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AUH failures

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jsalbre

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Assuming the frame of the hitch and the frame of the truck are both rigid and firmly atttached the position of the mounting points of the hitch are irrelevant from a force over the axle perspective. All that matters there is the location of the ball, and that is where the truck will “feel” the weight. I could put the mounting points all the way out at the stake pockets and if the ball is in the same place it would have the exact same effect.

This is not a comment on the merits of the AUH or any other hitch, just a clarification of physics.
 

Wmhjr

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Assuming the frame of the hitch and the frame of the truck are both rigid and firmly atttached the position of the mounting points of the hitch are irrelevant from a force over the axle perspective. All that matters there is the location of the ball, and that is where the truck will “feel” the weight. I could put the mounting points all the way out at the stake pockets and if the ball is in the same place it would have the exact same effect.

This is not a comment on the merits of the AUH or any other hitch, just a clarification of physics.

That is completely incorrect in terms of the AUS. Completely. Please look at the AUS structure. That lattice structure to the rear of the ball actually supports weight. If it did NOT then it would have no purpose. However, the architecture of the AUS demands that the rearward base place weight on the bed. That is the problem.

You are comparing the AUS to the effect of a B&W setback ball. That is a completely different design, and yes, it does not affect where the truck "feels" the weight. That is exactly the problem (or this particular problem) with the AUS.
 

Distillusion

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I'm going to have to disagree with your narrative. If in fact the frame of the truck is intended to be rigid (which I agree with) and if in fact the bed of the truck is relatively rigid with respect to mounting to the frame (which I mostly agree with), then positioning of weight is actually quite accurately that "fulcrum" concept. And in fact, as you move rearward behind the axle, you've added more arm length to that fulcrum. Now, I want you to recall that I never said "how much" the AUH should derate the truck. However, even in the apparently misunderstood threads concerning the movement of the GM "ball" (which is NOT the mounting of the assembly to the frame), actual weight measurements proved that moving that ball backwards increased the applied force by a resulting increased weight measurement at the pin - with the same exact trailer.

Now - my beef with the AUH and "derating" is that it doesn't move the application of weight an inch or so. It seems to significantly distribute that weight further back along the surface of the bed - at least back to the very back of the rear wheel houses. Now, how much weight does it move back there? We really don't know. And Anderson doesn't even mention it. Let's face it. Look at over the road tractors. Exactly how many of them have that pin all the way back? That would be none.

Now, when you combine this unknown change to weight distribution with people even using them in Cummins powered 2500's that already have a narrow payload window, to me it's like rolling the dice. Pulling a 9000lb trailer with a truck designed to PULL 18000lbs does NOT give you leeway if it's a gooseneck or 5th wheel trailer, on a truck with already limited payload. Then, you can even make it worse. If you then add air bags to stiffen the rear end, you're now lightening the front end of the truck further.

I do agree that the major issue with the design is - well - the design. We can argue all day long about how many AUH failures are the result of improper installation, etc. But we don't see those kinds of failures with B&W installed hitches do we? Gooseboxes? To me, if it were structurally sound (which frankly I don't believe) then one could just try and estimate the impact of that distributed weight. I believe you still should have to. I honestly think that there should be a very VERY caution and warning telling people about the likely change in applied pin load. But for me, it's like I said. Plenty of people have used them. Plenty of people drove Ford Pintos. A blind man can walk across a busy street and not get hit. That doesn't make any of those decisions "smart" - it just makes people a little luckier. Maybe your risk with the AUH isn't all that great. But I completely and totally believe it's a higher risk than with a traditional hitch assembly - and towing heavy is simply not something that I'm willing to take unnecessary risks with.
As I said, the physics is more complex. Yes, you add more length to the fulcrum as you move rearward past the axle, but the bulk of that weight change is around the fulcrum of the front axle, not the rear axle. The frame and engine are levering down on the front of the truck. Wheelbase of the truck is 149 inches. For example, let's say you have 10,000 lb trailer with 2,000 lbs on the kingpin, 2" in front of the rear axle. Torque around the fulcrum is 2000 lbs x .167 feet = 333 ft lbs. That puts 333 ft lbs of forward torque on the rear frame AT the axle - - down force ahead of the axle. Move the kingpin (or weight center) back to 2" behind the axle, back 4 inches, now it's moved to 333 ft lbs of rearward torque.

Now consider that the frame is rigid, as you agreed, it does not bend. The front curb weight of the truck keeps the truck from tipping backward due to forward torque of all the truck forward of the rear axle. If I recall correctly, the 2500 has about 65% of its unloaded weight on the front axle. I'll simplify and call it somewhere over 4,000 lbs of front axle weight. That's centered 149 inches ahead of the rear axle. The downward torque from this load rotating around the rear axle is 4000 lbs x 12.4 ft = 49,600 ft lbs of forward torque. Moving the trailer weight backwards 4 inches this is going to have little or no rotation effect on the rear of the truck. Sure, it counters a minute fraction of the front end weight, about 0.7% if you want to estimate. About 27 lbs of upward force at the front axle to counter the 4,000 lbs of downward force.

And if the hitch is rigid to the frame, you can't claim that the weight is redistributed to the back of the hitch body. It's distributed along the front of the hitch frame too, and any physicist or engineer will tell you that you'd calculate it at center of mass at the ball. If the AUH shifts the ball a few inches, then you calculate where the ball is shifted to, not to the back of the assembly. Because the bed is rigidly attached to the frame, and the hitch is rigidly attached to both, making all 3 into a single rigid structure. (With a weak point in the hitch construction, apparently.) But if the ball moved 4 inches, then my calculations above are reasonably accurate.

Of course, the effect of putting 2,000 lbs of extra weight on the rear axle does add load to the frame and axle at that point, and the rear suspension is going to compress slightly, depending on how it's configured. Putting it 2 inches ahead of the rear axle adds about 27 lbs to the front axle curb weight. Putting it 2" behind the rear axle reduces front axle curb weight by 27 lbs. Putting it directly above the axle does nothing to the front.

Last point - again - I said I didn't care about the AUH one way or another, I am just talking about the physics of the ball mounting location.
 

Distillusion

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That is completely incorrect in terms of the AUS. Completely. Please look at the AUS structure. That lattice structure to the rear of the ball actually supports weight. If it did NOT then it would have no purpose. However, the architecture of the AUS demands that the rearward base place weight on the bed. That is the problem.

You are comparing the AUS to the effect of a B&W setback ball. That is a completely different design, and yes, it does not affect where the truck "feels" the weight. That is exactly the problem (or this particular problem) with the AUS.
By your own logic, the lattice to the front of the ball actually supports weight too. If it did not then it would have no purpose. But in reality, the weight if rigid will be centered where the ball is. If the tubing or welds used aren't strong enough, that's a real issue with the construction. -
 

jsalbre

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That is completely incorrect in terms of the AUS. Completely. Please look at the AUS structure. That lattice structure to the rear of the ball actually supports weight. If it did NOT then it would have no purpose. However, the architecture of the AUS demands that the rearward base place weight on the bed. That is the problem.

You are comparing the AUS to the effect of a B&W setback ball. That is a completely different design, and yes, it does not affect where the truck "feels" the weight. That is exactly the problem (or this particular problem) with the AUS.
Well of course it supports weight. If it didn’t then the whole thing would tip over. But the front supports weight too, and all the weight that is put on the truck is centered over the ball, regardless of where the mounting points are, not matter what hitch you use.
 

Brutal_HO

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Well of course it supports weight. If it didn’t then the whole thing would tip over. But the front supports weight too, and all the weight that is put on the truck is centered over the ball, regardless of where the mounting points are, not matter what hitch you use.

In my mind, the supporting base of the AUH has as much to do with countering the lever effect of moving that ball (lever) up 16-17-18 inches(whatever that height is) as it does about supporting the (entire) pin weight that SHOULD be carried primarily at the base ball attachment. HOWEVER, the AUH installation is clear that you are pulling up on the gooseneck ball to secure the AUH, therefore transferring all that pin weight to the supporting base and through the tubes.

@Distillusion Not questioning your math entirely, but as mentioned, TFL measured 100 lbs less steer axle weight on the GM designed ball that sits 2" aft of the axle, but over the center of the spring pack. GM suggests it doesn't matter, but that's a Maury Povich Meme right there.
 

Wmhjr

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By your own logic, the lattice to the front of the ball actually supports weight too. If it did not then it would have no purpose. But in reality, the weight if rigid will be centered where the ball is. If the tubing or welds used aren't strong enough, that's a real issue with the construction. -
Again, not true. In this respect. When pulling uphill or accelerating, the weight will NOT be centered. It will be focused on the rear. Conversely, when braking or going downhill, that force will be focused on the front.

That being said, it doesn't matter where it's "centered" . BTW, you are assuming that the ball will be centered above that structure. I believe that is not always the case. If that load is distributed, then the highest force would be centered (when static and at rest) but that doesn't negate the fact that there will be force applied far to the rear of the axle.
 

Wmhjr

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Well of course it supports weight. If it didn’t then the whole thing would tip over. But the front supports weight too, and all the weight that is put on the truck is centered over the ball, regardless of where the mounting points are, not matter what hitch you use.
You really are not understanding the point. Again- "centered" is of relatively no merit if weight is still displaced to the rear.
 

Wmhjr

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any physicist or engineer will tell you that you'd calculate it at center of mass at the ball. If the AUH shifts the ball a few inches, then you calculate where the ball is shifted to, not to the back of the assembly.

This is completely inaccurate. I mean, wildly inaccurate. Wow. If that were the case, there would be a BUNCH of bridges that would have collapsed at this point.....
 

Wmhjr

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In my mind, the supporting base of the AUH has as much to do with countering the lever effect of moving that ball (lever) up 16-17-18 inches(whatever that height is) as it does about supporting the (entire) pin weight that SHOULD be carried primarily at the base ball attachment. HOWEVER, the AUH installation is clear that you are pulling up on the gooseneck ball to secure the AUH, therefore transferring all that pin weight to the supporting base and through the tubes.

@Distillusion Not questioning your math entirely, but as mentioned, TFL measured 100 lbs less steer axle weight on the GM designed ball that sits 2" aft of the axle, but over the center of the spring pack. GM suggests it doesn't matter, but that's a Maury Povich Meme right there.

This. Period

This is what I try to explain to people saying that you're redistributed weight behind the axle if you use a B&W ball extender or the offset adapter tube. In those applications, the actual gooseneck hitch and the ball (everything in the truck) remain exactly as they are, but the TRAILER is effectively extended back. Now, there is a slight reduction in pin weight in those applications because you've increased the lever arm. However, every ounce of load applied to the truck is applied in the standard position.

In this case, that is completely untrue. Effectively, the gooseneck ball receiver in the truck is there primarily to prevent horizontal movement. It "locks" the horizontal plane (and obviously keeps it from releasing). However, actual LOAD is applied all around the base. You've further created another lever arm multiplying that force being applied to the ball - which if I'm not mistaken can also be moved rearward to create offset for SWB trucks?

That's why the math that Distillution is trying to use is inaccurate. This is a good discussion, but it's frankly pretty obvious.

1 Where "most" of the weight is "centered" does not change the fact that there is more weight being applied to different points on that lever (front to back of frame respective of axle).

2. The effect of raising the ball (and moving it's location) amplifies force to the front and rear when braking or accelerating, etc.

3. Actual physical tests weighing pin weight have demonstrated a measurable change when displacing the ball by even just 2"

4. The architecture of the lattice goes back to the rear of the wheelhouse, creating force downward there.

5. Then add to this the flex that has TO occur in the aluminum struts and pinched tubes - which leads to the other (and frankly more important) concerns about failure.
 

kobra

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Wow, there's been lots of discussion here... It's clear opinions are divided on what the effect of the AUH ball location will have...

But, the original assertion was that the design of the AUH would "derate the carrying capacity". That has been proven false.

As I pointed out and was confirmed by @Brutal_HO , the latest generation of GM's have moved the ball behind the rear axle AND this has materially affected the weight distribution when hitched up - as TFL truck tested, the front axle weights were lighter by 50lbs+ when hitched. And yet, and this is the point to me, GM still passed all of the safety certifications necessary, and it did NOT reduce their carrying capacity. As I originally responded, some of the CCC actually went up on some of the new models.

What does that confirm, that has been true all along? CCC is a rating of the difference between the GVWR and the defined unladen weight. It is NOT -and never has been- a rating of where that load is carried.

Despite lots of opinions and lots of conjecture, I don't see anything about this discussion has proven the design to be inherently unsafe.

Now, do you know what absolutely will "derate the carrying capacity"? Adding more weight to the truck... such as adding a hitch that weighs 200-300lbs more than the AUH.
So, we bicker over a shift in weight of 27lbs, or maybe 50lbs or 100lbs, but we ignore that the AUH has improved practical carrying capacity by 200+ pounds?

B
 
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Distillusion

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This. Period

This is what I try to explain to people saying that you're redistributed weight behind the axle if you use a B&W ball extender or the offset adapter tube. In those applications, the actual gooseneck hitch and the ball (everything in the truck) remain exactly as they are, but the TRAILER is effectively extended back. Now, there is a slight reduction in pin weight in those applications because you've increased the lever arm. However, every ounce of load applied to the truck is applied in the standard position.

In this case, that is completely untrue. Effectively, the gooseneck ball receiver in the truck is there primarily to prevent horizontal movement. It "locks" the horizontal plane (and obviously keeps it from releasing). However, actual LOAD is applied all around the base. You've further created another lever arm multiplying that force being applied to the ball - which if I'm not mistaken can also be moved rearward to create offset for SWB trucks?

That's why the math that Distillution is trying to use is inaccurate. This is a good discussion, but it's frankly pretty obvious.

1 Where "most" of the weight is "centered" does not change the fact that there is more weight being applied to different points on that lever (front to back of frame respective of axle).

2. The effect of raising the ball (and moving it's location) amplifies force to the front and rear when braking or accelerating, etc.

3. Actual physical tests weighing pin weight have demonstrated a measurable change when displacing the ball by even just 2"

4. The architecture of the lattice goes back to the rear of the wheelhouse, creating force downward there.

5. Then add to this the flex that has TO occur in the aluminum struts and pinched tubes - which leads to the other (and frankly more important) concerns about failure.
Your private theories of mathematics and physics defy all Newtonian laws. By your own definitions and theories, the weight of a diver standing on a diving board would cause torque backwards away from the pool.

Bridges are not rigid bottomed lattices. They are designed with a certain amount of flex, and they have specific structural mounting points. They are called "spans" for a reason.

The AUH design does not have separate legs acting as levers. It has a pyramidal shape, with a solidly attached bottom. It may be weak, but it is from a physics standpoint equivalent to a pyramid shaped block of wood in how it distributes the trailer hitch weight to the truck. Take the same block, drill some holes in it to reduce weight, now you have struts. Your "theory" of how that weight all gets distributed to the rear of the ball along "levers" is just bad science fiction.

Having the ball raised causes towing force backward from the ball, as a torque around the rear axle. But that torque is going to be essentially the same for any hitch where the ball is raised that far above the axle. Moving it forward or backward several inches will not appreciably change the amount of torque.
 

Distillusion

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In my mind, the supporting base of the AUH has as much to do with countering the lever effect of moving that ball (lever) up 16-17-18 inches(whatever that height is) as it does about supporting the (entire) pin weight that SHOULD be carried primarily at the base ball attachment. HOWEVER, the AUH installation is clear that you are pulling up on the gooseneck ball to secure the AUH, therefore transferring all that pin weight to the supporting base and through the tubes.

@Distillusion Not questioning your math entirely, but as mentioned, TFL measured 100 lbs less steer axle weight on the GM designed ball that sits 2" aft of the axle, but over the center of the spring pack. GM suggests it doesn't matter, but that's a Maury Povich Meme right there.
Brutal, I would offer that I just used an imaginary trailer pin weight of 2,000 lbs. (20% of a hypothetical 10,000 lb trailer.) If I recall correctly, TFL used a higher actual pin weight of 3,000 lbs, so the effects of the calculation would be at least 50% higher. Wheelbase difference between the Ram and the GM also impacts the calculation. The TFL guys typically measure the axle weights on commercial truck scales, which could be off a bit. I think the standard for big scales is +/- 50 lbs, although some are +/- 20 lbs??? And to top that off, we don't know if it's an exact 2" behind the axle. If it's 2.5, there's an even bigger shift.

Yes, the transfer of all the pin weight through the tubes to the bottom is absolutely correct. Pulling on the gooseneck ball has the effect of making it a rigid structure - at least until structural damage occurs, or unexpected flex. If the AUX used solid steel instead of hollow tubing, there would probably never be a structural failure.
 
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Distillusion

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Again, not true. In this respect. When pulling uphill or accelerating, the weight will NOT be centered. It will be focused on the rear. Conversely, when braking or going downhill, that force will be focused on the front.

That being said, it doesn't matter where it's "centered" . BTW, you are assuming that the ball will be centered above that structure. I believe that is not always the case. If that load is distributed, then the highest force would be centered (when static and at rest) but that doesn't negate the fact that there will be force applied far to the rear of the axle.

Now you are conflating pin weight and momentum. Pin weight of a trailer will remain centered down on the pin. After all, it's gravity that's pulling it down, not the truck's driving. Momentum of the trailer mass is much greater than pin weight. In my example, you have 10k mass of the trailer, and only 2k of pin weight. Accelerating is overcoming momentum. Driving uphill is doing the same, as gravity pulls downward on the rest of the trailer. THAT combination of forces result in backward torque around the axle. Since the frame of the AUH is levered against the bed, which is levered against the frame, which is all rigid, the whole force applied is a torque effect on the frame as a whole, around the axle. Pretty straightforward. The torque would be calculated as a force applied at the pin height, which would be the direct distance from center of axle cross section to center of ball.

If the ball is centered 12" up from the axle, the distance 12 inches or 1 foot. If you then move the ball back two inches at the same height, it's a simple triangle/hypotenuse calculation. It would be 12.2 inches.

The apparent effect is that seemingly the truck front end is light from massive weight DOWN on the back. But it's not actually down weight, as that's all still resting on the trailer tires. It's actually just force backwards at the ball - above the axle, like a massive wrench, which becomes angular momentum or torque around the rear axle, lifting the front end of the truck up, but not applying the weight of the trailer to the rear axle.
 

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If you mean the whole thread has overestimated the title, then I agree completely, lol

B
 

Wmhjr

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Your private theories of mathematics and physics defy all Newtonian laws. By your own definitions and theories, the weight of a diver standing on a diving board would cause torque backwards away from the pool.

Bridges are not rigid bottomed lattices. They are designed with a certain amount of flex, and they have specific structural mounting points. They are called "spans" for a reason.

The AUH design does not have separate legs acting as levers. It has a pyramidal shape, with a solidly attached bottom. It may be weak, but it is from a physics standpoint equivalent to a pyramid shaped block of wood in how it distributes the trailer hitch weight to the truck. Take the same block, drill some holes in it to reduce weight, now you have struts. Your "theory" of how that weight all gets distributed to the rear of the ball along "levers" is just bad science fiction.

Having the ball raised causes towing force backward from the ball, as a torque around the rear axle. But that torque is going to be essentially the same for any hitch where the ball is raised that far above the axle. Moving it forward or backward several inches will not appreciably change the amount of torque.

Well, I guess we found common ground, as I believe your understanding of math and phyics are apparently as equally flawed as you consider mine. I have no idea where you're getting your analogies, and further, you're describing something quite different with respect to bridges.

Thats said, let's make it simple, shall we?

Go find a AUH. Stick you fingers under the rear most sideways base rail. It will be located at the very rear of the rear wheelhouse.

Now, go ahead, and have somebody hitch up a nice heavy fifth wheel or gooseneck.

If you still have fingers left, you're correct.

If you don't, then I guess you've got some 'splainin to do... lol!
 

jsalbre

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Well, I guess we found common ground, as I believe your understanding of math and phyics are apparently as equally flawed as you consider mine. I have no idea where you're getting your analogies, and further, you're describing something quite different with respect to bridges.

Thats said, let's make it simple, shall we?

Go find a AUH. Stick you fingers under the rear most sideways base rail. It will be located at the very rear of the rear wheelhouse.

Now, go ahead, and have somebody hitch up a nice heavy fifth wheel or gooseneck.

If you still have fingers left, you're correct.

If you don't, then I guess you've got some 'splainin to do... lol!

You’re arguing against a point that no one is making.

No has said there isn’t weight on all the mounting points (including the rear one).

What we’re saying is that the location of the mounting points has no bearing on where the whole system experiences the force.

Imagine you built a cart with 4 wheels and a hitch ball in the center with a trailer’s weight on it, then put each wheel on a scale and recorded the weight. If you now lifted that ball straight up and put it on legs it wouldn’t matter where those legs were attached to the cart, each scale would show exactly the same number they showed before (with the exception of the weight of those new legs themselves).

(Again, none of this is to say that the AUH is good, bad, or a flying purple unicorn. I’m just speaking about the physics.)
 

Wmhjr

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You’re arguing against a point that no one is making.

No has said there isn’t weight on all the mounting points (including the rear one).

What we’re saying is that the location of the mounting points has no bearing on where the whole system experiences the force.

Imagine you built a cart with 4 wheels and a hitch ball in the center with a trailer’s weight on it, then put each wheel on a scale and recorded the weight. If you now lifted that ball straight up and put it on legs it wouldn’t matter where those legs were attached to the cart, each scale would show exactly the same number they showed before (with the exception of the weight of those new legs themselves).

(Again, none of this is to say that the AUH is good, bad, or a flying purple unicorn. I’m just speaking about the physics.)

Let's agree to disagree. As a pilot for example, I simply can't even begin to comprehend how this is so difficult for people to understand - and clearly we're going to continue to disagree. Further, you're even making the fundamental mistake of assuming that the ball is in the center.

Let's do it differently. Put that "pyramid" on that scale - and not pull back on the top. What happens? There's a hint....... You guys are disregarding some pretty obvious fundamentals IMHO.
 

regal2800

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Showed up on my feed. Made me think of this chat. Not sure what happened but interesting to see.

 
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