Hitch height - please check my math

[JazzDad]

http://www.airforums.com/forums/f437...e-87787-2.html

(I hijacked my own thread, so I pose this over here now.)

OK, I've already been told I'm over-thinking some of this stuff, but...

The top of the TV receiver is at 16.5 inches from the ground, loaded. The top of the ball, for the trailer to be level, should be 18.25 inches. Assuming the ball height to be 3 inches, I think I need a drawbar with 1.25 inches of drop. The closest increment seems to be a 2 inch drop, which would make the trailer nose low by 0.75 inches. (This would be better than going with a straight stinger that would then put the front of the trailer too high.) I don't see where an adjustable hitch bar would get me any closer. Your thoughts?

[Single axle trailer.]

[AWCHIEF]

I went thru the whole process recently myself, finally got her all nice and level. Now I am going to have do it all again. I am getting a new axle, hopefully will raise the unit up 4 or 5 inches. Going to be needing a new receiver and have no way of knowing until after the new axle is installed and I can measure it all over again. It's not really rocked science, just a bit of fuzzy math and trail and error.☺

[Jammer]

Most of the weight distributing hitches have adjustable heads so it shouldn't matter much. Getting everything lined up will require a certain amount of trial and error.

You are using WD, right? If not, the 2" drop ball carriers are the most common and are reversible so you can get roughly 1" rise by turning them over and mounting the ball the other way.

[overlander63]

Hitch and ball height is not as critical on single axle trailers. If it's 3/4" low in front, that should be "good enough".

[JazzDad]

I am going to try it without a WD hitch. When I put the tongue weight on the truck, the receiver goes down nearly 2 inches. The rear wheel well drops 1.4 inches and the front drops 0.25 inches. The truck has built-in sway control and an integrated brake control (supposedly giving even the trailer anti-lock braking). I figure I can try it, then get a WD hitch if needed. I have been challenged to find one with bars that are in the 400 lb range so I wouldn't hammer the trailer.

Oh, this trailer has a 2 5/16" ball, so it's hard to find one of those flip-over hitches with that combination.

[TG Twinkie]

Jazzdad;
If you have a farm supply store like Big R you will find they carry much more in the way of hitch supplies than a auto parts store.
2 5/16" ball mounts are pretty common on farm trucks.

[Jammer]

I would strongly suggest WD for safety reasons.

Andy Rogozinski has been the source for the claim that heavy WD bars "hammer" the trailer. I respectfully believe that he's wrong, as do a number of other forum members with an engineering background (I agree with Andy that the large unsprung load, high rear axle spring rate, and light rear axle loading associated with unusually and disproportionately heavy tow vehicles with empty beds poses a problem. I just don't concur with his claim that the WD bars have something to do with it).

If you believe the readily available 600 pound spring bars are too heavy then you could tighten them less or just use one spring bar.

[ROBERT CROSS]

Jam's right on....

Also strongly recommend a WD hitch w/sway control,esp with single axle.

Ball height not as important as the TV and trailer being LEVEL with the proper weight transfer.

Bob

[Inland RV Center, In]

Originally Posted by Jammer

I would strongly suggest WD for safety reasons.

Andy Rogozinski has been the source for the claim that heavy WD bars "hammer" the trailer. I respectfully believe that he's wrong, as do a number of other forum members with an engineering background (I agree with Andy that the large unsprung load, high rear axle spring rate, and light rear axle loading associated with unusually and disproportionately heavy tow vehicles with empty beds poses a problem. I just don't concur with his claim that the WD bars have something to do with it).

If you believe the readily available 600 pound spring bars are too heavy then you could tighten them less or just use one spring bar.

Jammer.

When excessive rated bars are used, based on my 46 years of observations, damage to the trailer is very likely.

I have recommended dropping the bar rating to many owners over the course of those years, and yet, not one single person has stepped forward and said that was wrong. Those that did communicate, as some have on this Forums, the trailer ride improved and the damages stopped.

Extra heavy bars, extra heavy duty tow vehicles, have almost always caused damages to the Airstream products.

If my recommendation is wrong, then why "no" negative feedback.

I can also add, that when a trailer was restored to original condition, that was damaged by using excessive rated bars, the damage happen again. That bears out the cause.

On the other hand, if the front end of the trailer was beefed up, then using the excessive rated bars no longer caused a problem.

The problem is for the owner of original equipment. They pay more money for the heavier bars, when they are not needed.

Not to argue in any way, but no one has come forward with any documentation, or facts, that the excessive rated bars will not cause damages.

Dropping an extra link or two, really defeats the purpose of the load equalizing hitch, when using excessive rated bars.

It's common knowledge that the heavier the bars, the stiffer the ride. When that is coupled to a heavy duty tow vehicle, then even more road shock is transfered to the trailer. We all know that an Airstream "MUST" have a soft ride, or else. Same is true for a torsion axle that has bad rubber rods. For years many people felt that did not hurt anything. Today's feedback says the exact opposite.

Opinions are great, engineers opinions are usually even greater, but they cannot out rule simple facts.

Damages most often, have a cause behind them. Ignoring them, won't make it go away.

If I am wrong, then "what does cause the front end damages to an Airstream product" ?

Yes, sometimes it's Airstream problem, but most of the time it's the problem of the owners.

Until such time that it can be demonstrated that my theory is incorrect, I will to the best of my ability promote the "soft ride" hitching and tow vehicles.

That to me, is far better than saying "OH WELL", things happen.

Physics is pretty well straight forward.

Andy

[Jammer]

Andy,

I thought we'd been through this before on another thread. I do want to start by saying that I have the deepest respect for the knowledge and judgment that you gained through many years of work at Caravanner and subsequently at Inland RV.

As I note above, I agree with you that heavy rear suspension in the tow vehicle can damage the trailer, especially when the tow vehicle is lightly loaded -- as is so often the case with a pickup. This is because of the considerable hitch forces generated by the heavy tire and axle assembly being thrown upwards when the tires hit a bump, and it happens regardless of the size of the WD bars in use, and indeed whether there are WD bars in use at all. The problem is a combination of the large unsprung weight together with the high spring rate in the truck suspension, and the relatively small mass of the truck bed and front portion of the trailer.

I would be surprised to learn that slightly oversize bars on a suitable tow vehicle pose any problem. The physics isn't there. The load they pose is nearly all static. You could measure the tongue deflection with a straightedge and a dial indicator.

[Inland RV Center, In]

Originally Posted by Jammer

Andy,

I thought we'd been through this before on another thread. I do want to start by saying that I have the deepest respect for the knowledge and judgment that you gained through many years of work at Caravanner and subsequently at Inland RV.

As I note above, I agree with you that heavy rear suspension in the tow vehicle can damage the trailer, especially when the tow vehicle is lightly loaded -- as is so often the case with a pickup. This is because of the considerable hitch forces generated by the heavy tire and axle assembly being thrown upwards when the tires hit a bump, and it happens regardless of the size of the WD bars in use, and indeed whether there are WD bars in use at all. The problem is a combination of the large unsprung weight together with the high spring rate in the truck suspension, and the relatively small mass of the truck bed and front portion of the trailer.

I would be surprised to learn that slightly oversize bars on a suitable tow vehicle pose any problem. The physics isn't there. The load they pose is nearly all static. You could measure the tongue deflection with a straightedge and a dial indicator.

Jammer.

I think we are both saying the same things, but in different words.

Slightly oversized bars is not the proble. The problem is when 1200 and 1400 pound bars are used with a tongue weight of 500 to 600 pounds.

The static load, is not in question.

The load when a bump is hit, "is the question".

How big was the bump? Who knows, but we all know they are out there.

Now the question becomes how much energy is transfered to the A-frame, when that bump is hit?

Therein, lies the problem. Instead of the bars flexing because of the bump, when they are too strong, that flexing does not take place, as it should.

It's also interesting to note, that the majority of time that front end damage happens, the bars are usually Equalizer. Tests clearly indicate that the Equalizer bars, have the least bend to them when compared to other brands of equal ratings, when loaded the same amount.

Resilency within the bars, is extremely important.

Andy


Andy

[exthemius]

Originally Posted by Inland RV Center, In

Slightly oversized bars is not the proble. The problem is when 1200 and 1400 pound bars are used with a tongue weight of 500 to 600 pounds.

Andy

What about 1000# bars with a ~600lb tongue weight?

[Inland RV Center, In]

Originally Posted by exthemius

What about 1000# bars with a ~600lb tongue weight?

The rating of the bars depends on 2 things.

The trailer tongue weight and the exact tow vehicle.

What tow vehicle do you have?

The heavier the tow vehicle duty, the lighter tha bars should be.

In your case, unless your using a car, the bars are over rated.

And, if you are using a car, 750 to 800 pound bars are plenty.

Andy

[Jammer]

In the context of this thread, the OP has a 4500 pound trailer and is concerned about using 600 or 800 pound bars. I think that concern is misplaced.

I have never used the Equal-i-zer hitch myself. If the bars are too stiff it would show up first when crossing a dip as when entering a driveway or other incline. That is where the stress placed on the a-frame by the bars would be the greatest. The stress from the truck rear axle when hitting a bump would tend to relax the wd with the shock absorber on the truck taking the hit on the downstroke.

[Inland RV Center, In]

Originally Posted by Jammer

In the context of this thread, the OP has a 4500 pound trailer and is concerned about using 600 or 800 pound bars. I think that concern is misplaced.

I have never used the Equal-i-zer hitch myself. If the bars are too stiff it would show up first when crossing a dip as when entering a driveway or other incline. That is where the stress placed on the a-frame by the bars would be the greatest. The stress from the truck rear axle when hitting a bump would tend to relax the wd with the shock absorber on the truck taking the hit on the downstroke.

Jammer.

If the bump is a speed bump, then the front wheels of the tow vehicle get hit first, which drives down the rear, which adds stress to the bars. When the rear wheels hit the speed bump, then when they return to level, they should lower to some degree, however momentary, which again, adds stress to the bars.

When a chug hole is hit by a front wheel and the by the rear wheel of the same side of the tow vehicle, then the front wheel offers little change, but the rear wheel dropping in the hole, will add stress to the hitch bars.

Of course, that all depends on the depth of the chug hole. The deeper, the worse the reaction becomes.

Andy

[exthemius]

[QUOTE=Inland RV Center, In;1112994]The rating of the bars depends on 2 things.

The trailer tongue weight and the exact tow vehicle.

What tow vehicle do you have?

The heavier the tow vehicle duty, the lighter tha bars should be.

In your case, unless your using a car, the bars are over rated.
6

Well, it's an F150, so it's a bit springy....and I figure that the tongue weight is likely a bit higher than what I quoted, as the hitch is pretty heavy, so it's probably more around the 700# range. I haven't actually weighed it (I know I should), so this would be hypothetical, but the "factory" weight dry is 4480#/435#....we're pretty much fully loaded all the time, so let's just say it's 6300#/~600#...the hitch (a HaHa) will add another 100 or so to that, so 700# would be a good approximation.

[ROBERT CROSS]

Shawn...

This is a good investment to eliminate the estimation...mine was off by 300lbs.

Good tips on the site also...

Bob

[TG Twinkie]

I look at it this way.
With the palms of your hands facing you. Lock the fingers together then rotate both hands so the palms are facing away and push your hands away from your body.
Do you feel the stress in your fingers and forearms?
The stress in your fingers represents the tension of the spring bars and the stress in your forearms is what the frame of the truck and trailer go thru. The truck frame can handle it but the trailer frame and shell can't.
If you have over rated or maladjusted spring bars, I believe you will damage the trailer. The design of this trailer is to enable it to flex when necessary. If you hold the frame in the front ridged with spring bars that are over rated and the trailer wants to flex. It will, and it will result in rivets popping and dents showing up in the front lower sections and around the door.
When you have a tongue weight in the neighborhood of 15%. Most of the shock that the rear axle of the TV encounters is absorbed by the TV's suspension especially on long wheel based TV's.
I routinely come across threads or articles about the tube type receiver hitches experiencing damage. Where the tube or pipe across the rear of the TV has been twisted or torn. In my mind it's the result of an under rated or overloaded hitch or a combination of both. When you literally try to prevent the rear end of the TV from flexing down as you go thru a dip you are putting tremendous stress on the receiver hitch assembly and the trailer frame as well.
I believe if you are using a weight distribution hitch it must be rated to match the trailers tongue weight when towing by using and adjusting it correctly.

[Inland RV Center, In]

[QUOTE=exthemius;1113012]

Originally Posted by Inland RV Center, In

The rating of the bars depends on 2 things.

The trailer tongue weight and the exact tow vehicle.

What tow vehicle do you have?

The heavier the tow vehicle duty, the lighter tha bars should be.

In your case, unless your using a car, the bars are over rated.
6

Well, it's an F150, so it's a bit springy....and I figure that the tongue weight is likely a bit higher than what I quoted, as the hitch is pretty heavy, so it's probably more around the 700# range. I haven't actually weighed it (I know I should), so this would be hypothetical, but the "factory" weight dry is 4480#/435#....we're pretty much fully loaded all the time, so let's just say it's 6300#/~600#...the hitch (a HaHa) will add another 100 or so to that, so 700# would be a good approximation.

I would suggest dropping the bar ratings to 750 or 800 pounds, and experience and observe the positive difference.

Andy

[ROBERT CROSS]

''I routinely come across threads or articles about the tube type receiver hitches experiencing damage. Where the tube or pipe across the rear of the TV has been twisted or torn. In my mind it's the result of an under rated or overloaded hitch or a combination of both."

If your referencing the GM units... they are not under rated in what they are specced to tow, they are under rated/fail because they are junk...

Bob