Thread: Confused - D3/D4/RRS Towball Weight

Originally Posted by Tryanything

Hard to say. Certainly 3 tonne is better setup than 3.5 tonne. Could be your vehicle/trailer has some attributes favouring better stability ( shorter hitch overhang, lower yaw inertia, longer distance between hitch point and trailer axle).

I guess there will always be exceptions.... but I dont think this undermines the science. Just like the existance of a 98 year old smoker does not make smoking safe.

I don't think my vehicle has anything special towing wise. The only real difference over all the other RRC's built since 1970 is a heavier diesel in the front.

I think the research you are touting is over-conservative to the point where it appears irrelevant. More like the 16 year old smoker than the 98 year old smoker.

Certainly I have only ever witnessed one unstable trailer and it had everything wrong. I was lucky that it bounced the other way as it passed me.
1. Loose coupling (agricultural pin and eye with probably 15mm slop).
2. No trailer suspension (balloon tyres not rated for the speed).
3. Single Axle.
It hit a bump downhill while accelerating from a 50km/h zone to a 100km/h zone while I happened to be driving the other way. As luck would have it I knew the driver too and helped him roll his trailer back onto the wheels. He didn't make it to 100km/h, probably only 70. If he'd stayed under 50 he'd likely be okay. At 40km/h guaranteed safe.

But the trailer was much lighter than the towing vehicle (around 400kg max) and the nose weight would be around 10%. Of course when everything else is wrong, adhering to one rule of thumb ain't much help.

It could also be that you just haven't yet encountered a sufficiently large sideways disturbance, at a high enough speed to trigger instability.

Vehicle safety is built around engineering, not anecdotes. As I mentioned earlier, personally I trust the engineering, but everyone inevitably needs to make their own choice, conservative or otherwise. Just a shame that we sometimes have to live with the consequences of others choices.


Scott

Have a read of this

http://outbacktravelaustralia.com.au...abilitySTA.pdf

In real world tests (bath university) apparently 6-8% works best I suspect not everybody will agree

Originally Posted by Tryanything

It could also be that you just haven't yet encountered a sufficiently large sideways disturbance, at a high enough speed to trigger instability.

Well it handled safely and smoothly all the hills with uphill and downhill corners at the speeds which I wanted to drive them. It's not the only time I've towed such a load. Certainly such loads are routinely seen on the roads here.
All of this negative evidence suggests the weapons of mass destruction may not exist.

Originally Posted by Tryanything

Vehicle safety is built around engineering, not anecdotes. As I mentioned earlier, personally I trust the engineering, but everyone inevitably needs to make their own choice, conservative or otherwise. Just a shame that we sometimes have to live with the consequences of others choices.

Scott

Indeed, I am an engineer and I make a living working within the laws of physics. I am just not seeing the problems this guy is suggesting in the small amount of his work you have presented.
At the extreme cases, these problems certainly do exist. How big are the safety factors applied in his graphics?

My experience suggests the biggest single factor in how a vehicle tows is the suspension setup. The setup of landrover suspension (particularly their early coil spring and beam axle designs) has several advantages and I beleive this is why they have historically held a far higher tow rating than comparable vehicles with leaf springs and other coil-spring configurations.
This is also why IMO (and others opinions) why landrover engineers know more about landrover tow ratings than engineers in other fields trying to apply a best fit using data obtained from completely different vehicles.

Bristol study: Very familiar with that work. In fact that was the first bit of research I came across.

The work was sponsored by Bailey caravans in the UK and they have used the findings to refine their caravan design. The UK market generally have lighter weight caravans with lower yaw inertia. They need to because the typical tow vehicle is not a LC or landrover but a family sedan. The limiting factor for stability in this case is actually the GVM and axle load for the tow vehicle so they necessarily favour a lower towball load, and offset this with superior van stability characteristics mentioned above.

Hey guys - the reality is that the RRS/D3/D4 is cleared to tow 3500Kg and a max ball weight of 350kg. We know the rule of thumb is ball weight about 10% but between about 5-15% is "ok". We are talking about a tow point behind the rear wheel - not a B double or a 5th wheeler.

I am not sure the minutia that is being put up is all that helpful to us ordinary people.

Garry

Originally Posted by Dougal

Well it handled safely and smoothly all the hills with uphill and downhill corners at the speeds which I wanted to drive them. It's not the only time I've towed such a load. Certainly such loads are routinely seen on the roads here.
All of this negative evidence suggests the weapons of mass destruction may not exist.



Indeed, I am an engineer and I make a living working within the laws of physics. I am just not seeing the problems this guy is suggesting in the small amount of his work you have presented.
At the extreme cases, these problems certainly do exist. How big are the safety factors applied in his graphics?

My experience suggests the biggest single factor in how a vehicle tows is the suspension setup. The setup of landrover suspension (particularly their early coil spring and beam axle designs) has several advantages and I beleive this is why they have historically held a far higher tow rating than comparable vehicles with leaf springs and other coil-spring configurations.
This is also why IMO (and others opinions) why landrover engineers know more about landrover tow ratings than engineers in other fields trying to apply a best fit using data obtained from completely different vehicles.

Hey dont make me out to be a Landrover basher! If I didn't think a Landrover was the best towing vehicle out there after my research than I wouldnt have bought one a week ago for the purpose of taking my family on a caravaning holiday!

Re suspension: yes it is a factor, and bad suspension ( low cornering stiffness) can make a big difference.

"Small amount of work" as basis for conclusions?: well all I can say is I have read about 5 papers which all conclude that trailer weight to tow vehicle ratio, location of CoG, and speed are all critical factors in stability.... And I have been discussing the subject at length with the author of the papers listed below (Dick Klein) over the past month or so. Not my work - just sharing the conclusions of others.

DOT Reports
*
1.​Handling Test Procedures for Passenger Cars Pulling Trailers. Vol I: Summary Report, Vol II: Technical Report, Vol III: Appendices. NHTSA DOT HS-801-935, 936 and 937. June 1976. NTIS: PB-256 071, 072, 073.
*
2.​Effects of Weight Distributing Hitch Torque on Car-Trailer Directional Control and Braking, NHTSA DOT HS-803 246, 1977.
*
3.​Development of Car/Trailer Handling and Braking Standards. *Vol. I: *Executive Summary. *Vol. II: *Technical Report for Phase I - Rear Wheel Drive Tow Cars. *Vol. III: *Appendices for Phase I. *Vol. IV: *Technical Report for Phase II - Front Wheel Drive Tow Cars, NHTSA DOT HS-805 326, 327, 328 and 329, Nov. 1979.
*
4.​Recommendations for DOT HS-802 586 Additions to DOT/NHTSA Travel and Camper Trailer Safety Booklet, DOT HS-802 586, Aug. 1980.
*
SAE Papers
*
A.​Effects of Trailer Hook-up Practices on Passenger Car Handling and Braking, SAE Paper No. 780012, Feb. 1978.
*
B.​Determination of Trailer Stability Through Simple Analytical Methods and Test Procedures, Systems Technology, Inc. P-233, SAE Paper No. 790186, Feb. 1979.
*
C.​Development of Maximum Allowable Hitch Load Boundaries for Trailer Towing, SAE Paper No. 800157, Feb. 1980.
*
D.​Description and Performance of Trailer Brake Systems with Recommendations for an Effectiveness Test Procedure, SAE Paper No. 820135, June 1982.
*
E.​Crosswind Response and Stability of Car plus Utility Trailer Combinations, SAE Paper No. 820137, 1982.
*
F. * * * * Lateral/Directional Stability of Tow Dolly Type Combination Vehicles, SAE
* * * * * * Paper No. 960184, Feb. 1996.
*
G. * * * *Sway stability of 5th Wheel RV Trailers, SAE Paper No. 2012-01-0237, Feb.

Originally Posted by garrycol

Hey guys - the reality is that the RRS/D3/D4 is cleared to tow 3500Kg and a max ball weight of 350kg. We know the rule of thumb is ball weight about 10% but between about 5-15% is "ok". We are talking about a tow point behind the rear wheel - not a B double or a 5th wheeler.

I am not sure the minutia that is being put up is all that helpful to us ordinary people.

Garry

Very fair point - my apologies to all.

If anyone does want any further info/discussion, pm me as I'm happy to share what I have learned.