Technical Question re D3/4/RRS Air Suspension

[Rockylizard]

Gday...

We all know, and accept, that LR state that a WDH is NOT to be used with the D3/4/RRS.

Without a caravan/heavy trailer attached to the D3 there is obviously 'balanced' pressure/weight on the front wheels and rear wheels to maintain steering, braking, traction.

So, when I connect my van to the towball, the D3 does not sag at the rear but automatically levels itself with the added weight on the ball.

Does the air suspension restore the pressure/weight 'balance' to the front wheels to maintain steering, braking, traction? Does it maintain the weight distribution over each of the axles - van, vehicle rear and vehicle front?

If this is how LR designed the suspension setup, can anyone provide me with authoritative advice and/or source to confirm, and describe how it works?

Cheers
John

[Graeme]

The air suspenion system maintains height only. More weight at the rear makes the vehicle lower at the rear and higher at the front which is detected by the height sensors so the air volume in all the air springs is adjusted to make all the height sensors read the correct height.

[Rockylizard]

Gday...

So with the caravan/heavy trailer connected to the D3, I have lost some steering, braking and traction efficiency at the front of the vehicle?

Isn't that dangerous?

From the sensation of towing my van, I would suggest it does more than "just adjust the height" as it feels very normal to drive when the van is connected. So I am kidding myself then?

Cheers
John

[gghaggis]

No it's not particularly "dangerous" - search for WDH on this forum and get a plethora of arguments and counter-arguments from the religious wars this topic has generated.

The short story is that your EAS can react faster and without rebound when compared to a WDH system. So overall, you have greater control.

Cheers,

Gordon

[Graeme]

The vehicles have a reasonably long wheelbase and reasonably short overhangs so loads on the back don't affect the vehicle as much as some other vehicles. Add the stability control and the trailer/van effect that's felt on older vehicles is greatly reduced on these vehicles. Without a trailer or van attached, try throwing the vehicle around and feel how it wont let you unless DSC is disabled (as much as it will). The suspension height control reacts slowly by design but DSC is super quick.

[rmp]

Gday...

So with the caravan/heavy trailer connected to the D3, I have lost some steering, braking and traction efficiency at the front of the vehicle?

Isn't that dangerous?

From the sensation of towing my van, I would suggest it does more than "just adjust the height" as it feels very normal to drive when the van is connected. So I am kidding myself then?

Cheers
John

Yes, there's an element of danger. That's why trailers need to be driven differently.

If you connect a trailer to a Disco then you are creating a moment which increases the force on the rear wheels and lessens it on the front. That's basic physics and no different to any other vehicle. A WDH lessens this effect, transferring mass from the rear to the front wheels (and other factors as well). Discos cannot take WDHs but are quite capable of towing 3500kg. A WDH is basically there to stop the rear sagging - the EAS keeps it level hence no WDH required.

If DSC or its close friend TSC has to kick in then the trailer is poorly set up.

Lots more to it than that but bottom line is the Discos are great towcars but do not remove the need to set trailers up correctly and then drive them correctly.

[rmp]

Does the air suspension restore the pressure/weight 'balance' to the front wheels to maintain steering, braking, traction? Does it maintain the weight distribution over each of the axles - van, vehicle rear and vehicle front?


No, it doesn't maintain weight distribution. It can't transfer mass from one axle to another. It can only maintain height.

[Graeme]

Something that's often overlooked is that ABS allows rear wheels to do a lot more of the braking when the rear is loaded. Usually too much weight is transferred to the front wheels especially if the vehicle nose-dives, so having less weight on the front wheels doesn't necessarily mean less braking ability.

[Garry]

Have you assessed the weight in the trailer is placing on the hitch, it should not be that much. 150kg? I tow a tonne and a half on a regular basis and I forget sometimes it's there, it's a well balanced load so never had any issues

G

[Rockylizard]

Have you assessed the weight in the trailer is placing on the hitch, it should not be that much. 150kg? I tow a tonne and a half on a regular basis and I forget sometimes it's there, it's a well balanced load so never had any issues

G

Gday...

Van puts 240kg on tow ball ... and van is well balanced ... and it tows with absolutely no problems - uphill or downhill, smooth road or rough road.

I was just wondering, given the safety advantages of WDH, which I have towed with previously on other vehicles, whether the EAS on D3 was smart enough to actually not just level but also ensure the weight on front and rear was restored to close to 'normal'.

In some way, I guess it does ... but there is no definitive proof it does so.

Thanks for all the interest.

Cheers
John

[mowog]

One of the caravan mags did a test with a D3 on a weight bridge.

Quote.

"When a van with a ballweight of 160 kgs was connected, the front end weight went from 1240 to 1180 - a drop of 60 kilos, or only 4%. There was no noticeable difference in the feel of the steering."

[gps-au]

I was just wondering, given the safety advantages of WDH, which I have towed with previously on other vehicles,

Maybe it should be said as "perceived" safety advantages :angel:

[rmp]

Something that's often overlooked is that ABS allows rear wheels to do a lot more of the braking when the rear is loaded. Usually too much weight is transferred to the front wheels especially if the vehicle nose-dives, so having less weight on the front wheels doesn't necessarily mean less braking ability.

Plain ABS won't do that for you, as all it does is stop a rear wheel locking. What will help is EBD which will distribute brakeforce to the rear, in effect changing the brake bias instantly. Because of the extra weight you'll get more braking, but...because of the extra weight you'll need it!

[rmp]

One of the caravan mags did a test with a D3 on a weight bridge.

Quote.

"When a van with a ballweight of 160 kgs was connected, the front end weight went from 1240 to 1180 - a drop of 60 kilos, or only 4%. There was no noticeable difference in the feel of the steering."

exactly. pretty simple physics, measure distance from centre of rear wheels to towball, multiply by towball mass, then measure wheelbase and resolve to find the equivalent force to balance. Not a whole lot.

[rmp]

Maybe it should be said as "perceived" safety advantages :angel:

A WDH is definitely an advantage for many vehicles and indeed required for many at certain weights, so the advantage is very much more than perceived. As described the Disco's EAS keep the car level, and the reduction in weight off the front is negligble. For a lighter, softer-sprung car with a shorter wheelbase and greater rear overhang it becomes more important. This is why you need larger 4WDs to safely tow 3500kg.

[Graeme]

Plain ABS won't do that for you, as all it does is stop a rear wheel locking. What will help is EBD which will distribute brakeforce to the rear, in effect changing the brake bias instantly. Because of the extra weight you'll get more braking, but...because of the extra weight you'll need it!
Yeah, I took a shortcut and didn't explain what can be done with ABS.

[TerryO]

This is why I recently purchased a D3 to be able to tow our off road caravan without a WDH.

I take the van quite a bit of road and a WDH is a real pain in the backside off road.
I can see why most people swear by WDH's as most vehicles are pretty useless at towing so the WDH hides most of the weight balance problems. I spent the last two days towing the van around with the D2a while I get all the gear I want fitted to the D3 before I tow the van with it.

Over the last six months in most cases towing with the D2a has been quite good, I think this is the case especially because of the ACE which helps with body roll and handling. Though even with the standard air suspension on the rear it still sags and makes the front end light, add in heavy braking on dirt roads and it can become quite dangerous on occassion as the front locks up and then doesn't steer.

This happems with a ball weight of just over 200 kg depending on what is in the front boot of the van, I really wouldn't like to drive it with the D2a's maximum 250 kg ball weight on bumpy twisty dirt roads.

So rather then fit a WDH which would have helped considerably how the D2a rides and steers with a Van on the back I just brought the D3. Hopefully this will improve the driving safety levels aswell as comfort levels and more important then comfort the ability to go up steep hills at more then bloody 40 kph which often happened with the D2a.

cheers,
Terry