Thread: Confused - D3/D4/RRS Towball Weight

Originally Posted by discotwinturbo

My touareg with the wdh is a superior ride towing our 3.5 tonne triple axle horse float then my airbag equipped D4....period.
Brett....

Brett
When you use the WDH do you tension it until the touareg is restored to level? If so, then Whilst it might feel better for minimising pitching, the vehicle is likely to have lost most if not all of its original understeer bias and would be likely to oversteer at side loads ( eg cornering) of >0.3g. (Note that 0.3g would still feel very fast for cornering with a van attached, but even cornering at slower speed with a coincident side load (passing truck, wind etc) could get you there.

Apparently ( again according to papers I've read), the WDH should only be tensioned to restore approx 25-50% of the load lost on the car's front axle when the trailer is attached. Compare this to "levelling" which restores well over 100% of the original front axle load.

Originally Posted by gghaggis

Brett:
Never towed with a Touareg, so can't directly comment - but I have with a LC200 + wdh, and the RRS was far more stable at high speed.

Scott:
The info is interesting, but I don't see the relevance to a D4 - which is not an articulated vehicle?

I don't believe that a D4/RRS would have significant problems towing 3 tonne as long as there was some reasonable towball weight. What "reasonable" is seems to be the issue here - rule of thumb is around 10%, and it would appear that LR automotive engineers design around this figure. There doesn't seem to be any evidence that 6% or so is _not_ safe when considering a twin-axle caravan of this weight on the back of a D4, all other things being equal.

Cheers,

Gordon

Gordon, "artculated vehicle" (in the context of the paper) is simply a car towing a trailer. If you look at the diagrams later in the paper you will see it is exactly the setup you would use for either single or dual axle caravans.

As I mentioned earlier, the tow vehicle they examined was the same mass as a D4, but the trailer only weighed 1.2 tonne and they concluded you are in good shape with 11% towball load, but unstable at 105km/hr with 2.8%.

A heavier trailer reduces the damping, and lowers the critical speed. I would be surprised if a 3.5 tonne trailer would be stable up to 100km/hr with a 6% towball load and no dynamic trailer sway control.

Originally Posted by Tryanything

Brett
When you use the WDH do you tension it until the touareg is restored to level? If so, then Whilst it might feel better for minimising pitching, the vehicle is likely to have lost most if not all of its original understeer bias and would be likely to oversteer at side loads ( eg cornering) of >0.3g. (Note that 0.3g would still feel very fast for cornering with a van attached, but even cornering at slower speed with a coincident side load (passing truck, wind etc) could get you there.

Apparently ( again according to papers I've read), the WDH should only be tensioned to restore approx 25-50% of the load lost on the car's front axle when the trailer is attached. Compare this to "levelling" which restores well over 100% of the original front axle load.

I had it tensioned by a hayman Reese engineer who was in Perth for a show....he was a friend of my dad.

It's almost the same height without trailer at the rear. He had me weigh the car without trailer, with trailer without wdh and then with wdh at settings until we got it right. The weight was about 45/55 distribution with front being 45%.

Have had to do emergency braking on a couple of occasions over the years and all brakes on vw performed like they were designed, plus the trailer bakes have been set perfectly....it stopped quick as the front brakes could also perform their best.

The vw performs better then the D4 towing this weight with the wdh...cornering, braking, and comfort.

But it has been set up right, which I reckon very few would set it up this way.

Brett....

Originally Posted by Tryanything

Gordon, "artculated vehicle" (in the context of the paper) is simply a car towing a trailer.

Ah yes, my error .......

Originally Posted by Tryanything

As I mentioned earlier, the tow vehicle they examined was the same mass as a D4, but the trailer only weighed 1.2 tonne and they concluded you are in good shape with 11% towball load, but unstable at 105km/hr with 2.8%.

You presumably have some other source for that statement? The paper you're quoting concludes that the primary drivers of dynamic instability are the relative positions of the trailer centre-of-gravity and the normal load of the trailer axle(s). The variation in towball load is a consequence of that, but the precise figures will be specific to the dimensions of their test trailer (draw-bar length, distance-to-axles, weight distribution etc), so you cannot use this particular simulation to generalise the case for towball load. As Glynhouse said above, different towball loads aren't necessarily "dangerous", although I think we'd all agree that a negative load would be rather precarious!

Originally Posted by Tryanything

I would be surprised if a 3.5 tonne trailer would be stable up to 100km/hr with a 6% towball load and no dynamic trailer sway control.

I'd be surprised if anyone towed 3.5 tonne at 100kph with a car! At least the D4 _does_ have dynamic trailer sway control (asymmetric braking), so you have less chance of a runaway condition.

Cheers,

Gordon

Originally Posted by gghaggis

You presumably have some other source for that statement?

Gordon

No - not really necessary. The statement I made is just a summary of the conclusions drawn directly from the paper. The towball loads and trailer weight are all stated explicitly so the tow ball percentages I quoted are obtained by simply dividing one weight by the other. Apologies if I am misunderstanding where you see the problem??

Don't get me wrong, I'm not suggesting that the specific numeric conclusions from the paper are valid for all trailer/vehicle combinations. And I'm not for a moment suggesting I have all the answers in such a complex area, I definitely don't. In fact, many on this forum ( such as yourself) would have WAY more practical experience with towing and particularly Landrovers than I ever will.

Given I have already benefited from advice from others on this forum, I guess I was just trying to contribute something back in an area I have spent a fair bit of time researching.

Like many others, I had always thought the 10% towball load guide had no basis in engineering/physics, but I discovered that in general, it does, as this and other research demonstrates. But this rule of thumb does oversimplify the real learning with all this which is that there is a towball % weight range over which a rig will be most stable. If the towball load goes too low, the caravan will oscillate/sway and do so uncontrollably over a certain speed. Likewise, if the % towball load is too high, it makes the tow vehicle itself unstable leading to oversteer/jacknife.

In both cases, having a trailer much heavier than the tow vehicle substantially lowers the speed at which the instability can occur. This is the whole point of the orginal slide by Klein I posted.

Personally, I have taken what I have learned from this desktop review of available research on board when setting myself up for towing. Others can form their own view.

I guess my point is that (from what I read) you're calling the "cart" the "horse". Nowhere does the author specify that the towball load is the causal agent. Rather, the COG/axle-load positional ratio is the driver of instability. And from that, with the specific dimensions of a particular caravan you could (possibly) calculate ideal towball load. Did they do a separate experiment with towball load as the primary variable?

It seems 10% of total trailer mass is a good "guestimate" for being in the ballpark for an ideal COG/axle-load positional ratio, but it's quite possible that 5%, for a particular van, or 15% for a different one, would also be within the stable ratio range. Lacking all the sensors required to monitor all the dependent variables, the best thing one can do is try it. Don't necessarily panic if you towball mass is _not_ 10% of the caravan mass.

Cheers,

Gordon

Just as an devils adcocate example ,,
With my 2.2T D2(wheelbase is smaller than a D3/4) I tow a 18' 1.7T 4-wheel independent Van,
When I first brought it home, I weighed everything--

I have a ball weight of 70kgs,,

The van was built in 1990.

Tows like a dream,,
no sway from passing semi's,
in fact no sway at all--!
http://www.aulro.com/afvb/discovery-...our-d2-79.html

no, its not an add--

Pedro what page or post number is yours