I How Does Moving a Gooseneck Trailer Connection Rearward Affect Hitch Load?

[jeredpilot]

TL;DR Summary

How much weight is added to a beam point load by moving the load rearward 20 inches?

Forgive my ignorance of the proper terms. I may be using “leverage”, “lever”, and “cantilever load” incorrectly.

Description:

This concerns a gooseneck hitch connection in a pickup vehicle.

The gooseneck receiver hitch is properly attached to the vehicle and located ~3 inches forward of the rear axle. If I connected the gooseneck trailer to the hitch as designed the weight on the hitch would be directly above the hitch and be 2,500 pounds.

However, for certain reasons I must move the gooseneck trailer connection point rearward 20 inches. The hitch itself (permanently attached to the vehicle) will remain in its properly located position. I will build a hitch extension that displaces the hitch load point rearward 20 inches. This extension will not be in contact at any point with the vehicle other than to the hitch itself and the trailer when connected. So I am moving the 2,500 pound load from directly above the hitch to 20 inches rearward of the hitch.

So, what I need is the formula to calculate what the load on the hitch will be when the load is displaced rearward 20 inches. Is it simply 1.67 times 2,500 pounds which would be 4,166 pounds? (20/12*2500)

Also, I realize there will now be a ‘twisting’ force on the hitch itself. Is that twisting force equal to the new load? How would I calculate this twisting force?

Also, what is the correct terminology to properly describe my problem? This 20 inch extension is a sort of lever. And also this hitch extension acts like a cantilever beam of sorts. I’ve looked and looked for the proper terms to describe my problem, but as yet I am unsure what is correct.

Thanks to anyone that sheds light on my problem.

 

[Baluncore]

Welcome to PF.

The fifth wheel must remain in the same place on the pickup.
That is required for safety and stability.

A longer gooseneck will reduce the load on the fifth wheel, but that will depend on the axle position(s) and suspension on the towed trailer.

I think you need to produce before and after diagrams of the system.

 

[jeredpilot]

Yes. The hitch must remain in its position. I stated in the original post “The hitch itself (permanently attached to the vehicle) will remain in its properly located position.”

The weight on the hitch itself will actually increase, not decrease. Also, the axles on the trailer are fixed and will remain in their factory designed location.

I am merely moving the trailer connection point rearward 20 inches. I will do this by building a beam 20 inches in length. It will only be supported at the hitch itself. So in that sense it is a cantilever beam. (Supported only on one end)

One other minor point, this is a gooseneck hitch, rather than a fifth-wheel. But I think the calculation likely would not change all that much. A fifth-wheel spreads the load around a surface area (a fifth-wheel plate). While a gooseneck has the full load at a certain point.

You may be correct. I’ll draw a diagram for clarification. Thanks.

 

[Baluncore]

I am merely moving the trailer connection point rearward 20 inches.

That is an ambiguous statement.
If you are lengthening the gooseneck, then the trailer moves backwards.

The weight on the hitch itself will actually increase, not decrease.

That statement is not consistent with a longer gooseneck.

The line between the hitch and the trailer axle is a lever.
If you lengthen the hitch end of that lever, so the 2500 lb load moves backwards, then the load on the hitch will be reduced. The trailer axle position is important in that computation.

 

[jeredpilot]

I disagree on all points, but I certainly may be incorrect. (Due to not understanding each other)

Drawings incoming in a few minutes.

 

[jeredpilot]

Current Configuration

 

[jeredpilot]

Proposed Configuration

 

[jeredpilot]

That is an ambiguous statement.
If you are lengthening the gooseneck, then the trailer moves backwards.

That statement is not consistent with a longer gooseneck.

The line between the hitch and the trailer axle is a lever.
If you lengthen the hitch end of that lever, so the 2500 lb load moves backwards, then the load on the hitch will be reduced. The trailer axle position is important in that computation.

 

[jeredpilot]

That is an ambiguous statement.
If you are lengthening the gooseneck, then the trailer moves backwards.

That statement is not consistent with a longer gooseneck.

The line between the hitch and the trailer axle is a lever.
If you lengthen the hitch end of that lever, so the 2500 lb load moves backwards, then the load on the hitch will be reduced. The trailer axle position is important in that computation.

 

[Baluncore]

I assume the 20" is a rigid extension of the trailer gooseneck.

What is the distance between the hitch point now, and the mid-point of the tandem axle set?

 

[jeredpilot]

Yes. It is rigid.

Length from the trailer connection point to the center of the axles does not change in either configuration. That length is 318.5 inches.

 

[jeredpilot]

 

[jeredpilot]

I assume the 20" is a rigid extension of the trailer gooseneck.

What is the distance between the hitch point now, and the mid-point of the tandem axle set?

Rather than an extension of "the trailer gooseneck", I would say it is an extension of the hitch. Is that just semantics? Or does it make a difference?

 

[Baluncore]

Is that just semantics? Or does it make a difference?

It is critical.
Your diagram of the trailer does not show the position of the hitch, on the trailer now.

 

[jeredpilot]

It is critical.
Your diagram of the trailer does not show the position of the hitch, on the trailer now.

Correct me here if I am wrong, please.

But in my mind, if the trailer itself is never changed, and the weight of the downward force of the trailer never changes, then how does the distance of the axles come into play?

To me, if the trailer length never changes and the downward weight never changes, then the trailer axle position is irrelevant? The only thing that changes is the effective position where the trailer connect to the vehicle. Therefore, the trailer axle position is irrelevant? No?

 

[jeredpilot]

It is critical.
Your diagram of the trailer does not show the position of the hitch, on the trailer now.

The hitch is exactly at the front of the trailer. The very most front of the trailer.

 

[jeredpilot]

Yes. It is rigid.

Length from the trailer connection point to the center of the axles does not change in either configuration. That length is 318.5 inches.

318.5 inches

 

[Baluncore]

Therefore, the trailer axle position is irrelevant? No?

NO. The effect of moving the hitch point forward by 20" on the rigid trailer assembly, is proportional to the initial length of the trailer.
The fulcrum of the lever is the mid-point of the tandem axle set.
The effective load on the hitch will be reduced when the distance between the hitch and the axle set is increased.

What does the term gooseneck mean to you?

 

[jeredpilot]

NO. The effect of moving the hitch point forward by 20" on the rigid trailer assembly, is proportional to the initial length of the trailer.
The fulcrum of the lever is the mid-point of the tandem axle set.
The effective load on the hitch will be reduced when the distance between the hitch and the axle set is increased.

What does the term gooseneck mean to you?

Gooseneck Hitch:

 

[jeredpilot]

NO. The effect of moving the hitch point forward by 20" on the rigid trailer assembly, is proportional to the initial length of the trailer.
The fulcrum of the lever is the mid-point of the tandem axle set.
The effective load on the hitch will be reduced when the distance between the hitch and the axle set is increased.

What does the term gooseneck mean to you?

Fifth-Wheel Hitch (same as tractor-trailer semi truck):

 

[jeredpilot]

NO. The effect of moving the hitch point forward by 20" on the rigid trailer assembly, is proportional to the initial length of the trailer.
The fulcrum of the lever is the mid-point of the tandem axle set.
The effective load on the hitch will be reduced when the distance between the hitch and the axle set is increased.

What does the term gooseneck mean to you?

But the hitch point is being moved back, not forward.

So the hitch stays fixed, but the ball is moved back 20 inches. So the distance to the hitch itself grows by 20 inches. Since the extension piece is a rigid 20 inches, the length of the trailer increases. I get that. But and effective increased trailer length would add weight to the connection, not reduce it. (???)

 

[jeredpilot]

NO. The effect of moving the hitch point forward by 20" on the rigid trailer assembly, is proportional to the initial length of the trailer.
The fulcrum of the lever is the mid-point of the tandem axle set.
The effective load on the hitch will be reduced when the distance between the hitch and the axle set is increased.

What does the term gooseneck mean to you?

Fifth Wheel on Semi Truck:

 

[Baluncore]

Are you a troll ?

 

[jeredpilot]

Are you a troll ?

Am I a troll?

No. Why do you think I am a troll?

 

[jeredpilot]

I am answering every question and trying to understand.

Moving axles rearward adds weigh to the hitch - every single time.

Moving axles forward, lessens weight on a hitch - every single time.

 

[jeredpilot]

I am answering every question and trying to understand.

Moving axles rearward adds weigh to the hitch - every single time.

Moving axles forward, lessens weight on a hitch - every single time.

@Baluncore Is this controversial?

 

[jeredpilot]

If we place the axles at the very rear of a trailer then the axles are further from the mid balancing point. So since we are moving them to the extreme rear and away from the balancing point, the weight on the hitch increases.

If we place the axles perfectly at the balancing point, then there is no weight on the hitch.

 

[Baluncore]

The axles remain fixed to the trailer, they do not move relative to the gross trailer centre of mass. Why do you now discuss moving them?

 

[jeredpilot]

The axles remain fixed to the trailer, they do not move relative to the gross trailer centre of mass.

Yes.

 

[jeredpilot]

@Baluncore

Maybe this was a typo by you, and thus why I am having difficulty following. But you said this in post number 18.

"The effective load on the hitch will be reduced when the distance between the hitch and the axle set is increased."

 

[Baluncore]

There is one point, between the trailer and the tow vehicle, where it can bend. That is the hitch point. You said that is fixed on the tow vehicle.
But the hitch point is being moved on the trailer. In effect, you are lengthening the gooseneck by 20".
The distance between the hitch point and the axles on the trailer is being increased.

 

[jeredpilot]

Yes. I follow that.

But in your post number 18 you said: "The effective load on the hitch will be reduced when the distance between the hitch and the axle set is increased."

It should increase. Sorry man. I don't want to give you a headache! lol

 

[jeredpilot]

There is one point, between the trailer and the tow vehicle, where it can bend. That is the hitch point. You said that is fixed on the tow vehicle.
But the hitch point is being moved on the trailer. In effect, you are lengthening the gooseneck by 20".
The distance between the hitch point and the axles on the trailer is being increased.

Okay. I am starting to see why axle length difference to hitch plays into it better. Thanks.

But the weight on the tow vehicle should increase? Correct?

 

[Baluncore]

But in your post number 18 you said: "The effective load on the hitch will be reduced when the distance between the hitch and the axle set is increased."

Stop clouding the issue. I assumed you moved the hitch on the trailer, not the axles.

It should increase. Sorry man. I don't want to give you a headache!

It will increase only in your head. You are letting your confusion confuse you more.

 

[jeredpilot]

After further thought, the weight placed on the chassis itself doesn't change, because the tongue weight of the trailer doesn't change. i.e. the trailer's downward force is 2,500 pounds no matter where it is placed on the vehicle.

What does change is the 'twisting' force experienced by the vehicle's hitch itself. This is due to the hitch extension acting as a lever to the hitch. But the weight on the chassis itself stays at 2,500 pounds.

I intend to take the trailer and pickup to a set of truck scales and weigh the weight on the chassis at the varying positions. This will verify what is correct. Undoubtedly, the weight will not be less as you have said a couple of times.

@Baluncore thanks for attempting an answer, At least you now know the difference between a gooseneck hitch and a fifth-wheel hitch. I am glad I could help you.

 

[Lnewqban]

After further thought, the weight placed on the chassis itself doesn't change, because the tongue weight of the trailer doesn't change. i.e. the trailer's downward force is 2,500 pounds no matter where it is placed on the vehicle.

Not much perhaps, but it changes.
More or less of the total weight can be moved onto the tires.

Two extreme cases:
If all the weight (trailer plus usefull load) could be relocated on those wheels, no weight would be felt by the truck.
If it could be located aft the wheels, the truck would feel a lifting force.

Welcome!

 

[jbriggs444]

Not much perhaps, but it changes.

As I understand the class of scenarios being considered, the single variable is the fore-and-aft placement of the hitch on the towing vehicle. A fixed trailer with a fixed tongue arrangement is hitched at the chosen hitch point.

Edit: This understanding is not correct. We are not talking about moving the hitch around within the bed of the truck.

With this understanding in mind, for a fixed trailer the tongue weight would obviously be fixed. So the total weight supported by the towing vehicle tires would be fixed regardless of hitch placement. The ratio of front tire force versus rear tire force would vary, of course.

An equalizing hitch could change things. We had one of those on our family's Shasta trailer back in the day. The torque at the hitch tended to off-load the towing vehicle rear wheels while loading up the trailer wheels and the towing vehicle front wheels.

 

[Baluncore]

At least you now know the difference between a gooseneck hitch and a fifth-wheel hitch. I am glad I could help you.

My experience is with fifth wheels on semitrailers. It does not matter what type of hitch is employed, the hitch is the hinge point of the combination of tractor and trailer.

The gross weight of the trailer and load can be seen as two parts. The first part is carried by, and balanced about, the trailer axle set. That offers no static load to the tractor hitch point.
The second part is the unbalanced mass that provides a moment, that rests effectively on the hitch. That moment is 2500 lbs at the old hitch position, 318.5" from the axle-set, which works out at;
318.5" * 2,500 lbs = 796,250 inch⋅pounds
If you extend the trailer axle-set to hitch point length by 20", the length becomes 338.5", so the vertical load on the tractor hitch will become;
796,250 / 338.5 = 2,352 lbs, which is 148 lbs less than the original.

But I can have no confidence in the numbers, because posts like these contradict an extension of 20" between the axle-set and the modified hitch point.

I assume the 20" is a rigid extension of the trailer gooseneck.
What is the distance between the hitch point now, and the mid-point of the tandem axle set?

Length from the trailer connection point to the center of the axles does not change in either configuration. That length is 318.5 inches.

 

[jeredpilot]

Not much perhaps, but it changes.
More or less of the total weight can be moved onto the tires.

Two extreme cases:
If all the weight (trailer plus usefull load) could be relocated on those wheels, no weight would be felt by the truck.
If it could be located aft the wheels, the truck would feel a lifting force.

Welcome!

"Two extreme cases:
If all the weight (trailer plus usefull load) could be relocated on those wheels, no weight would be felt by the truck.
If it could be located aft the wheels, the truck would feel a lifting force."

Yes, 100% - Exactly correct.

As far as "but it changes" I think it will not be an appreciable amount. - it will be negligible.

 

[jeredpilot]

As I understand the class of scenarios being considered, the single variable is the fore-and-aft placement of the hitch on the towing vehicle. A fixed trailer with a fixed tongue arrangement is hitched at the chosen hitch point.

With this understanding in mind, for a fixed trailer the tongue weight would obviously be fixed. So the total weight supported by the towing vehicle tires would be fixed regardless of hitch placement. The ratio of front tire force versus rear tire force would vary, of course.

An equalizing hitch could change things. We had one of those on our family's Shasta trailer back in the day. The torque at the hitch tended to off-load the towing vehicle rear wheels while loading up the trailer wheels and the towing vehicle front wheels.

Yes, 100%

The only change is the torque applied to the hitch itself due to the 20 inch lever. But the pounds of weight placed on the pickup chassis does not change.

 

[jeredpilot]

But I can have no confidence in the numbers, because posts like these contradict an extension of 20" between the axle-set and the modified hitch point.

If any one has not used words correctly, sir, it is you. I mentioned one such instance last evening from post number 18 and it was a bit more than you could stand.

I do appreciate your effort though.

But the answer is very simple. My configuration does not change the weight placed on the vehicle. Think about and you'll realize your error. But I am just a dumb layman with no degree in physics. What do I know? ;-)

 

[jbriggs444]

Yes, 100%

But you go on to contradict this understanding

The only change is the torque applied to the hitch itself due to the 20 inch lever. But the pounds of weight placed on the pickup chassis does not change.

A change to the moment arm does change the weight applied to the pickup chassis. Extending the moment arm allows the same torque to be provided by a different force at the hitch.

There are two changes. One is extending the moment arm. This tends to reduce the required support force. The other is the weight of the extension. This tends to increase the required support force. Which effect dominates depends on the weight and imbalance in the trailer and the weight and length of the extension.

 

[jeredpilot]

But you go on to contradict this understanding

A change to the torque does change the weight applied to the pickup chassis. Extending the moment arm allows the same torque to be provided by a different force at the hitch.

I completely disagree. The torque is a twisting force applied to the hitch itself.. The weight on the chassis remains constant. (this is assuming a parked, non-moving position)

Part of the whole problem with this discussion is "vocabulary" which I conceded from the first post I was not fluent in. As well as the imperfections of conveying thought through words, which is inherent in language itself.

 

[jbriggs444]

I completely disagree. The torque is a twisting force applied to the hitch itself.. The weight on the chassis remains constant.

This is not correct.

 

[jeredpilot]

This is not correct.

Okay. Please help me understand.

 

[jbriggs444]

Okay. Please help me understand.

The torque that I have in mind is from the chassis support force applied to the tongue of the trailer and assessed about a rotational axis at the trailer axle. Torque is computed as force times distance from the axis of rotation. The torque can be reduced if the force is not at right angles to that distance, but the two are perpendicular here, so no reduction is needed.

For the trailer to be supported without tipping (i.e. in equilibrium), this torque is fixed. At least until we contemplate any additional weight from the tongue extension.

If the torque on the trailer is fixed, the required support force will decrease when the distance from trailer hitch to trailer axle is increased.

 

[Baluncore]

But the answer is very simple. My configuration does not change the weight placed on the vehicle. Think about and you'll realize your error. But I am just a dumb layman with no degree in physics. What do I know? ;-)

You have too much confidence for a beginner.
As time moves on, maybe you will realize I was right, that the weight applied to the tractor hitch, will fall by almost 150 pounds.

Vocabulary: A "torque" in physics, is called a "moment" in engineering.

 

[jeredpilot]

You have too much confidence for a beginner.
As time moves on, maybe you will realize I was right, that the weight applied to the tractor hitch, will fall by almost 150 pounds.

Vocabulary: A "torque" in physics, is called a "moment" in engineering.

I am indeed a 'beginner'. But I have quite a lot of years of actual real-world experience in working with such things. So if I am incorrect, please accept my apologies.

I clearly understand I do not have enough knowledge to unequivocally solve this problem. That is why I am asking questions.

But yesterday at least, my questions offended you. That was not my intent.

 

[jeredpilot]

The torque that I have in mind is from the chassis support force applied to the tongue of the trailer and assessed about a rotational axis at the trailer axle. Torque is computed as force times distance from the axis of rotation. The torque can be reduced if the force is not at right angles to that distance, but the two are perpendicular here, so no reduction is needed.

For the trailer to be supported without tipping (i.e. in equilibrium), this torque is fixed. At least until we contemplate any additional weight from the tongue extension.

If the torque on the trailer is fixed, the required support force will decrease when the distance from trailer hitch to trailer axle is increased.

So by that, it appears you are in agreement with @Baluncore ?

You seem to be saying, the fixed 2,500 lbs will lessen due to an effective lengthening of the overall wheelbase? That is what I understood @Baluncore to be saying last evening.

 

[jeredpilot]

You have too much confidence for a beginner.
As time moves on, maybe you will realize I was right, that the weight applied to the tractor hitch, will fall by almost 150 pounds.

Vocabulary: A "torque" in physics, is called a "moment" in engineering.

And- My plan is to test our answers by using an actual certified truck scale.

I am serious about understanding this. And I am open and willing to be wrong; but I am not willing to misunderstand it.