Sae towing standards for 2012

[wayner61]

All I would ask - or reasonably expect - is that there is some "standard" reference to what is "included" in the tow ratings...

I know from personal experience that it is often difficult to determine what the manufacturer included when establishing the "towing capacity". If they would just say that they started with a "base" truck and a 150 pound driver with no passengers and a 1/2 tank of fuel, we would all know the starting point. In my experience though, that information is typically buried in a document that is hard to find. Checking the web site or the dealer is often an effort in futility.

[Gene]

I agree the info is hard to find. It can be scattered through the owner's manual, a website and some brochures at the dealer. Toyota includes a full gas tank and coolant before it figures payload, other companies may not. That can make a difference of more 200 lbs.

Gene

[slowmover]

Revived:

Came across this article about Chev no longer needing WDH on some models. Part of a GM press release.

Towing capacity

That leads to the biggest news of all: The 2011 Chevy Silverado HD doesn’t require a weight-distributing hitch to up to its maximum 16,000-pound trailering limit on the Dually and 13,000 pounds on single-rear-wheel models.

The weight-carrying and weight-distribution limits are the same. The maximum towing capacity (13,000 to 16,000 pounds depending on model) is the result of using the protocols for the upcoming SAE J2807 testing standards, which will be put into play in 2013. This puts GM trucks two years or more ahead of the new towing certification program.

“You can tow up to 16,000 pounds [3500 model] in the conventional weight-carrying mode, which is towing on the ball and shank,” says Jim Mikulec, lead development engineer for GM HD trucks said during a recent press briefing.
“In short, the consumer no longer needs to use a weight-distribution hitch.”

In the world of towing, this is huge news.

Eliminate the hitch

In years past, to have your pickup properly-equipped as stated in the owner’s manual, all GM H-D pickups required the use of a weight-distributing hitch when trailering more than 7,500 pounds, while the majority of other manufacturer’s pickups required a W-D for trailered loads weighing more than 5,000 pounds.

Through the chassis, brakes and drivetrain changes GM engineers have found a way to eliminate the need for an aftermarket weight-distributing hitch. The new pickup’s door tag will probably show both the “weight-carrying” (trailer hitched straight to the ball/shank) and “weight-distributing” ratings being one and the same. (See SAE J2807 for details.)

Although GM marketing has overlooked this point, it’s probably the biggest news of all as GM becomes the first manufacturer to build a pickup and hitch package capable of towing this much weight without requiring the use of a weight-distributing hitch assembly.

This should great news to those who tow travel trailers and heavy equipment trailers on the factory hitch because this eliminates 1) having to deal with the set-up and expense of a W-D hitch, and 2) removes any confusion as to having the vehicle properly equipped when it comes to towing limits and related vehicle operator liability issues facing older pickups.

2011 CHEVY HD PICKUPS | Pro Pickup



SAE J2807 Tow Rating
Tow Ratings Finally Pass the Sniff Test - The Society of Automotive Engineers (SAE) - Automobile Magazine



Trailer Body Builder Magazine
LETTER TO EDITOR

The statement “too much tongue weight can force the truck down in the back, causing the front wheels to lift to the point where steering response and braking can be severely decreased” is not the real issue with heavy tongue weights. The real problem is that the tow vehicle's yaw stability, as measured by “understeer gradient”, is severely decreased. This increases the propensity of the tow vehicle to jackknife in turning maneuvers. Specifically, recent full scale testing conducted by the SAE Tow Vehicle Trailer Rating Committee (and now published in SAE J2807), determined that the use of weight distributing hitch torque should be minimized. In fact they recommend that the Front Axle Load Restoration (FALR) not exceed 100% (100% means that the front axle weight is brought back, via weight distribution, to a weight equal to its “no trailer” condition).

(Article referenced in letter)
Tips for understanding the dynamics of properly specifying a truck and trailer combination


(From a post on rv.net)

"Combination Handling Performance Requirement

This is the first time we've seen trailer handling as a requirement for creating a towing standard. The SAE test measures tow vehicle understeer and trailer sway response using specific calculations found in SAE J266. Information that goes into the calculations includes

- effective tongue length (ETL), which is the distance from the center of the trailer coupler ball to the center of the trailer wheels.

Another factor is the amount and positioning of the cargo on the trailer. In one test, weight is securely added to the trailer to bring the combination up to its intended gross combined weight rating (GCWR) and trailer tongue weight.

Then under acceleration they measure G forces at 0, 50, and 100 percent front axle load restoration (FALR).

FALR is the percent change in front axle load due to weight distributing hitch application divided by change in front axle load due to addition of trailer tongue weight. This test is pass or fail and is only used in testing bumper towed trailers."


Anyone come across other, more informative articles/links/posts about the changes made by GM to chassis, brakes & drivetrain?

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[bryanl]

interesting that decreasing steering response is not the real issue while decreasing steering response aka 'understeer gradient' is. It seems to me that that is playing games with words.

It is also interesting for someone having not seen something (handling) in a standard that hasn't existed before. I need someone to explain to me why not seeing something that hasn't existed is remarkable. I must be missing something.

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.

Now I have to go look (again) at the definitions of oversteer vs understeer as I get the names and the phenomena mixed up. Towing trailers tends to cause turning more than you steer, which I thought was oversteer. (answers at yahoo)

With the links and the questions it looks like I've got some researching to do and questions to find answers to! good stuff.

[Gene]

This reminds me again why I quickly learned in college that engineering was not for me. The fools at that university actually thought I was qualified for that major.

But, despite the fact I don't understand most of what I'm reading—I can't remember the difference between over- and understeer either—I don't get how GM can make the truck stay level when hitched up. The GM PR doesn't say anything to me except "look what we did" but doesn't explain how. Sounds like advertising fluff to me.

Gene

[Jammer]

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.

[Road Ruler]

SAE has taken a step forward by making it an equal playing field but they have really only scratched the surface when it comes to putting a combination together and having it run reliably and safely.

We still have the many other factors that influence.....

Aerodynamic factor
Amount of towing hours
Where will the towing take place ?
Handling characteristics of the TV and Trailer
Quality of hitch and connection hardware
Set up and adjustments
Age and mechanical condition of vehicle and trailer
Etc, etc, etc

[Jammer]

+1

The V-5 standard, when adopted, helped wring some of the BS out of the hitch industry. At that time, there weren't any OEM hitches to speak of.

I don't think that trailer hitches subject to stress loads from a WD hitch have an easier time handling the tongue load, because it's the inertial load when the rear wheels of the TV hit a bump that stresses the hitch the most. The V-5 standard relaxes the requirements, and it shouldn't. I haven't read the SAE standard but would guess that it imposes the same requirements in both scenarios, hence the change.

[slowmover]

Handling Requirements

Standard J2807 specifies that an understeering handling attitude must be maintained up to at least 0.4g cornering without a weight distributing hitch. With a weight distributing hitch . . an understeering attitude must be maintained up to only 0.3g cornering

As with above comments, disingenuity and narrow context. Even a piss-poor TV/TT combination pass "the test."

In other words, in a nasty situation on the road (high crown, bad repair, highway speed), the bar to "success" is low. That is to say, what is possible and what "meets standard" diverge pointedly, it appears in re beneficial handling/braking. Or . . . ?

Can of worms? . . . at what point does a rig benefit from a WDH?




2010 DODGE Ram 2500 shortbed, (empty)
Roadholding, 300-ft-dia skidpad: 0.70 g

2010 Dodge Ram 2500 Laramie Mega Cab 4x4 - Short Take Road Test - Auto Reviews - Car and Driver

The comparability of skidpads and roadways? Pertinence?




(March 13, 2009) RVIA’s “Current Issues in Designing Trailers” seminar was held on March 5 at the RV Hall of Fame in Elkhart, Ind.

RVIA Today Express

RVIA’s “Current Issues in Designing Trailers” seminar was held on March 5 at the RV Hall of Fame in Elkhart, Ind. Sponsored by AL-KO Kober Corporation, Dexter Axle, and Norco Industries, the seminar was attended by more than 80 engineers, designers, production line foreman and supervisors involved with trailer design and development.

RVIA Board Member Gregg Fore kicked off the five-hour training session by welcoming the attendees, who represented more than 36 member companies. Seminar leaders Richard Klein and Harley Holt focused on trailer design engineering, then on SAE standards and related activities. In addition David Kinder, Esq., and Steve Arndt, Ph.D., spoke to the group about warning labels and consumer information.


RVIA 45" Pay-per-view video (Richard Klein)
RVIA's Video Site - RVIA Video Clip Library





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[bryanl]

in looking at that steering issue, what I am finding of interest is the requirement that oversteer not be in evidence in nominal circumstances.

It is an inappropriate response to oversteer that is often behind loss of control incidents. This is being addressed in the standard.

I think bringing in "really nasty" is the reduce to absurd fallacy. When that is coupled with non referenced judgments like "piss-poor TV/TT combination" the example only supports the reason for the SAE standard: having some objective referent by which to evaluate capabilities. We can then argue about the relative merit of standard criteria rather than more subjective assessments of rigs.

re: "at what point does a rig benefit from a WDH?" -- the question like this would be better presented as something to a cost versus benefit point: "when is the benefit of a WDH worth the cost (both capital as well as ongoing, outlay and procedure)?"

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

[Airstreamer67]

Although the new process to determine standards for the industry will have some growing pains and get hit by a lot of slings and arrows, it is great that they are finally doing it.

I have long had the feeling that many Internet myths and lessons presumably learned from the days when sedans were the main towing vehicles for travel trailers are way off base when it comes to modern towing vehicles, particularly 250 and 350-class pickups.

Let the cards fall where they may. It's a great endeavor. Maybe the 80% ironclad rule won't be so seductive anymore. Maybe some of the self-made rules "police" will become less strident. Maybe there won't be the battles over things that heretofore have had no objective testing?

Maybe?

Nawwwwww.

[slowmover]

It is an inappropriate response to oversteer that is often behind loss of control incidents. This is being addressed in the standard.

Yes, "overcorrection" is one way of saying it. The "standard" appears to be a low bar to cross.

Reductio ad absurdum: No, there are -- and will be -- better and worse possibilities in re brand new TV's and TT's (alone, to leave out the huge range of other trailer types), and some WILL be piss poor in combination. Which begs the question of whether WDH might be of help. And why the standard appears to be so low as to tell the customer it isn't needed . . when it might be a very good idea.

All safety devices have a cost/benefit ratio. Nothing new. Still says nothing about efficacy of WDH.

A .3G turn is easily attained. Thus the "concern" about yaw. .5G might mean something (however scary to experience . . which is the point).

Maybe there won't be the battles over things that heretofore have had no objective testing?

It is a question of whether it actually is objective. "Definitions" that allow any and all to succeed cannot be said to be defining. Straw man arguments ensuing . . . .

I'm in favor of a better explanation of what is involved in meeting J2807 by GM. It may be a decent floor from which to work for the rest of us.

Thus far I have the impression that it is a way to forestall responsibility by manufacturers about what works -- and why -- in regards towing best practice. It appears minimal, and setting up WDH takes work . . so let's eliminate the need (via distortion of meaning). Keep the plaintiff lawyers away. Continue current practices without genuine change.

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[Airstreamer67]

Testing vehicle-specific factors to determine their towing abilities under a regimented formula is a giant leap forward.

No, as we've already seen, it won't be possible to get everyone to agree on what parameters should be incorporated in the formula.

However, the endeavor should help tremendously to determine safe towing limits of a vehicle...and to be able to better compare one vehicle to others...and to perhaps update good practices for modern vehicles used for towing.

I don't think the hitch manufacturers have the resources to get the job done. I think they have been necessarily winging it, basing their recommendations on a little engineering and a lot on outdated and overgeneralized anecdote. In defence of them, how could they possibly test every vehicle that has a tow rating on them and to give specific rigging advice for each?

I'm hoping the larger vehicle industry will be able to guide us better as to what their specific vehicles can do based on standarized criteria.

However, I don't expect them to set the criteria so high that a trailerist feels he can maneuver his rig like a sports car. I think too many accidents are already caused by high-speed drivers trying risky maneuvers on the highway with varying types of vehicles and trailers, combined with road adhesion factors that change with the weather.

I think we would all be better off if we all haul our trailers like we KNOW the things won't maneuver very well, certainly not as well as an unladened vehicle, and to set our speeds and driving techniques accordingly.

High levels of G-factor turning ability when towing doesn't seem very attractive to me given all the circumstances involved in towing heavy trailers, especially since developing and testing for a high level of maneuvering ability with the extreme variations of rig and road combinations would probably be impossible to realistically and consistently achieve anyway.

[Road Ruler]

Originally Posted by Airstreamer67

High levels of G-factor turning ability when towing doesn't seem very attractive to me

It seems a lot of folks have the same thoughts.

Consider the ones that tow large heavy 5th wheels with large heavy TV's that both have a high center of gravity and a high hitch mounting point. No doubt they have reduced control in an emergency maneuver.

On the positive side most of us tow an Airstream and it is no secret that these trailers when pushed have superior road handling qualities. This is a huge benefit when a situation unfolds (and they do happen) and one finds themselves at the mercy of those road handling abilities.

Not long ago we were heading out with Airstream in tow. It was getting dark and we were on a straight flat road on flat land. Out of nowhere we came upon a sharp right hand curve. I'm not sure whether I missed a sign of the sign was AWOL but we made it through the turn without an issue.

I was amazed at how well the TV and Airstream tracked doing this aggressive change in direction producing a multitude of "G's".

Sometimes crap happens out there on the roads and we need to be thankful the hardware is up to the task of handling it.

[Airstreamer67]

Road Ruler, I agree with that. I've towed my Airstream since 1986, and often feel lucky to be towing a low center-of-gravity, well-balanced and torsion-bar-suspended trailer. I think it's the trailer of choice for anyone who wants the best towing rig possible.

What I thought I was referring to are new testing standards for tow vehicles. My point is that there are so many types of vehicle-and-trailer combinations, that setting some arbitrarily high G-rating for safe towing for a particular vehicle would not be particularly helpful in determing what they can safely tow. If they did, Airstream likely would be the trailer of choice for testing, and perhaps a beefed-up Corvette would get the top tow vehicle G-factor rating :-)

[Jammer]

It would seem to me that a responsibly engineered combination would maintain steering stability until the point where the combination skids or rolls is approached, just as responsibly engineered brakes should provide stopping ability approaching the limits of the tires.

[bryanl]

Oh, but if steering and braking were simple things!

but they aren't.

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.

As for steering, what I find interesting is the concern for how it changes under various conditions, the change from understeer to oversteer, for instance. Out of control conditions often stem from the driver not reacting properly to rig handling. I don't have my thoughts well formed here, yet, so I can only suggest taking a closer look rather than just writing it off to some extreme. There is much for many to learn about some of the topics (especially sway) that get a lot of heat in discussions.

I think that caveat also applies to those trying to minimize the standards efforts. Rather than claim "arbitrarily" set criterion, why not see if you can find out how they were developed? The people involved have a lot at stake and are much closer to the issue than most here so it is probably not a good idea to dismiss their efforts without an extremely good basis.

From what I see here, I wonder if some folks understand what 'G' really measures in turns or its scale.

[slowmover]

My thoughts echo every same above. Yet, there is more to consider.

(Who has "dismissed effort"? Or, claimed "arbitrary"?)

Some "standards" are worked out in advance: a predetermined conclusion; in this case, I suspect, only to limit liability. While there would be nothing new in this for the automotive industry, to appearances it is disappointing. Which is why I asked if anyone had specific insight.

In other discussions I have seen references to papers by Korn and Bundorf (1965 & 1967, respectively). I see that (below) that there is a Tow Vehicle Trailer Rating Committee from which one might assume is not a purpose-specific recent assembly. Surely there is an institutional memory and more papers in the intervening years. Thus my hope of "enlightenment".



Performance Requirements for Determining Tow-Vehicle Gross Combination
Weight Rating and Trailer Weight Rating

Product Code: J2807 Date Published: 2008-04-23

Issuing Committee:
Tow Vehicle Trailer Rating Committee

Scope

This document establishes minimum performance criteria at
GCWR and calculation methodology to determine tow vehicle trailer rating for passenger cars, multipurpose passenger vehicles
and light trucks up to 19500 lb GVWR (Class 5).




A weight-distribution hitch is, in the experience of even the oldest of us, a strong recommendation or requirement in using travel trailers (to limit things) from a predetermined tongue weight.

To say that some vehicles no longer need a WDH is a big step.

A pickup truck is still a pickup truck. I see no announcement by GM that their trucks have some magical suspension/brakes or electronics (but suspect the latter is part of the "new" rating standard; and that using the "black box" this may be derivable after an accident; not my interest in asking).

Having searched I also find no announcement of revised towing guidelines for these 2011 trucks, or, a precis of what they may be.

In other words, why is it that a 1,200-lb TW off of a 25' lever no longer requires WDH even though dynamic forces may increase that weight x10. Or, x20?


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[bryanl]

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.

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.

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.

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.

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).

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.

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.

[Road Ruler]

Originally Posted by bryanl

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.

This is the way I see.