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Old 06-05-2010, 11:49 AM   #43
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Absent tricks such as different tires front and rear, any vehicle's ultimate behavior is predictable from weight balance: if the front is heavier, it will understeer, if the rear, oversteer. In addition, understeer is always expected initially to a sudden steering input, this effect is more pronounced with high polar moments of inertia.

With trailers this is much more complex.

For an interesting read on trailer dynamics, see:
http://delphi.com/pdf/techpapers/2008-01-1228.pdf

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Old 06-05-2010, 05:41 PM   #44
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Quote:
Originally Posted by barts View Post
high polar moments of inertia.
Does that have anything to do with being closer to the North Pole? All I know about "moments" are that they are very short. I can spell "dyne" but I don't know what it is except it has nothing to do with eating. You guys are way over my head.

My truck and trailer stick to the road as if they are on a track. I guess that's a good thing. Well, on washboard, the truck sometimes likes to dance showing it has rhythm.

I did sort of understand the oversteer/understeer explanations Marc posted. With drive wheels at the rear of the truck, and a trailer hitched up behind, what do you get? The WD hitch is supposedly transferring weight to the front of the truck along with the giant engine, there's less at the back of the truck, then this heavy trailer at the back. I know every truck and trailer and hitch are different, but maybe there are some general answers (in "Physics for Dummies" language).

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Old 06-06-2010, 09:24 AM   #45
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re: "With drive wheels at the rear of the truck, and a trailer hitched up behind, what do you get?" - the trailer will be pushing the rear out in a turn and that can cause oversteer where you get a lot more turn than you thought you'd get.

What struck me was the idea that tow vehicles could be designed to avoid oversteer in certain situations. I hadn't thought about that one but it certainly makes sense when I consider wheel alignment to avoid drift with road crowns.

I have also read about modern adaptive suspensions and the confusions some have had with them and setting up a hitch.

Then there's the SUV rollover thing that, I think, became a matter of regulation.

There's a lot more to modern suspensions than the simplistic 'where is the weight' game thing.

As for .4 g turns, that'd be like having an 80 pound sideways pull for a 200 pound driver. i.e. you'd be doing a job on the seat belts. (like a 40% grade or 21 degree slope sideways if I calc right (pse check)). I don't think such turns would be considered safe trailer towing.
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Old 06-07-2010, 02:15 PM   #46
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re: "Who has "dismissed effort"? Or, claimed "arbitrary"?" -- perceptions, mostly, as backed up by the above post and re-reading the thread. It needs clarification if it is not a reasonably accurate perception.


As before, I see no one dismissing that effort, but apparently there is difficulty in reading: A wide, low bar "may" have been established, but it "may" also preclude any of a number of vehicles from consideration as tow vehicles due, simply, to lack of testing at a higher rating. It would be more a matter of effort not expended (likely due to marketing/profit margin on particular vehicle lines). It "may" also, more importantly, fail to address what changes can improve the situations involved in towing due to new advances so as to meet a realistic standard (one which TV's CAN meet). And so on.

Are you surprised to learn that standards have built-in limitations?

And, as this is touted as being by agreement of auto manufacturers it is more likely a result of inter-industry lobbying by attorneys in light of impending "black boxes" on all vehicles. Increased numbers of cameras, in-road sensors and the like. The "available evidence" will increase should an accident occur. It's a pre-emptive defensive tactic. Admirably done. It's known as, "gaming the system".

Which means it would not be the "best" even as given, but the PR spin is to help you understand that you now have a "basis of comparison" among new tow vehicles when in fact it will be trotted out as "good faith" when Granny & Grampy go barrelling down the mountain . . the point is to always place the blame on the driver.

Is it difficult to understand that a foregone conclusion pre-empts other, equally valuable "efforts"? That the "answer" pre-supposes the questions? Answers can be forced by limiting questions. That, in turn, has nothing to do with the effort expended to publish a reviewed paper. But that standard deriving may not tell much of a story. Or even be useful beyond a low and narrowed point. That isn't the dismissal of effort to them that published.

It might be a start. And it might not.

Arbitrary is a word you chose. You've yet to explain, and left open uncivil interpretation. Make the attempt, for "clarification".




re: "A weight-distribution hitch is, in the experience of even the oldest of us, a strong recommendation or requirement" -- The trailer is only part of the equation, the tow vehicle also contributes. The appeal to authority (the "oldest of us") doesn't help either IMHO.

It would help if you understood of what an appeal to authority consists. The oldest farmer in the county may not be an authority as others consistently find a better crop yield . . but his memory may be quite good as to what has been tried and what hasn't. Published information by manufacturers, and law, is the only "authority" any of us can realistically cite.


re: " To say that some vehicles no longer need a WDH is a big step." -- not for many who don't use one. I know many who have found better towing performance by removing the WDH.

The anecdotal "evidence" you decry you then claim? At least you are consistent in this hypocrisy from one thread to another.

re: "why is it that a 1,200-lb TW off of a 25' lever" -- With 30' trailers and 20' tv's, I think this is a bit overdone.

Your words, above: "As for GM, the key point is what they are doing to the vehicle in order to be able to handle thousand pound bumper weights without its shifting the load on the axles sufficiently as to impact controllability".

Pick the example of TV and TT you want. I'm sticking with pickup trucks and travel trailers. This standard somehow applies for tongue weights HIGHER than these numbers as well as trailers with a LONGER effective lever. And, "overdone"? Gratuitious insult or only sly in posing yourself as metes and bounds in re this discussion?

In neither case do you help by answering the question, re-framing it for clarity, or directing the reader to another source.



What I find encouraging is that the spec is based on performance, not design criteria. That means it ties more directly with what people are after in a tow vehicle. From reading these forums, too many get hung up on design criteria like weight ratings, hitch configurations, weight ratios, and so on while most folks towing are after making the trip safe and sound without breaking anything.

How do you know this? The criteria can be designed to exclude more than it includes. If so, doesn't make it reasonable, valid or anywhere near true that the spec is "based on performance", except for those few vehicles tested under a narrow range of conditions. I suppose, though, we can be cheered that you are encouraged.


The issue is whether or not there needs to be a measurable reason or whether we should do things based on arbitrary assertions. Many of the nonproductive discussions here tend towards supporting the latter. I think we need much more of the former.


More bryanL misdirection, eh? There is no "issue" on any thread on this site or any other RV site of which I am aware concerning towing that does not concern itself with safety. In all ways questions of "measure" abound. A non-existent issue compounded by character attack, concluded by lordly assertion. Do you also write scripts for talk radio? At least the insult is clear.




As for .4 g turns, that'd be like having an 80 pound sideways pull for a 200 pound driver. i.e. you'd be doing a job on the seat belts. (like a 40% grade or 21 degree slope sideways if I calc right (pse check)). I don't think such turns would be considered safe trailer towing.

Now to considering what a .3g or .4g turn is. I don't think I hit that point in my RV very often.



Sorta misses the reason for a standard, don't you think? .4G is no difficult attainment on the best of roads under excellent weather conditions in an adverse situation. .7G is the number for a modern pickup on the skidpad. As I noted above, a reading problem: connect the dots from solo to towing and try to be helpful if you can answer why the gap between the two numbers.


A lot of vague generalizations often suggested to help guide decisions (but not make them for you) seem to get turned into inviolable rules and, as a result, a lot of folks make bad decisions for their own needs and circumstances.

You can cite these posts? Or, define "vagueness", or "inviolable" or show that "a lot of folks make bad decisions"? So far as I can tell the interest of these threads and posts is in trying to find out what works and why. This one is no different. What is it (J2807), and why does it work? Or, not. You wish to give the impression of being well-read in this subject, and cast aspersions by implication without otherwise enlightening us. Why do you bother to post?


What struck me was the idea that tow vehicles could be designed to avoid oversteer in certain situations. I hadn't thought about that one but it certainly makes sense when I consider wheel alignment to avoid drift with road crowns.

Yes, a "standard" with a low bar to cross. Problems that have decades behind them. Not encouraging. Glad you're catching on. J2807 may not have much meaning once out of the parking lot. Reading suggestion: "piss poor TT/TV combination" (the worst performing TV with a 6k tow rating coupled to the worst-performing 6k GVWR trailer) and "really nasty" road.


There's a lot more to modern suspensions than the simplistic 'where is the weight' game thing.

Again, no kidding? But where is the information we would use to establish best towing practice, to supplement that which has thus far been dependent on "where the weight goes"? Again, you can cite other, published information to which to direct our study?


Vehicle brakes are much stronger than any possible tire friction on the road - so much so that modern systems now have modulators to keep that state (skidding) from happening.

Skidding the trailer tires, though, is still how you can test your trailer brakes and breakaway switch. The real issue with braking is heat dissipation for long term braking such as using brakes rather than gears on a long downgrade.


Aha, something possibly useful emerges! But, sadly, has nothing to do with the thread. Or does the standard make clear any differences between brake system components or controls? Or, on that of trailers? We may suspect that Chevrolet is using TV brake/stability controls to meet J2807, but thus far no one has posted relevant information. That would be a start.



The idea of a specification is that now we have a set of criteria to argue (discuss?) about. Instead of doing that, though, we see allusions to conspiracy, appeals to authority, arbitrary rules that don't consider circumstances, and straw men (i.e. manufactured scenarios).


Enough with the puerility. This is a "voluntary" standard. Which doesn't have much meaning in and of itself. Can it meet all objective criteria when the "standard" is one made by those expecting a profit? Your hallowed "cost-benefit" analysis would tell us that a voluntary standard is one that limits liability to the manufacturers while at the same time appearing as though it meets interested third party parameters. In fact, it is made to exclude such input and to be presented to the public as meeting the needs of safety precisely that such other parties never have a chance for input. A well-documented corporate tactic as it has been so successful. Keeps that pesky DOT at bay when lapdog politicians can claim the private sector is working . . and never vote funds to investigate. Or, as the Great Moron used to intone: "Trust, but verify" (Guess you've not heard of the Deepwater Horizon problem, BP, and the assertions made by same to the MMS). Obfuscate, delay, deny.

Presented under the delusion that all parties have access to the same information, at the same time, and have the same tools to analyse same, they also have the same power to effect change and pursue justice. A world which doesn't exist except in Ayn Randian/Milton Friedman hothouses where inconvenient categories are denied. So 'tis better that some need never abide by rules established for a civil society?

This type of standard (J2807) may (and only, "may") meet sufficient criteria to earn the place it is is intended to occupy. Let me control the assumptions, and I can control the outcome. (The problem in thinking which eludes television news/talk radio devotees).

A reasonable person is naturally concerned by potential weaknesses in a standard, no matter the promulgating body. Which begs the question of why you participate in such discussions as, apparently, the auto and RV manufacturers have a spotless record in their concern for end-user safety and it behooves us to not question their integrity. 'Tis not for mortal men to question the ways of the gods . . and Warren Buffet's portrait faces your dining table, right?

For, indeed, it does matter as to what is included and why. And what was excluded and why.

From thread to thread BryanL you are consistent in misdirection and ad hominem attacks without ever adding to (answering) the question[s] posed by the thread. One would be led to think of what gain this poses for you, what consideration is being extended on your behalf.

"Conspiracy"? Yes, that would be the defining word for "cost-benefit analysis" by Ford (to cite but one example) in not sufficiently engineering rear-mounted gas tanks, and the subsequent coverup of the decision to pay small amounts out to the survivors of fiery collisions. In sealed decisions so as not to alert the public. Cheaper than fixing the vehicle. ENRON and plenty of other examples exist of corporate conspiracy. It is no leap of imagination to see a wink and a nod among the Big Three in finding a way to limit liability under the rubric of a "voluntary standard". This is news? History is full of such examples. The Continental Congress was explicitly a conspiracy to effect an end by a small group of men.



From reading these forums, too many get hung up on design criteria like weight ratings, hitch configurations, weight ratios, and so on while most folks towing are after making the trip safe and sound without breaking anything.

I have yet to find anyone, on any RV forum not interested in towing safety. Or is this sort of grand pronouncement -- having said precisely nothing -- but the beneficence cast by bored, lordly demeanor: having seen it all, tried it all, and tested it all?

So any appeal to authority should be directed towards you, eh? The arbiter of what is meet and proper in re towing dynamics.


I do wonder, though, why so many folks want to mandate their own decisions and judgments about what is best on others.

Yes, your behavior is tiring.

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Old 06-07-2010, 05:28 PM   #47
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Kudos to Rednax!

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Old 06-07-2010, 10:57 PM   #48
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Quote:
Originally Posted by Jammer View Post
It's hard to sort out towing claims from the big three into the relevant categories:

Category 1. Uprating a previously derated specification for marketing reasons without running any tests, performing any analysis, or changing the product.
Category 2. Changing the safety margin or testing methodology so that a higher specification can be claimed.
Category 3. Running enough new tests and performing more thorough analysis to figure out that the product will actually perform better than the previous rated specification.
Category 4. Actually changing the product to improve its performance.

I think this is a Category 2, but it's hard to tell for sure.
This is category 4, not 2. The 2011 GM Heavy Duty Pickups have significantly redesigned frames and suspensions, so I am sure the performance has been improved. This is not merely a case of "specification engineering" on an otherwise unmodified product, as would be suggested by your categories 1, 2, & 3.

And to address other posts in this thread, why is it that some people immediately assume that the creation of such a standard is merely to limit liability rather than to actually provide a basis for unbiased product comparison and as a impetus to product improvement? Being an automotive engineer, I know people that are involved with the Society of Automotive Engineers (SAE - but I am not a member) and they work for standardization and product improvement. Those people are not "corporate lawyer types" that are merely trying to limit liability. To think otherwise is a disservice to those hard working folks that spend their lives working to produce ever better, safe, reliable, and durable products.
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Old 06-08-2010, 12:35 PM   #49
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re: "Are you surprised to learn that standards have built-in limitations?" -- I see we still have reading and perception problems. I get the feeling its a pissin' contest (see the peanut gallery comments above!). I hate it when it gets into that territory.

As for arbitrary, look at the first post on page 4 about steering vs loading.

re: "but it "may" also preclude any of a number of vehicles from consideration as tow vehicles due, simply, to lack of testing at a higher rating." -- the issue of a standard is that manufacturers can test against it and claim compliance. If they don't test or don't meet the test criteria, they can't make the claim.

re: "It would help if you understood of what an appeal to authority consists." -- yes, let's get into the ad hominem and show our capabilities to divine personal attributes as we'd like them to be to support our views ... I don't think that helps. Much of post 46 is ad hominem character assassination even to the point of constructing misperceptions wildly at odds with common sense. The sad part is that such tactics are so typical.

re: "How do you know this?" -- because that is what I have seen of the specification so far. It involves criteria for factors such as acceptable acceleration, braking, steering, heat management, and other items by describing tests and how they must be managed to obtain certification.

re: ""Conspiracy"? Yes, that would be the defining word for "cost-benefit analysis" -- no, it is a description for such assertions as "being by agreement of auto manufacturers it is more likely a result of inter-industry lobbying by attorneys" and others easily found.

re: "Sorta misses the reason for a standard, don't you think?" -- no. It sets limits for the test regime and a reasonable and intellectually honest discussion would try to address whether or not such a limit was appropriate based on how people drive towed vehicles.

Quote:
And to address other posts in this thread, why is it that some people immediately assume that the creation of such a standard is merely to limit liability rather than to actually provide a basis for unbiased product comparison and as a impetus to product improvement?
As in the Rednax and crawford posts preceding, you can see that factors other than towing standards and issues are considered more important. They must attack and impugn people whose ideas they do not like, often in a disingenuous manner. There is a lot of that in these forums. It makes honest discussion difficult and drives away those who don't care for the personal contesting. (ever watch that movie Roadhouse? it's based on the same sort of behavior).
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Old 06-08-2010, 03:10 PM   #50
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Hi
This is my first post / question I am currently looking for a Airstream Safari 20 ft new or possibly 2006/2010 will my 2001 GMC Yukon Denali be ok to two with?
Thank you
Susan
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Old 06-08-2010, 03:15 PM   #51
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Tow vehicle

Is a 201 GMC Yukon Denali ok as a tow vehicle for a Safari 20ft I am very new at all this but hope to get better
My hope is to find a really great 2006/2009 used or possiblly buy new 2010
Thank you
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Old 06-08-2010, 04:27 PM   #52
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Some of you guys would get my vote if you didn't use such tortured syntax and laborious lexicology.
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