Hi GP,
Thanks for your reply.

As I'm sure that you realise, having the rear of the D3 low, means that the front is floaty. No wonder you are having problems. The Polyairs may be a solution.

Just to clarify, is the rear of the D3 low with or without the WDH? By how much?

I'm still concerned that the towball mass is too high. I suggest that you check that before anything. A rough guide would be to put some bathroom scales under the jockey wheel.

You are right that 310kPa = 45 psi. Why don't you run them at that?

I'm sorry that you live in "The Rat" ;) . If I head down that way, I'll check with you. In the meantime, please keep us posted.

Best Wishes,
Peter

[Gypsy_Pete]

Thanks Ducks. Nice to hear that the Polyairs have worked for you. I'm getting good reports from other people I talk to as well.

Regards, Peter

[Gypsy_Pete]

Hi Bushwanderer,

The rear of the D3 is higher than the front without the van on. Once I put the van on, it sinks badly. The WDH brings it back up but still not as high as the front and certainly not as high as it sits normally, that is, without the van.

I like your suggestion about using bathroom scales to estimate the ball weight. I'll try to get that done next Monday. By then, I'll double check the ID plate for ball weight. The van is in storage at the moment.

I didn't run the van tyres at 45 psi because someone told me that anything above 40 would cause excessive vibration on internal van fittings. So I went for a compromise. I used always run the previous single axle pop-top tyres at 45 psi. So I'll pump them up for the next trip.

Thanks for your continued responses. Peter

[Bushwanderer]

Hi GP,
My pleasure. :BigThumb:

I look forward to your further feedback.

Best Wishes,
Peter

[Gypsy_Pete]

Hi Peter, Our bathroom scales only measure to 120Kgs so the van went off the scale. I'm going to see if I can borrow a proper measuring device.

Regards, Peter

[rmp]

120kg will be fine. Just get a length of strong wood, mark it in half, balance on end on a small block, put the jockey wheel 1/2 of the way along and the scales at the other end. The load on the scales will be half the actual load and if it's more than 240kg...repeat but use thirds but it shouldn't be!

Also note that the jockey wheel is not at the end of the drawbar so the weight shown will be slightly higher than actual.

[Bushwanderer]

Hi Robert,
I was confused by your post until I realised that when you say "...balance on end...", you meant to say "...balance one end...".

It may be self-evident, but it would be best to use a block of wood (to balance on) about the same height as the scales.

Best Wishes,
Peter

[rmp]

correct...didn't really proof read it but I thought people would get the general idea, ie you can measure 120+ of TBM with scales of less than 120kg, thus saving people money on buying more expensive scales and allowing them to donate the difference to AULRO ;-)

[Bushwanderer]

Hi Robert,
Don't get me wrong, it's a great idea. :BigThumb:

Best Wishes,
Peter

[Gypsy_Pete]

Thanks rmp for that Idea. I'll go back over the weekend to the van storage and try that.

In the meantime, I have discovered that Polyair do not make a bag kit for the D3 coiler. I'm told it is because the D3 (unlike D2) uses struts through the rear springs and therefore the bags wouldn't be possible.

So I've booked it in to have some Pedder coils fitted which are 30% firmer and should give me 1.5" extra height in the rear. Thats happening next Thursday.

Hope to post again over the weekend.

Thanks to all, Peter