Andersen Weight Distributing Hitches

[Brian B-P]

Originally Posted by Jim Bennett

... I did learn how to discern between horizontal and vertical. I just don't see what horizontal movement has to do with weight distribution. Potential for sway, yes.

Jim, you don't see it because it does not exist. I agree, yaw oscillations (relative motion between the tug and trailer about the vertical axis, or in the horizontal plane) do not change the WD action of the Andersen No-Sway system.

[Brian B-P]

Originally Posted by MC1

There are many sources that talk about the WD limitations of the Andersen. Post #684 here sums it up the best. Also review the many weigh scale slips posted by Andersen users and you will see it is very limited by it's design.

The Andersen WD Hitch User Thread - Page 49 - Airstream Forums

Thanks for the direct link to the page of interest... post #684!

That post is by the well-known Andy Thompson of Can-Am RV. It is interesting that this is called out as the best summary, when it is immediately followed by posts by others who do not find the same limitation. Also, Andy doesn't show any illustration of the system setup beyond the degree of spring compression: we don't know if the chains are angled properly, for instance. He also reports no axle loads or hitch weight; this is typical of Can-Am RV, who sell $90,000 trailers but can't come up with ten bucks for a truck scale check of axle loads, and sell $3000 hitches but don't have a $150 tongue weight scale (I know, I asked them).

Without facts, Andy's comments are as Andy's comments about any towing subject usually are: interesting, but not fully developed enough to be of value. Just my opinion, of course... Months later, Andy did rejoin this discussion, and even discussed axle loads of a completely different rig with a completely different WD system (despite this being specifically the Andersen WD users thread) - so we know he can use a scale - but he never addressed any questions about his Charger/Airstream/Andersen setup. Such a missed opportunity...

I'll admit to not looking for those scale slips by Andersen users who do believe in measurement; the one that I noticed in earlier research showed axle loads and WD action right in the typical range for many FiberglassRV members' rigs, without requiring excessive compression of the urethane spring. That one was properly installed; I don't know about others.

My comments about chain angle and proper installation refer to a likely installation problem: if the chains are angled up toward the tongue, instead of level, the vertical component of the chain tension and increased downward load on the ball will produce no useful action, but will require more spring force for the same useful horizontal component of tension. This will happen if the frame brackets are not set to extend downward far enough, limiting the effectiveness of the WD system in much the same way as placing the chain bracket of a conventional WD system too far forward or back (instead of directly above the bar ends). Post #704 in the same Air Forums thread shows a moderate instance of this error by another member... although after 400 miles pulling a 27' Airstream he had still no problems with the setup.

[honda03842]

Originally Posted by Brian B-P

This is a common problem with discussion of WD systems, although usually regarding the front axle: people say that after the trailer is hooked up and without WD the front tires are "barely touching", when if fact they are carrying only a few percent less load than without the trailer.

Glad to read the above statement. Our front wheel drive vehicle has most of it's weight (60%) on the front axle and our 200 lb tongue weight is small compared to the existing load on the front axle.

I have enjoyed the discussion of the Anderson WD system.

[Brian B-P]

Originally Posted by honda03842

... our 200 lb tongue weight is small compared to the existing load on the front axle.

In addition, if the distance from rear axle to ball is - for instance - 40% of the wheelbase, the reduction in front axle load due to the trailer's weight on the hitch will be only 40% of that 200 pounds... or 80 pounds. Of course, most people considering WD with an egg are talking double that hitch weight or more, and thus maybe a couple hundred pounds front axle load change. In my case (and I don't use WD), it's 160 pounds, or about 4% of the front axle load.

Originally Posted by honda03842

I have enjoyed the discussion of the Anderson WD system.

It's entertainment for mechanical techies, also hopefully useful to trailer towing people.

[Byron Kinnaman]

Originally Posted by Brian B-P

Andersen design is just like every other WD system.

I disagree with this statement. Most WHD systems use spring bars (often incorrectly call torsion bars) to apply forces in the other axis. If looked from the side at the Anderson system the forces are applied from front to back along the tongue and the chains.
Standard WHD systems apply forces as seen from the side are applied up and down, along the chains and at the ball.

[honda03842]

Originally Posted by Brian B-P

In addition, if the distance from rear axle to ball is - for instance - 40% of the wheelbase, the reduction in front axle load due to the trailer's weight on the hitch will be only 40% of that 200 pounds... or 80 pounds. Of course, most people considering WD with an egg are talking double that hitch weight or more, and thus maybe a couple hundred pounds front axle load change. In my case (and I don't use WD), it's 160 pounds, or about 4% of the front axle load.

The above statement is the kind that's helps new trailer towers showing the importance of wheelbase and the importance of distance from the ball to axle.

We recently moved our ball 2+" closer to the rear axle. It's obviously a small difference but in the right direction.

[MC1]

Originally Posted by Byron Kinnaman

I disagree with this statement. Most WHD systems use spring bars (often incorrectly call torsion bars) to apply forces in the other axis.

Trivia... Back in the 60's my dad obtained a dealership for the Equalizer brand of WDH's. At that time the company rep called them torsion bars. On the Eq web site they now call them spring bars. Reese calls their bars round bars and trunnion bars.

[Jim Bennett]

The bottom line is that with the well proven torsion(or whatever your preferred terminology is) bar WDHs and the new Andersen ones, is that they both provide forward rotational torque on the ball hitch, effectively redistributing the hitch weight. They both use a different approach, but the resultant is the same. Maybe the older system can provide more torque, but for my trailer, the Andersen hitch has proved to provide more than adequate torque, and I had to even dial it back a bit.

[Brian B-P]

Originally Posted by Jim Bennett

The bottom line is that with the well proven ... bar WDHs and the new Andersen ones, is that they both provide forward rotational torque on the ball hitch, effectively redistributing the hitch weight. They both use a different approach, but the resultant is the same.

[Brian B-P]

Originally Posted by MC1

Trivia... Back in the 60's my dad obtained a dealership for the Equalizer brand of WDH's. At that time the company rep called them torsion bars.

Arggggh. One of many anecdotes which demonstrates why sales people should not be taken seriously on anything but pricing.

Byron is right - the spring bars are not used in torsion. They are cantilever bar springs (meaning that they are anchored at one end and pulled on the other end to bend).

Can we all promise never to use the "T-word" in connection to these spring bars again?

[MC1]

Originally Posted by Brian B-P

Arggggh. One of many anecdotes which demonstrates why sales people should not be taken seriously on anything but pricing.

The guy was the owner of the company.

[Brian B-P]

Originally Posted by Byron Kinnaman

I disagree with this statement.

I would disagree with that statement, too! Here's what I actually posted, with enough context to retain the meaning, and with added emphasis:

Originally Posted by Brian B-P

The hitch is not trying to push the tug forward, or pull it rearward; there is no net horizontal force. It is also not fundamentally trying to lift it up, or squash it down... although tug is lifted somewhat by the trailer due to the reactions to this torque. In this respect, the Andersen design is just like every other WD system.

The Andersen is not just like every other WD system in every respect; if it were, we wouldn't be discussing it. Some characteristics are alike, which is not surprising to me given the common purpose and common operating scenario (a ball hitch).

Originally Posted by Byron Kinnaman

Most WHD systems use spring bars (often incorrectly call torsion bars) to apply forces in the other axis. If looked from the side at the Anderson system the forces are applied from front to back along the tongue and the chains.
Standard WHD systems apply forces as seen from the side are applied up and down, along the chains and at the ball.

All true. In both traditional and Andersen systems, as I said, there is no net horizontal force due to WD system application.


I'm not sure that we're making much further progress toward enough understanding of the Andersen No-Sway to enable FiberglassRV members to assess whether or not they are interested in using this product to tow their trailers. Maybe everyone agree to at least some basics:

1. The Andersen No-Sway Weight Distribution system provides redistribution of load between the tug and trailer axles.
2. It can do this at levels useful for typical egg owners who have enough tongue weight to want WD action.
3. Rotation in the sway direction (yaw) is resisted by substantial friction, which helps reduce sway by damping the oscillation.
4. The details of how much force is applied to what component and in what direction are different from conventional two-bar WD systems, leading to different potential issues to consider.
5. The Andersen springs are hollow urethane cylinders in compression, while the conventional WD springs are steels bars in bending mode.

[ONEFORD]

Originally Posted by Brian B-P

I think this might be the most extensive discussion of the Andersen No-Sway Hitch so far in this forum:
http://www.fiberglassrv.com/forums/f...tch-57733.html It has been the subject of much discussion - some quite heated - in other forums.

I agree that it is an interesting design. That load on the back of the coupler is enormous, and is the most negative aspect of the product in my opinion.

As for suiting small trailers, I note that it comes in only one "size", so it is heavier than necessary and probably stiffer than ideal for most FiberglassRV members.

It can be adjusted to any weight transfer load down to the pound. Just turn the nut putting pressure on the die springs.

[ONEFORD]

Originally Posted by MC1

I agree. It is a huge load. Note the Andrsn is not compatible with at least one coupler and that is not mentioned when you buy it from Andrsn. Buyer beware.
Not

It is mentioned now and comes with a warning note also.

[Jim Bennett]

Originally Posted by Brian B-P

Byron is right - the spring bars are not used in torsion. They are cantilever bar springs (meaning that they are anchored at one end and pulled on the other end to bend).

The name most likely comes from the fact the bars applied torsion to the hitch, not that the bars themselves were in torsion.

[ONEFORD]

http://www.fiberglassrv.com/forums/members/37127-albums959-picture4736.html

It works! 4,000 miles of towing this year.3500LB trailer 400lb ton weight. Back to factory weight ratio on front and rear ,Sitting Level. Towed in 50mph cross winds with no sway. Don't have to unhook to back up, Doesn't have that loud metal snapping/sqeeking noise conventional have. Can adjust weight transfer down to the pound ,conventional has to go a link at a time. Only weigh's 52 pounds, conventional weigh's around 100lbs (have to add to ton weight).

[Brian B-P]

Originally Posted by ONEFORD

It can be adjusted to any weight transfer load down to the pound. Just turn the nut putting pressure on the die springs.

I understand that it can be adjusted as low as desired - it is more finely adjustable than conventional designs. The problem with only one spring stiffness is that if the trailer pitch angle changes, the change in force is excessive for a light tug and trailer. This is like conventional WD systems but with only one choice of spring bars: you can pull on the chains only a little bit to get the small amount of WD action required, but if you drive though a dip the overly stiff bars take too much force to bend.

Die springs? Off to a Google search.... there we go, an example: urethane compression springs Thanks - I hadn't heard that term. The "die" idea isn't very important here, but this randomly found supplier has a page about Urethane Spring Characteristics that people might find interesting.

I've seen the Andersen product in person, but didn't take measurements... does anybody have the (uncompressed) diameter, inside diameter, and length of the urethane springs?

[jwcolby54]

I think a graphic visual example would help.

Imagine that the hitch ball was replaced by a hollow very stout ring. IOW in the Anderson rig simply pull that ball thingie out. What remains is a very stout ring (well cone, but same thing).

Now place a 10 foot long steel bar down into that hole until the bottom barely touched the ground.Start pushing forward on the top of that bar, 10 feet up in the air.

What happens? The front of the car will be pushed down! The entire TV will attempt to rotate around the ring. If it were suspended in the air, the TV would start to spin around the ring, with the front bumper (and everything in between) moving down.

You are applying rotational force in an axis parallel to the bumper, in the plane where the hitch "ring" is attached. EVERYTHING forward of the axis of rotation tries to move downwards, applying more and more downward movement, the further you move towards the front of the TV. So assuming that the rotational axis stayed the same distance from the ground, you would actually cause the rear axle to drop, but the front axle to drop MORE.

So, replace the bar with the springs. The springs PULL the bottom of the tow hitch backwards and PUSHES the TOP of the hitch forwards, creating the same rotational action around the same point as we were doing with that bar.

However since we are attached to the trailer...

Turn your focus around for a moment and consider that you are applying an identical rotational force around the same axis, in the same plane, to the trailer. The rubber things act as a spring, PULLING the bottom of the trailer towards the tow vehicle and PUSHING the top of the ball towards the trailer. You have a rotational vector again, pushing the back of the trailer down.

You are now pushing the 10 foot bar TOWARDS the trailer which tries to push DOWN on EVERYTHING "aft" of the axis of rotation,

Voila, the front of the TV tries to move down, the REAR of the Trailer tries to move down, and the axis of rotation tries to lift. As long as the axis of rotation is free to move vertically (which the rubber and the ball allows) it will in fact rise.

If the trailer and the TV were welded solidly together, you would end up with a teeter totter! Assuming the bar again (remember the bar?) the front of the TV would drop and the trailer would RISE!

However since the axis of rotation is free to rise, and since lift is being generated from both directions, lift at that rotation point can (and does) occur.

The the ball forms the pin of a hinge, with the chassis of the TV and the trailer forming the hinge "plates". The spring connects the two plates, just like the spring on a door in your house.

The force vectors push up "under" the pin of the hinge and down at each edge of the hinge plates (the forward TV axle and the trailer axle).

The rear TV axle lifts simply because it is attached part way back on one of the hinge plates (the TV).

Whew!

Or at least that is my "vision" of how things work here.



Easy to visualize, hard to describe!

[Night Sailor]

The Anderson WDH is IMHO well suitable for light trailers which is why I started this thread. Perhaps Anderson will eventually sell a lighter weight version. I can see myself using one of these, if I towed longer distances with an Egg camper, and had a beefy coupler. I can also see myself modifying one to make it lighter without compromising strength. Then again 50 lbs is not that bad.

While some of the discussion might seem redundant, this forum more than an Airstream forum seems to be the place where it belongs as these WD hitch seem perfectly suitable for dialing in smaller amount of weigh redistribution and less suitable for heavy Airstreams trailers.

For those of you still confused about how it works, there are a number of video's on it both on youtube and the Anderson web site. Re-reading some of the posts here an elsewhere might help you get a grasp of it.

Thanks for the many responses. I particularly enjoyed reading Jim Bennet's real world user comments and those of other Andersen owners.

The chart posted was very interesting, as were the various summaries and discussions. I would have a hard time singling out the many excellent posts.

It anyone would care to let photos of their hitches that would also be appreciated.

[cpaharley2008]

Here a couple of pictures, the urethane bushings are approximately 2x4"