Weight Distribution and Sway Control -Obsolete for a Self Propelled Trailers?

[turbopilot]

Nothing to do with sway or J2807, but everything to do with the Rivian's pneumatic suspension system.

For those reading this interchange, it is exactly debates like this that need AI as a tie breaker. I have studied this subject as well as I can without getting an SAE membership. I have tried to confirm my facts with several sources. It appears Google Gemini is calling it right about this 5,000 lb WDH requirement found with many pickup truck tow vehicles.

The bottom line is this. For the Rivian they must use a high profile, high center of gravity, slab sided 11,000 lb trailer with 1,100 lbs on the tongue to run the test. In this configuration once it fails either the lateral g force requirement or the sway requirement without WDH, they can then continue the test up to the required maximum weight of 11,000 lbs using a WDH. Apparently most manufacturers that fail the test between 5,000 and 11,000 lbs without a WDH don't report the failure point in the test, instead they decide to slap on the WDH Required limitation at 5,000 lbs which is the default and call it a day.

If anyone else has better information please chime in. I visited this subject in detail several years ago and had an actual copy of the SAE J2807 test protocol but I can't find it right now.

So the 5,000 lb WDH required is sort of a "safe harbor" for a very demanding test involving an 11,000 lb trailer for trucks down to the half ton category. The mischief in structuring this test like this is that many trucks are "forced" to use these archaic, leveraged WDH systems that may be able to operate safely without them.

AI says much better than I can so here is how this SAE J2807 certification is arrived at.

From Google AI:

The question to Gemini:

Does this mean that if the truck can only pass the test with WDH at 11,000lbs it must require a WDH at 5,000lbs.

Gemini Response:

Not exactly. It’s better to think of the 5,000-lb limit as a pre-certified safety floor rather than a consequence of the 11,000-lb test.

Here is the nuance of how those two numbers interact:

1. The "Default" Safety Limit (5,000 lbs)​

In the world of light-duty trucks (half-tons and SUVs), 5,000 lbs is the industry-standard threshold for "weight-carrying" (standard ball hitch) towing.

• The Assumption: Engineers generally assume that up to 5,000 lbs, a typical vehicle's chassis, wheelbase, and suspension can handle the leverage of a trailer safely without mechanical assistance.
• The Testing: Rivian (and others) will test the vehicle without a WDH at this 5,000-lb mark. If it passes all the SAE J2807 handling and sway metrics, they can stamp it with a "5,000-lb Weight Carrying" rating.

2. The "Equipped" Rating (11,000 lbs)​

Once you go above that 5,000-lb floor, the physics change exponentially. The R1T might pass at 5,000 lbs, but it might fail the "Understeer" or "Sway Damping" test at 5,500 lbs.

• The Fork in the Road: Instead of capping the truck at 5,000 lbs forever, Rivian re-runs the tests with a Weight Distribution Hitch.
• The Result: The WDH "fixes" the physics failures that occurred at 5,500 lbs, allowing the engineers to keep piling on weight until they hit the next failure point—which for the R1T is 11,000 lbs.

3. Does the High End Force the Low End?​

No. If Rivian could theoretically pass the SAE J2807 sway and understeer tests at 8,000 lbs without a WDH, they would likely advertise an 8,000-lb "weight-carrying" limit.

However, they don't. This tells us that at some point shortly after 5,000 lbs, the R1T’s performance (likely the steering authority due to front-axle unloading) dropped below the SAE's strict safety requirements.

Why specifically 5,000 lbs?​

It is a "Class III" hitch standard. Most receiver hardware is designed such that:

• Below 5,000 lbs: The downward force (tongue weight) is manageable by the receiver and vehicle frame.
• Above 5,000 lbs: The rotational torque on the hitch receiver becomes high enough that a WDH is needed to "twist" that force back into the vehicle's frame more evenly.

In summary: The 5,000-lb requirement exists because that is the maximum weight at which Rivian can guarantee the truck meets SAE safety standards using just a standard ball. To go even one pound over that, you are moving into a "profile" where the truck only legally meets safety standards when the WDH is doing its job of restoring that front axle load.

 

[Kevin D Pem]

Sway has nothing to do with it. You're still confused. Rivian says no to towing anything over 5k without a WDH, end of story. Take it up with Rivian.

That applies to receivers as well. Plainly displayed in the literature and displayed on the tag. Tow capacity with and without a WDH.

it is the responsibility of the operator to use the proper equipment nessisary to safely tow the weights he/she plan to tow.

In case of accident, failure to do so shifts responsibility to that party. Produce all the claims you want,no matter how it was presented to you! If the injured party produces a manual in court for any manufacurered reciver hitch. And you didn't follow their guidelines! Well!