stabiliser-torsion-weight distribution bars

I WENT INTO THE ARCHIVE YESTERDAY PUT IN THE WORD springs & CAME UP WITH A LARGE REFERENCE WHICH ALSO TOOK IN WEIGHT DISTRIBUTION CHERERS & HAPPY READING

POLICY ON WEIGHT DISTRIBUTION HITCHES

On the issue of safety in towing, the weight distributing hitches are an advantage as they do help with stability on the highway, and should possibly be considered for mid size tow vehicles like Toyota, from about an 18’ van and up. Yes, they are an advantage from a safety perspective if you have to make a high speed traffic hazard move on the highway. However, they are only one part of the package, and should not necessarily be the primary focus, as there are sometimes deeper more serious issues to be dealt with. It is not the answer to problems such as a poor stock suspension or improperly loaded caravan that has too much ball-weight or even more dangerous- Too little tow-ball weight. Often the weight distribution hitch is touted as the cure all, but is just a panacea for the problem of a poorly equipped tow vehicle or improperly loaded caravan. Also it is very important that the vehicle and tow-bar manufacturers maximum weight specifications not be exceeded at any time.

For the tow vehicle, we would recommend a proper graduated heavy suspension spring system. They are graduated for a nice ride empty (a bit firm like a sports car), but they get down on a heavier part of the spring when loaded. From ARB it is called “Heavy Progressive”. The problem is really that the vehicles have too light of a suspension when new. That is OK for the city use, and necessary as ladies would not like the ride with a heavier suspension when not loaded with gear, so they would not sell in their unloaded empty new vehicle state, just off the ship. Those who travel much, immediately put on gear such as tow bars, bull bars, long range tanks, dual battery systems, snorkels, roof racks, air compressors, fridges in the back, tool kits, and more; and then the stock original suspension is woefully inadequate let alone safely carrying a van on the back as well. What we are really talking about is the high speed traffic hazard avoidance ability on the highway….. You want that firm upright control, not the wallow like a pig with a backpack on…. You can accomplish that best with the proper suspension upgrade, or help the bad situation of a mushy suspension with the Load Leveler system to try and make up the difference…. But we recommend the former as the first priority for the tow vehicle..…

On the caravan, the ADR recommendation is 5% to 10% on the tow ball. The vans have to be loaded properly, not out on the fore and aft polar ends, but as much over the suspension as possible. Too much weight out on the polar ends will cause fore and aft rocking that can damage the van and vehicle on a bad track. It can also cause the killer of caravans: sway. The van must also be loaded for the proper percentage on the tow-ball, too light and it is prone to sway; too heavy and it overloads the tow vehicle and lightens the steering by lifting the weight off the front end of the tow vehicle. In the case of maximum ball weights of heavily loaded vans, it can reduce the steering and braking capability, and in that case for some tow vehicles the weight distribution hitch should be viewed as a mandated necessity. But it is not to correct an improperly loaded van that is too heavy on the front end, and it is worth little on the van that is loaded so as to be too light on the hitch, which is even a more dangerous situation. If the van is too light on the front, the higher percentage of weight on the back of the van contributes to the sway potential of “the tail wagging the dog”. This sway action can build on itself with what is call in engineering language: “Harmonic Motion” -Where the movement builds on itself with disastrous effects, bouncing off the springing action of the suspension or moving in harmony with bumps on the road, to build increasing motion. This dangerous condition of “harmonic motion” can build to the point of getting totally out of control even to the point of turning a van over. It should also be noted that the WD Hitch alone is not an anti-sway device, but can improve handling. An anti-sway device is another bit of gear altogether that is an option on the WD Hitch from Hayman Reece for instance. After correcting the other problems, then assess if the weight distribution hitch is necessary. With larger vans and smaller tow vehicles it is advised, but the first two conditions in our view are to be corrected first. You should not have a false sense of security that the weight distribution hitch is going to cure all ills, while disregarding the tow vehicle suspension and proper loading of the van... Those priorities come first. And then, yes the Weight Distribution Hitch is a safety advantage for proper control of the vehicle in a high speed hazard avoidance situation. However, as I have said, the Weight Distribution Hitch is not by design an anti-sway device on it own. That is a separate piece of equipment. The WD Hitch does improve handling, steerage, and take some of the load off the tow vehicle, and so is an advantage for that high speed abrupt maneuver ; but does not cure all problems. The first two conditions of a proper suspension and loading of the van are the predominant issues.

Off road the weight distribution hitch is of reduced value. In fact they only work on the flat. The bars will bend if you try and go over a jump-up, or raised cattle grate; or down into a wash-out on a dirt track. There is an off-road version in preliminary development, but it has to be proven not to be too heavy or bulky, contributing to the weight problem. We await further testing on that in the future.

So in summary: Yes they are a safety advantage, but should be viewed as such and not a cure all for other problems addressed above.

From the Archives of the 'Tips" from the "Lone Ranger"....

Thank you Steve for your prompt and comrehnsive reply. Your input and advice is very much appreciated. Motherhen

I hope what Steve is saying is that it is essential that you address all the static issues that can create problems first.

Vehicle suspension load capacity and suitability (can take load, has adequate dampening, is not soft);
Correct loading of trailer (central, not fore and aft);
Tow ball weight (no less that 5% preferably around 10%, and depending on the tow vehicle probably not more than 12% of trailer).

And THEN fit a Weight Distribution Hitch to provide some level of control over the dynamic issues during driving.

Yes, a properly set up rig will benefit less from a WDH.
Yes, an improperly set up rig will not necessarily be made safe by a WDH.
But, Yes, a WDH will definitely make any rig safer.

And, just as you may have to adjust your tyre pressures according to the road conditions, you may also have to remove the bars to cross some obstacles. But that is just a normal part of driving according to the conditions.

If you cannot cross a (normal) kerb or gully drain because of the bars, then either you have the bars too tight, or you need to learn to cross at an angle, just like you would if you were in a low-slung sportscar.

Please do not take Steve's correct advice that it is things other than a WDH that cause the problems, to mean that a WDH is not needed.

However well balanced and correct your rig is, the WDH is the extra protection for the moments of the unexpected, that we all hope you never need.

Ken