Custom trailer questions

[SICARIO]

I'm in the process of designing a multi purpose trailer for trail riding and getting barkdust for the house. I want 33" tires to match my LX, as well as electric brakes/e-brake option. I'd also use a max coupler.

What I can't decide on is box size and suspension.

I was thinking of 4x6 with a long tongue so it's still easy to backup. If I went larger it would be 4x8.

For suspension I was originally planning for a solid axle with leaf springs, but is there really merit to the indipendand swing arm styles (timbren or something similar)?

Any feedback would be appreciated.

Here are a few pics of the model I'm working on:

 

[ntsqd]

With regard to frame design, the tongue tube(s) - contrary to how almost everyone except the Military & Harbor Freight does it on these little trailers - should go under the main frame and the diagonals should go under as well as tie into the forward suspension brackets. The reason is that the highest bending Moment in the whole frame is right at the front cross-member. Diagonals that tie into the front face of that cross-member do almost nothing to help in resisting that bending. Look at higher load capacity commercially built trailers and they're all built as I describe and for good reason.

Leaf springs are fine for a simple suspension system, but do not use typical trailer springs. They are too short which results in a stiff ride. Which is fine if you like shaken beer and scrambled eggs. Otherwise go with longer, more supple springs and include shocks. Typical trailer springs are short and stiff so that they do not need shocks and do not change ride height much between unloaded and fully loaded.

I am not convinced that trailers need independent suspension. All of the advantages claimed for independent suspensions don't really apply to trailers because people don't normally ride in them. Sort of an "anthropomorphism" of trailers if you will. I do see some advantages to simple linkage locating a live axle with coil springs or air springs; all with dampers.

We have two & 1/2 trailers, one built in 1952 by my grandfather with leafs and no shocks (originally rolled on war surplus DC3 wheels & tires!), one built by MISF & I with 3/4t truck springs and shocks, and another with a Dexter (rubber) Torsion Axle with shocks.

If you run large tires on the trailer do not be surprised if you find that you can drag it down the highway fully loaded at 80 mph with 8 psi in the tires and not get them hot. Ask me how I know this!

 

[SICARIO]

Thanks for the feedback. I'll go back and make some changes.

 

[Chris Wilcox]

I love my M101CDN. If it were me I'd google that to see how they did things. The other one that intrigued me was the Mil Spec M8. It is too short but if you lengthened the box a little bit it would be a nice unit.

 

[SICARIO]

I was looking at that M8 today, incorporated some of it into the design, here are some changes I made today. It's the same 4x8 box but a little heavier duty than the previous one. Also did a removable lid/rack

I

 

[Chris Wilcox]

I would recommend heeding the advice of post number 2. Also your shock angle is so low you might do without them. Do you need spring over because not having it would fix your angle. About the only reason to runs a continuous bar down the center is if you want a tow point at the center rear. Interpret the comments as constructive criticism, working in SW is great because you haven't locked yourself in to anything until you are happy with your design. When that time comes you can cut parts once and be done with it.

 

[SICARIO]

I was measuring it today, and I think I can go without the spring over, I'll swap that back over to get a better angle. Based on the feedback I'll likely look into a larger (non trailer) leaf spring pack.

I was thinking of putting a hitch on the rear so I might leave the center tube, but I'll drop the angled supports down so they run underneath to the front suspension point.

I do appreciate the feedback, this is my first trailer design, most of my design work is bolted to the ground...

 

[ntsqd]

Is this a dedicated camping trailer, or do you plan to use it for general utility hauling as well? If the latter you might consider making the floor an inch wider at 49" so that 4' X 8' sheets of whatever don't bind on the sidewalls. I realize that complicates how to make the bed's floor, but it will be worth it the first time that you can slide sheets in and out of the trailer instead of having to wrestle them in and out..

Can make the tongue tube from receiver tube and create a sliding length tongue. Our TrailBlazer trailer's tongue extends about 3.5':

I must say, though, that I've only ever used that feature for moving it around the yard by hand.

My grandad's RoT for unladen tongue length is for it to be 1/3 to 1/2 of the total length from coupler to the axle. For instance, that's ~167 lbs. worth of fuel, not counting the masses of the containers or mounts, shown on the front of the trailer. So for mt grandad's RoT the tongue length would be measured to the front of them, not the box. If you know all of the various masses of the bits going into the trailer and that the trailer is being made from can do a Shear-Moment Diagram to work out what the tongue length should be in a more Engineered manner.

Ball coupler, and/or?

Note that the sliding part in the pic above has a receiver tube section welded to it. This was so that different couplers could be used. The problem was that the receiver tube section was too short. I've since cut that off and now the coupler is attached to the receiver tube instead.

This is how I built a "wristed" lunette using a longer section of receiver tube:

For a sense of scale, those are 9/16" X 7" long Grade 8 bolts.

And this is the mod to the pintle to keep the assembly from being able to roll under and lock-up while backing the trailer around a corner:

This is what not to do with a pintle & lunette:

See how the lunette's ring isn't a tight fit in the pintle's opening? It should be. The ID of the lunette's ring should not be a tight fit on the hook of the pintle, but the opening in the pintle shouldn't be much larger than the cross-sectional diameter of the lunette ring. Done like in this picture they'll be noisy. When the lunette fits correctly there isn't any room for them to bang around. I do not think it is possible to achieve this fit using one of the pintles that has a std. ball coupler ball in it. I believe those will always be noisy.

 

[ntsqd]

Full disclosure; the TrailBlazer's frame doesn't have it's tongue under the main frame either. I didn't build it. It does have a full length section of receiver tube. The original owner and his builder's goal was to be able to use a winch at the rear of the trailer if need-be. Which is what those Anderson connectors are for, power to an M8 winch mounted on a cradle.

 

[SICARIO]

Awesome feedback, thanks.

The plan would be to use it for both camping and for around the house like a traditional trailer. I'll widen the box to 50", good call in the plywood fitting.

The tongue length to the front of the jerry can box is 34", coupler to centerline of axle is 90", so sounds about right to your grandpas RoT.

I moved the angled braces to the bottom of the frame as well. I also put in a c-channel box for the suspension to mount to, not sure how necessary that will be.

I'm working on changing up the axle to spring under. I see a lot of these trailers with torflex style axles, any reason to/not consider them?

For the coupler, I was planning on using the max coupler with the option of a traditional ball mount.

 

[SICARIO]

Here's a version with the angled braces at the same height of the main frame, but extend back to the suspension bracket. Would save about 70 lbs.

 

[ntsqd]

What I am thinking for leaf springs:

Box tubing only for me. Channel lacks torsional stiffness & I think it ugly.

Re: Torflex axles, their deterrents point to the sole reported case of one letting go of the spindle assembly, which would be a bad thing. However, the cited failure mechanism can't happen in the sequence theorized. The claim is the grit got into between the rubber and the steel causing it to abrade and fail. The rubber on our such axle and every one of these that I've looked at is vulcanized to both the spindle assembly and the mount body. For grit to get in there it came after the rubber was broken loose from the steel. And while supposedly pictures of this failure were taken, none have ever surfaced publicly. There has been some discussion here about this, with one advocate of them talking further to this supposed failure.

I've thought a lot about this and have come to a theory that I think fits the situation. Heat is the best way to de-vulcanize rubber from steel, and a high speed jaunt down a washboard road will generate a lot of that. Given that prior to our TrailBlazer trailer coming to us, which is fitted with a Torflex axle, it was towed down many such nasty roads both in the US and in Baja (Original Owner bought it specifically for exploring Mexico) and it has always had shocks on it I think they are the key. Typically in a Torflex axle the rubber is both the spring and the damper, with any suspension movement it can be thought of to have two means of heating the rubber. With a damper added to the suspension now some or most of the heat from damping the 'spring' is dissipated by the shock instead. I suspect that the whole separation thing was a ploy to justify the building of what I call an "ITS" system (Independent Trailer Suspension)

There is one gotcha and one downside to using them. The common thing is to order a higher load rated leaf spring axle than would otherwise be justified in order to get larger wheel bearings that will be more adept at handing severe off-pavement use. With leaf springs this is easy to do since you can mix and match axles with springs. With Torflex's you can only go a little bigger before the weight rating becomes something that the intended trailer will never deflect. The gotcha is that they come in several starting angles so you need to make sure you choose the correct one and that is the p/n that you receive.

 

[LAMBCRUSHER]

 

[Chris Wilcox]

I thought i liked torflex style axles for this type of trailer but over the years decided I don't. The ones I had became amazingly loud. I could hear every bump from my seat with the windows closed. ALso I found the ride too rough due to the higher than necessary load capacity that you had to buy to get the spindle I wanted. Maybe an influence but not certain... I feel like the non-linear nature of the bounce/droop was noticeable and unnecessary. If it were my design I'd use your post 10 and delete the square under the bed. Those four bits of HSS are unnecessary. Consider 1x2 upright for your intermediate crossmembers as the strength and stiffness far exceeds the 1x1 pictured.

Good advice given on the 50" width. I once had a 4'x8' trailer and the plywood would wedge in there real good, one corner down. It was a real challenge to remove.

 

[SICARIO]

Thanks for the input, I'll probably go for the leaf springs. I have torflex on my travel trailer, but I'm not doing anything too serious with it.

I've made all of the suggested changes and changed up the frame a little. Now I need to decide on the tailgate (swing down like a truck bed, or swing out like an old surburban door).

 

[ntsqd]

I still would extend that center tongue tube to the second or preferably the third cross-member of that design rather than stopping it at the front cross-member.

Another thought that is more a details thing than a prime design constraint is to use a trailer light socket on the trailer tongue too. Then the lighting lead can be a plug by plug jumper and different tow rig light sockets are a simple matter of having or building a different jumper. Accidental damage becomes simple to repair too.
That 1/2 a trailer that I own? My friend & I did this exactly on that trailer because we knew that various people (whom we trusted) would want/need to borrow it on occasion and right when we were starting into the wiring of that trailer another friend who had loaned his car-hauler trailer out got it back with the lighting lead butchered because they had a mismatch. That got me to thinking about how to make it easy to connect to different tow rigs and easy to repair should something happen.

Just as food for further thought, I once played around with building a space-framed, lightweight utility trailer with 1 or 2 dirt bikes as likely cargo (hence the double folding ramp tailgate) that would have a tongue that could be reversed for a high and a low position. This to accommodate towing it with both a passenger car and with a truck. My SW investigation resulted in this:

I never detailed how exactly the tongue would be connected to the main frame, that was "yet to be defined". With suitable "trussing" the side rail structure can help in carrying the load. You're carrying it around regardless, so why not use it to advantage?

 

[Chris Wilcox]

I really like where you are right now. I feel extending the tongue back a couple cross bars is optional and not necessary since you have good bending moment capacity with the two under the front cross member. But based on appearance I would agree that it seems the appropriate thing to do. Regarding the tailgate/barn doors. That is a tough call. You can tailgate it like it is but if you use doors you probably need a partial or full height diagonal just behind your gas cans. This wouldn't be for strength but for stiffness. The barn doors will want to swing and mate every time. Tie the rear uprights into the rear cross member with a 1" sq tube and you'd be golden. It would also protect the gas jug to some degree.
A tailgate will allow you to flip it down to carry a 4x8 sheet but not twenty 4x8 sheets because the tongue weight would go negative. Rule of thumb is approximately 10%, forget exact number. That brings up another point, you should assess whether or not you want to slide the axle back several inches so that an evenly loaded trailer adds tongue weight in the correct percentage. It looks centered on the bed and therefore with a load of dirt your tongue wt percent would decrease to dangerous levels. Consider making the gate so it can flip straight down for best access to load gear.
If you go barn doors you will eventually want to hang something on them. I feel like the construction is more complicated than a tailgate.

I've designed things like this in ProE, SW and Inventor including prototypes for the US Army FMTV LHS system. I would highly suggest adding all your holes and purchased parts to your best ability so there is no surprises when you go to build. Also a nice touch is to model in any tolerances and provide weld gaps etc. Another nice touch is to add materials and check your CG and total weight.

As for features, you maybe aren't there yet but consider tie down loops or integrated ones. Have a look at the M1102 bed, you can buy those at trailer stores. If you put the diagonals on the rear and moved the axle back, the gas can could go in front of axle and the taillights (military ones since they are so well sealed) might fit within the diagonal for protection. Anyway lots to think about and good fun.

 

[SICARIO]

Awesome feedback, thanks!

I didn't think about the rear diagonals, but those sound like a good addition. I originally had my axle sitting farther back (with decent angle in mind), but didn't think of the effect of tongue weight with the axle centered. I'll play around with that as well.

I think I'll stick with a dump tailgate for simplicity sake. I was thinking of making a removable spare tire swing out to use while camping. Hard to decide the best place for a spare (tongue/tailgate/lid/side by the fender).

I'm also getting rid of any channel (including the fender guards). It'll add a little weight but should strengthen it up.

Finally, trying to decide on the number/size of subframe crossmembers. I've seen some that use the same size tubing throughout (2x3). Right now I have 2x3 every 25" with a 1x2 inbetween. Having a 2x3 every 12" seems overkill, but having only the 2x3's every 24" with nothing in between seems like it could cause dipping in the floor over time with heavier loads.

I'll post up pics once I make the changes.

 

[ntsqd]

The trailer below is built from the sideboards of G.I. 2.5t truck by my grandfather. The sides are the frame, which is what gave rise to my comment above about using the sides for structural strength and not just for holding stuff in. It has a full perimeter ledge about 3/4" wide and a rather puny cross-member (that the tongue ties into) at mid-length with another at the rear mostly for the tailgate hinge. The floor is a piece of 1/2 plywood that was unsecured, only the load or the spare held it down. I changed that after it flew out on me. This is what also led me to comment about width as I thought the fit would be tight enough to keep it in place. Getting it out sure was a pain.

I've never seen the plywood dip or sag, not even the time we had it full to the top of the sideboards with gravel. If the loads are going to be high weight, small footprint loads then you might need more cross-members (or thicker plywood). With distributed loads like sheets of ply or sheet rock, or stuff like gravel I wouldn't get too worked up over needing a lot of cross-members.

For lights I'm a fan of the rubber "torsion" mounted sealed lights, LED if they're in the budget. Like these:
Maxxima® Oval LED Body Light with Grommet & Short Wire, Red

or these:
Maxxima 44 LED Rectangular S/T/T Light w/ Short Wire & Grommet, Red Lens

Being sealed they don't usually get dust in them and there is no bulb to socket corrosion problems and the wiring connector is reasonably sealed and secure. The ovals on edge also tuck in fairly tight while still meeting the DOT's minimum light area requirement.

 

[SICARIO]

Thanks for the feedback. I put in an oval tail light that looks similar to the maxxina.

I put in as much hardware as I could think of, changed most of the tubing to 2x2 square instead of rectangle.

I was planning on welding in sheet metal instead of plywood and having it bedlined.

What do you think?