Thread: The Discovery 4 is a second rate tow vehicle

Back when this thread started I did some online checking. There is stuff-all proper research on towball weights etc. The 10% seems to be something someone dreamed up. There was some decent work done back in the 70's, so modern suspension etc may have an impact but I think the generalities apply.

The bottom line was that there was always a benefit to the tow vehicle being heavier than the towed trailer, that central mass loading in the trailer/van was better than distributed (so caravans particularly bad) and that the two major problems of tow vehicle stability and trailer stability required opposite solutions with ball weight and WDH. Contrary to what I would think, WDH made the towed vehicle harder to drive and more likely to jacknife in a corner. The only solution was to lower front tyre pressure. The benefit to the WDH was in preventing trailer sway. Another way of saying this is that the WDH had the same vices and benefits of adding further towball weight. Go figure...

In the weight range of a Disco 4 and assuming an 18 foot, 1.8T van you would want about 15% tow ball weight without a WDH (270kg). See page 130 of the linked PDF:
http://www.edccorp.com/library/TechRefPdfs/EDC-1082.pdf

According to the research "there is definitely an optimum hitch load for each tow car and trailer combination." Now to find it!

Originally Posted by ozscott

Thanks Don. Excellent post mate.

So it's settled then that auto controlled bags still allow substantial weight to come off the front wheels (with negative effects on braking in particular) and only a wDh (if it could be used in this case) would be able to lever the weight back onto the front?

Perhaps the caravan forum blokes when talking about the cruiser being a heavyweight tower were talking of them cruisers weight - more the merrier. The kerb weight on any of these big wagons is not an issue at lower levels but at over 3k say every bit of extra kg of the tow vehicle is a good thing.
Cheers

You are assuming it has a negative effect on braking Scott, the amount of weight reduced on the front axle wasn't massive, only about 100 kgs if I read correctly. Which is roughly a 10% reduction in front end weight.

Having 1.2 ton of weight on the front wheels is still a very substantial amount of weight, just because there is 1.9 ton on the rear doesn't automatically mean the vehicle is unstable or loses braking effectiveness.

If it did then people would be reporting that their D3/4's are handling poorly when towing. To date I have not seen one comment saying this.

Has anyone else seen a comment from a D3/4 owner saying they have experienced handling and braking woes when towing large traliers or vans?

cheers,
Terry

Correct me if I'm wrong but isn't Land Rover the only manufacturer that has a demonstration video of its Trailer Stability Assist?

To the average punter this shows that LR put the research and development into engineering a superior tow vehicle and a tow bar is not just a add on after thought.

I know this was a big selling point along with its 3500kg towing ability that sold my parents on one to tow their van not just safely but in comfort.

Craig

There seems to be a dogged determinism to keep this 'wdh vs eas' debate alive??

Despite the facts that the manufacture tells us which is preferred, the owners that tow with both systems tell us which system they prefer, we still have to listen to the wisdom of a bunch of Toyota owners????

Weighbridge figures are for a STATIC system. On an undulating or bumpy road (which seems to be most of them), the leveraging effect of a WDH system can (and probably always does) intensify and vary the weight redistribution effect. Not good .....

Cheers,

Gordon

Gday...

Now THAT makes real sense ... when I had Cruisers etc I would never have towed without a WDH because it made everything 'feel and sit right'.

The D3 is incredibly stable in all conditions with my van on the back without a WDH. I was dubious when I first got the D3, but after 30,000km of towing my big van over outback QLD and NSW for the past two years on all sorts of roads - both minor and major, majority sealed but some dirt - the D3 is the most stable vehicle I have towed with.
Cheers
John

The July 2009 Caravan and Motorhome issue has an article on WDH and ordinary (non SLS) vehicles and, also a D3. The conclusions were a towball weight of from memory 140kg resulted in a 60kg lighter load on the front wheels which still left a weight of grater than 1100kg on the front tyres of a D3, If I remember their conclusion correctly, the D3 SLS took care of everything and a down-force of 1ton plus on the front wheels maintained directional control.

I have towed my three ton van without a WDH around OZ, all without any problems. Loading our van with approx 200kg plus nose weight works well for me, as does the tandem axle, now if only I had air suspension on the van to help level it when camped on a creek bank out in the bush

Ryall

Have to agree with John about the stability of the Discovery 3/4. I've never used a WDH on either the current D4 or any previous vehicles - maybe horse trailers tow differently? My summation of this whole WDH issue is;
- Yes a WDH has theoretical benefits, you can't argue with the science. The level of benefit will vary greatly depending on input parameters.
- Yes you'd be mad to tow a large trailer without one on some vehicles
- Land Rover say don't use one on a D3/4 so you shouldn't.
- As long as the loads are within stated limits then the D3/4 is a safe tow vehicle
Do I think a WDH could improve the towing capability of the D3/4? Maybe, but we'll never know. I couldn't be happier with the way the D4 tows and don't think it can be improved much. Guess we'll just have to live with an almost perfect tow vehicle.

Actually in a dynamic situation you can argue the science!

I'd be (and I am) more concerned with people's desire to tow 3000+ kg of Griswald family roadblocker!

And the heavy, overdone mass that van manufacturers are building!

It's ridiculous!

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