Bouncing when towing travel trailer

[mtofell]

Air bags should be the best solution for some of you guys. When you adjust your WDH to take weight off the truck you are lightening the tongue weight which increases sway. Heavier tongue weight lessens sway. This is the conundrum with battling payload. You want to keep weight off the truck but doing so causes other issues. Air bags allow you to load right up to your payload for the best possible towing experience while keeping your headlights from pointing at the sky.

 

[Mcgruff]

Air bags should be the best solution for some of you guys. When you adjust your WDH to take weight off the truck you are lightening the tongue weight which increases sway. Heavier tongue weight lessens sway. This is the conundrum with battling payload. You want to keep weight off the truck but doing so causes other issues. Air bags allow you to load right up to your payload

I’ll have to disagree slightly on tongue weight, or at least make a point I think often gets confused as to why measuring TW is so important. Tongue weight as it relates to trailer sway is not about the amount downward force applied to the back of the truck. It is used as an indicator of the trailer’s center of mass. 10-15% TW (measured when disconnected from truck) tells you that the trailer’s center of mass is directly over, or slightly in front of the trailer axles. That is what you need to prevent trailer sway (the rear end becoming a horizontal pendulum). A weight distribution hitch places torque on the truck and trailer frames to apply more or less pressure to the ground through different tires/axles but does not change the center of mass of the trailer. The 10-15% requirement should be measured disconnected from truck or with no weight distribution applied.

TW as it applies to payload is another issue and is changed by adjusting the WDH. Adding WD transfers a lot weight to the front truck axle but also a little weight to trailer axles, thus freeing up truck payload.

Regardless, as mtofell states, the battle/conundrum results a balancing act of maintaining a minimum tongue weight without exceeding a maximum amount of truck payload.

 

[BIG RED HEMI]

Based on my WDH instructions my setting is dead on. I will take it to a cat scale and get it weighed but I dont feel the steering is light or heavy so I dont think I have an issue with the weight distribution. I did forget to put down I have the 20" rims if that has anything to do with it.

I did read all the tips under the link you posted prior to asking the question.


The feel is definitely in the rear but this is my first truck with coil springs in the rear as well.

I guess I go to the scales this weekend to get a print out of weight and go from there.

Thank you for some guidance.

I have a 2016 Ram 2500 and I pull a 35' travel trailer with an Equalizer WDH and I still get bouncing or waves as described at times. It's very annoying but I've only noticed it on concrete freeways. I'm not sure if anything can be done to solve that. I'm going to get a 4" lift this spring, so it probably get worse after that.

 

[joshuaeb09]

I have a 2016 Ram 2500 and I pull a 35' travel trailer with an Equalizer WDH and I still get bouncing or waves as described at times. It's very annoying but I've only noticed it on concrete freeways. I'm not sure if anything can be done to solve that. I'm going to get a 4" lift this spring, so it probably get worse after that.

If you're still running the OE shocks I would start there or just make sure you get a proper set of monotubes when you do your lift. In a number of cases that wave comes from inadequate damping as you hit expansion joints. I know a number of people who have had the same issue with their OE shocks from any of the big 3 and a quick upgrade to something from Bilstein or one of the good KYB's usually solves that problem.

 

[mtofell]

I’ll have to disagree slightly on tongue weight, or at least make a point I think often gets confused as to why measuring TW is so important. Tongue weight as it relates to trailer sway is not about the amount downward force applied to the back of the truck. It is used as an indicator of the trailer’s center of mass. 10-15% TW (measured when disconnected from truck) tells you that the trailer’s center of mass is directly over, or slightly in front of the trailer axles. That is what you need to prevent trailer sway (the rear end becoming a horizontal pendulum). A weight distribution hitch places torque on the truck and trailer frames to apply more or less pressure to the ground through different tires/axles but does not change the center of mass of the trailer. The 10-15% requirement should be measured disconnected from truck or with no weight distribution applied.

TW as it applies to payload is another issue and is changed by adjusting the WDH. Adding WD transfers a lot weight to the front truck axle but also a little weight to trailer axles, thus freeing up truck payload.

Regardless, as mtofell states, the battle/conundrum results a balancing act of maintaining a minimum tongue weight without exceeding a maximum amount of truck payload.

I knew I should have paid more attention in physics class.... You've totally lost me. By increasing the action of the WDH, weight is taken off the hinge at the hitch point. Some goes to the truck, some to the trailer. The result is a lighter tongue weight which results in a great propensity to sway. What am I missing?

 

[BIG RED HEMI]

If you're still running the OE shocks I would start there or just make sure you get a proper set of monotubes when you do your lift. In a number of cases that wave comes from inadequate damping as you hit expansion joints. I know a number of people who have had the same issue with their OE shocks from any of the big 3 and a quick upgrade to something from Bilstein or one of the good KYB's usually solves that problem.

In your opinion which shock is better for a 4" lifted 4x4 that will be used for towing a travel trailer? I was thinking of either the Bilstein 5100 series or Fox 2.0 Stabilizer IFP

 

[joshuaeb09]

In your opinion which shock is better for a 4" lifted 4x4 that will be used for towing a travel trailer? I was thinking of either the Bilstein 5100 series or Fox 2.0 Stabilizer IFP

Honestly I think either would be fine both being monotubes, but it will be up to your preference with performance characteristics between them. Most of my experience is with the Billstein 4600's and 5100's which have always been a huge improvement over stock on any vehicle I've used them on. My old mans favorite shock for towing/hauling on HD's is the KYB monomax, but I'm not a big fan of them off the pavement.

 

[BruceMorgan]

I knew I should have paid more attention in physics class.... You've totally lost me. By increasing the action of the WDH, weight is taken off the hinge at the hitch point. Some goes to the truck, some to the trailer. The result is a lighter tongue weight which results in a great propensity to sway. What am I missing?

Yes, that can happen if your non-WDH tongue weight is low (close to 10%), and you add a WDH, and some weight transfers back to the trailer axle, putting your tongue weight below 10%

"Tongue weight" means what it says - "how much does the tongue weigh at the hitch ball". Say it weighs 700 pounds. Without a WDH, then you have 700 pounds on the ball of the truck. This will put all that weight on the rear axle, and raise the nose of the truck in the air. This also transfers part of the weight of the truck to the rear axle, making the front lighter than with no trailer attached.

A WDH transfers weight forward on the truck so the front axle bears a portion of the tongue weight, rather than just the rear axle. Also a little bit of weight goes back to the trailer axle (because it's level now). So now the tongue weight may actually be say 625 lbs after WDH, not 700. That may increase sway, especially if that is below 10% trailer weight.

This video explains it well enough in detail why an air bag solves sag issues, but does nothing to transfer weight forward and nothing to solve light steering and overloaded rear axle issues. For that you need a WDH. And you also need a CAT scale to give you weight for all three points (front axle, rear axle, trailer axle) otherwise its just guesswork.


Also see the classic conveyor belt video on proper trailer weight distribution:

 

[Mcgruff]

I knew I should have paid more attention in physics class.... You've totally lost me. By increasing the action of the WDH, weight is taken off the hinge at the hitch point. Some goes to the truck, some to the trailer. The result is a lighter tongue weight which results in a great propensity to sway. What am I missing?

Sway isn’t about how much pressure is applied at the ball. It’s about how much mass is in the trailer and where that mass is located.

We tend to use pounds and kilograms interchangeably but there is a difference between mass and weight. Mass is how much of something there is. Weight is how much force you are exerting. If you weigh 200lbs it means that due to your mass (kilograms), and the earths gravity, you exert 200lbs of force against the ground.

What will cause your trailer to become a pendulum (swing back and forth) is it’s mass, and the location of the center of that mass. Like flipping a whip back and forth with a ball attached to the end vs the ball being attached next to you hand. The further the center of mass is from the pivot point the more pronounced the swinging will be (in this case both the hitch ball and trailer tires act as pivot points).

If the center of mass is behind the trailer tires the trailer will have a tendency to start swaying left and right. Tensioning your WDH does not move any mass, thus it won’t effect trailer sway. Only adding/removing/moving cargo forward or rearward will do that.

The WDH uses spring bars to pull the truck and trailer frame into alignment and thus concentrate more weight (pressure against the ground) to the furthest most contact points (truck front axle and trailer axles).

Think of a gymnast doing a full split. So much so that his feet are almost off the ground and most of his body weigh is on his butt. Now he starts using his hip muscles to pull the legs together. As he does, his butt starts to rise and his weight shifts to his feet. He didn’t move or redistribute his mass, he simply changed the pressure points. Thats what WD hitches do. Shift the pressure points.

The truck rear axle is his butt and the trailer axles and truck front axle are his feet. The WDH lifts the rear axle and shifts weight/pressure out to the other axles. In fact if you cranked your WDH far enough eventually you would lift the rear tires of your truck off the ground.

I hope you can picture what I’m trying to describe. Applying adequate pressure between each tire and the ground IS important for maintaining steering and control. But “sway” is about trailer center of mass. The 10-15% tongue weight rule is a measurement intended to tell you where the center of mass of your trailer is.

 

[Mcgruff]

Yes, that can happen if your non-WDH tongue weight is low (close to 10%), and you add a WDH, and some weight transfers back to the trailer axle, putting your tongue weight below 10%

"Tongue weight" means what it says - "how much does the tongue weigh at the hitch ball". Say it weighs 700 pounds. Without a WDH, then you have 700 pounds on the ball of the truck. This will put all that weight on the rear axle, and raise the nose of the truck in the air. This also transfers part of the weight of the truck to the rear axle, making the front lighter than with no trailer attached.

A WDH transfers weight forward on the truck so the front axle bears a portion of the tongue weight, rather than just the rear axle. Also a little bit of weight goes back to the trailer axle (because it's level now). So now the tongue weight may actually be say 625 lbs after WDH, not 700. That may increase sway, especially if that is below 10% trailer weight.

This video explains it well enough in detail why an air bag solves sag issues, but does nothing to transfer weight forward and nothing to solve light steering and overloaded rear axle issues. For that you need a WDH. And you also need a CAT scale to give you weight for all three points (front axle, rear axle, trailer axle) otherwise its just guesswork.


Also see the classic conveyor belt video on proper trailer weight distribution:

Good videos for everyone to see. I will only disagree that SPECIFICALLY on the subject of sway, a weight distribution hitch would not reduce tongue weight in a way that would contribute to sway. Assuming a level truck/trailer with and without WD. 10% TW is about determining the location of your trailer’s center of mass. WD hitches DO change the tongue weight as it is felt by the truck, but do not change the location of the center of mass of the trailer.

 

[BruceMorgan]

Good videos for everyone to see. I will only disagree that SPECIFICALLY on the subject of sway, a weight distribution hitch would not reduce tongue weight in a way that would contribute to sway. Assuming a level truck/trailer with and without WD. 10% TW is about determining the location of your trailer’s center of mass. WD hitches DO change the tongue weight as it is felt by the truck, but do not change the location of the center of mass of the trailer.

OK I think get what you're saying, which is that the WDH will artificially shift weight backwards to the trailer axle, but not change the center of mass (the "balance point") which is static based on trailer loading alone and that balance point is what impacts sway.

But I'm no physicist and is it center of mass (which doesn't change regardless of level) that affects sway or is it center of gravity (which moves forward or backward if the trailer is nose down or or nose up, and with WDH) that affects sway?

However if the trailer is level then the center of mass should coincide with the center of gravity, so the only way to be accurate is to ensure the trailer is level when weighing things, and not shift weight with the WDH. You could do that with a trailer tongue scale directly (weight the trailer, then level and weigh the tongue weight), or level a truck/trailer combo with airbags (weight the trailer, then weigh the combined truck / trailer with the trailer leveled with the airbags with a 3 point scale, tongue weight is original trailer weight - trailer axle weight).

 

[crash68]

OK I think get what you're saying, which is that the WDH will artificially shift weight backwards to the trailer axle, but not change the center of mass (the "balance point") which is static based on trailer loading alone and that balance point is what impacts sway.

um..no
A WDH does just what it's name implies, it changes how the weight is distributed onto the tow vehicle. The weight of the trailer and how far forward the center of mass is will change how much tongue weight is on the truck, the WDH changes how that weight is distributed between the front and rear wheels of the tow vehicle.

 

[mtofell]

I will readily concede that people in this thread are far more knowledgeable than I with respect to physics. That being said, it seems we have gone down a road of splitting hairs. My original comment was that air bags are the best remedy for OP's problem and I stand by that.

During my time spent out of physics class I have run roughly a half dozen different trucks with roughly that many different trailers for tens of thousands of miles. Some I probably should never have left my driveway with and the experience was horrendous. Others were a dream setup.

In crude terms (and at the risk of violating a physics book), tongue weight is tongue weight and the % with respect to the trailer's weight is what matters. You can mask the problem with a WDH but it becomes a band-aid at some point. All the physics in the world doesn't change the reality that too heavy a trailer is not a good/safe match for a less than capable truck.

 

[Mcgruff]

We have forked from the original thread a bit and that’s partially my fault. I hoped to help everyone’s understanding as why and how tongue weight is related to sway. To point out that determining if you have the 10-15% tongue weight should (in my opinion) be based on the “natural” tongue weight, unmodified by a weight distribution hitch.

Weight distribution is an essential safety component for spreading the weight optimally to each axle. This ensures maximum control and grip on the road surface.

There are many details that contribute to towing dynamics and their interplay is complicated. Rules of thumb like minimum 10% tongue weight and a level trailer get us close enough to be reasonably safe without needing a physics degree and $100k worth of equipment before each tow.

Happy holidays and safe travels to everyone.

 

[Marine Les]

To set the WDH I tow a stretch of road that creates the hop or bounce and tow it without the WDH and then with the WDH at soft setting and step up the rate of pressure on the bars until it feels best. Make sure the trailer is level and properly loaded. I had a toy hauler that had to be heavily loaded toward the rear stop the constant hop.

 

[Elkman]

When there is porpoising with a trailer it is from the rear suspension not being able to handle the load. The shock absorbers cannot compensate for the load and with their increased range of motion will run hotter and fail sooner. Adding more load support at the rear is the only solution.

You can either install and work on tuning air bags or put on a set of SuperSprings if you vehicle has leaf springs at the rear. If it has coil springs then fixing the problem gets more complicated.

Changing tires to fix the bouncing is a waste of money. Stiffer sidewalls will reduce sidewall flex but that is only when making turns on sloping highway curves and not an issue with a travel trailer in tow.

 

[Marine Les]

I don't think its the rear suspension not handling the load as my 2500 has the cabover camper option that has added leaves that engage when there is a significant load, its heavy duty. How the trailer distributes the load and how you use the WDH to deal with it matters. If you are seriously under sprung sag will need to be dealt with and the WDH can only do so much to compensate but I don't think the jumping hop on my truck was do to weak suspension.

 

[Joe Merchak]

When there is porpoising with a trailer it is from the rear suspension not being able to handle the load. The shock absorbers cannot compensate for the load and with their increased range of motion will run hotter and fail sooner. Adding more load support at the rear is the only solution.

You can either install and work on tuning air bags or put on a set of SuperSprings if you vehicle has leaf springs at the rear. If it has coil springs then fixing the problem gets more complicated.

Changing tires to fix the bouncing is a waste of money. Stiffer sidewalls will reduce sidewall flex but that is only when making turns on sloping highway curves and not an issue with a travel trailer in tow.

I plan on putting airbags this spring. Alot cheaper then tires.

 

[Joe Merchak]

Put the airbags on and took 2 trips already. Bouncing is gone. I still use the WDH and add 30lb of air to the springs. Truck is level and no bouncing.

Sent from my SM-G973U1 using Tapatalk

 

[SoCal Bomber]

What brands of LT tires do you all recommend?