Need some help with my Trailer design

[shadowhaus]

The advice is to keep the tongue weight at 10-15%

So the advice is about weight and not length?????

 

[shadowhaus]

??

 

[Martyn]

So the advice is about weight and not length?????

No, the question I was replying to was about weight.

I was implying that sway could be caused by multipule factors, and I mentioned a few of them.

The list I gave were a few examples, there could be more, and they could be contradictory, as in too little tongue weight and too much tongue weight.

There is no clear cut single answer.

 

[ntsqd]

I think that the weight on the ball causes a small damping function from friction. How significant of important this is I do not know, but I bear in mind that with heavier trailers it is not the load levelers that are important to Anti-Sway, it is the Anti-Sway connector. Those of which that I've used and been around are a linear brake lined with friction material and have an adjustable pre-load. Set that too loose and you get sway. Set it too tight and the trailer really doesn't want to turn in tight spaces.

I think that it isn't that the rear of the truck needs that puny weight transferred to it, but that the coupler needs to have some friction within it.

 

[ex m38a1er]

The trailer is a triangle with the two sides equal.One peak is the coupler and the two others are the wheels.
Now cut a piece of plank wood in a triangular shape and put a nail where the
center of gravity should be.Tight a string and hang the plank.
Put a coin on the peak with the smaller corner.This is your tongue weight.
See what happens.Clear as mud????
I did my best...

 

[slimtwo]

Bruce ,
Here're a few rules of a thump for trailer designing:
-10-15 tongue weight as others have mentioned
-THe axle should be positioned in a 60/40 manner in the length of the tub
-The hitch to center of the axle=to your tow rig's wheelbase.(in order your trailer's track to be identicall to your towing rig's)
-For a tongue you can use a (single)straight tube an 'A' or a combination.
A lot of off roaders use a single because they don't want when jacknifing
their bumper to hit the side of the tongue.
I think all "A" tongue hitches come in a 50o set up and this pretty much dictates your tongue's lenght.

[/IMG]
(this comes i think from teardrop's forum)
Of course as many other fellows mentioned "ALWAYS" a design is a compromise.
NO having all the above in mind you can just copy the provem m101CND

[/IMG] and have sometimes problems swaying and manouvering
(I've been driving a m100 in the Greek behind a G-Wagen)
Or take some of the features of this

[/IMG](better for not so tight trails)
Anyway you're driving a SWB Jeep and it wouldn't make along combo.
Whetever you go with have fun
George

Thank you so much for the info, I'm realy gonna have to chew on this for a while. Thanks again!

Bruce

Happy Trails!

 

[R_Lefebvre]

I think that the weight on the ball causes a small damping function from friction. How significant of important this is I do not know, but I bear in mind that with heavier trailers it is not the load levelers that are important to Anti-Sway, it is the Anti-Sway connector. Those of which that I've used and been around are a linear brake lined with friction material and have an adjustable pre-load. Set that too loose and you get sway. Set it too tight and the trailer really doesn't want to turn in tight spaces.

I think that it isn't that the rear of the truck needs that puny weight transferred to it, but that the coupler needs to have some friction within it.

The friction from the ball is probably pretty insignificant. It's acting through such a small moment arm (2" on a 2" ball) I just don't see it. I think this is implausible.

It sounds good in theory, but in practice it's very complicated.

Here are some simple reasons for sway:

I agree with most of those inputs, but you forgot one of the most important: The stiffness of the sidewalls on the rear TV tires . I've had some weenies on DWeb tell me the Disco can't tow because of this that and the other thing... You know the "you need a Peterbuilt to tow a Seadoo" syndrome. I can say that with E-ply tires on, the truck tows beautifully and is very stable in yaw. Previously to getting these new tires, I spent a short amount of time on some 255/70/16 P-car tires, and let me tell you, that was one SPOOKY ride. I never would have towed like that.

Anyway, back to the topic at hand... yes, I think your factors are valid, and as the trailer-to-rig weight goes up, they become more and more important. But what I'm saying is that when the trailer is like, 1/4 the weight of the rig, it just doesn't matter what you do, you won't get sway.

I've towed some light trailers with some very light tongue weights with a Focus, and never had even a hint of a sway problem.

You forgot another factor as well: lateral stiffness of the rear suspension of the TV. I think leaf springs suck for this. The Disco has a nice watts-link which is why it tows well even despite the short wheelbase and long overhang.

 

[slimtwo]

I appreciate all the information everyone has provided, and surprisingly enough it makes sense. I have towed a trailer that did not have enough tongue weight before and wow, what a ride. it started swaying so bad that it literally picked up the back of the tow rig, throwing it from side to side, not fun.

So if my trailer is 60 inches long (the tub), then the centerline of the axle will be about 20 inches from the rear, 40 inches from the front, and the tongue is approx. the same length as the width of the trailer.

Is this about right?

 

[UK4X4]

I'm a practical type engineer, ie I did'nt build a dynamic stress model or similar
for a simple box trailer.

Uncle sam has already done all that for you in the previous posts.

I based my trailer on "the standard" too, why change something that works.


They put the wheel in the center of the box, so the load is spread evenly.

By the time you've added a full cooler, gas tanks or a battery box on the front you will have your weight distribution about right.

the mill specs posted earlier have a box length of 72"
and a total length of 114"

Thats a 1.58 ratio box to toungue..

so if your box is 60 your total length should be 94.8 giving you a toungue 34 " long.

That is if you want to give yourself a similar set up to the standard military trailer.

adding a few inches to the tounge won't matter that much, its just a question of balance.

Right now hitch to axle is too long, and too much weight on the hitch, as you will most likely fill that 58" with gear.

Here's mine basicly a balanced design if evenly filled with gear, water tank is forward of axle- battery is aft.

I'll be adding a 4 can holder in front of the box- giving me some weight on the hitch

 

[R_Lefebvre]

I appreciate all the information everyone has provided, and surprisingly enough it makes sense. I have towed a trailer that did not have enough tongue weight before and wow, what a ride. it started swaying so bad that it literally picked up the back of the tow rig, throwing it from side to side, not fun.

What was the relative weight of the trailer to the tow vehicle? Just trying to see if it ties into my theory.

I've had a case where I had a negative tongue weight. It was a standard 4x8 utility trailer with 12" lumber loaded in the back... This was being towed by a Chev. Celebrity. (Fwd). The ride was a bit spooky, but manageable. We didn't have *that* much lumber hanging off the back. I bet the tongue weight was about 100lbs upward. Relative to the ~1000lbs rear axle weight of the wagon, it wasn't that big of a deal.

Even the "too much tongue weight" isn't an absolute. We've done a lot of towing with our Focuses, which have a rear suspension geometry that really toes in the rear wheels when they squat. I know we've had "too much tongue weight" in many cases, but it's always stable as a rock. With a live axle, you never have toe-in no matter what. So that's another factor.

There are so many variable in this, which is why I always detest the people who proclaim you need an F-350 Dually to tow any trailer. I don't hear that sentiment much from people around here thankfully. But I get howls of protest on the Focus boards when I talk about towing a 1000lb Seadoo trailer with the Focus. And that's 1000lbs unbraked with a 2800lb car. So... Again, the reality is that the high performance tires (relative to truck tires) on the car offer so much more grip that it just isn't a real problem.

 

[ntsqd]

If you had an idea of where the weights will be within the trailer then with that diagram above you could predict what the tongue weight might really be. Engineers call it a Shear-Moment Diagram, but it's simply a graphical solve for the weight on the axle and the weight on the ball.

The friction from the ball is probably pretty insignificant. It's acting through such a small moment arm (2" on a 2" ball) I just don't see it. I think this is implausible.

I think that it's a small factor in a large equation. The moment may be small, but what is the normal force? It's not just the tongue weight. No, it will never be a huge number, but I would not discount it completely either.

But what I'm saying is that when the trailer is like, 1/4 the weight of the rig, it just doesn't matter what you do, you won't get sway.

In the book that I mentioned above there is a formula for predicting the Critical Speed of the combination of the trailer and the tow rig. One of the variables that I never found even a good WAG for was the trailer tire sidewall stiffness coefficient. I do not recall that there is a similar Cf for the tow rig's tires. I'll try to remember to check that tonight. Above that Critical speed it doesn't matter what you do, you will get sway. Each unique trailer/tow rig combo will have it's own unique Critical Speed. What that speed is depends largely on the design of the trailer.

 

[Box Rocket]

Dunno if it helps you or not but the box on my homebuilt work in progress trailer is 72"Lx48"Wx19"H and the tongue is 48" long. With the hitch a 48" tongue length clears the side of the truck is case of a jacknife. The edge of my rear bumper to the center of the hitch was right about 36" so the tongue gives me a little wiggle room. I think 58" would be way too long.

Also, I have my axle 2" rear of center on the tub. Only gauge I have at the moment is moving it around the garage by hand. It balances well and is easy to move. There is a slight weight bias toward the tongue and with gear I think it will be about right. I'm no expert but just sharing my experience so far.

 

[slimtwo]

I'm a practical type engineer, ie I did'nt build a dynamic stress model or similar
for a simple box trailer.

Uncle sam has already done all that for you in the previous posts.

I based my trailer on "the standard" too, why change something that works.


They put the wheel in the center of the box, so the load is spread evenly.

By the time you've added a full cooler, gas tanks or a battery box on the front you will have your weight distribution about right.

the mill specs posted earlier have a box length of 72"
and a total length of 114"

Thats a 1.58 ratio box to toungue..

so if your box is 60 your total length should be 94.8 giving you a toungue 34 " long.

That is if you want to give yourself a similar set up to the standard military trailer.

adding a few inches to the tounge won't matter that much, its just a question of balance.

Right now hitch to axle is too long, and too much weight on the hitch, as you will most likely fill that 58" with gear.

Here's mine basicly a balanced design if evenly filled with gear, water tank is forward of axle- battery is aft.

I'll be adding a 4 can holder in front of the box- giving me some weight on the hitch

You have a very nice trailer! Is it an off shoot of the AT's? I noticed the independant suspention underneath. What you've said makes sense, I didn't realize how involved building a trailer would be, however I want to make sure it is a sound rig, that's why I'm asking all these questions. Thanks for the information.

Bruce

 

[slimtwo]

Dunno if it helps you or not but the box on my homebuilt work in progress trailer is 72"Lx48"Wx19"H and the tongue is 48" long. With the hitch a 48" tongue length clears the side of the truck is case of a jacknife. The edge of my rear bumper to the center of the hitch was right about 36" so the tongue gives me a little wiggle room. I think 58" would be way too long.

Also, I have my axle 2" rear of center on the tub. Only gauge I have at the moment is moving it around the garage by hand. It balances well and is easy to move. There is a slight weight bias toward the tongue and with gear I think it will be about right. I'm no expert but just sharing my experience so far.

Niice job on your trailer!

Are you planning on building a top for it? It looks like the trailer will serve you well. Thank you for your input.

Bruce

 

[wely]

I like the way ya'll are building a bed for your trailer and then adding tops. one question i have is do any of yall use your trailer for anything else. I want on that i can modify so if i need a load of sand for the yard i can un bolt the camping box, slid it out and go. is this possible?