Trailer Sway Control

[SnoKing]

If that's the case, how do you get GCW?

Nick

With math! Weight of the truck plus weight for the trailer = Gross combined weight! Or you can go to a cat scale and add up the front axle, drive axle and trailer axles! Again math is used! SNOKING

 

[NIsaacs]

So if I weigh the hypothetical 12k trailer by itself on a scale it will weigh 12k. However, when I hook up the tow vehicle, it now weighs 10k. Where did the pin weight of 2k go? It "transferred" to the tow truck.

Nick

 

[SnoKing]

So if I weigh the hypothetical 12k trailer by itself on a scale it will weigh 12k. However, when I hook up the tow vehicle, it now weighs 10k. Where did the pin weight of 2k go? It "transferred" to the tow truck.

Nick

To weight the hypothetical 12K trailer by itself on a scale you have to weight the axles and jack or landing gear, right????? When you hook it to your hypothetical tow vehicle you are talking about now weighing the trailers axle weight at 10K NOT the trailer weight. Trailer is still 12K. SNOKING

 

[NIsaacs]

Ok, you are going to pick little black specks out of pepper......

Nick

 

[AH64ID]

I respect your opinion, but this time I can't agree. Perhaps 'transfer' wasn't the appropriate word here. If you place weight on the truck, that makes the truck heavier and the trailer lighter.

So when you step on a scale does the scale become heavier and you become lighter?

Yes that is how silly it is making a trailer sound lighter by hooking it up to a truck.

A 10K trailer weights 10K, regardless if it had 1.5K of hitch weight or 2.5K of pin weight. It's a 10K trailer.

 

[brods]

That seldom happens. A million 18 wheelers disprove your theory every day. Probably just as many pickups with trailers as well.

Tractor trailers are not comparable to pickups with trailers, especially bumper pulls. Among a host of other differences, semi’s carry close to 50% of the trailer weight on the fifth wheel which greatly increases stability.

While the tow vehicle does not “cause” sway all by itself it definitely plays a roll in the stability of the system. Truck trailer modeling from Iowa State University lists 35 parameters and 7 degrees of freedom used in the calculations. More parameters apply to the tow vehicle than the trailer. This shows how important the tow vehicle’s dynamics are to the stability of the truck trailer system. To discuss sway as only a trailer issue is to misunderstand that towing is a system where the truck’s wheelbase, suspension, tires, distance from the hitch to the rear axle, and more, all have an effect on the system’s stability.

A real world example of this was a 12K tandem axle flatbed bumper pull we towed for work. Pulled by the 1 ton van with a short rear overhang it was fine. Pulled with a ½ ton suburban with a long rear overhang, soft rear suspension and squishy tires it was a different story. One trip with the suburban pulling the trailer it was loaded with three large crates (about 5K total load). When going over 65 mph the hint of sway starting could be felt. When the other guy took the wheel I warned him of it and that he should not to go over 65. He proceeded to cruise at 70 and after starting down a hill on Route 80 in PA (around where the sign says it’s the highest point east of the Mississippi) he lost it.

I've wondered if some form of sway control would have prevented the incident (or if the jackass would have been going faster just making matters worse). After looking over the right side guardrail, down the steep embankment several hundred feet high and figuring we were dead if we went over it, I can certainly understand someone’s desire to try to prevent sway by any means available. Luckily after flirting with the right side guardrail a few times during the back and forth across the highway we wound up jackknifed by the center median with only minor damage.

Russell500 I can’t help you with what sway control device to choose, if any, but stick to your guns, educate yourself on trailering stability and if you feel some kind of sway control is a wise idea then go for it. The only exception would be if someone could show that a particular sway control device actually made things worse instead of better.

After the above incident I searched for information on how to prevent sway and what to do if it happens. I was surprised on how little was out there 25 years ago. I found literature by MM Smith to be informative. His “Trailers How to Buy & Evaluate” would be a good choice for getting a detailed understanding of the dynamics of sway and how to assess your present setup. Maybe some of our forum members can suggest a more up to date book which can explain the complex subject of towing dynamics in an easy to follow manner.

 

[GAmes]

While the tow vehicle does not “cause” sway all by itself it definitely plays a roll in the stability of the system.

No argument there. That is exactly the case with the motorcycle trailer.

One trip with the suburban pulling the trailer it was loaded with three large crates (about 5K total load).

One trip is your example? Of all the trips you made, you only encountered sway one time. Not much of a counterpoint.

I've wondered if some form of sway control would have prevented the incident

I can answer that. Proper loading would have prevented the trailer from swaying. I stake my life and my truck on that every time I hook up to a bumper pull trailer, and there have been literally hundreds of them over the last 12 years. If ONE of them had swayed, it would have been returned to it's starting point.

 

[Grizzly]

So when you step on a scale does the scale become heavier and you become lighter?
The scale does become heavier because you're on it. You do not become lighter because you still weigh the same.



Yes that is how silly it is making a trailer sound lighter by hooking it up to a truck.
The trailer still weighs the same, but some of that weight is now being carried on the truck. Nothing silly about it.



A 10K trailer weights 10K, regardless if it had 1.5K of hitch weight or 2.5K of pin weight. It's a 10K trailer.

Your right about that, but the 1.5K or 2.5K is now being carried on the truck. Now the trailer axles are not carrying that weight. Trailer manufactures select tires to carry the weight of the trailer minus the pin weight. Try to understand this concept, it's not that difficult.

 

[brods]

No argument there. That is exactly the case with the motorcycle trailer.



One trip is your example? Of all the trips you made, you only encountered sway one time. Not much of a counterpoint.



I can answer that. Proper loading would have prevented the trailer from swaying. I stake my life and my truck on that every time I hook up to a bumper pull trailer, and there have been literally hundreds of them over the last 12 years. If ONE of them had swayed, it would have been returned to it's starting point.

Do you really want to hear about every incident where I've experienced some form of sway? That one was the most dramatic and was a valuable lesson showing what can happen when things go wrong. With the suburban no change in trailer loading would have corrected the problem since it was really a problem with the tow vehicle not the trailer. More tongue weight would make the trailer more stable but putting more load on the rear of the suburban would have further reduced its stability. The solution in that particular case (besides using a more suitable tow vehicle or making modifications to the suburban) was simply to keep the speed down below the critical speed where uncontrollable sway could occur. Lead foot couldn't do that and we were lucky that only his ego was bruised.

Every trailer has a critical speed where it will sway, it is just that the well designed ones have a critical speed way above where anyone would pull them. But that is just the starting point, the best it can ever be. Almost everything (loading, tow vehicle dynamics, hitch stiffness, etc) will reduce the critical speed of the truck trailer system. And as in your example with the motorcycle trailer, if the trailer is light compared to the tow vehicle then it will have little effect on the stability of the system. As the trailer gets heavier its influence on the tow vehicle gets greater and greater until the tail can start wagging the dog and at that point attention to every detail of the setup is critical.

Trailer sway can and does happen and anything that can reduce the chance of uncontrolled sway is worth investigating imo. I do not agree with using sway control as a band aid for poor towing practices, but as cheap insurance I see no problem with it. At worst it does nothing. At best it prevents a wreck. YMMV

 

[GAmes]

Actually it would have more convincing (at least to the kool-aid drinkers) if you exaggerated the whole scenario to fit with the myth of sway control. Here is what would have been something they could take a drink from.

"I once worked at a place that had two tow vehicles. When we hooked a trailer to the suburban it would always sway, no matter the load. It never swayed behind the one ton van that had a short overhang behind the rear axle. We installed a (insert name of sway gimmick here) and all our problems were solved." See, that covers both the assertion that a tow vehicle causes sway and the ridiculous notion that a sway gimmick device is "insurance" or will "prevent a wreck". Of course you and I would know the story is a lie, but anything goes when a myth is perpetuated.

The suburban would have been a capable tow vehicle by merely using a weight distribution hitch to compensate for it's soft suspension and the leverage of the trailer tongue. I am constantly amazed by the assertion that weight distribution (and the sway gimmick too) is only required on travel trailers. TTs by design are the least likely of all tow behinds to sway, simply because of the way appliances, water/waste tanks and furnishings are placed. A person would have to work to get a TT to sway. Cargo trailers, on the other hand, are easy to load improperly and are frequently used in environments where their suspension could be damaged. If a sway device were to be proven to be effective I would be the first to cheer them on. If one was proven to be a safety item I would be there bolting one up to every trailer I pull. I'd like to learn more about the electronic one because I'm a believer that trailer brake application will straighten up a misbehaving trailer, and bring it and the tow vehicle to a safe stop. Would I continue my journey with said trailer? Not hardly.

 

[AH64ID]

Your right about that, but the 1.5K or 2.5K is now being carried on the truck. Now the trailer axles are not carrying that weight. Trailer manufactures select tires to carry the weight of the trailer minus the pin weight. Try to understand this concept, it's not that difficult.

Now your changing you are changing your story....

If you place weight on the truck, that makes the truck heavier and the trailer lighter.

The trailer still weighs the same

So which one is it?

By saying "now the trailer axles are not carrying that weight" implies they were carrying it at some point. So when is that? If the trailer isn't on a TV then the tongue jack or jack pads, it doesn't transfer the weight to the tires just because it's not hooked up to a truck. Aside from minor changes based on trailer angle the weight on the axles is the same regardless of being hooked up or not.

 

[AEdelheit]

Ill jump in on the weight transfer debate for fun!!

The way I see it when the trailer is hooked up there is weight transferred to the TV, I dont think anyone would disagree with that. However the physical weight of the trailer will not change just what carries the weight , IE landing gear, axles or TV and when a trailer sways the only thing that really matters is the physical trailer weight not the weight distributed though a hitch. To Clarify I understand that weight distribution is critical, but once a trailer starts to sway is where the physical trailer weight matter.

 

[AH64ID]

I will disagree, the weight is not transferred to the TV rather it is carried by the TV.

Transfer is to move it from one place to another. The trailer still has the same weight, therefor none of the weight is transferred but it is still carried by the TV. Just like a backpack you are carrying the weight of the backpack, not having the weight transferred to you.

 

[Grizzly]

Now your changing you are changing your story....






So which one is it?

By saying "now the trailer axles are not carrying that weight" implies they were carrying it at some point. So when is that? If the trailer isn't on a TV then the tongue jack or jack pads, it doesn't transfer the weight to the tires just because it's not hooked up to a truck. Aside from minor changes based on trailer angle the weight on the axles is the same regardless of being hooked up or not.

I'm not changing my story, the trailer axles are never carrying the weight Before the trailer, say 5th wheel, is hitch to the truck, the pin weight is on the landing gear.

 

[AH64ID]

I'm not changing my story

I quote your changed story... so does the trailer stay the same weight or does it get lighter?

 

[AEdelheit]

I will disagree, the weight is not transferred to the TV rather it is carried by the TV.

Transfer is to move it from one place to another. The trailer still has the same weight, therefor none of the weight is transferred but it is still carried by the TV. Just like a backpack you are carrying the weight of the backpack, not having the weight transferred to you.

Well It is transferred from the landing gear to the truck.

 

[Grizzly]

I quote your changed story... so does the trailer stay the same weight or does it get lighter?

I give up. Your not reading post 28 correctly. I never said the trailer gets lighter, I said that some of the weight of the trailer is being carried by the truck.

 

[AH64ID]

I give up. Your not reading post 28 correctly. I never said the trailer gets lighter, I said that some of the weight of the trailer is being carried by the truck.

Really??? Check out post #16 again.

If you place weight on the truck, that makes the truck heavier and the trailer lighter.

Looks like you said it to me.

 

[AH64ID]

Well It is transferred from the landing gear to the truck.

I'll buy that.

 

[NIsaacs]

I will disagree, the weight is not transferred to the TV rather it is carried by the TV.

Per: "Thesaurus.com" The following words are all related to transfer when used in relation to moved/transport. Carried, conveyed, shifted, hauled, lugged and trucked. I think we are all on the same page, just that we differ in how we perceive a trailer as a single vehicle, now hooked to a tow vehicle and becoming a combination/semi.

Oh yeah, if Grizz takes one foot off the scale and puts it on a skate board the scale will read less and he becomes a combination

Nick