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Old 06-04-2020, 02:12 PM   #1
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Can-Am Article Torsion Bar Set-Up

In another thread jcl posed the following question:

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Originally Posted by jcl View Post
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I had understood from your previous posts that you had reviewed articles by CanAm on hitch setup. Here, you continue to disagree with the concepts they promote for setting up a tow vehicle.

That includes using insufficient WD settings, failing to consider the angle of the hitch head, and placing full faith in SAE tow standards that fail to address a range of real world issues.

I would be interested in your thoughts on the attached article, as it includes test track results on how to reduce oversteer on a 1/2 ton pickup, by not following the standards you promote above.

https://www.canamrv.ca/blog/post/hit...sion-bars-441/
There are several concepts discussed in this article so I'll take them one at a time in the order encountered in the article.

Generally the article makes the primary point that the SAE test designs have the consequence of favoring insufficient weight distribution tension and they do so consistently for nearly all situations encountered.

I agree with the author and have consistently argued on this forum for more tension than a technician might apply while conducting the SAE combined handling tests because the tests generally discourage high tension. This is especially true for trucks but applies less less so to performance touring vehicles.

I agree that many vehicles have weak hitch mounts, braces and receivers that result in excessive slop and flex and prevent WD tension from imparting load to the proper spot. I suppose we should criticize the SAE for failing to have a ball mount to frame rigidity test.

I also agree with the author's point about the importance of hitch ball mount angle because the angle is necessary to prevent partial and unequal unloading of tension and thus wheel load in cornering particularly for vehicles like trucks which experience significant body roll in hard cornering. When the tension bars are biased downward these issues are mostly resolved. The SAE is silent about WD bar geometry so I take issue with criticizing the SAE about this, nevertheless, the point is valid.

Third the author makes the point that the SAE guidance on setting up weight distribution for the specific purpose of their handling tests (SAE does not make or extend these recommendations to vehicle owners) when there is no clear guidance from the manufacturer tends to result in less than ideal tension for most vehicles. I agree with this but, again take issue with criticizing the SAE since they are not making consumer recommendations. A slap on the hand with a wet noodle is more appropriate in my opinion.

All these concerns fall in the same category that tension for one reason or another is often insufficient to obtain optimal stability for most vehicles and certainly for trucks which is the topic of this particular article.

I'll pause for comments and then take up the issue of understeer gradient, the resulting violent over correction of many less experienced and skilled drivers often leading to oversteer.
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Old 06-04-2020, 03:06 PM   #2
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Thanks Brian

I don’t think the author was too hard on SAE, pointing out that they tried, but it really wasn’t their job. The error to me is in assigning significance to the SAE testing that isn’t justified, when considering the test standard limitations.

The result of the SAE test standard is that it can lead vehicle manufacturers to recommend WD setups that are suboptimal, but are what they tested their vehicle at, so they have no alternative. An example from the article is thinking of 50% FALR as being desirable.

The author points out that the people who should be responsible are not the manufacturers, who don’t know what will be towed, or SAE who came up with a test standard also not knowing what would be towed, but the RV dealer, who is the only one who sees the actual combination. That would of course require RV dealers to step up.

We are in a world where huge stock is being placed on manufacturer’s tow ratings. That is unfortunate. It can lead people to believe they are safe just because they come in under a number on a decal. And it leads directly to people believing that some vehicles are safer and some less safe, based just on things like tow vehicle weight.

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Old 06-05-2020, 03:31 AM   #3
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The SAE doesn’t set the amount of FALR for each vehicle, the vehicle manufacturer does. The reason for this is if they use high tension they won’t pass the Understeer Gradient test. This test is a measure of change in the vehicle steering response loaded and with a trailer attached. The SAE Understeer Gradient test is performed with vehicle specific loading conditions, the rear axle is loaded to RAWR, the vehicle to GVWR, and the combination to GCWR simultaneously if possible. So Andy did not duplicate the purpose or perform a Understeer Gradient test in this article, not even close. Maybe you guys can convince AT to start using a scale? Oh wait that would let everyone see how much he overloads these vehicles. I would like to see Andy actually perform the actual UG test with the combination in both states with real instruments that would prove something, otherwise what he shows is completely worthless.
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Old 06-05-2020, 08:03 AM   #4
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adjustment of the torsion bars

We picked out a Weight distribution/antisway after buying a new Airstream last summer. Initially the dealer installed and adjusted the torsion bars which i believe was a Fastway e2. They had the settings way off, so my wife and I went over to a empty lot and redid the adjustment from start to end. The instructions that came with our unit closely match the referenced method in link https://www.canamrv.ca/blog/post/hit...sion-bars-441/ It made a huge difference in the TV ride comfort after getting it setup correctly.
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Old 06-05-2020, 08:48 AM   #5
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Looks like someone didnít read the article, or talk to the author about their use of weigh scales. That makes your reply (fill in the blank).
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Old 06-05-2020, 09:29 AM   #6
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Societies like the SAE are industry groups intended to help their members do a better and more consistent job of competent design for their employers (auto manufacturers). The Auto companies benefit because with consistency, they can more accurately convey information to the buying public with apples to apples comparisons of their product vs. competitor products without facing anti-trust issues. The guidance is not intended to instruct consumers on how to set-up or operate their product. The author unfortunately conflates this and so, on this point, I agree with Profxd.

Andy is correct though that RV dealers should instruct their customers about how to tow their product safely, but they don't generally and consistently do this, and it is here where jcl has made a good point. It's a difficult issue because the drive to sell product creates competing priorities, so it seems unrealistic the RV Dealer Associations could ever come up with accurate guidance. The only groups with consistent priorities are consumers but there is no formal organization so informal forums and niche associations become perhaps the best that can be done.

I disagree that too much stock is placed on manufacturer's tow ratings. Because of the process used to derive them and the motivations to make them available they make an excellent starting point. The tests themselves are designed to maximize apples to apples comparisons and are therefore as simple as possible to avoid variation and yet still be a good predictor of real situations. The author criticizes the test for this, while I congratulate them.

Consumers who don't have the skills or interest in detailed vehicle research, but with no biases, who want to be sure the tow vehicle they have or select will safely and competently tow the trailer of their choice and haul the stuff they carry along will not go wrong following US towing guidance. The guidance is generally very accurate also, because stock, as configured and marketed from the factory, the limits represent the point where the vehicle is no longer able to competently perform the assigned tasks. If one purchases a vehicle marketed for crisp handling along with comfort should not be surprised or disappointed to learn their vehicle has relatively low towing and hauling limits nor should they complain that the hitch is weak or that it may be expensive, difficult or impractical to make the vehicle safely perform tasks the manufacturer didn't intend for it to perform. Someone who picks up a vehicle marketed for max tow should not be surprised that it is a bit clumsy, harsh and jarring when empty.

Those who prefer to test the limits may be able to safely do so in some cases because the tests are necessarily contrived and don't represent real situations, and as mentioned the manufacturers include other considerations including consumer preferences, brand reputation, liability, etc. in setting the final numbers.

This is were the rub comes in, because people who have competing motivations use the easy criticism of the standards and procedures, and the varying manufacturer's motivations along with their own confirmation bias to support conclusions that favor their prejudice. They tend to trust opinion that validates their belief and reject evidence that goes against it.

Returning to the article, Profxd correctly notes that the author did not duplicate the SAE tests, instead he attempted to create different tests that mimic real situations better. In doing so, it's no coincidence the author chose a 1/2 ton truck marketed for image, relative passenger comfort and light towing to support the points in the article. He was able to demonstrate truths that some OEM hitches are weak and poorly configured, and he was able to dramatically improve sway and cornering by adding much more tension than was required to pass the SAE tests and he was able to put a much heavier trailer behind it than the manufacturer (again targeting ride comfort, thus weak hitch and under damped suspension) recommended for this particular model and yet since the basic capability of the truck was high, he made it work. As I said before, I agree with the author that these issues are valid. Profxd indicates the author's demonstration was completely worthless, and I disagree. He made some very good points, but careful because they are valid only in context. They apply to limited situations and should not be extended to vehicles that are set up from the factory with very different characteristics.
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Old 06-05-2020, 09:54 AM   #7
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X2

Which hitch would you choose?🤔

OEM, 'round bar' or Reese, designed to provide the proper purchase to distribute the load for safe towing.

A properly designed receiver will help a lot in distributing the needed weight with lighter more compliant WD bars.👍

Bob...10 digit engineer.🤓
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Old 06-05-2020, 11:23 AM   #8
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All AndyT has to do is execute the SAE constant radius test with his setup and then the vehicle manufacturers setup and show the the data of the outcome. That would actually prove something now wouldn’t it? So why won’t he do that? Andy is a smart man and a good salesman, it’s all about the money to him not so much the facts. He’s good enough to convince many here that his way is better through deception like that article. FYI has AndyT ever posted a weigh ticket of any kind ever? Search around and see if you can find one.
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Old 06-05-2020, 12:41 PM   #9
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I'm certainly not a fan of all of Andy's tactics but at the same time I will defend facts for what they are, though I won't extend them beyond their useful context. In the case of the 1/2 ton described in the article, all available evidence about the truck set-up would lead me to conclude it would pass the SAE radius test when set up either way. I mentioned I believe it was not a coincidence a vehicle like this was chosen for this article. None of this diminishes the points your making though Profxd.

With specific regard to under steer which is what the SAE test intends to promote, the test criteria does give many the false impression that it is always better not to return very much of the shifted front axle load when many (not all or even most) vehicles, especially trucks, will tow much better with more WD tension applied.
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Old 06-06-2020, 04:25 AM   #10
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Ok here’s a simple test anyone can try. All you have to do to prove that less WD tension handles better is to travel some steep, tight, winding backroads. Better yet try the same route in the rain. It will be obvious that the combination will handle better with the bars off then with tension. Go a head and give it a try. I learned this by trial and error more then 25 years ago long before the SAE test standard was introduced and have used minimal tension ever since.
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Old 06-06-2020, 09:22 AM   #11
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Ok hereís a simple test anyone can try. All you have to do to prove that less WD tension handles better is to travel some steep, tight, winding backroads. Better yet try the same route in the rain. It will be obvious that the combination will handle better with the bars off then with tension. Go a head and give it a try.
That is exactly what the linked article already suggested, albeit in the dry. They did such a test and reported the results. And the results were the opposite of your conclusion. They also have an offer for anyone that is unsure to visit them and try it for themselves. There is a reason that people not satisfied with their setups seek them out to find out what is possible when a combination is set up correctly.
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Old 06-06-2020, 10:42 AM   #12
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Profxd, it would be useful to know what your tow vehicle and trailer was when you did these tests. Also since you used steep down grades, trailer brake gain can have a strong influence on over steer if the trailer brakes are not pulling slight tension on the hitch. The effect on rear axle tire slip will generally be stronger than WD tension.
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Old 06-06-2020, 07:44 PM   #13
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Some receivers, especially OEMs, twist while the load is being distributed during hook up. Obviously, that set up is defeating the designed purpose of the equalizing hitch. A higher class receiver made with square tubing would reduce that tendency.
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Old 06-06-2020, 08:18 PM   #14
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Profxd, it would be useful to know what your tow vehicle and trailer was when you did these tests. Also since you used steep down grades, trailer brake gain can have a strong influence on over steer if the trailer brakes are not pulling slight tension on the hitch. The effect on rear axle tire slip will generally be stronger than WD tension.
Three different TTís 22ft Nash, 26ft Mallard, and a 28ft Jayco. 4 different TVís 2001 1500 ECLB Chevy, 2006 2500 Chevy CCLB, 2016 Nissan Titan XD CC, and a 2019 RAM 2500 CCSB. Three different WDHís used, a standard Reese round bar, Reese Dual cam system, and a Equalizer. Each and every combination handled better with no tension on the WDH and many attempts were made with various different scaled setups. On several occasions with WDH tension I successfully pushed the TV rear axles sideways, completely losing grip on the rear tires ( not on purpose) at a low speed. Luckily no one was coming the other direction though the road lane isnít wide enough to accommodate the TT width in the first place. Yes I always adjust the trailer brakes to apply first. The same route has been traveled 100+ times to family property in the WV mountains over the last 25+ years. Before hitting the backroads the WD bars get removed completely now at a small local gas station. This is a simple test the average consumer can perform without instruments. Removing weight from the rear axle with a WDH reduces rear tire grip, these conditions will demonstrate it perfectly. All these setups traveled well in a straight line on the highway but until you get in a situation where lateral acceleration and angle increases the problem is not so obvious. Give it try for yourself, itís an excellent physics lesson.
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Old 06-06-2020, 09:33 PM   #15
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Very strange, completely contradictory to my own tests and the feedback models I use. I have done so several times on dry and wet pavement and consistently I get under steer with my ram 2500 and 25' airstream with 15% tongue weight. Even with over 100% front axle load return. Andy notes that the initial response is under steer but over correction by the driver leads to over steer which is quite plausible. I just let the front slide in my tests. Od and unexpected results indeed. there must be something different about your situation. You are much more likely to experience over steer at speeds in excess of guidance, was your speed high, where your back tires under inflated? I'm baffled, because with stiff rear tires, loose or no rear sway bars fixed rear camber and caster, my models indicate and my test confirm the couple hundred pounds load difference is not enough to shift under steer gradient that far. Excessive speed will do it though.....
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Old 06-06-2020, 10:25 PM   #16
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I also find that awfully hard to comprehend, maybe on gravel, wet blacktop or ice I might be able to break the Burbs rear axle free, but at 4680lbs, under normal conditions would be difficult at best.

Disclaimer...I will concede, that it would take much more effort to push the no WD, 5520lb axle sideways, but that has little to do with the way we travel, (and my headlights would probing the stars anywho).

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Old 06-07-2020, 05:36 AM   #17
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I also find that awfully hard to comprehend, maybe on gravel, wet blacktop or ice I might be able to break the Burbs rear axle free, but at 4680lbs, under normal conditions would be difficult at best.

Disclaimer...I will concede, that it would take much more effort to push the no WD, 5520lb axle sideways, but that has little to do with the way we travel, (and my headlights would probing the stars anywho).

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All I can say is try it and see what happens. The best solution that improved handling was no WDH tension. This outcome consistently agrees with the physics of a WDH reducing cornering stiffness and reducing tire grip.
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Old 06-07-2020, 05:54 AM   #18
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WV mountains over the last 25+ years. Before hitting the backroads.
Profxd,

WV backroad. Are they paved or unpaved?

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Old 06-07-2020, 06:28 AM   #19
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the final point I raise about the article is the current discussion of shat happens to under steer gradient as one increases WD tension. I previously noted the choice of a light weight 1/2 ton with relatively soft suspension was intentional to support the article conclusions.The lightweight stock hitch will flex substantially in dynamic situations and preferentially unload wheels at awkward points in time adding to instability that would provide incentive to reduce WD to avoid this unpredictable instability particularly since it has the effect of increasing under steer which the SAE tests favor. Andy described this a little differently but the point is valid. For his tests he corrected this problem to make the test rig more predictable and perform better.

He chose a slalom test to demonstrate the benefit of optimal tension. He was able get 50 mph from the set-up with no over steer which is still well below US highway speeds of 65 mph, so we still don't know how the truck will respond to 30% more trailer inertia at highway speeds, but no sane driver would try such tight corners at 65 anyway. With too little or poorly set up WD of course the rig has too much under steer along with the with the variable dynamic shifts described earler and must slow way down or it will slide out as Andy described.

So, jcl's conclusions that proper WD set-up makes a difference is accurate, and this article provides strong evidence to support his points. Weak receivers and mounts, incorrect geometry and loose sloppy fitting components defeat the purpose of WD and sway control hitches. They will feel as if they are doing a good job when you are cruising and not taxing their capability but they will add variability right at the worst possible time. The SAE handling test has the unfortunate effect of incentivizing manufacturers to recommend much lower tension than is optimal (or even no WD) especially when the receiver is weak.

The unfortunate aspect of this article is that it is written as if all of these concepts apply to all vehicle classes across the board when they don't. I am not sure, but I think jcl and others who seem to support the idea that one can take a very well handling light weight vehicle, shore up the receiver and mounts, set it up properly and then safely tow very large trailers, 10-40% heavier than the tow vehicle at US highway speeds. Andy did not test this case. Even for the 1/2 ton, he stayed below 51 mph. Profxd and I agree that on this point, the article could be described as misleading.
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Old 06-07-2020, 06:52 AM   #20
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All I can say is try it and see what happens. The best solution that improved handling was no WDH tension. This outcome consistently agrees with the physics of a WDH reducing cornering stiffness and reducing tire grip.
Profxd, we agree on many points including all the basic principles of steering, suspension and tire response. We even agree on the basic physics of WD. Clearly adding tension slightly reduces static cornering stiffness on rear axle tires while increasing stiffness to the front. When a tow set-up's base behavior is under steer and soft steering response, addition of WD tension will greatly improve handling as the article demonstrates. But only if everything is set up correctly and there are not dynamic situations baked into the system due to design or set-up weaknesses. Things like flexible receivers, loose shank fit, low rear tire pressure or incorrect load range, stiff rear sway bars, rear suspension that bottoms out in hard cornering, etc.

Suspension and steering are classical feedback control systems and I can easily model them to accurately predict performance. US marketed light trucks especially have under steer designed into them so they can competently tow north of 15,000 lbs without over steer. When they are instead towing 7,500 lbs, the system remains over damped and biased to under steer unless the driver unwisely chooses to drive too fast. WD does significantly improve handling performance in this case.

On the other hand, many US trucks are marketed for appearance, image and relative comfort. They are not heavy haulers though some think since it's a truck and fundamentally should be like the max tow cousins. Trouble is the hitches are weak (for a reason) the suspension is soft, the tire load ratings are low, the suspension is under damped, etc. Andy made great hay out of these realities because when one adds static tension, it does its job until the weak link in the system fails and an impulse response sends the vehicle unpredictably out of control.
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