Bravo Seijiro !!!

Good explanation of some basic chassis dynamics and anti-roll bars .

If you read some of the OP's answeres to questions I posted I agree with you that his "sway" is actually a wander issue with the Excursion that magnifies itself while towing. He needs to get the Ex stable on its own before chasing trailer sway.

 

I disagree.
Coming from road racing a '69 Mustang anti-roll bars are a very important component of good handling.
Lateral grip comes from all 4 tires.
Vehicle weight is shifted to the outside tires in a turn reducing overall lateral grip.
Anti-roll bars will keep more weight on the inner tires and reduce sliding.
Lateral Grip: What Sway Bars Actually Do And Why They're ImportantTurnology

Do the 4x4s have more of a problem with steering wander?
Our 2wd with coil spring front suspension has no wander.
Maybe the front leaf spring suspension in the 4x4s have more of an issue because of the weird ways a leaf spring can twist.
Our Ex handled poorly with the stock suspension and the shocks were shot.
After installing Bilstein shocks, F250 rear leafs and Hellwig front & rear bars the difference in handling is amazing.
Having a balanced set of anti-roll bars can control under/over steer.
Tires and front end alignment are important, too.
Once the tow vehicle is handling well pulling a trailer is lot better.

 

I do not ever recall a RWD Ex owner complaining about wander.

I've fixed several 4x4 Ex of wander and the culprit in my case has always come down to sagged front springs and loss of positive caster, usually a few other worn parts like unit bearings, leaf bushings, shackle bushings, track bar bushings , TRE's, or steering gear thrown in for good measure.

 

I understand your take on it. I also road race and set up other road racing cars. Sway bar setup is not intuitive, it's something learned.

(By the way I love the vintage muscle car road racing. I pitted for a few years for a man who ran a '65 Shelby 350R model clone - real 350 but not a real R model, and a '71 boss in Parnelli Jones livery and of all the road racing I've been involved in, those seasons and the people were the most enjoyable. I only wish I had the money to do it myself.)

Understanding that the sway bar resists body roll; in that context here's a quote from your article.

That's not exactly true for a race car but for a road car it is.

Now apply this to, and this is very important, *just* adding a sway bar to the rear of an Excursion. What you are doing is stiffening the roll rate of the rear and as the article describes, stiffening the roll rate in the rear increases the propensity of the vehicle to oversteer. I'm absolutely not saying that adding a rear sway bar turns your Excursion in to an oversteering donut machine, nor am I saying it guarantees to be more biased towards oversteer than understeer, but it does push the balance more towards oversteer than without the bar. In fact any increase in rear roll rate, all other things being equal, pushes the balance more towards oversteer. This can be accomplished by just helper springs.
Another way to describe this is that by increasing rear roll rate you reduce the lateral force necessary to cause the rear tires to break traction - a reduction in grip.

Depending on the circumstances increasing rear roll rate can be a good thing, but it's not the miracle fix that it's often prescribed to be.

Otherwise you're absolutely right. Correct roll rate front and rear is critical for maximum effort. I'm sure you've found at some tracks it's better stiffen the rear bar a little and create a "loose" car to help corner rotation. While in others, particularly ones with elevation changes or flat turns you want to relax the rear roll rate to create a "tight" car so you can get on the power sooner exiting a corner.

Not sure on 2wd vs 4wd with these, I've only owned superduties and excursions of the 4wd variety. I solve the problem with tight components, a touch of toe-in, and plenty of caster.

 

Just think how many crashed soccer mom Excursions we would have if the Ex didn't understeer. Lmao

lets face it, the Ex will likely always understeer and that's a good thing but the real reason ford left the a bar off the rear of the Ex is because it causes the rear to "waddle" at slow speed over bumps and driveways.

Have you ever sat in the 3rd row of a Ex with a sway bar driving around town ?
Bring a helmet so you do t knock yourself out hitting the side windows. They suck.

Unhook the bar and the back seats ride is vastly more mellow. Not more harsh side to side jolts over driveways and bumps.


Think about it, it's a huge brick with 3 rows of seats, it is a people mover not a twisty road racer.
the compromise or trade off ( and there is always a trade off ) is poor ride quality for improved twisty road handeling ? Kinda dumb.

 

How is tongue weight determined? Is there a tongue-weight-ometer?

Found it...https://www.ford-trucks.com/how-tos/...-weight-357076

 

Why yes there is

 

there are others, the Sherline is the most popular

 

My favorite though is converting a old bottle jack
Homemade Bottle Jack Pressure Gauge - HomemadeTools.net

 

And then there is the old fashion way.

Since we know a stock Ex has rear leaf spring that have a spring rate of 420 pounds per inch of deflection.

You can measure vehicle height before hitch up and hitch loaded and calculate the tounge weight.

 

Not sure if it was mentioned, but do you have E range tires on your Ex? Are they inflated to max pressure stamped on the tire (80 psi)? Don't go by the pressure on the door jam sticker.

 

Why would you inflate 265/75r16 tires to 80psi on the Ex ?

 

If you are towing, you want that firm sidewall so inflating it to max will lessen that squishy feeling when there's a load and any sway from the trailer.

 

I think Ford left the rear anti-roll bar off to save money, just like removing the radiator trans cooler.
The "waddle" is way worse in our E350 passenger van.
I think stiff springs contribute more to waddle.
When you go straight over speed bumps or dips the anti-roll bars add nothing to waddle.
I was surprised when my mom (who is used to Toyota sedans) was riding in the 2nd row commented how well our Ex rode.
Maybe that's the sweet spot.
I don't usually sit in the 3rd row anyway.

 

If your ex feels squishy towing with 265/75r16 tires @55 psi you likely have other handeling related issues. 55psi in those tires will support the full gvwr of the Ex.

Seriously, if you arrived at 80psi by trial and error testing I would go back to 55psi and look for the real problem. My guess is you either have a worn out shock or simply need shocks with more compression and or rebound valving.

Also, since you mention E rating I assume you are not running a "P" or passenger vehicle tire but it is worth checking.